U.S. patent application number 13/530006 was filed with the patent office on 2012-11-22 for massively parallel lithography with two-dimensional pen arrays.
This patent application is currently assigned to NanoInk, Inc.. Invention is credited to Joseph S. Fragala, Chad A. Mirkin, Khalid Salaita, Raymond R. Shile, Yuhuang Wang.
Application Number | 20120297509 13/530006 |
Document ID | / |
Family ID | 38353934 |
Filed Date | 2012-11-22 |
United States Patent
Application |
20120297509 |
Kind Code |
A1 |
Mirkin; Chad A. ; et
al. |
November 22, 2012 |
MASSIVELY PARALLEL LITHOGRAPHY WITH TWO-DIMENSIONAL PEN ARRAYS
Abstract
Massive parallel printing of structures and nanostructures at
high speed with high resolution and high quality using two
dimensional arrays comprising cantilevers and tip-based transfer of
material to a surface. The array is designed so only tips touch the
surface. This can be accomplished by long tips and bent cantilevers
and alignment. An article comprising: a two-dimensional array of a
plurality of cantilevers, wherein the array comprises a plurality
of base rows, each base row comprising a plurality of cantilevers,
wherein each of the cantilevers comprise tips at the cantilever end
away from the base, wherein the number of cantilevers is greater
than 250, and wherein the tips have an apex height relative to the
cantilever of at least four microns, and a support for the array.
Combinatorial arrays and bioarrays can be prepared. The arrays can
be manufactured by micromachining methods.
Inventors: |
Mirkin; Chad A.; (Wilmette,
IL) ; Salaita; Khalid; (Evanston, IL) ; Wang;
Yuhuang; (Evanston, IL) ; Fragala; Joseph S.;
(San Jose, CA) ; Shile; Raymond R.; (Los Gatos,
CA) |
Assignee: |
NanoInk, Inc.
Northwestern University
|
Family ID: |
38353934 |
Appl. No.: |
13/530006 |
Filed: |
June 21, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11690738 |
Mar 23, 2007 |
8220317 |
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13530006 |
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60792950 |
Apr 19, 2006 |
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Current U.S.
Class: |
850/60 ;
977/875 |
Current CPC
Class: |
B82Y 10/00 20130101;
B82Y 40/00 20130101; G03F 7/0002 20130101 |
Class at
Publication: |
850/60 ;
977/875 |
International
Class: |
G01Q 70/16 20100101
G01Q070/16 |
Goverment Interests
FEDERAL FUNDING STATEMENT
[0002] The present invention was developed with use of federal
funding from the following grant agencies and grant numbers: Air
Force Office Scientific Research, AFOSR FA9550-05-1-0348; AFOSR
28065-3/W91INF-04-1-071; and National Institutes of Health NIH DPI
0D000285-02. The federal government reserves rights in the
invention.
Claims
1.-60. (canceled)
61. A method of making article, wherein the article comprises a
two-dimensional array of a plurality of cantilevers, and a support
for the array, the method comprising: forming a two dimensional
array comprising a plurality of cantilevers comprising tips at
their ends, wherein the cantilevers are supported on a sacrificial
support structure; forming an array support comprising a plurality
of base rows which are adapted for bonding to the two dimensional
array comprising a plurality of cantilevers; bonding the
cantilevers to the base rows; and removing the sacrificial support
structure to release the cantilevers and form the array.
62. The method according to claim 61, wherein the array is adapted
to prevent substantial contact of non-tip components of the array
when the tips are brought into contact with a substantially planar
surface.
63. A method according to claim 61, wherein the tips have an apex
height relative to the cantilever of at least four microns.
64.-65. (canceled)
66. A method according to claim 61, further comprising the step of
bending the cantilevers at an angle of at least 10.degree. away
from the support.
67. A method according to claim 61, wherein the tips have an apex
height relative to the cantilever of at least 4 microns, and
wherein the cantilevers are bent at an angle away from the
support.
68. (canceled)
69. A method according to claim 61, wherein the array is
characterized by a cantilever yield of at least 95%.
70. A method according to claim 61, wherein the array is
characterized by a tip spacing of less than 200 microns in one
dimension and a tip spacing of less than 50 microns in a second
dimension.
71. A method according to claim 61, wherein the number of
cantilevers is greater than 10,000.
72. A method according to claim 61, wherein the base rows have an
average length of at least about 1 mm.
73. A method according to claim 61, wherein the cantilevers
comprise multiple layers adapted for bending of cantilevers.
74. A method according to claim 61, wherein the cantilevers are
coated with metal on the tip side of the cantilever.
75. A method according to claim 61, wherein the cantilevers are not
adapted for force feedback.
76. A method according to claim 61, wherein the base rows have a
height with respect to the support of at least about 5 microns.
77. A method according to claim 61, wherein the tips have an
average radius of curvature of less than 100 nm.
78. A method according to claim 61, wherein the cantilevers have an
average force constant of about 0.1 N/m to about 1 N/m.
79. (canceled)
80. A method according to claim 61, wherein the cantilevers are
bent on average about 10 microns to about 50 microns.
81. A method according to claim 61, wherein the bonding step is a
non-adhesive bonding.
82. (canceled)
83. A method according to claim 61, wherein the forming of the two
dimensional array comprises microfabrication.
84. A method according to claim 61, wherein the forming of the
array support comprises microfabrication.
85. A method according to claim 61, wherein after the bonding step,
the array support is scribed into sections about 2 square cm or
less.
86.-104. (canceled)
Description
RELATED APPLICATIONS
[0001] This application claims the priority benefit of U.S.
provisional application Ser. No. 60/792,950 filed Apr. 19, 2006 to
Mirkin et al., which is hereby incorporated by reference.
BACKGROUND
[0003] Dip-Pen Nanolithographic.RTM. (DPN).RTM. printing has been
developed in various embodiments as a scanning probe-based
technique that uses, at least in some embodiments, a coated sharp
tip such as an atomic force microscope (AFM) tip to pattern
surfaces on, for example, the sub-50 nm to many micrometer length
scale (see, for example, Piner et al. Science 283, 661-663 (1999)).
This novel printing technique in its various embodiments can
combine soft matter compatibility with the high resolution of
scanning probe and AFM methods, thereby affording unique
opportunities to use micro-and nano-patterned substrates in a
variety of fields ranging from molecular electronics to
biomedicine. However, an obstacle in commercially utilizing DPN
printing for some applications has been its relatively low
throughput (see, for example, Hong et al. Science 288, 1808-1811
(2000); Salaita et al. Small 1, 940-945 (2005)), a limitation
associated with the field of scanning probe lithography in general
(see, for example, Gates et al. Chem. Rev. 105, 1171-1196 (2005);
Tseng et al., J. Vac. Sci. & Tech. B 23, 877-894 (2005)). In
particular, the DPN method is generally used as a serial method
rather than a parallel method, and the exponential complexity and
cost arising from individually addressed feedback systems can
constrain its accessibility and the rate of patterning. Therefore,
a commercial need exists to improve throughput of the DPN method
while maintaining its simplicity.
[0004] In many cases, the lithography has been to date carried out
with one pen on one instrument to transfer a patterning compound or
material to the surface. However, one approach has been to use
multiple pen systems wherein multiple pens operate in parallel on
one instrument. For example, WO 00/41213 to Mirkin et al. describes
use of a plurality of tips with a single device, referring to U.S.
Pat. No. 5,666,190 to Quate et al. (Stanford) for descriptions of
cantilever arrays and nanolithographic application. In addition, WO
01/91855 to Mirkin et al. describes working examples with a
plurality of tips, wherein a linear array of eight tips were
obtained from a larger wafer block of tips and affixed to a ceramic
tip carrier and mounted to an AFM tip holder with epoxy glue.
