Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Particulate matter
Reexamination Certificate
1997-11-25
2001-05-15
Le, H. Thi (Department: 1773)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Particulate matter
C428S408000, C423S276000, C423S290000, C423S291000, C423S351000, C423S364000, C423S371000, C423S414000, C423S439000
Reexamination Certificate
active
06231980
ABSTRACT:
I. BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to nanotubes and nanoparticles and more specifically to nanotubes and nanoparticles containing boron, carbon and nitrogen.
2. Description of Related Art
Carbon nanotubes were discovered by S. Ijima (Nature, 354:56, 1991) and synthesized by T. W. Ebbesen and P. M. Ajayan (Nature, 358:220, 1992). Theoretical studies by N. Hamada, et al. (Phys. Rev. Lett., 68:1579, 1992) and M. S. Dresselhaus, et al. (Solid State Commun., 84:201, 1992) showed that carbon nanotubes exhibit either metallic or semiconducting behavior depending on the radii and helicity of the tubules. Hamada proposed a notation to classify the helicity using the indices (n,m). The (n,m) tubule is obtained by rolling a planar graphite sheet so that a first hexagonal carbon ring on one edge of the sheet will connect with a second hexagonal carbon ring, which in the planar configuration was separated from the first ring by nA
1
+mA
2
; where A
1
and A
2
are primitive translation vectors on the graphite sheet.
The carbon nanotubes have interesting and potentially useful electronic and mechanical properties. Among the barriers to actualizing the utility of carbon nanotubes are nonuniform electronic properties resulting from small band gaps.
A turbostratic tubular form of boron nitride (BN) having a diameter on the order of 1 to 3 micrometers was produced from the amorphous phase of BN (E. J. M. Hamilton et al., Science, 260:659, 1993). Hamilton's micron-scale, amorphous phase, BN tubes are characterized by a random, non-crystalline arrangement of atoms in the wall of the tube; the atomic arrangement does not map back on itself. Limitations of BN amorphous phase tubes, not having a high degree of crystallinity in the tube walls, include reduced mechanical strength, and ill-defined and unpredictable electronic properties, compared to tubes having a crystalline structure. Another characteristic of Hamilton et al.'s amorphous BN tubes is their size, on the order of 1000 times larger than nanoscale structures. Because BN is not an electrical conductor Hamilton et al. synthesized their amorphous micron-scale tube using a high temperature gas reaction instead of an arc system.
Theoretical studies by N. Hamada, et al. (Phys. Rev. Lett., 68:1579, 1992) and M. S. Dresselhaus, et al. (Solid State Commun., 84:201, 1992) showed that carbon nanotubes exhibit either metallic or semiconducting behavior depending on the radii and helicity of the tubules. Hamada proposed a notation to classify the helicity using the indices (n,m). The (n,m) tubule is obtained by rolling a planar graphite sheet so that a first hexagonal carbon ring on one edge of the sheet will connect with a second hexagonal carbon ring, which in the planar configuration was separated from the first ring by nA
1
+mA
2
; where A
1
and A
2
are primitive translation vectors on the graphite sheet.
Carbon nanotubes have small bandgaps that make their electronic properties nonuniform. In addition, the bandgap of a carbon nanotube is relatively sensitive to tube diameter, helicity, and multiplicity of walls. Furthermore, it is difficult to dope carbon nanotubes, that is to add small concentrations of non-carbon material to the tubes. Typically doping occurs at concentrations of about 1% or less.
II. SUMMARY OF THE INVENTION
Inventive nanoscale tubes (“nanotubes”) and nanoscale particles (“nanoparticles”) having crystalline walls were formulated comprising a variety of stoichiometries of B
x
C
y
N
z
. Typically x, y, and z are integers including zero, where no more than one of x, y, and z are zero for a given stoichiometry. The x, y, and z subscripts indicate the relative proportion of each element with respect to the others. For example, y may be zero yielding the formula B
x
N
z
; z may be zero yielding the formula B
x
C
y
; or x may be zero yielding the formula C
y
N
z
. In the circumstances that the inventive B
x
C
y
N
z
structures are doped with added elements or molecules, the subscripts x, y, and z will take on non-integer values. In general, it is not necessary that x, y, and z are integers. Since they indicate ratios, they may or may not be expressed as integers.
The inventive nanotubes and nanoparticles comprise carbon combined with boron and/or nitrogen. In a different embodiment, the inventive nanotubes and nanoparticles comprise essentially only boron and nitrogen. The inventive nanotubes and nanoparticles can be doped with other elements or molecules to alter their electronic properties. Examples of doping elements are boron, carbon, nitrogen, aluminum, silicon, phosphorous, beryllium, oxygen, and any of the alkali atoms. Examples of doping molecules are methyl or butyl groups and osmium tetroxide. There are several other possible elements and compounds that will be readily known by those skilled in the art. Typically the concentration of dopants is less than 1%.
REFERENCES:
patent: 5456986 (1995-10-01), Majetich et al.
patent: 5549973 (1996-08-01), Majetich et al.
patent: 5780101 (1998-07-01), Nolan et al.
Miyamoto, et al., Physical Review B, vol. 50, No. 24, “Electronic properties of tubule forms of hexagonal BC3”, pp. 18360-18366, 12/94.
Rubio, et al., Physical Review B, vol. 49, No. 7, “Theory of graphite boron nitride nanotubes” pp. 5081-5084, 2/94.
Hamada, et al., Physical Review Letters, vol. 68, No. 10, “New One-Dimensional Conductors: Graphite Microtubules”, pp. 1579-1581, 3/92.
Dresselhaus, Solid State Communications, vol. 84, Nos. 1/2, “C60Related Tubules”, pp. 201-205, 1992.
S. Ijima (Nature, 354:56, 1991).
T.W. Ebbessen and P.M. Ajayan (Nature, 358:220, 1992).
E.L.M. Hamilton, et al, Science, 260:659, 1993.
Weng-Sieh, et al., Phys Rev B, 51(16):11229, 1995.
N.G. Chopra, et al., Science, 269: 967, Aug. 18, 1995.
Cohen Marvin Lou
Zettl Alexander Karlwalter
Coudert Brothers
Le H. Thi
The Regents of the University of California
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