bluuebunny/crossref_metadata_2025 huggingface dataset:
Low Resistivity-Highly Transparent Zno:Ga Tco's Grown by Laser Ablation
Authors: Siqueiros J. M. , Díaz J.A. , Contreras O. , Hirata G.A. , McKittrick J.
Published: April 2011

Highly transparent with low electrical resistivity gallium-doped zinc oxide (ZnO:Ga) thin films were prepared on glass by Pulsed Laser Deposition at different substrate temperatures. ZnO:Ga evaporation targets were prepared by pressing and sintering powder materials obtained with a novel combustion synthesis technique.

An excellent transmittance of more than 85% in the visible range and a low sheet resistance value as low as 13 Ω/sq. were measured on a 200 nm thickness film grown at Ts=300°C. From optical measurements we observed an increase in the ZnO:Ga bandgap when the substrate temperature is raised from 150°C to 300°C. With this, a remarkable improvement in the blue-green region transmittance is obtained.

X-Ray diffraction patterns indicate that the films grow highly oriented in the basal plane direction (c-axis) of the hexagonal ZnO grains.
Phase Transitions Induced By Femtosecond Pulses
Authors: Glezer E. N. , Huang L. , Siegal Y. , Callan J. P. , Mazur E.
Published: April 2011

Optical studies of semiconductors under intense femtosecond laser pulse excitation suggest that an ultrafast phase transition takes places before the electronic system has time to thermally equilibrate with the lattice. The excitation of a critical density of valence band electrons destabilizes the covalent bonding in the crystal, resulting in a structural phase transition. The deformation of the lattice leads to a decrease in the average bonding-antibonding splitting and a collapse of the band-gap. Direct optical measurements of the dielectric constant and second-order nonlinear susceptibility are used to determine the time evolution of the phase transition.
Reversible Photoredox Processing of Transition Metal Oxides
Authors: Villarica R. Martin , Nash Fazio , Chaiken J. , Osman Joe , Bussjager Rebecca
Published: April 2011

We describe a novel laser chemical process having potential for optical data storage and processing applications. Reversible oxygen exchange involving WO3, using readily available laser sources offers improved durability and versatility over existing erasable optical data storage media. Being interconvertable using heat and blue-green laser sources, the well known yellow WO3and blue W2O5can function as erased and written states.
Investigation of Laser-Induced Etching of Ti in Phosphoric Acid
Authors: Nowak R. J. , Metev S. M. , Meteva K. B. , Sepold G.
Published: April 2011

Laser-induced chemical etching of Ti in phosphoric acid has been investigated using cw Nd:YAG (1.064 μιm) and Argon lasers (514 nm) operating in the fundamental Gaussian mode. Two different regions of etching were observed, which are separated by a characteristic threshold value of the laser power and ascribed to melting of the metal. Below the threshold an exponential dependence of etch rates on laser power suggest a thermally activated etching mechanism. Time-resolved measurements indicate in this region the dissolution of the passivation layer followed by surface etching of the metal grains. After laser illumination an immediate repassivation of the re-cooled surface stops the etch reaction.
Silicon Growth Rate Enhancement Using Trisilane in a Laser Direct-Writing Technique
Authors: Boughaba S. , Auvert G.
Published: April 2011

An argon-ion laser based direct-writing technique was used to deposit micron-size silicon lines from the decomposition of silane (SiH4) and trisilane (Si3H8) gases. The substrates used were 0.1 μrn polysilicon/1 μ.m silicon dioxide/<100> monosilicon multilayered structures. The vertical silicon deposition rate was investigated as a function of the laser-induced surface temperature and gas pressure. For temperatures ranging between 1000 and 1410 °C, the pressure was varied in the range 5-250 mbar and 0.1-30 mbar for SiH4 and Si3H8, respectively. For both gases, three growth regimes could be distinguished according to precursor pressure. The deposition rates achieved using trisilane are far higher than those obtained with silane in spite of the use of a reduced gas pressure range. For a laser-induced surface temperature of 1300 °C and a precursor pressure of 10 mbar, the deposition rates achieved using SiH4 and Si3H8 are, respectively, 0.42 and 20 μ.m/s, representing an enhancement factor of 50 with the later.
Interface Versus Diffusion Controlled Growth in Nanocrystallization Kinetic Studies
Authors: Clavaguera N. , Clavaguera-mora M.T.
Published: April 2011

Nanocrystallization by heat treatment of initially amorphous alloys occurs for high nucleation frequency I and low crystal growth rate u values. Calorimetrie data extracted, for instance, from differential scanning calorimetry are normally presented by the dependence of the crystallized fraction x, on: i) x=x(T,t) when obtained under isothermal annealing at temperature T as a function of time t; ii) x=x(τ,β) when obtained under continuous heating at a scan rate β as a function of temperature. Theoretical analysis of the crystallization kinetics is presented which accounts for nuclei either pre-quenched or created by homogeneous nucleation whose initial steps of growth are controlled by the interface formation between the nanocrystals and the matrix and subsequent growth is limited by diffusion.
Temporal Evolution of Bimodal Distribution of γ’ Precipitates in Ni-Al-Mo Alloys under the Influence of Coherency Strains
Authors: Sequeira A.D. , Calderon H.A. , Kostorz G.
Published: April 2011

