bluuebunny/crossref_metadata_2025 huggingface dataset:
Thin Film Growth using Ablation of Ceramics with a Lina-Spark™ Atomizer
Authors: Hourlet R. , Vacassy R. , Hofmann H. , Vogel W.
Published: April 2011

A laser spark atomizer (LINA-SPARK™), LSA, has been used for preparing powder particles from SnO2, Al2O3 and ZrO2 ceramic specimen. It is shown that this technique can be used for preparing thin films by direct deposition on a substrate. The as-prepared powder can also be redispersed and deposited using ultrasonic nebulization (Pyrosol) deposition. The latter approach is especially suited for deposition of controlled-size and multicomponent thin films.

The coupling of the LSA to an induced coupled plasma (ICP) emission spectrometer is also discussed and compared with laser ablation. Generally powder particles produced from LSA present a narrower size distribution as powders prepared by laser ablation. As a result, the quantitative elemental analysis of solids are improved with full benefit of the sensitivity and detection limits of the ICP are lowered.
Automatic Control and Real-Time Monitoring of Laser Cleaning and Laser Ablation
Authors: Lu Y.F. , Meng M. , Hong M.H. , Low T.S. , Chan D.S.H.
Published: April 2011

Closed-loop control and real-time monitoring of pulsed excimer laser cleaning and ablation have been realised by software and hardware design and development. The audible acoustic wave generated during excimer laser surface cleaning and ablation has been used as the feedback signal for the automatic control system of laser-surface interaction. Man–machine interface for laser operation and acoustic monitoring has been developed with LabVIEW 4.1 under Windows 95 environment. This system has been used to control and monitor laser cleaning and ablation processes in real-time and proven to successfully meet the requirements in our study. By database exchange, this automatic control system can also be applied to control drilling and materials removing.
Preparation of PZT/YBCO/YAIO Heterostructure Thin Films by KrF Excimer Laser Ablation
Authors: Ebihara Kenji , Kurogi Hiromnitsu , Yamagata Yukihiko , Ikegami Tomoaki , Grishin Alexander M.
Published: April 2011

The perovskite oxide YBa2Cu3O7-x (YBCO) and Pb(ZrxTi1-x)O3 (PZT) thin films have been deposited for superconducting-ferroelectric devices. KrF excimer laser ablation technique was used at the deposition conditions of 200-600mTorr O2, 2-3J/cm2 and 5-10 Hz operation frequency. Heterostructures of PZT-YBCO-YAlO3:Nd show the zero resistivity critical temperature of 82K and excellent ferroelectric properties of remnant polarization 32 μC/cm2, coercive force of 80kV/cm and dielectric constant 800. Cycling fatigue characteristics and leakage current are also discussed.
Mesoscopic Model for The Laser-Target Interaction
Authors: Ribeiro R. Mendes , Ramos Marta M.D. , Stoneham A.M.
Published: April 2011

We have developed a mesoscopic model for the study of pulsed laser ablation of transparent granular ceramics. The model enables the understanding of several features that happen at the surface of a transparent target and which play an important role in the evolution of the evaporation process.

The results show that electron emission happens early, much before atom evaporation. High defect concentration regions (including grain boundaries, surface) are crucial for energy absorption. The model also predicts the generation of high intensity electric fields in places with high defect concentration, such as grain boundaries. Low fluences should have selective species removal, but higher fluences should give congruent removal.

The dependence of the density of generated electrons, the evaporated species and energy on the material properties is included.
Laser Ablated CuCo Thin Films Exhibiting Controlled Anisotropic Giant Magnetoresistance
Authors: Madurga Vicente , Vergara J. , Ortega R.J. , Rao K.V.
Published: April 2011

Controlled microstructured thin films with nominal composition Cu95Co5 have been deposited on glass substrates by pulsed laser ablation at room temperature, in vacuum, for different target speed rotation. Atomic Force Microscopy, AFM, studies have shown a surface roughness not higher than 0.5 nm, for the as-deposited samples, which do not exhibit magnetoresistive, MR, behaviour. X-ray diffraction analysis show broad diffraction peaks, slightly shifted from pure Cu reflection peaks. After annealing, the samples show GMR. The AFM investigations reveal a surface roughness of =6.8 nm and =9.2 nm for the samples prepared with high and low target speed rotation, respectively. Furthermore the GMR data correspond to a strong anisotropic behaviour. A reversible MR is exhibited, for all the films, exclusively for perpendicular to the films plane applied magnetic field. Hysteretic MR behaviour is observed for any other direction: in the range of 70-80 deg., coercive MR fields from 0.17 Tesla to 0.05 Tesla are observed for the samples obtained at 10 rpm to 32 rpm respectively target speed rotation. These properties are discussed in terms of the shape anisotropy of magnetic Co nanoparticles.
Epitaxial Growth of YBa2CH3O7-δ Films on Rolling-Assisted Biaxially Textured Substrates (RABiTS) Produced by Pulsed Laser Ablation at Low Temperatures
Authors: Mathis J. E. , Goyal A. , Paranthaman M. , Specht E. D. , Kroeger D. M. , Lee D. F. , Martin P. M.
Published: April 2011

