bluuebunny/crossref_metadata_2025 huggingface dataset:
An Overview of Laser Chemical Processing
Authors: Osgood Richard M.
Published: March 2011

A overview of the recent developments in laser chemical processing is provided. The review covers advances in understanding fundamental process physics, the development of new techniques, and the implementation of applications.
The Transition Between Amorphous Regrowth and Explosive Crystallization
Authors: Bruines J. J. P. , Hal R. P. M. van , Koek B. H. , Viegers M. P. A. , Boots H. M. J.
Published: March 2011

The transition between amorphous regrowth and explosive crystallization of a 220nm thick amorphous Si layer on a crystalline Si substrate has been studied using time-resolved reflectivity, transmission electron microscopy, and Rutherford backscattering spectroscopy. Upon irradiation by 7.5ns FWHM pulses from a frequency-doubled Nd:YAG laser, interferences in the reflectivity indicate growth of amorphous Si from the surface. The observation of a narrow Cu peak, buried below the surface, points towards solidification from both the rear and the front. Transmission electron microscopy studies revealed the occurrence of small patches of polycrystalline Si. The relative amount of this polycrystalline Si is increased by longer laser pulses, higher substrate temperatures, and thicker amorphous Si layers. The results are discussed in terms of the temperature distribution and the time available for the nucleation of polycrystalline Si at the liquid-solid interface.
Photon-Induced Adhesion and Chemical Changes in Aluminium Films on Silicon.
Authors: Kellock Andrew J. , Liesegang J. , Nyberg G. L. , Williams J. S.
Published: March 2011

In the present study, thin layers of Al (<500 Å), deposited on Si under varying vacuum and substrate-cleaning conditions, have been irradiated with various wavelength photons. The films and interfacial oxide layers have been analysed with Rutherford backscattering and channeling (RBS-C), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) techniques both before and after irradiation. Results indicate that substantial oxygen uptake, indiffusion and interface reaction can take place in some thin Al films during photon irradiation at room temperature. Such photon-induced chemical changes correlate with an increase in film adhesion.
Deposition of a-Si Films Using Silane Molecular Beams Excited by Heated Wire and ArF Laser
Authors: Hanabusa M. , Tsuboi T. , Sato T. , Furuno S. , Iguchi S. , Inoue T.
Published: March 2011

Amorphous silicon films were deposited by using silane molecular beams excited either by ArF laser beams or heated tungsten wires. Reaction mechanisms are discussed on the basis of the dependence of deposition rates on substrate temperature and, in the case of the heated-wire method, on wire temperature.
Optically-Induced, Room-Temperature Oxidation of Gallium Arsenide
Authors: Yu Chien-Fan , Schmidt Michael T. , Podlesnik Dragan V. , Osgood Richard M.
Published: March 2011

Room-temperature, optically-induced oxidation of the gallium arsenide surface has been studied with laser radiation of different wavelengths. It was found that deep-ultraviolet light is much more effective in enhancing oxidation than near-ultraviolet or visible light. The growth rate of the oxide was also found to be drastically increased by the presence of chemisorbed water molecules on the surface.
Photoenhanced Deposition of Silicon Oxide Thin Films Using an Internal Nitrogen Discharge Lamp
Authors: Robertson Paul A. , Milne W. I.
Published: March 2011

This paper describes the optical and electrical properties of silicon oxide thin films produced using a novel photoenhanced deposition technique. Since there is no damage to the growing film surface from energetic ions, this process has the potential to produce better semiconductor/insulator interfaces than those grown using conventional RF glow discharge techniques. The deposition system is comprised of a windowless nitrogen discharge lamp contained within the reaction vessel. This unified approach allows the low wavelength UV light from the lamp to couple directly into the reaction gases without attenuation by a window material or the need for mercury sensitisation. Thin films of silicon oxide have been deposited onto single crystal silicon wafer substrates from a nitrous oxide/monosilane reaction gas mixture. The deposition rate and physical properties of films produced in this way are comparable to those of high quality insulator films deposited by plasma enhanced CVD techniques. The results of electrical tests indicate that this material could be used as a low temperature deposited insulator for thin film devices.
Laser-Induced Formation of Thin TiO2 Films from TiC14 and Oxygen an a Silicon Surface.
Authors: Kawai Tomoji , Choda Takahiro , Kawai Shichio
Published: March 2011

A uniform thin TiO2 film with the rutile structure which is usually made at higher than 700°C, can be formed at room temperature by the laser irradiation of adsorbed TiCl4 followed by oxidation and repeated cycles of this procedure on a silicon(100) single crystal surface. The laser irradiation to gaseous mixture of TiCl4 and oxygen from the direction parallel or perpendicular to the substrate, on the other hand, leads to the formation of a TiO2 film consisting of amorphous fine particles. The mechanism of the film formation is briefly discussed.
Oxidation and Nitridation by Pulsed Laser Irradiation of Solids Immersed in Liquids
Authors: Roorda S. , Polman A. , Ogale S. B. , Saris F. W.
Published: March 2011

Nitridation and oxidation of titanium is achieved by pulsed laser irradiation of Ti immersed in liquid ammonia or water. Rutherford Backscattering Spectrometry shows that large amounts of nitrogen and oxygen can be incorporated in the metal surface to a depth of several 1000 Å. X-ray diffraction shows evidence of compound formation. Scanning Electron Microscopy reveals that initial surface texture is smoothed, and that stress induced cracks and holes may appear. Irradiation of Fe and Si immersed in various liquids shows that modification depends on which combination of solid and liquid is used. Influence of processing parameters such as laser-energy density and number of laser pulses on compound formation has been investigated. The process is viewed as a reactive solute incorporation in the laser melted surface layer, followed by compound formation.
Ion Bombarment Effect on the Growth of Microcrystalline Germanium
Authors: Drevillon B. , Godet C. , Antoine A. M.
Published: March 2011