[0005] Salatia et al. Small, 2005, 1, No. 10, 940-945 describe
parallel printing with 250 pen arrays, 26 pen arrays, and blocks of
26 pen arrays. U.S. Pat. No. 6,642,129 to Liu et al. describes
parallel individually addressable probes for nanolithography
including linear arrays and two dimensional arrays. The review by
Ginger et al. Angew. Chem. Int. Ed. 43, 30-45 (2004)) describes
10,000 pen systems.
[0006] Massively parallel nanoarray platforms have been noted
including a system with 1.2 million pens per four inch diameter
wafer. See, for example, Demers et al., Genetic Engineering News,
vol. 23, no. 15, Sep. 1, 2003, 32.
[0007] Parallel probes have also been developed by IBM. See for
example, Vettiger et al., IBM J. Res. Dev. 2000, 44, 323; King et
al., J. Microelectromech. Syst. 2002, 11, 765. See also U.S. Pat.
No. 5,835,477 to Binnig et al.
[0008] However, a need yet exists to improve this approach in view
of, for example, the difficulties associated with fabricating large
numbers of pens in a confined space including in two dimensional
arrays and in adapting the pens to a larger or customized
instrument to control the printing process. For example, leveling
and alignment of massive numbers of cantilevers and tips is an
engineering challenge. The pens must be efficiently produced so
that as many of the pens as possible are usable. Fabrication should
be convenient, and the pens should be robust for commercial use
with a variety of patterning compounds and materials. High rates of
patterning structures, including nanostructures, are needed at high
resolution and registration. While multiple pen systems have been
used for patterning, the number of dots generated by contact has
typically been the same as the number of pens. Otherwise, no
registration exists between the two sets of dots. A need exists to
better demonstrate the writing capabilities of large pen systems
including better registration and alignment.
SUMMARY
[0009] The present invention comprises a plurality of different
embodiments. For example, one embodiment comprises a
two-dimensional array of a plurality of cantilevers, the
cantilevers comprising tips at the cantilever ends, wherein the
array is adapted to prevent substantial contact of non-tip
components of the array when the tips are brought into contact with
a substantially planar surface.
[0010] Another embodiment comprises an article comprising: (i) a
two-dimensional array of a plurality of cantilevers, wherein the
array comprises a plurality of base rows, each base row comprising
a plurality of cantilevers extending from the base row, wherein
each of the cantilevers comprise tips at the cantilever end away
from the base row, wherein the array is adapted to prevent
substantial contact of non-tip components of the array when the
tips are brought into contact with a substantially planar surface;
and (ii) a support for the array.
[0011] Another embodiment comprises an article comprising: (i) a
two-dimensional array of a plurality of cantilevers, wherein the
array comprises a plurality of base rows, each base row comprising
a plurality of cantilevers extending from the base row, wherein
each of the cantilevers comprise tips at the cantilever end away
from the base row, wherein the array is adapted to prevent
substantial contact of non-tip components of the array when the
tips are brought into contact with a substantially planar
surface.
[0012] In another embodiment, the invention provides an article
comprising: a two-dimensional array of a plurality of cantilevers,
wherein the array comprises a plurality of base rows, each base row
comprising a plurality of cantilevers, wherein each of the
cantilevers comprise tips at the cantilever end away from the base,
and wherein the tips have an apex height relative to the cantilever
of at least, for example, four microns, and a support for the
array.
[0013] Another embodiment provides an article comprising: a
two-dimensional array of a plurality of cantilevers, wherein the
array comprises a plurality of base rows, each base row comprising
a plurality of cantilevers, wherein each of the cantilevers
comprise tips at the cantilever end away from the base, and wherein
the tips are coated with metal on the tip side of the cantilever
and the cantilevers are bent at an angle of at least, for example,
10.degree. from their base.
[0014] In another embodiment, the invention provides, for example,
a method of making an article, wherein the article comprises a
two-dimensional array of a plurality of cantilevers, and a support
for the array, the method comprising: (i) forming a two dimensional
array comprising a plurality of cantilevers comprising tips at
their ends, wherein the cantilevers are supported on a sacrificial
support structure; (ii) forming an array support comprising a
plurality of base rows which are adapted for bonding to the two
dimensional array comprising a plurality of cantilevers; (iii)
bonding the cantilevers to the base rows; and (iv) removing the
support structure to release the cantilevers and form the
array.
[0015] Still further, another embodiment is a method comprising (1)
micromachining a two dimensional array of cantilevers wherein the
cantilevers are adapted to bond with a device which both supports
the cantilevers and can also couple the cantilevers to an
instrument for motion, and (2) bonding the cantilevers to the
device.
[0016] Also provided are instruments comprising the two dimensional
arrays and support structures and methods of building and using the
instruments, including for fabrication of micron-scale and
nanometer scale structures.
[0017] Also provided are patterned substrates made from the arrays,
devices, and instruments described herein.
[0018] Also provided are methods for fast patterning of
nanostructures including, for example, at least 100,000 or at least
1,000,000 nanostructures per minute.
[0019] In a preferred embodiment, a solution is provided to the
throughput limitation through the use of novel 55,000-pen
two-dimensional arrays in the context of parallel DPN printing
experiments for patterning, for example, gold substrates with
sub-100 nm resolution over large, square centimeter areas.
[0020] This new approach to parallel scanning probe lithography
over large areas can be contrasted with the work of others, which
has focused on the production of linear and two-dimensional
cantilever arrays with independent feedback systems, for the
controlled oxidation (see, for example, Minne et al. J. Vac. Sci.
& Tech. B 14, 2456-2461 (1996); Minne et al. Appl. Phys. Lett.
73, 1742-1744 (1998)) or melting of an underlying substrate (see,
for example, Vettiger et al. IEEE Trans. Nanotechnology 1, 39-55
(2002)).
[0021] Notably, if feedback is not used, the lack of feedback
systems coupled with the ability to pattern a surface with
molecule-based inks can make this massively parallel DPN capability
highly accessible and attractive for high throughput
nanofabrication experiments and commercialization involving, for
example, both soft organic and hard inorganic materials. It can be
particularly useful, for example, for fabricating combinatorial
libraries of structures and duplicates of a desired nanostructure
or particular type of nanopatterned substrate.
BRIEF DESCRIPTION OF DRAWINGS
[0022] FIG. 1. DPN patterning with 55,000 AFM cantilevers in
parallel: (a) Optical micrograph of part of the 2D array of
cantilevers used for patterning. Inset shows an SEM image of the
tips. (b) Large area SEM image (left) of part of an 88,000,000 gold
dot array (40.times.40 within each block) on an oxidized silicon
substrate. A representative AFM topographical image (right) of part
of a block. (c) Representative optical micrograph (inset shows AFM
image) of .about.55,000 features drawn in the form of the face of
the 2005 US five cent coins. The coin bears a picture of Thomas
Jefferson, who helped develop the polygraph, a macroscopic letter
duplicator that relies on an array of pens.
[0023] FIG. 2. A schematic diagram of the fabrication process for
2D cantilever arrays.
[0024] FIG. 3. Optical micrograph of part of a 2D 55,000 pen array.
Insets are SEM images of the pen array from side view (top), and
top view (bottom), respectively.
[0025] FIG. 4. (Left) Schematic diagram describing the procedure
for mounting the pen array. (Right) Photograph depicting the
mounted pen array being locked into the exact position as the epoxy
hardens.
[0026] FIG. 5. Optical image of a 2D pen array before and after
making contact with substrate.
[0027] FIG. 6. Dark Field optical micrograph of Au dots in
4.times.16 arrays demonstrating the wide writing range of the 2D
pen array.
[0028] FIG. 7. Optical micrograph of Au structures drawn in shape
of the characters "2D DPN" on a silicon substrate. Inset (center)
shows dark field micrograph of one of the structures produced by
one tip. Inset (right corner) is an SEM of these structures.
[0029] FIG. 8. Dark Field micrograph of a combinatorial Au
structures. Each pen produced a set of structures divided into four
quadrants comprising nine triangles, four lines, 25 dots, and a
"smiley face." (inset) SEM shows one of these structures at high
magnification.