Epitaxial YBa2Cu3O7-δ (YBCO) films were fabricated using laser ablation of YBCO onto rolling-assisted-biaxially-textured-substrates (RABiTS) at a temperature of 650°C. The configuration of the sample was YBCO/YSZ/CeO/Ni. The CeO2 and YSZ buffer layers were deposited using electron-beam evaporation and sputtering, respectively. Both of these techniques are considered to be industrially scalable. SEM images of the YBCO reveal a range of structures ranging from jumbled a-axis to dense c-axis morphologies depending upon the deposition conditions. X-ray θ-2θ scans show a similar c-axis dependence on the deposition conditions.
Pulsed Laser Deposition of Nd-Doped YBa2Cu3O7-x Films for Coated Conductor Applications
Authors: Varanasi C. , Biggers R.R. , Maartense I. , Dempsey D. , Peterson T.L. , Solomon J. , Mcdaniel J. , Kozlowski G. , Nekkanti R. , Oberly C.E.
Published: April 2011

Pulsed-laser ablation was used to deposit YBa2Cu3O7-x (YBCO) films on LaAlO3 and metallic substrates in an effort to understand and develop the processing of coated conductors with enhanced properties. Doping of YBCO films with Nd was utilized as an approach for increasing their flux pinning properties. Separate targets of Nd2O3 and YBCO were used instead of a pre-mixed Nd2O3-YBCO target. The critical current density (Jc) of the films was measured by whole body dc transport measurements and the transition temperature (Tc) by ac susceptibility. The composition vs. depth profiles of the films were obtained by Secondary Ion Mass Spectrometry. The critical current of a 5000 Å thick Nd-doped YBCO film on a LaAlO3 substrate was measured at 77 K and found to be 57 A (Jc = 1.1×106 A/cm2).
Pulsed Laser Deposition of Undoped and Ag-Doped Stacked Structures of YBaCuO for Bolometer Device Applications
Authors: Moxey D. E. , Kalyanaraman R. , Sharma A. , Narayan J. , Lee C. B. , Muth J.
Published: April 2011

In this paper we report our investigations related to the growth and characterization of superconducting stacked structures of YBaCuO(undoped)/YBaCuO(Ag-doped)/YSZ layers processed on Si(100) substrates. These films were deposited using pulsed laser deposition (PLD), and have been characterized using X-ray diffraction, scanning electron microscopy (SEM), and four probe electrical measurements. SIMS analysis has also been used to study the incorporation and diffusion of carbon in the superconducting layer. The focus of this work is on the issues of the role of silver in the superconductor, and its effects on the transport properties and microstructure of the structure. We also discuss the use of these films for bolometer device applications.
Study of Substrate Diffusion in Epitaxial N-Type CdSe Films Grown on GaAs (001) by Pulsed Laser Ablation
Authors: Park Jaewon , Rouleau Christopher M. , Lowndes Douglas H.
Published: April 2011

N-type CdSe films with thicknesses of 470 - 630 nm were grown on (001) and 2°- miscut GaAs wafers by ArF (193 nm) pulsed laser ablation of stoichiometric CdSe targets at platen temperatures (Tp) of 250 - 425°C in vacuum and ambient Ar gas. Film-substrate interdiffusion was studied with Auger depth profiling, as well as energy dispersive x-ray fluorescent spectroscopy (EDS). Both techniques showed that extensive interdiffusion took place at the film-substrate interface for CdSe films grown at Tp≥ 355°C but was greatly reduced at Tp=250°C. Tilting the substrate to be approximately parallel to the ablation plume as well as decreasing the ambient gas pressure also reduced film-substrate interdiffusion.
Synthesis of Single Crystal Gallium Nitride Films on Sapphire by Pulsed Laser Deposition
Authors: Sharma A.K. , Oktyabrsky S. , Dovidenko K. , Narayan J.
Published: April 2011

Pulsed laser deposition has been explored to synthesize gallium nitride films on c-plane sapphire by ablating a pressed GaN target in vacuum. The films were characterized by X-ray diffraction, and high resolution transmission electron microscopy to study the nature of epitaxy, growth, and defect content. Single crystal films with narrow o0-rocking curve width were deposited in the substrate temperature range 700-780°C. High resolution microscopy revealed uniform film surface at lower substrate temperature for films as thin as 150 nm. The predominant extended defects were found to be threading edge dislocations (Burgers vector 1/3<1120>) with the density ~1010 cm-2. The thickness of all these films were in the range 100-150 nm. The coexistence of zincblende phase of GaN alongwith wurtzite phase was found in the film deposited at 780°C. The stabilization of metastable zincblende phase at higher temperature point towards the noneqilibrium nature of laser ablation. These preliminary results indicate the potential of PLD to synthesize high quality GaN films free of hydrogen.
Microstructure and IR Range Optical Properties of Pure DLC and DLC Containing Dopants Prepared by Pulsed Laser Deposition
Authors: Wei Q. , Sharma A.K. , Narayan R.J. , Ravindra N.M. , Oktyabrsky S. , Sankar J. , Muth J.F. , Kolbas R.M. , Narayan J.
Published: April 2011

We have investigated the microstructure and the IR range optical properties(emittance, transmittance and reflectance) of diamond-like carbon (DLC) films with the incorporation of dopants. The DLC films were deposited by pulsed laser deposition with a novel target configuration allowing incorporation of dopants, such as silicon, titanium and copper, into the films. Raman spectroscopy, radial distribution function (RDF) and coordination defect analysis of the electron diffraction pattern of the films showed typical features of DLC with a structure dictated by sp3 bonded carbon, indicating that the overall DLC characteristics did not change upon doping. The IR range optical measurements showed that in addition to the general band-toband transitions, free carriers and phonon contributions, localized states also contribute to the emissivity in DLC and they smooth out the sharp features of the emissivity spectra. The effect of dopants is to enhance the contribution from the free carriers and localized states. The results were discussed on the basis of the effect of dopants on the electronic structure of DLC films.
Vacuum Ultraviolet and Visible Optical Emission Spectra from Laser Ablation of Graphite at 193 NM: Application to Carbon Nitride Thin Films Deposition
Authors: Henck R. , Fuchs C. , Fogarassy E. , Hommet J. , Le Normand F.
Published: April 2011

