bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser Ablation of Highly Oriented Cdse Thin Films and Cdte/Cdse Multilayers on Silicon Substrate
Authors: Ambrico M. , Martino R. , Smaldone D. , Capozzi V. , Lorusso G. , Perna G. , Giardini A. , Mele A.
Published: April 2011

Laser ablation technique has been successfully used for the deposition of CdSe and CdTe/CdSe multilayers on Si(100) and Si(l11) substrates. X-ray analysis showed that CdSe/Si films were highly oriented. Their orientation changed from (100) to (002) by varying the substrate temperature from 473 to 673K. High orientation was also obtained on multilayered polycrystalline structures of CdSe and CdTe on Si(lll). Photoluminescence experiments have also been carried out on the deposited films.
Laser Ablation Deposition of Ga2S3-La2S3 Glass Films
Authors: Asal R. , Rivers P.E. , Rutt H.N.
Published: April 2011

Gallium - lanthanum sulphide glasses (GLS) show wide range transparency and low non radiative relaxation rates for dopant ions such as Ho3+, Er3+ etc. They also show permanent photomodification of the refractive index under visible illumination. We report laser ablation deposition of these glasses and preliminary results on film stoichiometry and deposition rate as a function of excimer laser fluence. The sulphur to metal and Ga/La ratios are found to have marked fluence dependencies. The films show considerably more Urbach tail absorption than bulk material. A novel method has been developed for mapping the permanent photomodified index.
Mechanical Properties of Laser Processed Diamond-Like Carbon Films
Authors: Kumar Ashok , Inturi R. B. , Vohra Y. , Ekanayake U. , Shu N. , Kjendal D. , Wattuhewa G. , Barnard J. A.
Published: April 2011

Diamond-like carbon (DLC) films have a unique combination of physical and chemical properties such as high hardness, optical transparency, low coefficient of friction and chemical inertness. A pulsed laser (248 nm) has been used to ablate a pyrolytic graphite target to deposit DLC films on Si (100) and 7059 Corning glass substrates. The deposition was carried out in high vacuum (≤ 10−6 Torr) at different temperatures ranging from room temperature to 400°C. The films were characterized by x-ray diffraction, scanning electron microscope, and Raman spectroscopie techniques. The mechanical properties (hardness and Young's modulus) of these films were characterized by nanoindentation. We have found that the films deposited at room temperature and 100°C show the characteristic features of DLC films and have the better hardness and modulus properties compared to the films fabricated at higher temperatures, which transform into amorphous carbon. Correlations of pulsed laser deposition process parameters with the properties of deposited DLC films will be discussed in this paper.
Pulsed Laser Deposition of Si Nanocluster Films
Authors: Marine W. , Movtchan I. , Simakine A. , Patrone L. , Dreyfus R. , Sentis M. , Autric M. , Merk N.
Published: April 2011

Reactive laser ablation of Si targets by ArF* excimer laser (wavelength 193 nm, pulse width 15 ns (FWHM)) was performed in He, Ar or O2 0.05-1 Torr atmospheres and led to Si-SiOx nanocluster thin film formation within laser-induced plasma plume. Optical spectroscopy and optical Time-of-Flight (TOF) measurements were carried out during ablation-deposition experiments. A number of large weak emission bands in blue and green-yellow spectral branches were observed both in inert gases and in oxygen ambient atmospheres and attributed to the emission from excited nanoparticles in the plasma plume. TOF measurements proved a different spatio-temporal evolution of this emission compare to the emission of monoatomic particles. The films exhibit photoluminescence bands in the UV region (around 290 nm and between 310-370 nm), in the blue (between 420 and 500 nm), and in the green-yellow (at 520-560 nm). The relative intensities of the luminescence bands depend on the average cluster size, which is determined by preparation conditions (nature and pressure of the ambient gas, laser fluence).
Optimization and Transformation Analysis of Grain-Boundary-Location-Controlled Si Films
Authors: Kim H.J. , Im James S.
Published: April 2011

By optimizing various experimental parameters, we were able to extend the width of the microstructually optimized regions in grain-boundary-location-controlled (GLC) Si films up to 10 μm. In situ transient reflectance (TR) measurements during the solidification process reveal that the underlying GLC transformation sequence is consistent with the artificially controlled super-lateral growth (ACSLG) scenario, from which the GLC process was developed and is being optimized. A definite change in the slope of the TR signal was found to appear at the transition between the vertical-and-lateral -growth and lateral-growth-only modes. Protrusions at the center of the GLC Si microstructure, which are observed in cross-sectional TEM micrographs and surface profile measurements, are formed as a result of the positive volume change associated with freezing of Si.
Adhesive Property Enhancement by Photochemical Modification on Polyimide Sheet Surface by Irradiation with Excimer Lamp
Authors: Okamoto T. , Hatao K. , Shimizu T. , Aoike M. , Murahara M.
Published: April 2011

Polyimide sheet surface was photochemically modified to be hydrophilic property with Xe2* excimer lamp ( λ =172nm) irradiation and pure water solution. The solution was sandwiched between the surface and fused silica glass. With the excimer lamp irradiation, the solution and the surface were excited; the surface was dehydrogenated by the hydrogen atoms which were photodissociated from pure water and replaced the photodissociated OH radicals. The hydrophilic property of the modified surface was evaluated by measuring the contact angle with water. The replacement of the OH radicals were confirmed by FTIR. The modified surface was bonded to stainless steel with an epoxy resin for evaluation of the adhesive strength by the shearing tensile test. As a result, the adhesion was increased to 1.4 times that of the non-irradiated sample.
Ablation of Si and Ge Using UV Femtosecond Laser Pulses
Authors: Herbst G. , Steiner M. , Marowsky G. , Matthias E.
Published: April 2011

