CN1802727A - Methods and apparatus for patterned deposition of nanostructure-containing materials by self-assembly and related articles - Google Patents

Abstract

Methods and apparatus for patterned deposition of nanostructure-containing materials by self-assembly and related articles are described. According to typical embodiments, the self-assembly method for depositing the nanostructure-containing material includes forming the nanostructure-containing material. The nanostructure-containing material is chemically functionalized and dispersed in a liquid medium to form a suspension. At least a portion of the substrate having a surface that attractably functionalizes the nanostructure-containing material is contacted with the suspension. Separate the substrate and suspension. When separated from the suspension, the nanostructure-containing material adheres to the substrate portion. According to another exemplary embodiment, hydrophilic and hydrophobic regions are formed on the surface of the substrate before contacting the substrate with the suspension. The functionalized nanostructure-containing material is hydrophilic and adheres to the hydrophilic regions of the substrate when separated from the suspension.

Description

METHODS AND APPARATUS AND RELATED ARTICLES FOR DEPOSITING NANOSTRUCTURED MATERIALS USING SELF-ASSEMBLY PATTERNED DEPOSITION STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

At least aspects of this invention were made with Government support under Contract Nos. N00014-98-1-05907 and NAG-1-01061. The government has certain rights in this invention.

background

In the background description below, reference is made to certain structures and methods, however, such references should not necessarily be construed as an admission that these structures and methods qualify as prior art under applicable statutory provisions. Applicants reserve the right to state that any of the subject matter referred to does not constitute prior art to the present invention.

The term "nanostructured" material is used by those familiar with the art to refer to materials comprising nanoparticles, nanowires/nanorods, or single- or multi-walled nanotubes, wherein the nanoparticles are _C60 fullerenes, fullerene-type Concentric graphite particles, metals, compound semiconductors such as CdSe, InP, nanowires/nanorods such as Si, Ge, SiO _x , GeO _x , single-wall or multi-wall nanotubes made of single or multiple elements such as carbon, B _x N _y , Composition of C _{x By} N _z , MoS ₂ and WS ₂ . A common feature of nanostructured materials is their basic building blocks. A single nanoparticle or carbon nanotube has a dimension of less than 500 nm in at least one direction. These types of materials have been shown to exhibit specific properties of increasing interest in a variety of applications and processes.

U.S. Patents 6,280,697 and 6,422,450 to Zhou et al. (both titled "Nanotube-Based High Energy Material and Method") disclose the manufacture of carbon-based nanotube materials and their use as battery electrode materials, the entire contents of which are incorporated herein by reference.

U.S. Patent No. ______ (serial number 09/296572, titled "DeviceComprising Carbon Nanotube Field Emitter Structure and Process for Forming Device") discloses the structure of a carbon nanotube-based electron emitter, and its full text is incorporated herein as a reference.

U.S. Patent No. ______ (serial number 09/351537, titled "DeviceComprising Thin Film Carbon Nanotube Electron Field Emitter Structure") discloses a carbon nanotube field emitter structure with high emission current density, and its full text is incorporated herein as a reference.

U.S. Patent 6,277,318 to Bower et al. (titled "Method for Fabrication of Patterned Carbon Nanotube Films") discloses a method for fabricating adhered patterned carbon nanotube films on a substrate, the entire contents of which are incorporated herein by reference.

U.S. Patent 6,334,939 (titled "Nanostructure-Based High Energy Material and Method") discloses nanostructured alloys with alkali metals as a component, the entire contents of which are incorporated herein by reference. This material is described as being useful in certain battery applications.

U.S. Patent No. ________ (Serial No. 09/679303, entitled "X-Ray Generating Mechanism Using Electron Field Emission Cathode") discloses an X-ray generating device incorporating nanostructured materials, the entire contents of which are incorporated herein by reference.

U.S. Published Patent Application No. US2002/0140336 (titled "Coated Electrode With Enhanced Electron Emission And Ignition Characteristics") discloses an electrode and related devices incorporating such an electrode, the electrode comprising a first electrode material, an adhesion promoter, and an adhesion promoter disposed on an adhesive surface. A carbon nanotube-containing material on at least a portion of the facilitation layer, the entire contents of which are incorporated herein by reference.

U.S. Patent No. ______ (Serial No. 09/881684, titled "Method of Making Nanotube-Based Material With Enhanced Field Emission") discloses the technology of introducing external substances into nanotube-based materials to improve their performance, and the full text of which is incorporated herein as refer to.

U.S. Patent No. ________ (Serial No. 10/051183, entitled "Large-Area Individually Addressable Multi-Beam X-Ray System and Method of Forming Same") discloses an x-ray generating structure with a large number of fixed individually addressable electrically seekable Field emission electron sources, such as carbon nanotubes, the full content of which is incorporated herein by reference.

U.S. Patent No. ______ (Serial No. 10/103803, entitled "Method for Assembling Nanoobjects") discloses techniques for self-assembling macrostructures from preformed nanoobjects, wherein the nanoobjects can be processed to have desired aspect ratios and chemical function, the full text of which is incorporated herein as a reference.

U.S. Patent No. ______ (attorney case number 032566-043) (titled "Methods for Assembly of Nanostructure-Containing Materials and Related Articles") describes various electrophoretic methods for assembling and attaching nanostructure-containing materials to various objects, This article incorporates its entire content by reference.