The influence of coherency strains produced by the γ-γ’ lattice mismatch, δ, on the decomposition process of Ni-Al-Mo alloys with a bimodal size distribution is presented. Samples with δ ranging from positive to negative, were investigated in a double-step aging procedure. The evolution of the microstructure and the kinetics of coarsening were studied using transmission electron microscopy (TEM). The lattice mismatch between the matrix and the different classes of precipitates was determined by high-resolution high-temperature x-ray diffraction. It is shown that the strain fields produced by the lattice mismatch can influence dramatically the decomposition of metallic alloys. It is suggested that the reduction of the coarsening rate of the large precipitates, the fast coarsening rate of the small precipitates and the distortions detected in the matrix are all direct consequences of the elastic fields produced by the γ-γ’ lattice mismatch.
Wet Oxidation of Si1-x-yGexCy Layers on (100) Si
Authors: Bair A. E. , Atzmon Z. , Alford T. L. , Chandrasekhar D. , Smith David J.
Published: April 2011

Single crystal Si0.63Ge0.36C0.01 and amorphous Si0.65Ge0.27C0.08 layers have been oxidized in a wet ambient at 700 °C and 900 °C. The oxide growth has been studied using Rutherford backscattering spectrometry and transmission electron microscopy. A reference sample of Si0.63Ge0.37 was also oxidized in order to determine the influence of C on the oxidation behavior. The lower C content alloy behaved similar to the SiGe alloy. Uniform Si1-xGexO2 was obtained at 700 °C whereas SiO2 was formed at 900 °C, and Ge piled up underneath the oxide. In both cases, C was not detected in the oxide layer. The amorphous Si0.65Ge0.27C0.08 alloy behaved significantly different at both oxidation temperatures in comparison with the crystalline Si0.63Ge0.36C0.01 and Si0.63Ge0.37. Negligible oxidation occurred at 700 °C whereas SiO2 was obtained at 900 °C and the rejected Ge distributed uniformly throughout the SiGeC alloy. It is proposed that fast Ge diffusion during oxidation at 900 °C resulted from diffusion at grain boundaries, since crystallization of the amorphous SiGeC layer occurred in conjunction with oxidation, leading to nucleation of ∼5 nm nanocrystals.
XRD Study of the Influence of Heat Treatment on the Microstructure of Sol-Gel Processed ZrO2-Y2O3 Ceramics
Authors: Barrera-Solano C. , PiÑero M. , Jiménez-Solís C. , Gago-Duport L.
Published: April 2011

YSZ samples containing 5 and 10 mol% of Y203 were prepared by controlled hydrolysis of metal alkoxides. The dried powders were calcined at 800°C and then they were uniaxially pressed and sintered at different temperatures and next heated at 1400°C (∼ 5 MPa) or annealed at 1600°C for 24 h. The quantitative analysis of the experimental X-ray diffraction (XRD) spectra was performed by Whole Pattern Fitting (WPF). A Pseudo-Voigt (Thompson-Cox-Hastings) was used as shape profile function. The respective phase fractions (wt %) were fitted for both solid state solutions using the scale factor. The heat treatment induced changes are discussed.
Solidification Front Velocity of Ternary Titanium-Aluminides
Authors: Wettlaufer M. , Laakmann J.
Published: April 2011

Ternary titanium-aluminides with compositions of Ti51Al47Fe2, Ti51A147Cr2 and Ti51Al47Mn2 were investigated with respect to the correlation of their solidification front velocity v and bulk undercooling ΔT. The observation of the solidification front during the recalescence event has been realized using a high speed video system capable of recording up to 12,000 pictures per second. The temperature measurement was carried out by pyrometry, avoiding contact with the sample. The comparison of the experimental data with the LKT-theory (Lipton, Kurz, Trivedi; [1]) refers to a primary (hcp) β-Ti solidification for undercoolings below ΔT≈ 130 K and primary (bcc) α-Ti solidification for ΔT≥ 130 K. For undercoolings ≥ 150 K the theory differs greatly from the experimental results.

The maximum undercoolings achieved were 268 K (Ti51Al47Fe2), 285 K (Ti51Al47Cr2) and 280 K (Ti51Al47Mn2), corresponding to a solidification front velocity v ≈ 9-10 m/s for all alloys.
Progression of the Surface Roughness of N+ Silicon Epitaxial Films as Analyzed by AFM
Authors: John S. , Quinones E. J. , Ferguson B. , Pacheco K. , Mullins C. B. , Banerjee S. K.
Published: April 2011

We report on the morphology of heavily phosphorous doped silicon films grown by ultra high vacuum chemical vapor deposition at temperatures of ∼550° C. The effects of PH3 on epitaxial films have been examined for silicon deposited using SiH4 and Si2H6. It is found that films grown using silane experience an increase in surface roughness with increasing phosphine partial pressure. AFM and RHEED studies indicate 3-D growth. As epitaxy progresses, it is believed that phosphorus segregation on the growing film surface greatly diminishes the adsorption and surface mobility of the silicon bearing species. Initial Si deposition results in a pitted surface, but as growth advances and the phosphorus coverage increases, growth within the pits decreases the surface roughness. In contrast to SiH4, it is found that Si2H6 provides excellent quality, smooth films even at high PH3 partial pressures.
Molecular Dynamics Simulation of Energetic Deposition of AG/FE and AG/SI Bilayers and Multilayers
Authors: Mattei G. , Mazzone A.M.
Published: April 2011

The growth of Fe/Ag and Ag/Si multilayers is simulated by using molecular dynamics with quantum forces. The results of these calculations indicate that from ballistic motions irregular structures and smeared interfaces may be generated. The temperature of the processing is critical and good epitaxial growth is obtained by forcing a fast heat dissipation.
Temperature-Dependent Strain Relaxation and Islanding of Ge/Si(111)
Authors: Deelman P.W. , Schowalter L.J. , Thundat T.
Published: April 2011

