bluuebunny/crossref_metadata_2025 huggingface dataset:
Diode Laser Induced Chemical Vapor Deposition of WSIx from WF6 and SiH4
Authors: Desjardins P. , Izquierdo R. , Meunier M.
Published: March 2011

We have developed a compact and inexpensive laser direct writing system, based on the 796 nm radiation of a 1 W diode laser array for the deposition of tungsten silicides. The laser power incident on TiN substrates varies between 50 and 550 mW. Lines are deposited from a gas mixture of WF6 and SiH4, whose total pressure is kept below 15 Torr to avoid uncontrolled reactions. Experiments are performed in a static reactor with WF6/SiH4 ratios varying from 0.2 to 10. Lines written at speeds ranging from 2 to 100 μm/s have typical thicknesses and widths varying from 30 to 1000 μm and from 4 to 15 μm respectively. Auger Electron Spectroscopy (AES) shows that no fluorine is incorporated in the WSix film, within the limit of detection. Moreover, no oxygen, carbon or nitrogen are detected in the bulk, although some surface contamination is present. From AES measurements, the W/Si ratio is estimated to be between 1.1 and 1.4 for a reactive gas mixture of WF6: SiH4 (1: 3).
Nanometer Lithography by Fast Atom or Ion Beam Milling
Authors: Devaud G. , Fleming J. , Douglas K.
Published: March 2011

We have produced nanometer scale patterning (nanostructures) by metal shadowing of two-dimensional protein crystals (S-layers), followed by milling with ions or fast atoms. In this parallel process, the metal overlayer is formed into a metal screen consisting of hexagonal arrays of 10 nm size holes with a 20 nm periodicity. We have studied the time evolution of the milling process, and temperature effects. Nanostructure formation may be due to preferential sputtering of the troughs relative to the crests of the metallized S-layer. The effect of temperature on pattern formation indicates that thermal diffusion is also important.
Anisotropic Si Etching by a Supersonic Cl2 Beam
Authors: Teraoka Yuden , Uesugi Fumihiko , Nishiyama Iwao
Published: March 2011

Perpendicular etching profiles of n+-Si(100) are obtained with a supersonic Cl2 beam at substrate temperature of 900°C. Although small undercuts are observed just below the SiO2 mask, the side wall etching caused by the background Cl2 is almost negligible. An aspect ratio of greater than 6 and selectivity of greater than 8000 are obtained with 0.5 μm line & space mask pattern. From Arrhenius plots of etch rates, an effective activation energy of the nozzle beam etching is determined to 0.53 eV. Assuming that the reaction product is SiCl2, the reaction probability is estimated to be 19% at 900°C. Highly anisotropic etching of the Si(100) obtained here is due to the large reaction probability.
Thin Film Processing with Ecr and Downstream Oxygen Plasmas
Authors: Hess Dennis W.
Published: March 2011

Downstream oxygen plasmas are used routinely to etch and strip resist materials in integrated circuit (IC) process sequences. Differences in the electrical damage incurred in thin (26 nm) silicon dioxide films on silicon due to the afterglow of rf and microwave oxygen plasmas appear to be due to higher energy VUV emission and to a greater density of positive ions in the case of rf excitation at downstream distances less than 35 cm. The high flux of oxygen ions in electron cyclotron resonance (ECR) plasmas also permits reasonable silicon oxidation rates at low temperature. Oxidation rates ofsilicon in ECR oxygen plasmas at temperatures between 250 and 450 C are comparable to those obtained for thermal oxidation in dry oxygen at temperatures above 850 C. Although oxidation rates are adequate under floating, anodic or cathodic bias conditions, only oxides grown under floating or anodic conditions display comparable chemical, physical and electrical properties to those of thermal oxides.
Ebic Investigation of Etch Induced Defects in Silicon Introduced by Rie and Ribe.
Authors: Habermeier H.-U. , Eckstein M. , Ruf C. , Jäger-Waldau G. , Zwicker G.
Published: March 2011

Silicon single crystal wafers are lithographically patterned and etched for via holes by means of RIBE, RIE and ECR based techniques. The damage introduced by etching is analyzed using charge collection microscopy. This technique probes sensitively the occurrence of electrically active defects due to their altered electron hole recombination properties compared to the bulk material. Furthermore, investigations of the temperature dependence of the EBIC contrast give informations about the physical mechanisms for the recombination. The experiments revealed a substantial increase [several %] of the EBIC contrast in the etched part of the pattern, i.e. electrically active damage is introduced by the etching technique, giving rise to enhanced recombination. Measurements of the diffusion length in etched and unetched areas of the specimen reveal identical values, i.e. the damage is confined close to the surface. Using the different etching methods quantitatively different defect levels are found. Measurements of the temperature dependence of the EBIC contrast aimed to reveal the physical nature of the defects show a drastic increase of the contrast with decreasing temperature. This increase can be described by two regimes in an Arrhenius plot with a linear characteristic of different slopes.
The Effects of P2S5 Surface Passivation on Dry Etched GaAs
Authors: Glembocki O.J. , Dagata J.A. , Dobisz E.A. , Katzer D.S.
Published: March 2011