As demonstrated above, nanostructured materials, especially carbon nanotubes and other nanoobjects with large aspect ratios (i.e., lengths substantially greater than their diameters), possess promising properties that make them attractive for a variety of applications, including Examples are lighting elements, field emission devices such as flat panel displays, gas discharge tubes for overvoltage protection, x-ray generating devices, small wires, sensors, actuators and high resolution probes such as those used in scanning microscopes.

Efficient incorporation of nanostructured materials into devices has been hampered by difficulties encountered in materials processing. For example, nanostructured materials can be formed by techniques including laser ablation, arc discharge methods, solution synthesis, chemical etching, molecular beam epitaxy (MBE), chemical vapor deposition (CVD), and the like. Each of these techniques for assembling nanostructured materials poses their own challenges.

Post-formation methods including screen printing and spray coating have been utilized to deposit pre-formed nano-objects, such as carbon nanotubes, on substrates. These techniques also have drawbacks. For example, screen printing may require the use of a binder material as well as an activation step, which results in relatively low resolution deposition of the material. Spraying is inefficient and often not practical for large-scale manufacturing. In addition, screen printing and spray coating can result in random distribution of nanostructured materials on the substrate.

Carbon nanotubes have been grown directly on substrates using CVD techniques. See, eg, J. Hafner et al., Nature, Vol. 398, p. 761, 1999; US Patent 6,457,350; and US Patent 6,401,526. One potential application of the invention is the formation of wires made of nanostructured materials, such as circuits including carbon nanotubes. The carbon nanotubes can be formed by CVD process and then can be attached to specific positions of electrodes by CVD technology to form wires. These techniques require reaction environments at elevated temperatures (eg, about 600°C-1000°C) and use catalysts to efficiently grow nanotubes. The requirements for various harsh environmental conditions severely limit the types of substrate materials that can be used. In addition, CVD techniques often produce multi-walled carbon nanotubes. These multi-walled carbon nanotubes generally do not have the same level of structural perfection as single-walled nanotubes and thus may have poorer electro-emissive properties when compared to single-walled carbon nanotubes.

Other fabrication techniques involving nanostructured materials include precisely controlled deposition of individual or small populations of nanoobjects such as carbon nanotubes onto a substrate to form tips or protrusions. See eg Dai, Nature, Vol. 384, pp. 147-150 (1996); and R. Stevens et al., Appl. Phys. Lett, Vol. 77, pp. 3453, 2000. These technologies hold promise for large-scale production or batch processes.

Overview

Accordingly, methods and apparatus for patterned deposition of nanostructure-containing materials utilizing self-assembly and related articles are disclosed. According to an exemplary embodiment, a self-assembly method for depositing a nanostructure-containing material includes forming the nanostructure-containing material. The nanostructure-containing material is chemically functionalized and dispersed in a liquid medium to form a suspension. At least a portion of the surface-attractably functionalized nanostructured material-containing substrate is contacted with the suspension. Separate the substrate and suspension. When separated from the suspension, the nanostructure-containing material adheres to the substrate portion.

According to another exemplary embodiment, a material comprising carbon nanotubes is formed. Carbon nanotubes are chemically functionalized and dispersed in a liquid medium to form a suspension. Hydrophilic and hydrophobic regions are formed on the surface of the substrate that can attract the functionalized carbon nanotubes. At least a portion of the substrate is contacted with the suspension. Separate the substrate from the suspension. When separated from the suspension, the carbon nanotubes adhere to the hydrophilic regions of the substrate.

According to yet another exemplary embodiment, an apparatus for depositing a nanostructure-containing material on a substrate, including an apparatus for forming a nanostructure-containing material, is described. The apparatus includes means for chemically functionalizing nanostructure-containing materials. Additional equipment for dispersing the functionalized nanostructure-containing material in a liquid medium to form a suspension is included. The apparatus includes means for contacting at least a portion of a substrate having a surface attractably functionalized nanostructure-containing material with a suspension. The apparatus includes equipment for separating the substrate and the suspension.

Brief description of attached drawings

The accompanying drawings provide views used to more fully describe representative embodiments disclosed herein, and may be used by those skilled in the art to better understand them and their inherent advantages. In the figures, like reference numerals designate corresponding elements, and:

Figure 1 illustrates (A) TEM images of treated SWNTs with an average beam length of about 1-2 μm, and (B) Raman of treated SWNTs showing characteristic breath and tangent modes spectrum;

Figure 2 illustrates a low temperature fabrication process according to an exemplary embodiment;

Figure 3 illustrates optical microscope images of single-walled carbon nanotubes deposited on (A) glass and (B) aluminum surfaces according to exemplary embodiments;

Figure 4 illustrates a gradation of aligned carbon nanotubes deposited on a patterned substrate according to an exemplary embodiment;

Figure 5 illustrates the field emission characteristics of a film comprising carbon nanotubes deposited according to an exemplary embodiment;

6 illustrates a method of depositing a thin film containing nanostructured material, such as carbon nanotubes, onto a glass or indium-tin-oxide-coated (ITO-coated) glass substrate, according to a first exemplary embodiment;

7 illustrates a method of depositing a thin film containing nanostructured material such as carbon nanotubes onto a glass or ITO-coated glass substrate according to a second exemplary embodiment;

8 illustrates a method of depositing a film containing nanostructured material such as carbon nanotubes onto a glass or ITO-coated glass substrate according to a third exemplary embodiment; and

9 illustrates a method of depositing a thin film containing nanostructured material, such as carbon nanotubes, onto a glass or ITO-coated glass substrate, according to an exemplary embodiment;

A detailed description

Methods consistent with the principles of the invention and performed in accordance with preferred embodiments, as well as corresponding structures and devices, are described below.