[0030] FIG. 9. SEM image of pyramidal tip, where the measured tip
apex height is 8.8 microns and the base is 11.0 microns.
[0031] FIG. 10. Illustrating measurement of angle of cantilever
bending and distance of cantilever bending.
DETAILED DESCRIPTION
Introduction/DPN Printing
[0032] References will be made in detail to the preferred
embodiments, examples of which are illustrated in the accompanying
drawings. While the many facets of the invention will be described
in conjunction with the preferred embodiments, it will be
understood that they are not intended to limit the invention to
those embodiments. On the contrary, the invention is intended to
cover alternatives, modifications and equivalents, which may be
included within the spirit and scope of the invention as defined by
the appended claims and equivalents thereof.
[0033] Priority U.S. provisional application Ser. No. 60/792,950
filed Apr. 19, 2006 to Mirkin et al. is hereby incorporated by
reference.
[0034] For practice of the various embodiments described herein,
lithography, microlithography, and nanolithography instruments, pen
arrays, active pens, passive pens, inks, patterning compounds,
kits, ink delivery, software, and accessories for direct-write
printing and patterning can be obtained from NanoInk, Inc.,
Chicago, Ill. Software includes INKCAD software (NanoInk, Chicago,
Ill.), providing user interface for lithography design and control.
E-Chamber can be used for environmental control. Dip Pen
Nanolithography.TM. and DPN.TM. are trademarks of NanoInk, Inc.
[0035] The following patents and co-pending applications related to
direct-write printing with use of cantilevers, tips, and patterning
compounds are hereby incorporated by reference in their entirety
and can be used in the practice of the various embodiments
described herein, including inks, patterning compounds, software,
ink delivery devices, and the like: [0036] 1. U.S. Pat. No.
6,635,311 to Mirkin et al., which describes fundamental aspects of
DPN printing including inks, tips, substrates, and other
instrumentation parameters and patterning methods; [0037] 2. U.S.
Pat. No. 6,827,979 to Mirkin et al., which further describes
fundamental aspects of DPN printing including software control,
etching procedures, nanoplotters, and complex and combinatorial
array formation. [0038] 3. U.S. patent publication number
2002/0122873 A1 published Sep. 5, 2002 ("Nanolithography Methods
and Products Produced Therefor and Produced Thereby"), which
describes aperture embodiments and driving force embodiments of DPN
printing. [0039] 4. U.S. regular patent application, Ser. No.
10/366,717 to Eby et al., filed Feb. 14, 2003 ("Methods and
Apparatus for Aligning Patterns on a Substrate"), which describes
alignment methods for DPN printing (published Oct. 2, 2003 as
2003/0185967). [0040] 5. U.S. regular patent application, Ser. No.
10/375,060 to Dupeyrat et al., filed Feb. 28, 2003
("Nanolithographic Calibration Methods"), which describes
calibration methods for DPN printing. [0041] 6. U.S. Patent
Publication 2003/0068446, published Apr. 10, 2003 to Mirkin et al.
("Protein and Peptide Nanoarrays"), which describes nanoarrays of
proteins and peptides; [0042] 7. U.S. Regular patent application,
Ser. No. 10/307,515 filed Dec. 2, 2002 to Mirkin et al.
("Direct-Write Nanolithographic Deposition of Nucleic Acids from
Nanoscopic Tips"), which describes nucleic acid patterning (PCT
/US2002/038252 published Jun. 12, 2003). [0043] 8. U.S. Regular
patent application, Ser. No. 10/320,721 filed Dec. 17, 2002 to
Mirkin et al. ("Patterning of Solid State Features by Direct-Write
Nanolithographic Printing"), which describes reactive patterning
and sol gel inks (now published Aug. 28, 2003 as 2003/0162004).
[0044] 9. U.S. Pat. Nos. 6,642,129 and 6,867,443 to Liu et al.
("Parallel, Individually Addressible Probes for Nanolithography"),
describing active pen arrays. [0045] 10. U.S. Patent Publication
2003/0007242, published Jan. 9, 2003 to Schwartz ("Enhanced
Scanning Probe Microscope and Nanolithographic Methods Using
Same"). [0046] 11. U.S. Patent Publication 2003/0005755, published
Jan. 9, 2003 to Schwartz ("Enhanced Scanning Probe Microscope").
[0047] 12. U.S. patent application Ser. No. 10/637,641 filed Aug.
11, 2003, now published as 2004/0101469, describing catalyst
nanostructures and carbon nanotube applications. [0048] 13. U.S.
patent application Ser. No. 10/444,061 filed May 23, 2003, now
published as 2004/0026681 published Feb. 12, 2004, and US patent
publication 2004/0008330 published Jan. 15, 2004, describing
printing of proteins and conducting polymers respectively. [0049]
14. U.S. patent application Ser. No. 10/647,430 filed Aug. 26,
2003, now U.S. Pat. No. 7,005,378, describing conductive materials
as patterning compounds. [0050] 15. U.S. patent application Ser.
No. 10/689,547 filed Oct. 21, 2003, now published as 2004/0175631
on Sep. 9, 2004, describing mask applications including photomask
repair. [0051] 16. U.S. patent application Ser. No. 10/705,776
filed Nov. 12, 2003, now published as 2005/0035983 on Feb. 17,
2005, describing microfluidics and ink delivery. [0052] 17. U.S.
patent application Ser. No. 10/788,414 filed Mar. 1, 2004, now
published as 2005/0009206 on Jan. 13, 2005 describing printing of
peptides and proteins. [0053] 18. U.S. patent application Ser. No.
10/893,543 filed Jul. 19, 2004, now published as 2005/0272885 on
Dec. 8, 2005, describing ROMP methods and combinatorial arrays.
[0054] 19. U.S. patent application Ser. No. 11/056,391 filed Feb.
14, 2005, now published as 2005/0255237 published on Nov. 17, 2005,
describing stamp tip or polymer coated tip applications. [0055] 20.
U.S. patent application Ser. No. 11/065,694 filed Feb. 25, 2005,
now published as 2005/0235869 on Oct. 27, 2005, describing tipless
cantilevers and flat panel display applications. [0056] 21. US
Patent publication 2006/001,4001 published Jan. 19, 2006 describing
etching of nanostructures made by DPN methods. [0057] 22. WO
2004/105046 to Liu & Mirkin published Dec. 2, 2004 describes
scanning probes for contact printing.
[0058] All references cited in 1-20 above are incorporated by
reference and the teachings therein can be adapted for use with the
various embodiments described herein.
[0059] DPN methods are also described in Ginger et al., "The
Evolution of Dip-Pen Nanolithography," Angew. Chem. Int. Ed. 2004,
43, 30-45, including description of high-throughput parallel
methods.
[0060] Direct write methods, including DPN printing and pattern
transfer methods, are described in for example Direct-Write
Technologies, Sensors, Electronics, and Integrated Power Sources,
Pique and Chrisey (Eds), 2002.
[0061] The direct-write nanolithography instruments and methods
described herein are particularly of interest for use in preparing
bioarrays, nanoarrays, and microarrays based on peptides, proteins,
nucleic acids, DNA, RNA, viruses, biomolecules, and the like. See,
for example, U.S. Pat. No. 6,787,313 for mass fabrication of chips
and libraries; U.S. Pat. No. 5,443,791 for automated molecular
biology laboratory with pipette tips; U.S. Pat. No. 5,981,733 for
apparatus for the automated synthesis of molecular arrays in
pharmaceutical applications. Combinatorial arrays can be prepared.
See also, for example, U.S. Pat. Nos. 7,008,769; 6,573,369; and
6,998,228 to Henderson et al.
[0062] Scanning probe microscopy is reviewed in Bottomley, Anal.
Chem., 1998, 70, 425R-475R. Also, scanning probe microscopes are
known in the art including probe exchange mechanisms as described
in, for example, U.S. Pat. No. 5,705,814 (Digital Instruments).
