bluuebunny/crossref_metadata_2025_split huggingface dataset:
Threshold Level Laser Ablation of Yba2Cu3Ox+6 at 351 nm, 248 nm, and 193 nm: Ejected Product Population and Kinetic Energy Distributions
Authors: Wiedeman L. , Helvajian H. 
Published: March 2011

ABSTRACTUsing a sintered Yba2Cu3Ox+6 wafer in high vacuum, we have measured the photo-ejected products and kinetic energies at selected UV laser wavelengths (351 nm, 248 nm, and 193 nm) where the laser fluence is maintained near product formation threshold. At these fluences, we are well below the above surface plasma formation threshold and do not detect; any evidence for surface melting. Our results show that, for a specific laser wavelength, both the ion and the neutral mass spectrum agree. The measured spectrum shows that the photablated products consist only of atomic and diatomic species. In addition, the oxygen is bound only to the yttrium and barium. Our measurements further show that, for a specific ejected species, the yield is dependent on both the laser fluence and wavelength. However, the measured KE distribution is independent of the laser fluence for fluences near threshold. The species are ejected with mean KE between 6–9 eV and no species has kinetic energy in excess of 13 eV Our results imply that for UV laser threshold fluence ablation, the excitation/desorption process is nonthermal.
In Situ Pulsed Laser Deposition of Nd1.85Ce0.15Cu04−y
Authors: Horwitz J. S. , Chrisey D. B. , Osofsky M. S. , Grabowski K. S. , Vanderah T. A. 
Published: March 2011

ABSTRACTWe have deposited thin films of the electron-doped, high temperature superconductor Nd1.85Ce0.15CuO4−y by pulsed laser deposition. Films were deposited from a stoichiometric target using a KrF excimer laser (248 nm, 250 mJ/pulse, −2 J/cm2) as a function of substrate temperature, oxygen pressure and vacuum anneal conditions. The film composition and structure, as determined by RBS and XRD, were very sensitive to the deposition and subsequent anneal conditions. Stoichiometric films were deposited at low substrate temperatures (740 °C) but contained other orientations and phases. Predominantly c-axis oriented films were formed at high substrate temperatures (900 °C) and high background pressures of oxygen (200 mtorr). These films were semiconducting when quenched on oxygen or nitrogen following deposition. Slow cooling in a vacuum, yielded superconducting films with a maximum Tc-(onset) of 15 K and Tc(R=0) of 11 K. A variation of the deposition and anneal conditions indicated that loss of copper competed with the optimization of the carrier concentration.
Laser Deposited Cubic Boron Nitride Films
Authors: Doll Gary L. , Sell Jeffrey A. , Salamanca-riba Lourdes , Ballal Ashwin K. 
Published: March 2011

ABSTRACTWe report the successful growth of cubic boron nitride thin films on single crystal 100 silicon by using pulsed excimer laser ablation of a hexagonal boron nitride bulk target. Optical emission spectra were obtained during the film deposition giving insight into the deposition mechanism. The deposited films were characterized by transmission electron microscopy, scanning electron microscopy, optical microscopy, x-ray diffraction, and Auger electron microscopy. Regions of the films were found to exhibit epitaxy with the substrate.
Cluster Formation in Laser-Induced Ablation and Evaporation of Solids Observed by Laser Ionization Time-Offlight Mass-Spectrometry and Scanning Tunneling Microscopy
Authors: Tench R. J. , Balooch M. , Bernardez L. , Allen Mike J. , Siekhaus W. J. , Olander D. R. , Wang W. 
Published: March 2011

ABSTRACTLaser ionization time-of-flight mass analysis (LIMA) used pulses (5ns) of a frequency- quadrupled Nd-YAG laser (266 nm) focused onto spots of 4–100 μm diameter to ablate material, and a reflectron time of flight tube to mass-analyze the plume. The observed mass spectra for Si, Pt, SiC, and UO2 varied in the distribution of ablation products among atoms, molecules and clusters, depending on laser power density and target material.Cleaved surfaces of highly oriented pyrolytic graphite (HOPG) positioned at room temperature either 10 cm away from materials ablated at 10−5 Torr by 1–3 excimer laser (308 nm) pulses of 20 ns duration or 1 m away from materials vaporized at 10−8 Torr by 10 Nd-Glass laser pulses of 1 ms duration were analyzed by Scanning Tunneling Microscopy (STM) in air with Ångstrom resolution. Clusters up to 30 Å in diameter were observed.
Time Resolved Electroluminescence in a-Si:H p-i-n Junctions
Authors: Carius Reinhard 
Published: March 2011

