Patterned carbon nanotube films

Details Patterned carbon nanotube films Patterned carbon nanotube films

2002-03-15

2004-11-02

Duda, Kathleen (Department: 1756)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Making electrical device

C430S311000

Reexamination Certificate

active

06811957

ABSTRACT:

BACKGROUND OF THE INVENTION
This is a National Stage entry under 35 U.S.C. §371 of Application NO. PCT/AU00/00549 filed May 25, 2000, and the complete disclosure of which is incorporated into this application by reference.
This invention relates to carbon nanotube materials and processes for their preparation. In particular the invention relates to patterned aligned carbon nanotube films and to processes for their preparation which involve the use of photoresist materials. The invention also relates to the construction of devices from such materials for practical applications in many areas including as electron field emitters, artificial actuators, chemical sensors, gas storages, molecular-filtration membranes, energy-absorbing materials, molecular transistors and other optoelectronic devices.
Carbon nanotubes usually have a diameter in the order of tens of angstroms and the length of up to several micrometers. These elongated nanotubes consist of carbon hexagons arranged in a concentric manner with both ends of the tubes normally capped by pentagon-containing, fullerene-like structures. They can behave as a semiconductor or metal depending on their diameter and helicity of the arrangement of graphitic rings in the walls, and dissimilar carbon nanotubes may be joined together allowing the formation of molecular wires with interesting electrical, magnetic, nonlinear optical, thermal and mechanical properties. These unusual properties have led to diverse potential applications for carbon nanotubes in material science and nanotechnology. Indeed, carbon nanotubes have been proposed as new materials for electron field emitters in panel displays, single-molecular transistors, scanning probe microscope tips, gas and electrochemical energy storages, catalyst and proteins/DNA supports, molecular-filtration membranes, and energy-absorbing materials (see, for example: M. Dresselhaus, et al.,
Phys. World,
January, 33, 1998; P. M. Ajayan, and T. W. Ebbesen,
Rep. Prog. Phys.,
60, 1027, 1997; R. Dagani,
C
&
E News,
January 11, 31, 1999).
For most of the above applications, it is highly desirable to prepare aligned carbon nanotubes so that the properties of individual nanotubes can be easily assessed and they can be incorporated effectively into devices. Carbon nanotubes synthesised by most of the common techniques, such as arc discharge (Iijima, S.
Nature
354, 56-58, 1991; Ebbesen, T. W. & Ajayan, P. M.
Nature
358, 220-222, 1992) and catalytic pyrolysis (See, for example: Endo. M et al.
J. Phys. Chem. Solids
54, 1841-1848, 1994; Ivanov. V. et al.,
Chem. Phys. Let.
223, 329-335, 1994), often exist in a randomly entangled state (See, for example: T. W. Ebbesen and P. M. Ajayan,
Nature
358, 220, 1992. However, aligned carbon nanotubes have recently been prepared either by post-synthesis manipulation (see, for example: Aegean, P. M., et al.,
Science
265, 1212-1214, 1994; De Heer, W. A. et al.
Science
268, 845-847, 1995) or by synthesis-induced alignment (see, for example: W. Z. Li,
Science,
274, 1701, 1996; Che, G.,
Nature,
393, 346, 1998; Z. G. Ren, et al.,
Science,
282, 1105, 1998; C. N., Rao, et al.,
J. C. S., Chem. Commun,
1525, 1998).
The number of techniques which have been reported for the pattern formation of aligned carbon nanotubes is very limited (S. Fan, M. G. Chapline, N. R. Franklin, T. W. Tombler, A. M. Cassell, and H. Dai,
Science,
283, 512, 1999; S. Huang, L. Dai, and A. W. H. Mau,
J. Phys, Chem.,
103 issue 21, 4223-4227), and the achievable resolutions of the nanotube patterns was, at the best, at several micrometer scale in these cases.
It has now been found that pattern formation of perpendicularly aligned carbon nanotubes with resolutions up to a sub-micrometer scale can be achieved using a novel photolithographic technique.
SUMMARY OF THE INVENTION
According to a first aspect, the present invention provides a process for preparing a patterned layer of aligned carbon nanotubes on a substrate including:
applying a photoresist layer to at least a portion of a surface of a substrate capable of supporting nanotube growth,
masking a region of said photoresist layer to provide a masked portion and an unmasked portion,
subjecting said unmasked portion to electromagnetic radiation of a wavelength and intensity sufficient to transform the unmasked portion while leaving the masked portion substantially untransformed, said transformed portion exhibiting solubility characteristics different to said untransformed portion,
developing said photoresist layer by contacting with a solvent for a time and under conditions sufficient to dissolve one of said transformed and untransformed portions of the photoresist, leaving the other portion attached to said substrate,
synthesising a layer of aligned carbon nanotubes on regions of said substrate to which said remaining photoresist portion is not attached to provide a patterned layer of aligned carbon nanotubes on said substrate.
It has been found that this photolithographic patterning method, together with a novel contact printing transfer technique, allows the pattern formation of aligned carbon nanotubes on various substrates at a micrometer/submicrometer resolution. The technique provides a route to patterned formations of aligned carbon nanotubes which have not been achievable according to methods described in the prior art. The process according to the present invention is easy to perform and provides a convenient route to patterned aligned carbon nanotubes with controllable geometries.
The term “photoresist” is used herein in its broadest sense to refer to any organic material capable of polymerising or otherwise transforming upon exposure to electromagnetic radiation such that, upon exposure, its solubility characteristics are changed relative to unexposed material. Examples of such photoresponsive materials include, but are not limited to, diazonaphthoquinone (DNQ)-based photoresists, such as cresol novolac resin (from Shipley), Ozatec PK 14 (from Hoechst), as well as other possible polymers including, inter alia, epoxy resins, polyanilines, polymethyl methacrylate, polystyrenes, and polydienes.
The mechanism of the transformation following exposure to electromagnetic radiation is illustrated below with reference to the cresol novolac resin described above. Its structure is as follows:
The reactions which occur following illumination with UV light are illustrated diagrammatically in Scheme 1 below:
As can be seen the base insoluble resin is transformed into a base soluble entity following exposure to light.
The substrate to which the photoresist layer is applied can be any substrate which is capable of withstanding the pyrolysis or CVD (chemical vapour deposition) conditions employed, for nanotube growth and which is capable of supporting aligned carbon nanotube growth. Examples of suitable substrates include all types of glass that provide sufficient thermal stability according to the synthesis temperature applied, such as quartz glass, as well as alumina, graphite, mica, mesaporous silica, silicon water, nanoporous alumina or ceramic plates. Preferably the substrate is glass, in particular, quartz glass or silicon water. The substrate may also include a coating of a material which is capable of supporting carbon nanotube growth under the conditions employed. The coating may be of any metal, metaloxide, metal alloy or compound thereof, which may have conducting or semiconducting properties. Examples of suitable metals include Au, Pt, Cu, Cr, Ni, Fe, Co and Pd. Examples of suitable compounds are metal oxides, metal carbides, metal nitrides, metal sulfides and metal borides. Examples of suitable metal oxides include indium tin oxide (ITO), Al
2
O
3
, TiO
2
and MgO. Examples of semiconducting materials include gallium arsenide, aluminium arsenide, aluminium sulphide and gallium sulphide.
The patterning of the aligned carbon nanotubes is achieved by creating a region on the substrate which is incapable of supporting nanotube growth. The pattern is created on the substrate by applying an appropriate mask

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