U.S. patent application number 10/776427 was filed with the patent office on 2004-08-19 for methods of etching articles via micro contact printing.
This patent application is currently assigned to President & Fellows of Harvard University. Invention is credited to Berggren, Karl K., Biebuyck, Hans, Gorman, Christopher B., Jackman, Rebecca J., Kim, Enoch, Kumar, Amit, Mrksich, Milan, Prentiss, Mara G., Whitesides, George M., Wilbur, James L., Xia, Younan.
Application Number | 20040159633 10/776427 |
Document ID | / |
Family ID | 32854448 |
Filed Date | 2004-08-19 |
United States Patent
Application |
20040159633 |
Kind Code |
A1 |
Whitesides, George M. ; et
al. |
August 19, 2004 |
Methods of etching articles via micro contact printing
Abstract
Improved methods of forming a patterned self-assembled monolayer
on a surface and derivative articles are provided. According to one
method, an elastomeric stamp is deformed during and/or prior to
using the stamp to print a self-assembled molecular monolayer on a
surface. According to another method, during monolayer printing the
surface is contacted with a liquid that is immiscible with the
molecular monolayer-forming species to effect controlled reactive
spreading of the monolayer on the surface. Methods of printing
self-assembled molecular monolayers on nonplanar surfaces and
derivative articles are provided, as are methods of etching
surfaces patterned with self-assembled monolayers, including
methods of etching silicon. Optical elements including flexible
diffraction gratings, mirrors, and lenses are provided, as are
methods for forming optical devices and other articles using
lithographic molding. A method for controlling the shape of a
liquid on the surface of an article is provided, involving applying
the liquid to a self-assembled monolayer on the surface, and
controlling the electrical potential of the surface.
Inventors: |
Whitesides, George M.;
(Newton, MA) ; Xia, Younan; (Seattle, WA) ;
Wilbur, James L.; (Germantown, MD) ; Jackman, Rebecca
J.; (Boston, MA) ; Kim, Enoch; (Boston,
MA) ; Prentiss, Mara G.; (Belmont, MA) ;
Mrksich, Milan; (Chicago, IL) ; Kumar, Amit;
(MilPitas, CA) ; Gorman, Christopher B.; (Raleigh,
NC) ; Biebuyck, Hans; (Rockville, MD) ;
Berggren, Karl K.; (Arlington, MA) |
Correspondence
Address: |
Timothy J. Oyer, Ph.D.
Wolf, Greenfield & Sacks, P.C.
600 Atlantic Avenue
Boston
MA
02210
US
|
Assignee: |
President & Fellows of Harvard
University
17 Quincy Street
Cambridge
MA
02138
|
Family ID: |
32854448 |
Appl. No.: |
10/776427 |
Filed: |
February 11, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10776427 |
Feb 11, 2004 |
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09164733 |
Oct 1, 1998 |
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09164733 |
Oct 1, 1998 |
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08677309 |
Jul 9, 1996 |
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5900160 |
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08677309 |
Jul 9, 1996 |
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08676951 |
Jul 8, 1996 |
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6180239 |
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08676951 |
Jul 8, 1996 |
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08397635 |
Mar 1, 1995 |
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08397635 |
Mar 1, 1995 |
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08131841 |
Oct 4, 1993 |
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5512131 |
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Current U.S.
Class: |
506/18 ; 216/54;
257/E21.575; 506/19; 506/40 |
Current CPC
Class: |
B01J 2219/00621
20130101; B05D 1/283 20130101; B82Y 10/00 20130101; B01J 2219/0061
20130101; B01J 2219/00619 20130101; B82Y 30/00 20130101; B01J
2219/00617 20130101; B01J 2219/00605 20130101; G02B 5/1857
20130101; G03F 7/165 20130101; H01L 21/768 20130101; B01L 3/5085
20130101; C40B 60/14 20130101; H01L 21/4867 20130101; B01J
2219/00637 20130101; B01L 2300/0654 20130101; G02B 2006/12107
20130101; B01J 2219/0063 20130101; B01J 2219/00382 20130101; B82Y
40/00 20130101; B01J 2219/00659 20130101; G02B 6/136 20130101; G02B
6/124 20130101; G02B 2006/12104 20130101; B01L 2300/0851 20130101;
B01J 2219/00612 20130101; B01L 3/5088 20130101; G03F 7/0002
20130101; G02B 2006/12102 20130101; B01L 2300/0819 20130101 |
Class at
Publication: |
216/054 |
International
Class: |
B44C 001/22 |
Goverment Interests
[0002] This invention was made with government support under Grant
Number NIH GM30367 and ONR N00014-86-K-0756. The government has
certain rights in the invention.
Claims
What is claimed is:
1. A method of plating a pattern of material on a nonplanar surface
of an article, comprising: contacting a first, nonplanar portion of
a surface of an article with a stamp to transfer to the first
portion a self-assembled monolayer of a molecular species in a
first pattern, the self-assembled monolayer being contiguous with
an exposed portion of the surface in a second pattern; and plating
the surface of the article with a plating reagent in a pattern
dictated by the pattern of the self-assembled monolayer.
2. A method as in claim 1, wherein the article is a fiber.
3. A device comprising: an article defining a surface; and an
isolated region of a self-assembled monolayer of a first molecular
species on the surface, the isolated region including a lateral
dimension of less than about 10 microns, surrounded by a continuous
region of a self-assembled monolayer of a second molecular species
on the surface, wherein the first molecular species terminates in
an end exposed away from the surface having a first functionality
and the second molecular species terminates in an end facing away
from the surface having a second functionality.
4. A device as in claim 3, wherein the isolated region of the first
molecular species has a lateral dimension of less than about 5
microns.
5. A device as in claim 3, wherein the isolated region of the first
molecular species has a lateral dimension of less than about 1
micron.
6. A device as in claim 3, wherein the isolated region of the first
molecular species has a lateral dimension of less than about 0.25
micron.
7. A device as in claim 3, wherein the isolated region of the first
molecular species has an area of less than about 100 square
microns.
8. A device as in claim 3, wherein the isolated region of the first
molecular species has an area of less than about 25 microns.
9. A device as in claim 3, wherein the isolated region of the first
molecular species has an area of less than about 1 square
micron.
10. A device as in claim 3, wherein the isolated region of the
first molecular species has an area of less than about 0.06 square
micron.
11. A device as in claim 3, wherein the surface is nonplanar.
12. A device as in claim 3, wherein the first molecular species
terminates in an end facing away from the surface having a
hydrophilic functionality and the second molecular species
terminates in an end facing away from the surface having a
hydrophobic functionality.
13. A device as in claim 3, wherein the first molecular species
terminates in an end facing away from the surface in a hydrophobic
functionality and the second molecular species terminates in an end
facing away from surface in a hydrophilic functionality.
14. A device as in claim 13 wherein the surface is nonplanar.
15. A device as in claim 12 wherein the surface is nonplanar.
16. A kit, comprising: an article constructed and arranged to
transfer a molecular species to a substrate surface, comprising an
applicator surface having at least one indentation formed therein
and a stamping surface adjacent the at least one indentation, for
carrying a self-assembled monolayer-forming molecular species and
able to transfer the molecular species to the substrate, the
stamping surface formed of a swellable material which absorbs the
molecular species; and a self-assembled monolayer-forming molecular
species for application by the stamping surface.
17. The kit as recited in claim 16, the stamping surface comprising
at least one resolved feature providing stamping resolution of less
than about 100 microns.
18. The kit as recited in claim 17, the stamping surface comprising
at least one resolved feature providing stamping resolution of less
than about 10 microns.
19. The kit as recited in claim 18, the stamping surface comprising
at least one resolved feature providing stamping resolution of less
than about 1 micron.
20. The kit as recited in claim 19, the stamping surface comprising
at least one resolved feature providing stamping resolution of less
than about 0.25 micron.
21. The kit as recited in claim 16, the article formed from an
elastic material.
22. The kit as recited in claim 21, the elastic material formed
from a hardenable fluid.
23. The kit as recited in claim 21, the elastic material selected
from the group consisting of silicone polymers and copolymers,
epoxy polymers and copolymers, and copolymers thereof.
24. A kit, comprising: an article for transferring a molecular
species to a surface, comprising a flexible surface having at least
one indentation formed therein and an applicator surface adjacent
the at least one indentation for carrying a molecular species and
transferring the molecular species to a substrate, the applicator
surface including a portion having a lateral dimension of less than
about 10 microns, wherein the flexible surface comprises
polydimethyl siloxane; and a self-assembled monolayer-forming
molecular species for application by the applicator surface.
25. An optical fiber having a surface, and a self-assembled
monolayer on the surface of the optical fiber.
26. A method comprising: transferring to a surface of a fiber a
molecular species from an applicator in a pattern including a
portion having a lateral dimension of less than about 10
microns.
27. A method as in claim 26, wherein the pattern includes a portion
having a lateral dimension of less than about 1 micron.
28. A method as in claim 26, wherein the pattern includes a portion
having a lateral dimension of less than about 0.5 micron.
29. A method as in claim 26, wherein the fiber is an optical
fiber.
30. A method as in claim 26, further comprising etching a portion
of the surface of the fiber in a pattern dictated by the pattern of
the molecular species.
31. A method as in claim 26, further comprising plating a portion
of the surface of the fiber with a plating agent in a pattern
dictated by the pattern of the molecular species.
32. An article comprising: a flexible member having a flexible
surface including at least one indentation formed therein, the at
least one indentation formed such that electromagnetic radiation
passing through the flexible member when the member is in a first,
unstressed conformation forms a first detectable image and formed
such that electromagnetic radiation passing through the flexible
member when the member is in a second, stressed conformation forms
a second detectable image differentiable from the first image; and
a modulator contacting the flexible member and movable between a
first position placing the member in the first, unstressed
conformation and a second position placing the member in the
second, stressed conformation.
33. An article as in claim 32, further comprising: a source of
electromagnetic radiation positioned to irradiate the flexible
member; and an electromagnetic radiation detector positioned to
detect radiation emitted by the electromagnetic radiation source
and passing through the flexible member.
34. An article as in claim 33, the flexible member having a
flexible surface including a plurality of indentations formed
therein, the indentations formed such that electromagnetic
radiation passing through the surface when the member is in the
first, unstressed conformation is diffracted according to an
ordered diffraction pattern and formed such that electromagnetic
radiation passing through the surface when the member is in the
second, stressed conformation is blurred.
35. An article as in claim 34, wherein the source of
electromagnetic radiation is positioned to irradiate the flexible
member through the flexible surface.
36. An article as in claim 34, wherein the modulator includes a
modulating surface positioned against the flexible surface and
movable between the first and second positions.
37. An article as in claim 36, wherein the modulator includes a
peizoelectric member.
38. An article as in claim 37, further comprising an electrical
source in electrical communication with the peizoelectric member,
the electrical source switchable between a first signal state in
which the peizoelectric member is in the first position and a
second signal state in which the peizoelectric member is in the
second position.
39. An article as in claim 32, the article comprising a pressure
sensor.
40. An article as in claim 32, the article comprising an optical
switch.
41. A kit, comprising: an article constructed and arranged to
transfer a molecular species to a substrate surface comprising an
applicator surface having at least one indentation formed therein
and a stamping surface adjacent the at least one indentation, for
carrying a self-assembled monolayer-forming molecular species and
transferring the molecular species to the substrate, the stamping
surface formed of a swellable material which absorbs the molecular
species, wherein the stamping surface comprises polydimethyl
siloxane; and a self-assembled monolayer-forming molecular species
for application by the stamping surface.
42. The kit as in claim 24, wherein the applicator surface includes
a portion having a lateral dimension of less than about 1
micron.
43. A method comprising: providing an applicator having a surface
including at least one indentation formed therein, the indentation
contiguous with an applicating surface defining a first pattern;
coating the applicating surface with a molecular species comprising
a functional group selected to bind to palladium; positioning the
applicating surface in a first orientation and contacting a portion
of a substrate surface comprising palladium with the applicating
surface to hold the molecular species against the substrate surface
to allow the functional group to bind thereto; and removing the
applicating surface to provide a self-assembled layer of the
molecular species on the substrate surface according to the first
pattern.
44. The method of claim 43, further comprising providing at least
one second portion of the substrate surface free of the
self-assembled layer and contiguous with the substrate surface
portion onto which the self-assembled layer is provided.
45. The method of claim 44, wherein coating the applicator surface
further comprises allowing the molecular species to swell into the
applicator surface.
46. The method of claim 44, further comprising: positioning the
applicator surface in a second orientation different from the first
orientation, and contacting a portion of the substrate surface with
the applicator surface to hold the molecular species against the
substrate surface to allow the functional group to bind thereto;
and removing the applicating surface to provide a self-assembled
layer of the molecular species on the substrate surface according
to the first pattern in the second orientation.
