bluuebunny/crossref_metadata_2025_split huggingface dataset:
Vapor-liquid-solid Growth of III-Nitride Nanowires and Heterostructures by Metal-Organic Chemical Vapor Deposition
Authors: Su J. , Gherasimova M. , Cui G. , Han J. , Lim S. , Ciuparu D. , Pfefferle L. , He Y. , Nurmikko A. V. , Broadbridge C. , Lehman A. , Onuma T. , Kurimoto M. , Chichibu S. F. 
Published: April 2011

ABSTRACTWe report flexible synthesis of III-Nitride nanowires and heterostructures by metal-organic chemical vapor deposition (MOCVD) via a catalytic vapor-liquid-solid (VLS) growth mechanism. Indium is used as an in-situ catalyst to facilitate and sustain the stability of liquid phase droplet for VLS growth based on thermodynamic consideration. The employment of mesoporous molecular sieves (MCM-41) helps to prevent the coalescence of catalyst droplets and to promote nucleation statistics. Cathodoluminescence (CL) of GaN nanowires shows near band-edge emission at 370nm, and strong E2 phonon peak is observed at room temperature in Raman scattering spectra. Both binary GaN and AlN nanowires have been synthesized by MOCVD. Three-dimensional AlN/GaN trunk-branch nanostructures are reported to illustrate the versatility of incorporating the VLS mechanism into MOCVD process.
Effect of the polar surface on GaN nanostructure morphology and growth orientation
Authors: Nam C. Y. , Tham D. , Fischer J. E. 
Published: April 2011

ABSTRACTWurtzite gallium nitride nanostructures were synthesized by catalyst-free thermal reaction of gallium oxide and ammonia. Depending on ammonia flow rate the resulting morphology varied. At 75 sccm only nanowires were obtained, while polyhedral crystals and nanobelts were observed at 175 sccm. From scanning electron microscopy and transmission electron microscopy, both thin smooth and thick corrugated nanowires were observed. The growth orientations of most of the smooth ones, as well as the nanobelts, were perpendicular to the c-axis (<0001>), while the corrugated nanowires and the large polyhedra grew parallel to <0001>. We propose a model to explain these variations of morphology and growth orientation in terms of the Ga/N ratio and the different characteristic length of {0001} polar surface in each morphology.
Initial Stages of Growth of Gallium Nitride via Iodine Vapor Phase Epitaxy
Authors: Mecouch WJ , Rodriguez BJ , Reitmeier ZJ , Park J-S , Davis RF , Sitar Z 
Published: April 2011

ABSTRACTThin layers of GaN have been deposited on 1μm thick MOVPE GaN(0001) thin film substrates using a novel vertical iodine vapor phase epitaxy system. The system features three concentric flow zones that separate the reactant gasses until they reach the substrate. Hydrogen flows through the innermost zone to deliver iodine vapor from an external bubbler to the molten Ga maintained at ∼1050°C and GaI to the substrate; high-purity ammonia flows through the outermost zone; nitrogen flows through the middle zone to prevent reaction between the growth species at the GaI nozzle. GaN growth was found to be a function of time, with decreasing concentration of iodine the likely cause of a decrease in growth rate at longer growth times. The step-and-terrace microstructure of the MOVPE seeds was replaced with a smooth morphology film after the shortest growth experiment. Star-shaped features with hexagonal symmetry grew on the surface with increasing growth time. These features became the tops of hexagonal pyramids; these pyramids grew competitively and dominated the final growth surface. The surface of the films grown for the longest period contained a step-and-terrace microstructure; however, the density of steps of was lower than that on the surface of underlying MOVPE substrate.
Optimization of p-type AlGaN/GaN and GaN/InGaN Superlattice Design for Enhanced Vertical Transport
Authors: Kauser M. Z. , Osinsky A. , Dong J. W. , Hertog B. , Dabiran A. , Chow P. P. 
Published: April 2011

ABSTRACTWe report on p-type AlGaN/GaN and GaN/InGaN superlattice (SL) designs with significantly improved vertical and lateral electrical conductivity (σV and σL). Composition-graded p–AlGaN layers were used to produce eight fold reduction in barrier height and a ∼40% increase in the sheet hole density in the p-GaN wells compared to typical SL structures. Thirteen orders of magnitude and 35 times improvement is obtained for σV and σL compared to typical SL and bulk p-GaN, respectively. A similar approach for p-GaN/InGaN SL resulted in seven fold reduction in barrier height and a ∼30% increase in the sheet hole density in the p-InGaN wells compared to a typical SL structures. σL is strongly dependent on hole mobility in the well and about 19 times improvement is obtained for the optimized design, SL-B, with μp=30 cm2 V-1s-1 compared to bulk-InGaN. More than 10 orders of magnitude improvement in σV is obtained for SL-B compared to modulation doped SL.
RF-MBE Growth of InN Dots on N-polar GaN Grown on Vicinal c-plane Sapphire
Authors: Hashimoto Naoki , Kikukawa Naohiro , Che Song-Bek , Ishitani Yoshihiro , Yoshikawa Akihiko 
Published: April 2011