Laser ablation of silicon and germanium was carried out in moderate vacuum with l00fs to 400fs pulses at 248nm and intensities up to 3x1013 W/cm2. Evidence for non-thermal material removal was found. Imaged multishot ablation patterns display the intensity dependent self-structuring effect, forming well-known columnar structures. It is shown that continued irradiation of these structures eventually results in comparatively clean ablation. An increase of ablation rate with depth was observed. The reason is an intensity enhancement inside the pits by reflective focussing to a level where bond-breaking takes place. Furthermore, it was noticed that ablation contours can be significantly improved by electrically grounding the target.
Numerical Simulation of Fz Single Crystal Growth Process with Radio-Frequency Induction Heating
Authors: Masuda Y. , Tsukada T. , Hozawa M.
Published: April 2011

Analyses of a floating zone (FZ) crystal growth system with a radio frequency (RF) induction heating are carried out. The electromagnetic and temperature fields, and surface interfaces are solved for numerically. Finite element methods are used for the calculation of the temperature fields and interfaces and the hybrid finite element and boundary element methods are used for the calculation of the electromagnetic field. The calculation domain is divided into eleven regions, each of which, except for the RF coil region, require a coordinate transformation. In the present study, the silicon FZ growth system ,where the diameter of both feed-rod and single crystal were set to be 1cm was computed. The Lorentz force is found to play an important role in determining the melt free surface shape and the molten zone length. The effect of the current density, frequency of RF coil and crystal growth rate are investigated.
Formation of a Metastable Crystalline Phase During Ion Irradiation of Spinel
Authors: Devanathan R. , Yu N. , Sickafus K. E. , Nastasi M.
Published: April 2011

We have examined the radiation resistance of magnesio-aluminate spinel by irradiating single crystals of MgAl2O4 with 400 keV Xe++ ions at 100 K. At low irradiation doses, the material transformed into a metastable crystalline phase with half the lattice spacing of the original crystal. Electron diffraction analysis revealed that this structural change can be explained in terms of the redistribution of cations among octahedral, tetrahedral, and three-fold coordinated interstitial sites of the close-packed anion lattice. Corresponding to this transformation, the hardness and elastic modulus increased with dose to values about 10% greater than those of unirradiated spinel. We believe that the formation of this metastable phase plays an important role in determining the radiation resistance of spinel.
Influence of Stacking Faults and Alloy Composition on Irradiation Induced Amorphization of Zrcr2, Zrfe2 And Zr3(Fei. X,Nix)
Authors: Faldowski Joseph A. , Motta Arthur T. , Howe Lawrence M. , Okamoto Paul R.
Published: April 2011

The Zr-based intermetallic compounds ZrCr2, ZrFe2 and Zr3(Fei_x,Nix) were irradiated with high energy electrons at the HVEM/Tandem facility at Argonne National Laboratory to study their amorphization behavior. The results show that although ZrCr2 and ZrFe2 have the same Laves phase C15 fee crystal structure, their critical temperatures for amorphization under electron irradiation were 180 K and 80 K, showing that the substitution of Cr for Fe in the sublattice had a marked effect on the annealing characteristics of the material. The low temperature dose to amorphization was higher in ZrFe2 than in ZrCr2 by a factor of two. The presence of a high density of stacking faults had a strong effect on amorphization in both compounds causing the critical temperature to be increased by 10–15 K. By contrast, the addition of Ni to Zr3(Fei_x,Nix) had no effect on amorphization behavior for x=0. 1 and 0. 5. These results are discussed in terms of current models of amorphization based on defect accumulation and the attainment of a critical damage level, such as given by the Lindemann criterion.
Metastability at the nanometer scale
Authors: DESRÉ P.J.
Published: April 2011

Under constraints and at the nanometer scale, transitory metastable states can be generated in multicomponents materials. Examples illustrating such specific states are presented. They concern i) The crystalline nucleation in a growing undercooled liquid droplet formed from a liquid parent phase, ii) The suppression of intermetallic nucleation in solid solutions or glasses subjected to sharp concentration gradients, iii) The nanocrystalline transitory state preceding amorphisation by ball milling. In connection with this latter example, a thermodynamic model for the nanocrytal to glass transition, based on an hypothesis of a topological disorder wetting at the nanograin boundaries, is proposed. Thermodynamics - Nucleation - Phase transitions - nanocrystals - metallic glasses
The Influence of Structural Similarity on Phase Transformations Between Bcc and the Laves Compounds
Authors: Sinkler W.
Published: April 2011