47. The method of claim 46, wherein the self-assembled layer of the
molecular species on the substrate surface in the second
orientation intersects portions of the self-assembled layer in the
first orientation and forms a continuous self-assembled layer
therewith.
48. A method for patterning a surface, comprising: applying
instantaneously to a surface comprising palladium a plurality of
discrete isolated regions of a first, self-assembled layer forming
molecular species while leaving intervening regions free of the
species.
49. The method of claim 48, wherein the surface comprising
palladium is non-planar.
50. The method of claim 49, wherein at least one of the discrete
isolated regions includes a lateral dimension of less than 200
microns.
51. The method of claim 50, wherein at least one of the discrete
isolated regions includes a lateral dimension of less than about
100 microns.
52. The method of claim 51, wherein at least one of the discrete
isolated regions includes a lateral dimension of less than about 5
microns.
53. The method of claim 48, wherein the at least one of the
discrete isolated regions has an area of less than 1 square
micron.
54. The method of claim 53, wherein the at least one of the
discrete isolated regions has an area of less than 0.06 square
microns.
55. An article defining a surface comprising palladium; and a
self-assembled layer of molecular species on the surface defining a
pattern, the pattern corresponding to a pattern of an applicating
surface able to direct formation of the pattern of the monolayer of
the molecular species on the surface.
56. The article of claim 55, wherein the pattern includes a lateral
dimension of less than 10 microns.
57. The article of claim 56, wherein the pattern includes a lateral
dimension of less than about 5 microns.
58. The article of claim 57, wherein the pattern includes a lateral
dimension of less than about 1 micron.
59. The article of claim 58, wherein the pattern includes a lateral
dimension of less than about 0.25 micron.
60. A method of etching an article having a surface comprising
palladium, comprising: contacting a first portion of the surface
with an applicator to transfer to the first portion a
self-assembled layer of a molecular species in a first pattern, the
self-assembled layer being contiguous with an exposed portion of
the surface in a second pattern; and contacting the article with an
etchant that reacts chemically with the article thereby degrading a
portion of the article in a pattern dictated by the pattern of the
self-assembled layer.
61. The method of claim 60, further comprising coating a surface of
the applicator with a self-assembled layer forming molecular
species prior to contacting a first portion of the surface with the
applicator.
62. The method of claim 61, wherein the surface of the applicator
includes indentations and protrusions, the outward-facing surfaces
of which define an applicator surface, the contacting step
involving contacting the firs, non-planar portion of the surface
with the applicator surface.
63. The method of claim 62, the contacting step comprising
transferring the self-assembled layer to the non-planar portion of
the surface by rolling the firs, non-planar portion of the article
over the applicating surface of the applicator.
64. The method of claim 60, wherein the etchant is a first
etchant.
65. The method of claim 64, further comprising contacting the
article with a second etchant.
66. The method of claim 64, wherein the self-assembled layer
resists the first etchant.
67. The method of claim 61, comprising applying a protecting
species to the self-assembled layer.
68. The method of claim 67, wherein the protecting species is inert
with respect to the first etchant.
69. A device comprising: an article defining a surface comprising
palladium; an isolated region of a self-assembled layer of a first
molecular species on the surface, the isolated region including a
lateral dimension of less than 200 microns.
70. The device of claim 69, wherein the isolated region includes a
lateral dimension of less than about 110 microns, surrounded by a
continuous region of a self-assembled layer of a second molecular
species on the surface, wherein the first molecular species
comprises a first functionality and the second molecular species
comprises a second functionality.
71. The device of claim 70, wherein the isolated region of the
first molecular species has a lateral dimension of less than about
10 microns.
72. The device of claim 71, wherein the isolated region of the
first molecular species has a lateral dimension of less than about
5 microns.
73. The device of claim 72, wherein the isolated region of the
first molecular species has a lateral dimension of less than about
1 micron.
74. The device of claim 69, wherein the isolated region of the
first molecular species has an area of less than 1 square
micron.
75. The device of claim 74, wherein the isolated region of the
first molecular species has an area of less than 0.06 square
micron.
76. A method of plating a pattern of material on a surface of an
article comprising palladium, the method comprising: contacting a
first portion of a surface of an article with an applicator to
transfer to the first portion a self-assembled layer of a molecular
species in a first pattern, the self-assembled layer being
contiguous with an exposed portion of the surface in a second
pattern; and plating the surface of the article with a plating
reagent in a pattern dictated by the pattern of the self-assembled
layer.
77. The method of claim 76, wherein the surface of the article is
non-planar.
78. A device for adhering at least one biological species in a
specific and predetermined pattern comprising: a surface; a
plurality of immobilization islands in a specific and predetermined
pattern over the surface that adhere biological species to the
islands, the islands isolated from each other by a background
region contiguous with the islands and to which the biological
species do not adhere, and wherein the islands or the background
region or both comprise a self-assembled monolayer.
79. The device of claim 78, wherein the biological species is a
cell.
80. The device of claim 78, wherein the background region or the
immobilization islands comprise more than one self-assembled
monolayer.
81. A device for selectively adhering protein in a specific and
predetermined pattern comprising: a surface; a plurality of
immobilization islands in a specific and predetermined pattern over
the surface that selectively adhere protein to the islands, the
islands isolated from each other by a background region contiguous
with the islands and to which the protein does not adhere.
82. A device having a surface, comprising: islands of a
self-assembled monolayer terminating in a non-polar functionality
surrounded by regions of a polyethylene glycol-terminating
self-assembled monolayer, wherein the nonpolar functionality of the
islands is protein adherent, while the polyethylene glycol is not
protein adherent.
83. A device for immobilizing at least one biological material in a
specific and predetermined pattern comprising: a surface; an array
of immobilization islands in a specific and predetermined pattern
over the surface isolated from each other by at least one
background region; the array of immobilization islands comprising a
first self-assembled monolayer having a formula HS(CH.sub.2).sub.nR
in which R comprises at least one first functional group and
wherein the at least one first functional group is selected to be
biophilic; the at least one background region comprising a second
self-assembled monolayer having a formula HS(CH.sub.2).sub.nR in
which R comprises a second functional group wherein the second
functional group is selected to be biophobic; and wherein the
HS(CH.sub.2).sub.n portion of the first and second self-assembled
monolayers are the same.
84. An article defining a surface; the surface comprising a
plurality of isolated regions of a molecular species on the
surface, the plurality of isolated regions defining a pattern, the
pattern corresponding to a pattern of a stamping surface able to
direct formation of the pattern of the molecular species on the
surface, wherein the molecular species exposes a first chemical
functionality.
85. The article of claim 84, wherein the plurality of isolated
regions comprise a self-assembled monolayer on the surface.
86. The article of claim 84, wherein the first chemical
functionality selectively binds a species selected from the group
consisting of proteins, antibodies, antigens and carbohydrates.
87. A device having a surface, comprising: a layer of a molecular
species, comprising a biological attachment agent, in a first,
predetermined pattern, the layer being contiguous with a portion of
the surface that is in a second, predetermined pattern, wherein the
molecular species terminates in a functional group selected to bind
to a particular material.
88. A biological device having a surface, comprising: a plurality
of spaced apart isolated regions of a molecular species over the
surface in a predetermined pattern, wherein the molecular species
of the isolated regions is a biological attachment agent that
facilitates attachment of biomolecules while maintaining the
function of the biomolecules.
89. The device of claim 88, wherein each isolated region is less
than 10 microns.
90. The device of claim 89, wherein each isolated region is less
than 5 microns.
91. The device of claim 90, wherein each isolated region is less
than 0.1 microns.
92. The device of claim 88, wherein the isolated region of a
molecular species in a predetermined pattern is surrounded by an
inert background region.
93. A device comprising: at least one isolated region of a
molecular species over the surface in a predetermined pattern,
wherein the molecular species of the isolated region is a protein
attachment agent that facilitates attachment of at least one
protein to the isolated region.
94. An array device comprising: a surface; and one or more
immobilization islands in a pattern over the surface and surrounded
by a background region, the background region comprising a species
forming a self-assembled monolayer and terminating in a functional
group selected to bind to a particular material.
95. A device comprising: a substrate having a surface material; at
least one isolated region over the surface, each isolated region
comprising a molecular species comprising the structure R'-A-R",
where R' is selected to bind to the surface material, A is a spacer
and R" is a group that is exposed; the molecular species being a
biological attachment agent.
96. The device of claim 95, wherein the at least one isolated
region is surrounded by an inert background region.
97. A device for immobilizing at least one biological material in a
specific and predetermined pattern comprising: a surface; an array
of immobilization islands in a specific and predetermined pattern
over the surface isolated from each other by at least one
background region; the pattern corresponding to a pattern of a
stamping surface able to direct formation of the pattern of the
immobilization islands on the surface; the array of immobilization
islands comprising a first self-assembled monolayer having an at
least one first functional group and wherein the at least one first
functional group is selected to be biophilic; and the at least one
background region comprising a second self-assembled monolayer
having a second functional group wherein the second functional
group is selected to be biophobic.
98. A kit comprising: an article constructed and arranged to
transfer a self-assembled monolayer-forming molecular species to a
substrate surface, comprising an applicator surface having at least
one indentation formed therein and a protrusion pattern adjacent
the at least one indentation, the article able to transfer a
self-assembled monolayer-forming molecular species from the
applicator surface to the substrate surface; and a self-assembled
monolayer-forming molecular species for application to the
substrate surface by the article.
99. The kit as recited in claim 98, the article surface comprising
at least one resolved feature providing stamping resolution of less
than about 100 microns.
100. The kit as recited in claim 98, the article surface comprising
at least one resolved feature providing stamping resolution of less
than about 10 microns.
101. The kit as recited in claim 98, the article surface comprising
at least one resolved feature providing stamping resolution of less
than about 1 micron.
102. The kit as recited in claim 98, the article surface comprising
at least one resolved feature providing stamping resolution of less
than about 0.25 micron.
103. The kit as recited in claim 98, the article comprising an
elastic material.
104. The kit as recited in claim 103, the elastic material
comprising a hardenable fluid.
105. The kit as recited in claim 103, the elastic material selected
from the group consisting of silicone polymers and copolymers,
epoxy polymers and copolymers, and copolymers thereof.
106. The kit as recited in claim 98, the article comprising
polydimethyl siloxane.
107. A kit as in claim 24, the applicator surface including a
portion having a lateral dimension of less than about 1 micron.
108. A kit as in claim 24, the applicator surface including a
portion having a lateral dimension of less than about 0.25
micron.
109. A kit as in claim 24, the applicator formed of an elastic
material.
110. A kit as in claim 24, the applicator formed of an elastic
material formed form a hardenable fluid.
111. The kit as in claim 110, the elastic material selected from
the group consisting of silicone polymers and copolymers, epoxy
polymers and copolymers, and copolymers thereof.
112. The kit as in claim 41, wherein the applicator surface
includes a portion having a lateral dimension of less than about
0.25 micron.
113. A kit as in claim 41, the applicator surface including a
portion having a lateral dimension of less than about 1 micron.
114. A kit as in claim 41, the applicator surface including a
portion having a lateral dimension of less than about 0.25
micron.
115. A kit as in claim 41, the applicator formed of an elastic
material.
116. A kit as in claim 41, the applicator formed of an elastic
material formed form a hardenable fluid.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 09/164,733, by Whitesides et al., entitled "Methods of Etching
Articles via Microcontact Printing", filed Oct. 1, 1998, which is a
divisional of U.S. application Ser. No. 08/677,309, by Whitesides
et al., entitled "Methods of Etching Articles via Microcontact
Printing", filed Jul. 9, 1996, which is a continuation of U.S.
application Ser. No. 08/676,951, by Whitesides, et al., entitled
"Microcontact Printing On Surfaces and Derivative Articles", filed
Jul. 8, 1996, which is a continuation-in-part of U.S. application
Ser. No. 08/397,635, filed Mar. 1, 1995, which is a
continuation-in-part of U.S. application Ser. No. 08/131,841, filed
Oct. 4, 1993, now U.S. Pat. No. 5,512,131, issued Apr. 30,
1996.
FIELD OF THE INVENTION
[0003] The present invention relates generally to derivatization
and patterning of surfaces and more particularly to the formation
of self-assembled molecular monolayers on surfaces using
microcontact printing, derivative articles produced thereby, and
novel optical elements.
BACKGROUND OF THE INVENTION
[0004] In fields involving microelectronic devices, sensors, and
optical elements, the development of devices that are small
relative to the state of the art, controllable, and conveniently
and relatively inexpensively reproduced with a relatively low
failure rate is important.