In order to understand Ge island nucleation and evolution, we have studied strain relaxation and clustering of Ge grown on Si(111) by molecular beam epitaxy (MBE) with in situ reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM), and Rutherford backscattering spectrometry (RBS). Our goal is to tailor the size and density of the nanocrystals by controlling thermodynamics and kinetics. At low temperature (∼ 450°C), we observe a sharp 2D-3D growth mode transition after 2.5ML ±0.1ML (we define a thickness of 1ML to be one-third the length of the body diagonal of the Ge conventional unit cell), when transmission diffraction features appear in RHEED and the surface lattice constant begins to relax. The mechanisms of island growth and strain relaxation change with growth temperature. At ∼ 700°C, transmission diffraction spots never appear in RHEED for Ge/Si(111) and strain relaxation occurs gradually. After 37ML of growth, the apparent in-plane lattice parameter increases only 1.5% over that of the Si substrate. This behavior is explained by the different manner in which islands initially nucleate and grow in the two temperature regimes. At low temperature, small islands nucleate and grow on a relatively rough wetting layer (which itself provides preferential sites for dislocation introduction). The areal density of the small islands is relatively high. At high temperature, a small number of islands grow very large from the outset. A general model indicates how, at low temperature, the relative difficulty of overcoming the barrier to dislocation formation actually results in an apparent larger degree of strain relief than at high temperature.
Growth Kinetics and Structure of Ultrathin Copper Films on the W(110) Surface Studied by Leem
Authors: Altman M.S. , Luo E.Z. , Chung W.F. , Orr B.G.
Published: April 2011

Competing desorption during the epitaxial growth of Cu on the W(110) surface has been studied with low energy electron microscopy (LEEM). Direct imaging of a structural transformation from pseudomorphic (1×1) to relaxed (15×1) periodicity which occurs at a coverage of θCu = 2.13 monolayers is used as a very accurate, local probe of coverage during deposition. The desorption energy E = 3.67 eV and attempt frequency v = 2.15 × 1015 s−1 are determined by examining the balance condition when the incident and desorption fluxes are equal. A step-flow-like growth morphology occurs when the supersaturation is significantly reduced by competing desorption. An island nucleation and coalescence growth morphology results at higher supersaturation.
Atomistic Simulation of Nanocrystalline Materials
Authors: Wolf D. , Phillpot S. R. , Keblinski P.
Published: April 2011

Atomistic simulations show that high-energy grain boundaries in nanocrystalline copper and nanocrystalline silicon are highly disordered. In the case of silicon the structures of the grain boundaries are essentially indistinguishable from that of bulk amorphous silicon. Based on a free-energy argument, we suggest that below a critical grain size nanocrystalline materials should be unstable with respect to the amorphous phase.
Influence of Pressure on the Stability of Metastable TiSi(B2) Phase
Authors: Davidov Genady , Fuks David , Dorfman Simon
Published: April 2011

We study the influence of pressure on the temperature of order-disorder phase transition in metastable TiSi(B2) phase as well as the pressure dependence of thermodynamic functions describing the stability of this phase. The suggested model outlines the technique to calculate the values of the energy parameters of ordering process from the first principles.
Modeling of the Mechanical Alloying Process in Binary Systems
Authors: Herr U. , Klassen T. , Averback R.S.
Published: April 2011

The process of mechanical alloying in binary metallic systems is discussed in a microscopic picture. Special emphasis is put on systems with large positive heat of mixing. In these systems, a competition between thermal diffusion and forced transport takes place. Based on results from Monte Carlo studies of the effect of combined shear and diffusion processes on an atomistic scale, a simple rate equation approach is developed. The approach can reproduce the phase evolution in the simulation and the main features of the temperature dependence of the alloy phase fraction in steady state. The results are further compared with experimental data.
Anomalous Lattice Parameters in Iron-Copper Multilayers
Authors: Lloyd S. J. , Somekh R. E. , Stobbs W. M.
Published: April 2011

X-ray, magnetism and electron loss spectroscopy data were obtained for a series of coherent Fe-Cu face-centred multilayers which suggest that there is a lattice parameter anomaly in the structure. The use of high resolution electron microscopy (HREM) and dark field imaging to measure spacing changes along the layer normal are compared. Experimental dark field images suggest that the Fe has expanded lattice spacings in the growth direction in contradiction to the predictions of a conventional elastic model for a coherent multilayer structure.
Initial Stage of Titanium Slicide Formation on Si(Lll) Substrate
Authors: Shingubara S. , Takata S. , Takahashi E. , Konagata S. , Sakaue H. , Takahagi T.
Published: April 2011

Detailed analysis of Ti and/or TiSi2 islands growth have been made by UHV-STM observations after Ti deposition and subsequent annealing. It is shown that islands growth mode changes drastically at about 500 U for both cases on Si(111)-7×7 and on H-terminated Si(lll)-l×l. In the temperature regime higher than 500 °C, activation energies of islands growth are 1.12eV and 0.56eV for Si(M11)-7×7 and H-terminated Si(111) respectively. It is speculated that residual H-atoms combined with Si dangling bonds lowered surface diffusion activation energy.
Process Modeling and Integration of The Salicide Process Module for Sub-Half Micron Technology.
Authors: Apte Pushkar P. , Prinslow Douglas A. , Kittl Jorge A. , list R. Scott , Pollack Gordon
Published: April 2011