A fundamental aspect of martensitic or order-disorder phase transformations is the maintainence of correspondences between atoms or atomic sites in parent and precipitate phases. The present work concerns a structural relationship between initial and final phases in a transformation which is neither martensitic nor order-disorder. A structural relationship between the C14 Laves compound structure and body-centered cubic (bcc) is presented based on electron diffraction recorded in the course of the electron irradiation-induced transformation of the TiCr2 Laves compound to the bcc (β) phase. The diffraction evidence indicates a preferential orientation of β with respect to the initial Laves phase. Consistent with the diffraction data, it is shown how the structures can be formed from one another via small displacements of atom positions. It is suggested that structural relationships in first-order transformations may be significant as paths of minimal structural rearrangement by which such transformations may occur.
Calorimetric Study of the Energetics and Kinetics of Interdiffusion in Cu/Cu6sn5 Thin Film Diffusion Couples
Authors: Neils W. K. , Chromik R. R. , Dreyer K. F. , Grosman D. , Cotts E. J.
Published: April 2011

We find differential scanning calorimetry to be suitable for the characterization of the energetics and kinetics of interdiflusion in solder/metal diffusion couples. Differential scanning calorimetry studies of interdiffusion in Cu/Cu6Sn5 diffusion couples have shown that the driving force for interdiffusion is similar for thin film composites and for bulk diffusion couples. The heat of formation of Cu3Sn from Cu6Sn5 and Cu thin films was found to be ΔHr = −4.3 + 0.3 kJ/mol. Portions of our differential scanning calorimetry scans are identified with diffusion limited growth of Cu3Sn. From these calorimetry data we have estimated D(cm2 / s) = Do exp(−E / kbT), where kb is Boltzmann's constant, D0 = 3.2 × 10–2 cm2/s, and E=0.87 eV/atom.
Ordering and Grain Growth Kinetics in CoPt Thin Films
Authors: Ristau R. A. , Barmak K. , Hess D. W. , Coffey K. R. , Parker M. A. , Howard J. K.
Published: April 2011

Ordering and grain growth have been studied in a 10 nm thick CoPt alloy film of equiatomic composition annealed in the temperature range 550–700°C by quantifying ordered domain size, volume fraction ordered, grain size, and grain size distribution. Ordering occurs by nucleation and growth of Ll0ordered domains, with a mean size of 3 nm at 550°C and 19 nm at 700°C. The volume percent ordered shows a dramatic increase from <y1% to approximately 28% between the two extremes of annealing temperature. The mean grain size of the as-deposited films is 5 nm and the entire film is face-centered cubic. Upon annealing in the temperature range 550–600°C, the mean grain size reaches a stagnation limit of 27 nm and the grain size distribution is log-normal. Grain growth resumes beyond 600°C and the mean grain size reaches as high as 55 nm at 700°C. The increase in the coercivity of the annealed films follows the increase in the ordered fraction more closely than the increase in grain size. The shape of the M-H loop shows evidence of coupling between the magnetically hard (ordered) and soft (disordered) regions.
Models of Crystallisation in Evaporating Droplets
Authors: Ford I.J.
Published: April 2011

The spray drying of a droplet containing a substance in solution can produce solid particles with a variety of final shapes: hollow, punctured, squashed, as well as solid spheres. The geometry affects the properties of the product. Models are presented here which describe the processes of solvent evaporation and solute crystallisation as drying takes place. The formation of a crust on the surface of the droplet is addressed. It is proposed that such a crust with a thickness of two crystallite diameters can develop into dry hollow shell. Some example calculations of the spray drying of droplets of sodium chloride solution are described.
Effects of Diffusion of Co/Ni Cations on Sol-Gel Derived ZrO2 Polymorphic Transformations
Authors: Zeng H.C. , Qian M.
Published: April 2011

Transition metal incorporated ZrO2 gel matrices have been prepared by impregnation method and investigated with FTIR/DTA/XRD. The metastable tetragonal - monoclinic -tetragonal - cubic phase transformations are revealed in the DTA heating process up to 1400°C for the studied gels. High-temperature tetragonal to monoclinic transition is also observed in the cooling process. It is found that the diffusing metal cations stabilize the low-temperature tetragonal phase. However, for high-temperature (900°C) calcined gels, both as-prepared and metal-stabilized tetragonal phases are reduced substantially. Correlations between metal diffusion and gel polymorphic stabilities are also demonstrated.
Time-Dependent Nucleation and Growth of Crystalline Phase During a Rapid Quench into a Glassy State
Authors: Shneidman V.A. , Weinberg M.C.
Published: April 2011

Corrections to the standard expressions for the volume fraction of the crystalline phase which arise due to time-dependent nucleation effects are considered both for the isothermal (transient) and nonisothermal (quench) situations. Analytical results are tested against numerically exact solutions of the Turnbull-Fisher nucleation equations. Physical consequences of the obtained expressions are discussed.
Molecular Beam Epitaxial Growth of InAs/AIGaAsSb Deep Quantum Wells on GaAs Substrates
Authors: Kuze N. , Goto H. , Miya S. , Muramatsu S. , Matsui M. , Shibasaki I.
Published: April 2011

We have investigated InAs deep quantum well structures (InAs DQWs) made from InAs/A1GaAsSb materials on GaAs substrates by molecular beam epitaxy (MBE). In the InAs DQWs, AlGaAsSb layers are lattice-matched to InAs. Using reflection high-energy electron diffraction (RHEED) linescan image analysis, we show that AlGaAsSb on GaAs surfaces quickly relaxes within 3 to 7 monolayers (MLs). The initial stages of AlxGa1-xAsSb (0≤x≤0.5) growth on GaAs (100) substrates and InAs growth on AlGaAsSb layers have been investigated by atomic force microscopy. The ridgeline shapes of AlGaAsSb are observed at the initial stage on GaAs surfaces. In the interface of the InAs/AIGaAsSb, two-dimensional (2D) growth of InAs has been observed. With a thin buffer layer of 600 nm AlGaAsSb, we have achieved very high electron mobilities of more than 32000 cm2/V-s at room temperature.
The Stability of Lattice Mismatched Thin Films
Authors: Guyer J.E. , Voorhees P.W.
Published: April 2011