Two Dimensional Arrays
[0063] One embodiment is an article comprising: (i) a
two-dimensional array of a plurality of cantilevers, wherein the
array comprises a plurality of base rows, each base row comprising
a plurality of cantilevers extending from the base row, wherein
each of the cantilevers comprise tips at the cantilever end away
from the base row, wherein the arrays are adapted to prevent
substantial contact of non-tip components of the array when the
tips are brought into contact with a substantially planar surface;
and (ii) a support for the array. One particular embodiment is
illustrated in the non-limiting working examples and figures.
[0064] One embodiment also provides an article comprising: (i) a
two-dimensional array of a plurality of cantilevers, wherein the
array comprises a plurality of base rows, each base row comprising
a plurality of cantilevers, wherein each of the cantilevers
comprise tips at the cantilever end away from the base, wherein the
number of cantilevers is greater than 250, and wherein the tips
have an apex height relative to the cantilever of at least, for
example, four microns, and (ii) a support for the array. One
particular embodiment is illustrated in the non-limiting working
examples and figures.
[0065] Another embodiment provides an article comprising: a
two-dimensional array of a plurality of cantilevers, wherein the
array comprises a plurality of base rows, each base row comprising
a plurality of cantilevers, wherein each of the cantilevers
comprise tips at the cantilever end away from the base, wherein the
number of cantilevers is greater than 250, and wherein the tips are
coated with metal on the tip side of the cantilever and the
cantilevers are bent at an angle of, for example, at least
10.degree. from their base. One particular embodiment is
illustrated in the non-limiting working examples and figures.
[0066] Two-dimensional arrays of cantilevers are known in the art.
For example, the two-dimensional array can be a series of rows and
columns, providing length and width, preferably substantially
perpendicular to each other. The arrays can comprise a first
dimension and a second dimension. The two-dimensional array can be
a series of one dimensional arrays disposed next to each other to
build the second dimension. The two dimensions can be
perpendicular. The cantilevers can comprise a free end and a bound
end. The cantilevers can comprise tips at or near the free end,
distal from the bound end. The cantilevers of one row can point in
the same direction as the cantilevers on the next row, or the
cantilevers of one row can point in the opposite direction as the
cantilevers on the next row.
[0067] The two-dimensional arrays can be fabricated by combining
two parts, each part having a surface which is patterned in two
dimensions and adapted to be mated with each other in the two
dimensions.
[0068] One important variable is the fraction or percentage of the
cantilevers in the array which can actually function for the
intended purposes. In some cases, some cantilevers can be
imperfectly formed, or can be otherwise damaged after formation. A
cantilever yield reflects this percentage of usable cantilevers.
Preferably, the array is characterized by a cantilever yield of at
least 75%, or at least 80%, or at least 90%, or at least 95%, or
more preferably, at least about 98%, or more preferably at least
99%. In characterizing the cantilever yield, cantilevers at the
ends of rows may be neglected which are damaged by processing of
edges compared to internal cantilevers. For example, the central
75% can be measured. In many cases, the fabrication will be better
done in the middle rather than the edge as edge effects are known
in wafer fabrication. Defect density can increase in some cases as
one moves from the center to the edge.
[0069] The array can be adapted to prevent substantial contact of
non-tip components of the array when the tips are brought into
contact with a substantially planar surface. For example, the
cantilever arms should not contact the surface and can be
accordingly adapted such as by, for example, bending. The tips can
be adapted for this as well including, for example, long tips.
Factors which can be useful to achieve this result include use of
long tips, bending of the cantilever arms, tip leveling, row
leveling, and leveling of the cantilevers in all dimensions. One or
more combination of factors can be used.
[0070] The cantilever tips can be longer than usual in the art. For
example, the tips can have an apex height relative to the
cantilever of at least four microns on average, and if desired, the
tips can have an apex height relative to the cantilever of at least
seven microns on average. In addition, tip apex height can be at
least 10 microns, or at least 15 microns, or at least 20 microns.
No particular upper limit exists and technology known in the art
and improving can be used. This long length can help ensure that
only tips are contacting the surface. Apex height can be taken as
an average of many tip apex heights, and in general, apex height is
engineered not to vary substantially from tip to tip. Methods known
in the art can be used to measure tip apex height including methods
shown in the working examples.
[0071] In measuring parameters for the array, average measurements
can be used. Average measurements can be obtained by methods known
in the art including for example review of representative images or
micrographs. The entire array does not need to be measured as that
can be impractical.
[0072] Tipless cantilevers can be used in some embodiments,
although not a preferred embodiment. For example, one embodiment
provides an article comprising: (i) a two-dimensional array of a
plurality of cantilevers, wherein the array comprises a plurality
of base rows, each base row comprising a plurality of cantilevers
extending from the base row, wherein each of the cantilevers are
tipless cantilevers, wherein the cantilevers are bent at an angle
from their base.
[0073] In addition, the cantilevers can be bent including bent
towards the surface to be patterned. Methods known in the art can
be used to induce bending. The cantilevers can be bent at an angle
away from the base and the support. The cantilevers can comprise
multiple layers adapted for bending of cantilevers. For example,
differential thermal expansion or cantilever bimorph can be used to
bend the cantilevers. Cantilever bending can be induced by using at
least two different materials. Alternatively, the same materials
can be used but with different stresses to provide cantilever
bending. Another method is depositing on the cantilever comprising
one material a second layer of the same material but with an
intrinsic stress gradient. Alternatively, the surface of the
cantilever can be oxidized. The cantilevers can be bent at an angle
for example of at least 5.degree. from their base, or at least
10.degree. from their base, or at an angle of at least 15.degree.
from their base. Methods known in the art can be used to measure
this including the methods demonstrated in the working examples.
Average value for angle can be used. The cantilevers can be bent on
average about 10 microns to about 50 microns, or about 15 microns
to about 40 microns. This distance of bending can be measured by
methods known in the art including the methods demonstrated in the
working examples. Average distance can be used. The bending can
result in greater tolerance to substrate roughness and morphology
and tip misalignment within the array so that for example a
misalignment of about .+-.20 microns or less or about .+-.10
microns or less can be compensated.
[0074] To facilitate bending, the cantilevers can comprise multiple
layers such as two principle layers and optional adhesion layers
and can be for example bimorph cantilevers. The cantilevers can be
coated with metal or metal oxide on the tip side of the cantilever.
The metal is not particularly limited as long as the metal or metal
oxide is useful in helping to bend the cantilevers with heat. For
example, the metal can be a noble metal such as gold.
[0075] In preferred embodiments, the array can be adapted so that
the cantilevers are both bent toward the surface and also comprise
tips which are longer than normal compared to tips used merely for
imaging.
[0076] The tips can be fabricated and sharpened before use and can
have an average radius of curvature of, for example, less than 100
nm. The average radius of curvature can be, for example, 10 nm to
100 nm, or 20 nm to 100 nm, or 30 nm to 90 nm. The shape of the tip
can be varied including for example pyramidal, conical, wedge, and
boxed. The tips can be hollow tips or contain an aperture including
hollow tips and aperture tips formed through microfabrication with
microfluidic channels passing to end of tip. Fluid materials can be
stored at the end of the tips or flow through the tips.
[0077] The tip geometry can be varied and can be for example a
solid tip or a hollow tip. WO 2005/115630 (PCT/US2005/014899) to
Henderson et al. describes tip geometries for depositing materials
onto surfaces which can be used herein.