Metal silicides have been used extensively in CMOS technology for reducing electrical resistance. As wafer-scale features have shrunk to the sub-half micron domain, obtaining a self-aligned silicide - or salicide - process that satisfies all requirements has become a significant challenge. One part of this challenge lies in developing the necessary scientific insights and technological innovations for the actual salicide process, while the other part lies in building a complete salicide process module which meets requirements of performance, reliability, ease of integration, control, etc. at the least possible cost and cycle-time for technology development. This second part is seldom addressed by researchers, and yet, is fundamentally important for successful application of any salicide technology to actual integrated circuit products. This paper presents a complete picture of the salicide module in the context of all the aforesaid components; and describes the use of abstraction and hierarchical models to capture process information and to facilitate process design. Prototype compact models for key wafer-state and performance outputs such as TiSi2 thickness and resistance are presented to demonstrate implementation of this process module.
Phase Transformations in Layered Fe-Si Structures
Authors: Fanciulli M. , Rosenblad C. , Weyer G. , Von Känel H. , Onda N. , Nevolin V. , Zenkevich A.
Published: April 2011

The kinetics of the phase transformations of the Fe-Si system and the Si/Fe and Fe/Si interfaces have been investigated by 57Fe conversion electron Mössbauer spectroscopy (CEMS). Single crystalline Fe films grown on Si(111) by molecular beam epitaxy (MBE) and polycrystalline Fe films grown by pulsed laser ablation deposition (PLD) have been thermally treated in vacuum and the formation of the different silicide phases has been monitored as function of temperature and time by CEMS.
Phase Development in Pt/ Si-Ge Alloy Layers
Authors: Carmondy Michael W. , Johnson Andrew S. , Kvam Eric P.
Published: April 2011

The phase development sequences for Pt layers on Si, Ge, and Si-Ge at 327°C were studied by X-ray diffraction, energy dispersive spectroscopy, and transmission electron microscopy. The reactions on pure Si and pure Ge followed the sequences reported previously. The reactions on the alloy layers differed slightly from the simple binary reactions. A ternary Pt(Si,Ge) reacted layer was formed on the alloy samples as the final phase on the Si-Ge alloy layer. This is discussed in terms of enthalpies of formation and the relative diffusion rates of Pt, Si, and Ge.
The Growth Of Thin Ti Films on Si(111)-(7×7) Surfaces
Authors: Saleh Adli A. , Peterson D.
Published: April 2011

A study of the room-temperature growth of ultrathin Ti films (up to 7 ML) on clean and atomically flat Si(111)- (7×7) surfaces using Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) is presented. The variations in the Auger signal due to Si L2.3VV with binding energy of 92 eV are used to model the growth morphology of this system. These measurements indicate the growth of an initial disordered and continuous Ti film of up to 1.6 ML in thickness, where the LEED pattern completely disappears and the Si Auger signal is strongly attenuated. As more Ti is deposited, this is followed by the disintegration of the continuous film and the formation of an intermixed Ti/Si film. This is evidenced by a change in the slope of the Auger signal time (AST) plot, and the reappearance of the LEED pattern. The modification in the overlayer composition for films thicker than 1.6 ML is confirmed by a change in the Si L2.3VV Auger peak that resembles the peak shape due to TiSi2.
Rapid Self-Ion Stimulated Process for TiSi2 thin Film Formation
Authors: Chapljuk V. I. , Gusev I. V. , Belevsky V. P.
Published: April 2011

A method, technological arrangement, and some special features of the process for TiSi2 thin film formation is described in details. Rapid formation of low-resistivity single-phase TiSi2 layers is realized directly during deposition of Ti onto Si from DC plasma of metal vapour with simultaneous powerful self-ion bombardment at Wi > 2.5–3.1 W/cm2. Accelerated reactive diffusion is activated by thermal (dT/dτ ≥ 10°C/sec) and radiation (Eadd ≤ 2500 eV/atom) effects of powerful Ti+-ion bombardment. Thin TiSi2 layers with resistivity ρ = 13–20 μΩcm are formed on different Si substrates under optimum energetic conditions after 50 sec of the deposition. The film structure formation passes through three kinetic stages.
Low Temperature Transport Properties of Ru2Si3 Single Crystals
Authors: Gottlieb U. , Madar R. , Laborde O.
Published: April 2011

We present here low temperature transport properties of Ru2Si3 single crystals. Below room temperature the resistivity behaviour of this material is extrinsic. The Hall coefficient is positive down to about 10 K and the becomes negative below. We explain this crossover with a two band model. At very low T, the magnetoresistance of our crystals shows the typical behaviour for a doped semiconductor on the metallic side of the metal-insulator transition and can be described by a scaling law characteristic for weak localisation with strong electronelectron interactions.
The Use of Disordered Interlayers to Enhance Nucleation of Silicon Nitride During Chemical Vapor Deposition
Authors: Boekenhauer Rachel E. , Lauten Frederick S. , Sheldon Brian W.
Published: April 2011

Thin, disordered interlayers were used to enhance the nucleation of Si3N4. Continuous crystalline films were formed at relatively low temperatures (<1250°C) by using an amorphous, Sirich interlayer. The interlayer was produced by varying the CVD conditions (i.e., by using multistep processing). Samples were characterized with XPS, SEM, and TEM with concurrent EELS. The results indicate that the nucleation of crystalline material is very sensitive to the structure and composition of the disordered interlayers. Also, the structure and composition of the interlayers evolve during growth, such that crystalline material only nucleates when the interlayer provides favorable conditions.
Ar+ Implantation Effects on Polycrystalline Thin Films
Authors: Lee J. H. , Hwang C. W. , Shin J. E. , Jin Y. S. , Mah S. B.
Published: April 2011

