bluuebunny/crossref_metadata_2025_split huggingface dataset:
On Surface Cracking of Ammonia for MBE Growth of GaN
Authors: Kamp M. , Mayer M. , Pelzmann A. , Ebeling K. J. 
Published: April 2011

ABSTRACTWith the use of ammonia as nitrogen precursor for Group III-Nitrides in an on surface cracking (OSC) approach, MBE becomes a serious competitor to MOVPE. Homoepitaxial GaN exhibits record linewidths of 0.5 meV in PL (4K), whereas GaN grown on c-plane sapphire also reveals reasonable material properties (PL linewidth ≈ 5 meV, n ≈ 1017 cm-3 , μ 220 cm2/Vs). Beside results on hetero- and homoepitaxial growth of GaN, insights into the growth mechanisms are presented. The growth of ternary nitrides is discussed, p- and n-doping as well as first LED results are reported.
TOF-LEIS Characterization and Growth of GaN Thin Films Grown with ECR and NH3
Authors: Kim E. , Bensaoula A. , Rusakova I. , Shultz A. , Waters K. 
Published: April 2011

ABSTRACTGaN thin films were grown on various substrates by GSMBE using ECR nitrogen and ammonia. The growth of GaN was monitored by real time analysis, time of flight low energy ion scattering (TOF-LEIS) and RHEED.Growth of GaN on GaAs, ZnO, Ge and Al2O3 was investigated. The substrates’ surfaces were analyzed during pre-growth annealing and during GaN growth. The removal of surface contaminants and the modification of the surface stoichiometry from these surfaces are presented.GaN films on sapphire (0001) grown under different conditions were examined real time by low energy ion scattering mass spectroscopy of recoiled ion (MSRI) and the relationship between the in-situ surface composition with ex-situ photoluminescence measurement results are discussed.
Deposition of AlN on WS2 (0001) Substrate by Atomic Layer Growth Process
Authors: Chung J-W. , Ohuchi F.S. 
Published: April 2011

ABSTRACTClose proximity of the lattice constant for tungsten disulfide and aluminum nitride has lead to an investigation to use WS2 as a potential substrate for the growth of AIN. Metal organic chemical vapor deposition(MOCVD) has been develop to fabricated WS2 thin films on Si(001) with their basal planes parallel to the substrate. AIN thin film was subsequently grown by atomic layer growth (ALG) process using dimethylamine-alane (DMEAA) and ammonia (NH3). Deposition conditions for WS2 thin films by MOCVD, and AIN growth on WS2 by ALG are described.
Spatial distribution of electron concentration and strain in bulk GaN single crystals - relation to growth mechanism
Authors: Perlin Piotr , Suski Tadeusz , Polian Alain , Chervin Jean Claude , Litwin-Staszewska Elzbieta , Grzegory Izabella , Porowski Sylwester , Erickson J. W. 
Published: April 2011

ABSTRACTMicro-infrared reflectivity and micro-Raman scattering have been used to determine free electron density and residual strain distribution in bulk GaN crystals. As-grown samples exhibit significant variation of electron concentration and strain along their surfaces. Increase of electron concentration correlates with the growth direction. The observed inhomogeneities in the properties of bulk GaN crystals can be eliminated by mechanical polishing of the crystal and removing the surface layer or growth figures formed during the sample cooling, which follows its high-pressure, high-temperature growth. Properties of that surface layer can differ from the bulk due to different growth mechanisms and impurity distribution. We suggest that oxygen is a likely candidate for the donor impurity supplying high amount of electrons to the conduction band of GaN.
Electron-Phonon Scattering in Si-Doped GaN
Authors: Wetzel C. , Walukiewicz W. , Ager J. W. 
Published: April 2011