[0078] The two dimensional array can be characterized by a tip
spacing in each of the two dimensions (e.g., length dimension and
width dimension). Tip spacing can be taken, for example, from the
method of manufacturing the tip arrays or directly observed from
the manufactured array. Tip spacing can be engineered to provide
high density of tips and cantilevers. For example, tip density can
be at least 10,000 per square inch, or at least 40,000 per square
inch, or at least 70,000 per square inch. The array can be
characterized by a tip spacing of less than 300 microns in a first
dimension of the two dimensional array and less than 300 microns in
a second dimension of the two dimensional array. To achieve even
higher density, the tip spacing can be, for example, less than
about 200 microns in one dimension and less than about 100 microns,
or less than about 50 microns, in another dimension. Alternatively,
the tip spacing can be for example less than 100 microns in one
dimension and a less than 25 microns in a second direction. The
array can be characterized by a tip spacing of 100 microns or less
in at least one dimension of the two dimensional array. In one
embodiment, tip spacing can be about 70 microns to about 110
microns in one dimension, and about 5 microns to about 35 microns
in the second dimension. There is no particular lower limit on tip
spacing as fabrication methods will allow more dense tip spacing
over time. Examples of lower limits include 1 micron, or 5 microns,
or 10 microns so for example tip spacings can be one micron to 300
microns, or one micron to 100 micron.
[0079] The number of cantilevers on the two dimensional array is
not particularly limited but can be at least about three, at least
about five, at least about 250, or at least about 1,000, or at
least about 10,000, or at least about 50,000, or at least about
55,000, or at least about 100,000, or about 25,000 to about 75,000.
The number can be increased to the amount allowed for a particular
instrument and space constraints for patterning. A suitable balance
can be achieved for a particular application weighing for example
factors such as ease of fabrication, quality, and the particular
density needs.
[0080] The tips can be engineered to have consistent spacing for
touch the surface consistently. For example, each of the tips can
be characterized by a distance D spanning the tip end to the
support, and the tip array is characterized by an average distance
D' of the tip end to the support, and for at least 90% of the tips,
D is within 50 microns of D'. In another embodiment, for at least
90% of the tips, D is within 10 microns of D'. The distance between
the tip ends and the support can be for example about 10 microns to
about 50 microns. This distance can comprise for example the
additive combination of base row height, the distance of bending,
and the tip height.
[0081] Base row length is not particularly limited. For example,
the base rows can have an average length of at least about 1 mm.
Average length for base row can be, for example, about 0.1 mm to
about 30 mm, or about 0.1 mm to about 15 mm, or about 0.1 mm to
about 5 mm, or about 0.5 mm to about 3 mm.
[0082] The base rows can have a height with respect to the support
of at least about 5 microns. This height is not particularly
limited but can be adapted for use with the appropriate cantilever
bending.
[0083] Cantilever force constant is not particularly limited. For
example, the cantilevers can have an average force constant of
about 0.001 N/m to about 10 N/m, or alternatively, an average force
constant of about 0.05 N/m to about 1 N/m, or alternatively an
average force constant of about 0.1 N/m to about 1 N/m, or about
0.1 N/m to about 0.6 N/m.
[0084] A variety of methods can be used for bonding the cantilevers
to the base, and the methods are not particularly limited. Bonding
methods are described for example in Madou, Fundamentals of
Microfabrication, 2.sup.nd Ed., pages 484-494 which describes for
example field-assisted thermal bonding, also known as anodic
bonding, electrostatic bonding, or the Mallory process. Methods
which provide low processing temperature can be used. For example,
the cantilevers can be bound to the base by a non-adhesive bonding.
Bonding examples include electrostatic bonding, field-assisted
thermal bonding, silicon fusion bonding, thermal bonding with
intermediate layers, eutectic bonding, gold diffusion bonding, gold
thermocompression bonding, adhesive bonding, and glass frit
bonding.
[0085] The cantilevers can be engineered so they are not adapted
for feedback including force feedback. Alternatively, at least one
cantilever can be adapted for feedback including force feedback. Or
substantially all of the cantilevers can be adapted for feedback
including force feedback. For example, over 90%, or over 95%, or
over 99% of the cantilevers can be adapted for feedback including
force feedback.
[0086] The cantilevers can be bound to the base by electrostatic
binding.
[0087] The cantilevers can be made from materials used in AFM
probes including for example silicon, polycrystalline silicon,
silicon nitride, or silicon rich nitride. The cantilevers can have
a length, width, and height or thickness. The length can be for
example about 10 microns to about 80 microns, or about 25 microns
to about 65 microns. The width can be for example 5 microns to
about 25 microns, or about 10 microns to about 20 microns.
Thickness can be for example 100 nm to about 700 nm, or about 250
nm to about 550 nm. Tipless cantilevers can be used in the arrays,
the methods of making arrays, and the methods of using arrays.
[0088] The cantilevers can be supported on the base rows, and the
base rows in turn can be supported on a larger support for the
array. The base rows can extend from the larger support for the
array. The array support can be characterized by a surface area
which is about two square cm or less, or alternatively about 0.5
square cm to about 1.5 square cm. The size can be adjusted as
needed for coupling with an instrument.
[0089] Arrays can be adapted for passive pen or active pen use.
Control of each tip can be carried out by piezoelectric, capactive,
or thermoelectric actuation, for example.
[0090] The arrays can be adapted for integration of tip coating and
ink delivery. For example, microfluidics can be used to control
inking and coating of the tips. Tips can be dipped into devices or
ink can be delivered directly through internal regions of the tip
for hollow tip embodiments.
[0091] The tips can be coated with a patterning compound or ink
material. The coating is not particularly limited; the patterning
compound or ink material can be disposed at the tip end. Patterning
compounds and materials are known in the art of nanolithographic
printing and include organic compounds and inorganic materials,
chemicals, biological materials, non-reactive materials and
reactive materials, molecular compounds and particles,
nanoparticles, materials that form self assembled monolayers,
soluble compounds, polymers, ceramics, metals, magnetic materials,
metal oxides, main group elements, mixtures of compounds and
materials, conducting polymers, biomolecules including nucleic acid
materials, RNA, DNA, PNA, proteins and peptides, antibodies,
enzymes, lipids, carbohydrates, and even organisms such as viruses.
The references described in the INTRODUCTION section describe many
patterning compounds which can be used. Sulfur-containing compounds
including thiols and sulfides can be used.
[0092] The methods by which the tips can be coated can include for
example solution dipping or vacuum evaporation, as well as the
microfluidic methods noted above. See U.S. patent application Ser.
No. 10/705,776 filed Nov. 12, 2003, now published as 2005/0035983
on Feb. 17, 2005.
Methods of Making Two Dimensional Arrays
[0093] Another embodiment comprises a method of making two
dimensional arrays. For example, an embodiment comprises a method
of making article, wherein the article comprises a two-dimensional
array of a plurality of cantilevers, and a support for the array,
the method comprising: (i) forming a two dimensional array
comprising a plurality of cantilevers comprising tips at their
ends, wherein the cantilevers are supported on a sacrificial
support structure; (ii) forming an array support comprising a
plurality of base rows which are adapted for bonding to the two
dimensional array comprising a plurality of cantilevers; (iii)
bonding the cantilevers to the base rows; and (iv) removing the
support structure to release the cantilevers and form the array.
The non-limiting working examples below provide one method for
executing these steps. See FIG. 2. In FIG. 2, the structure shown
as "electrostatic binding" comprises patterned cantilevers
(patterning not shown).
[0094] In some embodiments, tipless cantilevers can be
fabricated.
[0095] The above description for the article comprising the two
dimensional arrays and support can be also applied to the methods
making the two dimensional arrays. For example, in the method of
making, the tips can be adapted to prevent substantial contact of
non-tip components of the array when the tips are brought into
contact with a substantially planar surface. In the method of
making, the tips can have an apex height relative to the cantilever
of at least four microns, or at least seven microns. In the method
of making, the method can further comprise the step of bending the
cantilevers at an angle away from the support. For example, the
method can comprise bending the cantilevers at an angle of at least
10.degree. away from the support. In the method of making, the tips
can have an apex height relative to the cantilever of at least four
microns, and wherein the cantilevers are bent at an angle away from
the support. Also, in the method of making, the tips can have an
apex height relative to the cantilever of at least seven microns,
and wherein the cantilevers are bent at an angle of at least
10.degree. away from the support.