ABSTRACTWe have grown InN quantum dots (QDs) on nitrogen-polarity (N-polarity) GaN under-layer by the radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE), and systematically investigated growth mechanism of the InN dots. The InN QDs with the N-polarity could be grown at about 500°C, which was much higher than that of previous reports on InN dots grown by MBE. When the nominal coverage of InN became more than 1 mono-layer (ML), lattice relaxation of InN occurred and high density InN dots were uniformly formed. These results indicated that InN dots were formed by Stranski-Krastanov (S-K) growth mode. For the InN deposition above about 8ML, InN dots tended to coalesce and resulted in remarakable decrease of the dots density.
Photoluminescence Study of Plastically Deformed GaN
Authors: Yonenaga I. , Makino H. , Itoh S. , Goto T. , Yao T. 
Published: April 2011

ABSTRACTWe report the photoluminescence characteristics of fresh dislocations introduced by the plastic deformation in GaN bulk crystals. GaN crystals prepared from free standing wafers grown by the HVPE technique were compressed plastically at 900 to 1000°C. In the deformed crystals (a/3) (1120) dislocations on the (1110) prismatic plane, corresponding to the so-called threading dislocations, were observed in TEM. In the PL studies at 11K the intensity of the near band-edge luminescence decreased drastically in the deformed GaN by about 1/12 than that of the as-grown GaN, which seems to imply the introduction of a high density of non-radiative reco!m bination centers into GaN! during the plastic deformation. By the plastic deformation the yellow band luminescence decreased remarkably meanwhile the red band and other new luminescence developed relatively. It is found that dislocations do not originate to the yellow luminescence but the red luminescence.
Micro-photoluminescence studies of excitonic and multiexcitonic states of quantum dot-like localization centers in InGaN/GaN structures
Authors: Sebald K. , Lohmeyer H. , Gutowski J. , Einfeldt S. , Roder C. , Hommel D. 
Published: April 2011

ABSTRACTWe present micro-photoluminescence measurements on unstructured InGaN/GaN quantum well samples. Single sharp emission lines were observed and their optical properties were studied as a function of temperature and excitation density. The experimental findings such as the independence of their spectral position on the excitation density and the observation of binding and antibinding multiexcitonic states give clear evidence for the existence of strong localization centers in the InGaN quantum well, which exhibit the same characteristics as they are known for quantum dot structures.
Ultrafast All-optical Switches Based on Intersubband Transitions in GaN/AlN Multiple Quantum Wells for Tb/s Operation
Authors: Dawlaty Jahan M. , Rana Farhan , Schaff William J. 
Published: April 2011

ABSTRACTTheoretical and experimental results on ultra-fast all-optical switches based on intersubband transitions for Tb/s operation are presented. Designs for engineering intersubband transitions (ISBT) in GaN/AlN quantum wells near communication wavelengths (∼1.55 μm) and for realizing all-optical switches requiring small pulse energies are discussed. Optimized designs show all-optical switching at Tb/s data rates with pulse energies as small as 200 fJ. Experimental realization of narrow line-width ISBT in GaN/AlN superlattices is also demonstrated.
Synthesis and Properties of GaxMn1-xN films
Authors: Zhang R. , Yu Y. Y. , Xiu X. Q. , Xie Z. L. , Gu S. L. , Shen B. , Shi Y. , Zheng Y. D. 
Published: April 2011

ABSTRATCT:Mn-doped GaN films were grown by hydride vapor phase epitaxy(HVPE). structural measurements show that Mn may substitute Ga atoms in the GaN lattice. Ferromagnetism is observed in these HVPE grown Mn-doped GaN films, which may come from the GaxMn1−xN phase in the films.
Multi-color luminescence from nanocrystalline silicon
Authors: Kunii Hiroshi , Sato Keisuke , Hirakuri Kenji , Izumi Tomio 
Published: April 2011

