U.S. patent application number 16/452186 was filed with the patent office on 2019-12-26 for interfacial convective assembly for high aspect ratio structures without surface treatment.
The applicant listed for this patent is Northeastern University. Invention is credited to Ahmed BUSNAINA, Nam-Goo CHA, Yolanda EHEGOYEN, Taehoon KIM.
Application Number | 20190389720 16/452186 |
Document ID | / |
Family ID | 45098387 |
Filed Date | 2019-12-26 |
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United States Patent
Application |
20190389720 |
Kind Code |
A1 |
CHA; Nam-Goo ; et
al. |
December 26, 2019 |
Interfacial Convective Assembly for High Aspect Ratio Structures
Without Surface Treatment
Abstract
A method for assembling colloidal particles onto a substrate
surface through fluid transport. The method comprises placing a
first fluid placed adjacent to the substrate surface, applying a
colloidal dispersion on top of the first fluid layer and removal of
the first fluid layer. The method is extremely versatile, and is
especially useful in depositing colloidal materials in high aspect
ratio channels and vias without the need for prior treatment of the
surface.
Inventors: |
CHA; Nam-Goo; (Ansan City,
KR) ; EHEGOYEN; Yolanda; (Somerville, MA) ;
BUSNAINA; Ahmed; (Needham, MA) ; KIM; Taehoon;
(Revere, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Northeastern University |
Boston |
MA |
US |
|
|
Family ID: |
45098387 |
Appl. No.: |
16/452186 |
Filed: |
June 25, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13702133 |
Jul 15, 2013 |
10329139 |
|
|
PCT/US11/39388 |
Jun 7, 2011 |
|
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16452186 |
|
|
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|
61352523 |
Jun 8, 2010 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 26/00 20130101;
B22F 2998/00 20130101; B05D 1/00 20130101; Y10T 428/24562 20150115;
B81C 1/0038 20130101; B81C 1/00373 20130101; B05D 1/36 20130101;
Y10T 428/24355 20150115; B32B 3/18 20130101; B05D 7/22 20130101;
B22F 2998/00 20130101; B05D 2401/32 20130101; B22F 1/0022 20130101;
B81B 1/002 20130101 |
International
Class: |
B81B 1/00 20060101
B81B001/00; B05D 7/22 20060101 B05D007/22; B81C 1/00 20060101
B81C001/00; C23C 26/00 20060101 C23C026/00; B05D 1/36 20060101
B05D001/36; B32B 3/18 20060101 B32B003/18; B05D 1/00 20060101
B05D001/00 |
Goverment Interests
GOVERNMENT RIGHTS
[0002] The invention was developed with government support from
Grant Nos. 0425826 and 0832785 from the National Science
Foundation. The government has certain rights in the invention.
Claims
1. A device comprising: a substrate having a surface which has not
been plasma etched, and a plurality of colloidal particles
deposited on said surface.
2. The device of claim 1, wherein the device is configured as a
chemical, biochemical, electrical, electromagnetic field or
frequency sensor, an information storage medium, an energy storage
unit, an energy conversion cell, a display device, or an optical
device.
3. The device of claim 1, wherein the substrate is hydrophobic.
4. The device of claim 1, wherein the substrate is hydrophilic.
5. The device of claim 1, wherein the substrate comprises a
material selected from the group consisting of glass, organic
polymer, inorganic polymer, ceramic, metal, metalloid, and layered
combinations or mixtures thereof.
6. The device of claim 1, wherein the surface is non-metallic and
at least partly metallized.
7. The device of claim 6, wherein the metallization is
lithographically patterned.
8. The device of claim 5, wherein the substrate comprises glass and
the glass comprises a silicate, borate, phosphate, or a combination
or mixture thereof.
9. The device of claim 5, wherein the substrate comprises an
organic polymer and the organic polymer comprises a thermoplastic
or thermoset resin or copolymer or mixture thereof.
10. The device of claim 5, wherein the substrate comprises an
organic polymer and the organic polymer comprises a partially or
perfluorinated polymer, polycarbonate, polyester, polyalkylene,
polyacrylate or polymethacrylate, polystyrene, polyacrylonitrile,
or a copolymer or mixture thereof.
11. The device of claim 5 wherein the substrate comprises an
organic polymer and the organic polymer is electrically conductive
or semi-conductive.
12. The device of claim 11, wherein the organic polymer comprises
poly(para-phenylene vinylene), polythiophene, poly(paraphenylene),
polyquinoline, polypyrrole, polyacetylene, polyfluorene, or a
copolymer or mixture thereof.
13. The device of claim 5, wherein the substrate comprises an
inorganic polymer and the inorganic polymer comprises polysiloxane,
silicate, aluminosilicate, or a combination or mixture thereof.
14. The device of claim 5, wherein the substrate comprises a
ceramic and the ceramic comprises a metal or metalloid oxide,
nitride, carbide, or a combination or mixture thereof.
15. The device of claim 14, wherein the ceramic comprises aluminum
oxide, aluminum nitride, aluminum carbide, titanium oxide, titanium
nitride, titanium carbide, silicon oxide, silicon carbide, silicon
nitride, boron carbide, boron nitride, antimony oxide, iron oxide,
magnesium oxide, nickel oxide, tin oxide, zinc oxide, zirconium
oxide, or a combination or mixture thereof.
16. The device of claim 5, wherein the substrate comprises a metal
and the metal comprises aluminum, gold, silver, platinum, cadmium,
copper, nickel, titanium, or iron, or a combination or mixture
thereof.
17. The device of claim 5, wherein the substrate comprises a
metalloid and the metalloid comprises doped or undoped Si, CdS,
CdSe, Ge, GaAs, GaAlAs, ZnS, InP, Ge, or a combination or mixture
thereof, and wherein the substrate is conducting, semiconducting,
or insulating.
18. The device of claim 5, wherein the substrate comprises silica,
polyethylene, or polycarbonate.
19. The device of claim 1, wherein the substrate comprises
patterned micro- or nano-dimensioned features.
20. The device of claim 19, wherein the patterned features have
aspect ratios of 10 or more.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S.
application Ser. No. 13/702,133, filed on Jul. 15, 2013, which is a
U.S. National Phase of PCT/US2011/039388, filed on Jun. 7, 2011,
which claims priority to U.S. Patent Application No. 61/352,523
filed on Jun. 8, 2010, the disclosures of which are hereby
incorporated by reference herein.
TECHNICAL FIELD
[0003] The present invention relates generally to methods of
self-assembly, particularly to self-assembly of component articles,
including those spanning the nanometer to micron range, and more
particularly into micro- and/or nanodimensioned vias and channels
of composite articles.
BACKGROUND
[0004] Controlling the deposition of nano-dimensioned solids at the
nanometer scale has the potential to revolutionize technology
through development of materials and devices with control of
mechanical, optical, electronic and structural properties.
