bluuebunny/crossref_metadata_2025 huggingface dataset:
Phason Strain In AL70NI10CO20 Decagonal Quasicrystal
Authors: Matsuo Y , Yamamoto K , Ohshima K , Ishii Y
Published: April 2011

The peak broadening and peak positions of Bragg reflections in a single-phase decagonal Al70Ni10Co20 quasicrystal has been studied by the synchrotron X-ray diffraction technique at SPring-8. Full-widths at half-maximum (FWHM) of the Bragg reflections along the longitudinal direction (L) and transverse direction (TI) which is perpendicular to L-direction in an aperiodic plane have linear Q⊥, dependence. This means that the Al70Ni10Co20 decagonal phase has random phason strains. On the other hand, another transverse direction (T2), which is perpendicular to the aperiodic plane, have linear Q, dependence. So the single crystal has some distortion of mosaics to the periodic layer stacking. Notable peak shifts from ideal Bragg peak positions were not observed.
Electrochemical Pitting And Repassivation On Icosahedral AL-CU-FE, And A Comparison With Crystalline Phases
Authors: Spurr Nicholas A. , Pinhero Patrick J. , Sordelet Daniel J. , Hebert Kurt R. , Thiel Patricia A.
Published: April 2011

We report the electrochemical potentials at which localized pitting and repassivation occur on icosahedral Al-Cu-Fe, and on a series of related alloys and elemental metals. The electrochemistry occurs in a buffered NaCI solution, pH 8.4. Under these conditions, pitting and repassivation appear to be controlled mainly by the chemical composition of the alloy, although the quasicrystalline phase displays an anomalous resistance to repassivation. Corrosion of this phase proceeds by dissolution of Al and Fe, leaving behind pits which are Cu-enriched.
Processing Of Al-Cu-Fe Quasicrystalline Single Grains
Authors: Lograsso T. A. , Ross A. R.
Published: April 2011

The phase equilibria of the Al-Cu-Fe quasicrystalline phase (y phase) is complex and conventional crystal growth techniques like the Bridgman and Czochralski methods are not applicable in preparation of large crystals. Large single grains of the y phase been have prepared by either slow cooling or isothermal anneals. In the later technique, arc melted ingots were subjected to either single or multiple heat treatments between 825 and 840°C to encourage grain growth. Following heat treatment, grains of the icosahedral phase are found either as isolated pentagonal-faceted crystals within the ingot or within clusters of intergrown grains. The growth of the large grains is independent of the sample processing history of the sample, is facilitated by the presence of liquid at the growth temperatures and is constrained by the physical dimension of the ingot. The microstructure of both grain types is similar containing a minor quantity (on the order of 5–10 %) of a second phase and a high degree of porosity in the as-grown state. The second phase is usually present as a thin layer between adjacent grains or associated with a pore within a single grain. The grain porosity is distributed throughout the ingot. These defects can be removed through post-growth hot isostatic pressing and anneal treatments.
Hybridization Effect On Electron Transport Properties Of Rhombic Triacontahedral-Type Al60-xMg40Xx. (X = Zn, Cu, Ag, and Pd) 1/1-Cubic Approximants
Authors: Mizuno T. , Takeuchi T. , Mizutani U.
Published: April 2011

We have measured in this experiment the XPS (x-ray photoemission spectroscopy) and SXES (soft x-ray emission spectroscopy) valence spectra, the electrical resistivity, the Hall coefficient and the Rietveld structural analysis for a series of the RT-type (Rhombic Triacontahedron) Al60-xMg40Xx (X = Zn, Cu, Ag and Pd; x = 5 - 40) 1/1-approximants. The electrical resistivity at 300 K is successfully analyzed in terms of the carrier concentration per atom e/a and the ratio of the lattice constant over the “ideal” lattice constant defined as LCR. The latter is chosen as a quantitative measure of the degree of the hybridization between Al and transition metal elements Cu, Ag and Pd. We show that a sharp resistivity increase with increasing the concentration of the transition metal element can be attributed to the deepening of the pseudogap at the Fermi level, which is brought about by the combination of the Fermi surface-Brillouin zone interaction and the growth of the hybridization effect.
Optical Properties Of Icosahedral Al59 B3 Cu25.5Fe12.5 Quasicrystalline Alloy
Authors: Demange V. , Vigneron B. , Maciuzaud F. , Dubois J. M.
Published: April 2011