ABSTRACTWe have investigated correlation between luminescence property and particle size of nanocrystalline silicon (nc-Si) fabricated by controlling Si concentration in an amorphous SiOx (a-SiOx) films. The Si concentration in the a-SiOx film was increased with increasing a RF power and lowering a gas pressure. The increase of Si concentration led to expansion of the particle size of nc-Si. The particle size of nc-Si was varied from 1.8 nm up to 3.5 nm for the sample introduced the Si concentration from 0.7 % up to 9 %. The luminescent color from nc-Si grains, which differs in size, showed a red/green/blue lights.
Surface Cusp Formation in Si Homoepitaxy
Authors: Baribeau J.-M. , Wu X. , Beaulieu M. , Lockwood D.J. , Rowell N.L. 
Published: April 2011

ABSTRACTWe report a study of the surface morphology and microstructure of Si epitaxial layers grown by MBE on (001) Si at temperatures at which epitaxy breakdown is observed. For films grown in the 400 - 450 °C temperature range the epitaxy breakdown is very sluggish and characterized by a columnar growth and the formation of surface cusps. We have used atomic force microscopy to study the shape, size and distribution of those surface cusps. Surface cusps are of square shape with sides predominantly oriented along <110> directions and are typically of 50 nm size and 5 nm depth. The cusps can be very regular in size and their surface density (typically of 109-1010 cm-2) is dependent on the growth temperature. The epitaxial Si in this temperature regime exhibits a residual strain of the order of -5 × 10−5 in the growth direction. Photoluminescence (PL) from cusped Si films is characterized by a broad PL at low energy possibly due to impurities incorporation at low growth temperatures. We have observed that Ge self-assembled dots can be grown on cusped surfaces. Large area AFM measurements reveal that surface cusps are “decorated” by clusters of large dome-like Ge dots, while a lower density of smaller dome and pyramid shape islands are seen away from the cusps.
Thermal Conductivity of Porous Silicon Evaluated from Phase Characteristics of Photoacoustic Spectroscopy
Authors: Ohmukai Masato , Shimizu Hirokazu , Tsutsumi Yasuo 
Published: April 2011

ABSTRACTPorous silicon (PS), well known as a visible luminescent material, has been revealed to be an attractive candidate for an ultrasonic emitter recently. Since the ultrasonic emission is based on a thermal process it is important to evaluate thermal properties of PS. We then evaluated the thermal conductivity of PS from the phase delay in a photoacoustic (PA) signal. We report the dependence of thermal conductivity on anodization time in forming PS.
Metal-free Growth of Si/SiO2 Nanowires by Annealing SiOx (x<2) Films Deposited by PECVD
Authors: Wang Xiaoxin , Zhang Jianguo , Wang Qiming 
Published: April 2011

ABSTRACTA new metal catalysis-free method of fabricating Si or SiO2 nanowires (NWs) compatible with Si CMOS technology was proposed by annealing SiOx (x<2) films deposited by plasma -enhanced chemical vapor deposition (PECVD). The effects of the Si content (x value) and thickness of SiOx films, the annealing process and flowing gas ambient on the NW growth were studied in detail. The results indicated that the SiOx film of a thickness below 300 nm with × value close to 1 was most favorable for NW growth upon annealing at 1000–1150°C in the flowing gas mixture of N2 and H2. NWs of 50–100nm in diameter and tens of micrometers in length were synthesized by this method. The formation mechanism was likely to be related to a new type of oxide assisted growth (OAG) mechanism, with Si nanoclusters in SiOx films after phase separation serving as the nuclei for the growth of NWs in SiOx films>200nm, and SiO molecules from thin SiOx film decomposition inducing the NW growth in films<100nm. An effective preliminary method to control NW growth direction was also demonstrated by etching trenches in SiOx films followed by annealing.
Growth and Characterization of SiOx nanowires by VLS and SLS growth mechanism
Authors: Rho Dae-Ho , Kim Jae-Soo , Byun Dong-Jin , Yang Jae-Woong , Lee Jae-Hoon , Kim Na-Ri 
Published: April 2011

ABSTRCT:SiOx nanowire were synthesized using VLS (vapor-liquid-solid) and SLS (ssolid-liquid-solid) growth mechanism. Grown nanowires had a different shapes by the kind of substrates and kind of catalysts. Diameters and lengths of grown nanowires were varied with growth conditions. By vapor evaporation method, used substrates effected growth scheme and density of nanowires because of differences of catalyst nucleation characteristics. Grown nanowires showed different microstructures and optical properties. By catalyst evaporation method, various shapes of SiOx nanowires were grown. These shapes of nanowire were formed by the typical reaction of catalyst and Si source. Measured optical properties show blue luminescence about 430nm because of oxygen defects in the nannowire.
Evolution of the Luminescence Spectrum During the Dry and Steam Oxidation of SiGe Films
Authors: Rodríguez A. , Sangrador J. , Rodríguez T. , Prieto A. C. , Avella M. , Jiménez J. 
Published: April 2011