[0005] A well-known method of production of such devices is
photolithography. According to this technique, a negative or
positive resist (photoresist) is coated onto the exposed surface of
a material. The resist then is irradiated in a predetermined
pattern, and irradiated (positive resist) or nonirradiated
(negative resist) portions of the resist are washed from the
surface to produce a predetermined pattern of resist on the
surface. This is followed by one or more procedures. For example,
the resist may serve as a mask in an etching process in which areas
of the material not covered by resist are chemically removed,
followed by removal of resist to expose a predetermined pattern of
the conducting, insulating, or semiconducting material on the
substrate. According to another example, the patterned surface is
exposed to a plating medium or to metal deposition under vacuum,
followed by removal of resist, resulting in a predetermined plated
pattern on the surface of the material. In addition to
photolithography, x-ray and electron-beam lithography have found
analogous use.
[0006] While the above-described irradiative lithographic methods
may be advantageous in many circumstances, all require relatively
sophisticated and expensive apparatus to reproduce a particular
pattern on a plurality of substrates, and are relatively
time-consuming. Additionally, no method of patterning nonplanar
surfaces is commonly available according to these methods. In the
field of electronic circuitry, an attempt is often made to save
space by stacking planar circuit boards or chips, the boards or
chips interconnected with auxiliary contacts. Alternately, a board
or chip may be bent or otherwise formed in a nonplanar manner so as
to save space, auxiliary contacts connecting components on
different sides of the bend. All too often these auxiliary contacts
are the cause of circuitry failure, and the attempt to move from
the two-dimensional domain to a three-dimensional domain fails.
Irradiative lithography provides no remedy to this complication,
nor does it provide a method of conveniently and inexpensively
reproducing an existing microelectronic circuit pattern, or the
surface morphological features of other objects of interest.
[0007] Additionally, the above-described irradiative techniques are
generally not amenable to the patterning of biological species such
as proteins, as they typically utilize resists and solvents that
are toxic to many biological species.
[0008] A need exists in the art for a convenient, inexpensive, and
reproducible method of plating or etching a surface according to a
predetermined pattern. The method would ideally find use on planar
or nonplanar surfaces, and would result in patterns having features
in the micron and submicron domain. Additionally, the method would
ideally provide for convenient reproduction of existing patterns.
Additionally, a need exists for the fabrication of surfaces that
can pattern portions amenable to attachment of biological species,
such as antibodies, antigens, proteins, cells, etc., on the
micrometer scale.
[0009] The study of self-assembled monolayers (SAMs) is an area of
significant scientific research. Such monolayers are typically
formed of molecules each having a functional group that selectively
attaches to a particular surface, the remainder of each molecule
interacting with neighboring molecules in the monolayer to form a
relatively ordered array. Such SAMs have been formed on a variety
of substrates including metals, silicon dioxide, gallium arsenide,
and others. SAMs have been applied to surfaces in predetermined
patterns in a variety of ways including simple flooding of a
surface and more sophisticated methods such as irradiative
patterning.
[0010] Accordingly, a general purpose of the present invention is
to solve problems associated with expense, complicated apparatus,
and other complications associated with patterning surfaces for
electronic, chemical, biological, and optical devices. One object
is to provide a method of conveniently and reproducibly producing a
variety of SAM patterns on planar and nonplanar surfaces, the
patterns having resolution in the submicron domain, and being
amenable to plating, etc. Another purpose of the invention is to
facilitate the attachment of biomolecules on the submicron scale
without loss of biological function. Another purpose of the
invention is to provide a method of forming a template from an
existing pattern having micron or submicron-domain features, the
template conveniently reproducing the preexisting pattern.
[0011] Another general purpose of the invention is to provide
optical elements and devices that are conveniently and
inexpensively manufactured, and that are adaptable to a variety of
systems.
SUMMARY OF THE INVENTION
[0012] The present invention provides a method of etching an
article that is coated with a thin layer of resist. The method
involves contacting a first portion of the resist surface with a
stamp to transfer to the first portion a self-assembled monolayer
of a molecular species in a first pattern. The self-assembled
monolayer is contiguous with an exposed portion of the resist
surface in a second pattern. The resist is removed from the surface
of the article, according to the second pattern, by contacting the
exposed portion of the resist surface with a first etchant that
reacts chemically with the resist and that is inert with respect to
the self-assembled monolayer. This exposes the surface of the
article in the second pattern. A second etchant is applied to the
exposed surface of the article that reacts chemically with the
article and that is inert with respect to the resist. According to
one aspect the resist is an electrical conductor. According to
another, the resist is a metal oxide, and can be an oxide of the
article. The article can be a semiconductor such as silicon gallium
arsenide, or the like, and can have a nonplanar surface.
[0013] According to one embodiment, the self-assembled monolayer
exposes a chemical functionality in the first pattern, and prior to
the removing the resist, the molecular species is coated with a
protecting species that is compatible with the chemical
functionality and incompatible with the first etchant.
[0014] The present invention provides also a method of etching an
article involving contacting a first portion of the surface of the
article with a stamp to transfer to the first portion a
self-assembled monolayer of a molecular species in a first pattern,
the self-assembled monolayer being contiguous with an exposed
portion of the surface in a second pattern and exposing a chemical
functionality. A protecting species that is compatible with the
chemical functionality is applied to the self-assembled monolayer,
and the exposed portion of the surface is contacted with an etchant
that reacts chemically with the resist and that is incompatible
with the protecting species. According to another embodiment, the
self-assembled monolayer exposes a chemical functionality, in the
first pattern, that is less compatible with the protecting species
than is the surface of the article that remains uncovered with the
self-assembled monolayer. In this embodiment, the protecting
species is positioned on the surface at regions not covered by the
self-assembled monolayer and, when the etchant is applied, the
etchant etches the article at regions not covered by the protecting
species (including those regions originally covered by the
self-assembled monolayer).
[0015] The present invention provides also a method of applying to
a surface of an article a self-assembled monolayer of a molecular
species. The method involves coating a portion of a stamping
surface of a stamp with a self-assembled monolayer-forming
molecular species, and transferring from the stamping surface to a
first portion of the article surface the molecular species, while
applying to a second portion of the article surface contiguous with
the first portion a species that is not compatible with the
molecular species. According to one aspect the method involves
allowing the molecular species to spread evenly from the first
portion of the article surface to the second portion of the article
surface. According to another aspect the first portion of the
article surface includes at least two isolated regions separated by
the second portion, and the method involves transferring the
molecular species from the stamping surface to the at least two
isolated regions of the first portion, while applying to a second
portion the species that is not compatible with the molecular
species. The molecular species is allowed to spread from each of
the at least two isolated regions of the first portion toward each
other. The molecular species can be lipophilic and the species that
is not compatible with the molecular species hydrophilic, or vice
versa, and the article surface can be nonplanar. Prior to or during
the transferring step the stamp can be deformed.
[0016] The present invention also provides a method involving
applying to a surface of an article a first region and a second
region of a self-assembled monolayer, where the first and the
second regions are separated from each other by an intervening
region. A species that is incompatible with the molecular species
that forms the self-assembled monolayer is applied to the
intervening region, and the molecular species is allowed to spread
evenly from the first region toward the second region and from the
second region toward the first region.
[0017] The present invention also provides a method of applying to
a surface of an article a self-assembled monolayer of a molecular
species. The method involves coating a portion of a stamping
surface of a flexible stamp with a self-assembled monolayer-forming
molecular species, deforming the stamp, and contacting at least a
portion of the surface with at least a portion of the stamping
surface. The stamp can be deformed by compressing it in a plane
approximately parallel to the stamping surface, and/or by applying
a force to it in a direction approximately perpendicular to the
stamping surface.
[0018] The present invention also provides a method of making an
article, involving etching a pattern into a surface of a template,
and molding the article on the surface of the template. This can
involve applying to the template a hardenable fluid and-allowing
the fluid to harden. For example, a prepolymeric fluid can be
applied to the template and polymerized. According to one aspect,
the hardenable fluid is a fluid precursor of an elastomer. The
etching can be anisotropic etching.
[0019] The present invention also provides a method of making an
article that involves providing a template having a surface
anisotropically etched in a pattern, applying a hardenable fluid to
the surface, and allowing the fluid to harden.
[0020] The present invention also provides a method of patterning a
self-assembled monolayer on a nonplanar surface of an article. The
method involves rolling the nonplanar surface of the article over a
stamping surface of a stamp carrying a self-assembled
monolayer-forming molecular species, thereby transferring to the
nonplanar surface a self-assembled monolayer of the molecular
species. According to one aspect, the rolling step involves
applying to the nonplanar surface the self-assembled monolayer in a
pattern, while leaving portions of the surface contiguous with the
self-assembled monolayer exposed. According to one aspect the
exposed portions of the surface are etched.
[0021] The present invention also provides a method of making a
lens, involving providing a hardenable fluid precursor of the lens,
contacting a surface of the fluid precursor with a liquid that is
incompatible with the fluid precursor, and allowing the fluid
precursor to harden to form a lens. The precursor can be a
prepolymeric fluid, and can be a precursor of an elastomer.
[0022] The present invention also provides a method of making an
article, involving providing a supporting surface having, on a
discrete isolated region, a self-assembled monolayer of a molecular
species, applying to the self-assembled monolayer a fluid precursor
of the article, the precursor having a surface including a first
region in contact with the self-assembled monolayer and a second,
exposed region contiguous with the first region, contacting the
exposed region of the precursor surface with a fluid that is
incompatible with the precursor fluid, and allowing the precursor
to harden.
[0023] The present invention also provides a method of making a
diffraction grating, involving coating a surface of a template with
a hardenable, fluid diffraction grating precursor, allowing the
fluid precursor to harden and form a diffraction grating, and
removing the diffraction grating from the template.
[0024] The present invention also provides a method of making an
optical element, involving molding an article by coating a mold
having an optical surface with a hardenable fluid and allowing the
fluid to harden to form an article having an optical surface that
correlates to the optical surface of the mold, removing the article
from the mold, and contacting the optical surface of the article
with a liquid metal.
[0025] The present invention also provides articles made by the
above and other methods, including an article including on its
surface an isolated region of a self-assembled monolayer of a
molecular species, the isolated region including a lateral
dimension of less than 10 microns. Preferably, the dimension is
less than 5 microns, more preferably less than 1 micron, more
preferably less than 0.5 micron, more preferably less than 0.25
micron, more preferably less than 0.2 micron, more preferably less
than 0.15 micron, and most preferably less than 0.1 micron. Also
provided is a device including on its surface an pattern of a
self-assembled monolayer of a molecular species, the pattern having
a lateral dimension of less than 10 microns, or one of the other
preferred dimensions above. Also provided is a device including on
its surface an pattern of a self-assembled monolayer of a molecular
species, the pattern including two closely-spaced regions of a
single self-assembled monolayer, or closely-spaced different
self-assembled monolayers, the dimension between them being less
than 10 microns, or one of the other preferred dimensions
above.
[0026] The present invention also provides a diffraction grating
including a liquid metal having a surface that is in contact with
and correlates to a surface of an article. The article surface
correlates to an diffraction grating, and the liquid metal surface
is formed thereby into a diffraction grating. The grating can be
transparent and flexible, preferably transparent and
elastomeric.
[0027] The present invention also provides an optical element
including an elastomer including a void having an optical convex or
concave surface, and a liquid metal adjacent the convex or concave
surface of the void. Preferably, the liquid metal fills the void
and is encapsulated by the elastomer.
[0028] The present invention also provides a device including an
article defining a surface, a first and a second isolated region of
a self-assembled monolayer on the surface, the first and second
regions separated from each other by less than 10 microns.
Preferably, the separation is one of the preferred dimensions
above.
[0029] The present invention also provides a device including an
article defining a surface, and a self-assembled monolayer on the
surface, forming a pattern having a lateral dimension of less than
10 microns. Preferably, the lateral dimension is one of the
preferred dimensions above.
[0030] The present invention also provides methods utilizing the
above and other devices and arrangements, including a method of
diffracting electromagnetic radiation. The method involves
directing electromagnetic radiation at a liquid metal having a
surface that is a diffraction grating to cause diffraction of the
electromagnetic radiation, and allowing diffracted electromagnetic
radiation to reflect from the surface. The surface of the liquid
metal that is a diffraction grating can be deformed (elongated or
stretched, bent, compressed, e.g.) to adjust the pattern of
diffraction of the electromagnetic radiation.
[0031] The present invention also provides a method of focusing
electromagnetic radiation, involving directing electromagnetic
radiation at a liquid metal having a concave surface, and allowing
the electromagnetic radiation to reflect from the surface.
[0032] The present invention also provides a method of controlling
the shape of a liquid, involving providing a supporting,
electrically-conductive surface having, on a discrete isolated
region, a self-assembled monolayer of a molecular species exposing
a chemical functionality that is compatible with the liquid,
positioning the liquid on the self-assembled monolayer of the
molecular species, surrounding the liquid with a fluid electrolyte
that is not compatible with the liquid, and adjusting an electrical
potential of the electrically-conductive surface to control the
shape of the liquid.
[0033] The present invention also provides a method of printing a
self-assembled monolayer on a surface of an article, involving
rolling over the surface of the article a nonplanar stamping
surface of a stamp carrying a self-assembled monolayer-forming
molecular species.