The solid phase crystallization behavior of argon ion (Ar+) implanted very thin polycrystalline silicon (poly-Si) films has been investigated. Poly-Si films of 500Å thickness were deposited at 625°C by low pressure chemical vapor deposition (LPCVD). The films were amorphized by Ar+ implantation with 7 ° tilt angle. The amount of ions implanted was varied from 2.0 × 1013 cm-2 to 1.2 × 1015 cm-2 and the acceleration voltages from 40KeV to 120KeV. The films were recrystallized by furnace annealing at 580°C for 48 hours in N2 atmosphere, followed by 1000°C annealing The crystallinity of the recrystallized Si films and the distribution of the argon atoms in the film were investigated. It was found that the crystallinity strongly depended on the Ar+ implantation dose. The average grain size of Ar+ implanted film was about 0.25μm, which was smaller than that of Si+ implanted film of the same dose, 0.45μm. Ar atoms retarded the grain growth rate during the annealing process and the excess Ar atoms in Si films were segregated at the surface of silicon films after 1000°C annealing Poly-Si thin film transistors (TFTs) were fabricated at high temperature using Ar+ implantation technique. Remarkable electrical characteristics (Ids- Vgs) were obtained such as an electron mobility of 35 cm2/V.s, which was attributed to the enhancement of crystallinity by Ar+ implantation. But, segregated Ar atoms near the interface would give rise to structural deformation and crystalline defects which can act as the scattering and’ trapping centers for carriers.
Effects of Deposition Parameters on Crystallization of Pecvd Amorphous Silicon Films
Authors: Wang Yaozu , Kingi Reece , Awadelkarim Osama O. , Fonash Stephen J.
Published: April 2011

Plasma-enhanced chemical vapor deposition was used to deposit a-Si:H thin films (∼ 1000 Å) at various temperatures below 300°C on Coming 7059 glass substrates using a silane-based plasma. These films were used as precursor materials to produce solid phase crystallized polycrystalline silicon (poly-Si) by conventional furnace annealing at 600°C in N2 ambient. The precursor a-Si and final poly-Si films were examined using spectroscopic ellipsometry and transmission electron microscopy. Precursor film deposition temperatures were found to affect the void density in the a-Si film and grain size in the resulting poly-Si film with lower deposition temperatures leading to higher void density in the a-Si film and larger grain size in the poly-Si film.
Electric and Optical Properties of μc-Si,Ge:H Alloys Deposited by Reactive Magnetron Sputtering (RMS)
Authors: Cho S. M. , Wolfe D. , Christensen K. , Lucovsky G. , Maher D. M.
Published: April 2011

Amorphous and microcrystalline silicon-germanium alloys, a-SixGel-x:H and μc-SixGel-x:H, respectively, have been prepared by reactive magnetron sputtering (RMS) from pure crystalline Si and Ge targets in a hydrogen ambient using argon as the sputtering gas. We have investigated the structural, optical, and electronic properties of the as-deposited films. The optical and electrical properties, e.g., the ambipolar diffusion length, photoconductivity, and photosensitivity, were found to be comparable to those of device-grade a-SixGe1-x:H alloys, e.g., films with x ∼ 0.5, and band-gaps ∼ 1.3–1.4 eV. In contrast to the behavior of the a-SixGel-x:H alloys, the μc-SixGe1-x:H alloys do not display a Staebler-Wronski effect, as manifested by a decay of the photoconductivity under intense illumination.
Effectiveness and Reliability of Metal Diffusion Barriers for Copper Interconnects
Authors: Bai G. , Wittenbrock S. , Ochoa V. , Villasol R. , Chiang C. , Marieb T. , Gardner D. , Mu C. , Fraser D. , Bohr M.
Published: April 2011

Cu has two advantages over Al for sub-quarter micron interconnect application: (1) higher conductivity and (2) improved electromigration reliability. However, Cu diffuses quickly in SiO2and Si, and must be encapsulated. Polycrystalline films of Physical Vapor Deposition (PVD) Ta, W, Mo, TiN, and Metal-Organo Chemical Vapor Deposition (MOCVD) TiN and Ti-Si-N have been evaluated as Cu diffusion barriers using electrically biased-thermal-stressing tests. Barrier effectiveness of these thin films were correlated with their physical properties from Atomic Force Microscopy (AFM), Transmission Electron Microscopy (TEM), Secondary Electron Microscopy (SEM), and Auger Electron Spectroscopy (AES) analysis. The barrier failure is dominated by “micro-defects” in the barrier film that serve as easy pathways for Cu diffusion. An ideal barrier system should be free of such micro-defects (e.g., amorphous Ti-Si-N and annealed Ta). The median-time-to-failure (MTTF) of a Ta barrier (30 nm) has been measured at different bias electrical fields and stressing temperatures, and the extrapolated MTTF of such a barrier is > 100 year at an operating condition of 200C and 0.1 MV/cm.
Crystallinity Effects in the Optical Modulation of Electrochromic Devices
Authors: Klein J. D. , Clauson S. L.
Published: April 2011

The electrochromic switching behavior of amorphous and crystalline WO3 thin films was investigated. The films were deposited on ITO-coated Corning 7059 glass substrates by sputtering. X-ray diffraction showed the crystalline film to have a mixed monoclinic/orthorhombic crystal structure. The coloration mechanisms in the visible and very near infrared were investigated by hydrogen insertion. A numerical fitting scheme allowed the coloration of the films to be expressed by means of the extinction index. As expected, crystalline WO3 exhibited more modulation in the very near infrared. A reversible crystallographic distortion was associated with the coloration of the crystalline WO3 films.
The Phase Diagram of Hydrogen in Ultra Thin Films
Authors: Jisrawi N. M. , Ruckman W. , Reisfeld G. , Wiesmann H. , Loeb F. , Gallego E. , Gorelik Y. , Thurston T. R. , Strongin Myron
Published: April 2011