ABSTRACTThe luminescence emission arising from SiGe layers oxidized in dry or wet atmospheres has been studied and the results obtained in both cases have been compared. Additional characterization of the samples by Raman and FTIR spectroscopies, which give information on the remaining SiGe layer and on the composition of the growing oxides respectively, have allowed the luminescence and the structural features of the samples at each stage of the oxidation processes to be correlated. SiGe layers of two different thickness have been used in order to clearly establish the origin of the different emissions, eliminating the contribution of the oxide and linking them to the presence of nanoparticles.
Double Interface Coatings on Silicon Carbide Fibers
Authors: Nable Jun C. , Nosheen Shaneela , Suib Steven L. , Galasso Francis S. , Kmetz Michael A. 
Published: April 2011

ABSTRACTInterface coatings on fibers are important in ceramic matrix composites. In addition to providing toughness, the interface coating must also protect the reinforcing ceramic fibers from corrosive degradation. A double interface coating has been applied onto silicon carbide fibers. The double interface coating is comprised of a combination of nitride and oxide coatings. Among the nitrides, boron nitride and titanium nitride were utilized. These nitrides were deposited by CVD. The metal oxides of choice were aluminum oxide and zirconium oxide which were applied onto the nitride coatings by MOCVD. The phases on the coated fibers were determined by XRD. The surface coating microstructures were observed by SEM. The effect of the coatings on the tensile strengths was determined by Instron tensile strength measurements.
Formation of High-Resistivity Silver-Silicon Dioxide Composite Thin Films Using Sputter Deposition.
Authors: Shover Ann Marie , Harper James M.E. , Dellas Nicholas S. , MoberlyChan Warren J. 
Published: April 2011

ABSTRACTComposite Ag-SiO2 thin films were deposited to examine the stability of materials with high resistivity above 5000 μΩ-cm. We found that the resistivity increases exponentially with SiO2 volume fractions larger than 0.50 which is consistent with a tunneling conductivity mechanism. In order to obtain a broad composition range, these films were deposited on a stationary substrate placed above Ag and SiO2 sputtering sources. This configuration allowed compositions ranging from 0.8 to 56.3% SiO2 to be deposited on the same sample. Resistance measurements were made using a four-point probe and a profilometer was used to measure thickness. Predicted values of thickness and composition were obtained by calibrating deposition rates from the separate sources, and were verified using Rutherford Backscattering Spectroscopy. Electron microscopy analysis revealed Ag agglomerating on the surface of the film. Because of the high mobility of Ag, the films should be capped to prevent Ag agglomeration. The results of this research demonstrate that high-resistivity thin films can be grown using Ag-SiO2 composites.
Comparison of Hardness Enhancement and Wear Mechanisms in Low Temperature Nitrided Austenitic and Martensitic Stainless Steel
Authors: Mändl S. , Manova D. , Hirsch D. , Neumann H. , Rauschenbach B. 
Published: April 2011

ABSTRACTEnergetic nitrogen implantation into austenitic stainless steel or nickel alloys leads to the formation of a very hard and wear resistant surface layer with an expanded lattice, while similar results are reported for selected martensitic steels. A comparison of the phase formation under identical process conditions at 380 °C using an austenitic (304) and a martensitic (420) steel grade (in an annealed ferrite/cementite condition) shows that the initial microstructure is retained in both of them. As the formation of dislocations and stacking faults cannot account for the dramatic hardness increase, the build-up of compressive stress is proffered as an explanation covering these two steel types. Furthermore the energetic nitrogen implantation apparently stabilizes the expanded lattice with suppressing the chemical transition to iron nitrides and, for steel 420, the metallurgical transition towards austenite at high nitrogen contents.
Buckling failure of compressive loaded hard layers in flexible devices
Authors: Bouten Piet C.P. , van Gils Marcel A.J. 
Published: April 2011

ABSTRACTSubstrate materials for flexible devices are multi-layer composite structures. On top of a base polymer functional inorganic layers such as permeation barriers and conductive layers are applied. Due to the thermal mismatch between polymer and inorganic layer, the layer is compressive loaded at ambient conditions. A characteristic failure mode, occurring with compressive loaded thin layers, is buckling failure. The interface between adjacent layers fails locally, and the thin top layer bends outwards. The buckles have a characteristic width and height. These sizes are used to analyse the compressive strain, present in the layer before failure, and the adhesion quality of the failed interface. A buckle map is introduced to guide this analysis.
Si(100) Nitridation by Remote Plasmas for Enhanced High-κ Gate Performance
Authors: Chen P. , Klein T. M. 
Published: April 2011