The influence of surface mobility on the growth of Ge films is studied as a function of preparation conditions. The positive ion bombardment during film deposition on chromium substrates is analyzed using an electrostatic analyzer. The dielectric functions of the films are measured over the range 1.7–4.5 eV using in-situ spectroscopic phase modulated ellipsometry (SPME). The spectra of microcrystalline germanium (μc-Ge) present a shoulder near 4.2 eV which corresponds to the E2. optical transition observed in single crystal germanium. For substrate temperatures greater than 150°C, a transition from a-Ge:H to μc-Ge appears when the ion kinetic energy exceeds a threshold energy Eth, around 120 eV. Eth decreases as a function of substrate temperature. The Eth value is found to be higher than the threshold value corresponding to the opposite transition, giving evidence of a substrate memory effect on the growth of μc-Ge. Kinetic ellipsometry measurements of the early stage of the μc-Ge deposition on chromium are accurately, modelled by microcrystalline nucleation at a 50 Å level. After 200 Å thickness, μc-Ge grows with an overlayer. The description of μc-Ge as a mixture of c-Ge, a-Ge:H and voids is discussed.
Surface Processes in Laser-Induced Etching of Silicon Studied by X-Ray Photoelectron Spectroscopy
Authors: Hirose Masataka , Ogura Tsuyoshi
Published: March 2011

A silicon surface exposed to NF3 gas was irradiated with an ArF excimer laser beam. The reaction products on the surface and their chemical bonding features were studied by in-situ x-ray photoelectron spectroscopy at each step of the photochemical etching. It was found that SiFX (1≤X≤4) units and molecular fluorine exist in the reacting surface region. The surface Si-Si bonds attacked with fluorine are progressively fluorinated and the final surface products are mainly SiF4 and SiF3. A possible mechanism of fluorine etching is discussed on the basis of a valence electron transfer (VET) model.
Etching of SiO2 with CO2 and CO2 + Ar+ Lasers
Authors: Pan D. , Dai B. T. , Agrawalla B. S. , Imen K. , Allen S. D.
Published: March 2011

Dry etching of fused SiO2 in the presence of several etchants using CO2 and CO2 + Ar+ lasers yields controlled, rapid removal rates of 10 Ao – 500 μm/sec and smooth, high quality surfaces. Etching occurs mainly by thermal ablation of SiO2 due to strong CO2 laser absorption. The addition of the Ar+ laser, which is absorbed by Br2 etchant to yield Br atoms, increases the etch rate as a result of a combination of photochemical and gas-phase heating effects.
Ultrafast Aqueous Etching of Gallium Arsenide
Authors: Willner A. E. , Podlesnik D. V. , Gilgen H. , Osgood R. M.
Published: March 2011

Very rapid room-temperature photochemical etching of n-type GaAs was achieved in aqueous hydrofluoric acid in conjunction with ultraviolet laser illumination. The etch rates of ˜500 μm/min represent an order of magnitude increase in etch rates over previously reported results for solutions that contained no hydrofluoric acid. Furthermore, incorporation of nitric acid into the hydrofluoric acid solution resulted in smooth etched surfaces thus allowing deep, waveguiding etching. This rapid process was used to etch deep, large-area structures in GaAs samples.
Excimer Laser Applications: Polymer Etching and Metal Deposition
Authors: Ritz Michael , Srinivasan V. , Babu S. V. , Patel Ramesh C.
Published: March 2011

Excimer laser induced ablative decomposition of polyimide and poly(methylmethacrylate) at high fluences (> 1 J/cm2) is discussed. It is shown that 0.4 μm sized features can be imaged in polyimide using ArF laser pulses. Preliminary results from experiments in which copper particles (<1 μm in size) have been deposited by exposing thin films of a copper formate and glycerol paste to KrF laser radiation are presented.
The Influence of Doping on the Etching of Si(111)
Authors: Winters Harold F. , Haarer D.
Published: March 2011

It has been recognized for some time that the doping level in silicon influences etch rate in plasma environments[1–8]. We have now been able to reproduce and investigate these doping effects in a modulated-beam, mass spectrometer system described previously [9] using XeF2 as the etchant gas. The phenomena which have been observed in plasma reactors containing fluorine atoms are also observed in our experiments. The data has led to a model which explains the major trends.
Constant Final-State Photoemission Study of Silicon Fluoride Reaction Layer Created During Etching: Morphology of the Reaction Layer
Authors: Yarmoff J. A. , McFeely F. R.
Published: March 2011

Soft x-ray core-level photoemission was used to study the reaction layer formed on a Si(111) surface during steady-state etching by XeF2. These surfaces show shifted Si 2p core levels which correspond to particular silicon fluoride species residing in the reaction layer. Spectra were collected in constant final state (CFS) mode for electron kinetic energies ranging from 2 eV to 90 eV. The use of CFS mode allowed the electron escape length to remain constant during individual spectra. The electron escape length for the reaction layer as a function of kinetic energy was then determined by monitoring the intensity of the bulk silicon signal. Thus, by analyzing the proportions of each silicon fluoride species observed in the individual CFS spectra as a function of the electron escape depth in the reaction layer, the distribution of the silicon fluoride species in the layer was obtained. The distribution determined placed SiF at the interface between the reaction layer and the bulk silicon, and the remaining species, SiF2, SiF3 and SiF4, successively layered on top. This observation leads to a model for the structure of the reaction layer.
Surface Temperature Rise Induced by a Focused Laser Beam. Application to Laser-Induced Chemical Vapor Deposition
Authors: Kodas Toivo T. , Baum Thomas H. , Comita Paul B.
Published: March 2011