ABSTRACTTime resolved and steady state electrololuminescence (EL) measurements have been performed in a-Si:H p-i-n junctions at 10K < T < 300K in order to study the recombination in these devices. At low temperatures the rise of the EL following a rectangular forward current pulse consists of a fast component with a time constant of a few μs and a slow component with a time constant of about a ms. The data suggest that the time response of the EL is determined not only by the recombination but also by the time to build up the carrier density for bimolecular radiative recombination. The fast component of the EL is attributed to the field enhanced recombination of carriers which survived from the preceding pulse. Steady state measurements reveal characteristics of bimolecular recombination. The EL spectrum is shifted by 50meV to lower energies with respect to the photoluminescence spectrum.
Optical Phenomena at the Absorption Edge of Crystalline and Amorphous Silicon
Authors: Cody George D. 
Published: March 2011

ABSTRACTOptical phenomena associated with the absorption edge of crystalline silicon (c-Si) and amorphous silicon hydride (a-Si:H) are presented and compared. The optical properties discussed include the energy dependence, dipole matrix element and density of states associated with the absorption edge; the temperature dependence of the relevant optical energy gaps, and finally the magnitude and temperature dependence of the slope of the Urbach edge for each material. The comparison suggests that the optical properties of the two materials are closely related and that the absorption edge of a-Si:H may be derived from the effect of site disorder on the zone center direct gap of c-Si.
Photothermal Investigation of Surfaces and Interfaces in Amorphous Silicon Films
Authors: Amato G. , Boarino L. , Benedetto Giuliana , Spagnolo R 
Published: March 2011

ABSTRACTA method for the determination of surface and interface states is suggested, based on the observation of interference fringe pattern in photo-thermal spectra. Some experimental results are presented and interpreted by means of a theoretical approach. The method allows in most cases to get an evaluation of surface and interface density of states.
Interface Roughness and X-Ray Reflectivity of Amorphous Semiconductor Multilayers
Authors: Persans P. D. , Ruppert A. F. , Pantojas V. , Liang K. , Hughes G. , Abeles B. 
Published: March 2011

ABSTRACTWe report high-resolution small-angle x-ray reflectivity measurements on plasma-deposited a-Ge:H/a-Si:H periodic amorphous multilayers. We show that reflectivity spectra are quite complex, involving components due to relatively smooth and rough layer interfaces at different depths in the sample respectively. Model computations show that interface roughness increases from 3 É at the substrate-sample interface to more than 15 É at the top surface of a 0.5 μm multilayer stack.
Space Charge Profiles in Thick Amorphous Silicon Diodes
Authors: Hollingsworth Russell E. , Xi Jianping , Buitrago Roman 
Published: March 2011

ABSTRACTAmorphous silicon p-i-n diodes with intrinsic layer thickness exceeding 50 microns have been produced. As a probe of the carrier collection, reverse bias collection efficiency measurements using weakly absorbed light were performed. The results have shown for the first time that amorphous silicon diodes of such thickness can be fully depleted. By analyzing the shape of the collection efficiency curve, profiles of the light induced space charge within the intrinsic layer are obtained. The space charge density in thick devices is found to vary strongly with position in the intrinsic layer as well as with excitation intensity.
Effect of Residual Phosphorus on Amorphous Silicon Thin Film Transistors
Authors: Tsutsu Hiroshi , Kawamura Tetsuya , Miyata Yutaka 
Published: March 2011

ABSTRACTEffects of residual phosphorus in the channel region of amorphous silicon thin film transistors(a-Si TFTs) on the TFT characteristics were quantitatively investigated. Concentration and the depth profile of the residual phosphorus were measured by high resolution secondary ion mass spectroscopy(SIMS). The OFF characteristics of a-Si TFTs were also measured.The SIMS data showed that the phosphorus exists about 100nm deep into intrinsic a-Si(i-a-Si), but the OFF characteristics showed that the activity of the residual phosphorus is 4 order of magnitude lower than that of heavily phosphorus doped a-Si(+-a-Si). The residual phosphorus is found to be inactive and stable, and has little effect on a-Si TFT characteristics.These results enabled us to fabricate inverted staggered a-Si TFTs by the simplest process using only 2 photo-mask steps and 1 self-aligned exposure.
The Programmability of Amorphous Silicon Analogue Memory Elements
Authors: Hajto J. , Rose M. J. , Snell A. J. , LeComber P. G. , Owen A. E. 
Published: March 2011