[0034] Other advantages, novel features and objects of the
invention will become apparent from the following detailed
description of the invention when considered in conjunction with
the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0035] FIGS. 1a-f illustrate microprinting of a self-assembled
molecular monolayer on a surface, utilizing controlled reactive
spreading in accordance with the invention;
[0036] FIGS. 2a-e illustrate silicon surfaces selectively patterned
with gold using controlled reactive spreading in conjunction with
microprinting in accordance with the invention;
[0037] FIGS. 3a-c illustrate deformation of a microprinting stamp
to achieve patterned self-assembled molecular monolayers with small
features in accordance with the invention;
[0038] FIGS. 4a-d illustrate silicon surfaces selectively patterned
with gold via mechanical deformation of a stamp in accordance with
the invention;
[0039] FIGS. 5a-c illustrate a method of applying a patterned
self-assembled molecular monolayer to a nonplanar surface in
accordance with the invention;
[0040] FIGS. 6a-c illustrate nonplanar surfaces derivatized using
the technique illustrated in FIGS. 5a-c;
[0041] FIG. 7 illustrates an optical fiber having an exterior
surface patterned with a self-assembled molecular monolayer
according to the invention;
[0042] FIGS. 8a-d illustrate a method of etching an article
according to the invention;
[0043] FIGS. 9a-f illustrate a method involving lithographic
molding of an article in accordance with the invention;
[0044] FIG. 10 is an atomic force microscope image of an article
lithographically molded in accordance with the invention;
[0045] FIGS. 11a-f illustrate methods of forming flexible
diffraction gratings in accordance with the invention, and a
diffraction grating formed thereby;
[0046] FIGS. 12a-d illustrate a method of forming a flexible lens
in accordance with the invention, and a lens formed thereby;
[0047] FIG. 13 illustrates a method for forming an optical element
in accordance with the invention;
[0048] FIG. 14 illustrates apparatus for controlling the shape of a
fluid on a surface in lo accordance with the invention;
[0049] FIGS. 15a and 15b illustrate apparatus for controlling the
shape of a fluid on two surfaces in accordance with the invention;
and
[0050] FIGS. 16a-e illustrate a method of etching an article in
accordance with one embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0051] Commonly-owned U.S. patent application Ser. No. 08/131,841,
filed Oct. 4, 1993 by Kumar et al. and entitled "Formation of
Microstamped Patterns on Surfaces and Derivative Articles", now
U.S. Pat. No. 5,512,131, issued Apr. 30, 1996, the entire content
of which is incorporated herein by reference for all purposes,
describes stamping, or microprinting, self-assembled monolayers
onto surfaces, etching and plating such surfaces, assembling
isolated regions of self-assembled monolayers exposing a particular
chemical functionality, optionally surrounded by a self-assembled
monolayer exposing a different functionality, and derivative
articles. U.S. application Ser. No. 08/397,635, filed Mar. 1, 1995,
co-pending and commonly-owned, is incorporated herein by reference
for all purposes.
[0052] Referring to FIGS. 1a-d, a method for applying a
self-assembled monolayer of a molecular species to a surface that
involves controlled, reactive spreading of the species on the
surface is illustrated schematically. The method results in two or
more self-assembled molecular monolayers, or two or more regions of
a single self-assembled molecular monolayer, that are very closely
spaced on the surface. At FIG. 1a, a stamp 20 is illustrated having
a surface 22 including a plurality of indentations 24 formed
therein that form an indentation pattern. The indentations are
contiguous with a stamping surface 26 that defines a stamping
pattern. The stamping pattern includes closely-spaced features,
that is, the indentations are closely-spaced and this results in
the presence of closely-spaced protrusions, the outward-facing
surfaces of which define the stamping surface 26.
[0053] Prior to microprinting, stamping surface 26, typically the
entire surface 22 of the stamp, is coated with a molecular species
27. Molecular species 27 terminates in a functional group selected
to bind to a particular material, and to form an ordered
self-assembled monolayer thereupon. In the embodiment illustrated
in FIGS. 1a-f, species 27 terminates in a functional group selected
to bind to a surface 28 of an article 30, and to form a
self-assembled monolayer on surface 28. A wide variety of species
suitable as species 27 and surfaces suitable as surface 28, that
is, species that terminate in a variety of functional groups, and
surfaces to which they chemisorb, are described in application Ser.
No. 08/131,841.
[0054] Stamp 20 of the present invention may be formed in a variety
of ways. In one embodiment, stamp 20 is formed by contacting a mold
surface with a hardenable material, typically a fluid, which serves
as a precursor of the stamp. The fluid is hardened, for example by
ionic, nonionic, or free-radical polymerization to form the stamp
having a surface contacting the mold surface. A mold surface is
advantageously selected to include at least one protrusion, and
when the stamp is removed from mold surface, a stamp having a
stamping surface including an indentation corresponding to mold
surface protrusion results.
[0055] The particular material chosen for formation of stamp 20
should satisfy certain physical characteristics. Stamp 20 is
advantageously chosen to be elastic, such that stamping surface 26
may very closely conform to minute irregularities in surface 28 of
material 30 so as to completely transfer molecular species 27
thereto, and so as to be amenable to transferring SAMs of molecular
materials to nonplanar surfaces. However, stamping surface 26
should not be so elastic that when it is pressed lightly against a
surface, stamping surface features deform to the extent that
blurring of molecular species 27 on material surface 28
results.
[0056] According to a preferred embodiment, stamp 20 is formed from
a polymeric material. Polymeric materials suitable for use in
fabrication of stamp 20 may have linear or branched backbones, and
may be crosslinked or noncrosslinked, depending upon the particular
polymer and the degree of formability desired of the stamp. A
variety of elastomeric polymeric materials are suitable for such
fabrication, especially polymers of the general classes of silicone
polymers, epoxy polymers, and acrylate polymers. Epoxy polymers are
characterized by the presence of a three-member cyclic ether group
commonly referred to as an epoxy group, 1,2-epoxide, or oxirane.
For example, diglycidyl ethers of bisphenol A may be used, in
addition to compounds based on aromatic amine, triazine, and
cycloaliphatic backbones. Another example includes the well-known
Novolac polymers. Materials which may not be suitable for
fabrication of stamping surface 26 according to preferred
embodiments include polyethylene and polystyrene, which are
generally too brittle, (not elastic enough), and polybutadiene,
which is generally too elastic.
[0057] Examples of silicone elastomers suitable for use as stamp 20
include those formed from precursors including the chlorosilanes
such as methylchlorosilanes, ethylchlorosilanes, and
phenylchlorosilanes, and the like. A particularly preferred
silicone elastomer is polydimethyl siloxane. Exemplary polydimethyl
siloxane polymers include those sold under the trademark Sylgard by
the Dow Chemical Company, Midland Mich., and particularly Sylgard
182, Sylgard 184, and Sylgard 186.
[0058] The ability to transfer SAMs to nonplanar surfaces is
particularly advantageous in the preparation of microelectronic
devices on curved surfaces, for example microconnections between
various circuit regions, the connections conforming to a bend to
conserve space in an overall circuit-containing region. Stamp 20
should also be formed such that stamping surface 26 comprises an
absorbent material selected to absorb SAM-forming molecular species
27 to be transferred to a surface 28 to form a SAM thereon.
Stamping surface 26 preferably swells to absorb molecular species
27, and/or to absorb molecular species 27 dissolved or suspended in
a carrier such as an organic solvent. Such swelling and absorbing
characteristics serve the important function of providing good
definition of an isolated SAM on a surface. For example, if a
dimensional feature of stamping surface 26 includes a substantially
square-shaped feature, surface 26 should transfer molecular species
27 to surface 28 of material 30 so as to form SAMs mirroring the
substantially square features of stamping surface 26, without
blurring. Such blurring results from selection of a stamp which
does not absorb molecular species 27. When such a stamp is
employed, molecular species 27 resides as a fluid on stamping
surface 26, rather than partially or fully within surface 26, and
when stamping surface 26 contacts material surface 28, molecular
species 27 is dispersed from under stamping surface 26. According
to the stamp of the present invention, however, molecular species
27 is absorbed into stamping surface 26, and when stamping surface
26 contacts material surface 28, molecular species 27 is not
dispersed, but binds to surface 28, and removal of stamping surface
26 from surface 28 results in well-defined SAM features.
[0059] Referring to FIG. 1b, stamp 20 is placed, in a predetermined
orientation, adjacent to article 30 such that stamping surface 26
contacts article surface 28. Prior to, during, or shortly after
stamping surface 26 is brought into contact with surface 28, a
species 32 is applied to portions of surface 28 of article 30 that
are not contacted by stamping surface 26. That is, surface 28 of
article 30 includes at least a first portion 34 to which the
self-assembled molecular species is transferred from the stamping
surface, and at least a second portion 36, contiguous with first
portion 34, to which is applied species 32.
[0060] Species 32 is incompatible with self-assembled
monolayer-forming molecular species 27. As used herein,
"compatible" is used to define species that have at least some
mutual attraction, or at least are not mutually repulsive. For
example, two polar species are compatible, and two nonpolar species
are compatible. Miscible liquids, for example two different aqueous
solutions, are compatible species. "Incompatible" is used herein to
define species that are mutually repulsive to the extent that they
are not miscible. For example, most organic liquids are
incompatible with most aqueous solutions. Incompatible liquids will
coexist separated by a phase boundary. An etchant that is inert
with respect to a species such as a self-assembled monolayer is
often inert with respect to the species since it is incompatible
with the species. One of ordinary skill in the art can readily
select such incompatible species, and a test to determine the
compatibility or incompatibility of such species is routine to one
of ordinary skill in the art. Species 32 is selected as one that
does not chemisorb to surface 28. Thus, species 32 has a lesser
affinity for surface 28 than does self-assembled monolayer-forming
molecular species 27.
[0061] Typically, species 27 is a hydrophobic liquid or is carried
in a hydrophobic liquid, as described in the above-referenced
application Ser. No. 08/131,841. Species 27 also can be a
hydrophilic liquid, or carried in a hydrophilic liquid. When
species 27 (or a liquid in which species 27 is dissolved) is
hydrophobic, species 32 is selected to be hydrophilic. When species
27 is hydrophilic, species 32 is selected to be hydrophobic. It is
important only that species 27 and species 32 are incompatible.
[0062] For example, species 27 can include a hydrophobic long-chain
alkyl group that terminates in a functional group that
spontaneously chemisorbs to surface 28, and species 32 can be water
or an aqueous solution. Alternatively, species 27 can be a
long-chain alkyl group including sufficient heteroatoms to make
species 27 hydrophilic and species 32 in that case can be a liquid
that is sufficiently hydrophobic to be incompatible with species
27.
[0063] Referring now to FIG, 1c, the method involves allowing
stamping surface 26 to remain in contact with surface 28 for a
period of time sufficient to allow molecular species 27 to spread
from portion 34 of surface 28 onto portion 36 of the surface. This
occurs as species 27, transferred from stamping surface 26, has a
greater affinity for surface 28 of article 20 than does species
32.
[0064] Stamp 20 is maintained in contact with article 30 for a
period of time sufficient to allow species 27 to spread over
surface 28 to a desired extent. The extent of spreading is,
typically, approximately proportional to the time of contact
between stamp 20 and article 30. Stamp 20 is advantageously allowed
to contact article 30 for a period of time sufficient to allow
species 27 to spread from each portion of stamping surface 26
toward an adjacent portion. In this way, species 27 is allowed to
spread across surface 28 to form an increasingly narrow gap 38
(FIG. 1d) on surface 28. Gap 38 on surface 28 thus is not coated
with species 27.
[0065] The presence of incompatible species 32 applied to portions
of surface 28 that are not coated with species 27 facilitates the
spreading of species 27 over surface 28 in a smooth, well-defined
manner. That is, species 27 does not spontaneously chemisorb at
random, isolated portions 36 of surface 28 between adjacent regions
of stamping surface 26 via vapor transport or the like. The method
of the invention results in very well-defined, very closely-spaced
regions of species 27 on surface 28.
[0066] In FIG. 1d, stamp 20 has been removed from article 30, and a
scanning electron micrograph of the surface of article 30 that has
been patterned according to the embodiment illustrated is shown in
FIG. 1e. In the embodiment illustrated, dimension 40, the width of
indentations 24 between protrusions of stamp 20 that define
stamping surface 26, is 3 microns, while the dimension of gap 38
between adjacent regions of self-assembled monolayer 27 that have
spread toward each other is 0.1 micron.
[0067] FIG. 1e is a scanning electron micrograph of a silicon
article 30, coated with a thin layer of gold, upon the surface of
which species 27 has been allowed to spread in accordance with the
method illustrated in FIGS. 1a-d. After removal of stamp 20, an
etchant is applied to the surface. The etchant is not compatible
with species 27, and species 27 is therefore undisturbed by the
etchant. The etchant contacts surface 28 of the thin gold layer on
silicon article 30 (not shown in FIGS. 1a-d) via gap 38, and
dissolves the gold layer at gap 38. The result is illustrated in
FIG. 1e, and an atomic force microscope image is shown in FIG. 1f.
