bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fabrication and characterization of UV Schottky detectors by using a freestanding GaN substrate
Authors: Shibata Yasuhiro , Motogaito Atsushi , Miyake Hideto , Hiramatsu Kazumasa , Ohuchi Youichiro , Okagawa Hiroaki , Tadatomo Kazuyuki , Nomura Tatsuya , Hamamura Yutaka , Fukui Kazutoshi 
Published: April 2011

ABSTRACTGaN ultraviolet (UV) detectors were fabricated on a freestanding GaN substrate with low dislocation density. The resulting dark current density was below 1 nA/cm-2 at -8 V reverse bias, which was about 3 orders of magnitude lower than that of a similar detector made on a sapphire substrate. Moreover, the ideality factor was nearer to unity than the device on a sapphire substrate. In addition, by comparing the GaN-based device to a commonly used Si photodetector, we found that the GaN device had a lower signal-to-noise ratio and greater temperature stability. Therefore, we found a drastic reduction of dark current by using GaN freestanding substrates and so the GaN substrate produced a more effective detector than the sapphire substrate.
Structural properties of Eu doped GaN and its relation with luminescence properties
Authors: Bang Hyungjin , Maruyama Takahiro , Naritsuka Shigeya , Akimoto Katsuhiro 
Published: April 2011

ABSTRACTThe Structural properties of Europium (Eu) doped GaN and its relation with optical properties were studied. Concentration quenching of the intensity of the Eu related luminescence observed when Eu concentration exceeds 3 at.%. In situ reflection high-energy electron diffraction (RHEED), transmission electron microscopy (TEM), and X-ray diffraction (XRD) were carried out to study this luminescence quenching and it was discovered that there is close relationship between the luminescence intensity at 622 nm and structural properties. The cause of the concentration quenching is likely related to the polycrystalline growth as well as to the EuN formation.
MBE Growth and Characterization of Device-Quality Thick InN Epilayers; Comparison between N-polarity and In-polarity Growth Processes
Authors: Yoshikawa Akihiko , Ishitani Yoshihiro , Che Song-Bek , Xu Ke , Wang Xinqiang , Yoshitani Masayoshi , Terashima Wataru , Hashimoto Naoki 
Published: April 2011

ABSTRACTEpitaxy of InN films with N-polarity and In-polarity was investigated by RF-MBE with several in-situ monitoring/controlling systems. It was found that the epitaxy temperature for N-polarity growth could be as high as 600 °C and this was about 100 deg higher than that for In-polarity case. This temperature difference in two polarities drastically affected not only the growth behaviors but also the properties of InN epilayers, i.e. N-polarity growth was preferable in both view-points. The step-flow-like surface morphology was achieved for the InN films grown with N-polarity at 580 °C. The FWHMs of X-ray rocking curves for InN (002) and (102) of 5–8 μm-thick InN films grown in N-polarity were about 200–350 and 650–950 arcsec, respectively. The highest Hall mobility was above 2000 cm2/V·s with a background carrier concentration of 1–2×1018 cm−3 at room temperature. For both polarity films, N-rich condition was necessary for the stable InN growth to obtain 5–8 μm-thick InN films.
Effects of the Nitridation Process of (0001) Sapphire on Crystalline Quality of InN Grown by RF-MBE
Authors: Muto Daisuke , Yoneda Ryotaro , Naoi Hiroyuki , Kurouchi Masahito , Araki Tsutomu , Nanishi Yasushi 
Published: April 2011

ABSTRACTThe effects of the nitridation process of (0001) sapphire on crystalline quality of InN were clearly demonstrated. The InN films were grown on NFM (nitrogen flux modulation) HT-InN or LT-InN buffer layers, which had been deposited on nitridated sapphire substrates. We found that low-temperature nitridation of sapphire is effective in improving the tilt distribution of InN films. Whereas the twist distribution remained narrow and almost constant, independent of nitridation conditions, when LT-InN buffer layers were used. The XRC-FWHM value of 54 arcsec for (0002) InN, the lowest reported to date, was achieved by using the LT-InN buffer layer and sapphire nitridation at 300°C for 3 hours.
Carbon-related Deep States in Compensated n-type and Semi-Insulating GaN:C and their Influence on Yellow Luminescence
Authors: Armstrong A. , Green D. , Arehart A. R. , Mishra U. K. , Speck J. S. , Ringel S. A. 
Published: April 2011