We examine the linear stability of a planar, alloy thin film, exposed to a deposition flux from the vapor. The film surface is subject to stresses generated by compositional inhomogeneity, as well as by film-substrate lattice mismatch. In addition to the misfit induced surface instability shown by numerous previous studies, we find that the deposition flux alone can produce instability and that complex interactions occur when both deposition and surface transport processes are present. Solute expansion stresses result in several novel behaviors. Under certain circumstances, the growing film can be completely stabilized by a tensile misfit and destabilized by the same magnitude of compressive misfit. The predictions of this theory are compared to the results of several experimental studies.
Solid-on-Solid Monte Carlo Investigation of Islanding Kinetics During Heteroepitaxy
Authors: Payne Ken , Drucker Jeff
Published: April 2011

We have investigated the kinetics of islanding during heteroepitaxy using a solid-on-solid Monte Carlo (SOS-MC) simulation. We simulate deposition by randomly depositing atoms onto a square grid with periodic boundary conditions. Arrhenius surface diffusion kinetics are dependent on the sum of a surface energy barrier (Ed) and the number of nearest neighbors multiplied by an adatom interaction strength (Eb). We confine growth to the first layer above the simple cubic substrate and investigate coverages < 1/2 monolayer. We monitor the evolution of film microstructure by producing island size distributions and plots which compare a cluster's area to perimeter ratio with that of a circle. We find that our simulation qualitatively correlates with results of classical film nucleation theory. A simple model is used to demonstrate the existence of a 'probabilistic nucleation barrier'.
Spectral Sensitivities of X-Ray Diffraction to the Roughness of Si/SiO2 Interfaces
Authors: Evans-Lutterodt K.W. , Tang Mau-Tsu
Published: April 2011

Results from X-ray diffraction studies of the morphology of the growing Si(001 )/SiO2 interface are presented. We show the evolution of the root mean square roughness as a function of the growth variables, and we try to go beyond the root mean square parametrization of the interface by measuring the spectral distribution of interface fluctuations. Within our current experimental sensitivies we cannot resolve any fluctuations with a finite in-plane momentum transfer.
Effects of Crystalline Microstructure on Epitaxial Morphology
Authors: Family Fereydoon , Amar Jacques G.
Published: April 2011

In the past simulations of epitaxial growth have used solid-on-solid (SOS) models to simulate the crystalline structure of both the substrate and the growing crystal. These models have produced results in the early stages of growth in good agreement with experiments for a number of different quantities, including the island density and the island size distribution. For multilayer growth, however, there exists a competition between microscopic effects such as the Ehrlich-Schwoebel step barrier and the crystalline microstructure. Therefore, the crystal structure and geometry are important in determining the dynamics and evolution of epitaxial structure and morphology. We present the results of large-scale realistic kinetic Monte-Carlo simulations of multilayer epitaxial growth on fcc(100) and bcc(100) surfaces. The influence of crystal structure on the formation and coarsening of mounds and facets is discussed. We also discuss and compare our results with recent experiments.
Kinetic Roughening of Fe/Fe(100) Epitaxial Thin Films
Authors: Bartelt M.C. , Evans J.W.
Published: April 2011

We model kinetic roughening during Fe(100) homoepitaxy, where the formation of mounds with selected slope has been observed. Our model incorporates irreversible nucleation and growth of two-dimensional square islands in each layer, and a step-edge barrier to diffusive downward transport (which exceeds the barrier, Ed, to terrace diffusion by ESch). We estimate that ESch≈45meV compared with Ed≈450meV. To reproduce observed behavior, it is also essential for the model to incorporate "downward funneling" of depositing atoms to four-fold hollow adsorption sites, as this controls slope selection. Finally, we discuss model predictions for the non-monotonic temperature dependence of kinetic roughening.
A Molecular Dynamics Study of the Terminal Zr(Ni) Solid Solutions
Authors: Cleri F. , Mazzone G. , Rosato V.
Published: April 2011

The Zr terminal portion of the Zr-Ni phase diagram has been evaluated by means of a many-body tight-binding potential. The internal energy curves of the Zr(Ni) solid solutions at T=300 K have been calculated by Molecular Dynamics simulations. These curves exhibit positive values, contrary to former empirical phase diagram calculations. Implications of these results relevant to the problem of amorphization in metallic systems by solid-state reactions are discussed.
APFIM Studies of Nanocrystallizations of Amorphous Alloys
Authors: Hono K. , Zhang Y. , Inoue A. , Sakurai T.
Published: April 2011