Surface temperatures of a laser-heated structure consisting of intersecting gold and nickel lines on an Si substrate with an SiO2 surface layer were determined experimentally and theoretically. Temperatures were measured with micron-sized thin-film thermocouples formed from intersecting gold and nickel lines. Temperature profiles were calculated using a finite difference method which took into account the optical and physical properties of the thermocouple metal lines, the silicon dioxide layer and the silicon substrate. For a 0.2 μm SiO2 layer, maximum surface temperatures were much higher with the metal lines than without because of the lower reflectivity of the gold relative to the silicon and the limited ability of the thin metal lines to conduct heat away from the irradiated region. Calculated maximum temperatures on the metal lines depended strongly on the thicknesses of the insulating SiO2 layer and the metal lines. Application of these results to the dynamics of laser-induced chemical vapor deposition is discussed.
Excited-Atom Production by Electron Bombardment of Alkali-Halides
Authors: Walkup R. E. , Avouris Ph. , Ghosh A. P.
Published: March 2011

We present experimental results which suggest a new mechanism for the production of excited atoms and ions by electron bombardment of alkali-halides. Doppler shift measurements show that the electronically excited atoms have a thermal velocity distribution in equilibrium with the surface temperature. Measurements of the absolute yield of excited atoms, the distribution of population among the excited states, and the dependence of yield on incident electron current support a model in which excited atoms are produced by gas-phase collisions between desorbed ground-state atoms and secondary electrons. Similarly, gas-phase ionization of ground-state neutrals by secondary electrons accounts for a substantial portion of the positive ions produced by electron bombardment of alkali-halides.
Laser Microfabrication Technology and its Application to High Speed Interconnect of Gate Arrays
Authors: Bernhardt Anthony F. , McWilliams Bruce M. , Mitlitsky Fred , Whitehead John C.
Published: March 2011

Nickel and doped polysilicon lines can be written at speeds exceeding 1000 microns/sec using laser direct-write deposition. We explore the roles of gas pressure, composition, and laser power in determining writing speed and line morphology. The use of a surface layer of amorphous silicon provides optical absorption, thermal and electrical insulation which help to maintain high, relatively stable, surface temperature.

Laser direct-write deposition is used to interconnect CMOS gate arrays by means of computer controlled laser pantography. Complex circuits, such as an array of five 16-stage shift registers and one 16-stage counter have been successfully fabricated and tested.
Nucleation and Growth of Silicon Microstructures by Direct-Laser Writing
Authors: Kotecki David E. , Herman Irving P.
Published: March 2011

This paper reports on a study of the nucleation phase of thin film growth during pyrolytic deposition by direct-laser writing. A Monte Carlo computer simulation is used to model the initial surface dynamics occurring during the deposition of silicon from silane (SiH4) on strongly binding substrates such as silicon, and on weakly binding substrates such as silicon dioxide (SiO2) and silicon nitride (Si3N4). Results show that for high peak temperatures (≥ 1200 K) and weakly binding substrates, the most probable location for the initiation of thin film growth is radialy displaced from the center of the locally laser-heated region of the surface. At low peak temperatures, thin film nucleation is found to begin at the center of the locally laser-heated surface for all substrates.
Characterization of Surfaces and Thin Films by Means of an Ion Microprobe Analyzer
Authors: Izumi Eiichi , Ikebe Yoshinori , Shichi Hiroyasu , Tamura Hifumi
Published: March 2011

A variety of materials such as semiconductors, metals, and insulators have been analyzed by use of the Hitachi IMA-3 ion microprobe analyzer. From the depth profile of a GaAs/AQ GaAs superlattice(50Å), a depth resolution of 45Å was obtained at 2350Å below the surface. The stable depth profile of a multilayer plastic film was obtained by using the negative ion beam(O) as a primary ion for charge neutralization. Further, the usefulness of the total ion monitoring method for correcting the changing factors of secondary ion intensity is demonstrated.
Plasma Stimulated Growth of InP from TEL and PH3
Authors: Reinecke H. , Grafahrend F. , Brauers A. , Lüth H. , Balk P.
Published: March 2011

This study describes the application of a dc-plasma to stimulate growth of InP in a MOCVD system using In(C2 H5)3 and PH3. Precracking of PH3 enables a substantial reduction of the growth temperature to well below 500 K. In addition, at temperatures where InP is commonly deposited (∼870 K) a significant lowering of the V/III input ratio is possible. The fact that InP is relatively insensitive to low energy ion bombardement permits deposition in a canal ray configuration.
Plasma Deposition of Tungsten
Authors: Greenberg K. E.
Published: March 2011