We report an optical investigation of single phase icosahedral Al59B3Cu25.5Fe12.5. The optical conductivity presents a striking depression at low frequencies and a prominent peak at 3 104 cm−1.A phenomenological analysis of the conductivity allows us to correlate the high energy excitations to a mechanism of electron hopping.
Mechanical Properties Of Quasicrystal Dispersed Al-Li-Cu Alloy
Authors: Okada T. , Nakamura T. , Mitsugi K , Kozawa K , Matumura T , Ishii H , Ozu Y. , Oguri K. , Nishi Y
Published: April 2011

To apply the ductile structural materials, the quasicrystal dispersion in aluminum alloys is one of effective methods. We have investigated mechanical properties of quasicrystal dispersed Al- Li-Cu alloy prepared by the twin-type piston anvil apparatus. The slow cooled samples are hard and ductile. The evaluated values of brittleness are from 6.0 to 14 erg for Ef, from 0.52 to 0.73MNm−3/2 for K1c and from 5.5 to 7.7 Nm−1 for Gic for the fastest and slowest cooled samples, respectively. The hardness of the quasicrystal dispersed Al-Li-Cu alloy is higher than that of the other commercial aluminum alloys. Based on the relationship between Vickers hardness and proof stress of aluminum alloys, we estimate the specific strength of Al-Li-Cu quasicrystal alloy. The maximum value is the higher than that of Ti alloys.
Study Of Al Surface Segregation In Icosahedral A162Cu25.5Fe12.5
Authors: GIL-GAVATZ M. , Rouxel D. , Pigeat P. , Weber B. , Dubois J.-M.
Published: April 2011

Surface segregation of aluminium was observed during oxidation experiments of icosahedral A162Cu25.5 Fel12.5, performed in-situ and at different temperatures in the ultra-high vacuum chamber of a scanning Auger electron spectrometer. Two regimes, below and above 770K, were observed in relation with severe segregation of Al atoms at the surface for T > 770K. We postulate that this temperature dependent segregation rate is representative of the aluminium transport towards the surface of the quasicrystal. By analogy with classical diffusion experiments, we can thus determine reasonable estimates of the activation energy for Al self-diffusion in this quasicrystal. The results are consistent with the existence of phason flips below 770K and thermal vacancies above this temperature.
Formation of Polymer Stabilized Ferroelectric Liquid Crystals using a Fluorinated Diacrylate
Authors: Guymon C. Allan , Bowman Christopher N. , Bowman Christopher N.
Published: April 2011

Ferroelectric liquid crystals (FLCs) have shown great potential for use in electro-optic and display technology due to their inherently fast switching speeds and bistability. Recently, considerable research has been devoted to FLCs mechanically stabilized by a polymer network. The network is formed typically by in situ polymerization of a monomer dissolved in the FLC. Because of the inherent order in the FLC, the polymerization behavior may be significantly different than what might be expected in solution polymerizations. These deviations result largely from the segregation properties of the monomer in the liquid crystal. One class of monomers, namely fluorinated acrylates, is a likely candidate for inducing novel segregation, polymerization and electro-optic behavior in polymer stabilized ferroelectric liquid crystals (PSFLCs). The use of fluorinated moieties has a significant impact on the phase and polymerization behavior of liquid crystal systems. This study focuses on the polymerization of a fluorinated diacrylate, octafluoro 1,6-hexanediol diacrylate (FHDDA), to form PSFLCs and the consequent impact of the polymerization on the ultimate performance. Interestingly, as the temperature is increased and the order of the system decreases, a dramatic increase in the polymerization rate is observed. This increase is especially prominent for polymerizations in the smectic C* phase for which the rate is more than five times that exhibited at much higher temperatures in the isotropic phase. As with other monomer/FLC systems, the segregation of the monomer plays a role in this polymerization behavior as the monomer segregates between the smectic layers of the liquid crystal. The segregation properties also significantly impact the ultimate electro-optic properties. Both ferroelectric polarization and response time of the PSFLC change markedly with different polymerization temperatures, and approach values very close to those of the neat FLC under appropriate polymerization conditions. This behavior not only provides a unique mechanism for rate acceleration in PSFLCs, but also paves the way for new methods to optimize performance in these materials.
Three-Dimensional Photoreorientation of Self-Organized Azobenzene Chromophores in Liquid Crystalline Polymer Films
Authors: Han M. , Morino S. , Ichimura K.
Published: April 2011

