Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – Forming a platelet shape or a small diameter – elongate,...
Reexamination Certificate
2001-12-10
2003-09-23
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
Forming a platelet shape or a small diameter, elongate,...
C117S084000, C117S103000, C117S105000, C117S108000, C117S953000
Reexamination Certificate
active
06623559
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method for producing nanometer-sized semiconductor particles, and more particularly, it relates to a method for producing quantum-sized compound semiconductor particles (diameter smaller than 20 nm or 200 Å) at a high production rate.
BACKGROUND
Nanometer-sized semiconductor crystallites or “quantum dots” whose radii are smaller than the bulk exciton Bohr diameter (up to 20 nm, but normally smaller than 10 nm in radius) represent a class of materials intermediate between molecular and bulk forms of matter. Quantum confinement of both the electron and hole in all three dimensions leads to an increase in the effective band gap of the semiconductor-material with decreasing crystallite size. As a result, both the optical absorption and emission of quantum dots shift to the higher energies (blue shift) as the size of the dots gets smaller. Nanometer-sized semiconductor crystallites that show such a quantum size effect are also referred to as quantum-sized crystals. They include I-VII, II-VI, III-V, III-VI and IV-VI compound semiconductors. As compared to I-VII and II-VI groups, the III-V semiconductor nano crystals have been studied to a lesser extent possibly due to the numerous difficulties encountered in the preparation of this class of nano crystals. However, as compared to the I-VII and I-VI semiconductors, the III-V materials have a greater degree of covalent bonding, a less ionic lattice, and larger exciton diameters (e.g., the exciton diameter in GaAs is 19 nm, compared to 6 nm for CdS). For this reason, the quantum size effect on the optical spectra has been predicted to be more pronounced in the III-V class of materials than in the II-VIs.
Quantum-sized compound semiconductors have been found to provide an electro-luminescent device capable of emitting light of various visible wavelengths in response to, external stimulus. In such an electro-luminescent device, variations in voltage could result in change of color of the light emitted by the device. Since these three classes of light emitting materials are inorganic materials, they are capable of withstanding higher temperatures than the conventional organic polymeric materials for light-emitting applications.
Fluorescent labeling of biological systems is a well known analytical tool used in modern biotechnology as well as analytical chemistry. Applications for such fluorescent labeling include technologies such as medical fluorescence microscopy, histology, flow cytometry, fluorescence in-situ hybridization for medical assays and research, DNA sequencing, immuno-assays, binding assays, separation, etc. Quantum-sized semiconductor crystals have been found to provide stable probe materials for biological applications having a wide absorption band. These crystals are capable of exhibiting either a detectable change in absorption or of emitting radiation in a narrow wavelength band, without the presence of the large red emission tails characteristic of dye molecules. This feature makes it possible to permit the simultaneous use of a number of such probe materials, each emitting light of a different narrow wavelength band and/or being capable of scattering or diffracting radiation. These stable probe materials can be used to image the same sample by both light and electron microscopy.
The following patents are believed to represent the state of the art of semiconductor quantum particles:
1. S. Weiss, et al., “Semiconductor nanocrystal probes for biological applications and process for making and using such probes,” U.S. Pat. No. 6,207,392 (Mar. 27, 2001).
2. A. P. Alivisatos, et al., “Process for forming shaped group II-VI semiconductor nanocrystals, and product formed using process,” U.S. Pat. No. 6,225,198 (May 1, 2001).
3. A. P. Alivisatos, et.al., “Preparation of III-V semiconductor Nanocrystals,” U.S. Pat. No. 5,505,928 (Apr. 9, 1996).
4. A. P. Alivestos, et al., “Electroluminescent devices formed using semiconductor nanocrystals and an electron transport media and method of making such electroluminiscent devices,” U.S. Pat. No. 5,537,000 (Jul. 16, 1996).
5. S. Weiss, et al., “Organic luminiscent semiconductor nanocrystal probes for biological applications and process for making and using such probes,” U.S. Pat. No. 5,990,479 (Nov. 23, 1999).