This paper reports recent atom probe analysis results of Fe-Zr-B(-Cu) and Al-Ni-Ce(-Cu) amorphous alloys, in which nanocrystalline microstructures develop by primary crystallization. In these alloy systems, enrichment of slow diffusing solute was found at the interfaces between primary crystals and amorphous matrix during the nucleation and growth stage. In the case of ternary Fe-Zr-B, no evidence for compositional heterogeneities were found prior to the onset of crystallization reaction. On the other hand, clustering of Cu atoms was observed in quaternary Fe-Zr-B-Cu alloy prior to the crystallization reaction. In the ternary Fe-Zr-B alloy, nucleation sites seem to be provided by the quenched-in nuclei which were observed as medium range ordered (MRO) domains by HREM. In the as-quenched Al-Ni-Ce(-Cu) alloy, compositional fluctuations were present from the as-quenched state. These observations suggest that nuclei for primary crystallization are provided in various forms such as MRO domains, solute clusters and compositional heterogeneities.
Crystallization of Sputter Deposited Ti-Al Amorphous Alloy
Authors: Ohnuma M. , Abei T. , Onodera H.
Published: April 2011

The crystallization process of Ti-Al amorphous alloy has been studied by X-ray diffraction, small-angle neutron scattering and high resolution electron microscopy. In the early stage of crystallization of a thick sample with 55at%Al, a metastable hcp(α, α2) phase appeares. For a thin sample with 52at%Al, a new metastable phase having primitive tetragonal symmetry is found in the early stage of crystallization. The lattice parameter of this tetragonal phase is a=c=0.69nm. The prototype structure which has the same atomic arrangement as this phase is only Cu4Pd type structure (P42/m) in the Peason's Handbook.
Microstructure of Extremely Fine Lamellae in a TiAl Base Alloy Studied by High-resolution Electron Microscopy
Authors: Abe E. , Kumagai T. , Nakamura M.
Published: April 2011

An extremely fine lamellar structure formed in a Ti-48at.%Al alloy, which was heat treated in the high-temperature α-Ti (disordered hcp) single phase field (1683K), followed by ice water quenching, has been examined by high-resolution and analytical transmission electron microscopy. The microstracture consists of thin plates of ordered α2-Ti3Al (D019: ordered version of hcp) and γ-TiAl (Ll0: ordered version of fcc) phases, and interfaces of lamellae are atomically flat in a wide range. From detailed analyses of the microstructure and composition in nm scale, the α→γ phase transformation, which occurs during quenching and produces the extremely fine α2-γ lamellae, has been discussed.
Hardness of thin Films of Nanocrystalline Silver and Nickel Composites Studied by Nanoindentation and Finite Element Analysis
Authors: Qiu Boqin , Cheng Yang-Tse , Blanchard James P.
Published: April 2011

While gas condensation and mechanical alloying have been used to produce nano-phase powders, an effective method of applying these powders as coatings is still lacking. Furthermore, fundamental studies of the mechanical properties of nano-phase powders may be complicated by the porosity associated with consolidation processes. Recently, we have made nano-crystalline composite thin films of Ag-Mo and Ag-Ni by depositing two immiscible elements simultaneous onto substrates. We found, using XRD and TEM, that the average grain size varies from 10 to 100 nm by choosing an appropriate substrate temperature. Nanoindentation measurements showed the hardness of the composite is increased four times by reducing the grain-size of both phases from 100 to 10 nm. The load vs. displacement curves were simulated using a finite element method (ABAQUS). A relationship between the hardness of the two-phase composite and the yield strength of each phase is obtained.
Structural Modification in Amorphous Magnetic Alloys Under Thermotreatment
Authors: Poperenko Leonid V. , Vinnichenko Mykola V. , Vovchak Vasyl’ V. , Yurgelevych Iryna V. , Zaichenko Sergei G.
Published: April 2011

The experimental results of research of structural modifications in amorphous magnetic alloys (AMAs) under thermotreatment obtained by angular and spectroellipsometric methods are presented and discussed. The ductile-brittle transition was observed for the ribbons of some 3d-metal-based amorphous alloys. The relationship between the principal angle of incidence φ0 and annealing temperature Ta of alloys was obtained for the ribbons of AMAs. The observed behaviour of φ0 is connected with appearance of the novel amorphous phase’s clusters inside the surface’s layers of alloys.

The influence of melt’s overheating on the atomic and electronic structure of AMAs was studied. It was found that the increase of melt’s overheating temperature leads to the decrease of absorption index within the whole spectral range (ħω=0.5–4.38 eV). The structural anisotropy of AMAs and its changes after annealings were determined by reflectometric and ellipsometric measurements.
Aerosol Synthesis of Metal and Metal Oxide, Nitride and Carbide Nanoparticles Using an Arc Evaporation Source
Authors: Mahoney W. , Kempe M.D. , Andres R.P.
Published: April 2011

Nanoparticle synthesis by condensation from the vapor is a versatile process which allows control of both particle size and composition. We have developed a novel aerosol source for producing nanoparticles of metals and metal oxides, nitrides and carbides with controlled mean size. Metal is vaporized by heating a liquid metal pool by means of an atmospheric pressure d.c. arc. The evaporated atoms are entrained in a steady stream of inert gas and are quickly transferred to a quench region where the hot stream from the arc plasma is mixed with a second stream of cold gas. The role of the quench gas is to suppress aggregation by both rapid cooling and dilution. Metal oxide, nitride, and carbide particles are formed by the addition of oxygen, nitrogen, and methane respectively to the inert gas flow in either the arc or the quench region. The size of the primary particles is controlled by varying the metal atom density and residence time in the arc plasma and in the quench region. Cluster aggregation is controlled by varying the cluster density in the flow downstream from the quench region.
Investigation of TiN/TiSi2Bilayer Thin Films on Si (100) Substrate
Authors: Shor Y. , Pelleg J.
Published: April 2011