ABSTRACTThis paper outlines recent results from work on non-volatile, analogue switching effects in amorphous silicon devices. The implication for the switching mechanism of these results and also the technological applications of such analogue devices are discussed. Particular reference is made to their use as re-programmable, non-volatile weighting elements in neural network synapses.
Compensating for Light Soaking Effects in Optically Addressed Spatial Light Modulators Incorporating A-Si:H Photodiodes
Authors: Walker C. M. , Landreth B. , Moddel G. 
Published: March 2011

ABSTRACTWe characterize the effects of light soaking on optically addressed spatial light modulators (OASLMs) incorporating a-Si:H photodiodes and relate these effects to the light-induced degradation observed in the photodiodes. After illuminating the OASLMs with white light for up to 100 hours, the rise time of the OASLM optical response decreases, the fall time increases, and the undesirable modulation in the absence of write light (electrical modulation) also increases. We were able to compensate for these effects and approximately restore the original optical transfer characteristics by applying a dc offset voltage across the device. The results can be interpreted by considering series resistance changes in the a-Si:H photodiode.
Growth of Amorphous, Microcrystalline, and Epitaxial Silicon in Low Temperature Plasma Deposition
Authors: Tsai C. C. , Anderson G.B. , Anderson R. 
Published: March 2011

ABSTRACTThis paper examines near-equilibrium and non-equilibrium film formation processes in the plasma deposition of Si and their effects on network propagation, defect generation and interface quality based on the concept of film formation as a balance between deposition and ‘etching.’ Using non-F reactant gases and conventional PECVD, epitaxial Si growth was achieved at 250°C. By adjusting the extent of ‘etching’, one can selectively obtain amorphous, microcrystalline, polycrystalline, and epitaxial Si using similar process gases and reactors.
Hydrogenated Silicon Films Prepared by Remote Plasma CVD
Authors: Kim Sung Chul , Lee Seung Kyu , Soe Sung Mo , Koh Sung Ok , Ihm Sung Shil , Jun Jung Mok , Kim Tae Gon , Chung Moon Hyun , Lee Kyung Ha , Song Hyon Kynn , Jang Jin , Hwang Jung Tae , Chung Kwan Soo 
Published: March 2011

ABSTRACTWe have studied the improvement of the quality of undoped a-Si:H deposited by remote-plasma chemical vapour deposition. The effects of reactant gas concentration, rf power, substrate bias voltage on the electrical and optical properties have been investigated. Some hydrogen dilution of si lane improves the photoeletric property and a high rf power gives rise to the defect creation due to the ion bombardment on the growing surface. The positive substrate bias improves the quality of undoped a-Si:H.
The Low-Temperature Metal-Organic Chemical Vapor Deposition (Ltmocvd) Route to Amorphous Silicon Semiconductors
Authors: Kaloyeros Aain E. , Corbett James W. , Tobcano Paul J. , Rizk Richard B. 
Published: March 2011

ABSTRACTPreliminary results are presented for a new approach proposed by the present investigators to solve the problem of light-induced degradation in amorphous silicon semiconductors. The approach uses low-temperature metal-organic chemical vapor deposition (LTMOCVD) of tailored organometallic precursors. The precursors employed are non-toxic, non-hazardous and easy to handle. In the present paper, a-Si:H films were grown, using argon with various hydrogen concentrations as carrier gas, in a cold-wall CVD reactor at a reactor pressure of 1-10 torr and substrate temperature in the range 300–450°C. Characterization studies were performed using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and extended electron-energy-loss fine structure spectroscopy (EXELFS). The results of these studies showed that the films were uniform, continuous, adherent and highly pure--contaminant levels were below the detection limits of XPS. In addition, EXELFS results showed that short-range order (SRO), consisting of the same tetrahedral coordinated units found in crystalline silicon, does exist in all the amorphous samples, regardless of hydrogen concentration. However, the degree of stuctural disorder in the silicon local tetrahedral units decreased as hydrogen was added.
Measurements of the Transient Photoconductivity During the Growth of A-Si:H Multilayers
Authors: Neitzert H. C. , Werner A. , Kunst W. , Kunst M. 
Published: March 2011