The effects of P2S5 surface passivation treatments on damage caused by chemically assisted ion beam (CAIBE) etching of GaAs have been examined using ex-situ photoreflectance. Epitaxially grown undoped GaAs on heavily doped GaAs substrates were used to determine surface electric fields. The etching process is observed to decrease surface electric fields, produce subsurface damage and to reduce surface photovoltages. Post-etching treatments with P2S5 are observed to increase surface photovoltages, but have no significant effect on the surface fields or subsurface damage. That the surface field is unaffected suggests that in etched materials the Fermi level pinning is not solely determined by the surface and that the near surface regions are important. We also find that samples pretreated with P2S5 exhibit more etch damage than those which are only degreased.
Simulations of Low-Energy Ion Bombardment and Epitaxial Growth
Authors: Chason E. , Bedrossian P. , Tsao J.Y. , Dodson B.W. , Picraux S.T.
Published: March 2011

We have performed computer simulations of epitaxial growth and low-energy ion bombardment for comparison with reflection high-energy electron diffraction (RHEED) mesurements. The simulations are based on a hybrid Monte Carlo/rate equation approach which includes the processes of defect creation (adatom and surface vacancy), surface diffusion, and attachment and detachment from steps and islands. In this work, we focus on simulating the experimental observations of ion-induced RHEED oscillations and cancellation of RHEED oscillations during simultaneous ion bombardment and growth. For the interaction of the low-energy ion with the surface, we consider two mechanisms: preferential sputtering (where the sputtering cross section depends on the atomic coordination) and mobile vacancies. Our results indicate that the primary interaction of the ion beam with the surface is probably through the creation of mobile vacancies, and that the degree of preferential sputtering is not large.
Low Temperature Silicon Oxidation with Electron Cyclotron Resonance Oxygen Plasma
Authors: Sung K. T. , Pang S. W.
Published: March 2011

Silicon was oxidized at low temperature with an oxygen plasma generated by an electron cyclotron resonance (ECR) source. The ECR source utilized a multicusp magnetic field formed by permanent magnets. Microwave power at 2.45 GHz was applied to the source and rf power at 13.56 MHz was applied to the sample stage. Si oxidation was studied as a function of source distance, pressure, microwave power, and rf power. The oxide thickness increases with microwave and rf power but decreases with source distance. The oxidation rate increases with pressure up to 12 mTorr, then decreases at higher pressure. The relative emission intensities in the plasma monitored using optical emission spectroscopy showed similar dependence on the source distance and microwave power. Oxidation temperature was estimated to be <100°C. Using ellipsometry and X-ray photoelectron spectroscopy, the oxidized films were found to be close to that of thermal oxide with refractive index at 1.45 and oxygen to silicon ratio of 2. From the current-voltage and capacitance-voltage measurements, the breakdown fields of these oxide films were 6.3 MV/cm and the fixed charge densities were 7×1010 cm−2.
Low-Energy Ar+ Implantation of Uhmw-Pe Fibers: Effect on Surface Energy, Chemistry, and Adhesion Characteristics
Authors: Schalek R. , Hlavacek M. , Grummon D. S.
Published: March 2011

Ultra-high molecular weight polyethylene (UHMW-PE) has a highly chain-extended and crystalline structure which is functionally inert and requires surface-modification before it can successfully operate as a reinforcement in polymer-matrix composites. Although plasma treatments are adequate for this purpose, recent work has shown that irradiation with low-energy inert gas ions can produce increases in interfacial shear strength (ISS), in epoxy matrices, which exceed those of commercial plasma treatments, and cause little degradation in tensile properties. Low energy ions are readily produced in high-current beams using gridded sources having moderate cost, and processing times may be a short as a few seconds. In this paper, we present results of recent experiments using argon ions accelerated to energies between 100 eV and 1 keV to irradiate 20-30 µm diameter UHMW-PE fibers to doses between 1×1016 and 1×1017 cm−2, and compare our findings with previous work at higher accelerating potentials. At the optimum dose (which increases with decreasing energy), greater than 9-fold improvements in ISS level, measured in epoxy-resin droplet pulloff tests, were found for ion irradiation at 0.25 keV. Scanning electron microscopy of fiber surfaces, of ion irradiated as well as commercial oxygen plasmatreated materials, revealed small crack-like pits in both cases, with the pits smaller and more uniformly distributed on the ion-irradiated fibers. Surface chemistry studies using X-ray photoelectron spectroscopy (XPS) and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) indicate that irradiation resulted in high surface concentrations of polar functional groups, and extensive surface oxidation. This was accompanied by a substantial increase in the polar component of surface energy, which resulted in improved fiber wetting by the resin.
Si-N Bonding at the SiO2/Si Interfaces During Deposition of SiO2 by the Remote Pecvd Process
Authors: Ma Y. , Yasuda T. , Habermehl S. , Lucovsky G.
Published: March 2011

Thin films of SiO2 were deposited on Si substrates by remote PECVD following an in-situ cleaning/surface passivation with atomic-H. Si-N bonds were found in the immediate vicinity of the SiO2/Si interface when nitrous oxide, N2O, was used as O-atom source gas in the remote PECVD process. Si-N bonds, as well as Si-surface roughening produced by H-atom etching, contribute to the formation of high densities of midgap trapping states, Dit ∼1011 cm−2eV−1, at the SiO2/Si interface. Eliminating the H-atom processing step, and exposing the Si surface to plasma-generated O-atoms prior to the SiO2 deposition: i) eliminated Si-N bonding at the Si/SiO2 interface; ii) reduced midgap Dit to ∼1−3×1010 cm−2eV−1; iii) eliminated surface roughening; and iv) improved process latitude and reproducibility.
Characterization of the Depositing Flux in Laser Ablation Deposition (LAD).
Authors: Kools Jacques C.S. , Dieleman Jan
Published: March 2011

Angular-resolved time-of-flight (ARTOF) studies have been performed on ablation plumes of copper generated by excimer laser fluences just above threshold in vacuum. Positive ions, Rydberg atoms and ground-state neutrals are observed. Relative concentrations, angular intensity distributions and angular- resolved velocity distributions are measured for ground state neutrals and ions.