Optical emission spectra in the ultraviolet and visible range (110-600 nm) were recorded during pulsed ArF laser ablation of graphite targets in vacuum and in low pressure N2 atmospheres. During graphite ablation in vacuo, the recorded spectrum consists only of several atomic lines lying below 300 nm. They are due to radiative transitions from upper carbon excited states down to the fundamental one. The most intense atomic lines are observed at 247.85 nm and near 165.5 and 156 nm. During ablation in increasing nitrogen pressure, the spectra are quickly dominated by the bands of the CN violet system whereas the intensity of the atomic lines only slightly increases. We have observed the bands corresponding to the vibrational sequences Δv = +1 (358.4-369.7 nm), Δv = 0 (384.7-394.4 nm) and Δv = -1 (414.3-421.6 nm). They already appear at nitrogen pressure as low as 0.05 mbar. Their intensity reaches a broad maximum between 0.5 and 0.8 mbar and slowly decreases.Taking into account the results of this optical study, the deposition of carbon nitride thin films has been undertaken. The surface analysis by X-ray photoelectron spectroscopy (XPS) of the obtained C1-xNx deposits shows a correlation law between the nitrogen incorporation (x) and the pressure of nitrogen.
Diamondlike Carbon, Carbon Nitride, and Titanium Nitride Coatings on Metal and Polymer Substrates
Authors: Narayan R.J. , Wei Q. , Sharma A.K. , Cuomo J.J. , Narayan J.
Published: April 2011

We have deposited diamondlike carbon, carbon nitride, and titanium nitride biocompatible coatings using pulsed laser deposition and magnetron sputtering on metallic (cobalt-chromium and titanium- 6% aluminum- 4% vanadium) and polymeric (high-density polyethylene) substrates commonly used in human prosthetic devices. A major advantage of the magnetron sputtering deposition technique is that it provides conformal coverage of large-area films. The coatings were characterized by electron diffraction and imaging, Raman spectroscopy, X- ray photoelectron spectroscopy, and electron- energy loss spectroscopy, and nanoindenter hardness measurements. The physical properties (especially hardness) of the diamondlike carbon films were controlled using carbide and noncarbide forming elements. By varying the doping concentration as a function of thickness, functionally gradient materials with superior tribological and mechanical properties can be created. The implications of these results are discussed in the context of biomedical applications.
Excimer Laser Ablation of Silicon at High Temperature
Authors: Zhang Y.F. , Tang Y.H. , Lee C. S. , Wang N. , Bello I. , Lee S.T.
Published: April 2011

Pulsed laser ablation of granulated Si target was carried out at 1200 °C in an Ar atmosphere. Multishot ablated target surface forms intensity dependent features, including porous, skeleton, and columnar structures. Very long columnar structures were observed when the angle of the target surface with respect to the direction of the laser beam was small. Evidence on preferable remove of smaller particles has been observed. Formation of the columnar structures started from the biggest particles at the surface and grew deeper, straight in the laser beam direction, by consuming the removed Si species from the deep channel between columns. The Si species ablated off the granulated Si target deposited as Si nanowires or nanoparticles down stream of the Ar flow. Significant decrease in the deposition rate of Si nanostructures has been observed upon the formation of the columnar structures at the target surface.
Real-Time Monitoring of Indium Tin Oxide Laser Ablation in Liquid Crystal Display Patterning
Authors: Hong M.H. , Lu Y.F. , Meng M. , Low T.S.
Published: April 2011

Audible acoustic wave detection is applied to investigate KrF excimer laser ablation of Indium Tin Oxide (ITO) thin film layer for Liquid Crystal Display (LCD) patterning. It is found that there is no acoustic wave generation if laser fluence is lower than ITO ablation threshold. For laser fluence higher than the threshold, audible acoustic wave will be detected due to shock wave generation during ITO laser ablation. The amplitude of the acoustic wave is closely related to the laser ablation rate. With more laser pulse applied, the amplitude is dropped to zero because the ITO layer is completely removed. However, if laser fluence is increased higher than ablation threshold for glass substrate, the amplitude is also dropped with pulse number but not to zero. It is due to laser ablation of ITO layer and glass substrate at the same time. Since the thickness of ITO layer is in a scale of 100 nm, laser interaction with glass substrate will happen even at the first pulse of high laser fluence irradiation. Laser ablation induced ITO plasma emission spectrum in visible light region is analyzed by an Optical Multi-channel Analyzer (OMA). Specific spectral lines are In I (325.8, 410.2 and 451.1 nm) and In II 591.1 nm. Spectral intensities of 410.2 and 451.1 nm lines are selected to characterize the evolution of ITO plasma intensity with laser fluence and pulse number. It is found that the spectral intensities are reduced to zero with laser pulse number. It is also found that spectral lines other than ITO plasma will appear for laser fluence higher than ablation threshold for glass substrate. Threshold fluences for glass and ITO ablation are estimated for setting up a parameter window to control LCD patterning in real-time.
Atomic Defects in Intermetallic Compounds and Diffusion Processes
Authors: Schaefer H.-E. , Frenner K. , Würschum R.
Published: April 2011