Moreover, recent research has led to a host of new fundamental
scientific insights, including controlled nanoscale synthesis and
processing of both organic (soft) and inorganic (hard) material and
the development of nano-scale precursors for these macroscopic
materials and devices. A challenge, therefore, is to develop an
approach that can combine a variety of organic and inorganic
building blocks, provide down to nanometer-scale structural control
and simultaneously lead to macroscopic devices or materials in a
practical and cost-effective way. Moreover, the approach must be
flexible so that it can be readily extended to a variety of
materials or properties without substantial revision of the entire
process. These are demanding goals that require novel approaches
and development of basic science.
[0005] Conventional metal deposition methods such as sputtering or
evaporation have poor selectivity, required elevated temperature
and need special vacuum systems. Methods such as dip-coating using
colloidal suspensions take long time and are difficult to apply on
thin and bendable substrates. Photolithography provides a means of
generating structure, generally planar in nature, with a spatial
resolution on the nanometer to micron size scale, but this
technique is limited to a small set of materials.
[0006] Chemical synthesis, for example synthesizing carbon and
other nanotubes, can provide molecular resolution, but is limited
in its ability to independently control mechanical, structural,
electronic and optical properties of a material.
[0007] One technique of recent interest involves the selective
deposition of nano- or micro-dimensioned particles by
self-assembly. Self-assembly is a term used to define the
spontaneous association of entities into structural aggregates. In
particular, molecular self-assembly provides the basis for a
successful strategy for generating large, structured molecular
aggregates, by the spontaneous association of molecules. See, for
example, Whitesides, et al., in "Noncovalent Synthesis: Using
Physical-organic Chemistry to Make Aggregates", Accts. Chem. Res.,
28, 37-44 (1995); Whitesides, G. M., "Self-Assembling Materials",
Scientific American, 273, 146-149 (1995); Philip, et al., Angew.
Chem., Int. Ed. Engl., 35, 1155-1196 (1996).
[0008] Self-assembly of molecules can be made to occur
spontaneously at liquid/gas, liquid/liquid, or solid/liquid
interfaces to form self-assembled monolayers of the molecules when
the molecules have a shape that facilitates ordered stacking in the
plane of the interface and each includes a chemical functionality
that adheres to the surface or in another way promotes arrangement
of the molecules with the functionality positioned adjacent the
surface. U.S. Pat. No. 5,512,131, and U.S. patent application Ser.
Nos. 08/695,537, 08/616,929, 08/676,951, and 08/677,309, and
International Patent Publication No. WO 96/29629, all
commonly-ownled, describe a variety of techniques for arranging
patterns of self-assembled monolayers at surfaces for a variety of
purposes.
[0009] Much of the literature in this area describes the
self-assembly of forming extended colloidal structures, but several
techniques are described for forming such nano- and microscale
patterning, including tethering colloidal gold nanoparticles to
surfaces with thiol groups (Mirkin, et al., A DNA-Based Method for
Rationally Assembling Nanoparticles Into Macroscopic Materials,
Nature, 382, (Aug. 15, 1996)).
[0010] The concept of using capillary action to deposit colloid or
nano-materials has been described as useful in providing patterned
self-assembled arrays. Yamaki, et al., in "Size Dependent
Separation of Colloidal Particles in Two-Dimensional Convective
Self-Assembly" Langmuir, 11, 2975-2978 (1995), relies on lateral
capillary force and convective flow to provide "convective
self-assembly" of colloidal particles ranging in size from 12 nm to
144 nm in diameter in a wetting liquid film on a mercury surface.
Cralchevski, et al., in "Capillary Forces Between Colloidal
Particles" Langmuir, 10, 23-36 (1994), describe capillary
interactions occurring between particles protruding from a liquid
film due to the capillary rise of liquid along the surface of each
particle.
[0011] Shi-Kai Wu, et al., "Self Assembly of Polystyrene
Microspheres Within Spatially Confined Rectangular Microgrooves," J
Mall. Sci., 43 (19), 6453-6458 (2008) describes the use of
capillary action to self-assemble 262 to 1000 nm polystyrene
spheres onto patterned silicon wafers with one-dimensional
microgrooves of different widths (0.76-6 microns). Processing
variables including evaporation temperature, particle size, groove
width, and groove height were examined to explain the results.
[0012] 0-0k Park, el al., "Method for Manufacturing Colloidal
Crystals Via Confined Convective Assembly," U.S. Pat. No.
7,520,933, issued Apr. 21, 2009, discloses methods of manufacturing
colloidal crystals using a confined convective assembly, comprising
infusing colloidal suspension between two substrates and
self-assembling the particles by capillary action. Substrates may
include glass, inorganic and organic polymers; particles may
include high molecular weight polymers, inorganic polymers, metals,
and metal oxides. Solvents useful for the convective transfer
include water and alcohol.
[0013] Peng Jiang, et al., "Polymers Having Ordered Monodisperse
Pores and Their Corresponding Ordered, Monodisperse Colloids," U.S.
Pat. No. 6,929,764 (issued Aug. 16, 2005) describes the deposition
of nano-silica "according to an appropriate technique, such as . .
. convective self-assembly method."
[0014] U.S. Pat. No. 5,45,291 (Smith) describes assembly of solid
microstructures in an ordered manner onto a substrate through fluid
transfer. The microstructures are shaped blocks that, when
transferred in a fluid slurry poured onto the top surface of a
substrate having recessed regions that match the shapes of the
blocks, insert into the recessed regions via gravity. U.S. Pat. No.
5,355,577 (Cohn) describes a method of assembling discrete
microelectronic or micro-mechanical devices by positioning the
devices on a template, vibrating the template and causing the
devices to move into apertures. The shape of each aperture
determines the number, orientation, and type of device that it
traps.
[0015] Self-assembly on patterned surfaces is particularly useful
as a way of making nano- and microscale devices, for example
electronic and electrochemical systems, sensors, photonic devices,
biosensors and devices, information storage medium, display devices
and optical devices, and medical (e.g., drug release) devices.
[0016] However, when attempting to apply convective self-assembly,
several problems become evident. These particular problems include
difficulties in depositing colloidal particles into high aspect
ratio trenches or wells.
[0017] The main problem in hydrophobic structures with high aspect
ratio is that water cannot penetrate and touch the bottom surface,
so it is impossible to use liquid assembly techniques as
dip-coating or convective assembly. Conventional plastic substrates
show water contact angles around 100.degree. and they are usually
reduced applying 0.sub.2 plasma or UV radiation to make the surface
hydrophilic (contact angle below 20.degree.). This problem is
exacerbated in high aspect ratio nanostructures showed
super-hydrophobicity (130.degree.) before applying 0.sub.2 plasma
and a high contact angle (90.degree.) after the plasma was applied.
