bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Photooxidation on the Transient Photoconductivity and Photoluminescence of Alq3
Authors: Sokolik I. , Walser A. D. , Priestley R. , Dorsinville R. , Tang C. W. 
Published: April 2011

ABSTRACTPhotogeneration of charge carriers and radiative excited states in pristine and photooxidized tris-(8-hydroxyquinoline) aluminum (Alq3) were studied by simultaneously measuring the photoconductive response and the kinetics of photoluminescence with subnanosecond resolution. 25 ps laser pulses at 355 nm were used for the excitation of vacuum-evaporated films of Alq3 2–4 μm thick. At equal excitation intensities the time dependence of the photoconductive response was very similar to that of the photoluminescence, independent of whether the sample was pristine or partially oxidized. Photooxidation of Alq3 substantially decreases the magnitude and lifetime of the photoconductivity and the photoluminescence. The decrease is shown to be a result of quenching of singlet molecular excitations by product(s) of photooxidation of Alq3. Photogeneration of charge carriers is controlled by the mutual annihilation of singlet excitons.
Chemistry and the Electronic Properties of Diamond Surfaces
Authors: Pehrsson Pehr E. 
Published: April 2011

ABSTRACTThe structure and chemistry of annealed and oxygen or hydrogen-terminated low-index (100, 110) diamond surfaces was determined with high resolution electron energy loss spectroscopy (HREELS), low energy electron diffraction (LEED) and other techniques. HREELS revealed carbonyl, hydroxyl and bridge-bonded oxygen groups on oxidized C(100) and C(110) surfaces. The surface chemistry was correlated with secondary electron emission spectra and other data. The oxidized and annealed (reconstructed) surfaces exhibited larger work functions and electron affinity than hydrogenated surfaces, which we attribute to both band-bending and dipole layer effects due to surface oxygen.
Observation of a new phase on the hydrogen terminated diamond (111)-surface by helium atom scattering
Authors: Lange† G. , Schaich Th. , Toennies† J. P. , Wöll Ch. 
Published: April 2011

ABSTRACTThe structural phase diagram of the hydrogen terminated diamond-(111) surface, which is of considerable relevance with regard to the low-pressure synthesis of diamond, has been investigated by the highly surface sensitive technique of thermal energy helium atom scattering. A new phase with a (2 × 1) symmetry has been observed to occur upon heating above 940 K, significantly below the well known transition to the hydrogen-free (2 × 1) π-bonded chain structure at 1250 K. It is proposed that the new phase consists of a hydrogen (2 × 1) overlayer on an unreconstructed (1 × 1) diamond substrate. Structural models for this new phase will be presented.
Electrochemical Studies of Boron-doped Diamond Electrodes
Authors: Argoitia A. , Martin H. B. , Rozak E. J. , Landau U. , Angus J. C. 
Published: April 2011

ABSTRACTThe evolution of hydrogen and oxygen from a 0.5 M H2SO4 solution on heavily borondoped diamond electrodes was studied. A very wide potential range without water decomposition, from approximately -1.5 to +2.75 V relative to the standard hydrogen electrode, was observed on high quality diamond. A much smaller range, from -0.7 to 1.7 V, and higher background currents were observed on diamond electrodes with significant sp2 content. The Ce(III)/Ce(IV) redox couple was observable on diamond electrodes, but was highly irreversible.
Development of Epitaxial, Tiling, and Cutting Processes for a Diamond Single Crystal Wafer Technology
Authors: Posthill J. B. , Malta D. P. , Humphreys T. P. , Hudson G. C. , Thomas R. E. , Rudder R. A. , Markunas R. J. 
Published: April 2011

ABSTRACTDevelopment of a diamond homoepitaxial deposition process that utilizes water and-ethanol at a growth temperature of ∼600°C is described. Topographies are excellent, and etch-pit densities (EPD) are in the 106cm-2range when growth is done on type Ia C(100) substrates.-This process has been used to epitaxially join diamond single crystals that were bonded in close-proximity to each other. This process of “tiling” single crystal diamonds in close proximity in-order to manufacture a large-area diamond single crystal template is also described. Specially-prepared diamonds that have had their faces and edges oriented to { 100} were coated with-heteroepitaxial Ni, then pressed onto a Si wafer while being heated in an inert gas atmosphere.-The resulting bond is excellent; thereby permitting our 600°C diamond deposition process to-epitaxially join the diamonds. A diamond wafer cutting technology has been addressed using a-specific sequence consisting of: ion implantation, homoepitaxial diamond growth, annealing, and-contactless electrochemical etching. This “lift-off” method of cutting has thus far resulted in a 2mm×O.5mm×17.5μm transparent, synthetic, free-standing, single crystal diamond plate being-fabricated. Raman spectroscopy and EPD show the plate to be comparable to our best-homoepitaxial diamond.
Boron Diffusion Coefficient in Diamond
Authors: Sung T. , Popovici G. , Prelas M. A. , Wilson R. G. 
Published: April 2011