Tungsten films were plasma-deposited using an abnormal glow discharge through a mixture of tungsten hexafluoride, hydrogen, and argon. The films adhered well to silicon, silicon dioxide, gallium arsenide, and aluminum substrates placed directly on the discharge cathode. Typical deposition rates were on the order of 160 Angstroms/minute with as-deposited film resistivities of 40 to 70 microohm-cm. The tungsten was analysed using a number of techniques including X-ray diffraction, scanning electron microscopy, and Auger spectroscopy, Low-resistivity (<10 microohm-cm) films that adhered well to silicon-dioxide were obtained with a two-step process utilizing plasma deposition and conventional chemical vapor deposition.
An Investigation into the Growth of Lead Titanate by MOCVD Using a Pyrolytic and a Sputter Assisted Plasma Process
Authors: Brierley Crofton J. , Considine Laurence , Sethi Rajinder S. , Whatmore Roger W.
Published: March 2011

The thin film growth of PbTiO3 by MOCVD has been investigated using both a pyrolytic process and a sputter assisted plasma deposition process. In the first process, lead tertiary butoxide and titanium iso-propoxide are introduced to a low pressure reactor simultaneously to deposit thin films containing lead and titanium onto a hot substrate (400–500 °C). In the alternative process lead is sputtered from a magnetron target in the presence of titanium isopropoxide vapour. Thin films containing lead and titanium are deposited onto a substrate which need not be heated. X-ray and EDAX analysis indicate the presence of Ti02 and elemental lead in the as grown layers. Oxygen annealing of ihese layers at 900° and 1100°C leads to the formation of polycrystalline PbTiO3 and where the substrate is silicon, a PbO/SiO2 glass phase.
Inductively-Coupled Plasma Nitriding of Fused Silica
Authors: Vethanayagam T. K. , Johnson P. F.
Published: March 2011

Plasma nitriding of fused silica has been performed over a temperature range of 750°C to 1300°C in a nitrogen-hydrogen plasma generated by an inductively coupled RF discharge. The plasma is used as both thermal and chemical source. The effects of various process parameters such as surface temperature, gas pressure and treatment time on total nitrogen content have been studied. The advantages and the drawbacks of this direct plasma nitriding technique are briefly discussed.
Corona-Discharge-Induced Stress Relaxation in Silicon Dioxide Films on Silicon
Authors: Landsberger L. M. , Tiller W. A.
Published: March 2011

Variations in refractive index (density) with growth temperature are taken as a rough measure of residual compressive stress in dry SiO2 films. This paper presents experimental data regarding the relaxation of these stresses by a low-temperature (600–900°C) oxygen corona discharge process. For an initial oxide layer of 1100 Å thickness grown at 800°C, relaxation is complete after a corona treatment of 10 minutes at -lμA. The dose of O− ions required is found to be about 1–1.5% of the total oxygen atoms in the initial layer. The difference in dose between oxide on (111) and (100) Si is found to be proportional to the respective density changes from the initial oxide to fully relaxed oxide.
Micromachining of Silicon Mechanical Structures
Authors: Kaminsky G.
Published: March 2011

Refined processing procedures for producing geometrically highly precise silicon structures are described. The structures are fabricated by the high-precision micromachining of silicon utilizing wet chemical orientation and/or concentration dependent, etching techniques. Very exact processing procedures required to reproducibly achieve good high quality structures with excellent large and small scale uniformity are detailed. Relief structures having features as small as 0.2μm have been produced. Some of the structures and devices attainable will be described including: (1) very high Q torsional oscillators useful as powerful probes of the mechanical properties of a variety of physical systems, (2) unstrained focusing x-ray mirrors, and (3) μm dimension mechanical “shadow masks” with multiple slit features having knife-edge acuity of much better than 1μm over an area ˜1cm2 and useful for noncontaminative, in situ patterning of thin films deposited in MBE or other vacuum deposition techniques.
Ion Beam Machining of Micromechanical Structures
Authors: Davies S. T. , Bowen D. K.
Published: March 2011

The needs of high precision engineering currently call for dimensional tolerances of the order of 0.1μm and surface roughness of order 0.01μm, often in hard, brittle materials or materials of relatively poor machinability. The development of argon ion beam machining for milling, drilling and turning or lathing is reported as a means of satisfying these requirements. Highly controllable material removal is achieved for the fabrication of micromechanical structures, profiling of surfaces and fine surface finishing. Surface evolution at submicron precision is demonstrated, with particular reference to the production of both circular and non-circular sections in an “ion beam lathe”.
Quantum Interference Effect in Narrow n+-GaAs Wires
Authors: Ishibashi Koji , Nagata Koh , Ishida Shuichi , Gamo Kenji , Aoyagi Yoshinobu , Kawabe Mitsuo , Murase Kazuo , Namba Susumu
Published: March 2011

Our experimental results about aperiodic magnetoconductance in narrow n+-GaAs wire are described. These wires are fabricated in an MOCVD grown n+-GaAs film by electron beam lithography and the dry etching technique. It is found that the aperiodic structure arises from the quantum interference which is important in small structures (<1in). The experimental results are compared to the recent theory.
Determination of the Threshold Energy of Noble Gas Defects in Silicon Created by Ion Beam Etching
Authors: Sawyer W. D. , Weber J.
Published: March 2011

Using photoluminescence we investigate defects introduced into silicon by ion beam etching. The luminescence spectra show the presence of various defects known from radiation damage studies. Ion-beam milling with different noble gas ions produces a family of defects which gives rise to almost identical photoluminescence spectra. The intensity of the Ar noble gas defect luminescence is studied for different ion-beam energies (200–2000eV) and crystal orientations. The threshold energy to create this defect leads to a model of the defect structure.
Thermal Reactions of Bisazides in Resists Containing Double Bonds
Authors: Pryde C. A.
Published: March 2011

Derivatives of 2,6-bis(4-azidobenzylidene) cyclohexanone are frequently used as photosensitizers in photoresists. These compounds are generally considered to be quite thermally stable. However, there have been reports of thermal degradation occurring at temperatures as low as 60'C.

