Abstract: A process for producing metastable nanocrystalline alpha-alumina (?-Al2O3) having particle sizes smaller than 12 nm. Starting crystallites of ?-Al2O3 having a particle size larger than 12 nm, typically on the order of about 50 nm, are ball-milled at low temperatures to produce a nanocrystalline ?-Al2O3 powder having a particle size of less than 12 nm, i.e., below the theoretical room temperature thermodynamic size limit at which ?-Al2O3 changes phase to ?-Al2O3, wherein the powder remains in the ?-Al2O3 phase at all times.

Abstract: A thermionic dispenser cathode having a refractory metal matrix with scandium and barium compounds in contact with the metal matrix and methods for forming the same. The invention utilizes atomic layer deposition (ALD) to form a nanoscale, uniform, conformal distribution of a scandium compound on tungsten surfaces and further utilizes in situ high pressure consolidation/impregnation to enhance impregnation of a BaO—CaO—Al2O3 based emissive mixture into the scandate-coated tungsten matrix or to sinter a tungsten/scandate/barium composite structure. The result is a tungsten-scandate thermionic cathode having improved emission.

Abstract: A method for making transparent nanocomposite ceramics and other solid bulk materials from nanoparticle powders and transparent nanocomposite ceramics and other solid bulk materials formed using that method. A nanoparticle powder is placed into a reaction chamber and is treated to produce a clean surface powder. The clean surface powder is coated with a second material by means of p-ALD to produce core/shell or core multi shell nanoparticles having a coating or coatings of a other material surrounding the nanoparticle. The core/shell nanoparticles are cleaned and formed into green compact which is sintered to produce a transparent nanocomposite ceramic or other solid bulk material consisting of nanoparticles or core/shell nanoparticles uniformly embedded in a matrix of a different material, particularly in a matrix of a different ceramic material, formed by outer shell of initial core/shell. All steps are performed without exposing the material to the ambient.

Abstract: A thermionic dispenser cathode having a refractory metal matrix with scandium and barium compounds in contact with the metal matrix and methods for forming the same. The invention utilizes atomic layer deposition (ALD) to form a nanoscale, uniform, conformal distribution of a scandium compound on tungsten surfaces and further utilizes in situ high pressure consolidation/impregnation to enhance impregnation of a BaO—CaO—Al2O3 based emissive mixture into the scandate-coated tungsten matrix or to sinter a tungsten/scandate/barium composite structure. The result is a tungsten-scandate thermionic cathode having improved emission.

Abstract: An enhanced symmetric multicycle rapid thermal annealing process for removing defects and activating implanted dopant impurities in a III-nitride semiconductor sample. A sample is placed in an enclosure and heated to a temperature T1 under an applied pressure P1 for a time t1. While the heating of the sample is maintained, the sample is subjected to a series of rapid laser irradiations under an applied pressure P2 and a baseline temperature T2. Each of the laser irradiations heats the sample to a temperature Tmax above its thermodynamic stability limit. After a predetermined number of temperature pulses or a predetermined period of time, the laser irradiations are stopped and the sample is brought to a temperature T3 and held at T3 for a time t3 to complete the annealing.

Abstract: A method for removing existing basal plane dislocations (BPDs) from silicon carbide epilayers by using a pulsed rapid thermal annealing process where the BPDs in the epilayers were eliminated while preserving the epitaxial surface. This high temperature, high pressure method uses silicon carbide epitaxial layers with a carbon cap to protect the surface. These capped epilayers are subjected to a plurality of rapid heating and cooling cycles.

Abstract: A process for producing metastable nanocrystalline alpha-alumina (?-Al2O3) having particle sizes smaller than 12 nm. Starting crystallites of ?-Al2O3 having a particle size larger than 12 nm, typically on the order of about 50 nm, are ball-milled at low temperatures to produce a nanocrystalline ?-Al2O3 powder having a particle size of less than 12 nm, i.e., below the theoretical room temperature thermodynamic size limit at which ?-Al2O3 changes phase to ?-Al2O3, wherein the powder remains in the ?-Al2O3 phase at all times.

Abstract: A process for producing metastable nanocrystalline alpha-alumina (?-Al2O3) having particle sizes smaller than 12 nm. Starting crystallites of ?-Al2O3 having a particle size larger than 12 nm, typically on the order of about 50 nm, are ball-milled at low temperatures to produce a nanocrystalline ?-Al2O3 powder having a particle size of less than 12 nm, i.e., below the theoretical room temperature thermodynamic size limit at which ?-Al2O3 changes phase to ?-Al2O3, wherein the powder remains in the ?-Al2O3 phase at all times.

Abstract: A method for making transparent nanocomposite ceramics and other solid bulk materials from nanoparticle powders and transparent nanocomposite ceramics and other solid bulk materials formed using that method. A nanoparticle powder is placed into a reaction chamber and is treated to produce a clean surface powder. The clean surface powder is coated with a second material by means of p-ALD to produce core/shell or core multi shell nanoparticles having a coating or coatings of a other material surrounding the nanoparticle. The core/shell nanoparticles are cleaned and formed into green compact which is sintered to produce a transparent nanocomposite ceramic or other solid bulk material consisting of nanoparticles or core/shell nanoparticles uniformly embedded in a matrix of a different material, particularly in a matrix of a different ceramic material, formed by outer shell of initial core/shell. All steps are performed without exposing the material to the ambient.