Photo-induced reorientational behavior of films of a liquid crystalline polymer with azobenzene side chains was studied by means of UV-Vis absorption spectroscopy and Fourier transform infrared transmission and reflection-absorption spectroscopy. The incident directions of light for photoisomerization played a critical role in the photocontrol of out-of-plane (three-dimensional) orientation of the azobenzenes in films. Tilted directions of the azobenzene residues were evaluated by using polarized UV-Vis absorption spectra. Photoreoriented states of azobenzene chromophores including photodichroism and tilted alignment were enhanced by successive annealing of photoirradiated films at temperatures close to the glass transition temperature of the polymer.
Internal Stress In Sputtered Silver Nickel Thin Films And Multilayers: Sputtering Pressure And Thickness Effects
Authors: Gergaud P. , Yang H. , PéLissonnier-Grosjean C. , Bottger A. J. , Sandström P. , Sundgren J. E. , Thomas O.
Published: April 2011

Nanometer thick films are often in a state of high residual stress. This may strongly influence physical properties such as magnetic anisotropy. The aim of our study is to investigate whether the overall stress in multilayers may be tailored via the control of the sputtering parameters or of the individual thicknesses. The coatings investigated were deposited at room temperature by magnetron sputtering on oxidised silicon substrates. Ag/Ni multilayers of superperiod between 4 to 20 nm and thin films (Ag or Ni) 200 nm thick have been deposited under a krypton partial pressure varying between 1 and 8 mTorr. Internal stress measurements were performed by curvature method and x-ray diffraction sin2ψ method. The latter one allows the determination of the stress and of the stress-free lattice parameter in the Ag or the Ni layers whereas the first one gives rise to a measure of the average stress in the coating. The main results are the followings: (i) The stress in Ni thin films changes from compressive to tensile at a pressure between 2 and 5 mTorr whereas Ag thin films are sligthly tensile whatever the pressure; (ii) The stress in multilayers is tensile in Ag and Ni and decreases with sublayer thickness; (iii) The stress free lattice parameter of Ag in thin films or multilayers is independent of the Kr pressure and of the layer thickness and is equal to the bulk value; (iv) On the opposite, the stress-free lattice parameter of nickel decreases with the layer thickness in multilayers and is equal to the bulk value in thin films. These results are discussed in terms of the respective influence of interfacial intermixing and atomic peening mechanism.
Temperature Dependence of Ag/Ni Multilayer Microstructure Studied by in Situ X-Ray Diffraction
Authors: Ghetta V. , Senateur J. P. , manna J. La , Delabouglise G. , Matko I. , Chenevier B. , Sandstrom P. , Sundgren J.-E.
Published: April 2011

The temperature evolution of the microstructure in a series of [111] fiber textured Ag/Ni multilayer samples has been studied by in situ X-ray diffraction. From the recorded pattern analysis, two regimes can be distinguished. At low temperature (TGB = 120–130°C) where diffusion is likely insignificant, the observed reduction of the width and the increase of the intensity (sharp and quick in some cases) of 111 line-profiles indicate that microstress and defects densities possibly located in column/grain boundaries are considerably lowered. At higher temperatures, diffusion of Ag leads to a transformation of the multilayer stacking essentially characterized by the formation of long Ag coherent domains with (111) planes parallel to the film surface accompanied with a similar but minor effect on Ni. In Ag, some 002 texture component also appears upon annealing. A simple model is proposed to describe the metal recrystallization competing with areas where the multilayer stacking is kept nearly unchanged.
In-Situ Characterisation of Precipitation in AI-Cu thin films
Authors: Lokker J. P. , Bottger A. J. , Janssen G. C. A. M. , Radelaar S.
Published: April 2011