Also, 0.sub.2 plasma is known to destroy or erode plastic
patterns.
[0018] Another problem is that plastic substrates are usually thin
and easy to bend and it is difficult to make conformal assembly at
large areas.
[0019] Still another problem is that the time necessary for
particles to move from, typically, aqueous dispersions into high
aspect ratio features (e.g., vias and trenches) tends to be long.
All of these problems become increasingly acute as the dimensions
of the vias and trenches shrink, and are especially problematic for
nano-dimensioned features.
[0020] What is needed is a versatile technique for facilitating
convective self-assembly that accommodates a wide range of nano- or
microparticles, works quickly over large areas, when the particles
(or other nano- or micro-building blocks) have to be assembled into
deep trenches or vias, whether the surface is hydrophobic or
hydrophilic, without surface treatment.
SUMMARY
[0021] The present invention is directed to a method of
facilitating convective self-assembly that accommodates a wide
range of colloidal particles, works quickly over large areas, when
the colloidal particles (or other nano- or micro-dimensioned
building blocks) have to be assembled into deep channels, holes,
wells, or vias, whether the surface is hydrophobic or hydrophilic,
without the need for high vacuum or surface treatment. As such, the
various embodiments described herein provide a flexible and cost
effective approach to achieving its intended purpose.
[0022] One embodiment of this invention is a method for depositing
colloidal particles onto a substrate surface comprising: (a)
providing a substrate having a surface; (b) depositing a first
layer of a first fluid onto the surface of the substrate; and (c)
depositing a second layer of an aqueous dispersion of colloidal
particles on top of the first layer of the first fluid; and (e)
removing the first layer of the first fluid. This process results
in the colloidal particles forming a layer on the surface of the
substrate, either over the entire substrate or over portions of the
substrate. Additional and separate additive embodiments include
this first embodiment plus either (d) optionally covering the
second layer with a cover so as to forming an assembly comprising a
sandwich of the first and second layers between the substrate and
the cover or (f) removing the water from the second layer of the
aqueous dispersion, leaving a layer of particles on the surface of
the substrate, or both (d) and (t).
[0023] The method is flexible in that is allows that the surface of
the substrate can be either hydrophobic or hydrophilic, or may
comprise sections which are both hydrophobic and hydrophilic.
Further, the substrate may be flat or curved, may be flexible or
rigid, or comprise a shape memory material. The substrate may
comprise a bulk material or at least a partial surface coating
comprising one or more glass, organic polymer, inorganic polymer,
ceramic, metal, or metalloid, or an area or layered combination or
mixture thereof.
[0024] The invention teaches that the substrate may contain
patterned features which either protrude or contain recesses or
indentations (e.g., channels, trenches, and/or holes, wells, or
vias).
[0025] Certain embodiments provide that the substrate comprises
insulative, conductive, or semi-conductive materials. Within these
categories, the substrate may comprise one or more glass, inorganic
or organic polymers, crystalline or polycrystalline ceramic, metal,
or metalloid. The substrate surface comprises patterned micro-
and/or nano-dimensioned features. Such micro- and/or
nano-dimensioned features include channels or trenches or holes,
wells, or vias which may be formed into the substrate or by
protruding surfaces. These surfaces may or may not be used in
combination with some form of chemical or physical etching.
[0026] In other separate embodiments, the first layer of a first
fluid and the second layer of the aqueous dispersion may be applied
by spin-, dip-, brush-, or spray-coating, or by the application of
a droplet using methods known to those skilled in the art.
[0027] In combination with any of the preceding or succeeding
embodiments, various embodiments of the method provides that the
first fluid wets the substrate. Such embodiments can be
accomplished with fluids comprising one or more of various organic
liquids, for example alcohols, aromatics, amines, esters,
hydrocarbons, or ketones, or mixtures thereof. Isopropanol is a
particularly well suited organic fluid to be used in this
invention.
[0028] The physical properties of boiling point (or more generally,
the vapor pressure at the then ambient temperature), the viscosity,
specific gravity, and the surface tension of the first fluid all
impact the efficiency of the method. In certain embodiments, this
first fluid may be immiscible, partially miscible, or completely
miscible with water and/or the aqueous dispersions of the colloidal
particles.
[0029] The aqueous layer comprises water and colloidal particles,
and may include other materials including surfactants, colorants,
fluorescents, markers, preservatives, and/or soluble dopants
depending on the final application. Virtually any potentially
available secondary material can be used, provided they do not
substantively interfere with the ability of the layer to deliver
and deposit the colloidal particles to the surface of the
substrate.
[0030] The first layer may be removed using several techniques,
including by the application of heat or vacuum or both. In such
cases, the first layer may be removed by some contribution of
evaporation or commingling with, and incorporating into, the
aqueous phase, or both. Once the first fluid is removed, and the
colloidal particles are deposited, the invention describes that the
liquid portion of the aqueous dispersion is removed by the
application of heat or vacuum or both. Generally, the application
of heat is referring to temperatures of about 80.degree. C. or
less, about 60.degree. C. or less, about 40.degree. C. or less, or
so-call room ambient temperatures (e.g., ca. 2025.degree. C.). The
skilled artisan will appreciate that higher temperatures will cause
faster evaporation, though the speed of evaporation is balanced
against the homogeneity and/or selectivity he or she wishes to
attain.
[0031] It should be appreciated that articles produced by these
methods are also within the scope of this invention. Such articles
include, for example, chemical, biochemical, electrical,
electromagnetic field or frequency sensors, information storage
media, energy storage units, energy conversion cells, display
devices, or video or optical devices. More complicated systems are
also contemplated herein, including chemical, biochemical,
electrical, or electromagnetic field or frequency sensing systems,
information transfer or communication systems, energy storage or
conversion systems, or video or optical communication systems
comprising a device made by these methods.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 illustrates a substrate containing patterned
features; when made of polyethylene, it also represents a
super-hydrophobic structure.
[0033] FIG. 2 is a schematic illustration of one embodiment of the
inventive procedure.
[0034] FIG. 3 is a numerical simulation of convective flow between
two different layers at room temperature.
[0035] FIG. 4 provides fluorescent microscope images of selective
assembly using 22 nm PSL particles. In this case, the substrate is
polyethylene, which is highly hydrophobic, exhibiting a contact
angle of 110-130.degree.. FIG. 4A shows the substrate before
assembly. FIG. 4B shows that large area after assembly. FIG. 4C
shows a bended area after assembly. FIG. 4D shows the assembly at
high magnification.
[0036] FIG. 5 shows 5 nm gold particles assembled in 300 nm
trenches (FIG. 5(A)) and 50 nm gold particles assembled in 300 nm
vias (FIG. 5(B)).