Following removal of the self-assembled monolayer of species 27, a
thin gold layer that has been etched at gap 38, to form adjacent
regions of gold on a silicon surface separated by approximately
0.100 micron, results.
[0068] FIGS. 1a-d illustrate an end view of a stamp 20 that
includes a plurality of elongated, linear ridges 26, separated by
recessed portions of the stamp. When such a stamp is brought into
contact with a surface of an article in a first orientation,
followed by removal of the stamp, rotation of the stamp through
90.degree. relative to the surface of the article, and
reapplication of the stamp to the surface, a grid pattern of
species 27 on surface 28 results. During each application of the
stamping surface to the surface of the article, the stamp can be
held in contact with the stamping surface for varying periods of
time, resulting in a grid of lines of molecular species 27 of
varying width. Scanning electron micrographs of such a procedure
are shown in FIGS. 2a-e. The surfaces shown in FIGS. 2a-e were
derivatized by covering a silicon article with thin layer of gold,
applying species 27 to the gold surface via microprinting with a
microstamp, and contacting exposed portions of the gold surface
(those portions not covered by the self-assembled monolayer) with
an etchant that is not compatible with species 27 and that
dissolves gold. The etchant is thus inert with respect to species
27. For each of FIGS. 2a-e, stamp 20 was applied to the surface in
a first orientation for a first period of time ("1st printing"),
and applied to the surface in a second orientation rotated
90.degree. from the first orientation for a second period of time
("2nd printing"). The time that stamping surface 26 was allowed to
contact surface 28, for each printing step, is listed beside each
figure. Control of the length and width of exposed portions of
silicon results. Dark portions 41 are exposed regions of silicon
following etch, and light regions 42 are the self-assembled
monolayer on the gold surface. The procedures described with
respect to FIGS. 1 and 2 are described in greater detail below in
Example 1.
[0069] Referring now to FIGS. 3a-c, a method for applying a
self-assembled monolayer of a molecular species to a surface of an
article according to another embodiment of the invention is
illustrated, in which a stamp is deformed prior to and/or during
transfer of the species to the surface. FIG. 3a illustrates,
schematically, an end view of a portion of a stamp 20 including a
surface 22 that includes a stamping surface 26 separated by
indentations 24. Stamp 20 is deformed prior to and/or during
transfer of a self-assembled monolayer-forming molecular species
27, which coats stamping surface 26 (typically coating the entire
surface 22 of stamp 20), to surface 28 of article 30. When stamp 20
is deformed prior to transfer, it generally is compressed by
applying to the stamp forces parallel to the stamping surface. That
is, with reference to FIG. 3b, force is applied to the stamp in the
direction of arrows 44. This results in reduction in the dimension
of individual portions of stamping surface 26 along the direction
of the application of force, as well as reduction of the dimension
of indentations 24 in the same direction. That is, features of
stamping surface 26 are reduced in size, and in spacing from each
other, in the direction parallel to the application of force.
[0070] When stamping surface 26 (generally the entire surface 22)
of stamp 20 is coated with molecular species 27 (not illustrated in
FIG. 3b) and allowed to contact surface 28 of article 30, a
self-assembled monolayer is formed on surface 28 that includes
regions having lateral dimensions that correspond approximately to
the dimension of features of stamping surface 26. Thus, when stamp
20 is deformed as illustrated in FIG. 3b, self-assembled
monolayers, or a self-assembled monolayer having separate regions,
is formed on a surface with dimensions smaller than those that
would be achieved typically when the stamp is not deformed.
Referring to FIG. 3c, stamp 20 is illustrated with stamping surface
26 in contact with surface 28 of article 30, where the stamp has
been deformed by applying a force perpendicular to stamping surface
26, that is, perpendicular to surface 28 of article 30. This
perpendicular force is represented by arrows 46, and can be applied
independently of, or in combination with, a compressive force on
the stamp that is parallel to the stamping surface and that is
represented by arrows 44. Application of a compressive force
represented by arrows 44 and/or a perpendicular force represented
by arrow 46 will result in reduced feature sizes of species 27 on
surface 28. When a force perpendicular to stamping surface 26 is
applied, as represented by arrows 46, gap 38 between regions of
species 27 on surface 28 is smaller than the dimension of
indentations 24 between regions of stamping surface 26. Thus, the
stamp is deformed as illustrated in FIG. 3c where the distance
between adjacent regions of stamping surface 26 is lessened.
[0071] Although only compressive forces are described with respect
to deformation of stamp 20 during microprinting, stamp 20 can be
deformed by stretching, as well.
[0072] Referring now to FIGS. 4a-c, scanning electron micrographs
showing surfaces derivatized via microstamp deformation are shown.
The figures represent printing using a microstamp deformed by
compressing the stamp by applying force parallel to the stamping
surface (arrows 44 of FIG. 3b), independently along perpendicular
axes. A silicon article covered with a thin layer of gold was
provided, with a self-assembled monolayer applied to the gold
surface. Gold was etched from regions to which the monolayer was
not applied. In FIGS. 4a-c, light regions 48 represent the
self-assembled monolayer on the thin gold film on silicon, and
regions 50 represent exposed silicon surface from which gold has
been etched. A stamp used to apply a self-assembled monolayer to
the gold surface was fabricated generally as described below in
example 1, and included a surface including indentations
represented by regions 50, defining a stamping surface represented
by regions 48. FIG. 4a illustrates a surface to which a
self-assembled molecular monolayer was applied from the stamp
without deformation of the stamp, followed by etching of gold from
regions to which the self-assembled monolayer was not applied. In
FIG. 4b, the stamp was compressed along an axis parallel to the
stamping surface, by applying force as illustrated by arrows 52. In
FIG. 4c, the stamp was compressed along an axis parallel to the
stamping surface, by applying force in the direction of arrows 54,
perpendicular to the compressive force applied in FIG. 4b. In FIG.
4d, the stamp was compressed along two perpendicular axes, both
axes being parallel to the stamping surface, by applying force as
illustrated by arrows 52 and 54.
[0073] Mechanical deformation of a stamp as described above and
illustrated in FIGS. 3a-c and 4a-d can be employed in conjunction
with controlled reactive spreading of molecular species as
described above and illustrated in FIGS. 1a-f and 2a-e. That is, a
stamp can be deformed, and held in contact with a surface to
transfer a self-assembled monolayer thereto, while applying, to
regions of the surface not contacted by the stamping surface, a
species that is not compatible with the molecular species that
forms the self-assembled monolayer. This procedure, as described
above, advantageously includes allowing the stamp to remain in
contact with the surface for a period of time sufficient to allow
the molecular species to spread accordingly.
[0074] All of the embodiments of the invention described thus far
can be used in conjunction with methods of etching and/or plating a
surface as described below, and as described in U.S. application
Ser. No. 08/131,841, referenced above.
[0075] Referring now to FIGS. 5a-c, a method of transferring a
patterned, self-assembled monolayer to a nonplanar surface is
illustrated schematically. As used herein, the term "nonplanar" is
meant to define a surface, at least a portion of which has a radius
of curvature. The method that is illustrated involves rolling a
nonplanar surface, that is, the surface of a nonplanar article,
over a stamping surface of a stamp carrying a self-assembled
monolayer-forming molecular species. The surface that is rolled
over the stamp can be that of a cylindrical article, a spherical
article, or any other article having a nonplanar surface. Stamp 20
in this embodiment is flat, that is, stamping surface 26 defines
portions of a plane. In other embodiments (not illustrated), the
stamp is nonplanar, that is, formed such that the stamping surface
does not define a plane, or is a flexible, planar stamp that is
deformed so as to be nonplanar.
[0076] Referring to FIG. 5a, an article 30 has a nonplanar surface
28. According to the embodiment illustrated, article 30 is silicon
dioxide, coated with a thin layer of titanium (not shown), which is
coated with a thin layer of 31 of gold. Stamping surface 26 of
stamp 20, and generally the entire surface 22 of stamp 20 is coated
with a self-assembled monolayer forming molecular species 27.
Article 30 is caused to roll over stamping surface 26, for example,
by placing article 30 between stamping surface 26 and a member 56,
moving stamp 20 and member 56 relative to each other along parallel
planes in opposite directions, to cause the article to roll over
the stamping surface. Member 56 can be made of any material that
will not disrupt or contaminate surface 28, and preferably a
material that will not disrupt a self-assembled monolayer formed on
surface 28. Member 56 can be made of the same material from which
stamp 20 is made.
[0077] As used herein, the term "roll" refers to action in which a
first surface is maintained in constant contact with a second
surface (for example, surface 28 of article 30 and stamping surface
26, respectively), but only a portion of each surface is in contact
with only a portion of the other surface at any given time, and the
portion of each surface that is in contact with the portion of the
other surface changes continuously.
[0078] Referring now to FIG. 5b, article 30 is illustrated after
having been rotated through approximately 260.degree. of rotation
on stamping surface 26. As a result, individual, isolated regions
of a self-assembled monolayer of molecular species 27 are formed on
surface 28 of article 30 around approximately 260.degree. of the
surface, corresponding to individual regions of stamping surface
26.
[0079] When this article is subject to a cyanide etch, as described
above and described below in Example 2, gold that is not protected
by molecular species 27 is removed, as illustrated in FIG. 5c,
exposing the thin layer of titanium (titanium dioxide) at regions
not covered by the self-assembled monolayer. A nonplanar article,
such as that illustrated in FIGS. 5a-c, can be etched in accordance
with embodiments of the invention described in application Ser. No.
08/131,841, and described below.
[0080] Referring now to FIGS. 6a-c, nonplanar articles covered by a
thin layer of gold, to which patterned, self-assembled monolayers
have been applied, followed by etching of gold from the surface at
regions not protected by the self-assembled monolayer, are
illustrated. In each case, the nonplanar article was rolled across
a substantially planar stamping surface including a stamping
pattern (pattern formed by stamping surface 26). The stamping
pattern includes features similar to those found in typical
electronic circuitry. Gold was etched as described above and
described below in Example 2.
[0081] FIG. 6a illustrates a 1 mm diameter glass capillary coated
with a thin layer of gold, which was printed according to the
pattern illustrated, followed by removal of gold from the areas not
covered by a self-assembled monolayer. FIGS. 6b and 6c show views,
at different magnification, of a lens having a 5 cm radius of
curvature, coated with a thin film of gold, microprinted and etched
as described herein. In FIGS. 6a-c, light regions are gold covered
with a self-assembled monolayer, and dark regions are glass.
[0082] FIG. 7 illustrates an etched optical fiber (glass). The
fiber was coated with approximately 200 angstroms of titanium,
which is coated with approximately 200-300 angstroms of gold. The
exterior surface of the fiber was microstamped with
hexadecanethiol, which served as a resist in a subsequent etch. The
etch step removed the gold layer not covered by the self-assembled
monolayer, and the light regions represent a self-assembled
monolayer of hexadecanethiol on gold, while the dark regions
represent the exterior surface of the optical fiber covered with
titanium.
[0083] In some instances, when it is desirable to use a
self-assembled monolayer as a resist in an etching process, the
self-assembled monolayer may not effectively resist the etchant.
The present invention provides, for such a situation, a protecting
species positioned on a self-assembled monolayer. The protecting
species is inert with respect to the etchant by, for example, being
incompatible with the etchant. The protecting species is compatible
with the exposed functionality of the monolayer. For example,
silicon coated with a thin, thermally-formed layer of silicon
dioxide, is conveniently etched using hydrofluoric acid/ammonium
fluoride. Then, silicon dioxide that has not been etched can serve
as a resist for the etching of silicon and, for example, potassium
hydroxide/isopropanol. However, many self-assembled molecular
monolayers will not withstand (are not inert with respect to) the
etchant used to remove silicon dioxide. The present invention
provides a protecting species that will resist the etch. Many
articles have a native layer of oxide. For example, silicon has a
native layer of oxide that is approximately 5 nanometers thick.
Generally, such a native layer will not serve as an effected
resist. A thermally-formed oxide layer will generally have a
thickness of approximately 0.2 microns. Articles having thermally
formed layers of oxide thereon are readily available commercially.
For example, silicon including a thermally-formed layer of silicon
dioxide thereon is available from Silicon Sense Corporation,
Nashua, N.H.
[0084] Referring to FIGS. 8a-d, a process for etching silicon in
accordance with the present invention is illustrated. FIGS. 8a-d
are schematic illustrations of the process.
