bluuebunny/crossref_metadata_2025_split huggingface dataset:
Self-Formation of Au Microwires on Au-Covered Si Electrode Surface by Electrochemical Etching in Dilute Hydrofluoric Acid Solution
Authors: Kimura Yasuo , Nemoto Jun , Kusakabe Atsushi , Kondo Yusuke , Niwano Michio 
Published: April 2011

AbstractWe have investigated the method of fabricating microstructures on a Si surface that is covered with a patterned gold (Au) mask, by electrochemical etching (anodization) in dilute hydrofluoric acid (HF) solution. We found that at electrode potentials below approximately 0.5 V, the Si surface is preferentially etched on the fringe of the Au mask, where a number of pores are formed. At higher electrode potentials, Au microwires with about 1 µm in width form along the fringe of the Au mask overlayer. We suggest that electromigration of Au towards the fringe of the Au mask induces self-assembling of Au atoms to form microwires. The observed self-formation of metal microwires would be beneficial to the fabrication of metal micro- or nano-structures on Si.
Development of Silicon-Based UV-Photodetector Prototypes using Photoluminescent Nanocrystalline Silicon Overlayers
Authors: Navarro Carlos , Fonseca Luis F. , Nery Guillermo , Resto O. , Weisz S. Z. 
Published: April 2011

AbstractThe maximum photoresponse of a normal silicon photodetector, that uses a p-n junction as the active zone, is obtained when the incident radiation wavelength is around 750nm. This response diminishes significantly when the incident radiation is near or in the UV region. Meanwhile, nanocrystalline silicon (nc-Si) films with high transparency above 650nm and high absorbance in the UV can be prepared. By quantum confinement effects, a fraction of this absorbed UV energy is re-emitted as visible photons that can be used by the junction. We study the enhancement of the UV-photoresponse of two silicon detector prototypes with a silicon p-n junction active zone and with a photoluminescent nc-Si overlayer. One prototype is made with a porous silicon/n-type silicon/p-type silicon/p++-silicon/metal configuration and the other with an Eu-doped Si-SiO2 overlayer instead of the porous silicon one. The comparison between both prototypes and the control is presented and discussed stressing on the enhancement effect introduced by the photoluminescent overlayers, stability and reproducibility.
Quantum Effects on the Dielectric Function of Porous Silicon
Authors: Cruz M. , Díaz S. F. , Wang C. , Rubo Y. G. , Tagüeña-Martínez J. 
Published: April 2011

AbstractIn this work, the imaginary part of the dielectric function of porous silicon is studied by means of both the tight-binding and the effective medium approaches, in the latter exact result is obtained for the case of 50% porosity. Within the tight-binding approximation, the dielectric function is calculated by using the interconnected and chessboard-like supercell models for the Si skeleton. These microscopic models give quantitatively similar results, which are by a factor of three larger than those from the effective medium theory.
Size Reduction of Silicon Nanopillars by Photo-Electrochemical Etching
Authors: Juhasz Robert , Linnros Jan , Kleimann Pascal 
Published: April 2011

AbstractSilicon nanopillars, formed by electron beam lithography, were electrochemically etched to provide controlled size reduction. The smallest dimensions achieved were pillars of 15 nm in diameter, restricted mainly by the scanning electron microscope used for characterization. The etch rate was mainly determined by the photogeneration of carriers, by the HF concentration and by the applied voltage bias. The applied bias also controlled the resulting shape of the pillars such that a high bias resulted in etching of the pillar top whereas a negative bias caused etching only at the pillar base. For 0 V, a relatively conform etching of the pillar was observed. We discuss these phenomena in terms of electropolishing or pore formation effects on a local scale.
Electronic Structure of GaN Quantum Dots with an Adjacent Threading Dislocation
Authors: Andreev A. D. , Downes J.R. , O'Reilly E. P. 
Published: April 2011

