bluuebunny/crossref_metadata_2025_split huggingface dataset:
Properties of Gallium Selenide Doped with Sulfur
Authors: Voevodin Valeriy G. , Bereznaya Svetlana A. , Korotchenko Zoya V. , Morozov Aleksandr N. , Sarkisov Sergey Yu. , Fernelius Nils C. , Goldstein Jonathan T. 
Published: April 2011

ABSTRACTThis paper presents the results of investigations on the influence of sulfur doping on properties of gallium selenide crystals, grown by the Bridgman method from melts with sulfur content of 0.01–3 mass %, using the Hall effect, optical absorption, photoconductivity and microhardness measurements on GaSe: S. The results obtained are explained by assuming the formation of solid solutions of GaSxSe1−x and the presence of the competitive processes of point defects and structural disorder formation.
Nominal PbSe nano-islands on PbTe: grown by MBE, analyzed by AFM and TEM
Authors: Moeck Peter , Kapilashrami Mukes , Rao Arvind , Aldushin Kirill , Lee Jeahuck , Morris James E. , Browning Nigel D. , McCann Patrick J. 
Published: April 2011

ABSTRACTNominal PbSe nano-islands were grown in the Stranski-Krastanow mode on (111) oriented PbTe/BaF2 pseudo-substrates by molecular beam epitaxy (MBE). The number density and morphology of these islands were assessed by means of atomic force microscopy (AFM). Transmission electron microscopy (TEM) was employed to determine the strain state and crystallographic structure of these islands. On the basis of both AFM and TEM analyses, we distinguish between different groups of tensibly strained islands. The suggestion is made to use such nano-islands as part of nanometrology standards for scanning probe microscopy.
Effect of GaN Surface Treatment on the Morphological and Optoelectronic Response of Violet Light Emitting Diodes
Authors: Jamil Muhammad , Grandusky James R. , Shahedipour-Sandvik Fatemeh 
Published: April 2011

ABSTRACTWe report on the study of the effect of various surface chemical treatment processes of n-GaN template layers used for subsequent growth of light emitting diode (LED) structures. The treatment procedure included cleaning in organic solvents, organic solvents followed by 5 minutes of HCl, organic solvents and 5 minutes of HCl followed by 2 minutes and finally 10 minutes of HF treatment. Chemical, optical and electrical properties of the surfaces of GaN and InGaN-based LED structures were systematically investigated by x-ray photoemission spectroscopy (XPS), auger electron spectroscopy (AES), atomic force microscopy (AFM), photoluminescence (PL) and electroluminescence (EL) spectroscopy. GaN layers that were grown on the samples treated with HCl and HF showed dramatically different surfaces having high density of 3D structures with high roughness. As measured by AFM, growth of the LED structure on top of the GaN layer continued the 3D-growth mode. LED structures grown on the HCl and HF treated GaN template layers showed minimal to no PL and EL emission and failed after a short period. We suggest a qualitative model of the growth that could potentially explain the underlying phenomena leading to such pronounced changes in the optoelectronic properties and surface conditions of the LED structures due to the treatment of the initial template layers.
Moth-Eye Light-Emitting Diodes
Authors: Kasugai Hideki , Miyake Yasuto , Honshio Akira , Kawashima Takeshi , Iida Kazuyoshi , Iwaya Motoaki , Kamiyama Satoshi , Amano Hiroshi , Akasaki Isamu , Kinoshita Hiroyuki , Shiomi Hiromu 
Published: April 2011

ABSTRACTNitride-based blue-light-emitting diodes having a moth-eye structure were fabricated on the backside of a 6H-SiC substrate. The light extraction efficiency and the corresponding output power were increased by 3.8 times compared with those of an LED having the conventional structure. The results of theoretical analysis agree with these findings.
Group III nitrides grown on 4H-SiC (3038) substrate by metal-organic vapor phase epitaxy
Authors: Honshio Akira , Kitano Tsukasa , Imura Masataka , Miyake Yasuto , Kasugai Hideki , Iida Kazuyoshi , Kawashima Takeshi , Iwaya Motoaki , Kamiyama Satoshi , Amano Hiroshi , Akasaki Isamu , Kinoshita Hiroyuki , Shiomi Hiromu 
Published: April 2011