In general, techniques for low-temperature fabrication of nanostructure-containing materials according to exemplary embodiments may include at least some or all of the following steps: (1) forming nanostructure-containing materials, such as materials including single-walled carbon nanotubes; (2) chemical functionalization the nanostructure-containing material; (3) dispersing the functionalized nanostructure-containing material in a liquid medium to form a suspension; (4) contacting at least a portion of the substrate having a surface attractive to the functionalized nanostructure-containing material with the suspension; (5 ) separating the substrate and the suspension; (6) forming hydrophilic and hydrophobic regions on the surface of the substrate prior to contacting the substrate with the suspension; (7) purifying the nanostructure-containing material; (8) annealing the nanostructure-containing material; and (9) removing the hydrophobic region from the substrate.

A typical fabrication method starts with a pre-formed raw nanostructure-containing material, preferably a high aspect ratio material or a nanotube-containing material such as a carbon nanotube-containing material. Such raw materials may include at least one of: single-walled carbon nanotubes, multi-walled carbon nanotubes, silicon, silicon oxide, germanium, germanium oxide, carbonitrides, boron, boron nitride, chalcogenides ( dichalcogenide), silver, gold, iron, titanium oxide, gallium oxide, indium phosphide, or magnetic particles such as Fe, Co, and Ni encapsulated in nanostructures. According to a preferred embodiment, the raw carbon nanotube-containing material comprises single-walled carbon nanotubes. Carbon nanotubes can be formed by means including apparatus for laser ablation, arc discharge apparatus and methods, solution synthesis means, chemical etching means, molecular beam epitaxy (MBE) means, chemical vapor deposition (CVD) means, and the like.

Raw nanostructure-containing materials can be in the form of nanotube structures of composition _BxCyNz (B= _boron , C=carbon and N=nitrogen), or can be used with composition _MS2 (M=tungsten, _molybdenum , or vanadium oxide) nanotube or concentric fullerene structure. Again, these raw materials may be formed by any suitable technique, such as the arc discharge technique described above.

Raw nanostructure-containing material can be purified after formation. There are a number of techniques for purifying raw materials. According to a preferred embodiment, the crude material may be purified using a reflux reaction in _a suitable solvent such as a combination of peroxide ( _H2O2 ) and water. The H ₂ O ₂ concentration can be 1-40% by volume, preferably about 20% by volume H ₂ O ₂ , followed by rinsing in CS ₂ , then in methanol, and then filtration. According to typical techniques, for every 1-10 mg of nanotubes in the medium, about 10-100 ml of H ₂ O ₂ is introduced into the medium, and the reflux reaction is carried out at a temperature of 20° C. to 100° C. (see, for example, U.S. Patent No. ______( Serial number 09/679303)).

According to another exemplary embodiment, raw nanostructure-containing material can be purified by suspending the material in a suitable liquid medium, such as an acidic medium, an organic solvent or an alcohol, preferably methanol. Raw material can be maintained in suspension in a liquid medium for several hours using a high powered ultrasonic horn while passing the suspension through a microporous membrane. In another embodiment, the crude material may be purified by oxidation in air or in an oxygen environment at a temperature of about 200°C to 700°C. Impurities in the raw material can be oxidized in this environment at a faster rate than nanotubes. In yet another exemplary embodiment, the raw material is purified by liquid chromatography to separate the nanotubes (or nanowires) and impurities in the material.

When the nanostructure-containing material includes nanotubes, further processing may be performed to reduce the length of the nanotubes and nanotube bundles prior to deposition on the substrate. For example, nanotubes can be shortened using chemical etching or grinding techniques.

The nanostructure-containing material of the raw material can be further processed to render the material hydrophilic. For example, a nanostructure-containing material can be chemically functionalized using a device such as a reaction tool configured to partially oxidize the nanostructure-containing material with an acid.

According to another exemplary embodiment, the purified raw nanostructure-containing material may be annealed at a suitable temperature, eg, a temperature of about 100°C to 1200°C. According to a preferred embodiment, the annealing temperature may range from about 100°C to 600°C. The material may be annealed for a suitable time, such as about 1-60 minutes. According to another embodiment, the material may be annealed for about 1 hour. The material can be annealed in a vacuum environment of about 10 ⁻² Torr, or can be annealed at even higher vacuum pressures. According to one embodiment, the vacuum pressure may be about 5×10 ⁻⁷ Torr.

Representative transmission electron microscopy (TEM) images of SWNT bundles processed according to each of the steps described above are shown in Figure 1A. As can be seen from the figure, the processing step involves chemically treating the material to render it hydrophilic without changing the basic structure of the nanotubes. Additionally, Figure 1B shows that the Raman effective breathing of the nanotubes and the oscillation frequency of the tangential mode remain unchanged after this treatment. Fourier Transform Infrared (FTIR) spectroscopy revealed a strong C=0 stretching mode at 1727 cm ⁻¹ , indicating that defects formed in the treated nanotube-containing material and dangling bonds were terminated by COOH groups.

The above-described preformed and functionalized nanostructure-containing material can now be dispersed in a liquid medium to form a suspension. Suspensions can be used to deposit materials onto objects or substrates, and/or to form articles such as wires and field emission cathodes, as described in more detail below.