ABSTRACTWe present a theoretical analysis of the electronic structure of GaN quantum dots (QD) with an adjacent threading dislocation. The QD carrier spectra and wavefunctions are calculated using a plane-wave expansion method within an 8-band k.p model. The method is very efficient, because the strain and built-in electric fields can be included through their discrete Fourier transforms. The QD structures considered have been analysed experimentally by other groups. The GaN QDs are truncated hexagonal pyramids on a wetting layer with an edge dislocation adjacent to each dot. The built-in piezoelectric potential strongly influences the localisation of the carrier wavefunctions. This potential pushes the electrons to the top of the dot, the holes to the bottom and, additionally, causes strong lateral confinement of the carriers. The effect of the dislocation strain field at the dot edge on the carrier states in each GaN/AlN QD is shown to be insignificant. Results are presented for the confined state energies and optical matrix elements for a range of different sized dots with and without dislocations. The size of the dot influences the energies and overlaps, but the presence of the dislocation has minimal effect. The dependence of the ground state optical transition energy on the size of the dot is in good agreement with experimental data.
Metal-Semiconductor Contacts and CPW MMIC Issues for AlGaN/GaN FETs
Authors: Jacobs Bart , Kramer Mark , Straaten Bram van , Kwaspen Thieu , Karouta Fouad , Hek Peter de , Dijk Raymond van , Vliet Frank van 
Published: April 2011

ABSTRACTIn this report two different aspects in the development of AlGaN/GaN power amplifiers will be discussed. In the first part of this paper we report on the optimization of the Ti/Al/Ni/Au metallization scheme on a doped AlGaN/GaN FET structure. By a systematic investigation we were able to reduce the contact resistance to 0.2 ωmm (7.3×10×7ωcm2). The Al/Ti thickness ratio for this contact was 6, which according to the Al-Ti binary phase diagram, does not result in excess Ti which should react with nitrogen in the AlGaN layer to render the surface heavily doped. Preliminary results on Schottky contacts indicate an improvement in the reverse leakage current if a RIE oxygen plasma in combination with a NH4OH dip is performed prior to metallization.Coplanar waveguides on AlN are discussed in the second part of this paper. These transmission lines can be used in AlGaN/GaN power amplifiers if no via-hole technology is available or if a hybrid solution is pursued. The signal line should have a large metal cross- sectional area (> 5 × 50 [.proportional]m2) in order to carry enough current in the output stage of an amplifier. It is shown that CPWs with large dimensions show non-quasi TEM behavior related to propagation of parallel plate modes.
Influence of Er depth profiles on luminescence properties of Er-doped GaN
Authors: Uekusa Shin-ichiro , Hirano Tomoaki 
Published: April 2011

ABSTRACTErbium (Er) ions were implanted into gallium nitride (GaN) and the temperature-dependent photoluminescence (PL) and PL lifetime were characterized. Thermal quenching of the Er3+ luminescence was restrained by using GaN as a host material and PL was observed from Er3+ at room temperature. We prepared a flat depth profile of the density distribution of Er by ion-implanted into GaN and monitored the thermal quenching process due to the residual defects after implantation and annealing. We also monitored the auger effect that is believed to be the main cause of the thermal quenching process and concluded that, in the temperature range 15 K to 100 K, the thermal quenching process is dominated by nonradiative recombination from the first excited state (4I13/2) to the ground state (4I15/2) of Er3+.
Optical and Electrical Properties of Al1−xInxN Films Grown on Sapphire (0001) by Plasma Source Molecular Beam Epitaxy
Authors: Danylyuk Y. V. , Lukitsch M. J. , Huang C. , Auner G. W. , Naik R. , Naik V. M. 
Published: April 2011

ABSTRACTA series of epitaxial InxAl1−xN alloy films (thickness ~ 150 nm) with 0 ≤ × ≤ 1.0 were grown by Plasma Source Molecular Beam Epitaxy (PSMBE) on sapphire (0001) at a low substrate temperature of 375 °C. X-ray diffraction (XRD) measurements confirm ac-axis oriented epitaxial growth of alloy films without any alloy segregation. However, the degree of crystalline mosaicity, compositional fluctuation and surface roughness, all increase with increasing x. The direct energy band gap of alloy films were determined using optical (UV-VIS) transmission and reflection measurements. The observed bowing of the direct gap versus x plot, when compared to the theoretical prediction, is less pronounced than seen in earlier studies reported in literature. Electrical resistivity and Hall effect measurements show n-type electrical conductivity in these alloys with carrier concentrations ~1019-1020cm−3for x > 0.5.
Visible Emission from Thin-Film Phosphors of Amorphous AlN:Cu, Mn, and Cr
Authors: Caldwell M. L. , Martin A. L. , Spalding C. M. , Patten P. G. Van , Kordesch M. E. , Richardson H. H. 
Published: April 2011