Experiments done here suggest that the thermal stability of the azide is adversely affected by the presence of unsaturated material in the formulation. Data from IR spectroscopy show that, by itself, 2,6-bis(4-azidobenzylidene) 4-methylcyclohexanone is thermally stable in a polyamic acid film at 75–80° C. However, addition of a monomeric aminoacrylate to the formulation results in a significant decay in the absorption of the azide moiety in just a few hours at these same temperatures. This decay is attributed to reaction of the sensitizer with the acrylate double bonds. In a thick film, which might require a 1–2 hour prebake, this thermal addition could result in a significant degree of crosslinking and thus to decreased contrast in the final pattern.
Reactive Ion Etching and Lithographic Characterization of a New Organosilicon Resist
Authors: Tarascon R. G. , Shugard A. , Reichmanis E.
Published: March 2011

We describe the use of a novel organosilicon novolac as a base resin component of bi-level resist systems for both photo and electron-beam lithography. The lithographic evaluation of the new material demonstrates submicron resolution and high aspect ratio images with little linewidth loss after reactive ion etching (RIE). The optimization of the RIE conditions will be also discussed.
Microporous Amorphous Superlattices
Authors: Deckman H. W. , Abeles B. , Dunsmuir J. H. , Roxlo C. B. , Tiedje T.
Published: March 2011

Lithographic fabrication techniques have been extended to the molecular dimension by using the layer pattern in deposited amorphous superlattices as an etching template for the creation of slot structures. Fabrication considerations are discussed for the formation of 10–50Å slots structures suitable for studying shape selective chemistry with fluoresence spectroscopy.
Exploring Magnetic properties of Epitaxial Films and Superlattices
Authors: Erskine J. L. , Onellion M. F. , Thompson M. A.
Published: March 2011

Recent advances in spin-sensitive spectroscopie techniques combined with the rapidly expanding capabilities to synthesize novel materials utilizing molecular beam epitaxy (MBE) are stimulating new interest in magnetism and magnetic materials. Epitaxial growth offers opportunities to stabilize and study crystal phases of elemental magnetic materials which do not naturally occur in nature, and to vary the crystal parameters and composition of epitaxial films in precisely controlled ways. Multilayer superlattice films can also be fabricated using MBE. These structures offer unprecedented new opportunities to explore the relationship between crystal structure and various magnetic properties such as spontaneous magnetization, the Curie temperature and magnetic anisotropy in well characterized systems. The present paper reviews some of the more recent work on thin film magnetic systems including structure analysis of film quality, new techniques for probing the electronic and magnetic properties of the films and the important role large scale numerical calculations are beginning to play in guiding the choice of magnetic systems for study.
Anomalous Dispersion Corrections to Surface and Interface Exafs Measurements Made Using Glancing Angles
Authors: Chen Huaiyu , Heald Steve M. , Tranquada John M.
Published: March 2011

EXAFS studies using glancing angle fluorescence on the interface of the Cu-Al thin film system show that the sputtering process generates a different interface structure than for an evaporated one. To obtain quantitative information, the anomalous dispersion effects have to be considered. Simple model calculations are presented for the correction factor which yield good results for Au thin film data. Extension of this model to bilayer systems is discussed.
Simulation of Atomistic Crystal Growth from the Vapor Phase
Authors: Taylor Paul A. , Dodson Brian W.
Published: March 2011

We are in the process of studying strained-layer growth of two-dimensional Lennard-Jones lattices. To do so, we have developed three techniques, based on the Monte Carlo method and molecular dynamics, of simulating atomistic crystal growth from the vapor phase. The Monte Carlo method efficiently simulates the effects of long time-scale processes on the growth of strained-layer systems, but omits the transient dynamics of particle adsorption. The second technique, using molecular dynamics, gives results suggesting that epitaxial growth of strained-layer systems can occur on the picosecond timescales. However, this technique cannot capture the influence of the long time-scale processes on the growth process. In view of the shortcomings of the previous two techniques, A hybrid technique incorporating both the Monte Carlo method and molecular dynamics, has been developed. In principle, this technique models the transient dynamics of adsorption as well as the long term evolution of the system. This technique, however, is limited by artifacts that may only be eliminated by use of unwarrented amounts of supercomputer time.
Interdiffusion of Al and Ga in (Al,Ga)As/GaAs Quantum Wells
Authors: Schlesinger T. E. , Lee Jyh-Chwen , Kuech T. F.
Published: March 2011

We have employed photoluminescence spectroscopy to determine the interdiffusion of Al and Ga in (Al,Ga)As/GaAs quantum wells. The luminescence due to the n=l electron to heavy hole transition in these wells before and after anneal was measured. A variational calculation was employed to determine the expected position of this luminescence peak both before and after the anneal. A single diffusion coefficient, D, was used to model the interdiffusion of the Al and Ga and from the shifted position of the luminescence peaks under various anneal conditions of time and temperature its value was determined. These measurements were performed as a function of temperature to yield ΔE where D = D0e -ΔE/KT. This diffusion coefficient was also studied as a function of the initial Al composition in the cladding layers which ranged from 0.3 to 1.0.
Characterization of the a-SN/CDTE(110) Interface by Angle-Resolved X-Ray Photoemission
Authors: Lin Tzer-Shen , Partin William J. , Chung Yip-Wah
Published: March 2011