ABSTRACTA study of boron diffusion into diamond lattice was performed. Diffusion was made in hydrogen atmosphere at 30 torr. Two type IIa diamonds were heated at 1200 and 1400 °C for 20 hours and 5 minutes, respectively. Boron powder was used as a dopant source. The boron concentration profiles of both samples were measured by secondary ion mass spectrometry. Based on Fick's law, the diffusion coefficients were computed.
High-Temperature Oxygen Dissolution in Liquid Zirconium
Authors: Molodetsky I. E. , Dreizin E. L. 
Published: April 2011

AbstractThe enthalpy of oxygen dissolution in liquid zirconium occurring during the combustion of Zr particles is estimated. The analysis presented uses direct experimental measurements of the temperature, size, and composition histories of burning Zr particles. The dissolution enthalpy is limited by the range of 700–830 kJ/mol and is somewhat less than that of Zr oxidation. This enthalpy determines the rate of the heat release during Zr combustion until stoichiometric ZrO2 forms out of the supersaturated Zr/O solution. Stoichiometric ZrO2 is formed near the end of combustion and the additional energy released at that time causes a rapid temperature increase which can trigger a particle explosion.
Aminonitroheterocyclic N-Oxides – a New Class of Insensitive Energetic Materials
Authors: Hollins Richard A. , Merwin Lawrence H. , Nissan Robin A. , Wilson William S. , Gilardi Richard D. 
Published: April 2011

AbstractThe need continues for new powerful but insensitive explosive ingredients, which match the performance of RDX with the insensitivity of TATB. One approach has been to take the inherent stability of an aromatic heterocycle, combine this with the explosive insensitivity and thermal stability associated with alternating amino and nitro groups, and to supplement the performance of the molecule with an energy contribution from the N-oxide functionality. The synthesis, characterization and properties (both sensitivity and performance) of aminonitropyridine-l-oxides and aminonitropyrimidine-1,3-dioxides will be described.
From Intelligent Materials to Smart Sensors: a-Si:H Position Sensitive Detectors
Authors: Fortunato E. , Fernandes M. , Soares F. , Lavareda G. , Martins R. 
Published: April 2011

AbstractThis work presents the main static and dynamic performances showed by one dimensional thin film position sensitive detectors (ID TFPSD), based on a-Si:H technology, with a size of 80 mm × 5 mm. The results obtained show that the TFPSD is able to respond to light powers as low as 2μ W/cm2, presenting a detection accuracy, linearity and response frequency better than 10 gm, 2% and 2 KHz, respectively. These results are quite promising regarding the application of these sensors to a wide variety of optical inspection systems where continuous quality control is required.
Amorphous Silicon-Carbon alloys Deposited by Electron-Cyclotron Resonance PECVD
Authors: Chu V. , Conde J. P. 
Published: April 2011

AbstractHydrogenated amorphous silicon-carbon alloys are prepared using electron-cyclotron resonance (ECR) plasma-enhanced chemical-vapor deposition. Hydrogen is used as the excitation gas in the resonance chamber while silane and methane (or ethylene) are introduced in the main chamber. A minimum of 95% hydrogen dilution is used. The microwave power is kept constant at 150 W. The effect of the type of carbon source gas, silane to carbon source gas ratio, deposition pressure, substrate temperature and hydrogen dilution on the deposition rate, bandgap and Urbach energy are studied. The photoconductivity and the Urbach energy of the ECR-deposited films are compared to those prepared with glow discharge with the same bandgap.
Plasma Post-Hydrogenation of Hydrogenated Amorphous Silicon and Germanium
Authors: Beyer W. , Zastrow U. 
Published: April 2011

AbstractIncorporation and kinetics of hydrogen during plasma post-hydrogenation and thermal treatment are discussed for a-Si:H and a-Ge:H films. For material of low hydrogen content, the hydrogen surface concentration reached by plasma treatment equals the hydrogen concentration obtained by deposition at the same temperature and under similar plasma conditions. Enhancements of the hydrogen diffusion coefficient and of hydrogen solubility observed for plasma treatment at temperatures ≤400°C and ≤300°C for a-Si:H and a-Ge:H, respectively, are attributed to a plasma induced rise of the surface hydrogen chemical potential.
Excitation and DE-Excitation of Yb3+ in Inp and Er3+ in Si: Photoluminescence and Impact Ionization Studies
Authors: Gregorkiewicz T. , Tsimperidis I. , Ammerlaan C. A. J. , Widdershoven F. P. , Sobolev N. A. 
Published: April 2011