ABSTRACTLuminescence studies of amorphous AlN doped with Cu, Mn, or Cr were performed at 300 K. Thin films of Cu, Mn, and Cr doped amorphous AlN, ∼200 nm thick, were grown on p-doped silicon (111) substrates using RF magnetron sputtering in a nitrogen atmosphere. Cathodoluminescence (CL) showed that pure Cu doped amorphous AlN has strong emission in the blue (∼420 nm) and Mn and Cr doped films luminesce in the red (∼690 nm). Cr+3 emission is more intense than Mn+4 because chromium does not suffer from incomplete charge compensation in the III-V semiconductor. Luminescence studies of crystalline and amorphous AlN:Mn thin films showed a red shift in the emission peak by almost 100 nm and is believed to be caused by the different crystal field of the amorphous host compared to the crystalline host material. Secondary ion mass spectrometry (SIMS) depth profiling was conducted to confirm the presence of the Cu and Cr in the films and to show the amount of dopant in relation to the Si substrate.
A High-Temperature STM-Study of Iron Silicide Formation on High Index Silicon Surfaces
Authors: Kneppe Martin , Kot Evgueni , Dorna Volker , Kahler Ulrich 
Published: April 2011

AbstractThe nucleation and initial growth of iron silicide on Si(113), Si(5 5 12) and Si(114) is studied using high temperature STM. During MBE and gas source deposition (precursor Fe(CO)5 STM-“movies” at temperatures up to 600°C directly show the kinetics of silicide formation on the surface. A complete 2D-wetting layer is formed on all vicinal surfaces for temperatures below 510°C. A chain-like silicide structure with a mixture of different periodicities (4×n), with n ranging from 2-6, is found. Above one monolayer growth proceeds with anisotropic 3D-silicide-islands. The wetting layer was found to be only metastable at lower growth temperature. At temperatures above 510°C the 2D-silicide layer does not wet the substrate anymore. In the equilibrium growth mode, 3D-islands directly grow on the bare Si-substrate. The anisotropy of the 3D-islands is extremly temperature dependent resulting in an aspect ratio up to 50 at 600°C. Especially on Si(114) a one-dimensionally nanostructured silicide layer can be grown in this way. A lateral spreading of the 3D-islands forming an interconnected silicide layer is achieved on Si(113) by a stochiometric codeposition of Fe and Si.
Relationship Between Graded Layer Structures and Defects in Silicon-Germanium Virtual Substrates
Authors: Mizushima Kazuki , Shiono Ichiro , Yamaguchi Kenji , Muraki Naoki 
Published: April 2011

AbstractSilicon-germanium virtual substrates have been synthesized by low-pressure chemical vapor deposition. We obtained threading dislocation densities ranging from 105 to 106 cm−2, surface roughness ranging from 1.5 to 4 nm, and also cross-hatch pattern densities, depending on the grading rate and top layer germanium composition. For the typical sample, which has a linear-graded structure with a grading rate of 20%/[µm, and germanium composition of 30 % at the top layer, we obtained dislocation densities of about 106 cm−2 and root mean squared surface roughness of about 3 nm. The obtained dislocation densities are equivalent with the virtual substrates synthesized by ultra-high vacuum system. On the other hand the surface roughness is superior to the typical reported values. In this study three kinds of structures, i.e. linear-graded, stepwise, and graded-step structures, were considered. We found the defects are effectively reduced by introduction of an optimum number of steps in the graded layer.
Electronic Structure of Ag/Cu/Ag/Cu(111) Double Nanofilm Structures Studied by Angle-Resolved Photoemission Spectroscopy
Authors: Tanaka Akinori , Takahashi Kazutoshi , Sasaki Hiroyuki , Suzuki Shoji , Sato Shigeru 
Published: April 2011

AbstractWe have carried out an angle-resolved photoemission study of double Ag nanofilm structures, composed of an outer Ag nanofilm / Cu barrier layer / inner Ag nanofilm / Cu(111) substrate. From these results, we discuss the electronic coupling between the quantized electronic states in the double Ag nanofilm structures with various configurations.
Simulations of molecular beam epitaxy growth of GaAs
Authors: Zhang Z. , Orr B. G. 
Published: April 2011

AbstractNumerical simulations have been performed for generic III-V MBE growth. The key aspects of the simulation include two deposited species one volatile and the second with high surface mobility. Simulations reproduce the experimentally observed adatom concentrations for GaAs and show that smooth surfaces are produced for films deposited with a substrate temperature in a crossover regime between kinetically limited and entropically roughened growth.
Ultra-Thin Zirconium Silicate Filmsc With Good Physical And Electrical Properties For Gate Dielectric Applications
Authors: Dharmarajan Easwar , Qi Wen-Jie , Nieh Renee , Kang Laegu , Onishi Katsunori , Lee Jack C. 
Published: April 2011