For the understanding of the properties of the technically important intermetallic compounds as transition metal aluminides and silicides the understanding of atomic defect properties is pivotal. From recent positron lifetime studies high or low values for the effective vacancy formation enthalpy were found for close-packed or for more open-structured bcc type compounds, respectively, which can be well understood theoretically. In B2-FeAl the vacancy migration enthalpy could be additionally derived at high temperatures from vacancy equilibration processes. It is shown here by a study on B2-FeAl in comparison to the positron annihilation experiments that the thermal formation and migration of defects can be specifically investigated by time-dependent length-change experiments at high temperatures by the defect equilibration behavior after temperature changes. With the present data on vacancy formation and migration the wide variation of the transition-metal self-diffusivities in intermetallic compounds can be understood.
Theory and Simulation of Diffusion Kinetics in Intermetallic Compounds
Authors: Murch G.E. , Belova I.V.
Published: April 2011

In this paper we provide an overview of the progress that has been made in the understanding of diffusion kinetics in intermetallic compounds. Both analytical theories and computer simulation are dealt with and the following ordered structures are covered: B2 (and B1), L12, A15 and DO3.
Point Defects and Diffusion in Ni3Ga
Authors: IKEDA T. , Almazouzi A. , Funao A. , Numakura H. , Koiwa M. , Shirai Y. , Nonaka K. , Sprengel W. , Nakajima H.
Published: April 2011

The properties of intrinsic point defects and the self-diffusion behaviour of the constituent elements in Ni3Ga have been studied by positron annihilation, tracer diffusion and interdiffusion experiments. Thermal vacancies have been detected by positron lifetime measurements for specimens quenched from high temperatures. The vacancy formation energy is in the range between 1.7 and 1.8 eV, and is not dependent strongly on the composition. The tracer diffusion coefficients of Ni and Ga are of the same order of magnitude, and the interdiffusion coefficient is about 10 times larger than the diffusion coefficient of Ni. The diffusion in Ni3Ga has been found to satisfy the Darken-Manning equation, as expected from the model of the self-diffusion in this type of materials, where both the species of atoms are assumed to migrate primarily in the sub-lattice of the major element via the ordinary vacancy mechanism.
Mechanism of “Order-Order” Kinetics in Ll2 Superstructure Studied by Computer Simulation
Authors: Oramus P. , Kozubski R. , Cadeville M.C. , Pierron-Bohnes V. , Pfeiler W.
Published: April 2011

Monte Carlo simulations of the isothermal long-range order (LRO) relaxation in A3B system with Ll2 superstructure have been performed within a model based on a vacancy jump mechanism between nearest neighbour lattice sites. The studies aimed at the explanation of the origin of two simultaneous LRO relaxation processes experimentally observed in Ni3Al. An effect of pair interaction energies and saddle-point energies (assigned to jumping atoms) was studied. The preference of vacancies for the A-sublattice (face centres), commonly postulated for Ni3Al, occurred only for a narrow range of pair-interaction energies within the domain corresponding to Ll2 ordering. It was found that the appearance of the fast relaxation process is definitely correlated with the efficiency of B-atom jumps, as well as with the values of the saddle-point energies. The results lead to a microscopic model of the “order-order” relaxation in Ll2 superstructure and yield new indications for the choice of pair-interaction energy parameters applied in Monte Carlo simulations of atomic migration in Ll2 intermetallic compounds.
Grain Boundary Diffusion and Segregation in the Solid State Phase Transformations
Authors: Rabkin E. , Gust W.
Published: April 2011

We consider the problem of solute diffusion and segregation in the grain boundaries moving during a phase transformation in the framework of Cahn's impurity drag model. The concept of a dynamic segregation factor for the diffusion along moving grain boundaries is introduced. The difference between static and dynamic segregation factors may cause the apparent difference of the triple product of the segregation factor, grain boundary width and grain boundary diffusion coefficient for stationary and moving grain boundaries. The difference between static and dynamic segregation is experimentally verified for the Cu(In)-Bi system, for which the parameters of static segregation are well-known. It is shown that the complications associated with the dynamic segregation may be avoided during the study of the discontinuous ordering reaction. From the kinetics of this reaction, the activation energy of the grain boundary self-diffusion can be determined.
Respective Roles of Surface, Grain Boundary and Volume Diffusions in Driving Structural, Microstructural and Magnetic Properties of MBE Alloy Thin Films
Authors: Pierron-Bohnes V. , Maret M. , Bouzidi L. , Cadeville M.C.
Published: April 2011

The co-deposition of two metals using a molecular beam epitaxy (MBE) technique at various growth temperatures (TG) yields single-crystal alloy thin films with a columnar microstructure whose structural and magnetic properties can be different from those of the corresponding equilibrium bulk alloys. A general overview of results obtained in hcp Co-Ru and hcp or fcc Co-Pt thin films grown on a hcp (0002) substrate will be presented. Around the A 3B composition (A = Co, B = Ru or Pt) the films display a composition modulation along the growth direction whose amplitude is strongly dependent of TG passing through a maximum at respectively 600 and 650 K. This long range order (LRO) that does not exist in equilibrium phases is explained as resulting from the competition between two phenomena occurring simultaneously during the growth process: a surface effect driven by surface interactions and surface diffusion that tends to enrich the surface layer in one element (Co, Ru or Pt segregation) and a bulk effect driven by bulk interactions and bulk diffusion that tends to restore the bulk equilibrium phase when the bulk diffusion becomes efficient during the growth time. A thermally activated model that takes into account both surface and bulk diffusion during the growth time reproduces quite satisfactorily the TG dependencies of the LRO in Co3Ru and Co3Pt as well as that of the uniaxial magnetic anisotropy in CoPt3.