ABSTRACTPhonon-plasmon scattering in non-resonant Raman spectroscopy is used to determine the free electron concentration in Si doped GaN films. For various doping concentration and variable temperature the correlation with magneto-transport data is established. The freeze-out of the carrier concentration at low temperature is thus observed in a purely optical detection scheme. We observe a very long transient time of several hours for the carrier concentration as a reaction to temperature variation. This indicates an indirect capture and emission process with a very small cross section. The value of the Faust-Henry coefficient is determined.
Effect of the Nitridation of the Sapphire (0001) Substrate on the GaN Growth
Authors: Grandjean N. , Massies J. , Vennègues P. , Laugt M. , Leroux M. 
Published: April 2011

ABSTRACTThe analysis of the sapphire surface nitridation by in situ reflection high-energy electron diffraction evidences the formation of a relaxed AIN layer. Its role on the early stage of the GaN growth is investigated by transmission electron microscopy (TEM). GaN crystallites of high structural quality, with the c axis perpendicular to the sapphire basal plane, are observed when the starting surface is nitridated. On the other hand, the growth of GaN on a bare substrate involves the formation of larger islands with numerous defects. TEM study reveals that the c axis of these latter crystallites is systematically tilted by about 19° with respect to the sapphire basal plane. Actually, this orientation corresponds to a particular epitaxial relationship between GaN and sapphire (0001) substrates. Finally, the optical properties of GaN thin layers are shown to be strongly dependent on the nitridation state of the sapphire surface.
Mapping of Donor Impurities in Gan By Raman Imaging
Authors: Ponce F. A. , Steeds J. W. , Dyer C. D. , Pitt G. D. 
Published: April 2011

ABSTRACTRaman scattering experiments on silicon-doped GaN show that donor impurities quench the Al(LO) Raman line at 735 cm−1. This is due to interaction between lattice vibrations and the free carrier plasma. The spatial variation of the Al(LO) signal has been imaged directly using newly developed instrumentation. Features with dimension under on micron are observed in faceted GaN crystallites. The variation in free carrier concentration is attributed to preferential incorporation of donor impurities during growth.
Optical Transitions and Recombination Lifetimes in GaN and InGaN Epilayers, and InGaN/GaN and GaN/AlGaN Multiple Quantum Wells
Authors: Smith M. , Lin J. Y. , Jiang H. X. , Khan A. , Chen Q. , Salvador A. , Botchkarev A. , Morkoc H. 
Published: April 2011

ABSTRACTTime-resolved photoluminescence (PL) has been employed to study the optical transitions and their dynamical processes in GaN and InxGa1-xN epilayers, and GaN/GaN and GaN/ALxGa1-xN multiple quantum wells (MQW). We compare the results from both metal-organic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) grown samples. In addition, results are also compared with GaAs/ALxGa1-xAs MQW. It was found for all samples that the low temperature emission lines were dominated by radiative recombination transitions of either localized or free excitons, which demonstrates the high quality and purity of these III-nitride materials.
Bound Exciton Energies, Biaxial Strains, and Defect Microstructures in GaN/AlN/6H-SiC(0001) Heterostructures
Authors: Perry W. G. , Zheleva T. , Linthicum K. J. , Bremser M. D. , Davis R. F. , Shan W. , Song J. J. 
Published: April 2011

ABSTRACTBiaxial strains resulting from mismatches in thermal expansion coefficients and lattice parameters in 22 GaN films grown on A1N buffer layers previously deposited on vicinal and on-axis 6H-SiC(0001) substrates were measured via changes in the c-axis lattice parameter (c). Six of the films were in compression, indicating the residual strain due to lattice mismatch was not relieved. A Poisson's ratio of v=0.18 was calculated. The bound exciton energy (EBx) was a linear function of these strains. The shift in EBx with film stress was 23 meV/GPa. The role of the SiC off-axis tilt was investigated for GaN films grown concurrently on the vicinal and on-axis 6H-SiC substrates. Marked variations in EBx and c were observed, with a maximum shift of ΔEBx = 15 meV and Δc = 0.0042 Å. Threading dislocations densities of ~1010/cm2 and ~108/cm2 were determined for GaN films grown on vicinal and on-axis SiC, respectively. A 0.9% residual compressive strain at the GaN/AIN interface was observed by high resolution transmission electron microscopy (HRTEM). It is proposed that the on-axis SiC substrate does not offer a sufficient density of steps for defect formation to relieve the lattice mismatch between GaN and A1N and A1N and SiC.
The Composition Pulling Effect in InGaN Growth on the GaN and AlGaN Epitaxial Layers Grown by MOVPE
Authors: Kawaguchi Yasutoshi , Shimizu Masaya , Hiramatsu Kazumasa , Sawaki Nobuhiko 
Published: April 2011