Abstract: A symmetric multicycle rapid thermal annealing (SMRTA) method for annealing a semiconductor material without the material decomposing. The SMRTA method includes a first long-time annealing at a first temperature at which the material is thermodynamically stable, followed by multicycle rapid thermal annealing (MRTA) at temperatures at which the material is not thermodynamically stable, followed in turn by a second long-time annealing at a second temperature at which the material is thermodynamically stable. The SMRTA method can be used to form p-type and n-type semiconductor regions in doped III-nitride semiconductors, SiC, and diamond.

Abstract: A thermionic dispenser cathode having a refractory metal matrix with scandium and barium compounds in contact with the metal matrix and methods for forming the same. The invention utilizes atomic layer deposition (ALD) to form a nanoscale, uniform, conformal distribution of a scandium compound on tungsten surfaces and further utilizes in situ high pressure consolidation/impregnation to enhance impregnation of a BaO-CaO-Al2O3 based emissive mixture into the scandate-coated tungsten matrix or to sinter a tungsten/scandate/barium composite structure. The result is a tungsten-scandate thermionic cathode having improved emission.

Abstract: A symmetric multicycle rapid thermal annealing (SMRTA) method for annealing a semiconductor material without the material decomposing. The SMRTA method includes a first long-time annealing at a first temperature at which the material is thermodynamically stable, followed by multicycle rapid thermal annealing (MRTA) at temperatures at which the material is not thermodynamically stable, followed in turn by a second long-time annealing at a second temperature at which the material is thermodynamically stable. The SMRTA method can be used to form p-type and n-type semiconductor regions in doped III-nitride semiconductors, SiC, and diamond.

Abstract: A method for removing existing basal plane dislocations (BPDs) from silicon carbide epilayers by using a pulsed rapid thermal annealing process where the BPDs in the epilayers were eliminated while preserving the epitaxial surface. This high temperature, high pressure method uses silicon carbide epitaxial layers with a carbon cap to protect the surface. These capped epilayers are subjected to a plurality of rapid heating and cooling cycles.

Abstract: A method to remove basal plane dislocations in post growth silicon carbide epitaxial layers by capping post growth silicon carbide epilayers with a graphite cap and annealing the capped silicon carbon epilayers at a temperature of 1750° C. or greater with a nitrogen overpressure of 60-110 psi, wherein basal plane dislocations in the epilayers are removed while surface morphology is preserved. Also disclosed is the related silicon carbide substrate material made by this method.

Abstract: A method to remove basal plane dislocations in post growth silicon carbide epitaxial layers by capping post growth silicon carbide epilayers with a graphite cap and annealing the capped silicon carbon epilayers at a temperature of 1750° C. or greater with a nitrogen overpressure of 60-110 psi, wherein basal plane dislocations in the epilayers are removed while surface morphology is preserved. Also disclosed is the related silicon carbide substrate material made by this method.

Abstract: A new Enhanced High Pressure Sintering (EHPS) method for making three-dimensional fully dense nanostructures and nano-heterostructures formed from nanoparticle powders, and three-dimensional fully dense nanostructures and nano-heterostructures formed using that method. A nanoparticle powder is placed into a reaction chamber and is treated at an elevated temperature under a gas flow to produce a cleaned powder. The cleaned powder is formed into a low density green compact which is then sintered at a temperature below conventional sintering temperatures to produce a fully dense bulk material having a retained nanostructure or nano-heterostructure corresponding to the nanostructure of the constituent nanoparticles. All steps are performed without exposing the nanoparticle powder to the ambient.

Abstract: Millimeter-scale GaN single crystals in filamentary form, also known as GaN whiskers, grown from solution and a process for preparing the same at moderate temperatures and near atmospheric pressures are provided. GaN whiskers can be grown from a GaN source in a reaction vessel subjected to a temperature gradient at nitrogen pressure. The GaN source can be formed in situ as part of an exchange reaction or can be preexisting GaN material. The GaN source is dissolved in a solvent and precipitates out of the solution as millimeter-scale single crystal filaments as a result of the applied temperature gradient.

Abstract: Millimeter-scale GaN single crystals in filamentary form, also known as GaN whiskers, grown from solution and a process for preparing the same at moderate temperatures and near atmospheric pressures are provided. GaN whiskers can be grown from a GaN source in a reaction vessel subjected to a temperature gradient at nitrogen pressure. The GaN source can be formed in situ as part of an exchange reaction or can be preexisting GaN material. The GaN source is dissolved in a solvent and precipitates out of the solution as millimeter-scale single crystal filaments as a result of the applied temperature gradient.

Abstract: A GaN sample in a sealed enclosure is heated very fast to a high temperature above the point where GaN is thermodynamically stable and is then cooled down very fast to a temperature where it is thermodynamically stable. The time of the GaN exposure to a high temperature range above its thermodynamic stability is sufficiently short, in a range of few seconds, to prevent the GaN from decomposing. This heating and cooling cycle is repeated multiple times without removing the sample from the enclosure. As a result, by accumulating the exposure time in each cycle, the GaN sample can be exposed to a high temperature above its point of thermodynamic stability for a long time but the GaN sample integrity is maintained (i.e., the GaN doesn't decompose) due to the extremely short heating duration of each single cycle.

Abstract: Millimeter-scale GaN single crystals in filamentary form, also known as GaN whiskers, grown from solution and a process for preparing the same at moderate temperatures and near atmospheric pressures are provided. GaN whiskers can be grown from a GaN source in a reaction vessel subjected to a temperature gradient at nitrogen pressure. The GaN source can be formed in situ as part of an exchange reaction or can be preexisting GaN material. The GaN source is dissolved in a solvent and precipitates out of the solution as millimeter-scale single crystal filaments as a result of the applied temperature gradient.