Ions have the highest kinetic energies ( 20-80 eV). Their angular distribution is isotropic. Their concentration at the substrate is very low ( ≤ 10−6). Ground state neutrals have lower energies ( ≈ 1 eV). Their intensity and velocity is a strongly decreasing function of the polar angle. Rydberg-atoms have energies in between those of ground-state neutrals and ions. Their angular distribution is also dependent on tile polar angle.

The concentration, kinetic energy and angular distribution of the ionised species arc very well explained by a mechanism of thermal ionization and subsequent space-charge induced repulsion. The velocity distributions and angular intensity distributions of the ground-state neutrals are quantitatively predicted by a model for the flow dynamics of pulsed laser generated gas clouds.
The Role of Hydrogen in Laser Deposition of Diamond-Like Carbon
Authors: Thebert-Peeler D. , Murray P.T. , Petry L. , Haas T.W.
Published: March 2011

Thin films have been grown on Si (100) substrates by pulsed laser evaporation of graphite using both IR and UV radiation. The character of the resulting film is found to be independent of the presence of H°. Diamond-like films are found to be a result of low (RT) temperature deposition of the higher energy incident particles of the UV (versus IR) laser ablation process.
Uhv-Tem Studies of Laser-Induced Damage in Silicon
Authors: Savage T. S. , Xu P. , Ai R. , Dunn D. , Marks L. D.
Published: March 2011

The effects of pulsed laser irradiation on silicon (111) single crystal thin samples were studied in a ultra-high vacuum transmission electron microscope. Samples were found to cleave along (110) planes under the laser beam. The formation of dislocation networks was also observed. The cleaving did not seem to originate from previously observed defect areas, but from random places, and is believed to be caused by thermal shock from laser beam heating. Bulk defects in the specimens, such as stacking fault tetrahedra and dislocations, were not observed to be affected by the laser treatment.
Laser Damage Thresholds of Several Metal-Containing Acrylic Polymers at Four Different Wavelengths.
Authors: Yip Pearl W.
Published: March 2011

Single- and multiple-pulse laser damage thresholds of six different metal-containing acrylic polymers were determined at 10.6, 1.06, 0.53 and 0.355 μm. Light transmission of these samples before and after irradiation was measured. A variety of observed laser-materials interactions are discussed in this paper. Physical and chemical damage properties of these metal-containing acrylic polymers were examined and compared with poly (methyl methacrylate) and polycarbonate using scanning electron microscopy (SEM), infrared spectroscopy (IR), and electron spectroscopy for chemical analysis (ESCA). In general, it was found that the multiple-pulse damage thresholds were lower than the single-pulse, and damage thresholds decreased as wavelength of the testing laser beam became shorter.
Dry Etching of Copper at High Rates
Authors: Farkas Janos , Rousseau Francois , Chi Kai-Ming , Kodas Toivo T. , Hampden-Smith Mark J.
Published: March 2011

Three new methods for dry etching of copper at temperatures below 200°C have been developed. The first relies on the formation of volatile CICu(PR3)2 species via reaction of PR3 with CuCI where R = ethyl, and butyl. The second relies on the reaction of Cu(hfac)2 and neutral ligands L such as butyne, pentyne or bistrimethylsilylacetylene to form (hfac)CuL. The last approach involves reaction of CuO with hexafluoroacetylacetone (hfacH) to form Cu(hfac)2 and water. These approaches have provided etch rates as high as 1 μm/min at 150°C.
Theoretical Aspects on Spatial Thickness Variations in Laser-Deposited Thin Films.
Authors: Singh Rajiv K. , Carignan James
Published: March 2011

We have studied predicted thickness uniformity of thin films deposited by the pulsed laser ablation technique. Unlike a conventional evaporation process, the spatial thickness characteristics of laser-deposited films is controlled by a number of laser and other deposition variables including laser wavelength, pulse energy density, substrate-target distance, area and shape of the laser irradiated spot, etc. The effect of these parameters on the spatial thickness variations have been analyzed by using a model proposed by Singh et. al. [1]. This model is based on the anisotropic expansion of the laser-generated high-temperature and high-pressure plasma, which is initially confined to small dimensions and then expands anisotropically in vacuum. The results show that spatial film uniformity can be improved by decreasing plasma temperature and specific heat capacity ratio of the plasma gas. For large laser irradiated spot diameters (> 8 mm), the film uniformity was found to decrease with decreasing spot diameters, but this trend reversed at smaller: irradiated spot sizes. Depending on the laser irradiated conditions and substrate-target geometry, the thickness variations have been found to vary from (cos θ)2.5 to (cos θ)12. Optimization of various parameters to decrease the spatial-thickness inhomogeneities across the film are also discussed.
Surface Laser Plasma in Laser Treatment of Materials in High Pressure Gases
Authors: Smirnov A. , Dupuy C. , Flamant G.
Published: March 2011