In this work the conditions of forming a bi – layer structure of TiN/TiSi2thin film on Si (100) substrate is investigated. Two methods of producing this structure were used: a) Deposition of Ti on Si (100), followed by reactive sputtering to obtain TiN on top of this layer and b) codeposition of Ti and Si on Si (100) and then deposition of TiN by reactive sputtering. The reactive sputtering was carried out in a mixture of N2/Ar with 20% N2. This amount is believed to be optimal for obtaining good quality and stoichiometric TiN films. Annealing is essential to form TiSi2and it was performed either in the sputtering chamber immediately after the deposition or by rapid thermal annealing (RTA). The structure of the specimens was analyzed by X-ray diffraction using step scanning, Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). TEM analysis was done on cross sectional specimens and also electron diffraction results were recorded. Resistivity measurements were performed by four – point probe method. The influence of TiN on the silicide formation was established. The results indicate that in the presence of TiN the phase TiSi2was obtained, but in its absence Ti5Si3is formed under the same conditions of deposition and annealing. The stress distribution was investigated by Hall – Williamson curves and it was found that TiN stabilizes the silicide film and no peeling was observed. The effectiveness of TiN as diffusion barrier against Al and Si penetration was tested at 500°C/lh. It was found, that under these conditions, the TIN/TiSi2structure is about the same, as before the heat treatment. No Al penetration is observed.
Study on the Phase Transition from Amorphous Phases to Crystalline TiSi2
Authors: Nam H. G. , Cho Nam-Ihn
Published: April 2011

Titanium silicides were prepared by coevaporation of Ti and Si on Si substrates at intermediate substrate temperatures followed by high temperature annealing. Depending on the deposition conditions, transmission electron diffraction analyses revealed two different halo patterns from the as-deposited samples. Variations in the deposition conditions included substrate temperature, deposition rate, and film thickness. Radial distribution functions were calculated to estimate the short range ordering of the amorphous phases. The interatomic distances of all the titanium silicide compounds were also calculated in order to compare them with the atomic ordering of amorphous phases. Phase transition from these amorphous phases to the first crystalline silicide is discussed in terms of kinetic variations as well as the atomic ordering.
Transient Phase Formation During the Growth of Epitaxial CoSi2 by Annealing of Co/Ti Bi-Layers on (100) Si
Authors: Miller D. J. , Selinder T. I. , Gray K. E.
Published: April 2011

Phase evolution during the annealing of Co/Ti bi-layers on (100) Si has been studied by x-ray diffraction and analytical electron microscopy. X-ray diffraction performed in situ during annealing revealed a reaction pathway involving the formation of a transient phase when epitaxial CoSi2 films were grown. Analytical electron microscopy was used to identify this phase as a spinel-related phase, isostructural with Co2TiO4. This phase grows as a result of the presence of the Ti interlayer and a small amount of oxygen from the annealing ambient. Annealing in vacuum or other purified inert gases yielded polycrystalline CoSi2 films which form via a different reaction pathway that does not involve a spinel phase. This spinel phase may serve both to reduce the native oxide from the underlying Si substrate and to control interdiffusion between Si and Co during the reaction, thereby promoting epitaxial growth.
Theoretical Considerations about Phase Growth and Phase Formation
Authors: D'Heurle F. M.
Published: April 2011

The first part of this paper constitutes a summary account of reactive phase formation as seen from a purely kinetic point of view. In the longer second part a more detailed analysis of phase formation based on microscopic, and calorimetric observations is presented. It is shown that these phenomena also tend to be dominated by kinetic factors. This explains why purely kinetic considerations (which should always prevail in any case at some point) usually provide a fairly accurate account of the growth of new chemical phases forming on a solid substrate, regardless of the physical state (solid, liquid or gas) of the second reactant.
Influence of Stoichiometric Variations and Rapid Thermal Processing of β-FESI2 thin Films on their Electrical and Microstructural Properties
Authors: Döscher M. , Selle B. , Pauli M. , Kothe F. , Szymanski J. , Müller J. , Lange H.
Published: April 2011

Amorphous irondisilicide thin films were deposited on silicon substrates in a RF sputtering process, followed by rapid thermal crystallization by means of moving the thin film beneath a line-shaped electron beam to form β-FeSi2. Depending on the deposition process parameters, films of a different stoichiometry can be produced. The deviations from the 1:2 stoichiometry, which have been determined by Rutherford Backscattering (RBS), are related to changes in the microstructure (studied by microscopic methods like TEM and AFM), the infrared phonon spectra (measured by FTIR spectroscopy) and the electrical properties of the crystallized films. The microstructure of the iron disilicide thin films is improved when the composition significantly deviates from 2.0, probably due to silicon interstitials in the silicide thin film. Films of different stoichiometry result in p- or n-type thin films with carrier densities below 5×1018cm−3 and hall mobilities up to 180cm 2/Vs. First results show that not only β-FeSi2-siliconheterojunctions as reported before but also pn-β-FeSi2-homojunctions show rectifying behavior. Rapid thermal processing with the line electron beam leads to a further improvement of the film quality when the scan velocity is increased up to the order of several cm/s.
Anisotropic Optical Response in β-FeSi2 Single Crystals and Thin Films
Authors: Bocelli S. , Guizzetti G. , Marabelli F. , Parravicini G. B. , Patrini M. , Henrion W. , Lange H. , Tomm Y.
Published: April 2011