ABSTRACTThe physical origin of the yellow luminescence in MBE-grown GaN co-doped with C and Si was investigated. Deep level optical spectroscopy (DLOS), deep level transient spectroscopy (DLTS), and photoluminescence (PL) were used to study the deep level spectrum as a function of C incorporation. In the absence of C co-doping, samples were n-type and demonstrated a weak yellow luminescence band, likely related to VGa. For increasing C co-doping, samples became semi-insulating concurrent with increased intensity of the yellow luminescence and the concentration of C-related deep acceptors. The DLOS results were used to develop a configuration-coordinate model for a C-related deep level with optical ionization energy of 3.0 eV and Franck-Condon shift of 0.4 eV that is consistent with the observed yellow luminescence and DLTS results. From these findings, a general model for independent mechanisms of the yellow luminescence related to VGa for n-type GaN and C for n-type and semi-insulating GaN:C:Si is discussed.
The Ga-Nitride/air Two-Dimensional Photonic Quasi-crystals Fabricated on GaN-based Light Emitters
Authors: Zhang Bei , Zhang ZhenSheng , Xu Jun , Wang Qi , Yang ZhiJian , Chen WeiHua , Hu XiaoDong , Qin ZhiXin , Zhang GuoYi , Yu DaPeng 
Published: April 2011

ABSTRACTThe two-dimensional (2D) Ga-nitride/air photonic quasi-crystals (PQC) were successfully fabricated by the technique of focused Ga ion beam (FIB) milling on GaN based epitaxial wafers. The effects of the PQC on the current injected edge emitting GaN-based light emitters were investigated. The quasi-crystal structures studied in this work are based on square-triangular tiling with 8-fold or 12-fold symmetry. The air hole diameter in the different PQC patterns was varied from 95nm up to 1200nm, the filling factor of air hole was in the range of 10% to 50% and the depth of the hole was 90nm to 370nm, respectively. Among these, the nearest center-to-center distance of the holes and/or the lattice constant was reached to be 170nm. The photonic quasi-crystals on the GaN-based light emitters demonstrated a two to three factor of magnitude enhancement of surface extractive emission. The blocking of the propagation of planar-guided modes by the photonic quasi-crystals was observed. By comparison of symmetry effect among the triangular lattice PC and PQCs, it was found that the GaN-based photonic quasi-crystal (PQC) with 12-fold symmetry provided a much favorable enhancement of the extractive light emission over that of triangle lattice PC and 8-fold symmetric PQC as well.
Aquamarine Luminescence Band in Undoped GaN
Authors: Reshchikov M. A. , He L. , Molnar R. J. , Park S. S. , Lee K. Y. , Morkoç H. 
Published: April 2011

ABSTRACTWe report a new defect-related photoluminescence (PL) band peaking at 2.56 eV at 15 K in undoped GaN layers grown by molecular beam epitaxy (MBE) on GaN templates. The maximum of the aquamarine luminescence (AL) band shifts to higher energies by about 100 meV with increasing temperature from 15 to 300 K. In spite of the fact that the shape and the peak position of the AL band are close to the characteristics of the green luminescence band in a freestanding GaN template, we were able to delineate these two bands for their markedly different behavior with temperature and excitation intensity. The origin of defect responsible for this PL band remains unknown.
Luminescence of Rare Earth Doped Si/Al/SiO2 Co-Sputtered Films
Authors: Rozo C. , Fonseca L. F. , Resto O. , Weisz S. Z. 
Published: April 2011

ABSTRACTEr3+, and Nd3+ doped Si/Al/SiO2 and thin films have been prepared by rf co-sputtering. Some of these films were annealed to 700°C. Erbium doped Si/Al/SiO2 films were prepared with two different sputtering configurations: one configuration with a large quantity of Al and a second configuration with a smaller quantity of Al. The configuration with large quantity of Al shows a diminished luminescence at 1.53 μm, but this emission is increased by substrate heating. The configuration with smaller quantity of Al shows emission at 1.525 μm similar in intensity to the Er-doped Si/SiO2. The spectral shape for the 4I13/2→4I15/2 emission is broader than for an analogous Er3+ doped Si/SiO2. The smaller quantity of Al configuration increases the solubility of Nd3+ (and luminescence for high Nd3+ concentration) in Si/SiO2 films and changes the spectral shape of the 4F3/2 emission with respect to the Nd3+ doped Si/SiO2 films.
Formation of Hydrogen-passivated Silicon Nanochains by Pulsed Laser Ablation without Thermal Annealing
Authors: Inada Mitsuru , Umezu Ikurou , Tanaka Shukichi , Mashiko Shinro , Sugimura Akira 
Published: April 2011