[0096] Microfabrication methods are described extensively in for
example Madou, Fundamentals of Microfabrication, 2.sup.nd Ed., CRC
Press, 2002; and Van Zant, Microchip Fabrication, 5.sup.th Ed.,
2004.
[0097] In one part of the fabrication method, the two dimensional
array can be formed by microfabrication and micromachining methods.
The sub-product can comprise the cantilevers supported on a
sacrificial support which can be later removed before use.
Microfabrication steps including wafers, oxidation, patterning,
etching, deposition, deep reactive ion etching (Bosch process) and
other steps known for making cantilevers and tips can be used.
[0098] In another part of the fabrication method, an array support
is formed which is adapted for bonding to the two dimensional array
of cantilevers. It can be also adapted for coupling the two
dimensional array of cantilevers to the instrument for movement.
Base rows can be formed which extend out from the surface of the
array support and provide support for the cantilevers upon
fabrication.
[0099] The cantilevers can be bonded to the base rows. An example
of a bonding method is electrostatic bonding.
[0100] The sacrificial support for the cantilevers can be removed
to free up or release the cantilevers. Methods known in the art can
be used to execute this step.
[0101] FIG. 2 from the working examples below illustrates a
fabrication method, although the parameters and materials described
therein can be modified. For example, the 200 nm layer of silicon
oxide can be, for example, 100 nm to 300 nm; the 950.degree. C. can
be for example 850.degree. C. to 1050.degree. C.; the 30 minutes
can be for example 15 minutes to 45 minutes; the 10 micron square
openings do not have to be square can be for example 5 microns to
15 microns; the 400 nm silicon nitride layer can be 200 nm to 600
nm, or 300 nm to 500 nm; the 200 nm thick chromium layer can be for
example 100 nm to 300 nm; the 100 micron trenches can be for
example 50 microns to about 150 microns; the eight micron recesses
can be for example 3 microns to 13 microns so as to allow
cantilever free movement; and the like.
[0102] The working examples also provide a method for annealing pen
arrays and the parameters described therein can be modified. For
example, the 5 nm Ti adhesion layer can be 2 nm to 20 nm thick, and
the 25 nm gold layer can be 5 rim to 100 nm thick. The annealing
temperature can be for example 150.degree. C. to about 500.degree.
C., and the time for annealing can be for example 30 minutes to 250
minutes.
[0103] Also provided is a method comprising (1) micromaching a two
dimensional array of cantilevers wherein the cantilevers are
adapted to bond with a device which both supports the cantilevers
and can also couple the cantilevers to an instrument for motion,
and (2) bonding the cantilevers to the device. The device can be
called a handle wafer. One side is for bonding to the cantilevers.
The other side is for coupling to a larger instrument. The working
examples below, for example, also illustrate this embodiment.
Leveling
[0104] Level can be carried out to provide leveling in each
dimension of the two dimensional array. Leveling can help with
adapting the array so only tips contact the surface. The working
examples below provide an example of leveling the cantilevers
before the two dimensional array of cantilevers are mounted onto an
instrument. For example, gravity forces and forces near to gravity
forces can be used to level the cantilevers on a sacrificial
substrate. External force can be used. Other forces can be used as
needed for a particular two dimensional array. For example, forces
can be about 0.2 nN/tip to about 2,000 nN/tip, or about 2 nN/tip or
about 200 nN/tip, or about 20 nN/tip. The sacrificial substrate can
be made as flat as possible and practical for a given
application.
[0105] The adhesive mounting method also allows one to improve
leveling and avoid use of a feedback system if desired.
[0106] Optical microscopy can be used to facilitate leveling.
[0107] One embodiment provides a method comprising: (i) preparing a
two-dimensional array of a plurality of cantilevers, wherein the
array comprises a plurality of base rows, each base row comprising
a plurality of cantilevers extending from the base row, wherein
each of the cantilevers comprise tips at the cantilever end away
from the base row, (ii) contacting tips of the array with a
sacrificial substrate under pressure, (iii) forming an aligned
array on the substrate, and (iv) attaching the aligned array to an
instrument adapted for motion of the array. The pressure can be
generated either externally or with gravity. The attaching can be
an adhesive or mechanical attaching. The method can further
comprise removing the sacrificial substrate from the tips of the
array.
Mounting the Supported Two Dimensional Arrays on an Instrument
[0108] Mounting of arrays to the instrument can be achieved by one
or more mechanisms operating individually or in combination. For
example, mounting can be carried out with use of mechanical
coupling, friction fit or magnetic coupling. Adhesives and glues
can be used including fast curing and UV curing systems. Epoxy glue
is described below including its use as a gap filler or space
filler.
[0109] Adhesive mounting can be used to couple the supported two
dimensional arrays to an instrument which provides x motion, y
motion, z motion, or combinations thereof including x,y,z motion.
Motion is provided which allows for high resolution patterning and
high resolution such as found with for example scanning probe
instruments.
[0110] The instrumentation can be also adapted to have the pens
stand still and have the substrates move in x, y, and/or z
motion.
[0111] In a preferred embodiment, the bonding agent functions to
both mount the two dimensional array to the instrument and also the
facilitate leveling of the tip array.
Instrument
[0112] Also provided are instruments including printing and
patterning instruments, as well as nanolithography instruments.
Instruments can be used which provide both imaging and patterning
capability. While the methods and devices herein can be used with
scanning probe and AFM instrumentation, the instruments are not so
limited. Dispensing instruments and tools for delivering small
scale amounts of materials to surfaces are known. See for example
U.S. Pat. Nos. 6,024,925; 6,087,274; 5,981,733;
[0113] A preferred example of an instrument for lithography
including microlithography and nanolithography is the NScriptor.TM.
from NanoInk (Chicago, Ill.). Commercial AFM instruments can be
used.
[0114] An instrument is described in U.S. Pat. No. 7,008,769 to
Henderson et al.
Using the Two Dimensional Arrays
[0115] DPN patterning is describe in the references noted above in
the Introduction Section and other references cited herein.
[0116] Substrates can be made with massive numbers of micron-scale
or nanometer-scale structures, or nanostructures, formed at
massively fast rates. For example, one important parameter is the
rate at which structures can be formed. Using methods described
herein, structures can be formed at a rate of at least 100,000 per
minute, or at least 1,000,000 structures per minute, and even
further at least 2,000,000 structures per minute, and even further
at least 3,000,000 structures per minute, and even further at least
4,000,000 structures per minute, and even further at least
5,000,000 structures per minute, and even further at least
10,000,000 structures per minute. For example, structures formed at
fast rates can be dot features having a diameter of for example
about 25 nm to about 500 nm, or about 50 nm to about 200 nm. The
structures can be dots and circles, wherein the tip is not moved in
the X-Y direction during deposition of the patterning compound.
[0117] Other rate parameters can be used. For example,
direct-writing can be carried out at a rate of at least 1.0
meter/min, or at least 3.3 meters/min (for example, if the tips are
moved at appropriate rates such as for example a rate of 1 um/s).
Patterning can be executed at 10,000,000 square microns per hour.
Rates can be in some cases determined by the rate of diffusion
spreading for one pen with multiplication by the number of
pens.
[0118] A preferred embodiment comprises a method for direct-write
nanolithography comprising: directly writing nanostructures at a
rate of at least 100,000 per minute, wherein the directly writing
comprises contacting a tip having a patterning compound thereon
with a substrate. The rate can be at least 1,000,000 per minute, or
at least 4,000,000 per minute. The nanostructures can comprise
dots, lines, or substantially complete circles. The nanostructures
can comprise dots having diameter about 50 nm to about 1,000 nm.
The nanostructures can be separated by a distance between about 50
nm and about 1,000 nm, or about 100 nm to about 750 nm.
[0119] Substrates can be coated and patterned with for example at
least 25,000,000 structures, or at least 50,000,000 structures, or
at least 75,000,000 structures, or at least 1,000,000 structures,
or at least 500,000,000 million structures, or at least
1,000,000,000 structures.