AbstractIn the paper the existing information on the optical excitation of the erbium ion in crystalline silicon is critically reviewed. The proposed excitation mechanism is compared to the one which is believed to be responsible for the luminescence of ytterbium in indium phosphide. To this end the influence of constant and microwave electric field on the photoluminescence of both systems is inspected. It is shown that, although both systems show some similarities, their analogy is limited.The particular role of excitons and electrons in both the excitation as well as the de-excitation mechanism is investigated for the Si:Er system. The results of photoluminescence decay studies (T=4.2 K) are presented. It is argued that a nonradiative energy transfer to conduction electrons is responsible for the limitation of the energy transfer to the Er core and for its nonradiative recombination. Also, a prominent role of excitons in the energy transfer mechanism is confirmed. Finally, the origin of the 873 meV photoluminescence band recently reported in Er-implanted Si is discussed in relation to a possible defect-mediated activation of Er.
Ohmic Contacts to n-Type 6H-SiC Without Post-Annealing
Authors: Teraji Tokuyuki , Hara Shiro , Okushi Hideyo , Kajimura Koji 
Published: April 2011

AbstractWe formed titanium Ohmic contacts to n-type 6H-SiC epitaxial layer byreducing the Schottky barrier heights. The barrier heights were reduced enough toform the Ohmic contacts by releasing the Fermi level from pinning through makingatomically-flat surfaces. The current transport by thermionic emission wasdominant at the Ti/SiC interface. Since the Ti contacts were formed without postannealing,surfaces of the Ti electrodes were flat and homogeneous maintaining asdepositedstructures. Contact resistivity was (6±1)×10−3 Ω-cm2, which is comparableto that of the annealed Ni contact formed on the SiC epitaxial layer with the samecarrier concentration.
Growth of High Quality (In,Ga,Al)N/GaN Heterostructure Materials and Devices by Atmospheric Pressure MOCVD
Authors: Denbaars S. P. , Keller S. , Keller B. P. , Wu Y. F. , Kapolnek D. , Mishra U. K. 
Published: April 2011

AbstractUsing atmospheric pressure MOCVD we have obtained high quality InGaN/GaN and AlGaN/GaN heterostructure materials and devices. For nominally undoped 4 μm thick GaN films, we obtained 300 K mobilities of 780 cm2/Vs and an unintentional background impurity level of n300K = 6*1016 cm−3. For InGaN/GaN heterostructures we have obtained direct band-edge transitions with FWHM as narrow as 7.9 nm (59 meV) for 50Å thick In0.16Ga0.84N quantum wells at 300K, which is the among the best reported values. The quantum wells display energy shifts towards shorter wavelength with decreasing well thickness, and the shift agrees with predicted quantum effects. These materials have been incorporated into InGaN single quantum well LEDs that emit at 450 nm. In addition AlGaN/GaN heterostructure materials have been incorporated into HFETs and MODFETs. Gate-drain breakdown voltage well exceeding 100 V, and extrinsic transconductance gm of up to 140 mS/mm were realized in the MODFET.
Kinetics Approach To The Growth Of Cubic Boron Nitride
Authors: Taylor C. A. , Clarke Roy 
Published: April 2011

AbstractWe have deposited cubic BN films on silicon (100) using a novel ion-assisted RF-sputtering process. Our efforts over the past several years have enabled us to significantly reduce the ionenergy needed to form the cubic phase, with values now substantially less than 100 eV. Through a better understanding of the growth process we have been able to make improvements in film crystallinity and orientation, with an associated reduction of the high film stress which has severely limited film thickness in the past. The combination of low-energy nitrogen ions and high temperature growth has enabled us to deposit cubic BN films as thick as 1.9 μm. A nucleation study, performed using scanning force microscopy, shows that the cubic BN is nucleating as triangular crystallites, indicative of (111) growth. More specifically, the cubic BN appears to be nucleating on the edges of perpendicularly oriented hexagonal planes such that the cubic BN [ 111] is normal to the hexagonal BN [0002] (c-axis). The results suggest a pathway to “compliant” oriented growth on a variety of substrates.
Lattice-Matched InAsN(X=0.38) on GaAs Grown by Molecular Beam Epitaxy
Authors: Kao Y. C. , Broekaert T. P. E. , Liu H. Y. , Tang S. , Ho I. H. , Stringfellow G. B. 
Published: April 2011