[0037] FIG. 6 provides SEM images of selective assembly using 5 and
50 nm gold particles in 200 and 300 nm vias and trenches. In this
case, the substrate is PMMA, which is hydrophobic, exhibiting a
contact angle of approximately 70.
[0038] FIG. 7 provides images of selective assembly using 50 nm PSL
particles. In this case, the substrate is SiO.sub.2, which is
hydrophilic, exhibiting a contact angle of less than 20. FIG. 7(A)
is a fluorescent microscope image, and FIG. 7(B) is an SEM
image
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0039] The present invention is directed to a method of
facilitating convective self-assembly that accommodates a wide
range of colloidal particles, works quickly over large areas, when
the colloidal particles (or other nano- or micro-dimensioned
building blocks) have to be assembled into deep channels, holes,
wells, or vias, whether the surface is hydrophobic or hydrophilic,
without the need for high vacuum or surface treatment. As such, the
various embodiments described herein provide a flexible and cost
effective approach to achieving its intended purpose.
[0040] The present invention may be understood more readily by
reference to the following detailed description taken in connection
with the accompanying Figures and Examples, which form a part of
this disclosure. It is to be understood that this invention is not
limited to the specific products, methods, conditions or parameters
described and/or shown herein, and that the terminology used herein
is for the purpose of describing particular embodiments by way of
example only and is not intended to be limiting of any claimed
invention. Similarly, any description as to a possible mechanism or
mode of action or reason for improvement is meant to be
illustrative only, and the invention herein is not to be
constrained by the correctness or incorrectness of any such
suggested mechanism or mode of action or reason for improvement.
Throughout this text, it is recognized that the descriptions refer
both to the method of preparing such devices and to the resulting,
corresponding physical devices themselves, as well as the
referenced and readily apparent applications for such devices.
[0041] In the present disclosure the singular forms "a," "an," and
"the" include the plural reference, and reference to a particular
numerical value includes at least that particular value, unless the
context clearly indicates otherwise. Thus, for example, a reference
to "a material" is a reference to at least one of such materials
and equivalents thereof known to those skilled in the art, and so
forth.
[0042] When values are expressed as approximations, by use of the
antecedent "about," it will be understood that the particular value
forms another embodiment. In general, use of the term "about"
indicates approximations that can vary depending on the desired
properties sought to be obtained by the disclosed subject matter
and is to be interpreted in the specific context in which it is
used, based on its function, and the person skilled in the art will
be able to interpret it as such. In some cases, the number of
significant figures used for a particular value may be one
non-limiting method of determining the extent of the word "about."
In other cases, the gradations used in a series of values may be
used to determine the intended range available to the term "about"
for each value. Where present, all ranges are inclusive and
combinable.
[0043] It is to be appreciated that certain features of the
invention which are, for clarity, described herein in the context
of separate embodiments, may also be provided in combination in a
single embodiment. Conversely, various features of the invention
that are, for brevity, described in the context of a single
embodiment, may also be provided separately or in any
subcombination. Further, reference to values stated in ranges
include each and every value within that range.
[0044] Generally terms are to be given their plain and ordinary
meaning such as understood by those skilled in the art, in the
context in which they arise. To avoid any ambiguity, however,
several terms are described herein.
[0045] One embodiment of this invention is a method for depositing
colloidal particles onto a substrate surface comprising: (a)
providing a substrate having a surface; (b) depositing a first
layer of a first fluid onto the surface of the substrate; and (c)
depositing a second layer of an aqueous dispersion of colloidal
particles on top of the first layer of the first fluid; and (e)
removing the first layer of the first fluid. This process results
in the colloidal particles forming a layer on the surface of the
substrate, either over the entire substrate or over portions of the
substrate. Additional and separate additive embodiments include
this first embodiment plus either (d) optionally covering the
second layer with a cover so as to forming an assembly comprising a
sandwich of the first and second layers between the substrate and
the cover or (f) removing the water from the second layer of the
aqueous dispersion, leaving a layer of particles on the surface of
the substrate, or both (d) and (t).
[0046] These steps are shown schematically in FIGS. 1 and 2. FIG. 1
shows a substrate containing patterned channels. A cross-sectional
view of a similar configuration is shown in FIG. 2A, showing a
pattern having high aspect ratio channels 20 having been applied to
a glass substrate 21. In FIG. 2B, a layer of the first fluid 22 is
applied to the pattern. In FIG. 2C, a layer of aqueous colloidal
material 23 is applied on top of this first layer, and in FIG. 2D
an optional cover plate 24 is placed on top of the aqueous
colloidal layer 23, to provide conformal water film thickness. In
the particular embodiment shown in FIG. 2E, heat is applied to
accelerate the mass exchanges between the two layers using
interfacial convection, and in FIG. 2F, both fluid layers have been
removed, leaving behind deposited colloidal particles 25.
[0047] FIG. 3 shows a numerical simulation of convective flow
between the first layer of first fluid and the water of the aqueous
colloidal layer.
[0048] FIG. 4 shows fluorescent microscope images of selective self
assembly using 22 nm polystyrene latex (PSL) particles. Of
particular interest, FIG. 4D shows the selectivity of the
deposition relative to the entire surface.
[0049] It should also be appreciated that any of the embodiments
described herein may be employed more than once to the same
substrate, either in different or over the same areas of the
substrate, such that the substrate may ultimately comprise multiple
layers of colloidal particles, such that these particle layers may
or may not overlap one or more preceding layer, and the individual
layers may comprise the same or different materials.
[0050] As used herein, the term "nano-" as in "nano-dimensioned,"
"nano-scale," or "nano-structured" refers to a dimension, scale, or
structure having at least one dimension in the range of 0.5 to
about 1000 nm, preferably in the range of about 1 to about 500 nm,
more preferably in the range of about 5 to about 350 nm, more
preferably in the range of about 5 to about 250 nm, still more
preferably in the range of about 10 to about 100 nm; i.e., having a
dimension in the range independently bounded at the lower end by
about 0.5, 1, 5, 10, 15, 20, 25, 50, 75, 100, 250, or 500 nm and at
the upper end by about 1000, 750, 500, 350, 250, 150, 100, 50, 25,
and 10 nm. Non-limiting exemplary ranges, for example, include
those in the range of about 5 to about 50 nm, about 50 to about 100
nm, about 100 to about 350 nm, about 75 to about 500 nm, or about
500 to about 1000 nm. When the terms "nano-channel" or
"nano-trench" is used herein, these nano-dimensions refer at least
to the width of said "nano-channel" or "nano-trench."