ABSTRACTHydrogen-passivated silicon nanochains were synthesized by pulsed laser ablation of silicon target in hydrogen gas atmosphere at room temperature. When the hydrogen gas pressure was higher than 670Pa, nanochains, which have crystalline silicon core, were formed. Transmission electron microscopy showed the silicon nanochains consist of connections of silicon nanocrystals with mean diameter of 4.6 nm. It is of great interest that the silicon nanochain has crystalline structure without any intentional annealing process. Optical properties of the hydrogen-passivated silicon nanochains were presented.
Analysis of growth rate of silicon nanowires
Authors: Kikkawa J. , Ohno Y. , Takeda S. 
Published: April 2011

ABSTRACTWe have measured the growth rate of silicon nanowires (SiNWs) in the diameter range of 3 to 40 nm (8.4 nm on average), which were grown by chemical vapor deposition (CVD) at temperatures between 365 °C and 495 °C. It is found that SiNWs with smaller diameters grow slower than those with larger ones, and a critical diameter at which growth stops completely exists. The growth rate of the thinner SiNWs stronger depends on growth temperature than that of thicker ones in previous studies. We discuss the dependence by thermodynamics theory.
Precipitation of highly luminescent phases from PECVD Si suboxides
Authors: Perálvarez M. , López M. , Garrido B. , Morante J.R. , Barreto J. , Cadarso V.J. , Riera M. , Zinoviev K. , Dominguez C. 
Published: April 2011

ABSTRACTSi nanoclusters (Si-nc) embedded in SiO2 present outstanding luminescent emission in the visible and are the material of choice for the realization of efficient light sources integrated with Si technology. PECVD is an attractive preparation route but there is still the need to understand how Si excess and matrix composition affect the precipitation of Si-nc and their photoluminescence (PL) efficiency. The SiOx PECVD layers studied here have a Si excess up to 50% and a thickness between 50 and 100 nm. The phase separation, precipitation and growth of the Si-nc have been achieved by annealing at 1250 °C. For reference, the same study has been performed in Si-nc/SiO2 materials synthesized by ion implantation and annealing. Refractive index and thickness measured by ellipsometry show a densification of the layers after the H release during annealing. A detailed composition profile has been determined by XPS and FTIR analyses and shows almost complete phase separation except for the interfaces, where a depletion of Si-nc is found. EFTEM demonstrates that isolated Si-nc are formed for Si excess up to 25% while for higher Si excess a continuous Si phase is observed. The PL efficiency in PECVD samples is maximized for a Si excess of 17% which is the same Si excess than that for the most emitting implanted samples. No dependence of PL efficiency has been found on the presence of Nitrogen in the matrix (up to the 10%).
The Tribological Behavior of MoS2-Cr Films Sliding Against an Aluminum Counterface
Authors: Krzanowski James E. 
Published: April 2011

ABSTRACTThe tribological performance of MoS2-Cr films in a pin-on-disk test sliding against an aluminum ball has been examined in this study. The MoS2-Cr films were deposited by pulsed laser deposition (MoS2) and simultaneous sputter deposition of Cr, giving a Cr content in the film of 10 mol. %. The results were also compared with films of MoS2 alone. The frictional behavior of MoS2-Cr films was not improved compared to the MoS2 alone, so SEM/EDS studies of the ball and flat were conducted to determine the nature of the transfer films and examine any interface reactions that occurred during the pin-on-disk (POD) test. In the early stages of the POD test (500 cycles) on the MoS2-Cr film, Al-oxide particles formed and caused cratering and scratching of the wear track, and the coefficient of friction neared 0.7. At later stages (9000 cycles), a thick oxide-based transfer film formed on the ball, but on the flat the track composition was closer to that of the original coating. For the films without Cr, after 104 cycles a smooth wear track was observed, and a thin transfer film of MoS2 was found within grooves on the ball wear scar along with Al oxide, which resulted in superior tribological performance.
Investigations of the effect of (Cr1−x, Alx)N coatings’ micro Structure on Impact Toughness
Authors: Bobzin K. , Lugscheider E. , Knotek O. , Maes M. 
Published: April 2011