At high TG ( > 800 K) or after ex situ anneals, the diffusion of the Ru buffer through the grain boundaries of the columnar microstructure, that occurs before the inside grain diffusion, isolates the columns magnetically and is thought to be responsible of the large observed coercive field and of a substantial modification of the magnetic domain shapes.
Effect of Surface Segregation on the Temperature Dependence of Ion-Bombardment Induced Surface Morphology
Authors: Aufray B. , Giordano H. , Petrova V. , Seidman D. N.
Published: April 2011

We present a scanning tunneling microscopy (STM) study, performed at different elevated temperatures, on the influence of Sb surface segregation on the morphology of the (111) surface of a Cu-0.45 at.% Sb solid-solution single-crystal; the surface was initially cleaned at room temperature by Ar+ ion sputtering. Unexpectedly, when the temperature is increased from room temperature to 380°C, the typical (111) surface morphology, obtained after sputtering, evolves in two very different manners that depend on the heating rate. If the heating rate is rapid (approximately a few minutes), it evolves to a structure with large terraces, whereas if it is slow (about 10 hours) the morphology does not evolve -- i.e., it is frozen. These unexpected results are interpreted in terms of excess subsurface point defects (vacancies and self-interstitials) created during ion bombardment, which are mobile and can mediate Sb diffusion at low temperatures. This is mainly on step edges, but the point defects can precipitate out of solution, for a rapid heating rate, thereby forming small secondary clusters in the near-surface region, in which Sb atoms are trapped.
Kinetic Monte Carlo Simulation of Diamond Film Growth with the Inclusion of Surface Migration
Authors: Netto Armando , Frenklach Michael
Published: April 2011

Diamond films are of interest in many practical applications but the technology of producing high-quality, low-cost diamond is still lacking. To reach this goal, it is necessary to understand the mechanism underlying diamond deposition. Most reaction models advanced thus far do not consider surface diffusion, but recent theoretical results, founded on quantum-mechanical calculations and localized kinetic analysis, highlight the critical role that surface migration may play in growth of diamond films. In this paper we report a three-dimensional time-dependent Monte Carlo simulations of diamond growth which consider adsorption, desorption, lattice incorporation, and surface migration. The reaction mechanism includes seven gas-surface, four surface migration, and two surface-only reaction steps. The reaction probabilities are founded on the results of quantum-chemical and transition-state-theory calculations. The kinetic Monte Carlo simulations show that, starting with an ideal {100}-(2×1) reconstructed diamond surface, the model is able to produce a continuous film growth. The smoothness of the growing film and the developing morphology are shown to be influenced by rate parameter values and by deposition conditions such as temperature and gaseous species concentrations.
Evidence for Non-Equilibrium Vacancy Concentrations Controlling Interdiffusion in III-V Materials
Authors: Gillin W.P. , Khreis O.M. , Homewood K.P.
Published: April 2011

Interdiffusion and self-diffusion in III-V semiconductors has usually been assumed to operate through the diffusion of point defects, the concentrations of which are at thermal equilibrium values. We have studied the interdiffusion of multiple quantum well samples, grown under a range of growth conditions, each containing a thin source of vacancies. This has enabled simultaneous measurements of the interdiffusion coefficient, diffusion coefficient for vacancies and the concentration of those vacancies in a single experiment. We have shown that independent of growth conditions, within a wide window of III-V flux ratio and temperature, the diffusion at all temperatures is governed by a constant background concentration of vacancies.
Molecular Simulations of Pore Diffusion in Zeolites
Authors: Pohl P.I. , Fisler D.K. , Nenoff T.M.
Published: April 2011

A combination of molecular dynamics and energy barrier mapping has been used to study diffusion of xylene gas molecules in silica zeolites. Rigid ion models were created for silicalite phases and the energy barriers to xylene permeation by pore diffusion were mapped using constrained steps and energy minimization. Zeolite ZSM-5 proved to exhibit the desirable properties of a high degree of selectivity while retaining a high permeability to p-xylene. The model zeolite was then minimized with various cation dopants using a shell model to mimic ionic polarization, and changes in cell size and energy surface were examined. Long term molecular dynamics simulations showed an increased diffusion rate for the structures doped with cations of larger ionic size.
DC Conductivity of Potassium Titanyl Phosphate Crystal along ITS Z-AXIS
Authors: Guan Qingcai , Wang Jiyang , Cui Weihong , Wei Jingqian , Liu Yaogang , Yin Xin
Published: April 2011

The J-U relation of the KTP crystal along its z-axis under low DC field deviates from linearity, which is different from that of the crystal along the other two principle axis. The resistance of the crystal along its z-axis increases with the time under high DC stress and the crystal becomes dark. The dark color can be removed by annealing. Electrode reactions were also observed. The phenomena are related to the easy movement of ions along the z-axis of the KTP crystal.
Simulation of Intrinsic Diffusion in Multicomponent Multiphase Systems
Authors: Hunkel M. , Bergner D.
Published: April 2011