For example, a suitable liquid medium is selected in which the raw nanostructure-containing material forms a stable suspension. According to a preferred embodiment, the liquid medium comprises water. When adding the raw material to the liquid medium, the mixture may optionally be subjected to ultrasonic energy or stirred using, for example, a magnetic stir bar to facilitate the formation of a stable suspension. The amount of time the ultrasonic energy is applied can vary, but stirring at room temperature for about 2 hours has been found to produce acceptable results. The concentration of raw material in the liquid medium can be varied so long as a stable suspension is maintained. For example, the concentration of carbon nanotubes included in the suspension may range from about 0.0001 to 1 gram of nanotubes per liter of water.

Once formed, the use of the suspension facilitates deposition of the nanostructure-containing material on a suitable substrate. Figure 2 illustrates a low temperature fabrication process for depositing a nanostructure-containing material on a substrate. Preferably, at least a portion of the substrate has hydrophilic properties. The substrate may comprise silicon, glass, indium-tin-oxide (ITO) coated glass, metals such as aluminum or chromium, metal coated glass, plastic or ceramics. In step (1), a hydrophilic substrate such as a glass substrate is patterned with a hydrophobic polymer such as a photoresist such as Shiplcy 1813. The photoresist can be patterned using photolithographic techniques and other methods known to those skilled in the art. According to one exemplary embodiment, a nanostructure-containing material such as single-walled carbon nanotubes is deposited on a hydrophilic region of the substrate (eg, an exposed glass surface) using a self-assembly process as shown in step (2a). Preferably the hydrophobic polymer coating is removed in step (3a), for example by washing the coated substrate in acetone.

In an alternative embodiment, the patterned substrate may be metallized in step (2b), for example by thermal evaporation of metals such as chromium and aluminum and a photoresist "lift-off" process. In step (3b), octadecyltrichlorosilane (OTS) molecules may be formed on the hydrophilic (hydroxyl-terminated) surface of the glass substrate, rendering this portion of the surface hydrophobic. The nanostructure-containing material can then be deposited onto the metallized portion of the substrate surface, as shown in step (4).

As shown in Figure 2, the substrate can be patterned to have hydrophobic and hydrophilic regions to define the portion of the substrate where the nanostructure-containing material will be deposited. These regions can vary in length and/or width depending on application requirements. For example, control line widths varying between 10 μm and 100 μm have been fabricated, but other dimensions are available if desired. Different types of substrates are shown in the various embodiments shown in the figures. In a first embodiment shown in step (2a), a pattern is formed on a hydrophilic substrate such as glass using standard photolithographic methods, for example using a printed polymer foil as a photomask.

In a second embodiment shown in step (2b), the hydrophilic glass substrate is metallized using a thermal evaporation and photoresist "lift-off" process prior to depositing the nanostructure-containing material. The metallized substrate can then be cleaned, for example using ultraviolet (UV) ozone cleaning, as described in detail below. After cleaning, the exposed portion of the glass substrate can be silanized in step (3b) in a dry box using a suitable 1 mM OTS mixed solvent solution such as hexadecane and tetrachlorocarbon. Silanization of exposed portions of the glass substrate renders these portions hydrophobic. Prepared substrates can be sonicated in, for example, chloroform and ethanol prior to deposition of nanostructure-containing materials.

As noted above, a homogeneous suspension containing nanostructured material, eg, including single-walled carbon nanotubes, can be stabilized in a liquid medium, such as deionized water, at a nanotube concentration of up to about 1.0 g/L. At least a portion of the substrate having the nanostructured material-containing surface attractably functionalized is contacted with the suspension. For example, a device, such as a device capable of submerging a patterned substrate vertically into the suspension, can be used to contact a portion of the substrate with the suspension at room temperature.

After contacting part of the substrate with the suspension, the substrate is separated from the suspension, e.g. by immersion, to allow the nanotubes to rest on the hydrophilic regions of the substrate along the water/substrate/air triple line (see Figure 4). Assemble. The means for separating the substrate and the suspension may include means for pulling the substrate from the suspension at a predetermined speed and means for evaporating the liquid, such as a hot plate, while the substrate remains in contact with the suspension. Nanotubes were not found to assemble on the hydrophobic regions of the substrate. When, for example, the substrate is pulled out of water or the water gradually evaporates, a continuous film of single-walled carbon nanotubes forms in the hydrophilic regions of the substrate as the triple-phase line moves downward.

The nanotubes adhere strongly to the hydrophilic substrate and cannot be removed by washing in solvents such as methanol, ethanol, and buffered hydrofluoric acid. Therefore, these solvents can be used to remove photoresists after deposition. The bonding of SWNTs to the substrate can be attributed to the interaction between the -OH groups present on the glass substrate and the functional groups that end capped nanotube defect sites.

Figures 3A and 3B illustrate optical microscope images of well-defined single-walled carbon nanotube patterns deposited using the method described above. The images show that line widths as small as 10 [mu]m can be obtained using the "dip coating" process described above. The single-walled carbon nanotube strips shown in FIG. 3A have line widths of 100 μm, 40 μm, and 10 μm, respectively. The shadowing shown in Figure 3A may be the result of reflections from the underlying surface of the glass substrate when the image is taken. A thin film of single-walled carbon nanotubes was obtained at a deposition rate of about 1 cm/day. Currently, line widths are believed to be limited by the resolution of printed polymer photomasks rather than by the deposition method. The SWCNT strips exhibit stepped sharp edges at the interface and are smooth and continuous. The conductivity of the self-assembled film deposited on an insulating surface was measured at room temperature to be 0.2 S/cm. For comparison, the conductivity of a comparable "freestanding" single-walled carbon nanotube film was shown to be about 0.3 S/cm.