[0085] Referring to FIG. 8a, a silicon article 60 includes, on its
surface 62, a thermally-formed layer 64 of silicon dioxide, having
a surface 66. A self-assembled monolayer 68 (for example
alkylsiloxane) is patterned onto the surface 66, using any method
described herein or other method known to those of skill in the
art. Referring to FIG. 8b, molecular species 68 is coated with a
protecting species 70 that is compatible with the molecular
species. That is, molecular species 68 exposes a chemical
functionality that is compatible with the protecting species. If
the chemical functionality exposed by molecular species 68 is
significantly polar, protecting species 70 should be significantly
polar. Protecting species 70 can be a liquid, and can be a
polymerizable species that is polymerized prior to application of
the etchant.
[0086] Referring to FIG. 8b, following application of protecting
species 70 to molecular species 68, a first etchant (for example
HF/NH.sub.4F, not shown) is brought into contact with exposed
portions of surface 66, whereupon the portions of silicon dioxide
resist layer 64 that are not covered by self-assembled monolayer 68
and protecting species 70 are dissolved, exposing corresponding
portions of surface 62 of silicon. Subsequently, a silicon etch
(for example, KOH/I--PrOH) is added, and the silicon dioxide that
had been covered by the self-assembled monolayer and protecting
species 70 acts as a resist for a silicon etch.
[0087] Referring to FIGS. 8a-d, according to one embodiment an
etchant is used that is destructive of a self-assembled monolayer,
and in this embodiment a protecting species is advantageously used.
According to another embodiment, a resist is used that can be
etched with an etchant that does not destroy a self-assembled
monolayer, and in this embodiment the protecting species need not
be used. An example of the latter embodiment involves etching a
silicon article coated with a thin film of gold. The gold in that
embodiment defines a resist having a surface, to which can be
transferred a self-assembled monolayer in a pattern, the
self-assembled monolayer being contiguous with exposed portions of
the gold surface in a second pattern. The surface of the article
(the surface of silicon) can be exposed by removing gold from the
surface (according to the second pattern) by contacting the exposed
portions of gold with an species that reacts chemically with gold
and that is inert with respect to the self-assembled monolayer.
This exposes the surface of the article, according to the second
pattern. Then, the exposed surface of the article can be etched, if
the etchant is inert with respect to the resist (gold).
[0088] In an alternative method, a self-assembled monolayer can be
applied to the surface according to a first pattern, exposing a
first functionality. The remaining portions of the surface are
filled in with a self-assembled monolayer of a second species
exposing a second chemical functionality. A protecting species that
is compatible with the second chemical functionality is applied to
the surface, and adheres to the self-assembled monolayer of the
second species, protecting a pattern on the surface that is
complementary to the first pattern, that is, protecting regions of
the surface that do not include the first pattern.
[0089] A variety of materials can be deposited on the surface of
the article to serve as a resist. For example, thin layers of metal
such as gold, silver, copper, nickel, cadmium zinc, palladium,
platinum, iron, chromium, alloys of these and the like can
be-deposited by those of skill in the art. Etchants that will
dissolve resist such as these should be selected to oxidize atoms
from the surface, and to include ligands, such as chelating or
coordinating ligands, that will dissolve the oxidized atoms removed
from the surface. Etchants or such resists are known to those in
the art, and include aqueous etches such as ferricyanide etch,
thiosulfate etch, thiourea etch, and the like. Often an adhesive
layer is advantageously placed upon the surface of the article
prior to application of the resist layer. The adhesive layer
generally will be at least ten angstroms thick, and may be much
thicker. The thickness of the resist layer, if it is a metal such
as gold, is generally approximately 1000 angstroms. However, the
resist can be from about 50 angstroms to many thousands of
angstroms, depending upon the application.
[0090] Many etchants will not attack a self-assembled monolayer on
a surface, thus the self-assembled monolayer can be printed on such
a surface, the resist can be etched from regions where the
self-assembled monolayer does not lie, and the article can be
etched at regions where the resist has been removed. Some etchants,
however, that are particularly reactive, for example, aqua regia,
carbon tetrafluoride, potassium iodide-iodine and the like, may
harm self-assembled monolayers in some circumstances. Etchants that
are particularly destructive of self-assembled monolayers are
useful, in some circumstances, to etch certain resists from the
surface of articles. For example, etching silicon dioxide from the
surface of silicon requires etchants that generally at least
partially destroy self-assembled monolayers.
[0091] According to one embodiment, protecting species 70 is
applied to self-assembled monolayer 68 in the following manner. A
bath of a fluid that is incompatible with the exposed functionality
of self-assembled monolayer 68 is prepared, including a layer of
fluid protecting species (or protecting species precursor) over the
incompatible fluid. The article illustrated in FIG. 8a is passed
through the region of the protecting species, which adheres to
self-assembled monolayer 68, and passed into the fluid that is
incompatible with the self-assembled monolayer. Where the
protecting species is a fluid that is hardened, for example via
polymerization, polymerization may take place in the bath, or the
article may be removed from the bath prior to polymerization.
[0092] The invention also provides a method for making an article,
which utilizes any of the above-described, or known, methods for
etching a surface. The etched surface serves as a template for the
article according to this method of the invention. The method
involves etching a pattern into a surface of a template and molding
an article on the surface of the template. An article, formed by
molding on the surface of a template, results. An example of such a
process is illustrated schematically in FIGS. 9a-f. FIG. 9a
illustrates a silicon article 60 including a surface 62 coated with
a layer of resist 64 having a surface 66. In the embodiment
illustrated, the resist is a thin layer of gold over titanium
(100/1000 angstroms). A self-assembled monolayer-forming molecular
species 27 is applied to surface 22 (in particular, stamping
surface 26) of a stamp 20. Referring to FIG. 9b, a self-assembled
monolayer of molecular species 27 is thereby transferred to surface
66 of resist 64 in a pattern corresponding to the pattern of
stamping surface 26 of stamp 20. Self-assembled monolayer 27 can be
applied to surface 66 according to methods described above and
illustrated with reference to FIGS. 1a-5c. An etchant that is
chemically reactive with a resist and that is inert with respect to
the self-assembled monolayer is brought into contact with exposed
portions of the resist surface (portions not covered by
self-assembled monolayer 27). The resist is etched, exposing
portions of surface 62 of article 60 (FIG. 9c). Subsequently,
article 60 is etched by applying to the exposed portions of surface
62 a second etchant that reacts chemically with article 60 and that
is inert with respect to resist 64. The result, as illustrated in
FIG. 9d, is a pattern etched into article 60, which pattern
corresponds approximately to a pattern of gaps between
closely-spaced regions of self-assembled monolayer 27 (FIG. 9a).
Removal of resist 64 and self-assembled monolayer of molecular
species 27 (if it has not yet been removed) results in a patterned
article 60 that is useful for many purposes. One useful purpose, in
accordance with the invention, involves using the etched surface of
article 60 as a template for fabrication of an article. In FIG. 9e,
an article has been molded onto surface 62 of article 60. In
particular, a hardenable fluid 72, such as a prepolymeric solution,
is applied to surface 62 of article 60 and hardened (polymerized,
for example), to form article 74. Article 74 then is removed from
surface 62 of article 60, and as illustrated in FIG. 9f includes a
surface 76 that corresponds to surface 62 of article 60. Article 74
can be a stamp used for microprinting, as described above.
Alternatively, article 74 can be used as an optical element as
described below and as described in U.S. application Ser. No.
08/131,841, referenced above.
[0093] An advantage to forming article 74 from a substrate etched
lithographically as illustrated in FIGS. 9a-f, from a
self-assembled monolayer applied by a microstamp, is that the
surface of template 60, if it is an oriented crystal, can be etched
to form grooves or pits that form an approximate ridge or point at
their deepest portions. The method preferably uses a template that
can be etched anisotropically. Generally, any material that forms
an oriented crystal can be etched anisotropically using etchants
available to those of skill in the art. Such a material can be
etched such that a feature etched into its surface has a dimension
much smaller than the dimension of the region at the surface of the
material to which etchant is applied. For example, silicon is
etched anisotropically resulting in grooves that become narrower
with depth. An article molded on such a template will include
protrusions that decrease in size in a direction away from the
center of the article.
[0094] As discussed, according to one embodiment a thin film of a
resist, such as gold, coats the surface of the article that is
etched. According to another embodiment, the article includes an
oxide layer on its surface that can serve as a resist. For example,
silicon, titanium, zirconium, germanium, aluminum, copper, and
other articles known to those of skill in the art would include a
surface layer of oxide that can serve as a resist, or a layer of
oxide that can serve as a resist can be grown at the surface by,
for example, heating the article in the presence of oxygen. Other
articles that can be used in accordance with the invention and that
can be coated conveniently with a thin layer of resist are
semiconductors including gallium arsenide, indium phosphide, cesium
chloride, diamond and the like. These and other materials known to
those of skill in the art form oriented crystals that can be etched
anisotropically. The articles discussed above including layers of
oxide can define articles including resist layers, as described
above with reference to FIGS. 8a-d.
[0095] FIG. 10 is an atomic force microscope image of a
polydimethyl siloxane (PDMS) article 74 formed according to the
method illustrated with reference to FIGS. 9a-f. According to
embodiments in which the article is a microstamp, stamping surface
81 include features having a lateral dimension of approximately
0.100 micron or less. Similar articles can be fabricated including,
rather than linear ridges defining stamping surface 81 as
illustrated in FIG. 10, small, isolated projections that define
stamping surface 81, which projections approximate a point. The
projections can be in, for example, an ordered array. In one
embodiment the stamping surface comprises at least one resolved
feature providing stamping resolution of less than about 100
microns. In another embodiment, the stamping surface comprises at
least one resolved feature providing stamping resolution of less
than about 10 microns, and preferable less than about 1 micron.
[0096] According to another embodiment of the invention a method is
provided for simultaneously writing, on a surface of an article, at
least two self-assembled monolayer patterns. The method involves
coating a stamping surface of a microstamp with a self-assembled
monolayer-forming species, contacting an article surface with the
stamping surface, and moving the stamping surface relative to the
article surface to write on the surface. For example, a stamp that
includes a plurality of protrusions that, at their terminus
(stamping surface), approximate points can be used to write,
simultaneously, a plurality of lines on an article surface. Such
lines can define a pattern that forms the basis of a corresponding
electronic circuit, an etched region, or other feature as described
in accordance with the invention or apparent to those of ordinary
skill in the art. A stamp with such features can be obtained
conveniently by patterning a surface of an article that can be
anisotropically etched with resist, forming on the surface of the
resist a self-assembled monolayer in a grid pattern while leaving
isolated regions of the surface of the resist free of self
assembled monolayer, etching the resist that is not covered by the
self-assembled monolayer, and etching the surface of the article
anisotropically to form a plurality of indentations that become
narrower with depth until they approximate a plurality of points.
This serves as a template for a stamp that includes a plurality of
protrusions that terminate in approximate points at their stamping
surface (or writing surface).
[0097] As used herein, the term "writing" is given its ordinary
meaning. In the context of a self-assembled monolayer, this means
forming a pattern of a self-assembled monolayer on a surface not
instantaneously, but progressively, in a manner analogous to the
way ink is applied to paper when writing with a pen. In this way, a
method is provided that involves writing on a surface of an article
simultaneously at least two separate lines of a self-assembled
monolayer-forming species.
[0098] According to embodiments of the present invention in which a
self-assembled monolayer is formed on silicon dioxide or glass,
advantage can be achieved in aspects of the invention that involve
etching, and aspects that involve preparation of surfaces of
interest in biological arenas. In aspects that involve etching,
when silicon dioxide is used as a resist layer on silicon,
advantage in the etching of silicon is achieved as discussed above.
Additionally, bulk silicon dioxide or glass can be etched by
patterning a self-assembled monolayer of alkylsiloxane, such as
octadecylsiloxane, on a surface thereof, optionally coating the
self-assembled monolayer with a protecting species, and contacting
the surface with an etchant that etches the silicon dioxide or
glass.
[0099] According to aspects of the invention involving the
preparation of surfaces of biological interest, a surface such as a
silicon dioxide or glass slide or petri dish can be patterned with
a self-assembled monolayer of alkylsiloxane that exposes a chemical
functionality of biological interest, facilitating studies at that
surface. For example, a self-assembled monolayer of alkylsiloxane
terminating in a cytophilic functionality can be patterned onto a
silicon dioxide or glass surface in accordance with the invention,
followed by adherence or immobilization of a cell or cells to the
cytophilic functionality. Biological, specifically cytophilic,
functionalities in association with self-assembled monolayers are
described in copending, commonly-owned application Ser. No.