ABSTRACTOriginated from the tooling industry, PVD (Physical Vapor Deposition) coating development focused on increasing the wear resistance. Nowadays, a steadily increasing market is evolving by coating machine parts. The requirements that have to be met due to the needs of this new market segment focus on tribological behavior. This means, that the focus of wear resistance is shifted towards properties like coefficient of friction, wetting behavior and the response of coatings towards dynamic loads. For many tribological applications, coatings are exposed to severe alternating loads, which are usually left out in common test methods. The approach of common coating test methods are based on the static behavior of deposited coatings. The impact tester is a testing device with a novel approach to dynamic load behavior of both bulk and coated materials. In this paper, the effect of the coatings' microstructure and Young's modulus on the impact toughness was investigated. A change in microstructure was provoked by changing deposition parameters like aluminum content. In a second stage these coatings were then tested with respect to their response to high alternating loads. For this purpose both load and number of impacts were varied.
Control of Stress in Surface Engineered Silicon
Authors: Ma Y. , Job R. , Zölgert B. , Düngen W. , Huang Y. L. , Fahrner W. R. 
Published: April 2011

ABSTRACTHydrogen plasma (H-plasma) treatments applied on (100)-oriented standard Czochralski (Cz) silicon wafers cause a structuring of the surface regions in the sub-100 nm scale. The reconstruction of the ‘nano-structured’ surface layers by high temperature vacuum annealing induces strong tensile stress (∼ GPa) at the surface and in the subsurface regions of the wafers, as can be verified by depth resolved μ-Raman spectroscopy (μRS). Although the H-plasma caused ‘nano-structured’ surface layer is very thin (100 – 200 nm), the stressed subsurface regions of the annealed samples are quite extended, i.e. up to ∼ 10 μm depth. The impacts of several process parameters including 1) the doping type of the wafer substrate, 2) the frequency of the H-plasma, 3) the power and duration of the H-plasma, 4) the temperature and duration of the vacuum annealing on the stress are investigated. It is found that the stressed region in the surface engineered silicon wafer can be controlled by the process parameters. The presented results might be important for various applications in semiconductor technology. For example, the H-plasma exposure could be done in local areas near the electrically active regions on the forefront of the wafer. After appropriate annealing, stressed local regions for external getter purposes can be created. Such a method might especially be useful for the formation of getter regions on SOI substrates.
On the Erosion of Material Surfaces caused by Electrical Plasma Discharging
Authors: Soldera Flavio A. , Mücklich Frank 
Published: April 2011

ABSTRACTThe erosion of material surfaces produced by electrical discharges plays an important role on the degradation of many electrical devices, such as electrical contacts, switches or spark plugs. A discharge produces an extreme and concentrated flow of energy into the material that heats it and can even cause melting or vaporization. The plasma pressure may cause an even greater removal of material by the emission of droplets of molten material, producing craters in the surface of the material. In this contribution the microscopic erosion mechanisms on RuAl basis intermetallic compounds are compared with those for pure metals. Single discharge experiments at high pressure were done and the erosion structures were characterized with white light interferometry and scanning electron microscopy. The effects of microstructure on the surface erosion are discussed on the basis of different samples of RuAl. In certain high temperature applications, formation of oxide scales is an important process that may influence the discharge characteristics and erosion mechanisms. These effects are discussed on results in pre-oxidized samples. It was shown, that the surface can be additionally stabilized by controlling the protecting oxide coatings.
Mammalian Cell Interactions with Nanophase Materials
Authors: Bizios Rena 
Published: April 2011

ABSTRACTAdhesion of differentiated mammalian cells from various hard and soft tissues, including adult mesenchymal stem cells is different on nanophase than on microphase/conventional ceramics (such as alumina, titania and hydroxylapatite) as well as on composites of these ceramics with either poly(L-lactic) acid or poly(methyl) methacrylate. Most importantly, nanophase materials promote selective interactions, for example, of osteoblasts but not of fibroblasts. The type, amount and conformation of adsorbed proteins (such as fibronectin, collagen and vitronectin) are key aspects of the underlying mechanism(s) of subsequent cell interactions with nanophase materials. These cellular/molecular results provide evidence that nanophase biomaterials have the potential for improving the efficacy of implants and for promoting neotissue formation pertinent to tissue engineering, regenerative medicine and other clinical applications.
Ink Jet printing of mammalian primary cells for tissue engineering applications
Authors: Saunders Rachel , Gough Julie , Derby Brian 
Published: April 2011