Film thickness and uniformity may depend on the concentration of the suspension and the speed at which the substrate is pulled from the suspension or the evaporation rate of the suspension. Relatively thick films can be obtained using high suspension concentrations (eg, about 1.0 g/L) and at low pull-off/evaporation rates. When the suspension includes water, the thickness of the single-walled carbon nanotube film can decrease with increasing temperature. When the temperature rises above about 40°C, the film can become discontinuous. A similar discontinuity can be observed when water is replaced in the suspension by a rapidly evaporating solvent such as ethanol. Temperature fluctuations during deposition can also lead to variations in film thickness, thought to be a result of variations in solvent evaporation rates. Furthermore, films comprising short single-walled carbon nanotubes may be more uniform than those comprising longer tubes, which is believed to be related to the difference in the quality/stability of the suspension. In some cases, streaks extending parallel to the deposition direction can be observed on the deposited film. This is believed to be due to the instability of the exiting fluid at the three-phase interface.

Similar to previously reported CNT films assembled on chemically uniform structures, bundles of single-walled CNTs deposited within each stripe are aligned "in-plane" along the water/substrate/air triple-phase line direction. For patterned substrates, the triple-phase line can vary from parallel to the deposition direction at the interface between the hydrophobic and hydrophilic regions to perpendicular to the deposition direction at the middle of the hydrophilic region of each stripe, as shown in FIG. 4 . Thus, the orientation of the SWCNT bundles can gradually change from parallel to perpendicular to the deposition direction between each stripe edge and midpoint. This was confirmed by obtaining TEM images of single-walled carbon nanotube films that had been removed from the substrate. The overall orientation of single-walled carbon nanotubes can depend on the stripe width. For larger stripes, eg about 100 μm stripes, the preferred direction is perpendicular to the deposition direction.

Field emission cathodes for use in various applications such as light emitting elements, field emission devices such as flat panel displays, gas discharge tubes for overvoltage protection, x-ray generating devices, small wires, sensors can be fabricated using the self-assembly method described above , actuators, and high-resolution probes such as those used in scanning electron microscopy. Nanostructure-containing emissive materials fabricated using the self-assembly techniques described herein can produce field emission devices that have advantages over devices produced by other methods such as screen printing or electrophoresis. For example, pastes used to produce field emission devices using screen printing techniques can include impurities that can limit the density of emitters in the device and degrade performance. Furthermore, the feature sizes of emissive structures produced by screen printing can be much larger than those produced using the self-assembly techniques described herein. In addition, field emission devices produced by electrophoresis must be produced on conductive substrates. The substrates used in the self-assembly techniques described herein can be conductive or insulating, depending on the application requirements.

The electron field emission characteristics of this self-assembled single-walled carbon nanotube film can be measured in a vacuum chamber, for example, at a reference pressure of 5×10 ⁻⁷ Torr. To provide electrical contact to the single-walled carbon nanotubes, two stripes of chromium can be evaporated on the edge of the single-walled carbon nanotube stripes. Figure 5 shows the emission current-voltage (IV) characteristics of patterned films (100 μm line width, 300 μm pitch) deposited with 5 μm long SWNT bundles. The plots shown in the insets are Fowler-Nordheim plots of the same data. Data can be collected using a hemispherical tip (eg, with a 5 mm radius) as an anode with a cathode-anode spacing of about 168 μm. In the first measurement shown, the threshold electric field required to generate a current density of 10 mA/ ^cm2 may be about 11 V/μm.

The threshold electric field can be further greatly reduced using an electrically regulated process. For example, the threshold field can be reduced by about 6 V/μm after treatment (see solid curve in the figure). For free-standing films of long single-walled carbon nanotube bundles of 10 A/cm ² , this threshold electric field value is similar to previously reported threshold fields of 4-7 V/μm.

In the self-assembled cathode fabricated using the method described above, the single-walled carbon nanotubes can be aligned in-plane on the surface of the substrate. Similar to the field-induced alignment of isolated SWNTs, it is believed that when an applied electric field is made sufficiently large, bundles of SWNTs first bend and protrude along the direction of the field, and then emit electrons from their tips. Thus, the threshold field may depend on both the aspect ratio of the nanotubes and the interaction between the carbon nanotubes and the substrate. The activation process is thought to remove so-called "hot" spots on the cathode and make it easier for the nanotubes to protrude along the field direction to reduce the threshold field. The activation process may include removing excess material from the substrate surface after deposition, for example using sonication and/or mechanical removal techniques.

The electron field emission properties of the self-assembled structures fabricated according to the method described above can be compared favorably with structures fabricated using CVD-grown carbon nanotubes and cathodes fabricated using screen printing methods. Self-assembly methods such as those described herein can be used to obtain emissive cathodes with much higher pixel resolution than those obtained using so-called "thick film" techniques. In addition, similar results can be obtained from the deposition of single- and multi-walled carbon nanotubes on various substrates, including silicon, glass, ITO-coated glass, aluminum, and chromium, using self-assembly methods. Assembly and integration of nanostructured materials for device applications including field emission displays can be achieved using the self-assembly method.

After depositing the nanostructure-containing material using the self-assembly method described above, the coated substrate can be subjected to further processing, such as annealing. For example, the coated substrate can be annealed to remove the liquid medium residue after the substrate is pulled from the suspension or the suspension evaporates, to improve the electrical and thermal properties of the nanostructure-containing material, and to promote the relationship between the material layer and the substrate. combination between. According to a typical embodiment, the coated substrate may be heated to a temperature of about 100°C to 1200°C for about 1 hour, and then further annealed at a temperature of about 800°C for about 2 hours. Both anneals can be performed at a vacuum pressure of about 5 x 10 ^-7 Torr.