[0051] As used herein, the term "micro-" as in "micro-dimensioned,"
"micro-scale," or "micro-structured" refers to a dimension, scale,
or structure having at least one dimension in the range of about
0.5 to about 1000 micron, preferably in the range of about 1 to
about 500 micron, more preferably in the range of about 5 to about
350 micron, more preferably in the range of about 5 to about 250
micron, still more preferably in the range of about 10 to about 100
micron; i.e., having a dimension in the range independently bounded
at the lower end by about 0.5, 1, 5, 10, 15, 20, 25, 50, 75, 100,
250, or 500 micron and at the upper end by about 1000, 750, 500,
350, 250, 150, 100, 50, 25, and 10 micron. Non-limiting exemplary
ranges, for example, include those in the range of about 1 to about
5 micron, about 5 to about 50 micron, about 50 to about 100 micron,
about 100 to about 350 micron, about 75 to about 500 micron, or
about 500 to about 1000 microns. When the terms "micro-channel" or
"micro-trench" is used herein, these micro-dimensions refer at
least to the width of said "micro-channel" or "micro-trench."
[0052] As used herein, the term "colloidal" refers to separate
embodiments independently comprising either micro- or
nano-dimensioned particles or both micro- and nano-dimensioned
particles.
[0053] The method is flexible in that is allows that the surface of
the substrate can be either hydrophobic or hydrophilic, or may
comprise sections which are both hydrophobic and hydrophilic. The
method is especially discriminating on hydrophobic substrates,
especially those containing hydrophobic channels, trenches, holes,
wells, or vias. That is, when hydrophilic substrates are subjected
to the methods described herein, colloidal materials tend to
distribute over much of the entire surface, including within the
channels, trenches, holes, wells, or vias, whereas when hydrophobic
substrates are subjected to the methods described herein, colloidal
materials tend more to aggregate more within the channels,
trenches, holes, wells, or vias, and less over the larger
hydrophobic surfaces.
[0054] Further, the substrate may be flat or curved, may be
flexible or rigid, or comprise a shape memory material. The
substrate may comprise a bulk material or at least a partial
surface coating comprising one or more glass, organic polymer,
inorganic polymer, ceramic, metal, or metalloid, or an area or
layered combination or mixture thereof. As used herein, the phrase
"combination or mixture thereof" is intended to reflect embodiments
comprising layered structures of the preceding materials, as well
as homogeneous or heterogeneous mixtures of the preceding materials
and combinations of layered homogeneous or heterogeneous materials.
That is, different areas of the substrate may comprise different
materials or mixtures of materials (e.g., where the substrate is a
composite of several materials) and/or may comprise layers of
different materials, such that one or more of the different
materials may be exposed to the environment.
[0055] The invention teaches that the substrate may contain
patterned features which either protrude or contain recesses or
indentations (e.g., channels, trenches, and/or holes, wells, or
vias). The terms "channels" and "trenches" carry the same meaning,
recognized by those skilled in the art, and may be used
interchangeably herein. Similarly, the terms "holes," "wells," and
"vias" are intended to reflect recessed or indented features whose
presented surface geometry is approximately that of a circle or
regular polygon. These patterned features may be lithographically
patterned and/or may be provided by other standard semiconductor
processing techniques, such as masking, sputtering, chemical vapor
deposition, sol-gel processing, plasma deposition or etching,
drilling, micromachining, or any combination of these techniques.
For example, in but one non-limiting example, the substrate may
comprise lithographically patterned sputtered metallic
conductors.
[0056] Certain embodiments provide that the substrate comprises
insulative, conductive, or semi-conductive materials.
[0057] The substrate and/or surface may include one or more glass
comprising a silicate, borate, or phosphate, or combination or
mixture thereof. Inorganic polymers or precursors similarly may
include polysiloxanes, including polydimethylsiloxanes, silicates
or aluminosilicates, or a combination or mixture thereof.
[0058] Other embodiments provide that the substrate and/or surface
comprises at least one organic polymer, which may include at least
one thermoplastic or thermoset resin or copolymer or mixture
thereof. Representative polymers which may be applied include those
comprising at least one partially or perfluorinated polymer, a
polycarbonate, a polyester, a polyalkylene, a polyacrylate or a
polymethacrylate, a polystyrene, or a polyacrylonitrile, or a
copolymer, combination, or mixture thereof. The organic polymers
can be electrically conductive or semiconductive. Non-limiting
examples of such materials include polymers comprising a
poly(para-phenylene vinylene), polythiophene, poly(paraphenylene),
polyquinoline, polypyrrole, polyacetylene, or polyfluorene, or a
copolymer or mixture thereof.
[0059] As described herein, the various polymers may comprise
materials which are natural, synthetic, biocompatible,
biodegradable, non-biodegradable, and/or biosorbable. Unless
specifically restricted to one or more of these categories, the
polymers may comprise materials from any one of these categories.
To be implantable, such as may be required for biosensors, for
example, such embodiments provide that the materials used are at
least biocompatible, and preferable approved by the United States
Food and Drug Administration in the United States (or a
corresponding regulatory agency in other countries).
[0060] The phrase "synthetic polymer" refers to polymers that are
not found in nature, even if the polymers are made from naturally
occurring biomaterials. Examples include, but are not limited to,
aliphatic polyesters, poly(amino acids), copoly(ether-esters),
polyalkylenes oxalates, polyamides, tyrosine derived
polycarbonates, poly(iminocarbonates), polyorthoesters,
polyoxaesters, polyamidoesters, polyoxaesters containing amine
groups, poly(anhydrides), polyphosphazenes, polysiloxanes, and
combinations thereof.
[0061] The phrase "biocompatible polymer" refers to any polymer
(synthetic or natural) which when in contact with cells, tissues or
body or physiological fluid of an organism does not induce adverse
effects such as immunological reactions and/or rejections and the
like. It will be appreciated that a biocompatible polymer can also
be a biodegradable polymer.
[0062] The phrase "biodegradable polymer" refers to a synthetic or
natural polymer which can be degraded (i.e., broken down) in the
physiological environment such as by enzymes, microbes, or
proteins. Biodegradability depends on the availability of
degradation substrates (i.e., biological materials or portion
thereof which are part of the polymer), the presence of
biodegrading materials (e.g., microorganisms, enzymes, proteins)
and the availability of oxygen (for aerobic organisms,
microorganisms or portions thereof), carbon dioxide (for anaerobic
organisms, microorganisms or portions thereof) and/or other
nutrients. Aliphatic polyesters, poly(amino acids), polyalkylene
oxalates, polyamides, polyamido esters, poly(anhydrides),
poly(beta-amino esters), polycarbonates, polyethers,
polyorthoesters, polyphosphazenes, and combinations thereof are
considered biodegradable. More specific examples of biodegradable
polymers include, but are not limited to, collagen (e.g., Collagen
I or IV), fibrin, hyaluronic acid, polylactic acid (PLA),
polyglycolic acid (PGA), polycaprolactone (PCL),
poly(Lactide-co-Glycolide) (PLGA), polydioxanone (PDO),
trimethylene carbonate (TMC), polyethyleneglycol (PEG), Collagen,
PEG-DMA, alginate or alginic acid, chitosan polymers, or copolymers
or mixtures thereof.