Using holographic interferometry the surface laser plasma generation in high pressure gases has been investigated. Additional information about the generation of surface cover laser plasma, optical breakdown in the presence of aerosol particles and condensation front forming in high pressure gases is given.
Excimer Laser Removal of Cr Contaminants from Polyimide Surfaces for Packaging Applications
Authors: Radhakrishnan Gouri , Marquez Nicholas , MÜller Heinrich
Published: March 2011

Excimer laser radiation at 248 nm has been used for the maskless and selective removal of chromium (Cr) contamination from polyimide surfaces containing gold (Au) metallizations. Ablation thresholds and rates have been determined in air, vacuum, and oxygen. These results have been used to establish the optimum ablation medium and a corresponding process window that allows for selective removal of Cr from polyimide. The substantial differences between the ablated and unexposed regions of the polyimide surface have been established by electrical measurements, while the variations in their respective surface morphologies have been examined using optical and scanning electron microscopy. Quantitative determinations of Cr on the ablated and unablated regions of polyimide have been performed, using secondary ion mass spectrometry, to establish the threshold for the complete removal of Cr.
A Fast Laser Alloying Process for the Selective Electroplating of Metal on SiO2 and Polyimide
Authors: Malba Vincent , Bernhardt Anthony F.
Published: March 2011

A new laser direct-write process for patterning of metal on multichip modules has been developed. The process involves the laser modification of the non-conductive surface of a seed multilayer, converting it to a conductive surface, which can be electroplated with metal. The seed multilayer is composed of a TiW adhesion layer, onto which a Au film is sputtered, followed by an a-Si layer, which forms the non-conductive surface. The laser modifies the surface by alloying (or mixing) the Si and Au to form the conductive surface. This laser process has been shown to be capable of writing speeds of 2.5 m/s. With a silicon dioxide interlevel dielectric layer, the process works over a large range of laser power (Pmax/Pmin ∼ 5). A polyimide interlevel dielectric layer can be used without damage or loss of adhesion, although the process margin is substantially reduced (Pmax/Pmin ∼ 2).
Computer Simulation Studies of the Temperature Dependence of Domain Growth Kinetics
Authors: Fichthorn Kristen A. , Henry Weinberg W.
Published: March 2011

Understanding the kinetics of domain growth in quenched systems is a significant fundamental problem with particular relevance to materials science. The temperature dependence of domain growth has interesting manifestations which lie outside current theoretical developments. In a series of Monte Carlo studies, we have investigated and obtained a detailed resolution of the temperature dependencies of domain growth in a model of a two-dimensional, quenched, chemisorbed overlayer with a nonconserved order parameter. We discuss our findings.
In-Situ Time-Resolved X-Ray Studies of Eutectic Crystallization in Amorphous Fe1−xBx and Co1−xZrx
Authors: Fischer Henry E. , Brauer S. , Sutton M. , Ström-Olsen J. , Zaluska A. , Stephenson G. B. , Koster Uwe
Published: March 2011

Using a millisecond time-resolved x-ray scattering technique at the National Synchrotron Light Source, we have simultaneously obtained in situ both large-angle (LAXS) and small-angle (SAXS) diffraction patterns for isothermal crystallization of amorphous Fe1−xBx (0.16 < x < 0.21) and Co1−xZrx (0.08 < x < 0.11). The large-angle x-ray data are analyzed to determine which of the two crystalline products nucleate first in each compound, and also to assess the evidence for eutectic growth as shown by a time-independent ratio of volume fractions of these product phases. The small-angle data give the length scales of the eutectic structure as well as information about its time evolution. Combining our x-ray results with TEM studies, we examine the effects of changes in temperature and composition on the structural evolution of both the amorphous and crystalline phases.
Scanning Tunnelling Microscopy Investigation of Surface Morphology in the Growth of GaAs(001)
Authors: Heller E. J. , Lagally M. G.
Published: March 2011

The surface morphology of MBE - grown GaAs(001) has been investigated using scanning tunnelling microscopy (STM) and reflection high - energy electron diffraction (RHEED). STM shows that the missing - dimer - row structure of the (2 × 4)/c(2 × 8) reconstruction consists of rows of clusters of two As dimers separated by rows of two missing dimers, in agreement with previous reports. Layers grown on nominally flat substrates display a multi - level system of terraces elongated along [110] suggesting that growth occurs primarily by sticking at B - type steps. For films grown under certain growth conditions, B - type steps on vicinal substrates exhibit a dendritic step morphology, which may be an example of a step flow growth instability consistent with limited Ga diffusion over steps.
Optical Second Harmonic Generation of Thiols Adsorbed on Gold
Authors: Buck M. , Eisert F. , Fischer J. , Grunze M. , Träger F.
Published: March 2011

The adsorption kinetics of self-assembling n-alkyl thiol films on poly cry stalline gold substrates was studied in situ by optical second harmonic generation (SHG). The relation between the SHG signal change and the thiol coverage was established by comparison with ex situ X-ray photoelectron spectroscopy measurements. We find that the temporal dependence of the adsorption is well described by Langmuir adsorption kinetics. The source of the SHG signal is found to be linearly related to the nonlinear susceptibility of the adsorbate-substrate interaction. Experiments with chain lengths ranging from 1 to 22 showed, that the saturation coverage for thiols longer than hexanethiol is equal.
Self-Assembled Monolayers as Models for Studying Protein Adsorption to Polymer Surfaces
Authors: Prime Kevin L. , Whttesides George M.
Published: March 2011

