Chemistry of inorganic compounds – Carbon or compound thereof – Elemental carbon
Reexamination Certificate
2001-06-18
2004-09-07
Hendrickson, Stuart L. (Department: 1754)
Chemistry of inorganic compounds
Carbon or compound thereof
Elemental carbon
C423S44500R, C423S44500R
Reexamination Certificate
active
06787122
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of improving certain properties of nanotube and nanoparticles-based materials. For example, the present invention relates to a method of intercalating a nanostructure or nanotube-containing material with a foreign species thereby causing the material to exhibit one or more of the following: reduction of the work function; reduction in the threshold electrical field for electron field emission; conversion of the semiconducting material to a metal; an increase in the electrical conductivity; an increase in the electron density of state at the Fermi level; and an increase the electron field emission site density.
BACKGROUND OF THE INVENTION
In the description of the background of the present invention that follows 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 the applicable statutory provisions. Applicants reserve the right to demonstrate that any of the referenced subject matter does not constitute prior art with regard to the present invention.
The term “nano-structured” or “nanostructure” material is used by those familiar with the art to designate materials including nanoparticles such as C
60
fullerenes, fullerene-type concentric graphitic particles; nanowires
anorods such as Si, Ge, SiO
x
, GeO
x
, or nanotubes composed of either single or multiple elements such as carbon, B
x
N
y
, C
x
B
y
N
z
MoS
2
, and WS
2
. One of the common features of the “nano-structured” or nanostructure” materials is their basic building blocks. A single nanoparticle or a carbon nanotube has a dimension that is less than 500 nm at least in one direction. These types of materials have been shown to exhibit certain properties that have raised interest in a variety of applications.
U.S. Pat. No. 6,280,697 entitled “Nanotube-Based High Energy Material and Method”, the disclosure of which is incorporated herein by reference, in its entirety, discloses the fabrication of carbon-based nanotube materials and their use as a battery electrode material.
U.S. Pat. No. 6,630,772 entitled “Device Comprising Carbon Nanotube Field Emitter Structure and Process for Forming Device” the disclosure of which is incorporated herein by reference, in its entirety, discloses a carbon nanotube-based electron emitter structure.
Ser. No. 09/351,537 entitled “Device Comprising Thin Film Carbon Nanotube Electron Field Emitter Structure”, the disclosure of which is incorporated herein by reference, in its entirety, discloses a carbon-nanotube field emitter structure having a high emitted current density.
U.S. Pat. No. 6,277,318 entitled “Method for Fabrication of Patterned Carbon Nanotube Films, the disclosure of which incorporated herein by reference, in its entirety, discloses a method of fabricating adherent, patterned carbon nanotube films onto a substrate.
U.S. Pat. No. 6,334,939 entitled “Nanostructure-Based High Energy Material and Method, the disclosure of which is incorporated herein by reference, in its entirety, discloses a nanostructure alloy with alkali metal as one of the components. Such materials are described as being useful in certain battery applications.
U.S. Pat. No. 6,553,096 entitled “X-Ray Generating Mechanism Using Electron Field Emission Cathode”, the disclosure of which is incorporated herein by reference, in its entirety, discloses an X-ray generating device incorporating nanostructure-containing material.
Ser. No. 09/817,164 entitled “Coated Electrode With Enhanced Electron Emission And Ignition Characteristics” the disclosure of which is incorporated herein by reference, in its entirety, discloses an electrode including a first electrode material, an adhesion-promoting layer, and a carbon nanotube-containing material disposed on at least a portion of the adhesion promoting layer, as well as associated devices incorporating such an electrode.
As evidenced by the above, these materials have been shown to be excellent electron field emission materials. In this regard, such materials have been shown to possess low electron emission threshold applied field values, as well as high emitted electron current density capabilities, especially when compared with other conventional electron emission materials.
For example, it has been shown that the electronic work functions of carbon nanotube materials, which is one of the critical parameters that determines the electron emission threshold field, are in the range of 4.6-4.9 eV (electron Voltage). See, e.g.—“Work Functions and Valence Band States of Pristine and Cs-intercalated Single-walled Carbon Nanotube Bundles,” Suzuki et al, Appl. Phys. Lett., Vol. 76, No. 26, pp. 407-409, Jun. 26, 2000.
It has also been shown that the electronic work functions of carbon nanotube materials can be reduced substantially when they are intercalated with alkali metals, such as cesium. See, e.g.—Ibid., and “Effects of Cs Deposition on the Field-emission Properties of Single-walled Carbon Nanotube Bundles,” A. Wadhawan et al., Appl. Phys. Lett., 78 (No. 1), pp. 108-110, Jan. 1, 2001.
As illustrated in
FIG. 1
, the spectral intensity at the Fermi level of the pristine single walled carbon nanotubes is very small. On the other hand, a distinct Fermi edge is observed for the Cs-intercalated sample. From the spectral intensity at the Fermi level, we can conclude that the density of states at the Fermi level of the Cs-intercalated sample is roughly two orders larger than that of the pristine material. Further, as illustrated in
FIG. 2
, the results show that the work function of the single-walled carbon nanotube decreases with increasing Cs deposition time. (The spectra were measured at room temperature using a He lamp Hv=21.22 eV).
By reducing the electronic work functions of carbon nanotube materials, the magnitude of the applied electrical field necessary to induce electron emission can be significantly reduced. This relationship can be understood from the Fowler-Nordheim equation:
I=aV
2
exp(−
b&phgr;
3/2
/bV
)
wherein I=emission current, V=applied voltage, &phgr;=electron work function, and &bgr;=field enhancement factor, a and b=constants.
Thus, as evident from the above equation, a reduction in the work function value &phgr;, has an exponential effect on the emission current I. Experimental evidence has verified the above-noted relationship.
Nanotubes, such as carbon nanotubes synthesized by the current techniques such as laser ablation, chemical vapor deposition, and arc-discharge methods typically have enclosed structures, with hollow cores that are enclosed by the graphene shells on the side and ends. Carbon nanotubes, especially single-walled carbon nanotubes have very low defect and vacancy density on the side walls. The perfect graphene shells can not be penetrated by foreign species. The interior space of the nanotubes is usually inaccessible for filling and/or intercalation. Although defects are commonly observed on the sidewalls of the multi-walled carbon nanotubes, only the space between the concentric graphene shells is partially accessible.
Previous techniques for intercalating the carbon nanotube materials have included techniques such as vapor phase reaction between the raw carbon nanotube materials and the material to be intercalated (e.g.—alkali metal), and electrochemical methods. Examination of carbon nanotube materials intercalated in this manner has revealed that the alkali metal atoms intercalate into space between the single-walled nanotubes inside the nanotube bundles or the space between the concentric graphene shells in multi-walled carbon nanotubes.
However, such intercalated carbon nanotube materials possess certain disadvantages.
First, since alkali metals are extremely air-sensitive, the interaction with carbon nanotube materials must take place in a vacuum environment. This makes these materials difficult to process, and difficult to incorporate into practical devices.
Second, alk
Burns Doane Swecker & Mathis L.L.P.
Hendrickson Stuart L.
Lish Peter J
The University of North Carolina at Chapel Hill
LandOfFree
Method of making nanotube-based material with enhanced... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of making nanotube-based material with enhanced..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of making nanotube-based material with enhanced... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3244350