ABSTRACTA piezoelectric drop on demand printer has been used to print primary human osteoblast and bovine chondrocyte cells. After deposition the cells were incubated at 37°C and characterised using optical microscopy, SEM and cell viability assays. Cells showed a robust response to printing exhibiting signs of proliferation and spreading. Increasing the drop velocity results in a reduced cell survival and proliferation rates but both cell types grew to confluence after printing under all conditions studied.
Tissue Engineered Bone Using Polycaprolactone Scaffolds Made by Selective Laser Sintering
Authors: Williams J. M. , Adewunmi A. , Schek R. M. , Flanagan C. L. , Krebsbach P. H. , Feinberg S. E. , Hollister S. J. , Das S. 
Published: April 2011

ABSTRACTPolycaprolactone is a bioresorbable polymer that has potential for tissue engineering of bone and cartilage. In this work, we report on the computational design and freeform fabrication of porous polycaprolactone scaffolds using selective laser sintering, a rapid prototyping technique. The microstructure and mechanical properties of the fabricated scaffolds were assessed and compared to designed porous architectures and computationally predicted properties. Compressive modulus and yield strength were within the lower range of reported properties for human trabecular bone. Finite element analysis showed that mechanical properties of scaffold designs and of fabricated scaffolds can be computationally predicted. Scaffolds were seeded with BMP-7 transduced fibroblasts and implanted subcutaneously in immunocompromised mice. Histological evaluation and micro-computed tomography (μCT) analysis confirmed that bone was generated in vivo. Finally, we have demonstrated the clinical application of this technology by producing a prototype mandibular condyle scaffold based on an actual pig condyle.
New Materials and Methods for Hierarchically Structured Tissue Scaffolds
Authors: Comeau Benita M. , Umar Yusif , Gonsalves Kenneth E. , Henderson Clifford L. 
Published: April 2011

ABSTRACTThe overall goal of our work is to develop new methods and materials for the fabrication of hierarchically structured, three-dimensional (3D) tissue scaffolds. Conventional scaffolds commonly lack substantial mechanical strength, and there is difficulty in controlling porosity, pore distribution, and pore interconnectivity. Additionally, the chemical nature of these scaffolds is typically homogenous. The ability to chemically modify selected areas on a scaffold is one method to direct cell growth in deliberate patterns; which could aid in the engineering of complex, functioning tissues. The general aim of this work is to address these issues through the application of stereolithography (SL) to the fabrication of hierarchically structured scaffolds.In order to achieve this goal, photopolymerizable materials must be developed that are both compatible with cell growth and with SL processing. SL methods are designed to produce arbitrary control over the physical structure of the part. In addition to physical structure control, control over the local surface chemistry of the scaffold is also desired. This would permit the use of both physical and chemical cues to control cell behavior in a tissue engineering construct. Chemical control could be achieved in SL methods by using photopolymerizable materials that can also be selectively chemically modified during the SL part building process. This paper provides an update on our work directed at using combined photoradical initiated polymerization and photoacid generator based chemical modification of a polymeric scaffold via multi-wavelength SL to produce hierarchically structured scaffolds.
Synthesis and Application of Gold Nanoparticles Functionalized with Collagen Mimetic Peptides
Authors: Mo Xiao , Yu Seungju M. 
Published: April 2011

ABSTRACTCollagen is the principal tensile element of the extra-cellular matrix in animals and is the basic scaffold for cells and tissues. Abnormalities in its structure are known to result in a number of debilitating human diseases. Collagen mimetic peptides (CMPs) with repeat unit of (Pro-Hyp-Gly) are capable of forming right-handed triple-helical structures similar to that of the collagen triple helices. Recently, our group has shown that CMPs exhibit specific binding affinity to natural collagen under controlled thermal conditions. Using solid phase peptide synthesis, we have prepared a CMP cysteine derivative that was used to modify gold nanoparticles. Transmission electron microscopy (TEM) shows that the Cys-CMP functionalized gold nanoparticles have affinity to collagen fibers. We are investigating the interactions between Cys-CMP functionalized gold nanoparticles and collagen fibers. The Cys-CMP conjugated nanoparticles can potentially be used as a tool to visualize and understand unstable domains of collagen fibers which are related to a number of pathological conditions of extra cellular matrices.