ABSTRACTThe heteroepitaxial growth of a GaN single crystal by metal-organic vapor phase epitaxy on a 4H-SiC (3038) substrate was demonstrated. The crystallographic orientation of GaN was found to be dependent on growth pressure. When the growth pressure was 1000 hPa, the orientation of the GaN single crystal was consistent with that of the SiC substrate, where the c-plane of the GaN was single crystal tilted 54.7° from the surface plane. Then, we fabricated a violet-light-emitting diode (LED) with a GaInN multiple-quantum-well (QW) active layer grown on the GaN layer, which coherently grew on the 4H-SiC (3038 ) substrate. The blue shift of the peak wavelength with increasing injection current of up to 100 mA was confirmed to be two times smaller than that of a conventional LED on a c-plane sapphire substrate due to a low internal polarization.
High-Frequency Generation in Low-Mobility Superlattices
Authors: Litvinov Vladimir , Manasson Alexander 
Published: April 2011

ABSTRACTWe study the transport properties of miniband electrons in an electromagnetic field as related to the high-frequency generation in a semiconductor superlattice (SL). We study the regimes where the external ac-field is in resonance and out of resonance with the two lowest SL minibands.In the diffusive quasi-static regime Bloch oscillations and electrical domains do not develop and high-frequency generation may occur as a result of the negative high-harmonic nonlinear conductivity. This regime is different from the frequency conversion in a stable nonlinear media. We point out that AlGaN/GaN material system has a great potential for the high-power SL terahertz (THz) source.
Metalorganic Chemical Vapor Deposition of Non-polar III-Nitride Films over a-plane SiC Substrates
Authors: Li Jiawei , Gong Zheng , Chen Changqing , Adivarahan Vinod , Gaevski Mikhail , Kuokstis Edmundas , Shatalov Maxim , Gao Ying , Zhang Zehong , Arjunan Arul , Sudarshan T. S. , Paul Maruska H. , Yang Jinwei , Asif M. 
Published: April 2011

ABSTRACTWe report progress in growing non-polar a-plane III-nitride films and heterostructures over a-plane 4H-SiC. a-plane SiC is more closely lattice-matched to a-plane GaN than is r-plane sapphire. Consequently, better structural quality a-plane nitride films may result over a-plane SiC substrates. By migration enhanced metalorganic chemical vapor deposition (MEMOCVD), an atomically smooth (1120)AlN layer with RMS roughness of 0.3nm was obtained. From the results of XRD, the structural defects in the AlN layer on SiC substrates were strongly reduced compared to those grown on r-plane sapphire. Also by applying our selective area lateral epitaxy (SALE) growth procedure, we achieved high structural and optical quality a-plane GaN films on 4H-SiC with RMS roughness only 0.4nm. Therefore, non-polar III-nitride films and heterostructures on SiC substrates are promising building blocks for realizing high performance polarization-free devices.
Determination of surface barrier height and surface state density in GaN films grown on sapphire substrates
Authors: Park Seong-Eun , Kopanski Joseph J. , Kang Youn-Seon , Robins Lawrence H. , Shin Hyun-Keel 
Published: April 2011

ABSTRACTPhotoreflectance (PR) modulation spectroscopy was performed to investigate surface properties of GaN films grown on sapphire substrates. From the period of the Franz-Keldysh oscillations, the surface electric field across the GaN space charge region was found to be (197 ± 11) kV/cm, which corresponds to a surface state density of 1.0×1012 cm−2. A surface barrier height of 0.71 eV was determined by fitting the dependence of the PR intensities on pump beam power density. We suggest that a deep level is formed at 2.68 eV above the GaN valence band edge due to the large density of surface states.
Excess Carrier Lifetime Measurements for GaN on Sapphire Substrates with Various Doping Concentrations and Surface Conditions by the Microwave Photoconductivity Decay Method
Authors: Kato Masashi , Watanabe Hideki , Ichimura Masaya , Arai Eisuke 
Published: April 2011

ABSTRACTWe have measured excess carrier lifetimes in GaN with various doping concentrations and surface conditions by the microwave photoconductivity decay method. GaN samples were grown by metalorganic chemical vapor deposition (MOCVD) without intentional doping and with Si doping or Mg doping on a-face sapphire substrates. By using the microwave photoconductivity decay method, we obtained 1/e excess carrier lifetimes of larger than 50 μs for the Si doped and undoped GaN and of less than 10 μs for the Mg doped GaN. We changed surface conditions for the samples by the inductively coupled plasma (ICP) etching and investigated effects of surface conditions on the carrier recombination behavior. The ICP etching has negligible effects on carrier lifetime in the Si doped GaN. On the other hand, in the undoped GaN, the ICP etching lengthened the carrier lifetime compared with the as-grown sample. On the contrary, the ICP etching shortened the carrier lifetime in the Mg doped GaN. The ICP etching seems to form hole traps and recombination centers at GaN surfaces and thus the carrier lifetime became longer in the undoped GaN and shorter in the Mg doped GaN.
Influence of Mis-Orientation of C-plane Sapphire Substrate on the Early Stages of MOCVD Growth of GaN Thin Films
Authors: Kim Seong-woo , Aida Hideo , Suzuki Toshimasa 
Published: April 2011