Stoichiometric and atomically clean CdTe(110) surfaces have been prepared by suitable chemical etching, followed by argon sputtering, and sample annealing in ultra-high vacuum. Cubic (α) -tin was grown on CdTe(110) by tin evaporation from a tungsten filament at a substrate temperature of 30 °C. Angle-resolved X-ray photoelectron spectroscopy (ARXPS) was used to determine the a-Sn growth mechanism and the composition profile of this semiconductor heterostructure nondestructively. From our analyses, we conclude that a-Sn grows on CdTe(110) at 30 °C by a layer by layer mechanism and forms an abrupt junction with CdTe(110).
Transition from Schottky Limit to Bardeen Limit in the Schottky Barrier Formation of al on n- and p-GaAs(110) Interfaces
Authors: Chin K. K. , Cao R. , Kendelewicz T. , Miyano K. , Williams M. D. , Doniach S. , Lindau I. , Spicer W. E.
Published: March 2011

Schottky barrier formation at room temperature (RT) and low temperature (LT) is studied by photoemission. In the low Al coverage regime (from 0.001 to about 1 ML), it is found that, compared to RT pinning behavior, the n-GaAs(110) surface band bending is attenuated, while the p-GaAs(110) surface band bending is enhanced. This striking phenomenon indicates that, by lowering the substrate temperature, one reduces the disturbance of the GaAs(110) surface, and the surface Fermi level of the n- and p-GaAs(110) tends to go to the same position, the so-called Schottky limit that characterizes a perfect defect-free interface. However, as the coverage increases (up to 30 ML), a new mechanism (in the framework of the unified defect model, it is the formation of defect levels due to the energy released as the adsorbed Al atoms start to form clusters and replace Ga) associated with a disturbed surface becomes dominant. Thus, the LT Fermi level positions of n- and p-GaAs move towards the RT positions, the so-called Bardeen limit. This demonstrates that, by controlling the surface disturbance, one can modify the Schottky barrier formation process, going from the Schottky limit which does not have pinning centers to the Bardeen limit which suggests the existence of pinning centers.
Monte Carlo Simulation of the Growth of ZnSe by MBE
Authors: Venkatasubramanian R. , Otsuka N. , Datta S. , Kolodziejski L. A. , Gunshor R. L.
Published: March 2011

A Monte Carlo study of the growth of ZnSe by Molecular beam epitaxy is presented. The study is focused on the role of surface kinetic reactions on the structural quality of the epilayers. Two different models for the incorporation of Se molecules, one with a highly reactive physisorbed state and the other with a relatively nonreactive physisorbed state are employed for simulations. It is shown that the structural quality of the epilayers is very sensitive to the flux ratio if the physisorbed state is relatively nonreactive. It is also shown that if the physisorbed state is highly reactive, good quality epilayers are obtained over a wide range of flux ratio.
Modulated Amorphous Alloy Films
Authors: Chien C. L. , Liou S. H. , Natan M.
Published: March 2011

We have made modulated solids consisting of several hundred layers of a-Fe80Zr20/a-Ni30Nb70 in which the layer thicknesses are a few nanometers. The modulating nature of the sample and the flat growth of the layers are confirmed by cross sectional TEM. The layers of a-Ni30Nb70 are non-magnetic and serve as inert layers separating the magnetic a-Fe80Zr20 layers. By varying the thickness of the a-FegoZr20 layers, the thickness dependence of the magnetic properties has been studied. The sign of the magnetic surface anisotropy constant has been determined.
Rf Magnetron Sputter Deposition and Characterization of Aluminum Nitride thin Films
Authors: Krupanidhi Saluru B.
Published: March 2011

Highly crystalline and resistive thin films of aluminum nitride have been rf magnetron sputter deposited. The films were characterized in terms of structure, electrical and optical properties. A perfect c-axis orientation along (002) direction was obtained, in the reactive sputtered films from a metal target, keeping the substrates as low as 350°C. The structural and electrical properties were observed to be sensitive to deposition conditions. It has also been observed that the combination of higher powers and low sputtering pressures, exposed the films to high energy neutral ion bombardment. A correlation between deposition parameters and the physical properties is presented.
Structure of Copper-Hafnium Multilayers
Authors: Clemens B. M. , Stec J. P. , Heald S. M. , Tranquada J. M.
Published: March 2011

The structure of copper-hafnium multilayers has been studied as a function of composition modulation wavelength by x-ray diffraction and EXAFS. Sputter deposited samples were produced with composition modulation wavelengths of 1/2, 5, 7, 10, 14, and 20 close packed planes of each constituent per layer. The structure evolved anisotropically from amorphous to crystalline with increasing composition modulation wavelength, with crystalline order first appearing in the growth direction in the 7 mono-layer sample. Structural coherence in the growth direction was not observed to extend beyond one elemental layer in any sample, and evidence for a disordered interfacial layer was observed by EXAFS for all samples. Small angle x-ray diffraction showed strong composition modulation for all but the 1/2 monolayer sample. The amorphous interface is the result of reaction during deposition similar to the solid state reaction observed in other systems such as nickel-zirconium.
TI-X Alloy Composition Modulated Layered Structures
Authors: Jankowski A. F. , Adams R. O. , Williams L.
Published: March 2011

The binary alloy series of Ti-X metallic, composition modulated layered structures has been fabricated via magnetron sputtering. The Ti-X systems (where X is Ta, Mo, or V) explored are exemplary of solid solution systems, such as the supermodulus systems of Cu-Ni, Ag-Pd, Au-Ni, and Cu-Pd (which all feature fee crystalline compatibility). In the present case, the beta-phase of Ti sought in these Ti-X systems suggests bec crystalline compatibility, with interlayer misfit strains not exceeding 10%.