Ellipsometric and reflectance spectroscopy in the range 1.4-5.0 eV as well as reflectance measurements in the infrared (10–80 meV) were performed on small single crystals of β FeSi2. The results show a clear anisotropy in the optical response which has been compared with theoretical calculations and data obtained on thin epitaxial films. Such a comparison gives evidence of the dependence of the optical response on the crystalline orientation of the film with respect to the surface.
Evolution of the Optical Response from a Very Narrow Gap Semiconductor to a Metallic Material in (FexMn1−x)Si
Authors: Bocellip S. , Marabelli F. , Spolenak R. , Bauer E.
Published: April 2011

A study of the electrical resisitivity of (Fex.Mn1−x)Si with 0 < x < 1 indicates a crossover from an almost semiconducting state in FeSi to a metallic one in MnSi. Optical measurements show that the electronic structure and the vibrational behaviour appears to be essentially uneffected by the Fe/Mn substitution. Instead, a change of the free carrier density occurs, yielding a temperature and stoichiometry dependent plasma frequency.
Voltage-Tunable PtSi/SiGe/Si Schottky Diode Infrared Detectors
Authors: Jimenez Jorge R.
Published: April 2011

The theory of recently-reported cut-off wavelength-tunable silicide/SiGe/Si detectors is presented. The SiGe layer provides voltage-tunable barrier heights by tailoring the shape of the Schottky barrier. The increased tunability provided by the SiGe layer is now understood as being due to two related effects: first, keeping the barrier peak position fixed with bias, and second, moving the barrier peak further away from the interface. The second effect decreases quantum efficiency, which depends on the peak-to-interface distance. However, maximizing the first effect allows us to obtain desired levels of tunability without potential decreases in quantum efficiency. For voltage-switched, dual-window imaging, a tunable range of 5-12 μm is required over moderate voltages (10-15 volts), for which calculated detector parameters are total SiGe thicknesses (uniform plus graded) of ∼ 60-100 Å and boron doping levels of ∼ 4-8 × 1016cm−3throughout the depletion layer width (∼ 4000 Å, in the SiGe and in the underlying Si).
Process Windows of Nickel and Platinum Silicides in Deep Sub-Micron Regime
Authors: Xu D.-X. , Das S. R. , McCaffrey J. P. , Peters C. J. , Erickson L. E.
Published: April 2011

It has been observed that the sheet resistance of a Ti-salicided polysilicon-gate electrode or source/drain region increases significantly as the dimension reaches the lower sub-micron range. The resistance of platinum and nickel silicide (PtSi and NiSi), however, does not increase with reduced linewidth. We have studied PtSi and NiSi films with deep sub-micron linewidths on single crystal or poly-Si substrates. In this study, the material properties such as sheet resistance, grain structure and surface morphology of these silicide films in confined geometries are reviewed and compared with TiSi2. Process windows for forming and maintaining these silicides are explored.
Materials Compatibility Between Si/Sio2 Substrates and Batio3 Thin Films
Authors: Caballero J. V. , Fuenzalida V. M. , Ávila R. , Eisele I.
Published: April 2011

BaTiO3 thin films, 50–60 nm in thickness, were evaporated in Ultra High Vacuum as well as under 1 mPa O2 pressure onto Si/SiO2 (30 nm) wafers. The substrate temperature during the evaporations was approximately 70 °C. The films were flash annealed in oxygen at 500 °C. The interfacial reactions were studied by XPS and AES Ar ion assisted depth profiling, and by RBS. Interdiffusion took place even at 70 °C. The XPS/AES depth profiles suggested strong interdiffusion, with Ba being the dominant moving species. The SiO2/BaTiO3 interface smears out with significant Ba concentrations up to half of the SiO2 thickness. Ti diffusion is remarkably lower. Barium is detected up to the SiO2/Si interface.
Tem Study of Diamond Films Grown from Fullerene Precursors
Authors: Csencsitsi R. , Gruen D. M. , Krauss A. R. , Zuiker C.
Published: April 2011

Transmission Electron Microscope (TEM) techniques are applied to study the microstructure of diamond films grown from fullerene precursors. Electron diffraction and electron energy loss spectra (EELS) collected from the diamond films correspond to that of bulk diamond. Microdiffraction, high resolution images and EELS help determine that the first diamond grains that nucleate from fullerene precursors generally form on a thin amorphous carbon nterlayer and seldom directly on the silicon substrate. Grain size measurements reveal nanocrystalline diamond grains. Cross section TEM images show that the nanocrystalline diamond grains are equiaxed and not columnar nor dendritic. The microstructure of small equiaxed grains throughout the film thickness is believed responsible for the very smooth surfaces of diamond films grown from fullerene precursors.
Polycrystalline Silicon Films for Microelectromechanical Devices
Authors: Kahn H. , Stemmer S. , Mullen R. L. , Huff M. A. , Heuer A. H.
Published: April 2011

Polycrystalline silicon is the most widely used structural material for surface micromachined microelectromechanical systems (MEMS). There are many advantages to using thick polysilicon films; however, due to process equipment limitations, these devices are typically fabricated from polysilicon films less than 3 μm thick. In this work, microelectromechanical test structures were designed and processed from thick (up to 10 μm) in situ boron-doped polysilicon films. The elastic modulus of these films was about 150 GPa, independent of film thickness. The thermal oxidation of the polysilicon induced a compressive stress into the top surface of the films, which was detected as a residual stress in the polysilicon after the device fabrication was complete.
Origin of In-Plane Texturing in Sputtered Mo Films
Authors: Malhotra A. K. , Yalisove S. M. , Bilello J. C.
Published: April 2011