ABSTRACTInGaN has been grown on GaN and AlGaN epitaxial layers by metalorganic vapor phase epitaxy (MOVPE) and ‘the composition pulling effect’ at the initial growth stage of InGaN has been studied in relation to the lattice mismatch between InGaN and the bottom epitaxial layers. Crystalline quality of InGaN is good near the interface of InGaN/GaN and the composition of InGaN is close to that of GaN. With increasing growth thickness, the crystalline quality becomes worse and the indium mole fraction is increased. The composition pulling effect becomes stronger with increasing lattice mismatch.
Improvement of the Luminescing Behaviour of Simmplanted SiO2 Films
Authors: Schuster T. , Dittrich T. , Porteanu H. E. , Fischer T. , Hechtl E. , Petrova-Koch V. , Koch F. 
Published: April 2011

AbstractIn previous work we reported on the observation of continuously tunable photoluminescence in Si+-implanted SiO2-films with moderate intensities. In this paper we demonstrate improved performance of such samples. The photoluminescence intensity increases abruptly up to two orders of magnitude when the anneal temperature is elevated to values higher than 1000…1100°C. This strong photoluminescence degrades less than that of porous silicon. Very fine tunability in the spectral range from 2.1 eV to 1.3 eV is achieved in samples implanted with a graded dose. In the analysis of the results we try to distinguish between the contributions of the Si-nanocrystals and of the oxide related defects.
Self-Assembling Formation of Silicon Quantum Dots by Low Pressure Chemical Vapor Deposition
Authors: Nakagawa K. , Fukuda M. , Miyazaki S. , Hirose M. 
Published: April 2011

AbstractThe growth of Si dots on thermally-grown SiO2/c-Si from a thermal decomposition of pure silane has been systematically studied in the temperature range from 500 to 650°C. It has been suggested mat the Si dot height and dot diameter on as-grown SiO2 are rate-limited by the cohesive action of adsorbed precursors and the thermal decomposition of silane on Si nucleation sites, respectively. The nucleation site on as-grown SiO2 is likely to be generated by the thermal dissociation of surface Si-O bonds. It has been also found that in Si dot formation on OH-terminated SiO2 surface the nucleation density is dramatically enhanced and consequently the dot size and its distribution become small. This implies that surface OH bonds can provide the nucleation sites.
Structural Investigations of Colloidal Semiconductor Nanocrystal Heterostructures: Faceting and Epitaxy
Authors: Kadavanich A. V. , Mews A. , Tolbert S. H. , Peng X. , Schlamp M. C. , Lee J. C. , Alivisatos A. P. 
Published: April 2011

AbstractWe use High Resolution Transmission Microscopy (HRTEM) to study CdSe, CdS/HgS/CdS quantum-dot quantum well (QDQW), and CdSe/CdS core-shell nanocrystals, grown by wet-chemical techniques. The nanocrystals have faceted Wulff polyhedron shapes.In addition to HRTEM, we employ multi-wavelength anomalous dispersion (MAD) x-ray diffraction. We use computer modeling to help interpret the experimental data.Growth of a heterogeneous phase proceeds epitaxially preserving the overall shape and point-group symmetry of the original seed nanocrystals, both for wurtzite (CdSe/CdS) and zincblende (CdS/HgS/CdS) type structures.Recently prepared InAs nanocrystals also show evidence of faceting as observed by HRTEM and may lend themselves equally well to epitaxy.
Synthesis and Optical Properties of MoS2Nanoclusters
Authors: Wilcoxon J. P. , Newcomer P. P. , Samara G. A. 
Published: April 2011