Self-assembled monolayers (SAMs) of functionalized alkanethiolates on gold are a well-characterized system for studying the interfacial properties of organic materials. We have used SAMs as models for the surfaces of organic polymers and used mem to study the adsorption of proteins onto organic materials. We have formed SAMs from mixtures of alkanethiols in which one alkanethiol is hydrophobic and the other is terminated by a short (2 ≤ n ≤ 17) oligomer of poly(ethylene oxide). These “mixed” SAMs effectively resist the adsorption of fibrinogen from moderately concentrated (1 mg/mL) solutions. Protein adsorption begins when < 5% of the accessible area of the surface consists of hydrophobic groups. These findings suggest that real protein-resistant monolayers must present an almost defect-free surface of oligo(ethylene oxide) groups in order to eliminate adsorption.
Digital Electrochemical Etching of Compound Semiconductors
Authors: Lei Q. Paula , Stickney John L.
Published: March 2011

The principles for an electrochemical digital etching method for compound semiconductors are described and initial results reported. The method is designed to allow atomic level control over the etching process, resulting in the removal of a bilayer of the compound for each cycle. An atomic layer of one element is removed at one potential and then an atomic layer of the second element is removed at a second potential to complete one cycle. The results reported here are for the etching of CdTe. For CdTe, Te is stripped by reduction to Te2- while Cd is stripped by oxidation to Cd2+. Underpotentials are chosen so that only the top atomic layer of an element is removed. Potentials sufficient to strip the elemėnt from the bulk of the CdTe substrate are avoided. Application of the method should involve the use of a simple electrochemical cell, with solution convection. The substrate is placed in the cell and a square wave applied, where each cycle results in the dissolution of a bilayer of the compound. The two potentials of the square wave correspond to underpotential stripping potentials for Cd and Te respectively. Directions for the future development of this etching method are discussed.
Pinning of Misfit Dislocations in film Growth Studied by Grazing Incidence X-ray Scattering
Authors: Liang K. S. , Lee C. H.
Published: March 2011

Using grazing incidence x-ray scattering, we have studied incommensurate structures of Pb adlayers on Cu(110) surface and epitaxial Al films grown on Si(111) surface. Similar diffuse scattering profiles were found in both cases, which can be fitted with a Gaussian-plus-Lorentzian lineshape. The results are attributed to a overlayer structure with pinned misfit dislocations at the interface.
Epitaxy Development in thin Superconducting YBa2Cu3O7 Films
Authors: Yen A. , Li L. , Klein J. D. , Nowak W. B. , Cogan S. F.
Published: March 2011

Ultrathin superconducting YBa2Cu3O7, films were grown on (100) YSZ (yttria-stabilized-zirconia) substrates by off-axis if magnetron sputtering at a relatively high deposition rate. The structure, orientation, and morphology of the films were examined by x-ray diffraction, reflection high-energy electron diffraction (RHEED), and scanning electron microscopy. X-ray diffraction patterns of films deposited on YSZ substrates exhibited strong c-axis alignment with the YBa2Cu3O7 peaks sharpening as the film thickness was increased. The degree of epitaxy apparent in RHEED photographs was found to increase dramatically as the film thickness was increased from 12 nm to 108 nm. This behavior is attributed to a nucleation and growth process in which epitaxy develops as a result of a 3 stage progression from a random to an oriented film.

The films were in-situ superconducting, exhibiting superconducting transition temperatures, Tc(0)'s, of 80 K for a 12 nm film and 88 K for a 280 nm film. However, the relatively low critical current densities (Jc < 1 × 106 A/cm2) at 77 K are probably due to a lack of in-plane epitaxy.
Low Temperature Silicon Epitaxy Grown by Electron-Beam Evaporation in an Ultra-High Vacuum System
Authors: Lin Yung-Jen , Yew Tri-Rung
Published: March 2011

This paper presents the results of silicon epitaxial growth on silicon windows surrounded with oxide walls by electron-beam evaporation in an ultra-high vacuum system with a load-lock chamber. The wafer surface was in-situ cleaned in the growth chamber to remove native oxide by thermal desorption at about 840 °C and a base pressure of better than 2 × 10-9 Torr. The growth temperature was 200°C or higher. The pre-epitaxial silicon surface structure was inspected by reflection high energy electron diffraction (RHEED). The influence of the thermal desorption on the quality of the epi/substrate interface and epitaxial layers was studied. In addtion, the deposition parameters which control the epitaxial quality were investigated. The epitaxial films were characterized by cross-sectional trasmission electron microscopy (XTEM) and secondary ion mass spectroscopy (SIMS).
In-Situ Heavy as Doping in Si Selective Epitaxial Growth
Authors: Ohshita Y. , Kitajima H.
Published: March 2011

Role of in-situ heavy As doping in Si selective growth is studied using the SiH2Cl2/H2/HCl/AsH3 gas system. By increasing AsH3 flow rate, the growth rate decreases in proportion to In (AsH3 flow rate). This result is explained well using a Frumkin-Temkin adsorption model. The As concentrations in grown films depend on surface orientation. Moreover, the maximum As concentration is about ten times lower than the solubility limit at a given temperature. These results are able to be explained qualitatively, if equilibrium concentrations of impurities at the Si(100), the Si(111), and the bulk are assumed to be different from one another, and that the concentration at the surface is frozen in the grown film.
Growth Process of Si and GaAs in the Heterostructure GaAs/Si/GaAs(100).
Authors: Lopez M. , Takano Y. , Pak K. , Yonezu H.
Published: March 2011