The precipitate formation occurring in Al-Cu thin foils with copper concentrations of either 1.15 at.% or 0.3 at.%, has been studied. In-situ X-ray diffraction analysis and differential scanning calorimetry are applied to determine the phases formed and the enthalpy changes in the same samples. Both X-ray diffraction and differential scanning calorimetry indicate that the precipitation behaviour of thin films (about 500 nm thickness) differs significantly from that of bulk material. In the films studied the precipitation of Al2Cu occurs at a much lower temperature than expected on the basis of the (bulk) phase diagram. Moreover, no intermediate phases are observed prior to Al2Cu precipitation. Also the amount of Cu in solid solution (0.20 at%Cu) observed by electron-probe micro-analysis after slowly cooling from 500°C to room temperature, exceeds the solubility of bulk Al-Cu.
STI Pattern Density Characterization for the System on a Chip
Authors: Xie J. , Rafftesaeth K. , Huang S.-F. , Jensen J. , Nagahara R. , Parimi P. , Ho B.
Published: April 2011

Shallow-Trench Isolation (STI) relies on integrated process optimization to achieve the requirement of chip-level process variation across different device features. Characterization of pattern density dependency was investigated through Chemical Mechanical Polishing (CMP) process optimization by Design of Experiment (DOE) and modification of masks by adding dummy structure. Four mask sets with different device features and pattern densities were tested. Effects of slurry selectivity, over-polish extent, silicon trench depth, high-density plasma film thickness, and dummy structure were evaluated. Correlation between physical and electrical data illustrates the process margin in which both logic and memory devices could perform their respective functions. KEYWORDS: Shallow-Trench Isolation, System-on-a-Chip, Pattern Density, Chemical-Mechanical Polishing.
Abrasive Effects in Oxide Chemical Mechanical Polishing
Authors: Mahajan Uday , Bielmann Marc , Singh Rajiv K.
Published: April 2011

In this study, we have characterized the effects of abrasive properties, primarily particle size, on the Chemical Mechanical Polishing (CMP) of oxide films. Sol-gel silica particles with very narrow size distributions were used for preparing the polishing slurries. The results indicate that as particle size increases, there is a transition in the mechanism of material removal from a surface area based mechanism to an indentation-based mechanism. In addition, the surface morphology of the polished samples was characterized, with the results showing that particles larger than 0.5 μm are detrimental to the quality of the SiO2 surface.
Process and Manufacturing Challenges for High-K Gate Stack Systems
Authors: Gilmer M.C. , Luo T-Y , Huff H.R. , Jackson M.D. , Kim S. , Bersuker G. , Zeitzoff P. , Vishnubhotla L. , Brown G.A. , Amos R. , Brady D. , Watt V.H.C. , Gale G. , Guan J. , Nguyen B. , Williamson G. , Lysaght P. , Torres K. , Geyling F. , Gondran C.F.H. , Fair J. A. , Schulberg M.T. , Tamagawa T.
Published: April 2011

A design-of-experiments methodology was implemented to assess the commercial equipment viability to fabricate the high-K dielectrics Ta2O5, TiO2 and BST (70/30 and 50/50 compositions) for use as gate dielectrics. The high-K dielectrics were annealed in 100% or 10% O2 for different times and temperatures in conjunction with a previously prepared NH3 nitrided or 14N implanted silicon surface. Five metal electrode configurations—Ta, TaN, W, WN and TiN—were concurrently examined. Three additional silicon surface configurations were explored in conjunction with a more in-depth set of time and temperature anneals for Ta2O5. Electrical characterization of capacitors fabricated with the above high-K gate dielectrics, as well as SIMS and TEM analysis, indicate that the post high-K deposition annealing temperature was the most significant variable impacting the leakage current density, although there was minimal influence on the capacitance. Further studies are required, however, to clarify the physical mechanisms underlying the electrical data presented.
Thermal and Chemical Instability Between Iridium Gate Electrode and Ta205 Gate Dielectrics
Authors: Mao A. Y. , Sun Y. M. , White J. M. , Kwong D. L.
Published: April 2011