A simulation model for intrinsic diffusion of multicomponent multiphase systems is presented. The model is not restricted onto a certain number of components or phases. For simplicity, Manning's random alloy model with vanishing vacancy wind effect is used. Then the cross terms of the diffusion flux can be neglected. The simulation routine uses equations for the fluxes, the equation of continuity and an equation for the change of the thickness of volume elements due to the vacancy flux. With this model diffusions paths, concentration profiles, fluxes of the components as well as marker positions can be calculated. The shift of interfaces and the growth of new phases can also be determined. The simulation results were compared with experimental data of the Cu-Fe-Ni system. Diffusion was studied in single-phase areas and across interfaces.
A Model for Oxygen Transport in Microencapsulated Islets
Authors: Iwata H. , Park Y. G. , Ikada Y.
Published: April 2011

Oxygen supply is expected to be one of major limiting factors that determine survival of islets in microcapsules after transplantation. Fick's law is applied to derive equations describing the oxygen pressure (PO2) profiles. The PO2 profiles calculated demonstrate that the thickness of the microcapsule membrane does not significantly affect oxygen supply to the islet. On the other hand, it drastically decreases as the fibrous tissue surrounding the microcapsule becomes thicker. The islet will be destroyed non-immunologically by limiting oxygen supply, when the microencapsulated islets are surrounded by the thick fibrous tissue.
Construction of Biomimetic Environments with A Synthetic Peptide Analogue of Collagen.
Authors: Bhatnagar Rajendra S. , Qian Jing Jing , Wedrychowska Anna , Smith Nancy
Published: April 2011

The flow of chemical and mechanical signals among cells, and between cells and their environment plays a crucial role in cell differentiation and morphogenesis. In tissues, type I collagen serves as the template for cell anchorage and migration, and it mediates the flux of regulatory signals via highly specific receptors. Cells respond to mechanical cues by secreting growth factors and remodeling their surrounding matrix in an exquisitely orchestrated spatial and temporal program of matrix turnover and organization. Cellular tractional forces contribute to the organization and orientation of the newly synthesized matrix, establishing the template for subsequent morphogenesis. The junction between cells and collagen plays a key role in cell differentiation, morphogenesis and tissue remodeling. An optimal biomimetic environment would emulate this pathway for the exchange of stimuli. To achieve this goal, we have constructed templates which place cells in apposition to P-15, a synthetic peptide ligand for collagen receptors. These environments prompted 3-D colony formation, induced increased osteogenic differentiation, and the deposition of highly oriented and organized matrix by human dermal and gingival fibroblasts and by osteoblast like HOS cells. These observations support our concept for biomimetic environments for tissue engineering.
Osteocompatibility of Photopolymerizable Anhydride Networks
Authors: Shastri V.R. , Marini R.P. , Padera R.F. , Kirchain S. , Tarcha P. , Langer R.
Published: April 2011

A new family of polyanhydrides has been developed which can be cured photochemically to produce degradable networks. These degradable polyanhydride networks can be useful in orthopedics as bone cements and for drug delivery. This system, which is a semi-interpenetrating network (semi-IPN), has been evaluated for tissue compatibility in subcutaneous sites in rats and shown to undergo degradation by surface erosion. It was observed that the inflammatory response to the semi-IPN implants was minimal at both short (3, 6 weeks) and long (28 weeks) time points and the fibrotic response was largely absent throughout the duration of this study. Furthermore, excellent tissue infiltration and integration with good neovascularization was observed around the semi-IPN implants. The osteocompatibility and osteoconductive properties of this system have been evaluated in a longitudinal defect model in the articular surface of the distal femur in adult rabbits. This study compared the semi-IPN implants to control groups consisting of unfilled defects and PLA implants. Histological evaluation (H&E and Trichrome Masson staining) of the implant site revealed that the semi-IPN implant is osteocompatible and well tolerated by the surrounding cancellous bone and marrow constituents. The tissue reaction to the implant is characterized by an ingrowth of vascularized connective tissue and a mild fibrous capsule. Furthermore, partial to complete closure of the articular surface with fibrocartilage and fibrous tissue was observed in all experimental animals containing the semi-IPN polymer implants.
Moment-based Modeling of Extended Defects for Simulation of TED: What Level of Complexity is Necessary?
Authors: Gencer Alp H. , Dunham Scott T.
Published: April 2011

Accurate modeling of extended defect kinetics is of primary importance for predictive modeling of transient enhanced diffusion (TED). Our previously developed model accurately accounts for extended defects and can be used predictively for TED. Using some experimental knowledge about the distribution of the extended defect population we can simplify our model. We demonstrate that reducing the number of solution variables by one doesn't affect the predictive capabilities of the model for extended defect kinetics and TED. However, some caution has to be used when applying the same principles to modeling of dopant deactivation.
Computer Simulation of Channeling Profile Analysis of Implantation Damage
Authors: Posselt Matthias
Published: April 2011

Channeling profile analysis is simulated using the dynamic binary collision code Crystal- TRIM. A good agreement between theoretical and experimental data is found for silicon targets which were predamaged by Si+ ions of different energies and analyzed by 140 keV B+ ions. For each example the depth profile of the defects relevant for the dechanneling of the analyzing ions is given. An estimate of the annealing of such defects is obtained by comparison of results for as-implanted and annealed samples.
Surface Science Studies of NF3 Plasma and Ion Beam Interactions with Silicon
Authors: Little T. W. , Briggs S. C. , Ohuchi F. S.
Published: April 2011