ABSTRACTWe have studied the early stages of GaN growth to realize the growth mechanism of GaN thin films on mis-oriented sapphire substrates which affects the surface and crystal quality of GaN thin films. As the result, it was found that the larger mis-orientation angle helps the growth of the larger grain of GaN and leads to the earlier shift of growth mode from 3D to 2D. The AFM observation of closed-coalesced GaN thin films revealed the difference in the micro-step structures by the mis-orientation angle of sapphire substrate. The result of x-ray rocking curve as a function of mis-orientation angle well matched with the microstructure of GaN surface, indicating that the larger mis-orientation angle helps the column ordering of GaN crystals.
Mechanisms of Raman Scattering in doped Indium Nitride
Authors: Pinquier Claire , Demangeot François , Frandon Jean , Gaio Miguel , Briot Olivier , Maleyre Bénédicte , Clur-Ruffenach Sandra , Gil Bernard 
Published: April 2011

ABSTRACTHighly n-doped InN layers are investigated by means of Raman scattering: a strong mode is evidenced near the frequency of the A1(LO) phonon, despite the high conductivity of the films. This observation is interpreted assuming the breakdown of the wave-vector conservation leading to the decoupling of the plasmon from the phonon. The lineshape of the longitudinal optical mode is simulated using the Lindhard-Mermin dielectric function for various light scattering processes: we found that the charge density fluctuation mechanism is dominant, at least in the visible excitation range.
Recombination Mechanism in Short-Wavelength GaN/AlGaN Quantum Wells
Authors: Fuhrmann D. , Retzlaff T. , Rossow U. , Hangleiter A. 
Published: April 2011

ABSTRACTTo date, light emission by AlGaN-based heterostructures and LED's operating in the ultraviolet region is far less efficient than emission from longer wavelength structures based on GaInN. We have realized GaN/AlGaN quantum well structures emitting in the 360–320 nm range with peak room-temperature internal efficiencies reaching more than 20 %. From detailed studies of the temperature and excitation power dependence of the efficiency we find that excitons play a crucial role enhancing radiative recombination in such structures. Except for the peak internal efficiency, which reaches 73 % in GaInN/GaN, the overall behavior in GaN/AlGaN and GaInN/GaN is very similar, suggesting that the main difference is the nonradiative recombination mechanism.
Influence of Substrate Misorientation Angle and Direction in Growth of GaN on Off-axis SiC (0001)
Authors: Suda Jun , Nakano Yuki , Kimoto Tsunenobu 
Published: April 2011

ABSTRACTGrowth of GaN on 4H- or 6H-SiC (0001) Si-face substrates with various misorientation angles and directions is presented. GaN layers were directly grown on the SiC substrates by molecular-beam epitaxy using elemental Ga and rf plasma-excited active nitrogen. First, 4H-SiC (0001) 8°-off toward the [11–20] direction was investigated. Before the growth of GaN, ex-situ high-temperature gas etching was carried out, resulting in a smooth SiC initial surface. However, the surface of the subsequently grown GaN layer has wavy features with peak-to-valley height of 30 nm. Since the direction of the undulations is parallel to the misorientation direction, this feature must originate from the substrate misorientation. Step bunching and large faceting along <01–10> and <10–10> directions occurred during the growth of GaN. Lowering the growth temperature suppresses large faceting, and results in reduction of the peak-to-valley height to 3 nm. However, the surface still has the same undulating features on a smaller length scale. On the other hand such morphology was not observed for GaN grown on (0001) on-axis SiC substrates (misorientation < 0.3°). The influence of the polytype of the SiC substrate and the misorientation angle and direction are also discussed.
Optical activation of Si nanowires using Er-doped sol-gel derived silica
Authors: Suh Kiseok , Park Oun-Ho , Bae Byeong-Soo , Lee Jung-Chul , Choi Heon-Jin , Shin Jung H. 
Published: April 2011