08/131,841 and in an article entitled "Engineering Cell Shape and
Function", by Singhvi, R., et al. Science, 264, 696 (1994), both
incorporated herein by reference. This article describes the
formation of islands of self-assembled monolayer terminating in a
non-polar functionality (--CH.sub.3 ) surrounded by regions of
polyethylene glycol-terminating self-assembled monolayer. The
non-polar terminal functionality of the islands is protein
adherent, while the polyethylene glycol functionality is not
protein-adherent. Exposure of a surface derivatized as such to a
protein matrix such as the purified extracellular matrix protein
laminin results in cytophilic, protein-coated islands surrounded by
cytophobic regions. Exposure of this surface to cells results in
cell attachment preferentially to the adhesive (cytophilic),
laminin-coated islands and the cells are prevented from extending
onto surrounding non-adhesive (cytophobic) regions. Alternatively,
a surface derivatized as described above with a patterned,
self-assembled monolayer terminating in non-polar, such as methyl,
functionality can be contacted with a cell or cells without first
treating the surface with a protein matrix such as laminin.
According to some embodiments, the cell or cells will secrete a
protein matrix such as laminin that will coat the exposed non-polar
functionality, and the cell or cells then will adhere thereto.
[0100] A variety of cell studies can thereby be conducted that
involve immobilization of a cell or cells on one or more islands.
Procedures involving cell growth, differentiation, culturing, and
the like can be tailored by varying the size and/or shape of
islands, spacing between islands, and the like. Those of ordinary
skill in the art will appreciate that alkylsiloxane-based
self-assembled monolayers on glass or silicon dioxide can be
prepared that terminate in a variety of chemical or biochemical
functionalities amenable to attachment of biological species such
as antibodies, antigens, haptens, proteins, sugar and other
carbohydrates, etc., prepared in accordance with methods of
patterning described herein. Functionalities such as chelates, etc.
as described in commonly-owned, copending U.S. patent application
Ser. No. 08/312,388 (Bamdad, et al.), incorporated herein by
reference, can be provided at the exposed end of molecules making
up self-assembled monolayers patterned on glass or silicon dioxide
as well.
[0101] According to some embodiments of the invention the
above-described techniques involving patterning glass or silicon
dioxide-can be applied to other polar surfaces including polar
polymeric surfaces such as oxidized polyethylene or polystyrene.
According to these embodiments alkylsiloxane can be patterned onto
a polymeric surface oxididized for example via plasma etch to
expose polar functionalities such as hydroxyl, carboxylic acid,
aldehyde, or the like. These surfaces can form the basis for all
embodiments of the invention described herein, including the
biological aspects described above.
[0102] Patterning of alkylsiloxane onto glass, silicon dioxide, or
polar polymeric surfaces can be carried out according to chemistry
known to those of skill in the art. For example, trichlorosilane or
trialkoxysilane such as triethoxysilane, when applied to these
surfaces in essentially any solvent in which they can be carried
(such as water, hexane, toluene, and the like) will form
alkylsiloxane on that surface.
[0103] The techniques described above involving patterning of
alkylsiloxane on glass, silicon dioxide, or polar polymeric
surfaces can be carried out on planar or non-planar surfaces, as
described herein, and can be combined with techniques described
herein involving allowing alkylsiloxane or its precursor to spread
onto the surface while contacting the surface simultaneously with a
species that is not compatible with the alkylsiloxane or precursor,
and involving deforming a stamp from which the alkylsiloxane or
precursor is transferred, or both.
[0104] The present invention also provides a variety of optical
elements and devices. One such element is a diffraction grating
that can be formed as described above with respect to article 74
(FIG. 9f) or as described in U.S. application Ser. No. 08/131,841,
referenced above, in which a variety of optical elements including
an optical switch are described. According to a preferred
embodiment of the invention, a reflective liquid, such as a liquid
metal, is brought into contact with a surface that correlates to a
surface of an optical element, and a surface of the liquid metal is
thereby formed into an optical surface. A method for making such an
article is illustrated schematically in FIGS. 11a-f. In FIG. 11a, a
template 78, for example a commercial diffraction grating, is
provided. Template 78 can be mounted on a support 80, for example a
glass slide. At FIG. 11b, a fluid precursor 82 is brought into
contact with optical surface 79 of template 78. In the embodiment
illustrated, fluid precursor 82 is a prepolymeric solution of
polydimethylsiloxane, and is contained in a container 84, for
example a petri dish. Fluid precursor 82 is allowed to harden in
contact with the optical surface 79. Where precursor 82 is a
prepolymer fluid, it is polymerized. When hardened, an article 86
that results from hardening of the fluid precursor is removed from
template 78 (FIG. 11c), and can be removed from container 84 (FIG.
11d; alternatively, article 86 can remain in container 84 during
application of a liquid metal to surface 88, and optional
encapsulation, discussed below with reference to FIGS. 11e and f).
The resultant article 86 (FIG. 11d) has an optical surface 88 that
corresponds to optical surface 79 of the template. Article 86 is
preferably transparent, and is a transparent elastomeric
diffraction grating according to a preferred embodiment.
[0105] According to a preferred embodiment, optical surface 88 of
article 86 is contacted with a liquid metal 90, for example
gallium, mercury, or other liquid known to those of skill in the
art (FIG. 11e). Liquid metal 90 includes a surface 92 that is in
contact with and correlates to surface 88 of article 86, and
surface 92 of liquid metal 90 is thereby formed into a diffraction
grating. If article 86 is transparent, electromagnetic radiation
can be directed through article 86 at surface 92, and diffracted
(FIG. 11e). After liquid metal 90 is brought into contact with
article 86 so that a surface 92 of liquid 90 contacts and
correlates with surface 88 of article 86, liquid metal 90 can be
encapsulated by coating exposed surfaces of the liquid metal with a
hardenable fluid, preferably the same fluid as fluid precursor 82,
and the fluid allowed to harden. The result, as illustrated in FIG.
11f, is an optical element 93 that is a liquid metal having a
surface 92 that is an optical surface, which liquid metal is
encapsulated in a transparent article 86.
[0106] According to an embodiment in which article 86 is flexible,
optical surface 92 of liquid metal 90 can be deformed. For example,
surface 92 can be compressed, elongated or bent. Where article 86
is an elastomer, surface 92 can be repeatedly elongated and bent.
Thus, where the electromagnetic radiation is directed at surface 92
and diffracted, the pattern of diffraction can be adjusted, that
is, changed, by manipulating optical element 93, for example by
stretching it.
[0107] The method and article described above with reference to
FIGS. 11a-f can be used in conjunction with any optical element
having a reflective surface, such as diffraction gratings including
holographic gratings, blaze gratings (illustrated in FIGS. 11a-f),
and the like. For example, a concave mirror can be formed according
to one embodiment, and this is described with reference to FIGS.
12a-d. At FIG. 12a a template 94 having an optical surface 95, for
example a glass plano-concave lens, is immersed in a fluid
precursor 82, for example polydimethylsiloxane. Precursor 82 is
hardened and template 94 is removed, and an article 96 having an
optical surface 98 that corresponds to optical 95 of template 94
remains (FIG. 12b). Referring to FIG. 12c, a liquid metal 90 is
placed in contact with optical surface 98 of article 96, thus an
optical surface 100 is formed on liquid metal 90, defining an
optical element 102. According to one embodiment article 96 is
flexible. According to a preferred embodiment article 96 is an
elastomer. Article 102 according to this embodiment includes an
elastomer 96 including a void 104 having a convex or concave
surface (convex surface 100 as illustrated) and a liquid metal 90
adjacent the surface of the void, the liquid metal having an
optical surface 100 (a concave mirror surface is illustrated that
corresponds to the concave optical surface 95 of template 94).
[0108] Optical element 102 can be used to focus electromagnetic
radiation directed at optical surface 100 of liquid metal 90 and
allowed electromagnetic radiation to reflect from the optical
surface. According to an embodiment in which article 96 is
flexible, article 96 can be adjusted, thereby adjusting optical
surface 100 of liquid metal 90 and adjusting the focus of the
electromagnetic radiation. According to a preferred embodiment in
which article 96 is an elastomer, this can be done repeatedly.
[0109] Referring to FIG. 12d, optical element 103 is illustrated.
Optical element 103 results from complete encapsulation of liquid
metal 90 by article 97, which can be formed by taking steps as
described above with respect to FIG. 11f. In the embodiment
illustrated in FIG. 11f, liquid metal 90 completely fills void 104
in article 96.
[0110] Referring now to FIG. 13, a method of making an optical
element is illustrated schematically. The method involves providing
a substrate 106 that has, on a surface 108 thereof, a
self-assembled monolayer 110 exposing a first chemical
functionality. Monolayer 110 is formed in a predetermined shape on
surface 108 that corresponds to a shape desired for one portion of
the surface of the optical element. A fluid precursor 12 of the
optical element then is placed upon monolayer 110, and a surface
114 of fluid precursor 112 is contacted with a fluid 116 that is
incompatible with the fluid precursor 112. Alternatively, the
incompatible fluid 116 can first be applied to surface 108 of
article 106 (and monolayer 110), and fluid precursor 112 then can
be applied to monolayer 110, for example using a pipet 118.
Portions of surface 108 of article 106 that are not covered with
monolayer 110 do not attract fluid precursor 112. If such portions
of surface 108 are attractive to fluid precursor 112, a
self-assembled monolayer 120 can be formed around self-assembled
monolayer 110, isolating monolayer 112, that exposes a chemical
functionality that does not attract precursor 112.
[0111] When precursor 112 is polydimethylsiloxane that is
polymerized to form an optical element that is a plano-convex lens,
self-assembled monolayer 110 can be formed from a molecular species
terminating in a non-polar functionality, for example
hexadecanethiol. In this case, if surface 108 is not sufficiently
repulsive of fluid precursor 112, then the remaining portions of
surface 108 can be coated with a self-assembled monolayer of a
species terminating in a polar functionality, for example a
long-chain thiol terminating in a carboxylic acid. This arrangement
can be used when surface 108 is a gold surface. Other combinations
of surfaces and functional groups that adhere to surfaces are
described in application Ser. No. 08/131,841, and/or are known to
those with skill in the art.
[0112] The present invention also provides a method for controlling
the shape of a liquid, for example a fluid precursor of an optical
element. Referring to FIG. 14, the method involves providing a
supporting, electrically conductive surface 120. Surface 120 can,
for example, be an exposed surface of a thin, transparent gold film
121 on a transparent (e.g. glass) support 122. A self-assembled
monolayer is applied to a region 124 of surface 120 and a fluid 126
that is attracted to the chemical functionality exposed by the
self-assembled monolayer is applied to the self-assembled
monolayer. If surface 120 is not repulsive of fluid 126, then the
portion of surface 120 not covered by the self-assembled monolayer
can be covered by a self-assembled monolayer exposing a chemical
functionality that is repulsive of fluid 126. An electrolyte fluid
128 that is not compatible with fluid 126 is placed over fluid 126,
and an electrical circuit including surface 120 and electrolyte 128
is arranged. For example, a reference electrode 130 and a counter
electrode 132 can be immersed in electrolyte 128, and surface 120
can define a working electrode, the working, counter, and reference
electrodes being controlled by potentiostat 135. By altering the
electrical potential at surface 120, the contact angle formed by
liquid 126 at surface 120 changes. The change in contact angle is
dependent upon the electrical potential. According to one
embodiment, the self-assembled monolayer at region 124 is caused to
desorb and resorb, during change in electrical potential, at the
outermost point of contact between fluid 126 and the surface
selectively, and this causes the contact angle between the fluid
and the surface to change.
[0113] In this way, liquid 126 can be used as a lens that can be
focused depending on the electrical potential of surface 120
relative to reference electrode 130. A source of electromagnetic
radiation 134 can direct electromagnetic radiation at fluid 126,
which electromagnetic radiation can be focused and utilized by a
sensor or other electromagnetic radiation-receiving apparatus 136.
If fluid 126 is a hardenable fluid, it can serve as a precursor of
a solid lens, and adjusting the electrical potential between
surface 120 and reference electrode 130 can adjust the focal length
of fluid 126, followed by hardening of fluid 126 to produce a lens
126 having a focal length that has been set by adjusting the
potential at surface 120 during lens formation. Hardenable fluids
useful as fluid 126 include those described above with respect to
formation of microstamps and optical elements, and include
generally any hardenable fluid that is incompatible with a suitable
electrolyte, and that can be placed upon an exposed surface of a
self-assembled monolayer.
[0114] When a self-assembled monolayer exposes a redox
functionality, the species that forms the spacer portion of the
self-assembled monolayer-forming species can advantageously be
selected as one that has a reasonably good electron transfer
function, for example polyenes, poly-ynes, polyaromatics, and the
like can be selected.
[0115] According to another embodiment, region 124 of surface 120
(or the entire surface 120) is covered with a self-assembled
monolayer exposing a redox functionality. Examples of suitable
redox functionalities include ferrocene, quinone, thiophene,
pyrrole, and the like. The redox state of the exposed chemical
functionality of the self-assembled monolayer can be controlled,
which can control the contact angle of a fluid 126 at the surface
of the self-assembled monolayer.
[0116] While the arrangement in FIG. 14 involves an electrolyte
contacting surface 120, surrounding fluid 126, and contacting the
working and reference electrodes, according to an embodiment in
which fluid 126 is an electrolyte, the working and counter
electrodes can contact fluid 126 directly. In this embodiment,
electrolyte 128 is not necessary if not needed to aid in the
formation of the shape of fluid 126.