The interaction of nitrogen trifluoride (NF3) with silicon (Si) surfaces has been investigated by x-ray photoelectron spectroscopy (XPS). Si (100) surfaces were subjected to plasmas created by NF3 gas mixtures and ion bombardment from NF3-generated ion beams as a means of approximating the ion component of plasma processing under controlled conditions. NF 3 plasma processing has lead to the appearance of an interesting high binding energy component in F 1s XPS spectra. Investigation into the mechanism responsible for the high binding energy component suggests that the unusual component is directly influenced by diluent gas ions in the gas mixtures. It is postulated that the high binding energy component is the result of neutral fluorine incorporated in the Si lattice as a result of an ion damage mechanism.
On the «A Symmetrical» Behavior of Transient Enhanced Diffusion in Pre-Amorphised SI Wafers
Authors: Alquier D. , Cowern N. E. B. , Pichler P. , Armand C. , Martinez A. , Mathiot D. , Omri M. , Claverie A.
Published: April 2011

We have studied by SIMS the diffusion of boron in Ge-preamorphised silicon over a range of anneal temperatures and times, focusing on the influence of the depth of the boron profile relative to the crystalline-amorphous (c/a) interface. It is shown that, for all durations, transient enhanced diffusion (TED) occurs on both sides of the c/a interface. For short annealing times, the amplitude of TED varies by about two orders of magnitude between the surface and the end-of-range (EOR) defect band, formed just below the original c/a interface. We propose a model in which TED arises from the coupling between a Si-interstitial supersaturated « box », the EOR defect region, whose supersaturation decreases with time as the EOR defects grow, and a surface whose recombination efficiency is close to that of a perfect sink. The model successfully describes the different behavior of deep and shallow boron profiles, without requiring the existence of a diffusion barrier.
In Situ Deep Level Transient Spectroscopy of Defect Evolution in Silicon Following Ion Implantation at 80 K
Authors: Cho C. R. , Brown R. A. , Kononchuk O. , Yarykin N. , Rozgonyi G. , Zuhr R.
Published: April 2011

The evolution of defects in Czochralski and epitaxial p- and n-type silicon wafers following irradiation with He. Si or Ge ions at 80 K has been investigated by in situ deep level transient spectroscopy (DLTS). Defect annealing and formation reactions have been observed over the temperature range 80–350 K. In p-type silicon, new species-dependent levels are observed immediately after implantation, but these levels anneal out at or below room temperature. The wellknown divacancy and interstitial defects, usually reported after room temperature implantation, are revealed in the DLTS spectra only upon annealing at 160–200 K. In n-type silicon, vacancy-oxygen pairs are observed immediately after implantation. However, vacancy-related defects continue to form over a broad temperature range in samples implanted with Si or Ge. These observations are consistent with a model whereby vacancies and interstitials are released from defect clusters at temperatures >200 K to form divacancies and other defect pairs which are stable at room temperature.
Ge-Quantum Dots on SI(001) Tailored by Carbon Predeposition
Authors: Leifeld O. , Grützmacher D. , Müller B. , Kern K.
Published: April 2011

The morphology of Si(001) after carbon deposition of 0.05 to 0.11 monolayers (ML) was investigated in situ by ultrahigh vacuum scanning tunneling microscopy (UHV-STM). The carbon induces a c(4×4)-reconstruction of the surface. In addition, carbon increases the surface roughness compared to clean Si(001) (2×1). In a second step, the influence of the carbon induced restructuring on Ge-island nucleation was investigated. The 3D-growth sets in at considerably lower Ge coverage compared to the clean Si(001) (2×1) surface. This leads to a high density of small though irregularly shaped dots, consisting of stepped terraces, already at 2.5 ML Ge. Increasing the Ge-coverage beyond the critical thickness for facet formation, the dots show { 105 }- facets well known from Ge-clusters on bare Si(001) (2×1). However, they are flat on top with a (001)-facet showing the typical buckled Ge rows and missing dimers. This indicates that the compressive strain is not fully relaxed in these hut clusters.
Epitaxial Growth And Electronic Characterization Of Carboncontaining Silicon-Based Heterostructures
Authors: Hoyt J. L. , Mitchell T. O. , Rim K. , Singh D. V. , Gibbons J. F.
Published: April 2011

Epitaxial Si1-x-yGexCy and Si1-yCy layers grown on Si are opening up new possibilities for bandstructure engineering of electronic devices. Thin Si1-yCy layers containing a few atomic percent substitutional carbon, grown on Si substrates, experience biaxial tensile strain, which produces a conduction band energy splitting that is expected to be favorable for in-plane electron transport. For other applications, C may be useful as a means of compensating the compressive strain of Ge in ternary Si1-x-yGexCy alloys. Although the understanding of the electronic properties of these materials is still at an early stage, interesting trends are emerging.