A number of specific exemplary embodiments consistent with the principles of the invention will now be described. These examples are illustrative and should not be considered limiting in any way.

Embodiment 1: deposit carbon nanotube film on glass

Substrates comprising glass of various sizes and thicknesses are first cleaned to remove organic contamination and restore the hydrophilic nature of the glass surface. An example of a cleaning method may be to sonicate a glass substrate in a sonication bath using a solvent such as acetone, alcohol, or deionized water. After sonication, the glass substrate can be blown dry using filtered nitrogen. _The substrate can be further cleaned using other methods, such as "Piranha" solution cleaning, in which the substrate is exposed to concentrated sulfuric acid and 30% _H2O2 in a ratio of about 4:1 for about 30 minutes. Alternatively, the substrate may be cleaned using a UV-ozone cleaning method in which the substrate is exposed to UV for about 30 minutes in an oxygen environment. The fully cleaned glass surface can be terminated with hydroxyl (-OH) groups capable of forming chemical bonds with carboxyl groups attached to carbon nanotubes.

One method of transferring carbon nanotubes onto a glass surface is to immerse the cleaned substrate into a suspension of carbon nanotubes and water at room temperature. The concentration of the carbon nanotube/water suspension may range from about 0.0001 to 1 gram of nanotubes per liter of water. The concentration of raw material in the liquid medium can vary so long as a stable suspension is maintained. Nanotubes can be assembled on the hydrophilic surface of glass. A continuous film of carbon nanotubes forms on the substrate surface when the triple line moves downward due to the gradual evaporation of water from the substrate surface or due to the gradual pulling of the substrate from the suspension. A process consistent with the above is illustrated in FIG. 6 .

Film thickness can be controlled by various process factors, including the rate at which the substrate is removed from the liquid or the rate at which water evaporates from the substrate surface and the concentration of the suspension. Films can be as thin as a monolayer of carbon nanotubes, or can include bundles of single-walled carbon nanotubes as thick as a few microns. After deposition, the film can be annealed to remove the solvent included in the suspension. Under some deposition conditions, the carbon nanotubes deposited on the substrate may be partially aligned in a direction parallel to the triple phase line.

Other methods of contacting carbon nanotubes with a suspension to deposit nanotubes on a glass substrate may include equipment such as spin-coating or spray-coating tools, electrophoretic devices, and printing, casting and dropping tools. One example of a printing method involves first placing a suspension containing carbon nanotubes on one end of the substrate surface. The suspension can then be moved across the substrate surface. As the suspension moves across the substrate surface, carbon nanotubes precipitate out of the suspension and deposit on the substrate surface.

Example 2: Deposition of patterned carbon nanotube structures on glass

The cleaned glass substrate can be covered with a hydrophobic film. Examples of suitable hydrophobic films include photopatternable adhesive polymers, such as photoresists (Shipley 1813), and self-assembled monolayers with hydrophobic end-group-terminated organosilanes, such as ethyl-terminated organosilanes such as OTS. In a subsequent step, the hydrophobic film can be removed from the glass surface area where the carbon nanotube film is to be deposited. Methods used to create patterned templates included UV lithography, e-beam lithography, and UV-ozone treatment (as described in Example 1 above).

Carbon nanotubes may be deposited on the surface of a glass substrate including a patterned hydrophobic film by suitable techniques such as self-assembly, spin coating, spray coating, electrophoresis, printing, casting and dropping as described above. According to a particular embodiment, the deposition can be carried out by immersing at least a part of the glass substrate in a suspension of carbon nanotubes and water at room temperature. The nanotubes are preferably assembled on the hydrophilic regions of the glass. When the water gradually evaporates or the substrate is gradually pulled out of the suspension and the triple-phase line moves downward, a continuous carbon nanotube film is formed on the hydrophilic regions of the patterned substrate.

After deposition, the hydrophobic coating can be removed. When the hydrophobic coating is a photoresist, the photoresist can be removed by first annealing the coated substrate at a lower temperature, such as at about 100°C for about 2 minutes to remove any moisture remaining on the substrate agent. The photoresist can then be removed by applying acetone to the resist and/or by placing the substrate in an ultrasonic bath of acetone for about 5 minutes. Due to the strong adhesion of the carbon nanotubes to the substrate, the carbon nanotube film remains adhered to the hydrophilic regions of the substrate.

A process performed in concert with the process described above is illustrated in FIGS. 7 and 8 .

Example 3: Deposition of patterned carbon nanotube structures on ITO/glass substrates

A glass substrate can be patterned with an ITO coating using an alignment mask. For example, an ITO-patterned substrate can be cleaned using a series of ultrasonic treatment baths of acetone, alcohol and deionized water followed by UV-ozone treatment (described in connection with Example 1 above). A photopatternable hydrophobic film can then be added to the surface of the cleaned ITO glass. For example, self-assembled monolayers of photoresist (Shipley 1813) or organosilanes can be added to the above-mentioned surfaces. The pattern of ITO on the glass surface can then be used to align the photomask used to pattern the hydrophobic thin film. UV lithography can be performed in the usual manner and the hydrophobic film can be removed from the ITO area of the substrate. Carbon nanotubes can be suspended in a liquid medium and deposited on a substrate using any of the methods disclosed in Examples 1 and 2. The hydrophobic coating can be removed by the method disclosed in Example 2.