ABSTRACTOptical activation of Si nanowires (Si-NWs) using sol-gel derived Er-doped silica is investigated. Si-NWs of about 100 nm diameter were grown on Si substrates by the vapor-liquid-solid method using Au catalysts and H2 diluted SiCl4. Afterwards, Er-doped silica sol-gel solution was spin-coated, and annealed at 950 °C in flowing N2/O2 environment. Such Er-doped silica/Si-NWs nanocomposite is found to combine the advantages of crystalline Si and silica to simultaneously achieve both high carrier-mediated excitation efficiency and high Er3+ luminescence efficiency while at the same time providing high areal density of Er3+ and easy current injection, indicating the possibility of developing sol-gel activated Si-NWs as a new material platform for Si-based photonics.
Computer Simulation of Charging and Erasing Transients of a Ge/Si Hetero-nanocrystal-based Flash Memory
Authors: Zhao Dengtao , Zhu Yan , Li Ruigang , Liu Jianlin 
Published: April 2011

ABSTRACTThe transient process of the programming and erasing is very important for a nanocrystal-floating-gate flash memory. In this work, a computer simulation was carried out to investigate the charging, retention and erasing processes of our proposed Ge/Si hetero-nanocrystal floating gate flash memory. The transient gate current, the transient drain current and the average charge in one dot were simulated respectively. Evident hysteresis features can be observed in the transient processes in a voltage-sweeping measurement mode. While measuring the transient process in a constant voltage mode, the time decay of transient current and charge are weakened if Ge is used on the Si dot, indicating a longer retention time for Ge/Si-floating-gate flash memory.
Fabrication and Electrical Characterization of Silicon Nanowire Arrays
Authors: Dilts Sarah M. , Mohmmad Ahmad , Lew Kok-Keong , Redwing Joan M. , Mohney Suzanne E. 
Published: April 2011

ABSTRACTHigh density boron-doped silicon nanowire arrays were fabricated within the pores of anodized alumina membranes via vapor-liquid-solid (VLS) growth Anodized alumina membranes with a nominal pore diameter of 200 nm served as templates for the sequential electrodeposition of silver, cobalt, and gold which served as the backside electrical contact, ohmic contact metal and catalyst metal for VLS growth, respectively. Boron-doped silicon nanowires were then synthesized within the pores by VLS growth using silane (SiH4) and trimethylboron (TMB) gas sources. Arrays of Al dots were deposited on the top surface of the membrane after nanowire growth. A series of samples was prepared with different SiNW lengths and boron doping levels. Two point probe measurements were used to measure the I-V characteristics of the silicon nanowire arrays before and after annealing. Nanowire resistivity and contact resistance were determined from plots of resistance versus nanowire length. The resistivity of the SiNW was observed to decrease with the addition of TMB during growth.
Photochemical Deposition of Transparent Low Refractive Index SiO2 Topcoat for Laser Head at Room Temperature
Authors: Tezuka Y. , Murahara M. 
Published: April 2011

ABSTRACTA transparent, low refractive index SiO 2 film was photo-chemically laminated on a glass slab laser head by the Xe2* excimer lamp in the atmosphere of NF3 and O2 mixed gas at room temperature; which made it possible to inhibit the decrease in the laser output power caused by the evanescent wave leakage.The transparent SiO2 film of 260nm thickness was laminated on the non-heated substrate by the lamp irradiation for one hour. The hardness of the film before annealing was 3 by Mohs’ Scale of Hardness, and its hardness improved to 5 after annealing at 250 degrees centigrade for one hour. The refractive index of the film was 1.42, being lower than the index of silica glass that is 1.46. Furthermore, the transmittance in the visible region increased by 2% with it s antireflection coating.
Structural Nanocomposite Bonding Reinforced by Graphite Nanofibers with Surface Treatments
Authors: Roy Xu L. , Lukehart Charles M. , Li Lang , Sengupta Sreeparna , Wang Ping 
Published: April 2011

ABSTRACTGraphitic carbon nanofibers were used to reinforce epoxy resin to form nanocomposite adhesive bonding. GCNFs having a herringbone atomic structure are surface-derivatized with bifunctional hexanediamine linker molecules capable of covalent binding to an epoxy matrix during thermal curing and are cut to smaller dimension using ultrasonication. Good dispersion and polymer wetting of the GCNF component is evident on the nanoscale. Tensile and shear joint strength measurements were conducted for metal-metal and polymer-polymer joints using pure epoxy and nanocomposite bonding. Very little bonding strength increase, or some bonding strength decrease, was measured.
Structural factors determining the nanomechanical performance of transition metal nitride films
Authors: Sarakinos K. , Kassavetis S. , Patsalas P. , Logothetidis S. 
Published: April 2011