AbstractHighly crystalline nanoclusters of MoS2were synthesized and their optical absorption and photoluminescence spectra were investigated. Key results include: (1) strong quantum confinement effects with decreasing size; (2) preservation of the quasiparticle (or excitonic) Nature of the optical response for clusters down to ∼2.5 nm in size which are only two unit cells thick; (3) demonstration that 3-D confinement produces energy shifts which are over an order of magnitude larger than those due to 1-D confinement; (4) observation of large increases in the spin-orbit splittings at the top of the valence band at the K and M points of the Brillouin zone with decreasing cluster size; and (5) observation of photoluminescence due to both direct and surface recombination.
Optical Properties of Deuterium Terminated Porous Silicon
Authors: Matsumoto Takahiro , Masumoto Yasuaki , Koshida Nobuyoshi 
Published: April 2011

AbstractWe have studied the optical properties of deuterium-terminated porous silicon. The photoluminescence spectrum was different from that of usual hydrogen-terminated porous Si despite porous Si showing both the same structure and the same absorption spectrum. These results indicate that the surface vibration of terminated atoms couples to the quantum confined states.
Effects of Nanocrystalline Structure and Passivation on the Photoluminescent Properties of Porous Silicon Carbide
Authors: Spanier Jonathan E. , Cargill G. S. , Herman Irving P. , Kim Sangsig , Goldstein David R. , Kurtz Anthony D. , Weiss Ben Z. 
Published: April 2011

AbstractWe present the results of an investigation of the dependence of the photoluminescence (PL) spectra on preparation conditions, the resulting microstructure, and post-anodization treatment of porous silicon carbide films which were formed from both p and n-type 6H-SiC substrates. Porous samples were prepared by anodic dissolution under different galvanostatic conditions, resulting in different porosities and crystallite sizes. Selected-area electron diffraction patterns taken on similarly prepared porous silicon carbide (PSC) samples confirmed that the films were monocrystalline. Transmission electron microscopy of as-anodized films revealed an isotropie porous network; a dependence of porosity and nanocrystallite size on porous layer formation current density was established. Some PSC samples were passivated using a short, thermal oxidation treatment. The effects of porosity and crystallite size, and of oxide passivation in these PSC films, on PL spectra and intensity were studied using a 365 nm Kr-ion laser as excitation. Under certain conditions, the spectrally integrated PL intensity of a passivated film is more than 450x that for the original bulk SiC substrate. PL spectra are presented, and possible mechanisms are discussed.
Photoluminescence from Porous Silicon Anodized with Monochromatic Light Illumination
Authors: Matsumoto Takahiro , Masumoto Yasuaki , Arata Go , Mimura Hidenori 
Published: April 2011

AbstractThe effect of monochromatic light during the anodization of porous silicon is investigated from the points of view of structural characterization and photoluminescence. A clear correlation is observed between the photoluminescence peak energy and the bandgap energy determined by the illuminating photon energy. The difference of these two energies is analyzed by a size-dependent Stokes shift.
Auger Ionization of Silicon Nanocrystals
Authors: Averboukh B. , Kovalev D. , Ben Chorin M. , Koch F. , Efros Al.L. , Rosen M. 
Published: April 2011