6. A. P. Alivestos, et al., “Semiconductor nanocrystals covalently bound to solid inorganic surfaces using self-assembled monolayers,” U.S. Pat. No. 5,751,018 (May 12, 1998).
7. M. G. Bawendi, et al., “Water-soluble fluorescent nanocrystals,” U.S. Pat. No. 6,251,303 (Jun. 26, 2001).
8. M. G. Bawendi, et al., “Highly luminescent color-selective materials and method of making thereof,” U.S. Pat. No. 6,207,229 (Mar. 27, 2001).
9. N. M. Lawandy, “Semiconductor nanocrystal display materials and display apparatus employing same,” U.S. Pat. No. 5,882,779 (Mar. 16, 1999).
10. A. L. Huston, “Glass matrix doped with activated luminiscent nanocrystalline particles,” U.S. Pat. No. 5,585,640 (Dec. 17, 1996).
11. H. F. Gray, et al. “Nanoparticle phosphors manufactured using the bicontinuous cubic phase process,” U.S. Pat. No. 6,090,200 (Jul. 18, 2000).
12. J. Yang, “Formation of nanocrystalline semiconductor particles within a bicontinuous cubic phase,” U.S. Pat. No. 6,106,609 (Aug. 22, 2000).
13. S. L. Castro, et al., “Functionalized nanocrystals and their use in detection systems,” U.S. Pat. No. 6,114,038 (Sep. 5, 2000).
14. E. Barbera-Guillem, “Lipophilic, functionalized nanocrystals and their use for fluorescence labeling of membranes,” U.S. Pat. No. 6,194,213 (Feb. 27, 2001).
15. D. Gallagher, et al., “Method of manufacturing encapsulated doped particles,” U.S. Pat. No. 5,525,377 (Jun. 11, 1996).
16. C. Lawton, “Biomolecular synthesis of quantum dot composites,” U.S. Pat. No. 5,985,353 (Nov. 16, 1999).
17. O. Siiman, et al., “Semiconductor nanoparticles for analysis of blood cell populations and method of making same,” U.S. Pat. No. 6,235.,540 (May 22, 2001).
18. J. C. Linehan, et al. “Process of forming compounds using reverse micelle for reverse microemulsion systems,” U.S. Pat. No. 5,770,172 (Jun. 23, 1998).
Bawendi and co-workers have described a method of preparing monodisperse semiconductor nanocrystallites by pyrolysis of organometallic reagents injected into a hot coordinating solvent [Ref.8]. This permits temporally discrete nucleation and results in the controlled growth of macroscopic quantities of nanocrystallites. Size selective precipitation of the crystallites from the growth solution provides crystallites with narrow size distributions. The narrow size distribution of the quantum dots allows the possibility of light emission in very narrow spectral widths. Although semiconductor nanocrystallites prepared as described by Bawendi and co-workers exhibit near monodispersity, and hence, high color selectivity, the luminescence properties of the crystallites are poor. Such crystallites exhibit low photoluminescent yield, that is, the light emitted upon irradiation is of low intensity. This is due to energy levels at the surface of the crystallite which lie within the energetically forbidden gap of the bulk interior. These surface energy states act as traps for electrons and holes which degrade the luminescence properties of the material.
Since mid-1980's, various synthetic approaches have been developed in preparing nano-sized II-VI (Zn and Cd chalcogenides) and IV—VI (Pb chalcogenides) semiconductors. Much of this effort has been aimed at achieving a very narrow particle size distribution. The basic idea is to use the spatial or chemical confinement provided by matrices or organic capping molecules to terminate the growth of nanocrystallites at any desired stage. In most cases, lack of a microscopically uniform environment in the substrates might be the cause for relatively wide size distribution. Both organic and inorganic matrices, such as monolayers, polymers, inverse micelles, and zeolites have been used to control the particle size. Recently, other researchers have obtained mono-dispersed CdSe nan
Kunemund Robert
Nanotek Instruments, Inc.
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