ABSTRACTThe deposition process of multiple layer structures of intrinsic and p-type hydrogenated amorphous silicon was followed by measuring the microwave detected transient photoconductivity (TRMC) during the film growth. In an i-p-i structure we can show that after deposition of an upper layer of about 500 nm, former deposited layers do not influence the TRMC-signal any more. In an i-p+-i-p structure we can clearly distinguish between p-layers of different doping concentration.
Optical Studies of Microstructure in a-Si:H
Authors: Vaněček M. , Červinka D. , Favre M. , Curtins H. , Shah A. V. 
Published: March 2011

ABSTRACTA set of samples grown under different substrate temperature has been characterised by complex optical, photoelectrical and transport measurements. A very sensitive and simple method for detection of optical scattering in a device quality amorphous silicon has been demonstrated. The spectral dependence of the optical scattering coefficient αs(E) can give us information on the nature and concentration of the scattering centers in a-Si:H thin films.
Hydrogen Stability in Hydrogenated Amorphous Germanium
Authors: Beyer W. , Herion J. , Wagner H. , Zastrow U. 
Published: March 2011

ABSTRACTThe thermal stability of hydrogen in hydrogenated amorphous germanium films was studied by hydrogen evolution and by deuterium and hydrogen inter-diffusion experiments. Similar to a-Si:H, the hydrogen stability in a-Ge:H is found to depend strongly on the film structure and on the position of the Fermi level.
Thermally-Induced Change of Conductivity and Defect Density in Amorphous Silicon-Germanium Alloys
Authors: Shimizu Tatsuo , Xu Xixiang , Sasaki Hiroyuki , Yan Hui , Morimoto Akiharu , Kumeda Minoru 
Published: March 2011

ABSTRACTThermally-induced metastable phenomena in amorphous silicon-germanium alloys were studied by conductivity and ESR measurements. Fast cooling from 250 °C reduced both dark- and photo-conductivities by a factor of 3–4 while the neutral defect density remained unchanged. Thermally-induced change in conductivity relaxed towards equilibrium with a stretched exponential form. The thermal equilibrium temperature was found to be roughly proportional to the optical gap for a–Si:H, a–Sii−xCx:H, a–Si1−xNx:H and a–Si1−xGex:H:F.
Hydrogen Diffusion in a-Sic:H
Authors: Demichelis F. , Pirri C. F. , Tresso E. , Amato G. , Della Mea G. 
Published: March 2011

ABSTRACTIn order to improve our understanding of the motion of hydrogen and the mechanism by which structural changes occurr, two sets of a-SiC:H samples obtained by glow-discharge at different substrate temperatures and power densities, respectively without and with hydrogen flow, were analyzed.Results from structural, optical and electrical measurements show that annealing and hydrogen diffusion allow for a possible reorganization of the a-SiC:H amorphous network.
Material Properties of P-Type A-Sic Layers Using Either Diborane or Trimethylboron as Doping Gas
Authors: Lechner P. , Gorn M. , RÜbel H. , Scheppat B. , Kniffler N. 
Published: March 2011

ABSTRACTHydrogenated amorphous SiC:H films prepared by rf glow discharge from a silane-methane mixture have been B-doped either from diborane or from trimethyl boron (TMB). In the latter a higher hydrogen content is found explaining a higher Tauc optical gap EG, however also a lower dark conductivity for the same boron concentration in the film. Thus the figure of merit of our p-layers doped from TMB is not improved. Further the observed narrowing of the Tauc gap could not be correlated with a decrease of the hydrogen content at high B-doping. The reduction of EG is mainly explained by a drastic broadening of the absorption edge caused by creation of boron induced defects and structural disorder but not due to a shift of the absorption edge.
The Movement of Mobility Edges in Hydrogenated Amorphous Silicon
Authors: Lee S. , Heller D. , Wronski C. R 
Published: March 2011

ABSTRACTInternal photoemission of both electrons and holes is used to investigate the movement of the mobility edges in high quality intrinsic, undoped hy-drogenated amorphous silicon (a-Si:H) with temperature and electrical field. The electron mobility edge is found to move up in energy by ∼40meV between 298K and 120K. On the other hand, the hole mobility edge remains essentially unchanged between 298K and 160K. The injection (and collection) of photoemitted holes is less efficient than that for electrons and in the films studied could not be measured below 160K.
Theoretical Calculations of the Nonlinear Dielectric Function of Inhomogeneous Thin Films
Authors: Risser Steven M. , Ferris Kim F. 
Published: March 2011