The thermal and chemical stability of thin CVD iridium films deposited on thin CVD tantalum pentoxide (Ta2O5) films on Si(100) have been investigated by means of in-situ X-ray Photoelectron Spectroscopy (XPS) and ex-situ Angle Resolved XPS (ARXPS). It was found that upon annealing in vacuum at 800 °C for more than 1 min, tantalum oxide at the Ir-Ta2O5 interface was decomposed and formed metallic tantalum which diffused through Ir, while changes in iridium film itself were negligible. When annealed at 750 °C within 15 minutes, intermediate partially oxidized Ta was formed and coexisted with metallic and oxidized Ta. A portion of metallic Ta near Ir-vacuum interface was subsequently oxidized when the films were exposed in air.
Two Step O2/N2O Plasma Annealing for the Reduction of Leakage Current in Amorphous Ta2O5 Films
Authors: Lau W.S. , Perera M.T. Chandima , Han T. , Sandler N. P. , Tung C.H. , Sheng T.T. , Chu P.K. , Chong T.C.
Published: April 2011

As deposited tantalum pentoxide (Ta2O5) films are amorphous. The films will remain amorphous after O2 or N2O plasma annealing at low temperature. High temperature annealing will produce polycrystalline films where grain boundaries can generate leakage current. Previously, we have shown that N2O plasma annealing is superior to O2 plasma annealing in terms of leakage current reduction for AI/Ta2O5/Si capacitors. However, for TiN/Ta2O5/Si capacitors, the leakage current tends to be higher at low bias voltage for N2O plasma annealing compared to O2 plasma annealing. By adding an 02 plasma annealing step and then comparing TiN/Ta2O5/Si capacitors with two step O2/N2O plasma annealing with respect to similar structures with two step O2/O2 plasma annealing, it can be easily seen that TiN/Ta2O5/Si capacitors with two step O2/N2O plasma annealing have lower leakage current compared to similar structures with two step O2/O2 plasma annealing throughtout the voltage range tested.
The Influence of Damage and Dopant on the Blister Formation in Hydrogen Implanted Silicon
Authors: Hochbauer T. , Nastasi M. , Lau S.S. , Zheng Y. , Mayer J. W.
Published: April 2011

We have studied the formation of surface blisters in <100> n-type silicon following coimplantation with boron and hydrogen. In this work we study the effect of having the boron depth larger than the hydrogen depth. The silicon substrates had four different dopant levels, ranging from 1014 cm−3 to 1019 cm−3. The Si substrates were first implanted with B ions at 240 keV (Rp = 705nm) to a dose of 1015cm−2. Some of the B implanted samples were left in their as-implanted state, others were given a rapid thermal anneal (RTA) at 900°C. Boron implanted and virgin n-type Si samples were then implanted at cryogenic temperatures with 40 keV H+ (Rp= 475nm) to a dose of 5 x 1016 cm−2. Following H+ implantation, all the samples were vacuum annealed at 390°C for 10 minutes and examined for hydrogen blister formation. No blistering was observed in samples implanted with H only. In all cases, the blister depth was consistently found to be strongly correlated with H damage profile rather than the H or B concentration profiles. These results will be discussed in terms of defect-dopant interactions and the influence of doping on H kinetics and H-bubble nucleation.
Transient Enhanced Diffusion of Phosphorus and Defect Evolution in P+ Implanted Si
Authors: Li J. , Keys P. , Chen J. , Law M. E. , Jones K. S. , Jasper Craig
Published: April 2011