In this paper, we discuss changes in the phase diagram of hydrogen in both bilayer (i.e. 200–2000 Å Nb/ 100 Å Pd on glass) and multilayer configurations. In fact, it is the changes in this phase diagram, in addition to the Pd coating, that makes theses bilayer systems useful for hydrogen gas sensors. Comparison of x-ray diffraction, electrical resistivity and volumetric measurements of the films before and after hydrogen charging indicate that the phase equilibria between a correlated (high concentration) and a dilute phase of hydrogen in Nb is not sensitive to the number of layers in the films. On the other hand, the experimental methods show different behavior for 200 Å thick Nb films and thicker (>400 Å) Nb layers. Diffraction results showing unisotropic lattice expansion will also be discussed..
Characteristics of a Reactively Sputtered Indium Tin Oxide Thin Film Strain Gage for Use at Elevated Temperatures
Authors: Gregory Otto J. , Dyer Stephen E. , Amons Paul S. , SLOT Arnout Bruins
Published: April 2011

Strain sensors based on thin films of indium tin oxide (ITO) have been developed for a variety of applications, where the measurement of both static and dynamic strain are required at elevated temperatures. ITO thin films were prepared by rf reactive sputtering in Ar:02 mixtures from high density, electrically conductive targets having a nominal composition of 90% In203 and 10% Sn02. The resulting ITO films exhibited room temperature resistivities between 2x10−2 and 2x102 ω cm, an optical bandgap of 3.5 ev and tested “n” type by hot probe. These same films exhibited large negative gage factors (G=δρ/ ρδε) when tested at room temperature and a relatively low temperature coefficient of resistance when tested at elevated temperature in air. Specifically, gage factors approaching -100 with little hysteresis were observed for strains up to 700 μin/in and TCR's as low as 195 ppm/°C have been measured for the sputtered ITO films. In addition, these films were electrically stable and readily formed ohmic contacts with platinum at temperatures up to 1180°C. In this paper, we report on the electrical properties and piezoresistive properties of ITO based strain gages at temperatures up to 1180°C. Prospects of using ITO thin films as the active strain elements in high temperature strain gages and the characteristics of strain sensors based on ITO are discussed.
Initial Stage of Cvd Copper Deposition on Teos Oxide
Authors: Nguyen Tue , He Shusheng , Charnesky Lawrence J.
Published: April 2011

Selective deposition of copper on metal (such as TiN) versus dielectric (such as oxide) requires understanding of the mechanism of chemical-vapor-deposition copper deposition. This work studies the initial stage of CVD copper deposition with hexafluoroacetylacetonate Cu(I) trimethylvinylsilane (Cu-hfac-tmvs) precursor on tetraethylorthosilicate (TEOS) oxide using Fourier transform infrared spectroscopy (FTIR).
Magnetic Properties of Sputtered Fe-O and Co-O Thin Films
Authors: Dimitrov D. V. , Murthy A. S. , Hadjipanayis G. C. , SWANN C. P.
Published: April 2011

Fe-O and Co-O films were prepared by DC magnetron sputtering in a mixture of Ar and O2 gases. By varying the oxygen to argon ratio, oxide films with stoichiometry FeO, Fe3O4, α-Fe2O3, CoO and Co3O4 were produced. TEM studies showed that the Fe – oxide films were polycrystalline consisting of small almost spherical grains, about 10 nm in size. Co-O films had different microstructure with grain size and shape dependent on the amount of oxygen. X-ray diffraction studies showed that the grains in Fe-O films were randomly oriented in contrast to Co-O films in which a <111> texture was observed. Pure FeO and α-Fe2O3 films were found to be superparamagnetic at room temperature but strongly ferromagnetic at low temperatures in contrast to the antiferromagnetic nature of bulk samples. A very large shift in the hysteresis loop, about 3800 Oe, was observed in field cooled Co-CoO films indicating the presence of a large unidirectional exchange anisotropy.
Simulation of Dislocations in Ordered Ni3Al by Atomic Stiffness Matrix Method
Authors: Hsu Y. E. , Chaki T. K.
Published: April 2011

A simulation of structure and motion of edge dislocations in ordered Ni3Al was performed by atomic stiffness matrix method. In this method the equilibrium positions of the atoms were obtained by solving a set of linear equations formed by a stiffness matrix, whose terms consisted of derivatives of the interaction potential of EAM (embedded atom method) type. The superpartial dislocations, separated by an antiphase boundary (APB) on (111), dissociated into Shockley partials with complex stacking faults (CSF) on (111) plane. The core structure, represented by the Burgers vector density distribution and iso-strain contours, changed under applied stresses as well as upon addition of boron. The separation between the superpartials changed with the addition of B and antisite Ni. As one Shockley partial moved out to the surface. a Shockley partial in the interior moved a large distance to join the lone one near the surface, leaving behind a long CSF strip. The decrease in the width of the APB upon addition of B and antisite Ni has been explained by a reduction of the strength of directional bonding between Ni and Al as well as by the dragging of B atmosphere by the superpartials.
First Principles Simulations of Nanoindentation and Atomic Force Microscopy on Silicon Surfaces
Authors: Perez R. , Payne M. C. , Stich I. , Terakura K.
Published: April 2011