Sputtered Mo films with a thickness of 2μm or greater have been previously shown by xray and TEM studies to grow with strong in-plane and out-of-plane textures under dynamic deposition conditions. In this work, the geometric conditions and mechanisms causing preferential grain alignment in the plane of growth for sputtered Mo films, with a nominal thickness of 2μm, were explored. Four different deposition configurations, obtained by varying the parameters such as the deposition angle and the rotation speed of the substrates, were used in order to modify the texture as studied by x-ray and SEM techniques. While a [110] type out-of-plane texture was observed for all four deposition configurations, a (110) type in-plane texture, and the corresponding grain alignment in the plane of growth, was observed only when the flux of adatoms was hitting the substrates at an oblique angle. The texture characteristics and the microstructure of the Mo films, as analyzed using the pole figure x-ray and SEM techniques, were observed to be very similar for films deposited on three different substrates, namely the Si(100) and Ni3Al(321) single crystals, and laboratory grade glass slides. The in-plane texture development under oblique deposition conditions was proposed to be due to a combination of two mechanisms, namely the preferential resputtering of some of the grains normal to and in the plane of growth caused by the higher energy adatoms in the flux, followed by termination of the preferentially sputtered grains due to geometric shadowing.
Growth and Texture of Polycrystalline Thin Films
Authors: Smith Richard W. , Ying Feng , Srolovitz David J.
Published: April 2011

Two dimensional non-equilibrium molecular dynamics simulations are performed to study microstructural evolution during the growth of polycrystalline thin films. Attention is focused on the interaction between grain boundaries and voids which form during deposition, and on the development of a preferred, crystallographic texture during film growth. In an intermediate temperature regime, where the film is cold enough to allow void formation but hot enough to allow grain boundary motion, boundaries move such as to attach themselves to voids as the voids form from depressions in the film surface. At lower temperatures, the boundaries have insufficient mobility to migrate toward the voids. At higher temperatures, films grow in the absence of voids. At low deposition kinetic energies, there is no tendency for polycrystalline films to develop a preferred texture. At moderate or high energy deposition kinetic energies, however, as in the case of magnetron sputtering, significant texture formation can result due to preferential (re)sputtering of atoms from the surface of grains with low-binding-energy exposed surfaces. Such preferential (re)sputtering provides a height advantage for grains possessing high-binding-energy exposed surfaces. The taller grains are seen to widen as deposition continues, resulting in the development of a preferred crystallographic orientation.
Growth and Structural Studies of Thin Films in the Mo-Bi-O System
Authors: Depero L. E. , Sangaletti L. , Zocchi M. , Rizzi G. A.
Published: April 2011

In the present contribution an X-ray diffraction (XRD) study of thin films in the Mo-Bi-O system is reported. The samples were grown by MOCVD on A12O3substrates. Several thin films have been grown starting from a Mo:Bi ratio in the two metallorganic precursors ranging from 6:1 to 1:1, thus obtaining films constituted by MoO3and Mo-Bi-O layers with different thicknesses. The effect of the underlying Mo-Bi-O layer on the preferred orientation of the MoO3layer, which is found in the samples with a high Mo:Bi ratio in the precursors, is discussed. Moreover, an equation is proposed relating the percentage of the phase constituting the film, as given by the Rietveld leastsquares procedure, and the film thickness. Thus it is shown that the growth rate of the pure MoO3film is much higher than that of the Mo-Bi-O oxide film. A tentative explanation can be given by considering a possible growth inhibiting action by Bi in this system.
Sol-Gel Route To Oxygen Ion Conductors in Thin Film Form
Authors: Pell J. W. , Delak K. M. , Loye H.-C. zur
Published: April 2011

The oxygen-ion conducting Aurivillius phases Bi2Cu0.1V0.9O5.35 and Bi2Nb0.3V0.7O5.5 were synthesized as bulk powders by the sol-gel method, and gave single-phase powder X-ray diffraction patterns at calcination temperatures as low as 450 °C. Crack-free films of both materials were spin-coated onto quartz, platinum, and silver substrates and heat-treated in a twostep firing process. The effects of different process parameters were investigated.
Optical Indices of Tin-Doped Indium Oxide and Tungsten Oxide Electrochromic Coatings
Authors: Von Rottkay K. , Rubin M. , Ozer N.
Published: April 2011

Thin films of tin-doped indium oxide are widely used for transparent conductors. One application of ln203:Sn (ITO) is transparent contacts for electrochromic electrodes. Optical design of electrochromic devices requires knowledge of the optical constants for each layer from the near ultraviolet and visible to the mid infrared. Determination of the optical constants of the electrochromic layer cannot be made in isolation; a complete device or at least a half-cell including a layer of ITO is required to change the optical state of the electrochromic material. Measurements on ITO were made using variable-angle spectral ellipsometry, and spectral transmittance and reflectance. A series of structural models were fit to this data. The problem is complicated because of inhomogeneity in the films, variability in the manufacturing process, and sensitivity to environmental conditions. The spectral dependency was modeled by a single Lorentz oscillator and a Drude free-electron component. This data was then used as the basis for a model to extract the optical constants for a tungsten oxide electrochromic film.