The growth mode of Si on GaAs(100) substrates and that of GaAs on very thin (1/4 ∼ 3 ML) Si films grown pseudomorphically on GaAs was investigated by observing the behavior of the reflection-high energy electron diffraction (RHEED) specular spot intensity. From the presence of RHEED oscillations during the initial stage of the growth of Si on GaAs we infer a two-dimensional growth with nucleation on the terraces up to a thickness of 3 ML. During the posterior growth of GaAs on the pseudomorphic Si films, a tendency towards three dimensional growth was observed. This tendency increased with the Si interlayer thickness. The causes of the formation of these islands are discussed.
Morphology and Interface chemistry of the Initial Growth of GAN and ALN on α-SIC and Sapphire
Authors: Sitar Z. , Smith L. S. , Paisley M. J. , Davis R. F.
Published: March 2011

The morphology and interface chemistry occurring during the initial stages of growth of GaN and A1N layers has been obtained. Films were grown using gas source MBE equipment containing an ECR plasma source to activate molecular nitrogen. The experiments consisted of sequential depositions of about one monolayer thick films and XPS analysis. Evidence for silicon nitride formation on the SiC surface was obtained from the studies of both the Si oxidation states and the substrate peak intensity dependence on film thickness. The growth of GaN on sapphire appeared to occur via the Stranski-Krastanov mode, while the growth on SiC showed characteristics of three-dimensional growth. AlN grew in a layer-by-layer mode on both substrates.
Orientation Dependent Epitaxial Growth of CeO2 Layers on Si Substrates
Authors: Inoue T. , Ohsuna T. , Yamamoto Y. , Sakurai Y. , Luo L. , Wu X. D. , Maggiore C. J.
Published: March 2011

Cerium dioxide (CeO2) layers epitaxially grown on (100), (111) and (110) silicon substrates by electron beam evaporation in an ultra-high vacuum were investigated. CeO2 layers on Si (111) substrates were proved to be epitaxially grown at the substrate temperature above 200°C, and had considerably good crystalline quality. On the other hand, CeO2 layers grown on Si (100) at 800°C consisted of more than 98% volume fraction of (110) component. Cross-sectional high resolution transmission electron microscopy and selected area electron diffraction verified clearly the above crystallography orientation and that the <100> direction in the CeO2(110) plane was parallel with the <110> direction in the Si (100) plane. The cross-sectional lattice image confirmed the existence of ∼ 6 nm-thick intermediate amorphous layer between the CeO2 layer and the Si substrate.
Mechanism of Stress-Enhanced Solid-Phase Epitaxy
Authors: Chaki T. K.
Published: March 2011

Enhancement of solid-phase epitaxial growth (SPEG) due to hydrostatic pressures and bending stresses is explained by stress-enhanced mobility of point defects in the amorphous solid. The crystallization is by the adjustment of atomic positions in the vicinity of the crystallization/amorphous (c-a) interface due to self-diffusion in the amorphous phase, assisted by a free energy decrease equal to the difference in free energies between the amorphous and crystalline phases. Due to a mismatch in the bulk moduli between the amorphous and crystalline phases, the application of a hydrostatic pressure can develop tensile stresses in the amorphous layer near the c-a interface. Non-hydrostatic stresses in the amorphous layer enhance the mobility of point defects in the amorphous layer and, therefore, an enhancement of the SPEG rate. In the cases of both hydrostatic pressure and bending, the enhancement occurs in the tensile side, indicating that vacancy-like mechanism is predominant in SPEG.
The Universal Instability of the Separation Boundary Between a Non-Hydrostatically Stressed Elastic Crystal and its Melt
Authors: Grinfeld Michael A.
Published: March 2011

In the absence of surface tension and external force fields, the equilibrium between a hydrostatically stressed crystal and its melt is neutral with respect to the perturbations associated with particle transfer from one region of the boundary into another. However, under the action of arbitrary small nonhydrostatic components of the stress field in the elastic crystal, the neutral equilibrium is transformed to an unstable equilibrium [1]. This instability is very general in nature; for example, for it to be seen the liquid media need only to be able to dissolve the solid phase or in some way to assist the transport of particles along the crystal's surface. In contrast, the surface tension, roughly speaking, stabilizes the shape of the interphase boundary but it cannot suppress the instability generated by the nonhydrostatic components of the stress field in the region of sufficiently long perturbations. Until now the basic instability mechanism discussed here seems to have escaped the attention of theorists. This mechanism allows one to look in a completely new way at a broad range of phenomena. We discuss tentative manifestations and role of this instability in low temperature physics, in materials science, in theory of crystal growth, and, in particular, in theory of epitaxy and of the Stranski-Krastanow pattern of growth of thin crystalline films.
Removable External Seeding for Solid phase Epitaxy of Amorphous Silicon on Glass Substrates
Authors: Doi Atsutoshi , Tsuda Takanori , Kumikawa Masa-ICHI , Nakamizo Yoshiyuki , Ueda Kazuyuki
Published: March 2011

A new method for obtaining a planar silicon film on glass substrates (SOG) with controlled crystal orientation has been introduced. This technique uses solid phase epitaxy (SPE) with external seed to fabricate the orientation-controlled SOG structure. Heat treatment of amorphous SOG substrate in contact with mesa striped Si seed crystal was performed at 540°C for 16 hours to form the SPE layer. The planar surface of the SOG structure is due to the most important feature of the present technique-the separation of the seed from the substrate after SPE.
Plasma Surface Interaction During the Growth of Semiconductor Thin Films Studied byin Situ Infrared Ellipsometry
Authors: Blayo N. , Drevillon B.
Published: March 2011