Total-Energy pseudopotential calculations are used to study both the onset and development of plasticity in nanoindentation experiments and the contrast mechanism in non-contact AFM images on Si (111) surfaces. As regards nanoindentation, plastic flow of atoms towards interstitial positions and extrusion of material towards the tip walls, stabilized by the adhesive interactions with the tip, are the dominant mechanisms. These plastic deformations are triggered by the delocalization of the charge induced by the stress in the elastically compressed structure. Atomic resolution contrast in AFM is shown to be clearly enhanced by the partial covalent chemical interaction between the dangling bonds of the adatoms in the surface and the apex atom in the tip. The contrast mechanism can be understood in terms of the coupling between the tip and the charge transfer modes among the different dangling bonds in the surface.
Configuration Dependence of the Vibrational Free Energy in Substitutional Alloys and Its Effects on Phase Stability
Authors: Garbulsky G. D. , Ceder G.
Published: April 2011

The lattice vibrations influence the ordering tendencies in substitutional alloys through the configurational dependence of the vibrational free energy. In this paper we study the size of this effect and the trends with chemical affinity and size mismatch. By analyzing available experimental information and by studying simple model systems for which the phonon frequencies can be easily computed, we find that a) changes in transition temperatures of order-disorder transformations of 30% due to the lattice vibrations may not be uncommon; b) the transition temperatures are usually lowered when the vibrations are included in the modeling of the system, except for certain combinations of size mismatch and chemical affinity; and c) that the largest contribution to the configurational dependence of the vibrational free energy is due to the intermediate and high frequencies of the spectrum.
Structural Phase Transition from Fluorite to Orthorhombic FeSi2 by Tight Binding Molecular Dynamics
Authors: Miglio Leo , Celino Massimo , Meregalli Valeria , Tavazza Francesca
Published: April 2011

In this paper we report a molecular dynamics simulation at constant pressure and constant temperature of the structural phase transition occurring in epitaxial FeSi2 from the fluorite phase (metallic and pseudomorphic) to orthorhombic one (semiconductor and bulk stable). The evolution of the electronic density of states is carefully monitored during the transformation and we can show that the Jahn-Teller coupling between the density of states at the Fermi level and the lattice deformation drives the metal-semiconductor transition.
Molecular Dynamics Simulations of SiSe2 Nanowires
Authors: Li Wei , Kalia Rajiv K. , Vashishta Priya
Published: April 2011

Structural and mechanical behavior of SiSe2 nanowires is investigated with the moleculardynamics (MD) method. Nanowires contain finite number of non-intersecting chains of edgesharing Si(Sel/2)4 tetrahedra. The simulations are based on an effective interatomic potential containing both 2- and 3-body interactions. It is found that the nanowires remain highly crystalline and stay in the elastic deformation regime up to a critical strain. Under large uniaxial strain, fracture of the nanowires is initiated by broken bonds in one of the chains at the outermost layer. This induces cross-linking among the neighboring chains, which leads to the presence of cornersharing tetrahedra and local amorphization. Local amorphization propagates across nanowires while multiple cracks start at the boundaries of the amorphous region. The dynamics of amorphization and fracture are discussed.
Sintering of Amorphous Si3N4 Nanoclusters: A Molecular Dynamics Study of Stress Analysis
Authors: Wang Jinghan , Tsuruta Kenji , OmeItchenko Andrey , Kalia Rajiv K. , Vashishta Priya
Published: April 2011

We investigate the onset and growth of the neck between amorphous Si3N4 nanoclusters at zero and finite pressures. Local stress fluctuations and atomic self-diffusion in the interface region are found to be responsible for neck formation. External pressure has a dramatic influence on the rate of sintering.
Adhesion In NiAl-Cr From First Principles
Authors: Raynolds James E. , Smith John R. , Srolovitz David J. , Zhao G.-L.
Published: April 2011

We have calculated the work of adhesion (i.e. energy for rigid fracture) and peak interfacial stress for NiAl, Cr, and NiAl–Cr using self-consistent density functional calculations to obtain the complete energy vs. separation curve for each system. Our calculations indicate that the work of adhesion is largest for Cr and smallest for NiAI while those for interfaces of NiAI with Cr are intermediate. We have also estimated that segregation processes could alter the work of adhesion for the AlNi/Cr interface by up to 20% since Al tends to segregate to the free NiAl surface while Ni tends to segregate to the AlNi/Cr interface.
Preparation Of Metal Nitrides Via Laser Induced Photolytic Decomposition Of Metal-Amides
Authors: Narula Chaitanya K. , Maricq M. Matti
Published: April 2011

Irradiation of {[(CH3)3Si]2N}3Y, Zr[N(C2H5)2]4, and Nb[N(C2H5)2]4 by the 1.064 μm line of a pulsed Nd:YAG laser results in the decomposition of Zr[N(C2H5)2]4 and Nb[N(C2H5)2]4 while {[(CH3)3Si]2N}3Y remains unaffected. The decomposition is photolytic and is accompanied by a visible emission tracing the path of the incident beam. The decomposition products form corresponding carbide/nitrides on pyrolysis in vacuum and nitrides on pyrolysis in an ammonia atmosphere. The spectroscopic investigation of the visible emission, and the pyrolysis of the decomposition products to metal nitrides is described.
Produiion of a-Si1-x Cx:H powders using radiofrequency glow discharges of silane and methane mixtures.
Authors: Costa J. , Viera G. , Zhang R. Q. , Andújar J. L. , Pascual E. , Bertran E.
Published: April 2011

a-Si1-x Cx:H powders have been produced in radiofrequency glow discharges of SiH4 and CH4. Samples produced in discharges with different gas flow ratios (R=[CH4] / [SiH4]+[CH4], R ∼ 0.2 to 0.95) were analyzed by several techniques: Infrared spectroscopy, transmission electron microscopy and thermal desorption spectrometry of hydrogen. The microstructural properties of the a-Si1-x Cx:H powders obtained ranged between those previously reported in silicon particles and those of amorphous carbon particles. As a general rule, the particles, whose diameter ranged between 5 and 400 nm in diameter, showed an amorphous microstructure and high hydrogen content. Infrared spectroscopy showed that the hydrogen was mainly located on the particle surface and in microvoids forming CHi and/or SiHi (i=2,3) groups.