[0063] The phrase "non-biodegradable polymer" refers to a synthetic
or natural polymer which is not degraded (i.e., broken down) in the
physiological environment. Examples of non-biodegradable polymers
include, but are not limited to, carbon, nylon, silicon,
polyurethanes, polycarbonates, polyacrylonitriles, polyanilines,
polyvinyl carbazoles, polyvinyl chlorides, polyvinyl fluorides,
polyvinyl imidazoles, polyvinyl alcohols, polystyrenes and
poly(vinyl phenols), aliphatic polyesters, polyacrylates,
polymethacrylates, acyl-substituted cellulose acetates,
nonbiodegradable polyurethanes, polystyrenes, chlorosulphonated
polyolefins, polyethylene oxides, polytetrafluoroethylenes,
polydialkylsiloxanes, and shape-memory materials such as poly
(styrene-block-butadiene), copolymers or mixtures thereof.
[0064] Crystalline or polycrystalline ceramic composites may be
used as substrates and/or surface coatings where the ceramic
comprises a metal or metalloid oxide, nitride, or carbide, or a
combination or mixture thereof. Such ceramic compositions may
include binary, ternary, quaternary carbide, nitride, or oxide
compositions. Non-limiting examples include oxides of aluminum,
antimony, calcium, indium, iron, magnesium nickel, silicon, tin,
titanium, zinc, or zirconium; nitrides of aluminum, boron, carbon,
silicon, or titanium; and/or carbides of aluminum, boron silicon,
or titanium, or solid solutions or mixtures thereof.
[0065] In separate embodiments, the conductive materials may
comprise metals, including, but not limited to aluminum, gold,
silver, platinum, cadmium, copper, nickel, titanium, or iron, or a
combination or mixture thereof.
[0066] The substrate and/or surface may also comprise metalloid
comprising conducting, semi-conducting, or insulating, doped or
undoped Si, CdS, CdSe, Ge, GaAs, GaAlAs, ZnS, InP, or Ge, or a
combination or mixture thereof.
[0067] Silica, glass, polyethylene, or polycarbonate are preferred
substrates for these methods.
[0068] The methods of the invention further provides embodiments
wherein the substrate surface comprises patterned micro- and/or
nano-dimensioned features. Such micro- and/or nano-dimensioned
features include channels or trenches or holes, wells, or vias
which may be formed into the substrate or by protruding surfaces.
In one non-limiting example, a 10 nm channel may be formed by
lithographically etching it into the substrate surface or by
forming protruding structures separated by this distance. The
skilled artisan is familiar with the means to form such structures.
Preferred embodiments include those where the channel width or hole
diameter has dimensions on the order of about 5 nm to 1000 microns,
preferably about 10 nm to about 500 nm, more preferably about 50 to
about 300 nm, and still more preferably about 100 to about 300 nm,
but the full scope of these allowable dimensions is as defined
above for nano- and micro-dimensioned features.
[0069] The invention is particularly attractive when these channels
have aspect ratios of about 10 or more, where aspect ratio is
defined to be the ratio of height to width of the channel or the
ratio of height to the cross-sectional distance of the hole, well,
or via. However, the method is not limited to aspect ratios of this
dimension and also includes embodiments where the aspect ratio is
about 0.5 or more, about 1 or more, about 2 or more, about 5 or
more, about 50 or more, about 75 or more, or about 100 or more.
Similarly the ratio of the dimension of the colloidal particle to
the width of the channel is important, but the method provides
flexibility here as well. In order for the method to provide
deposition of the colloidal particle within the channel, the ratio
of the channel width to particle size obviously must be at least
one, preferably greater than about 2, more preferably greater than
about 5, more preferably greater than about 10, more preferably
greater than about 20, and still more preferably greater than about
50.
[0070] While many of the various embodiments do not include the use
of chemical or physical etching to improve the wetting of the
substrate surface, many other embodiments provide that such
chemical or physical etching be used. In these embodiments, etching
can be accomplished by plasma or wet chemical etching, or physical
abrasive techniques.
[0071] Moving beyond the embodiments related to the substrate, in
other separate embodiments, the first layer of a first fluid and
the second layer of the aqueous dispersion may be applied by spin-,
dip-, brush-, or spray-coating, or by the application of a droplet
using methods known to those skilled in the art.
[0072] In combination with any of the preceding or succeeding
embodiments, various embodiments of the method provides that the
first fluid wets the substrate. In the context of this
specification, "wetting" is intended to reflect that the contact
angle of the fluid with the substrate material is less than the
contact angle of water with the same substrate material. Such
embodiments can be accomplished with fluids comprising one or more
of various organic liquids, for example alcohols, aromatics,
amines, esters, hydrocarbons, or ketones. Preferred embodiments of
this invention tend to be alcohols, esters, and ketones, especially
where the normal boiling point is less than that of water. While
obviously, for a given class of organic materials, this boiling
point limit depends on a variety of parameters, including, for
example, degree of hydrogen bonding, specific geometry, and number
and position of double bonds, the skilled artisan would appreciate
that generally this refers to preferably C1_5 alcohols, ketones,
esters, more preferably C1-4 alcohols, C1_6 ketones and esters, and
still more preferably C1-3 alcohols, acetone, and ethyl acetate.
Isopropanol is a particularly well suited organic fluid to be used
in this invention.
[0073] The most preferred embodiments of the present invention tend
to be these types of chemicals, because of the physical
characteristics which they exhibit. Without intending to be bound
by any particular theory, it is believed that the use of organic
fluids as described herein works is that the first fluid wets the
narrow, high aspect ratio channels or features more efficiently
than does water. When subjected to heat or vacuum, the first fluid
is removed, either by evaporation from beneath or dissolution or
commingling in the water or both, depending on the miscibility of
the first fluid with water. Once the first fluid is removed, the
aqueous dispersion can more efficiently and quickly occupy the
space left by the removed first fluid within the narrow channels or
features, thereby accelerating the deposition of the dispersed
colloidal dimensioned materials. Under this model, the physical
properties of boiling point (or more generally, the vapor pressure
at the then ambient temperature), the viscosity, and the surface
tension of the first fluid all impact the efficiency of the method.
It is also determined that the density of the first fluid relative
to that of water is important, the method improving as the density
of the first fluid decreases, relative to that of water, such that
the density difference is increased. Certain embodiments, then,
provide that the specific gravity of the first fluid be in the
range of about 0.5 to about 1.1, in the range of about 0.6 to about
0.95, more preferably in the range of about 0.6 to about 0.85, more
preferably in the range of about 0.6 to about 0.75, and more
preferably in the range of about 0.6 to about 0.65, where specific
gravity is defined as the ratio of the density of the fluid,
typically at 25.degree. C. to that of water, when measured at
4.degree. C.