[0120] An important aspect is that the pattern formed on the
substrate substantially matches either (1) a pattern generated with
software and made with tip motion, or (2) the pattern of the array
when the tips are not moved over the surface.
[0121] An important embodiment comprises the elimination of a
feedback system. This embodiment, having this eliminated, is a
basic and novel feature.
[0122] The substrates for patterning can be single layer or
multilayer. They can be solids including polymers, glasses,
composites, silicon, mica, diamond, ceramics, metals, and various
oxides and complex mixtures.
[0123] The ink-substrate combination can be selected to provide
stable structures. Stability can be enhanced by use of covalent
bonding or chemisorption, or electrostatic attraction.
[0124] Arrays can be formed of inorganic, organic, or biological
materials including nanostructures such as viruses, proteins,
carbon nanotubes, nanowires, dendrimers, fullerenes, and the like.
Combinatorial arrays can be formed. Each spot in the array can
provide the same composition or a different composition compared to
the next spot.
[0125] Vibration isolation tables can be used. Environmental
chambers can be used including nebulizer, real-time sensors for
temperature and humidity control, and heating and cooling fans.
High resolution optics can be used. Independent three motor
leveling can be used. Tip biasing can be used.
[0126] If AFM-like instrumentation is used, the mode can be contact
mode, non-contact mode, or intermittent contact mode.
[0127] Another example of a use can be found in Lenhert et al,
"Massively Parallel Dip-Pen Nanolithography of Heterogeneous
Supported Phospholipid Multilayer Patterns," Small, 2007, 3, No. 1,
71-75, which is hereby incorporated by reference including FIGS.
1-4, experimental section, and noting references cited therein. The
instruments described herein can be used to control multi-bilayer
stacking (FIG. 1); phospholipid patterns including fluorophore
doping (FIG. 2); parallel writing of multiple inks including for
testing membrane fluidity; and generation of fluorescent
micrographs.
[0128] The various embodiments are further illustrated by the
following non-limiting examples.
WORKING EXAMPLES
[0129] Using conventional photolithographic techniques, a 55,000
pen two-dimensional array was fabricated (pen yield >98%; pen
spacing 90.times.20 .mu.m, FIG. 1a). The challenge of leveling all
55,000 pens over a substrate during a patterning experiment was
overcome, without the need for independent feedback on each tip.
Several important parameters were developed.
[0130] First, arrays of Si.sub.3N.sub.4 (or silicon rich nitride
material) cantilevers with pyramidal tips were fabricated such that
the tips are about three times larger than conventional silicon
nitride AFM tips (the apex of each tip was 7.6.+-.0.2 .mu.m taller
than its cantilever base).
[0131] Second, the cantilevers were bent at a .about.20.degree.
angle from their base by coating them with 25 nm of Au (and 5 nm Ti
adhesion layer) and then annealing at 300.degree. C. This curvature
is a result of the different thermal expansion coefficients of
Si.sub.3N.sub.4 and Au (see, for example, Wenzler, et al. T. P.
Rev. Sci. Instrum. 67, 4191-4197 (1996)). This array architecture
leads to greater tolerance to the substrate morphology and inherent
tip misalignment within the array (.+-.10 .mu.m misalignment can be
compensated).
[0132] Third, gravity (.about.20 nN/tip), instead of a complex set
of feedback systems, was used to bring all of the tips in contact
with a sacrificial substrate prior to use.
[0133] Finally, the tip array was locked into position with respect
to the piezo scanner head by taking advantage of the malleability
of a rapidly curing epoxy resin (see supplementary information).
This alignment procedure was useful so all of the tips within the
array could be engaged and disengaged in a deliberate and
controlled fashion without a feedback system. Once engaged, the pen
array can be used to directly write virtually any pattern of
molecules on the underlying substrate and simultaneously generate
.about.55,000 duplicates.
[0134] To test the writing capabilities of the pen array, its
cantilevers were uniformly coated with 1-octadecanethiol (ODT) by
vapor deposition and subsequently used to pattern a 25 nm film of
polycrystalline gold on an oxidized silicon substrate with a 5 nm
Ti adhesion layer. Using ODT as a chemical etch resist, the
molecular patterns were developed into gold nanostructures,
allowing the use of an optical or scanning electron microscope to
characterize the patterns over large areas. In an initial
experiment, the 55,000 pen array was used to generate .about.88
million dot features (each tip generating 1,600 100.+-.20 nm dots
in a 40.times.40 array) in less than 20 min (FIG. 1b).
Significantly, >99% of all the pens (excluding 1-2% of pens
damaged during processing) are in operation. AFM and SEM images
confirm that registry and alignment are maintained within the field
of view of each tip and between tips as well. One can even generate
very sophisticated structures using this approach along with
integrated software that controls the relative movement of the tip
array over the underlying substrate. Indeed, the likeness of Thomas
Jefferson was taken from a 2005 United States five cent coin and
duplicated .about.55,000 times at a pixel resolution of 80 nm (FIG.
1c).
[0135] Materials. Gold substrates were prepared according to
literature procedures. (Weinberger et al., Advanced Materials, 12,
1600 (2000); Zhang et al., Langmuir, 20, 962-968 (2004).
1-octadecanethiol (ODT) (98%) and 1-octanol (99%) were purchased
from Aldrich Chemical Co. Fe(NO.sub.3).sub.39H.sub.2O (99%) was
purchased from Acros Chemicals, thiourea (ACS grade) was purchased
from Fisher Scientific, and ethanol (ACS/USP grade) was purchased
from Pharmco Products Inc. 5-min epoxy gel was purchased from
Devcon and used as specified by the manufacturer. All chemicals
were used as received.
[0136] Fabrication of 55,000 Cantilever Arrays: The
Microfabrication process used to generate the tips was designed to
be simple and robust, which affords high yields and is amenable for
future modifications (FIG. 2). A 200 nm layer of silicon oxide was
thermally grown (950.degree. C., 30 min) on a silicon <100>
wafer and lithographically patterned with 10 micron square openings
at a spacing of 90.times.20 microns. The oxide patterns were then
used as an etch mask for an anisotropic silicon etch (37% KOH, 20
min) to form pyramidal tip molds in the silicon wafer. The oxide
etch mask was removed in buffered HF (6:6:1 H.sub.20:NH.sub.4F:HF,
5 min), and a 400 nm thick thin film of Si.sub.3N.sub.4 was
deposited using a low pressure, low stress chemical vapor
deposition process. The Si.sub.3N.sub.4 layer on the front side of
the wafer was then lithographically patterned to form arrays of
cantilevers. No oxide layer remains on the backside.
[0137] Separately, a Pyrex wafer was coated with a 200 nm thick
chromium layer and lithographically patterned to form 100 micron
rectangular trenches. The Pyrex was etched in a reactive ion
etcher, forming 8 micron recesses to allow the cantilevers free
movement, and the chromium was then removed. The nitrided silicon
wafer and the Pyrex wafer were then electrostatically bonded, and
the back of the Pyrex wafer was scribed into 1 cm.sup.2 substrates
by a diamond saw. Finally, the silicon wafer was etched, leaving
the nitrided tip arrays attached to the Pyrex. The resulting
cantilever structures were characterized by optical and electron
microscopy (FIG. 3). The measured radius of curvature for
fabricated tip arrays was 60 nm.+-.20 nm.
[0138] The force constant (k) of a fixed-free cantilever beam with
a length, width, and thickness of l, w, and t is given by
k=Ewt.sup.3/4t (l), under a small displacement assumption. The term
E denotes the modulus of elasticity of the probe material. The
approximate modulus of elasticity is 145 GPa for the thin film of
low-stress deposited layer of Si.sub.3N.sub.4. The cantilevers had
measured dimensions of l=45 microns, w=14.5 microns, and t=400 nm,
which correspond to a force constant k=0.40.+-.0.10 N/m. Annealing
of pen arrays. To induce tip curling away from the cantilever base,
the tip-side of the cantilevers were first coated with a 5 nm Ti
adhesion layer and 25 nm Au using a BOC 306 Edwards vacuum
evaporator operated at a base pressure below 5.times.10-7 mbar.