The hydrogen was removed from the powder by thermal annealing (< 700°C) under vacuum. Anlysis of the a-Si1-x Cx:H powders after this thermal treatment revealed new microstructural and optical features.
Structure and Properties of TiC, VC and TiC/VC Thin Films Deposited by Pulsed Laser Deposition
Authors: Krzanowski J. E. , Leuchtner R. E.
Published: April 2011

A study has been conducted on the mechanical, tribological and chemical properties of pulsed laser deposited (PLD) TiC, VC and TiCNC thin films. The TiC films were deposited at 375°C and 5 mTorr Ar, while the TiCNC films were deposited from a composite target at 475°C at pressures of base vacuum and 50 mTorr Ar. XRD analysis revealed the films had the expected B1 structure, although XPS analysis showed a significant oxygen content. Tribological studies were conducted using a ball-on-disk test, and the wear behavior depended on the surface condition and film composition. One TiCNC film exhibited little wear but caused significant ball wear, indicating mixed carbide films are promising candidates for wear-resistant coatings.
CP-Mas NMR AND In-Situ FTIR Study of AIN Surface Reactivity
Authors: Monie S. A. , Aurentz D. J. , Pantano C. G.
Published: April 2011

The hydrolytic stability of aluminum nitride (AlN) is an important issue from the standpoint of technology development of AlN as an electronic packaging material. Although numerous studies have been made of the hydrolysis of AlN and characterization of the reaction products, an understanding of the interaction between surface sites and molecular species is still lacking.

A combination of Magic-Angle-Spinning Nuclear Magnetic Resonance (MAS NMR) and in-situ Fourier Transform Infrared (FTIR) spectroscopies was used to study the surface reactivity of AlN. The specimens used were specially fabricated self-supported AIN films of high-surface-area (∼25 m2/g), made by nitridation of sol-gel derived pseudoboehmite (AIO(OH)). The in-situ FTIR spectra suggest the formation of a surface layer on the AlN films upon storage. MAS NMR was used to further characterize the surface layer. Using the chemical shifts obtained by 1H-27Al Cross Polarization (CP) MAS NMR experiments, we were able to identify the surface cation sites. The assignment of these sites to Al3+ cations in either tetrahedral coordination with nitrogen or octahedral coordination with oxygen was used to monitor the evolution of the surface upon exposure to the atmosphere. The results indicate that high-surface-area AlN rapidly acquires a surface layer (probably AlO(OH)/Al(OH)3) upon exposure to the atmosphere.
Production of a Novel, Self-Assembled, Collagenous Matrix Mimicking the Hierarchical Structure of Native Aligned Connective Tissue
Authors: Pins G. D. , Christiansen D. L. , Patel R. , Silver F. H.
Published: April 2011

The primary goal of the biomaterials scientist and tissue engineer is to create a biocompatible implant which mimics the mechanical and morphological properties of the tissue being replaced.In vitroexperimentation has documented the propensity of soluble type I collagen to self-assemble and form microscopic collagen fibrils with periodic banding analogous to native collagen fiber. Our laboratory has further investigatedin vitroself-assembly by incorporating several of the “natural” processes into a multi-step fiber formation procedure which generates macroscopic collagen fiber from its molecular constituents. Results of uniaxial tensile tests and ultrastructural analyses indicate that these coextruded and stretched collagen fibers have mechanical properties and fibrillar substructure comparable to that observed in native collagen fiber.
Polypyrrole - A Potential Candidate for Stimulated Nerve Regeneration
Authors: Shastri V. R. , Schmidt C. E. , Kim T.-H. , Vacanti J. P. , Langer R.
Published: April 2011

The proposed research is aimed at gaining a fundamental understanding of in vitro nerve cellbiomaterials interactions, with the immediate goal of engineering materials to specifically enhance expression of the neuronal phenotype. Long term goals include (1) optimizing the innervation (connection) of the host neurons with implanted bioartificial tissue constructs and, (2) facilitating the regeneration of damaged peripheral and central nerves. In this study, the interactions of neuronal like PC-I12 cells with the electrically conducting polymer, polypyrrole, (PP) have been investigated. It has been shown by quantitative image analysis that neurite extensions of PC-12 cells are more pronounced on PP surfaces as compared to tissue culture polystyrene. Application of an electrical stimulus to cells cultured on PP film significantly increased (based on morphological evaluation) the expression of neurites in these cells compared to controls. Tissue compatibility and transected sciatic nerve regeneration studies in rat models show that PP films invoke little negative response and support nerve regeneration.
Formation of Titanium Dioxide Containing Calcium Phosphate Crystallites: A New Process
Authors: Piveteau Laurent-Dominique , Schlapbach Louis , Gasser Beat
Published: April 2011

A method for producing titanium dioxide (TiO2) containing hydroxyapatite (HA) crystallite isproposed. Solutions of CaCI2+H3PO4 and TiCL4+HCI combined with KOH are used to precipitatefirst the HA and then the TiO2.The precipitate is then sintered between 900°C and 1000°C for 18 to48 hours. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Energy DispersiveX-ray Analysis (EDX) and scanning electron microscopy (SEM) have been used to determine thecrystallinity, the chemical composition and structure of the samples.