ABSTRACTChromium nitride (CrN) and Titanium nitride (TiN) thin films were deposited employing unbalanced magnetron sputtering (UBMS) for various values of substrate bias voltage (Vb). The structural characterization of the films in terms of phase identification and the density determination was achieved utilizing X-Ray techniques (XRD and XRR respectively), while the internal stresses were calculated by the change of the substrate's curvature using Stoney's equation. The nanomecahnical properties of the films (hardness and elastic modulus) were investigated using the Nanoindentation (NI) technique in the Continuous Stiffness Measurement (CSM) configuration. According to the NI results the hardness of the films ranges between between 15–25 GPa while the elastic modulus between 180–250 GPa. The analysis revealed that the hardness of the films is maximum when their orientation is pure (either [111] or [100]), while it is minimized under mixed orientation regime. Furthermore, the hardness of the films increases as the internal compressive stresses and the mass density increase. The latter can be validated through the comparison of the results concerning the above films to reported results for TiN films prepared by balanced magnetron sputtering (BMS)
Biocompatibility of CAD/CAM ORMOCER polymer scaffold structures
Authors: Doraiswamy A. , Patz T. , Narayan R. , Chichkov B. , Ovsianikov A. , Houbertz R. , Modi R. , Auyeung R. , Chrisey D. B. 
Published: April 2011

ABSTRACTA fresh approach with a novel process and a hybrid material is explored for developing designer 3-dimensional functional tissue scaffolds. The process of two photon-induced polymerization generally used for electronic and optical materials is introduced for developing biological scaffolds. Hybrid materials containing organic-inorganic units, ORMOCERs, fabricated with this process are tested for biocompatibility using various cell-types and compared with known standards such as polystyrene and ECM (Extracellular Matrix). Results show good adherence of different cells to these materials, and a growth rate comparable to bioactive materials. Structures with various surface topologies are developed and tested for preferential growth. The study is a first step towards developing bioactive and bioresorbable heterogeneous three-dimensional scaffolds.
Novel Angiogenic Compounds for Targeted Drug Delivery
Authors: Wieghaus Kristen A. , Capitosti Scott M. , Brown Milton L. , Botchwey Edward A. 
Published: April 2011

ABSTRACTInduction of angiogenesis is necessary for the success of engineered implantable tissues in order to meet oxygen and nutrient requirements of cells during tissue repair. Insufficient vascularization in bone graft reconstruction may impede healing and initiate hypoxic cell death at the interior of the implant. As a result, endogenous growth factors have been studied to enhance angiogenesis during wound repair. However, these peptide-based molecules are highly sensitive to processing that occurs during scaffold biomaterial fabrication and treatment for tissue engineering purposes. We report here the development of new small molecule regulators of angiogenesis that may circumvent the impediments associated with protein-based growth factor delivery. In this study, we report the design and evaluation of SC–3–143 as a regulator of endothelial function. We show that the compound significantly increases the formation of microvascular networks in vitro, and selectively enhances endothelial survivability by reducing endothelial cell death under serum deprived culture conditions.
Preparation of drug delivery biodegradable PLGA nanocomposites and foams by supercritical CO2 expanded ring opening polymerization and by rapid expansion from CHCIF2 supercritical solutions
Authors: Asandei Alexandru D. , Erkey Can , Burgess Diane J. , Saquing Carl , Saha Gobinda , Zolnik Banu S. 
Published: April 2011

ABSTRACTThe synthesis of poly(lactic-co-glycolic acid) (PLGA) by the ring opening copolymerization of D, L-lactide and glycolide was performed at 110 °C to 130 °C using Sn(Oct)2 as catalyst, 1, 10-decanediol as initiator in a supercritical sc-CO2 expanded medium at pressures of up to 3, 500 psi. Due to the limited monomer solubility in sc-CO2 at low temperatures (70 °C), only Mn = 2, 500 is typically obtained. However, molecular weight increases with both temperature and sc-CO2 pressure. Thus, Mn = 13, 000 (PDI = 1.28) was obtained at 110 °C - 130 °C even in the absence of fluorinated surfactants. Biodegradable drug delivery nanocomposites based on dexamethasone and poly(lactic acid) (PLA) and poly(lactide-co-glycolide) (PLGA) were prepared by the rapid expansion of the corresponding supercritical CHClF2 solutions (110 °C, 200-300 bar) in air (RESS) and in toluene (RESOLV). The RESS process leads to a broad particle size distribution (100-500 nm) while the RESOLV generates a narrower distribution centered around 100 nm and is accompanied by the formation of a few large particles, most likely due to aggregation.