AbstractThe need for alternative gate dielectrics to replace conventional SiO2 is increasing to facilitate further CMOS scaling. One of the most promising materials for use as an alternative gate dielectric is Zr silicate due to its thermodynamic stability on Si and its good interface quality with Si. In this study, ultra-thin Zr silicate films (45 – 60 Å thick) with different Zr compositions have been deposited on Si using magnetron reactive co-sputtering. The Zr composition was kept below the stoichiometric value of about 16% to prevent precipitation of ZrO2and to have Si rich films for better interface quality. Films were rapid thermal annealed in N2 ambient up to 9000C and Pt was used as the gate electrode. Electrical characterization of these films was done using HP 4156 and HP 4194 parameter analyzers. Based on these studies, we demonstrate Zr silicate films with equivalent oxide thickness (EOT) of less than 14 Å with gate leakage significantly lower thanSiO2 of similar thickness and hysteresis of < 20mV ( in a sweep from –3 to 3 V). The films exhibit good thermal stability on Si even after 900 0C annealing as shown by a minimal increase in EOT with annealing. TEM and XPS analyses show high quality Zr silicate films that remain stable and amorphous even at 900 0C.
Characteristics of Laser-Ablated Plasma and Properties Of Diamond-Like Carbon Film In Pulsed Laser Deposition
Authors: Yamagata Yukihiko , Ohshima Tamiko , Ikegami Tomoaki , Thareja Raj K. , Ebihara Kenji , Sharma Ajay , Mayo Robert M. , Narayan Jagdish 
Published: April 2011

AbstractCharacteristics of laser-ablated carbon plasma and properties of diamond-like carbon film in KrF pulsed laser deposition were investigated using laser-induced fluorescence (LIF) and optical emission spectroscopy. Two-dimensional LIF images of C2 (Swan band, d3Φg – a3Φu) and C3 (Comet Head System, A1Φu –X1Σg+) molecules were detected as a function of laser energy density by narrow band pass filters and an intensified CCD camera. C2 LIF intensity is found to be weaker in the central part of the plume than that at the periphery at incident energy greater than 6 J/cm2. It is conjectured that C2 molecules are dissociated by collision with energetic species in the central part of the ablation plume, and degrade the diamond-like property of deposited films.
Growth of AlN and TiN Structures by Plasma-Enhanced Pulsed Laser Deposition
Authors: Poindexter Edward , Xin Yan , Durbin Steven M. 
Published: April 2011

AbstractNitride materials are of interest for a wide variety of applications, including wear-resistant coatings, insulating layers, high-temperature semiconductor devices, and short-wavelength emitters and detectors. TiN and AlN appear to be particularly amenable to crystalline thin film deposition, with stoichiometric material easily obtained even without the use of active nitrogen species. This paper describes the growth of crystalline AlN and TiN thin films on silicon and sapphire substrates using a KrF excimer laser (λ = 248 nm) to ablate elemental metallic targets, and an inductively-coupled RF plasma source to supply active nitrogen species. Growth was monitored in-situ using reflection high-energy electron diffraction (RHEED), and films were characterised using fourier-transform infrared spectroscopy (FTIR) and electron microscopy techniques. Optimised growth conditions led to single-crystal growth of TiN on both substrates, but only polycrystalline AlN was formed directly. Use of a TiN buffer layer on (0001) sapphire led to the successful growth of a single-crystal AlN layer as confirmed by RHEED and high-resolution transmission electron microscopy (HRTEM).
The Heteroepitaxial Nucleation and Growth of Metal Oxides by Llvsztu Oxidation
Authors: Bharadwaj Mridula D. , Zhou Gnang-wen , Yang Judith C. 
Published: April 2011

AbstractHere we report our investigations on the initial stages of Cu(OO1) oxidation in dry and moist atmosphere using in situ ultra high vacuum (UHV) transmission electron microscopy (TEM), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Cu20 islands were observed to grow 3-dimensionally into the Cu film as seen through the above mentioned techniques. Further, we discuss our interpretation of the experimental observations that presence of water vapor in the oxidizing atmosphere retards the rate of Cu oxidation and Cu20 shows surprising reduction when exposed to water vapor.
Modeling Gas Separation Membranes
Authors: Malanoski Anthony P. , Swol Frank van 
Published: April 2011