AbstractPhotoluminescence saturation under intense CW optical excitation and optical degradation of photoluminescence from porous Si are studied. The anisotropy of the luminescence is observed under intense linearly polarized illumination at room temperature and after polarized light induced degradation at low temperature. The Auger process is shown to be responsible for these observations.
Silicon as an Active Biomaterial
Authors: Canham L. T. , Reeves C. L. , Wallis D. J. , Newey J. P. , Houlton M. R. , Sapsford G. J. , Godfrey R. E. , Loni A. , Simons A. J. , Cox T. I. , Ward M. C. L. 
Published: April 2011

AbstractThe response of a range of porous Si and poly Si films to storage in acellular simulated body fluids is summarised and its implications discussed. It is suggested that the combination of VLSI technology, micromachining and surface microstructuring achievable with silicon, could establish this prominent semiconductor as a very useful biomaterial by the next century. The ‘biocompatibility’ of a variety of silicon microstructures, and even bulk silicon has received surprisingly little study, but now warrants detailed in-vitro and in-vivo assessment.
Electroluminescent Devices Made from Silicon Nanocrystals Embedded in Various Host Matrices
Authors: Delgado Gildardo R. , Lee Howard W. H. , Pakbaz Khashayar 
Published: April 2011

AbstractSi nanocrystals produced by ultrasonic fracturing of porous silicon (PSi) were used to fabricate electroluminescent (EL) devices. The active EL material consists of Si nanocrystals embedded in various host matrices such as polyvinylcarbazole (PVK), polymethylmethacrylate (PMMA), and silica sol-gels. Several device configurations were used to induce EL processes that rely on radiative electron-hole recombination via carrier injection or impact excitation of the nanocrystals. We report on the optical and electrical properties of these devices. We discuss relevant physics pertaining to the Si nanocrystals/host and discuss advantages and disadvantages among the different host matrices.
Growth and Structure of Microcrystalline Silicon Prepared with Glow Discharge at Various Plasma Excitation Frequencies
Authors: Finger F. , Carius R. , Hapke P. , Houben L. , Luysberg M. , Tzolov M. 
Published: April 2011

AbstractMicrocrystalline silicon was prepared with glow discharge deposition from silane/hydrogen mixtures at plasma excitation frequencies in the range 13.56 MHz - 116 MHz. The influence of the plasma excitation frequency on the growth and the structural properties of the material is investigated. At high excitation frequencies, higher growth and etching rates, larger grain sizes with less disorder within the grains, higher crystalline volume fractions, a reduced amorphous but more porous interface layer on glass and quartz substrates, and faster nucleation on amorphous silicon substrates are obtained. The results are discussed within a schematical growth model.
Charge Carrier Absorption in Doped Microcrystalline Silicon Films
Authors: Heintze M. , Lotter E. , Abel C.-D. , Schubert M. B. 
Published: April 2011

AbstractThe infrared absorption in doped microcrystalline silicon thin films is analyzed by modelling the complex permittivity as the sum of the contributions resulting from interband transitions and from absorption by charge carriers. Their density and the drift mobility within grains is described by free carrier motion according to the Drude theory. However, for a good fit to experimental data a small trapping energy, reflecting the effect of grain boundaries, is included in the model. By comparing results obtained from the analysis of infrared data with conductivity and Hall measurements in films grown in a very high frequency (VHF) plasma and by hot-wire chemical vapor deposition (CVD), we show that infrared transmission measurements provide a simple access to transport parameters in these films.
Application of MeV Ion Implantation in the Formation of Nano-Metallic Clusters in Silica
Authors: Ila D. , Wu Z. , Zimmerman R. L. , Sarkisov S. , Smith C. C. , Poker D. B. , Hensley D. K. 
Published: April 2011