ABSTRACTThe optical response of thin dielectric films can be influenced by grain morphology and the presence and distribution of defects. In the limit of random defects and small electric field amplitudes, approximate methods exist to model the real part of the dielectric constant in terms of volume fractions and bulk dielectric constants of the film components. Explicit inclusion of nonlinear polarizabilities and details of the microstructure, such as particle phase, shape, and orientation requires a more exact approach.We have developed a method to self-consistently determine the local internal electric field and polarization in the long wavelength limit for model films with a random distributions of defects of arbitrary phase and orientation. From this we have calculated the real part of the dielectric constant as a function of nonlinear polarizability of the components, and have shown the effect of defect phase and orientation on the dielectric constant of the film.
Elastic Constants in C-plane of Single Crystal Bi 2Sr 2Ca Cu 208 between 80 K and 260 K
Authors: Wu Jin , Wang Yening , Yan Yifeng , Zhao Zhongxian 
Published: March 2011

ABSTRACTThe temperature dependence of the in-plane C11 C22. C12 and C66 modes between 80 and 260 K of superconducting crystals of Bi2Sr2Ca1Cu208 have been obtained via the measurements of ultrasonic-velocities. The anisotropic elasticity in the a-b plane of single crystal Bi2 Sr2Ca1Cu2O8 is manifest. The shear modulus of sound propagation along the [110] with the polarization has been also calculated and shows an overall trend of softening over a wide temperature range above Tc. The shear modulus C6 6 shows three obvious softening minima around 240–250 K, 150 K and 100 K.
Electronic Structures at Metal/Alumina Interfaces
Authors: Kohyama M. , Kose S. , Kinoshita M. , Yamamoto R. 
Published: March 2011

ABSTRACTThe electronic structure of the interface between α-Al2O3(0001) and Nb layers has been calculated using the empirical tight-binding method and the slab model. It has been shown that a direct chemical bond of both covalent and ionic characters can be established at the interface between the surface O atoms of α-Al2O3 and the Nb atoms, which is consistent with the recent photoelectron spectroscopy study. General trends of the electronic structure and chemical bond at the interfaces between α-Al2O3.(0001) and a series of 4d transition metals have been examined using the same theoretical method. In all cases, there exist similar interactions between the surface O atoms and the metal atoms, and it has been observed that the occupancy in the portion of the antibonding peaks of the local density of states at the interface increases as the atomic number of the transition metal increases.
Dynamical Simulation of the Motion of Curved Grain Boundaries Composed of Pyramidal-Shaped Ledges
Authors: Jhan Re-Jhen , Bristowe P. D. 
Published: March 2011

ABSTRACTA dynamical simulation of curved grain boundaries composed of pyramidal-shaped ledges has shown that the boundaries can move by local conservative shuffles of atoms or groups of atoms such that one adjoining crystal grows at the expense of the other. In the model system studied, the shuffles often take the form of correlated rotational displacements about the axis normal to the boundary. The simulations provide support for the atomic mechanism proposed by Babcock and Balluffi to explain their observation of grain boundary migration without the participation of SGBDs.
Molecular Dynamics Simulations of Cluster Impacts on Metallic Targets
Authors: Shapiro Mark H. , Tombrello T. A. 
Published: March 2011

ABSTRACTA modified version of the multiple-interaction code SPUT2 has been used to simulate impacts of 63-atom Cu clusters on six–layer Cu targets. Simulations were carried out with cutoff times of 100 and 500 fs for an incident cluster energy of 63 keV (1 keV/atom). Significant enhancements were observed in the maximum potential and kinetic energies achieved in the early phase of the collision cascade. Some hard collisions yielded atoms with potential energies as high as 925 eV (in the CM frame). This is almost twice the energy allowed in an isolated two-body collision. The number of hard collisions per time-step vs potential energy is well-fitted with a decaying exponential, allowing extrapolation to higher energies. These results together with similar results for Al clusters impacting Au targets suggest that non-linear collisional effects cannot explain the high D–D fusion rates seen in Beuhler, Friedlander, and Friedman's recent experiment [l].
Favored Boundaries in the Structural Unit Model of Grain Boundaries
Authors: Khantha M. , Vitek V. , Goldman M. 
Published: March 2011

ABSTRACTA systematic geometrical procedure for predicting favored boundaries in the structural unit model is presented. The method is applicable to both symmetric and asymmetric tilt boundaries. The predictions are confirmed by modeling the structures of tilt boundaries belonging to low symmetry ( and [221]) axes in f.c.c. and b.c.c. structures. The results confirm the applicability of the structural unit model for relatively high-index tilt axes.