AbstractIn this paper, we report the MBE growth of high nitrogen content lattice-matched InAs1−xNx (x=0.38) single crystal epitaxial films on GaAs. The nitrogen incorporation is about an order higher than previously reported on other mixed group V nitride alloys. These data are consistent with a nitrogen solubility limit calculation in various III-V binary alloys, which predicts orders of magnitude higher nitrogen incorporation in InAs than any other alloys. InAsN growths were obtained using a modified ECR-MBE system with atomic-nitrogen generated by an ECR plasma source. Improved crystal quality was obtained using a “template” growth technique. An x-ray linewidth of 270 arc-s was achieved on a 0.4 μm thick InAs0.62N0.38/GaAs multi-layer structure. Hall effect data show these InAsN films are semi-metallic.
Tetrahedral Amorphous Carbon Thin Film Transistors
Authors: Clough F. J. , Kleinsorge B. , Milne W. I. , Robertson J. 
Published: April 2011

AbstractThis paper describes the design and fabrication of a carbon based thin film transistor (TFT). The active layer is formed from a novel form of amorphous carbon (a-C) known as tetrahedrally bonded amorphous carbon (ta-C) which can be deposited at room temperature using a filtered cathodic vacuum arc (FCVA) technique. In its ‘as grown’ condition, ta-C is p-type and the devices described here, produced using undoped material, exhibit p-channel operation.
Influence of the Growth Atmosphere on the Properties of AIN Grown by Plasma - Assisted Pulsed Laser Deposition
Authors: Ogawa T. , Okamoto M. , Mori Y. , Sasaki T. 
Published: April 2011

AbstractWe have grown highly oriented aluminum nitride (AIN) thin films on Si (100) substrates by using pulsed laser deposition from sintering AIN targets. Three different growth environments, vacuum, nitrogen gas, and nitrogen plasma, have been used in order to investigate the effect of the ambient on the film quality. Rutherford backscattering spectrometry suggests that the N/Al ratio increases when the AIN film is grown in a nitrogen-contained ambient. Cathodoluminescence study implies the decrease of oxygen content in the film grown in a nitrogen plasma ambient.
Atomic Force Microscopy Study of GaN-Buffer Layers on SiC(0001) By MOCVD
Authors: Lim Dongsup , Byun Dongjin , Kim Gyeungho , Nam Ok-Hyun , Choi In-Hoon , Park Dalkeun , Kum Dong-Wha 
Published: April 2011

AbstractBuffer layers promote lateral growth of films due to a decrease in interfacial free energy between the film and substrate, and large 2-dimensional nucleation. Smooth surfaces of thebuffer layers are desired. Optimum conditions for GaN-buffer growth on the vicinal surface of 6H-SiC(0001) were determined by atomic force microscope (AFM). AFM analysis of the GaN nucleation layers led to an optimum growth conditions of the GaN-buffer layer which was confirmed by cross-sectional transmission electron microscopy, Hall measurements and photoluminescence spectra. Optimum growth conditions for GaN-buffer layer on SiC(0001) was determined to be 1 minute growing at 550°C.
Electron Paramagnetic Resonance Studies of Hf-CVD Diamond Films
Authors: Ramakrishnan B. , Keeble D. J. , Rodrigo H. , Kulkarni A. 
Published: April 2011

AbstractDiamond thin films have been deposited on silicon substrates by hot-filament chemical vapor deposition (HF-CVD). Substrate temperature and methane concentration have been varied and the resulting structural properties of the deposited films studied. Raman spectroscopy, scanning electron microscopy and electron paramagnetic resonance (EPR) measurements were performed. The EPR measurements showed a single spectrum at g = 2.0027(2). The bulk concentration of the paramagnetic species, as determined from the total EPR absorption were found to vary in the range 1017 to 1019 cm−3. Low paramagnetic defect concentrations were found for samples exhibiting a low non-diamond carbon contribution to the Raman spectrum. These samples were those grown with a methane concentration of I % or less.
CVD Diamond Wires as X-Ray Detectors
Authors: Manfredotti C. , Fizzotti F. , Galetto M. , Giudice A. Lo , Margherita D. , Ongaro C. , Polesello P. , Vittone E. 
Published: April 2011

AbstractMiniature metal-diamond wire detectors have been fabricated by Hot Filament Chemical Vapor Deposition (HFCVD) method and characterized as x-ray dosimeters in the energy range 50 keV–250 keV. Linearity of the response and the sensitivity as a function of energy have been accurately determined in a range routinely used for x-ray radiotherapy. With a Mo wire substrate, a 10 μm thick CVD diamond film can reach sensitivities of the order of 4×10−8 A/Gy/min, more than one order of magnitude larger than for a 6 cm3 standard ionization chamber.
Material Properties of Sipos Films Prepared by XeCl Excimer Laser Annealing of a-Si:Nx Films
Authors: Choi Hong-Seok , Jun Jae-Hong , Jang Keun-Ho , Han Min-Koo 
Published: April 2011