A key issue for synthesis of these alloys is the low equilibrium solubility of carbon in silicon. However, a number of non-equilibrium methods have been employed to grow these materials. This work focuses on the properties of Si1-yCy and Si1-x-yGexCy grown by chemical vapor deposition. There is a strong influence of the growth conditions on the fraction of the total carbon concentration which is substitutional on the silicon lattice. Using low temperatures (e.g. 550°C) and very high silane partial pressures for Si1-yCy growth, good agreement is obtained between the carbon contents determined by x-ray diffraction and secondary ion mass spectrometry, for carbon concentrations up to about 1.8 atomic percent. Metal-oxidesemiconductor capacitors fabricated on Si1-x-yGexCy and Si/Si1-yCy epitaxial layers show wellbehaved electrical characteristics. Temperature dependent capacitance-voltage analysis is used to extract the band offsets, and indicates that the conduction band energy is lowered as carbon is added to Si. Complementary to the case of strained Si1-xGex grown on Si, for which most of the energy offset is in the valence band, the band offset appears primarily in the conduction band for Si1-yCy/Si heterojunctions.
Carbon Incorporation in Si1-yCy Alloys Grown by Ultrahigh Vacuum Chemical Vapor Deposition
Authors: Mocuta A. C. , Greve D. W.
Published: April 2011

Thin heteroepitaxial Si1-yCy films have been grown on Si (100) by Ultrahigh Vacuum Chemical Vapor Deposition (UHV/CVD) using silane and methylsilane as silicon and carbon precursors. Carbon incorporation has been studied in the growth temperature range of 550°C to 650°C. The layers have been characterized using high resolution X-ray diffraction and secondary ion mass spectrometry. The total carbon content of the alloys increases linearly with the methylsilane partial pressure and a methylsilane sticking coefficient approximately 2 times higher than that of silane was extracted. Layers with up to 1.34 % substitutional carbon have been obtained at the lowest growth temperature. Fully substitutional carbon can be obtained for levels up to 0.65%. Variations of the growth rate with temperature and carbon content are also discussed.
Investigation of Plastic Relaxation in Si1-xGex/Si Deposited by Selective Epitaxy
Authors: Wickenhäuser S. , Vescan L.
Published: April 2011

Si1-xGex/Si heterostructures with different layer thicknesses grown by selective LPCVD epitaxy at different growth temperatures were investigated with regard to plastic relaxation. AFM and optical micrograph were performed to determine the dislocation density. From the analysis of the misfit dislocations at the initial stage of relaxation of the samples grown at 700°C it was possible to determine the nucleation site density and an activation energy of 2.8 eV for the heterogeneous nucleation of misfit dislocations. While the critical thickness hc for a given Ge content increases with decreasing growth temperature between 800°C-680°C one observes a dramatic decay of hc, at a growth temperature of 625°C. For growth at 625°C it was found that this activation barrier is drastically decreased.
Mosaic Crystal Tilts and Their Relationship to Dislocation Structure, Surface Roughness and Growth Conditions in Relaxed SiGe Layers
Authors: Wallis D. J. , Robbins D. J. , Pidduck A. J. , Williams G. M. , Churchill A. , Newey J.
Published: April 2011

In recent years the growth of virtual substrates using graded SiGe buffer layers has shown great promise for the development of high performance devices. Whilst significant progress has been made in the control of growth conditions to produce low threading dislocation densities of the order suitable for commercial exploitation, several technological problems still have to be overcome. An example of such problems are cosmetic surface defects such as pits and the cross hatched surface roughness associated with mosaic crystal tilts. The work described here utilises a variety of techniques, including X-ray diffraction reciprocal space maps, TEM, AFM and SIMS to provide a comparison between several SiGe virtual substrates grown using low pressure-CVD at high (≈800°C) and low (≈6000°C) temperatures, and at different grade rates (5–50% Ge μm−1). The growth conditions are seen to have a strong effect on the crystal tilts present in the layers with the low temperature layers showing a much larger spread of mosaic tilts. The origin of these tilts is seen to occur during the early stages of the relaxation process irrespective of growth temperature and at similar Ge fractions for all samples. TEM imaging close to the initial growth interface shows that dislocation pileups occur in this region and also suggest that the pileups have a characteristic spacing of 1–2μm. A similar characteristic length scale is also observed in the surface roughness by AFM, the form of which is seen to depend upon the growth conditions.
Characterization of Single-Crystal 3C-SIC Epitaxial Layers on SI Substrates
Authors: Saddow S. E. , Okhusyen M. E. , Mazzola M. S. , Dudley M. , Huang X. R. , Huang W. , Su H. , Shamsuzzoha M. , Lo Y. H.
Published: April 2011

In this paper we discuss the growth and characterization of 3C-SiC epitaxial layers grown on both a Si substrate as well as on a novel substrate. The growth uses a typical three step process. First an etch of the Si surface is performed, second the surface of the Si is carbonized and third 3C-SiC is grown on the carbonized surface. Several characterization techniques were used to verify the quality of the 3C-SiC film. Microscopy was used to investigate the surface morphology, X-ray and electron diffraction were used to determine crystal structure, cross section TEM was used to verify crystal structure and highlight twinning, and x-ray topography was used to measure the strain fields induced in Si substrate at the 3C-SiC/Si interface.
Photonic Bandgap Formation by Wafer Bonding and Delamination
Authors: Wada Kazumi , Chen Thomas , Michel Jurgen , Kimerling Lionel C. , Aga Hiroshi , Mitani Kiyoshi , Abe Takao , Suezawa Masashi
Published: April 2011

A new approach for one-dimensional photonic bandgap formation is introduced. The method consists of wafer bonding and delamination, which is capable of stacking single crystalline semiconductor layers on non-crystalline insulator layers. Si and SiO2 layers with sub-wavelength periodicity are successfully stacked to form photonic crystals consisting of 3 pairs without a defect layer and of 4.5 pairs with a defect layer. The transmittance spectra are well reproduced by transfer matrix calculations. This clearly verifies the potential of the wafer bonding and delamination method.