ABSTRACTThe implantation of metal ions into photorefractive materials followed by thermal annealing leads to an increase in resonance optical absorption as well as an enhancement of the nonlinear optical properties. We have implanted ions of Au (3.6 MeV), Ag (1.5 MeV) and Cu (2.0 MeV) into pure silica followed by careful heat treatment. Using optical absorption spectrophotometry and rutherford backscattering spectrometry we have measured the cluster size for each heat treatment temperature and determined the activation energies for their formation. The third order electric susceptibility for silica with 2 nm gold clusters has been determined by Z-scan to be 65×10−8 esu.
Self Organized Growth and Ultrafast Electron Dynamics in Metallic Nanoparticles
Authors: Stella A. , Cheyssac P. , De Silvestri S. , Kofman R. , Lanzani G. , Nisoli M. , Tognini P. 
Published: April 2011

ABSTRACTWe present ultrafast transient reflectivity measurements performed on metallic tin nanoparticles with an average radius between 20 and 60 Å in amorphous matrix. The samples, grown using an evaporation-condensation technique, were characterized by a relatively low nanocrystals size dispersion and a negligible clusters-matrix interaction. The excitation decays exhibited a size-dependent behaviour, which is interpreted in terms of the important role played by the electron-surface interactions.
Characterization of Nanosized Silicon Prepared by Mechanical Attrition for High Refractive Index Nanocomposites
Authors: Bhagwagar Dorab E. , Wisnfficki Peter , Papadimtrakopoulos Fotios 
Published: April 2011

ABSTRACTHigh pressure nanomilling provides an inexpensive, environmentally conscious method to fabricate large quantities of nanoparticles. The presence of large particle sizes, inherent in mechanical attrition processes pose obstacles in identifying the optical properties of these nanosized particles. The high refractive index and relatively small absorption coefficient of silicon (Si) directed our research efforts towards Si nanoparticles. We presently report simple separation procedure which allows us to utilize a range of tools to characterize and exploit properties in the nano size range. Employing these Si nanoparticles, high refractive index nanocomposites in gelatin were fabricated with values as high as 3.2.
Direct Observation of Fracture Mechanisms in Polymer-Layered Silicate Nanocomposites
Authors: Manias Evangelos , Han Wook Jin , Jandt Klaus D. , Kramer Edward J. , Giannelis Emmanuel P. 
Published: April 2011

AbstractConventional three point bending and TEM techniques are employed to determine the fracture toughness and identify the failure mechanisms in model layered-silicate polymer nanocomposites.
Nanophase Copper Ferrite Using an Organic Gelation Technique
Authors: Sriram D. , Snyder R. L. , Amarakoon V. R. W. 
Published: April 2011

ABSTRACTNanocrystalline copper ferrite (Cu0.5Fe2.5O4) was synthesized using a forward strike gelation method with polyacrylic acid (PAA) as a gelating agent. The dried gel was calcined at a low temperature of 400 °C to get the final powder. The effect of pH and the ratio of the cation to the carboxylic group in the initial gel were studied with respect to both the phases and the crystallite size of the final powders synthesized. Phase and crystallite size analysis were done using x-ray diffraction and TEM. Saturation magnetization results were obtained using a SQUID magnetometer. The reactions occurring in the nano-size copper ferrite, in air as a function of temperature, were tracked using adynamic high temperature x-ray diffraction (HTXRD) system.
Coulometric Titration Studies of Nonstoichiometric Nanocrystalline Ceria
Authors: Porat O. , Tuller H. L. , Lavik E. B. , Chiang Y.-M. 
Published: April 2011

ABSTRACTOxygen nonstoichiometry measurements in nanocrystalline ceria, x in CeO2-x, were performed using coulometric titration. The measurements reveal large apparent deviations from stoichiometry, of the order of 10−3 − 10−4 at T = 405 − 455 °C and Po2 = 0.21 − 10−5 atm, as compared to levels of ∼10−9 for coarsened materials under the same conditions. The level of nonstoichiometry is, however, larger then expected from previous electrical conductivity data of nanocrystalline ceria. In addition, x ∝ Po2−½ while Σ ∝po2−1/6. The observed dependence of x(Po2, T) can be explained by either the formation of neutral oxygen vacancies at or near the interface, or by surface adsorption.