ABSTRACTHafnium oxide is the leading high-κ candidate for next generation CMOS devices, however, it is plagued by problems such as a propensity to react with the Si(100) substrate, to crystallize, and to have fixed and trapped charges and low transistor mobilities. A remote N2/He plasma was used as a reactant during MOCVD with Hf (IV) t-butoxide which incorporates 6 at.% nitrogen located at the film-substrate interface and reduces the interdiffusion problem upon anneal [1]. A new process for pretreating the silicon wafer with a N2/He plasma was developed to improve nitrogen concentrations at the interface and reduce interdiffusion further. Films deposited with N2/He plasma and the pretreatment method were compared to O2/He plasma deposited films and N2/He plasma deposited films without the nitridation step. It is shown that a 16Å interface SiNx layer is sufficient to prevent reaction during a 1000°C Ar/O2 anneal at atmosphere and an intermediate annealing step is crucial for desired reduction in interdiffion. Thick films show some crystalline peaks by XRD which are suppressed using the N2 process. Electrical measurements on thick films show the pretreatment process results in the lowest leakage current density and the highest dielectric constant of 21.5.
Biodegradable Microfluidic Scaffolds for Vascular Tissue Engineering
Authors: Bettinger C. J. , Borenstein J. T. , Langer R. S. 
Published: April 2011

ABSTRACTThis work describes the integration of novel microfabrication techniques for vascular tissue engineering applications in the context of a novel biodegradable elastomer. The field of tissue engineering and organ regeneration has been borne out of the high demand for organ transplants. However, one of the critical limitations in regeneration of vital organs is the lack of an intrinsic blood supply. This work expands on the development of scaffolds for vascular tissue engineering applications by employing microfabrication techniques. Unlike previous efforts, this work focuses on fabricating single layer and three-dimensional scaffolds from poly(glycerol-sebacate) (PGS), a novel biodegradable elastomer with superior mechanical properties. The transport properties of oxygen and carbon dioxide in PGS were measured through a series of time-lag diffusion experiments. The results of these measurements were used to calculate a characteristic length scale for oxygen diffusion limits in solid PGS scaffolds. Single layer and three-dimensional microfluidic scaffolds were then produced using fabrication techniques specific for PGS. This work has resulted in the fabrication of solid PGS-based scaffolds with biomimetic fluid flow and capillary channels on the order of 10 microns in width. Fabrication of complex, three-dimensional microfluidic PGS scaffolds was also demonstrated by stacking and bonding multiple microfluidic layers.
Bioreactor Based Bone Tissue Engineering: Influence of Wall Collision on Osteoblast Cultured on Polymeric Microcarrier Scaffolds in Rotating Bioreactors
Authors: Yu Xiaojun , Botchwey Edward A. , Levine Elliot M. , Pollack Solomon R. , Laurencin Cato T. 
Published: April 2011

ABSTRACTRotating bioreactors have been used to overcome the limitations of passive nutrient diffusion in three-dimensional (3D) constructs for tissue engineering of bone. It is hypothesized that conventional scaffolds undergo repeated wall collisions in rotating bioreactors, which may disrupt bone tissue formation. In this study, we investigated the effects of wall collision on osteoblastic cells cultured on a microsphere based scaffold of varying densities in comparison to water. The conventional heavier than water (HTW; density > 1 g/cm3) scaffolds were fabricated by sintering HTW microspheres of 85:15 poly (lactide-co-glycolide) (PLAGA), and mixed scaffolds were designed by mixing lighter than water (LTW; density < 1 g/cm3) and HTW microspheres of PLAGA. We quantified average velocities of the two types of scaffolds using a particle tracking system, and no significant difference in average velocities was observed between the two types of scaffolds. However, HTW scaffolds have frequent wall collision and mixed scaffolds can avoid wall collision in bioreactors. When human Saos-2 osteoblast like cells were cultured on the scaffolds in bioreactors for 16 days, bone cell proliferation and cell differentiation on HTW scaffolds were significantly inhibited as compared to those cultured on mixed scaffolds in rotating bioreactors. These results indicate that collision between scaffolds and bioreactor wall is a confounding factor in osteoblastic cell proliferation and differentiation. These studies provide a foundation for development of 3D scaffolds for tissue engineering of bone in rotating bioreactors.