Subsequently, the pen arrays were placed in an oven, held at
300.degree. C. for 2 hr, and then slowly cooled to room temperature
at a rate <5.degree. C./min. The degree of cantilever bending
was inspected by optical microscopy and quantitatively measured by
SEM. Although annealing the pen arrays at 400.degree. C. induced a
larger degree of cantilever bending, the high temperature also
resulted in coarsening of the gold grains due to enhanced Au
diffusion. Therefore, 300.degree. C. was chosen as the annealing
temperature. Cantilever bending is caused by the different thermal
expansion of gold (.alpha..sub.Au=13.8.times.10.sup.-6.degree.
C..sup.-1) and Si.sub.3N.sub.4
(.alpha..sub.Si.sub.3.sub.N.sub.4=16.times.10.sup.-6.degree.
C..sup.-1). By modeling the gold coated Si.sub.3N.sub.4 cantilevers
as a bimorph system, the annealing induced curvature, expressed as
the radius of an arc R, can be calculated from equation 2,
R = 3 ( D 1 + D 2 ) 2 D 1 D 2 E 1 E 2 + ( D 1 E 1 + D 2 E 2 ) ( D 1
3 E 1 + D 2 3 E 2 ) 6 .DELTA. .alpha. .DELTA. T ( D 1 + D 2 ) D 1 D
2 E 1 E 2 ( 2 ) ##EQU00001##
where D is the thickness (D.sub.1=D.sub.Au=25 nm;
D.sub.2=D.sub.Si.sub.3.sub.N.sub.4=400 nm), E is Young's modulus
(E.sub.1=E.sub.Au=0.8.times.10.sup.11 N m.sup.-2;
E.sub.2=E.sub.Si.sub.3.sub.N.sub.4=3.8.times.10.sup.11 N m.sup.-2,
.DELTA..alpha. is the difference in the coefficients of thermal
expansion, and .DELTA.T is the change in temperature. The
deflection or distance moved by the free end of the cantilever d
can be represented by d=L.sup.2/2R, where L is the length of the
cantilevers.
[0139] Heating the tips to 300.degree. C. would produce the
expected deflection or curling of 14 microns. However, the
experimentally determined value is about 20-30 microns, which is
most likely a result of deviations in the thickness of Au and the
Si.sub.3N.sub.4 layers across the entire tip arrays. (Wenzler et
al., Review of Scientific Instruments, 67, 4191-4197 (1996).
[0140] Ink Coating: The pen arrays were placed inside a sealed
metal container with ODT (the pen arrays were attached to the cover
of the container with a piece of double-sticky tape). The container
was heated to 70.degree. C. and held for 30 minutes, and then
allowed to slowly cool. This vapor coating process was repeated
(typically 2-3 times) until the tips were sufficiently coated with
ODT for DPN printing experiments. Importantly, the coated pen array
could be used to pattern more than 25 samples over a period of
three days without the need of recoating the tips with more ODT
ink.
[0141] Pen Array Mounting: The pen array was gently placed onto a
sacrificial Au-coated SiOx substrate, letting the weight of the tip
array (about 100 mg, 20 nN/tip) bring all tips into contact with
substrate. An epoxy coated magnetic tip holder (1 cm.times.0.2 cm)
was then gently brought down in contact with the Pyrex support of
the pen array using the z motors of the AFM (FIG. 4, right). Enough
pressure was applied using the motors (about 20-50 micron lower
than the epoxy-tip array contact point) until the epoxy starts
spreading to fill the void between the tip holder and the tip array
(FIG. 4). The epoxy was then left to fully harden over a period of
at least 1 hr. Note that it was important in this example to use a
thin film of epoxy, avoiding excess, since epoxy can undergo a
1-10% volume shrinkage during polymerization. (Schoch et al.,
Thermochimica Acta, 417, 115-118 (2004); Ramos et al, Polymer, 46,
3323-3328 (2005), After the epoxy was fully cured, all the tips
could then be engaged with the substrate by moving the z-motors to
the same (.+-.0.2 microns) curing position. Interestingly,
tip-substrate contact can be observed by monitoring the
bending-induced change in the optical reflectivity of the
cantilevers (FIG. 5). Note that the Au-coating enhances tip
reflectivity. The exact position of the tip-substrate contact is
maintained to within .+-.1 micron, and over 20 substrates were
patterned by coming back to the same z position. Remarkably, the
pen arrays could be remounted on the scanner head and used for high
resolution patterning. This system provided for successfully
patterning over cm square areas after remounting the tip array on
the scanner head. Remounting the magnetic tip holder was
facilitated by allowing a small amount of epoxy to mold onto one
edge of the scanner head.
[0142] Dip Pen Nanolithography: DPN experiments were performed with
an Nscriptor.TM. (NanoInk, Inc., Chicago, Ill.) equipped with a
100-micron scanner and closed-loop scan control and commercial
lithographic software (DPNWrite, .TM.DPN System-1, NanoInk, Inc.,
Chicago, Ill.). All DPN patterning experiments were carried out
under ambient laboratory conditions without the aid of a clean room
(about 30% relative humidity, about 20.degree. C.).
[0143] Selective Etching of Au: Etching was performed on
DPN-patterned gold substrates by immersing in a bath of 13.3 mM
Fe(NO.sub.3).sub.39H.sub.2O, 20 mM thiourea, 0.3% HCl in octanol
saturated nanopure water (15 mL of etch solution for a about 1
square cm substrate). (Xia et al., Chemistry of Materials, 7,
2332-2337 (1995); Geissler et al, Langmuir, 18, 2374-2377 (2002);
Zhang et al., Nano Letters, 3, 43-45 (2003). The bath was gently
stirred as the substrate was visually inspected for etching (rate
about 6 nm/min). The color of the substrate changed from yellow to
dark blue as the gold was dissolved.
[0144] Pattern Characterization. Patterned structures, post
etching, were characterized by SEM (Leo Gemini 1525), and optical
microscopy (Zeiss Axiovert 100A inverted microscope, Thornwood
N.Y.) equipped with a Penguin 600CL digital camera and StreamPix
software. These tools provide a relatively high throughput method
for evaluating the quality of the patterned structures. Tapping
mode AFM images were collected with a Nanoman AFM equipped with a
Nanoscope IV controller from Veeco (Santa Barbara, Calif.) with
silicon tips (NCH-W, Veeco, spring constant 40 N/m) scanned at a
rate of 0.5 Hz and set to a pixel resolution of 512.times.512. Gold
coated commercial AFM cantilevers (sharpened Si.sub.3N.sub.4, Type
A, NanoInk, Inc.) with a spring constant of 0.05 N/m were used for
contact mode imaging.
[0145] Additional Examples of 2D Parallel DPN: Shown below are
three additional examples that demonstrate the rapid prototyping
capability of 2D parallel DPN reported herein. FIG. 6 shows Au dot
arrays spanning nearly the entire writing range of each cantilever.
FIG. 7 shows Au structures developed from molecular ODT patterns in
the form of the characters "2D DPN." Each pen generated five
structures occupying an area of 9.times.7 microns with a total
patterning time of 9 min. FIG. 8 shows Au structures in the shape
of nine triangle, four lines, 5.times.5 dots, and a "smiley face"
occupying four quadrants of the patterning area of each pen. The
total patterning time in this case was about five minutes. Note
that these structures are just two examples and virtually any
pattern geometry can be generated.
[0146] Apex height was measured for a pyramidal tip as shown in
FIG. 9.
[0147] FIG. 10 shows how distance of bending and angle of bending
was measured when the cantilevers are bent at an angle from their
base and the cantilevers are bent at an average distance.
[0148] All references cited herein are hereby incorporated by
reference in their entirety.
* * * * *