The Ti-X series examined, matches elements of high and low atomic number. (Z of Ti, V, Mo, and Ta are 22, 23, 42, and 73, respectively.) Difficulties which arise in a conventional tungsten basket - alumina crucible physical vapor deposition process, i.e. obtaining thr vaporization temperatures for Ti, V, Mo and Ta of 1235, 1332, 1822, and 2240 °C at 130 mPa, respectively, are overcome by magnetron sputtering. Thin films produced by alternate deposition of Ti with V, Mo, or Ta, are desired with individually unique, regular repeating layer thicknesses which range from 1.5 to 15 nm.

An initial characterization of the Ti-X composition modulated alloys has been conducted using X-ray diffraction. The pole figure constructions of the various composition wavelengths give a qualitative look at the strain accomodation within the thin films and possible manifestations in mechanical properties.
Superconducting Properties of v/cr Artificial Metallic Superlattices
Authors: Davis B. M. , Zheng J. Q. , Ma M. R. , Jin B. Y. , Hilliard J. E. , Ketterson J. B.
Published: March 2011

We have studied the superconducting properties of V/Cr superlattices. Superlattices of V100Crx, V150Crx, and V200Crx, with x varying between 3 and 80 atomic planes have been prepared. The films have a strong (110) texture and were grown on sapphire substrates at 250°C in an ultra-high vacuum system. The zero field transition temperature of the V150Crx and V200Crx, but not the V100Crx films have been adequately modeled using Werthamer's theory for proximity effect coupled films. The films have a dimensional crossover in the parallel upper critical field when the thickness of the Cr layers is about 60 atomic planes.
Phase Transitions in the Picosecond Time Domain
Authors: Elsayed-Ali Hani E. , Mourou Gerard A.
Published: March 2011

The physical processes occurring during the initial stages of ultrafast laser heating of metals are described. Femtosecond laser irradiation is used to create nonequilibrium heating in metals. In such a nonequilibrium state, the electron temperature can be heated up to a few thousand degrees above the lattice temperature. Electron-lattice relaxation is time-resolved in copper and found to be 1 – 4 ps depending on the laser heating ffuence. The technique of time-resolved electron diffraction (a lattice structural and temperature probe) is described. Utilization of this technique for lattice temperature measurement of thin metal films is demonstrated.
High Temperature Stability of Amorphous TaxCu1-x Diffusion Barriers on GaAs
Authors: Oh J. E. , Pouch J. J. , Ingram D. C. , Alterovitz S. A. , Woollam J. A.
Published: March 2011

The x value of the most thermally stable co-sputtered TaxCu1-x alloy films are found to correlate with measured maximum temperature coefficients of resistance as a function of alloy composition. To investigate the possible application of these materials as diffusion barriers for the Au-GaAs system, vacuum annealing and infrared rapid thermal annealing are made over a wide temperature range. Resistivity changes, X-ray diffraction, Auger electron spectroscopy, and Rutherford backscattering measurements are performed to find the metallurgical stabilities of these materials at elevated temperatures.

For high x values, the reaction temperature for TaxCu1-x, in contact with GaAs lies between 500 and 700°C. For Au in contact with TaxCu1-x the TaxCu1-x/GaAs reaction occurs at about 600°C. Amorphous Ta93Cu7 exhibits uniform mixing with surrounding elements, whereas Ta80Cu20 exhibits phase separation.
Propagation of Acoustic Phonons in Amorphous Superlattices
Authors: Santos P. V. , Ley L. , Mebert J. , Koblinger J.
Published: March 2011

We have investigated the Raman and the phonon transmission spectra of a-Si:H/a-SiNx:H super lattices. At low wavenumbers, the Raman spectrum shows sharp peaks corresponding to the excitation of modes from the folded branches of the dispersion relation for longitudinal acoustic phonons propagating perpendicular to the layers. Energy gaps in the folded phonon dispersion occur at the center and at the boundary of the mini-Brillouin zone due to the differences in the acoustic impedances of the layers. The size of the lowest gaps was determined by light scattering. The phonon transmission spectra show transmission minima that we attribute to the frequency gaps in the dispersion of transversal acoustic phonons. The position and width of these minima are compared with the dispersion obtained from the Raman data.
Structure of Amorphous Semiconductor Interfaces Determined from in Situ Optical Reflectivity Measurements
Authors: Yang L. , Abeles B.
Published: March 2011

The optical reflectivity at 6328Å of a-Si:H, a-Ge:H, a-Si:H/a-SiNx:H and a-Si :H/a-SiOx:H interfaces can be explained by a model of chemically abrupt interfaces that are macroscopica!ly rough on a scale of 10–20Å.
Photoemission Study of the a-Si-H/a-SiOx:H and a-Si:H/a-SiN:H Interface Formation
Authors: Eberhardt W. , Abeles B. , Yang L. , Stasiewski H. , Sondericker D.
Published: March 2011