[0074] In certain embodiments, this first fluid may be immiscible,
partially miscible, or completely miscible with water and/or the
aqueous dispersions of the colloidal particles. The term
"immiscible" as used herein, refers to a fluid exhibiting a mutual
solubility with water at 25.degree. C. of less than about 5%.
"Partially miscible" is defined as exhibiting a mutual solubility
with water at 25.degree. C. in the range of about 5 to about 95%,
and "completely miscible" refers to liquids which exhibit mutual
solubility with water at 25.degree. C. of more than about 95%.
[0075] As applied to vapor pressure, a convenient (if not
surrogate) measure is the normal boiling point (i.e., the boiling
point at one atmosphere) is an important property of the first
fluid. In certain embodiments, the normal boiling point of the
first fluid is about 99.degree. C. or less, about 80.degree. C. or
less, more preferably about 60.degree. C. or less, more preferably
about 50.degree. C. or less, still more preferably about 40.degree.
C. or less.
[0076] As applied to viscosity, certain embodiments provide that
the viscosity of the first fluid be about 2 centipoise or less, at
25.degree. C., more preferably about 1 centipoise or less, still
more preferably about 0.5 centipoise or less, at 25.degree. C.
[0077] With respect to surface tension, certain embodiments provide
that the surface tension at 25.degree. C. be about 40 dyne/cm or
less, more preferably about 25 dyne/cm or less, and still more
preferably in the range of about 20 to about 25 dyne/cm.
[0078] The more preferable embodiments for the first fluid exhibit
the combination of properties characterized above as more or most
preferable embodiments of the respective property. For example, one
such category would include those fluids having specific gravities
of about 0.85 or less, surface tensions of about 25 dyne/cm or
less, and normal boiling points of about 85.degree. C. or less.
[0079] The attached Table provides characteristic values for these
parameters, for selected solvents. While not intended to be
limiting, the Table provides allows the skilled artisan to select a
first fluid with the balance of properties appropriate for his or
her conditions.
TABLE-US-00001 Surface Normal Temp. at Viscosity at Tension Boiling
which 400 25.degree. C. Specific (dyn/cm) Point, mm Hg (centipoise)
Gravity Acetone 23.3 56.3 39.5 0.316 0.792 Acetonitrilc 19.1 81.6
62.5 0.345 0.786 Benzene 28.9 80.1 61 0.652 (20.degree. C.) 0.879
tert-Butanol 23.6 82.5 68 2.54 0.779 n-Butyl Chloride 23.8 77.8 59
0.469 (15.degree. C.) 0.887 Carbon 27.0 76.7 58 0.969 (20.degree.
C.) 1.595 Chloroform 27.2 61.2 43 0.542 1.489 Cyclohexane 25.0 80.7
61 1.02 (17.degree. C.) 0.779 Cyclopentane 22.4 49.3 31 0.493
(14.degree. C.) 0.745 Dichloromethane 28.1 39.8 24 0.449
(15.degree. C.) 1.336 Diethyl Ether 17.1 34.6 18 0.222 0.708
Ethanol 22.3 78.3 64 1.200 (20.degree. C.) 0.789 Ethyl Acetate 23.7
77.1 59 0.441 0.901 Ethylene Dichloride 32.2 83.5 64 0.79
(20.degree. C.) 1.256 Heptane 20.3 98.4 78 0.386 0.684 Hexane 17.9
68.7 50 0.294 0.659 Methanol 22.6 64.7 50 0.547 0.792 Methyl Ethyl
24.0 79.6 * 0.426 (20.degree. C.) 0.805 Methyl t-Butyl 19.4 55.2 *
0.36 0.740 iso-Propyl Alcohol 21.8 82.3 68 1.96 0.789 n-Propyl
Alcohol 23.7 97.2 82 2.256 (20.degree. C.) 0.804 Pentane 15.5 36.1
19 0.24 0.630 Tetrahydrofuran 26.4 66 * 0.48 0.888 Triethylamine
20.7 89 * 0.363 0.729 Water 72.8 100 83 0.890 1.000 Values for
these properties taken from various sources including R. H. Perry
and C. H. Chilton, Chemical Engineers' Handbook, 5th Edition,
McGraw-Hill, 1973 and Handbook of Chemistry and Physics, CRC Press,
1982.
[0080] As with many of the other parameters, the invention is
flexible in its choice of colloidal particles, both size and
composition. While the terms "colloidal" has been used to describe
"micro-" and/or "nano-" dimensioned particles, with the terms
"micro-" and "nano-" having been described above, the colloidal
particles may also be characterized in terms of aspect ratio--i.e.,
the ratio of the longest to shortest dimension. While there is no a
priori limit to the aspect ratio for the present invention,
preferred embodiments, particularly for those cases where the
skilled artisan is depositing these colloidal particles in high
aspect ratio channels or holes, are those where the particle aspect
ratio is less than about 100, less than about 10, less than about
2, or spherical or near spherical.
[0081] These colloidal particles may comprise at least one
allotrope of carbon, a glass, organic polymer, bioactive material,
magnetic material, inorganic materials, ceramic, inorganic salt,
metal or metalloid, or a combination or mixture thereof. The types
of glasses, organic and inorganic polymers, ceramics, metals, and
metalloids may be the same materials as described above in the
context of the substrates. Additionally, inorganic salts may
include photonic or similar materials, for example including CdS or
AgCl. Allotropes of carbon, inorganic materials, metals, metalloids
include carbon or inorganic nanotubes, graphenes, fullerenes, or
functionalized/addivated version thereof, said nanotubes defined
herein to include single-walled nanotubes, multi-walled nanotubes.
In addition to the organic materials described above, the colloidal
particles may also comprise at least one biopolymer, said
biopolymer including peptides, nucleotides, or polynucleotides. The
term "bioactive material" refers to a material capable of eliciting
a pharmacological response in a patient.
[0082] The particles may comprise crystalline, non-crystalline
(amorphous), or a mixture of crystalline and non-crystalline
materials. Particles may be charged or uncharged.
[0083] The colloidal particles may include single materials or
multiple materials. In the latter case, the particles may comprise
composites wherein one component is intimately mixed with one or
more different materials, wherein one component is intimately mixed
with a different physical form of the same material (such as where
a microcrystalline form of a material is homogeneously or
heterogeneously contained within an amorphous form of the same
material), wherein multiple material or forms of materials are
arranged in layers, or combinations thereof. Included in such
arrangements are those embodiments wherein, for example, optionally
coated nanotubes contain fill materials, such as functionalized,
unfunctionalized, substituted, and/or unsubstituted fullerenes,
metallocenes, organic polymers, inorganic molecules, polymers, or
salts, metal or metalloid, metallic cluster, molecular cluster,
semiconducting cluster, semi-metallic cluster, or insulating
cluster.electron donor or acceptor to said nanotube, or a molecule
neutral to said nanotube or a mixture thereof.