[0117] In the embodiment described with reference to FIG. 14, where
fluid 126 is an organic fluid, it may be conveniently applied to
region 124 of surface 120 as follows: an aqueous fluid 128 is
prepared, and a layer of organic fluid 126 is placed on top of
aqueous solution 128. Article 122 is passed through the layer of
organic fluid 126, whereupon some of fluid 126 adheres to region
124 of surface 120, and into aqueous solution 128.
[0118] In FIG. 14, one article only is formed from fluid 126.
However, a plurality of articles on a plurality of isolated regions
of surface 120 can be fabricated, and/or used as individual optical
elements as illustrated.
[0119] According to another embodiment similar to that illustrated
in FIG. 14, a plurality of articles are formed on a surface 120
without the use of electrochemistry. A self-assembled monolayer
including an isolated region exposing a particular chemical
functionality, or an isolated region of a self-assembled monolayer
exposing a chemical functionality surrounded by a surface free of
self-assembled monolayer, can be passed through an organic fluid
layer 126 on top of an aqueous layer 128, whereupon portions of
fluid 126 adhere to compatible portions of the self-assembled
monolayer, as illustrated in FIG. 14. Fluid 126 can then be
hardened, for example via curing, under an aqueous solution, or the
article can be removed and fluid regions 126 can be cured.
[0120] The present invention also provides a method of forming an
article that includes providing a precursor of the article in
contact with at least two discreet self-assembled monolayer
regions. Referring to FIGS. 15a and 15b, a first article 140 and a
second article 142 are illustrated schematically. Article 140
includes a thin layer of a conductive species 144 on one of its
surfaces and article 142 includes a thin layer of a conductive
species 146 on one of its surfaces. Articles 140 and 142, including
conductive layers 144 and 146 can be identical. On the surface of
conductive layers 144 and 146, respectively, it is a first region
148 and a second region 150 of a self-assembled monolayer exposing
a first chemical functionality. The remaining portions of the
surface of conductive layers 144 and 146 remain free of
self-assembled monolayer, or are covered with a self-assembled
monolayer exposing a chemical functionality different from the
first chemical functionality. A fluid 152 is caused to contact both
self-assembled monolayer 148 and 150. Fluid 152 is compatible with
the first chemical functionality exposed by self-assembled
monolayers 148 and 150. Fluid 152 is surrounded by fluid 154, which
is incompatible with fluid 152. Fluid 154 can be applied to fluid
152 after fluid 152 is applied to self-assembled monolayers 148 and
150, or fluid 152 can be applied to self-assembled monolayers 148
and 150 under fluid 154, for example using pipette 156. If fluid
152 is a hardenable fluid, for example, a precursor of a solvent
polymer, it can be cured to form article 158. Article 158 can be
removed from self-assembled 148 and 150. According to an alternate
embodiment, conductive layers 144 and 146 are not present.
[0121] According to one embodiment, electrochemical apparatus as
illustrated in FIG. 14 (not shown in FIGS. 15a and b) is provided
to adjust the electrical potential of conducting layers 144 and
146. Conducting layers 144 and 146 can be adjusted independently,
and thus, the area of contact between fluid 152 and self-assembled
monolayers 148 and 150, respectively, can be adjusted.
[0122] FIGS. 16a-e illustrate schematically a process for etching
an article that is similar to the process described in connection
with FIGS. 8a-d, with like numerals referring to corresponding
components. An article 60, for example silicon, includes, on its
surface 62, a layer 64 that can be a thermally-formed layer of
silicon dioxide having a surface 66. A self-assembled monolayer 68
(for example alkyl siloxane) is patterned onto surface 66, using
any method described herein or other method known to those of skill
in the art. Referring to FIG. 16b, a protecting species 70 is
added. While in FIGS. 8a-d protecting species 70 is selected to be
compatible with the self-assembled monolayer and relatively
incompatible with the surface 66 of the layer of silicon dioxide
64, in the embodiment illustrated in FIGS. 16a-e protecting species
70 is more compatible with surface 66 than with self-assembled
monolayer 68. The protecting species can be a liquid, a
polymerizable species, or the like. The compatibility of the
protecting species with the self-assembled monolayer or with the
surface 66 can be selected and/or adjusted by those of ordinary
skill in the art.
[0123] FIG. 16c illustrates the arrangement after application of an
etchant to the surface. Portions 63 of layer 64 of silicon dioxide
that are protected by protecting species 70 remain on surface 62 of
article 60 as mask 65. Remaining portions of layer 64 are etched by
the etchant. The etchant and protecting species 70 are selected so
as to be incompatible and protecting species 70 thereby protects
portions 63 that define mask 65. Subsequently, a silicon etch as
described above is added, and silicon dioxide mask 65 acts as a
resist for the silicon etch. An exemplary process is described in
greater detail below in Example 3, and a photocopy of a scanning
electron micrograph (SEM) of a resultant etched surface is shown in
FIG. 16e.
[0124] In all of the embodiments described and illustrated herein,
methods and devices described in accordance with one embodiment can
be utilized with any other embodiment where feasible. For example,
the controlled spreading described with reference to FIGS. 1a-d can
be used in conjunction the stamp deformation as described with
reference to FIGS. 3a-c, and these embodiments together or alone
can be used for methods and devices discussed with reference to
other figures, where feasible. For example, stamp deformation can
be used on nonplanar surfaces, controlled spreading can be used in
etching as described with reference to FIGS. 8a-d, with
lithographic molding as in FIGS. 9a-f, etc. As another example,
articles provided in accordance with the inention, especially
articles that are diffraction gratings, optical element
encapsulants, microstamps, lenses, and the like, all can be
fabricated from material or precursors from which others are
fabricated, and/or from material described in U.S. application Ser.
No. 08/131,841. Many of these articles are tranparent polymers,
elastomers, and the like, and these materials are known to those of
skill in the art.
[0125] In all of the embodiments described and illustrated herein,
self-assembled monolayers that expose a variety of chemical
functionalities can be formed. Hydrophobic, hydrophilic,
cytophobic, cytophilic, and other functionalities are described in
application Ser. No. 08/131,841, and the following references, all
incorporated herein:
[0126] Co-pending, commonly-owned U.S. application Ser. No.
08/312,388, entitled "Molecular Recognition at Surfaces Derivatized
with Self-Assembled Monolayers", by Bamdad, et al.;
[0127] "Controlled outgrowth of dissociated neurons on patterned
substrates", Kleinfeld, et al, Journal of Neuroscience, 8(11): 4098
(1988);
[0128] "Growth Control in Miniclones of Human Glial Cells",
Westermark, B. Experimental Cell Research, 111, 295-299 (1978);
[0129] "Micropatterned Substratum Adhesiveness: a Model for
Morphogenetic Cues Controlling Cell Behavior", Britland, S., et al
Experimental Cell Research, 198, 124-129 (1992);
[0130] "Engineering Cell Shape and Function", Singhvi, R., et al.
Science, 264, 696 (1994);
[0131] "Convenient Methods of Patterning the Adhesion of Mammalian
Cells to Surfaces Using Self-Assembled Monolayers of Alkane Thiols
on Gold", Journal of the American Chemical Society 115: 5877-5878
(1993).
[0132] In accordance with the teachings in these and other
references, those of skill in the art can utilize the surfaces
produced in accordance with the invention in a variety of
biological, chemical, physical, and analytical arenas.
[0133] The function and advantage of these and other embodiments of
the present invention will be more fully understood from the
examples below. The following examples are intended to illustrate
the benefits of the present invention, but do not exemplify the
full scope of the invention.
EXAMPLE 1
Fabrication of a Microprinting Stamp
[0134] A polydimethyl siloxane stamp was fabricated. Sylgard.TM.
184 silicone elastomer, parts "a" and "B" (10, 1 by weight Dow
Corning) were mixed in a plastic cup; trapped air was removed under
vacuum. The mixture was poured over a master as described by Kumar,
et al., Langmuir, 10, 1498-1511 (1994). The master was held in a
polystyrene petri dish and left at room temperature for
approximately two hours. It was cured by heating in an oven at
60.degree. C. for approximately two hours.
EXAMPLE 2
Controlled Reactive Spreading of a Self-Assembled Monolayer on a
Surface
[0135] Hexadecanethiol was selected as species 27 and was purified
by chromatography through silica gel in ethanol with concentrations
from 0.01 mM to 6.5 mM. Gold films on silicon were prepared by
electron beam sputtering. A piece of gold substrate was put into a
polystyrene petri dish that was half-filled with deionized water,
and the stamp including species 27 applied to surface 22 was
brought into contact with the gold surface. To avoid smearing the
gold surface with the stamp, one of two methods were employed.
According to the first, the stamp and the gold substrate were taken
out of the water together while still in contact, carefully dried
in a stream of nitrogen, and then separated. According to the
second, the stamp was separated from the gold substrate while under
water. The water was replaced with several volumes of clean water
to remove any residual species 27 (alkanethiol) and the gold
substrate then was removed from water and dried in a stream of
nitrogen. Each time the stamp was re-used, it was first rinsed with
excess ethanol to remove alkanethiol. Gold was removed from the
surface of the silicon article using a cyanide solution (KCN) 0.1
M; KOH: 1 M) with vigorous stirring using air (oxygen) as an
oxidant.
EXAMPLE 3
[0136] A process for etching silicon is described. The process is
described with reference to FIGS. 16a-e. A silicon wafer
(<100>orientation) covered with 0.2 micron-thick thermal
silicon dioxide (used as received from MEMC) was cleaned in piranha
solution (a mixture 7:3 (v/v) of 98% H.sub.2SO.sub.4 and 30%
H.sub.2O.sub.2), thoroughly rinsed with deionized water, and used
immediately (Caution: piranha solution is an extremely strong
oxidant and should be handled with care. Contact with skin can
cause serious injury. Contact with eyes can cause blindness). The
surface of the wafer was patterned, using a stamp fabricated in
accordance with Example 1, with a self-assembled monolayer of
--Cl.sub.3SiR, --(EtO).sub.3SiR (R.dbd.--(CH.sub.2).sub.3NH.-
sub.2, --(CH.sub.2).sub.3SH, --(CH.sub.2).sub.3BR, --(CH.sub.2)NCO,
--(CH.sub.2).sub.2(CF.sub.2).sub.5CF.sub.3, or
--(CH.sub.2)15(CH.dbd.CH.s- ub.2) in hexane for ca. 5 min.
Subsequent treatment of the patterned self-assembled monolayers
contining vinyl-terminated regions with an aqueous solution of
KMnO.sub.4 and KiO.sub.4 convereted the olefins to carboxylic
acids. FIG. 16a illustrates schematically these self-assembled
monolayers. A drop of a prepolymer of polymethyl methacrylate
(SK-9, Edmund Scientific) or polyurethane (J-91, Edmund Scientifir;
NOA81, Norland Products, inc.) was placed on the patterned area.
The excess prepolymer was removed by tilting the substrate and
allowing the prepolymer to drain off of the surface. The prepolymer
was compatible with the chemical functionality exposed by the
surface silicon dioxide surface rather than the self-assembled
monolayer, thus (FIG. 16b), the prepolymer remaining on the surface
selectively wetted regions 63 of silicon dioxide uncovered by
self-assembled monolayer 68. The prepolymer was cured under a
mercury lamp (medium pressure; the distance between the sample and
the lamp was about 1 cm) for about 20 minutes to form protecting
species 70 at regions 63 interventing regions covered by
self-assembled monolayer 68. The surface was exposed to an etchant,
specifically NH.sub.4F-buffered aqueous HF solution (250 mL of
H.sub.2O, 165.5 g of NH.sub.4F, and 40 Ml of 48% HF). The etchant
was incompatible with the protecting species 70, but removed
self-assembled monolayer 68 and the underlying layer of silicon
dioxide except at those regions 63 protected by species 70, which
served as mask 65 in a subsequent etch of silicon. Anisotropic
etching of silicon was carried out in an aqueous solution of KOH
and I--PrOH at 70.degree. C. (400 mL of H.sub.2O, 92 g of KOH, 132
mL of I--PrOH). This etchant removed the protecting species 70, but
not the underlying silicon dioxide mask 65. That is, portions of
silicon not protected by mask 65 were anisotropically etched (FIG.
16d). The result is an etched surface of silicon, as represented by
the photocopy of the SEM image in FIG. 16e.
[0137] Those skilled in the art would readily appreciate that all
parameters listed herein are meant to be exemplary and actual
parameters will depend upon the specific application for which the
methods and apparatus of the present invention are being used. It
is, therefore, to be understood that the foregoing embodiments are
presented by way of example only and that, within the scope of the
appended claims and equivalents thereto, the invention may be
practiced otherwise than as specifically described.
* * * * *