AbstractThe material properties of laser-annealed a-Si:Nx films were investigated. The a-Si:Nx films for laser-annealing were deposited by rf plasma enhanced chemical vapor deposition (PECVD) with NH3 and SiH4 gas mixtures. At the 0.35 of NH3/SiH4 ratio, the optical band-gap was abruptly increased to 2.82 eV from 2.05 eV by laser-annealing which indicates that Si-N bonding comes to be notable at that ratio. The electrical conductivity showed the maximum value of 4× 10-6 S/cm at the 0.11 of NH3/SiH4 ratio where the grain growth and the increase of Si-N bonding are optimized for the enhancement of electrical conductivity. The σP/σD ratio which is related to the defects states for photo generation centers was decreased with increasing NH 3/SiH 4 ratio. Our experimental data showed that the optical band gap and electrical conductivity of laserannealed a-Si:Nx films were dominantly affected by the NH3/SiH4 ratio at the 250 mJ/cm2 of laser-annealing energy density.
Approaches to modifying solid phase crystallization kinetics for a-Si films
Authors: Kingi Reece , Wang Yaozu , Fonash Stephen , Awadelkarim Osama , Li Yuan-Mn 
Published: April 2011

AbstractThree approaches to modifying the solid phase crystallization kinetics of amorphous silicon thin films are examined with the goal of reducing the thermal budget and improving the poly-Si quality for thin film transistor applications. The three approaches consist of (1) variations in the PECVD a-Si deposition parameters; (2) the application of pre-fumace-anneal surface treatments; and (3) using both rapid thermal annealing and furnace annealing at different temperatures. We also examine the synergism among these approaches.Results reveal that (1) film deposition dilution and dilution/temperature changes do not strongly affect crystallization time, but do affect grain size; (2) pre-anneal surface treatments can dramatically reduce the solid phase crystallization thermal budget for diluted films and act synergistically with deposition dilution or dilution/temperature effects; and (3) rapid thermal annealing leads to different crystallization kinetics from that seen for furnace annealing.
Investigation of Electron Emission From Si and Hot Filament CVD Diamond
Authors: Shim J. Y. , Chi E. J. , Rho S. J. , Baik H. K. 
Published: April 2011

ABSTRACTThe field emission characteristics of the Si emitters and the diamond coated Si emitters are investigated. The Fowler-Nordheim plots of the two types of Si emitters show linear slopes. It means that the I-V characteristics follow the Fowler-Nordheim relation. Field emission for the two types of diamond coated Si emitters exhibits significant enhancement both in turn-on voltage and total emission current. The Raman spectrum shows that the high intensity graphite peak is observed with diamond peak and thereby large amounts of graphite may be included in the diamond grain boundary. It seems to be thought that the graphite participates in the low field emission. However, further investigations are needed to understand whether the graphite may enhance the emission characteristics of diamond or not.
Electroluminescent Diodes Using Cyclohexane-Based Glass Forming Liquid Crystals and Their Analogues
Authors: Lin C. P. , Tsutsui T. , Saito S. , Chen S. H. , Mastrangelo J. C. , Shi H. 
Published: April 2011

AbstractOrganic electroluminescent(EL) diodes using spin-coat films of cyclohexane-based glass-forming liquid crystal (LC) materials were fabricated. The cyclohexane-based LC materials were found to be useful for EL diodes. Blending the LC materials with charge transport molecules was found to be a promising method for improving device performance. Conventional hole transport and electron transport molecules were found to show a tendency to form exciplexes with cyclohexanebased LC materials. This difficulty was overcome by the introduction of cyclohexane-based charge transport molecules. The EL quantum efficiency of 0.06% was attained in the single-layer devices with two-component blends.
Synthesis and Mesomorphic Properties of Chiral Biphenylol Benzoates
Authors: Lu Wan-Fang , Zhang Zhi-Yong , Shang Yong-Jia 
Published: April 2011

AbstractTen new chiral liquid crystalline compounds I1–10 of 4′ -acyl-4-biphenylol (S) -4- (2-methyl-l-butoxy) benzoates were synthesized and their mesomorphic properties were tested. They are all smectic liquid crystals with wide temperature ranges and except for compounds I1, all exhibit a Sc*phase. The influence of molecular structure on phase behavior is discussed.