[0084] Provided the dispersion remains fluid, there is no specific
limit to the loading of the colloidal particles within the aqueous
second layer. Preferably, the aqueous dispersion comprises
particles in the range of about 0.1 to about 25% by weight relative
to the weight of the entire aqueous dispersion, though various
separate embodiments of this invention also provide that
dispersions may include those containing in the range of about 0.1
to about 90 wt %, about 0.1 to about 50%, about 0.1 to about 25%,
about 0.1 to about 20%, about 0.1 to about 15%, about 0.1 to about
10%, about 0.1 to about 5% by weight, or in the range of about 1 to
about 90 wt %, about 1 to about 50%, about 1 to about 25%, about 1
to about 20%, about 1 to about 15%, about 1 to about 10%, about 1
to about 5% by weight, or in the range of about 5 to about 10%,
about 10 to about 20%, about 20 to about 30%, about 30 to about
40%, about 40 to about 50%, or about 50 to about 60% by weight
relative to the weight of the entire aqueous dispersion, again
provided the dispersion remains fluid. The skilled artisan is well
able to determine optimal loadings of the aqueous dispersion: at
higher loadings, the channels, trenches, holes, wells, or vias tend
to fill preferentially to the whole surface.
[0085] In still other embodiments, the aqueous dispersion further
comprises an internally dispersed phase of a partially immiscible
or immiscible liquid, these terms having been defined above,
wherein some portion of the colloidal particles is positioned
within the internally dispersed liquid phase. Separate embodiments
also provide that some portion of the colloidal particles are
positioned at the interface between the aqueous and the internally
dispersed liquid phase. As used herein, "some of is given its
common meaning, that being "less than all." More specific
embodiments describe the situation where the portion of the
colloidal particles positioned within or at the interface of the
between the aqueous and the internally dispersed liquid phase is
about 10%, about 20%, about 30%, about 40%, about 50%, about 60%,
about 70%, about 80%, about 90%, or more, by weight relative to the
weight of the entire aqueous dispersion.
[0086] The invention also teaches that other embodiments of the
method include those wherein the colloidal particles further
comprise a ligand or surfactant. These ligands or surfactants may
be chemically bonded, electrostatically attached, or physically
entangled with the colloidal particles.
[0087] The optional cover plate has several effects on the methods
described herein. In addition to promoting a uniformly thick
coating of the two fluid layers, the presence (or absence) of the
plate affects the homogeneity of the assembly on the surface and
the time taken to remove the fluids. That is, in the absence of a
cover plate, a "coffee ring" effect is noted with respect to the
deposition of the colloidal material, where with the plate, the
deposition is more uniform. Also, the presence of the cover plate
extends the time it takes for the fluids to be removed. So as to
give an indication of the gross effect, in non-limiting
side-by-side experiments, at room temperature, evaporation times
for uncovered substrates were on the order of 20-25 minutes,
whereas covered substrates took between 90 and 120 minutes to dry.
At 80'C, these times were less than one minute and 10-20 minutes,
respectively
[0088] The first layer may be removed using several techniques,
including by the application of heat or vacuum or both. In such
cases, the first layer may be removed by some contribution of
evaporation or commingling with, and incorporating into, the
aqueous phase, or both. Obviously, the contribution of each
potential mechanism depends on the physical properties of the first
fluid. The skilled artisan would appreciate, for example, that the
contribution by evaporation would be more likely for a volatile,
non-polar liquid than it would be for a relatively non-volatile,
water miscible fluid, and that the efficiency of such a mechanism
would be enhanced by the absence of edge sidewalls adjacent to the
first fluid layer.
[0089] Once the first fluid is removed, and the colloidal particles
are deposited, the invention describes that the liquid portion of
the aqueous dispersion is removed by the application of heat or
vacuum or both. Generally, the application of heat is referring to
temperatures of about 99.degree. C. or less, 80.degree. C. or less,
about 60.degree. C. or less, about 40.degree. C. or less, or
so-call room ambient temperatures (e.g., ca. 20-25.degree. C.). The
skilled artisan will appreciate that higher temperatures will cause
faster evaporation, though the speed of evaporation is balanced
against the homogeneity and/or selectivity he or she wishes to
attain.
[0090] As described above, additional embodiments include those
wherein the colloidal particles remaining after the removal of the
first and second layers of liquid form patterned deposits on the
substrate. These deposits can be positioned over wide areas, or
within constrained features, such as channels or holes. In some
embodiments, the patterned layer of particles on the substrate form
at least one electrical conductor or semiconductor device; e.g., a
micro-/nano-wires or diode. In other embodiments, the patterns may
comprise particles containing residual surfactants, ligands, or
biopolymers, making them particularly suitable for sensor
applications. In still other embodiments, the pattems may comprise
photosensitive or photoactive materials, making them suitable for
photonic applications. In still other applications, the patterns
may comprise magnetic materials, making them particularly suitable
for information storage or transfer applications.
[0091] To this point, the various embodiments of this invention
have described methods for depositing colloidal particles onto a
substrate surface. However, it should be appreciated that articles
produced by these methods are also within the scope of this
invention. Such articles include, for example, chemical,
biochemical, electrical, electromagnetic field or frequency
sensors, information storage media, energy storage units, energy
conversion cells, display devices, or video or optical devices.
More complicated systems are also contemplated herein, including
chemical, biochemical, electrical, or electromagnetic field or
frequency sensing systems, information transfer or communication
systems, energy storage or conversion systems, or video or optical
communication systems comprising a device made by these
methods.
[0092] As those skilled in the art will appreciate, numerous
modifications and variations of the present invention are possible
in light of these teachings, and all such are contemplated hereby.
For example, in addition to the embodiments described herein, the
present invention contemplates and claims those inventions
resulting from the combination of features of the invention cited
herein and those of the cited prior art references which complement
the features of the present invention. Further, to the extent that
the descriptions provided for the methods of improving the
interfacial self-assembly processes are not specifically reflected
in the descriptions for the articles produced by this methods, it
should be readily apparent that these are considered to be within
the scope of the latter, and vice versa. Similarly, it will be
appreciated that any described material, feature, or device may be
used in combination with any other material, feature, or device, so
as to provide a flexible toolkit of options.
[0093] The disclosures of each patent, patent application, and
publication cited or described in this document are hereby
incorporated herein by reference, in their entirety.
* * * * *