A process consistent with the above is illustrated in FIG. 9 .

Example 4: Using photoresist as template for patterned deposition of carbon nanotubes

A viscous liquid type photopolymer such as Shipley 1813 photoresist can be applied to a clean surface of a glass substrate or an ITO-coated glass substrate. The substrate can then be subjected to standard photolithography processes to transfer the pattern contained in the phototool to the coated photoresist film. The phototools used may consist of a chrome photomask on a soda lime glass plate, or may be a polymer film printed on the substrate using a high resolution printer.

The substrate with the patterned photoresist film is then deposited with carbon nanotubes. According to a typical embodiment, the substrate may be immersed in a suspension of carbon nanotubes and water at room temperature. The nanotubes assemble along the water/substrate/air triple phase line, preferably on the hydrophilic regions of the glass not covered by photoresist. When the water is gradually evaporated or the substrate is gradually pulled out of the suspension and the triple-phase line moves downward, a continuous patterned carbon nanotube film is formed in the hydrophilic region of the substrate.

After deposition, the substrate can be annealed to remove any residual moisture by placing the substrate on a hot plate at a temperature of about 100°C for about 2 minutes. The photoresist coating can then be removed by applying acetone and/or by placing the substrate in an ultrasonic bath of acetone for about 5 minutes. Also, due to the strong adhesion of the carbon nanotubes to the substrate, the carbon nanotube film remains adhered to the substrate after the resist is removed.

Example 5: Using a self-assembled monolayer as a template for patterned deposition of carbon nanotubes

Self-assembled monolayers of silane molecules with hydrophobic functional groups can be formed on the surface of clean glass or and ITO-coated substrates by solution-phase or vapor-phase reactions (a process known as silanization). An example of a solution-phase silylation process may include placing a clean glass or ITO-coated glass substrate under dry conditions (e.g., a dry box with filtered nitrogen for about 30 minutes creating an environment of about 5% humidity or less) Immerse in a dilute OTS solution (eg, about 1 mM OTS in a mixed solvent of about 4:1 ratio of hexadecane and tetrachlorocarbon) with substantially constant stirring. An example of a vapor phase silylation process may include sealing and cleaning a glass or ITO-coated glass substrate with about 1 mL of concentrated OTS in a glass container (eg, a glass desiccator) for about 12 hours. Then, the substrates were cleaned each time in an ultrasonic bath of chloroform and ethanol for about 5 minutes before drying. When silanized glass or ITO-coated glass substrates are exposed to UV light in the atmosphere through e.g. , the exposed portion of the substrate is rendered hydrophilic by oxidation.

Alternatively, clean glass or ITO coated glass substrates can be coated with photoresist and UV photolithography can be performed using a photomask with an inverse pattern (or a negative photoresist can be used). The substrate patterned with photoresist can be sealed with about 1 mM concentrated OTS in a glass desiccator for about 12 hours. The substrate is then rinsed with ethanol or with acetone to dissolve the photoresist coating. The substrates can then be rinsed in ultrasonic baths of ethanol and deionized water for about 5 minutes each. The areas where the photoresist was removed form hydrophilic areas of the substrate suitable for depositing carbon nanotubes.

Carbon nanotubes were then deposited on glass or ITO-coated glass substrates with patterned organosilane self-assembled monolayers using any of the deposition methods disclosed in conjunction with Examples 1 and 2 at room temperature.

Example 6: Depositing amines or other functional groups to improve interfacial bonding between carbon nanotubes and substrates

Glass or ITO-coated glass substrates can be cleaned to form hydroxyl terminations on the surface of the substrate. For example, as described above, the substrate may be subjected to an ultrasonic bath of organic solvent followed by UV-ozone treatment and/or Piranha solution cleaning. The substrate can then be functionalized with an organosilane capped with amine end groups such as aminopropyltriethoxysilane. An example of amine functionalization includes maintaining the substrate in a solution of about 1 wt% aminopropyltriethoxysilane in anhydrous toluene at about 60°C for about 5 minutes. The substrates were then rinsed with toluene and ethanol, and then placed in an ultrasonic bath of ethanol for about 5 min.

Carbon nanotubes can then be deposited on glass or ITO-coated glass substrates with patterned organosilane self-assembled monolayers using any of the deposition methods disclosed in Examples 1 and 2 at room temperature.

Those of ordinary skill in the art can recognize that the principles and techniques described herein can be embodied in various specific forms without departing from the essential characteristics herein. The embodiments disclosed herein are to be considered in all respects as illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than the above description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced.

Claims (28)

1. self-assembling method that is used for deposition of nanostructure-containing materials, this method comprises:

Form nanostructure-containing materials;

The chemical functionalization nanostructure-containing materials;

The dispersing functional nanostructure-containing materials forms suspension in liquid medium;

At least a portion with the substrate that can attract the functionalized nanostructure-containing material surface is contacted with suspension; With

Separate substrate and suspension, wherein when separating with suspension, nanostructure-containing materials is adhered on the substrate part.

2. the method for claim 1 comprises:

Before making substrate and suspension contact, on substrate surface, form hydrophilic and hydrophobic region, wherein functionalized nanostructure-containing material is hydrophilic, and is adhered to when separating with suspension on the hydrophilic region of substrate.