We report a study of the interface formation between a-Si:H and a-SiOx:H or a-SiN:H in the coverage regime from a submonolayer to a few layers. The films were grown by plasma assisted CVD and characterized by photoemission. Our studies show that the growth mechanism is different for a-SiOx:H on a-Si:H than for a-Si:H on a a-Si:Ox:H. The growth of the a-SiNx:H/a-Si:H interface on the other hand is independent of the direction.
Optical Properties and Interface Study of a-Si:H/a-C:H Superlattices
Authors: Fangqing Zhang , Deyan He , Xixiang Xu , Jinzhong Cui , Guosheng Sun , Guanghua Chen , Yuliang He
Published: March 2011

Experimental results on a-Si:H/a-C:H superlattices, including the blue-shift of the optical band gap, the light-induced conductivity effect, the interface structure and the interfacial defects, are presented. Differences between our glow-discharge and sputter-prepared a-Si:H/a-C:H super lat t ices are described.
Initial Stages of Interface Formation in the Si/Sn System
Authors: Zinke-Allmang M. , Gossmann H.-J. , Feldman L. C. , Fisanick G. J.
Published: March 2011

Group IV-IV heterostructures with Sn as one constituent have potentially important applications. We report on an investigation of the initial stages of interface formation for deposition of Sn on Si(100)2×1 and Si(111)7×7. We find that simple growth occurs up to a critical coverage θc. (α1.25×1015 cm-2), independent of temperature. Beyond θc. growth continues to be laminar for deposition at 150 K only, while island formation is observed at temperatures at and above room temperature. The Si(111)7×7 reconstruction seems unperturbed by Sn deposition at room temperature while the Si(100)2×1 begins to order. However, the reordering, a necessary condition for perfect growth, is incomplete.
Compositional Determination of Silicon Oxynitride Films
Authors: Hatton Kenneth S. , Wachtman John B. , Haber Richard A. , Wilkens Barry
Published: March 2011

Silicon oxynitride thin films made by RF reactive sputtering can be made with varying composition along the silicon dioxide - silicon nitride tie line by control of the sputtering gases. Compositional determination was made by the Rutherford backscattering technique. A simple model relating film composition to the composition of the reactive gases is proposed which fits the experimental results.
Elastic Stresses in InGaAsP Heterostructures with Alloyed Contact Metallizations
Authors: Swaminathan V. , Lopata J. , Lee J. W.
Published: March 2011

We have measured the radius of curvature of InGaAsP/InP heterostruc-ture wafers grown by liquid phase epitaxy, after growth and after broad area p-and n-metallizations used in the fabrication of 1.3vm lasers, by the x-ray automatic Bragg angle control technique. The heterostructure consisted of an n-InP buffer layer (0.2μm), an InGaAsP active layer (0.3 – 0.4μm), a p-InP layer (0.7μm) and either a p-InGaAsP or a p-InGaAs cap layer (0.6 – 0.7μm) grown on a 250 μm thick n-Inp substrate. The radius of curvature measured after growth was found to be in good agreement with the value calculated using the lattice mismatch strains. The changes in the radius of curvature after deposition and alloying of a 1000 Å thick AuZnAu p-metallization and after thinning the substrate to 86μu followed by 2900 Å thick alloyed GeAu n-metallization are such that the metal films are under a tensile strain. The value of the strain is calculated to be 8 × 10-3 and 1.6 × 10-3 respectively for the p- and n-metals. The radius of curvature was measured after the final metallization and annealing of 2500 A thick TiPt layer on the p-side. The annealed TiPt layer was found to have a compressive strain of 6 × 10-3. The stress in the active layer remained tensile at all times for both wafers and it was in the range 9 × 10 – 1.4 × 10 dyne cm-2. These values are less than the estimated fracture stress of InGaAsP by an order of magnitude.
Molecular-Dynamics Simulation of Thin-Film Growth
Authors: Schneider Matthias , Schuller Ivan K. , Rahman A.
Published: March 2011

The epitaxial growth of thin films has been studied by molecular-dynamics computer simulation. In these simulations atoms are projected towards a temperature-controlled substrate, and the equations of motion of all atoms are solved for a given interaction potential. The calculations give insight into the microscopic structure of thin films, the dynamics of the adsorption process, and they help answer the way in which substrate temperature, form of the substrate, flux of impinging atoms, and form of the interaction potential, affect epitaxial growth. Simulations were performed for monatomic and binary systems with spherically symmetric atomic interactions, and for systems in which the atoms are interacting via a three-body potential to simulate the epitaxial growth of silicon.
Strength Improvement in Transformation Toughened Ceramics using Compressive Residual Surface Stresses
Authors: Cutler R. A. , Hansen J. J. , Virkar A. V. , Shetty D. K. , Winterton R. C.
Published: March 2011

A1 2 03–15 vol. % ZrO2 bar shaped composite specimens were fabricated by pressing three layers. The two outer layers consisted of Al2O3 and unstabilized ZrO2 (primarily in the monoclinic polymorph), and the inner layer consisted of Al2O3 and partially stabilized zirconia in the tetragonal polymorph. The transformation of ZrO2 from tetragonal to monoclinic, upon cooling from sintering temperature, led to the establishment of residual compressive stresses in the outer layers. Flexural tests at room temperature showed that residual stresses contributed to strength increasing from 450 to 825 MPa. The existence of these stresses was verified by measuring apparent fracture toughness, as well as using strain gages. Strength and toughness data were obtained at 500, 750, and 1000°C. X-ray diffraction was used to explain the elevated temperature data by monitoring the monoclinic to tetragonal transformation upon heating to 1000°C.