AbstractRecent advances in the development and application of self-assembly templating techniques have opened up the possibility of tailoring membranes for specific separation problems. A new self-assembly processing route to generate inorganic membrane films has made it feasible to finely control both the three-dimensional (3D) porosity and the chemical nature of the adsorbing structures. Chemical sites can be added to a porous membrane either after the inorganic scaffolding has been put in place or, alternatively, chemical sites can be co-assembled in a one-step process. To provide guidance to the optimized use of these ‘designer’ membranes we have developed a substantial modeling program that focuses on permeation through porous materials. The key issues that need to be modeled concern 1) the equilibrium adsorption behavior in a variety of 3D porous structures, ranging from straight pore channels to fractal structures, 2) the transport (i.e. diffusion) behavior in these structures. Enriching the problem is the presence of reactive groups that may be present on the surface. An important part of the design of actual membranes is to optimize these reactive sites with respect to their strength as characterized by the equilibrium constant, and the positioning of these sites on the adsorbing surface. What makes the technological problem challenging is that the industrial application requires both high flux and high selectivity. What makes the modeling challenging is the smallness of the length scale (molecular) that characterizes the surface reaction and the confinement in the pores. This precludes the use of traditional continuum engineering methods. However, we must also capture the 3D connectivity of the porous structure which is characterized by a larger than molecular length scale. We will discuss how we have used lattice models and both Monte Carlo and 3D density functional theory methods to tackle these modeling challenges.
Probing Dynamics of water Molecules in Mesoscopic Disordered media by NMR Dispersion and 3D Simulations in Reconstructed Confined Geometries
Authors: Levitz P. , Korb J.P. , Quynh A. Van , Bryant R.G. 
Published: April 2011

AbstractDisordered mesoporous materials with pore sizes ranging from 2 nm to some 10 nm develop large specific surface areas. These matrices can be easily filled with polar fluids And the interfacial region between the solid matrix and the pore network strongly influences the molecular dynamics of the entrapped fluid. A promising way to probe such a coupling on a large time-scale is to look at the dispersion of the nuclear spin-lattice relaxation rate of the polar liquid using field cycling NMR relaxometry technique. We have performed such an experiment on a fully hydrated porous Vycor glass, free of electron paramagnetic impurities. The proton nuclear magnetic relaxation rate (1/T1) exhibits a logarithmic dependence on Larmor frequency over the range from 0.01 to 30 MHz. A cross-over is observed below 0.1 MHz. In order to understand the relationship between geometric disorder, interfacial confinement, and nuclear magnetic relaxationdispersion (NMRD), we first compute an off-lattice reconstruction of the Vycor glass This model agrees with available experimental data (specific surface, porosity, chord length distributions, small angle scattering and tortuosity). A Brownian dynamics simulation is performed to analyze long time molecular self-diffusion and NMRD data. These later are well reproduced and appear to be connected with the translation diffusion of water near the SiO2 interface. The logarithmic character of the NMRD is specifically related to the interfacial geometry of the Vycor glass. Several other multiconnected interfacial structures such as periodic minimal surfaces do not exhibit such an evolution. Therefore, NMRD appears to be selectively sensitive to the interfacial geometry of mesoscopic disordered materials (MDM).
Probing Confining Geometries with Molecular Diffusion: A Revisited Analysis of NMR-PGSE Experiments
Authors: Rodts Stéphane , Levitz Pierre 
Published: April 2011

AbstractWe present an interpretation of the self diffusion propagator for a molecular fluid confined in a porous medium. Breaking with conventional routes of interpretation, we focus in reciprocal space on the time dependence of the propagator at a fixed wave vector q. New theoretical results are reported, as well as NMR measurements on a water-saturated packing of glass beads and on a stack of plastic platelets with rough surfaces. It is shown that at least three time regimes may be distinguished, characteristic of new ways in which the propagator is affected by the geometry of the system: a short-time exponential regime of almost unrestricted diffusion, a pseudo-exponential regime probing the transport process across the material at the length scale λ=2π/q, and an algebraic regime at long times with exponent -d/2, where d is the dimensionality of connected parts of the pore space.
Static Friction between Elastic Solids due to Random Asperities
Authors: Sokoloff J. B. 
Published: April 2011

AbstractSeveral workers have argued that should be negligible static friction per unit area in the macroscopic solid limit for interfaces between both incommensurate and disordered atomically flat weakly interacting solids. In contrast, the present work argues that in the low load limit, when one considers disorder on the multiasperity scale, the asperties act independently to a good approximation. This can account for the virtual universal occurence of static friction.