Continuous scaling of device dimensions requires better understanding of non-equilibrium diffusion phenomena such as transient enhanced diffusion (TED). To this end, it is important to understand the relationship of the defect evolution with TED. Defect evolution in P+ implanted Si has been investigated by transmission electron microscopy (TEM). Secondary ion mass spectroscopy (SIMS) has been used to study phosphorus TED. These studies show that another type of defect, i.e. dot defects are present in P+implanted Si (100 keV, 1.OX104/cm2). The evolution of defects in P+ implants is compared with that in Si+ implants. P+ implants give rise to small dot defects mixed with {311} defects while Si+ implants give rise to only {311} defects. The dot defects and {311} defects in P+ implants dissolve faster than the {311} defects from Si+ implants. The interstitial concentration trapped in the dot defects and the {311} defects from P+ implants is slight lower than that from Si+ implants. Dot defects seem to have only a small role in phosphorus TED. Interaction of silicon interstitials emitted from the dissolution of {311} defects with phosphorus dopant atoms is believed to be the dominant driving force for the TED. There may also be a contribution from dissolution of non-visible phosphorus interstitial clusters (PIC's). Correlation of defect evolution and TED has been addressed.
Modeling and Validation of Sensor and Actuator Dynamics for, And Real-Time Feedback Control of Thermal Chlorine Etching of Gallium Arsenide
Authors: Rosen I. G. , Parent T. , Mancera R. , Chen P. , Madhukar A.
Published: April 2011

A dynamic model for the simulation of thermal chlorine etching of gallium arsenide is developed. The primary motivation for the development of the model is the design and testing of real time feedback controllers which rely upon in-situ optical measurements of etch depth obtained via spectroscopic ellipsometry. Unmeasurable parameters which appear in the model are identified, and the model is validated using experimental data. A linear-quadratic controller based on our model is designed and tested.
In-Situ Spectroscopy of Ion-Induced Photon Emission During Metal Nanoparticle Formation in Silica Glass with High-Flux Cu Implantation
Authors: Lay Thi Thi , Amekura H. , Takeda Y. , Kishimoto N.
Published: April 2011

Ion-induced photon emission from a silica glass irradiated with high-flux Cu ions was measured in a wavelength range from 450 nm to 800 nm, while nanoyarticles spontaneously formed in the silica glass. Current density was varied up to 100 µA/cm2 at a constant total dose of 3×106ions/cm2. The photon emission primarily arose from the vicinity of the substrate surface and consisted of sharp peaks due to neutral and singly-ionized species, Cu(I), Cu(II) and Si(II) ions, as well as a broad-band background. Intensity of Si(II) and Cu(I) increased with increasing current density. On the other hand, Cu(II) did not show a monotonic increase, decreasing around 100 µA/cm2. Measurements of in-situ EDX and ex-situ RBS were also conducted to study the relevant mechanisms. The ion-induced photon emission was attributed to recombination processes of sputtered ions and electrons in the plasma, induced by the high-flux Cu beam.
Modeling and Real-Time Process Monitoring of Organometallic Chemical Vapor Deposition of III-V Phosphides and Nitrides at Low and High Pressures
Authors: Bachmann K.J. , Cardelino B.H. , Moore C.E. , Cardelino C.A. , Sukidi N. , Mccall S.
Published: April 2011

The purpose of this paper is to review modeling and real-time monitoring by robust methods of reflectance spectroscopy of organometallic chemical vapor deposition processes in extreme regimes of pressure. The merits of p-polarized reflectance spectroscopy under the conditions of chemical beam epitaxy (CBE) and of internal transmission spectroscopy and principal angle spectroscopy at high pressure are assessed. In order to extend OMCVD to materials that exhibit large thermal decomposition pressure at their optimum growth temperature we have designed and built a differentially-pressure-controlled (DCP) OMCVD reactor for use at pressures ≤ 6 atm. We also describe a compact hard-shell (CHS) reactor for extending the pressure range to 100 atm. At such very high pressure the decomposition of source vapors occurs in the vapor phase, and is coupled to flow dynamics and transport. Rate constants for homogeneous gas phase reactions can be predicted based on a combination of first principles and semi-empirical calculations. The pressure dependence of unimolecular rate constants is described by RRKM theory, but requires variational and anharmonicity corrections not included in presently available calculations with the exception of ammonia decomposition. Commercial codes that include chemical reactions and transport exist, but do not adequately cover at present the kinetics of heteroepitaxial crystal growth.
Transient Nucleation in Co-Zr Metallic Glasses
Authors: Köster Uwe , Blank-Bewersdorff Margret
Published: April 2011

