Multilayer carbon nanotube films and method of making the same

Details Multilayer carbon nanotube films and method of making the same Multilayer carbon nanotube films and method of making the same

2002-01-11

2004-10-26

Beck, Shrive P. (Department: 1762)

Coating processes

Coating by vapor, gas, or smoke

Carbon or carbide coating

C427S249400, C427S255150, C427S255700, C427S402000, C427S903000, C423S447300, C423S44500R, C216S095000, C216S097000, C216S109000

Reexamination Certificate

active

06808746

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to multilayer carbon nanotube materials with controllable layer thicknesss, diameter and packing density of the constituent nanotubes in each of the layers, and processes for their preparation. The invention also relates to hetero-structured multilayer carbon nanotube materials including one or more layers of carbon nanotubes and to processes for their preparation. 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
, Jan. 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 and catalytic pyrolysis, often exist in a randomly entangled state (see, for example: T. W. Ebbesen and P. M. Ajayan,
Nature
358, 220, 1992; M. Endo et al.,
J. Phys. Chem. Solids
, 54, 1841, 1994; V. Ivanov et al.,
Chem. Phys. Lett
., 223, 329, 1994). However, aligned carbon nanotubes have recently been prepared either by post-synthesis manuipulation (see, for example: M. Endo, et al.,
J. Phys. Chem. Solids
, 54, 1841, 1994; V. Ivanov, et al.,
Chem. Phys. Lett
., 223, 329, 1994; H. Takikawa et al.,
Jpn. J. Appl. Phys
., 37, L187, 1998) 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).
SUMMARY OF THE INVENTION
Multilayer structures built up from aligned carbon nanotubes are of vital interest, as the use of multilayered semiconductor materials and devices has been demonstrated to be highly desirable for many applications. Examples include the use of molecular-beam epitaxy for making superlattices consisting of the alternating layers of gallium arsenide and aluminium arsenide as hetero-structured semiconductor materials (M. A. Herman and H. Sitter, “
Beam Epitaxy: Fundamentals and Current Status
”, Springer-Verlag, Berlin, 1989), the use of Langmuir-Blodgett and chemical vapor deposition techniques for construction of organic field-emission transistors (M. F. Rubner and T. A. Skotheim, in “
Conjugated Polymers
”, J. L. Brédas and R. Silbey (eds.), Kluwer Academic Publishers, Dordrecht, 1991; G. Horowitz,
Adv. Mater
., 10, 365, 1998), and the use of layer-by-layer adsorption and solution-spinning methods for preparing multilayer thin films of conjugated polymers as organic light-emitting diodes (S. A. Jenekhe and K. J. Wynne, “
Photonic and Optoelectronic Polymers
”, ACS Sym. Ser. 672, ACS Washington, D.C., 1995; L. Dai,
J. Macromole. Sci., Rev. Macromole. Chem. Phys
. 1999, 39(2), 273-387). The overall properties of multilayer materials and/or devices are highly dependent on not only the intrinsic properties characteristic of the constituent materials in each of the layers but also the particular layer stacking sequence, the interface and surface structures, thus adding additional parameters for the design and control of their behaviours. It has now been found that multilayer structures of the perpendicularly-aligned carbon nanotubes over large areas can be prepared either by sequential syntheses or by transferring substrate-free nanotube films.
According to a first aspect, the present invention provides a process for the preparation of a substrate-free aligned nanotube film comprising:
(a) synthesising a layer of aligned carbon nanotubes on a quartz glass substrate by pyrolysis of a carbon-containing material in the presence of a suitable catalyst for nanotube formation; and
(b) etching the quartz glass substrate at the nanotube/substrate interface to release said layer of aligned nanotubes from the substrate.
Separating the layer of aligned nanotubes by etching the quartz glass substrate allows the resulting nanotube film to be deposited on another substrate, such as an electrode, and/or to be included as a layer in a multilayer materials, with the integrity of the aligned nanotubes being largely maintained in the transferred films.
The carbon-containing material may be any compound or substance which includes carbon and which is capable for forming carbon nanotubes when subjected to pyrolysis in the presence of a suitable catalyst. Examples of suitable carbon-containing materials include alkanes, alkenes, alkynes or aromatic hydrocarbons and their derivatives, for example methane, acetylene, benzene, transition meal phthalocyanines, such as Fe(II) phthalocyanine, and other organometallic compounds such as ferrocene and nickel dicyclopentadiene.
The catalyst may be any compound, element or substance suitable for catalysing the conversion of a carbon-containing material to aligned carbon nanotubes under pyrolytic conditions. The catalyst may be a transition metal, such as Fe, Co, Al, Ni, Mn, Pd, Cr or alloys thereof in any suitable oxidation state.
The catalyst may be incorporated into the substrate or may be included in the carbon-containing material. Examples of carbon-containing materials which include a transition metal catalyst are Fe(II) phthalocyanine, Ni(II) phthalocyanine, nickel dicyclopentadiene and ferrocene. When the catalyst and carbon-containing material are included in the same material it may be necessary to provide sources of additional catalyst or additional carbon-containing material. For example, when ferrocene is used as the catalyst and a source of carbon, it is necessary to provide an additional carbon source, such as ethylene, to obtain the required nanotube growth.
The pyrolysis condition employed will depend on the type of carbon-containing material employed and the type of catalyst, as well as the length and density of the nanotubes required. In this regard it is possible to vary the pyrolysis conditions, such as the temperature, time, pressure or flow rate through the pyrolysis reactor, to obtain nanotubes having different characteristics.
For example, performing the pyrolysis at a higher temperature may produce nanotubes having different base-end structures relative to those prepared at a lower temperature. The pyrolysis will generally be performed within a temperature range of 800° C. to 1100° C. Similarly lowering the flow rate through a flow-type pyrolysis reactor may result in a smaller packing density of the nanotubes and vice versa. A person skilled in the art would be able to select and control the conditions of pyrolysis to obtain nanotubes having the desired characteristics.
The quartz glas

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