The early stages of the growth of plasma deposited amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si) on glass substrates are investigated by in situ infrared phase modulated ellipsometry (IRPME) in the silicon-hydrogen stretching mode region. μc-Si are prepared by alternating SiH4 and H2 plasmas. New insights on the plasma-surface interactions during the growth of these films are given. During the deposition of the first 20 Å of a-Si:H, the hydrogen is incorporated as SiH2. During the further growth of a-Si:H the SiH2 bonds are located at the film surface inside a very thin hydrogen rich overlayer. During the deposition of the first 10–20 Å of μc-Si, the SiH2 bonds are predominantly removed by the H2 plasma, the material being amorphous. After this selective removal of the SiH2 groups, a transition from amorphous to microcrystalline growm is observed. A systematic hydrogen etching during the further growth of μc-Si is observed.
Structure of Grain Boundaries in L12 Alloys at Finite Temperatures: Effects of Deviations from Stoichiometry
Authors: Yan M. , Vitek V. , Ackland G. J.
Published: March 2011

Atomic structures of grain boundaries in Ni3Al and Cu3Au has been studied using a Monte Carlo relaxation technique and many body central force potentials to describe interatomic forces. The purpose of this work is to investigate the temperature dependence of the compositional order in the boundary region for both stoichiometric and non-stoichiometric alloys. In the former case the boundaries in Ni3Al remain ordered up to very high temperatures while boundaries in Ni3Al disorder at relatively low temperatures. In the non-stoichiometric case, the surplus of nickel in the bulk leads to segregation to grain boundaries and to a significant chemical disordering in the boundary region. The surplus of aluminum also leads to segregation but without disordering in the boundary region. Using these results we discuss the intrinsic brittleness of grain boundaries in Ni3Al as well as the effect of stoichiometry on the intergranular brittleness.
Reconstruction of a High-Angle Twist Grain Boundary by Grand-Canonical Simulated Quenching
Authors: Phillpot S. R. , Rickman J. M.
Published: March 2011

A formalism for obtaining the zero-temperature structure of mono-component solids by simulated quenching in the grand-canonical ensemble is outlined. The structure of a high-angle twist grain boundary on the (110) plane of an fee metal is investigated. The lowest energy structure is found to have a density approximately 20% higher than the structure obtained from canonical-ensemble energy-minimization.
Grain Boundary Transformations in Bi-Doped Copper
Authors: Urdaneta Elsie C. , Luzzi David E. , McMahon Charles J.
Published: March 2011

Bismuth-induced grain boundary faceting in Cu-12 at ppm Bi polycrystals was studied using transmission electron microscopy (TEM). The population of faceted grain boundaries in samples aged at 600°C was observed to increase with heat treatment time from 15min to 24h; aging for 72h resulted in de-faceting, presumably due to loss of Bi from the specimen. The majority of completely faceted boundaries were found between grains with misorientation Σ=3. About 65% of the facets of these boundaries were found to lie parallel to crystal plane pairs of the type {111}1/{111]2- The significance of these findings in light of recent high resolution electron microscopy experiments is discussed.
The Determination of Interfacial Structure and Phase Transitions in Al/Cu and Al/Ni Interfaces by Means of Surface Extended X-Ray Absorption Fine Structure
Authors: Barrera E. V. , Heald S. M.
Published: March 2011

Surface extended x-ray absorption fine structure (SEXAFS) was used to investigate the interfacial conditions of Al/Cu and Al/Ni shallow buried interfaces. Previous studies using glancing angle extended x-ray absorption fine structure, x-ray reflectivity, photoemission, and SEXAFS produced conflicting results as to whether or not the interfaces between Al and Cu and Al and Ni were reacted upon room temperature deposition. In this study polycrystalline bilayers of Al/Cu and Al/Ni and trilayers of Al/Cu/Al and Al/Ni/Al were deposited on tantalum foil at room temperature in ultra high vacuum and analyzed to evaluate the reactivity of these systems on a nanometer scale. It became overwhelming apparent that the interfacial phase reactions were a function of the vacuum conditions. Samples deposited with the optimum vacuum conditions showed reaction products upon deposition at room temperature which were characterized by comparisons to standards and by least squares fitting to be CuAl2 and NiAl3 respectively. The results of this study showed that the reacted zone thicknesses were readily dependent on the deposition parameters. For both Al on Cu and Al on Ni as well as the metal on Al conditions 10A reaction zones were observed. These reaction zones were smaller than that observed for bilayers of Al on Cu (30Å) and Al on Ni (60Å) where deposition rates were much higher and samples were much thicker. The reaction species are evident by SEXAFS, where the previous photoemission studies only indicated that changes had occurred. Improved vacuum conditions as compared to the earlier experiments is primarily the reason reactions on deposition were seen in this study as compared to the earlier SEXAFS studies.
Surface Reconstruction of Platinum and Gold and the Embedded Atom Model
Authors: Haftel Michael I.
Published: March 2011

We investigate the surface reconstructions of various faces of gold and platinum theoretically with a number of embedded atom potentials. We find that whereas all potentials examined predict equivalent bulk properties, only those with a relatively steep embedding function at surface electron densities predict the experimentally observed buckled quasihexagonal reconstruction for the (100) faces and surface energies in close agreement with experiment. Almost all embedded atom potentials considered predict the observed 2×1 missing row structure for the (110) faces, and some the observed missing row structure for the (311) face of platinum.
Thermodynamic and Kinetic Characteristics of Variations in Shapes of Ridges Formed on {100} Lithium Fluoride Surfaces
Authors: Bullard J. W. , Glaeser A. M. , Searcy Alan W.
Published: March 2011