3. the method for claim 2 wherein forms hydrophilic and hydrophobic region comprises:

On substrate surface, form the self-assembled monolayer of organosilan with hydrophobic end group end-blocking; With

In the oxygen environment, expose the part of self-assembled monolayer to ultraviolet (UV) light; Wherein the expose portion of self-assembled monolayer forms the hydrophilic region of substrate, and the remainder of self-assembled monolayer forms the hydrophobic region of substrate.

4. the method for claim 2 wherein forms hydrophilic and hydrophobic region comprises:

The hydrophobic photoresist of deposition on substrate surface;

A part that exposes photoresist is to ultraviolet (UV) light; With

Remove a part of photoresist to expose the hydrophilic region of substrate, wherein remain the hydrophobic region that photoresist forms substrate.

5. the method for claim 4 comprises:

Remove hydrophobic photoresist in separate substrate and the after-applied solvent of suspension to substrate, wherein nanostructure-containing materials keeps being adhered on the substrate after applying solvent.

6. the method for claim 5 comprises:

Annealed substrate before removing hydrophobic photoresist.

7. the method for claim 2, wherein when substrate comprised glass, this method comprised:

Part with the functionalized glass substrate surface corresponding to the substrate hydrophilic region of the organosilan with amine end groups end-blocking.

8. the method for claim 1 comprises:

Separating the after annealing substrate with suspension.

9. the method for claim 1 comprises:

After separating, remove unnecessary nanostructure-containing materials from substrate with suspension.

10. the method for claim 1 comprises:

Before making part and suspension contacts, clean substrate.

11. the method for claim 10 wherein when substrate comprises glass, is cleaned substrate and is comprised following at least a:

Place substrate in ultra sonic bath with solvent;

Make substrate stand the mixture of sulfuric acid and hydrogen peroxide; With

In the oxygen environment, expose substrate to ultraviolet (UV) light.

12. the process of claim 1 wherein that substrate is contacted with suspension to be comprised:

The submergence substrate is in the suspension of nanostructure-containing.

13. the method for claim 12, wherein separate substrate and suspension comprise at least a in following:

From suspension, pull out the substrate of submergence; With

Evaporation suspension in the submergence substrate.

14. the process of claim 1 wherein that substrate is contacted with suspension to be comprised:

On the part of substrate surface, arrange suspension; With

Move suspension across substrate surface, the nanostructure-containing materials that wherein is dispersed in the suspension is adhered on the surface that can attract functionalised materials.

15. the process of claim 1 wherein at least a to the substrate of the suspension that substrate contacted comprise spin coating and spraying nanostructure-containing with suspension.

16. the process of claim 1 wherein that liquid medium comprises that water is to form the aqueous suspension of nanostructure-containing.

17. the process of claim 1 wherein that the material concentration that comprises in the suspension is between every liter of liquid medium of about 0.0001-1 gram nanostructure-containing materials.

18. the method for claim 1, wherein nanostructure-containing materials comprises at least a in following: Single Walled Carbon Nanotube, multi-walled carbon nano-tubes, silicon, silica, germanium, germanium oxide, carbonitride, boron, boron nitride, chalcogenide, silver, gold, iron, titanium oxide, gallium oxide, indium phosphide or be wrapped in magnetic-particle in the nanostructure comprise at least a among Fe, Co and the Ni.

19. the process of claim 1 wherein that the chemical functionalization nanostructure-containing materials comprises:

By with acid reaction partial oxidation nanostructure-containing materials.

20. the process of claim 1 wherein that substrate comprises at least a in glass, plastics and the pottery of glass, metal, metal coat of silicon, glass, indium-Xi-oxide (ITO) coating.

21. the process of claim 1 wherein that the nanostructure-containing materials that is adhered on the substrate arranges substantially in one direction.

22. the method by self assembly manufacturing pattern carbon nano tube field-transmitting cathode, this method comprises:

Formation comprises the material of carbon nano-tube;

The chemical functionalization carbon nano-tube;

The material that disperses to comprise functionalized carbon nanotubes in liquid medium forms suspension;

On the substrate surface that can attract functionalized carbon nanotubes, form hydrophilic and hydrophobic region;

At least a portion of substrate is contacted with suspension; With

Separate substrate and suspension, wherein when separating with suspension, carbon nano-tube is adhered on the hydrophilic region of substrate.

23. the method for claim 22 comprises:

Separating the after annealing substrate with suspension; With

After separating, remove unnecessary carbon nano-tube from substrate with suspension.

24. the method for claim 22, wherein the chemical functionalization carbon nano-tube comprises:

By with acid reaction partial oxidation carbon nano-tube.

25. the field-transmitting cathode of producing according to the method for claim 1.

26. the field-transmitting cathode of producing according to the method for claim 22.

27. a device that is used for deposition of nanostructure-containing materials on substrate, this device comprises:

Be used to form the equipment of nanostructure-containing materials;

The equipment that is used for the chemical functionalization nanostructure-containing materials;

Be used for forming the equipment of suspension at liquid medium dispersing functional nanostructure-containing materials;

The equipment that is used to make at least a portion to contact with suspension with the substrate that can attract the functionalized nanostructure-containing material surface; With

The equipment that is used for separate substrate and suspension, wherein when separating with suspension, nanostructure-containing materials is adhered on the substrate part.

28. the device of claim 27 comprises:

Be used for forming on substrate surface before making substrate and suspension contacts the equipment of hydrophilic and hydrophobic region, wherein functionalized nanostructure-containing material is hydrophilic, and is adhered to when separating with suspension on the hydrophilic region of substrate.

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