Channels with widths in the range from 5 μm to 25 μm were formed in {100} surfaces of LiF single crystals by a photolithographic technique. Specimens annealed at or above 0.90 Tm, where Tm is the melting point, and then quenched showed die channels and the ridges between them develop rounded profiles. Evolution of these profiles was evaluated for the various channel widths and for interchannel ridge spacings of 5 to 100 μm in terms of: a) an accepted theoretical model for a surface diffusion controlled process, and b) a model which assumes that shape changes depend only on the relative energies of attachment of atoms in surface sites with various surface curvatures. Either model is consistent with the experimental observations to within the reproducibility in measurements.
Coarsening of a Population of Precipitates in a Soud
Authors: Lavine J. P. , Hawkins G. A.
Published: March 2011

Coarsening of a population of second-phase precipitates in a solid affects the physical properties of the solid. A numerical model of coarsening is introduced to treat both diffusion-controlled and interface reaction-controlled coarsening. The model is based on the escape probabilities of particles from precipitates. The experimental time dependences of precipitate coarsening are obtained.
Diffusion-Controlled Decohesion Using a Cu-Sn Alloy as a Model System
Authors: Bika Dafni , McMahon Charles J.
Published: March 2011

This research deals with a mode of brittle intergranular fracture in which a surface-adsorbed embrittling element is driven into a grain boundary as a result of the application of a tensile stress across the boundary. A Cu-8%Sn alloy has been employed to explore this phenomenon, since tin is a surface-active element, and this alloy is known to suffer intergranular weakness at elevated temperatures. Intergranular cracking occurred by brittle, discontinuous crack advance at 265°C in vacuum with an average rate of 0.1μm/sec. This behavior is analogous to sulfur-induced stress-relief cracking in steels and several cases of liquid-metal embrittlement, suggesting that this phenomenon has a generic nature.
Analysis Of Oxygen Distribution In Interfaces In SiC Whisker Reinforced Si3 N4-Based Composites.
Authors: Das Chowdihury K. , Carpenter R. W. , Braue W.
Published: March 2011

Discontinuous and continuous interfacial layers at the whisker/matrix and grain boundary interfaces in silicon carbide whisker reinforced silicon nitride based composites were investigated by high resolution electron imaging and analytical microscopy. Wide differences in chemical and structural widths of the interfaces were observed.
The Effect Of Trace Element Segregation To Fe/Sapphire Interfaces
Authors: Pope D. P. , Smith M. A.
Published: March 2011

The effects of segregation of tramp impurities such as sulfur on metal/ceramic bonding is discussed. Microstructural and chemical information is given for the Fe/sapphire interface. The segregation behavior of the interface is evaluated between 500–800 °C. The interfacial structure is shown to be important to the segregation behavior. A possible link between the segregation of sulfur and interface void formation is presented.
Effects Of Cation Segregation At Oxide Grain Boundaries On Grain Boundary Diffusion And Oxidation Kinetics Of Nickel
Authors: Cotelia C. M. , Bennett M. J. , Garratt-Reed A. J.
Published: March 2011

The oxidation behavior of Ni, implanted with either divalent Ce2+ or trivalent Y3+, has been studied to test the general applicability of the grain boundary segregation explanation for the reduction in rate of oxidation resulting from reactive element additions to metals that form protective oxide scales. Oxidation of Ce- and Y-implanted Ni at 900°C resulted in grain boundary segregation of the implanted species in the NiO scales formed. The rate of oxidation of Ni was reduced and there was evidence for a change in oxidation mechanism. Additionally, the grain size of the oxides was much smaller. All the observations were entirely consistent with a reduction in cation transport resulting from segregation of foreign ions at the oxide grain boundaries. These results on Ni are compared with recent studies of Ce- and Y-implanted Cr to draw general conclusions about the relationship between grain boundary segregation in oxides and the reactive element effect on oxidation.
Kinetics Of Dopant Distribution In Lpe Grown GaAs Epi-Layer
Authors: Okamoto Y. , Akagi Y. , Koba M.
Published: March 2011

We have studied the distribution and diffusion of Te, Mg, and Zn dopants in GaAs which was grown by an LPE process. It was found that the distribution of the dopant atoms of Te and Zn in the Te-doped n-type epi-layer on the Zn-doped p-type substrate showed a sharp and clear interface. In contrast, the dopant distribution of Mg and Zn in the Mg-doped p-type epi-layer on the Zn-doped substrate indicated a diffuse interface because of significant interdiffusion. The X-ray diffraction of these epi-layers and substrates revealed that the Mg-doped epi-layer showed rather poorer crystalline quality than the other specimens. These experimental results can be accounted for by a model of charged vacancies in a p-type GaAs.
Preferred Orientations in Metal/Non-Metal Interface Systems
Authors: McCafferty K. , Soper A. , Shirokoff J. , Erb U.
Published: March 2011

Results of recent studies of preferred orientations for metal/non-metal interface systems are presented and discussed in terms of some of the general concepts derived from interface structure models. The limitations of geometric models used to predict preferred orientations for metal/ionic crystal interfaces are demonstrated, and the effects of temperature and impurity segregation on the low energy interfaces for metal/glass interfaces are discussed.