Crystallization kinetics and crystal size distributions in Co33Zr67-glasses have been analyzed by quantitative electron microscopy. The polymorphic crystallization of spherical CoZr2 crystals is very suitable reaction for such an analysis. Calculated crystal size distributions at different temperatures were compared to those experimentally revealed. Parameters controlling crystallization were varied within reasonable limits until theoretically calculated and experimentally observed crystal size distributions were in good agreement. It has been found that crystal size distribution can be explained by transient nucleation; the time lag and its temperature dependence can be evaluated. These results are discussed in the light of recent theories on transient nucleation.
Interphase Boundary Diffusion in Eutectic Alloys
Authors: Chadwick G. A.
Published: April 2011

Turnbull and co-workers have shown that the noble metals Cu, Ag, and Au diffuse into single crystals of Pb and Sn by an interstitialcy mechanism with measured diffusion coefficients of ∼10−6cm2s−1. These experiments have been extended to study the diffusion rates of the noble metals along the interphase boundaries of single crystal of Pb-Sn eutectic alloys and to measure the diffusion coefficient of silver along the interphase boundaries of Ag-Cu eutectic single crystals.

The measured interphase boundary diffusion coefficients of the noble metals in the Pb-Sn single crystals are extremely high, being 2.6 × 10−3cm2s−1for Cu and ∼10−4cm2s−1for Ag and Au at room temperature. These results again imply an interstitialcy mechanism of diffusion at the interphase boundaries. In contrast, the diffusion coefficient of Ag110in a Ag-Cu eutectic single crystal worked out to be ∼8×10−9cm2s−1at 500°C, two orders of magnitude lower than the value obtained by Turnbull and Hoffman for self-diffusion along low-angle (8∼10°) boundaries in silver.
Kinetics of the Nucleation of a Crystalline Droplet from the Melt
Authors: Grant Martin , Gunton J. D.
Published: April 2011

Theory for the rate of nucleation of a crystalline solid from its melt is discussed. An expression for the dynamical prefactor of the nucleation rate is presented, which is derived using Langer's field theory of nucleation. The theoretical result generalizes the classical theory of Turnbull and Fisher, and can be tested experimentally. The analysis makes use of the formalism of Ramakrishnan and Yussouff, as extended to solid-melt interfaces by Oxtoby, Haymet, and Harrowell.
Optical Spectroscopy of Single Self Assembled Quantum Dots
Authors: Dekel E. , Gershoni D. , Ehrenfreund E. , Garcia J.M. , Petroff P.M.
Published: April 2011

We applied low temperature diffraction limited confocal optical microscopy to spatially resolve, and spectroscopically study photoluminescence from single self-assembled semiconductor quantum dots. Using selective wavelength imaging we unambiguously demonstrated that a single photoexcited quantum dot emits light in a few very narrow spectral lines. By solving numerically a many body Hamiltonian for a model quantum dot, we show that the multi-line emission spectrum is due to optical transitions between confined exciton multiplexes. We explain the measured spectrum and its dependence on the power of either cw or pulsed excitation by analytically solving the coupled rate equations for the excitation relaxation between these exciton multiplexes.
Optical Property Characterization of Silicon Quantum Wires
Authors: Yu D. P. , Bai Z. G. , Zou Y. H. , Wang J. J. , Zhang H. Z. , Ding Y. , Feng S. Q.
Published: April 2011

The recent success of bulk synthesis of pure nano-scale silicon quantum wires (SiQW's) enables us to evaluate their photoluminescence (PL) characteristics under ultra-violet photoexcitation. Intense multiple light emissions ranging from dark red to blue regions were revealed for as-grown and partially oxidized SiQW samples. The physical origin of the multiemissions is discussed on the basis of quantum confinements, or defect centers.
Few-Particle Effects in Nonlinear Optical Spectra of Semiconductor Quantum Dots
Authors: Hohenesteri Ulrich , Rossi Fausto , Molinari Elisa
Published: April 2011

We present a density-matrix approach for the description of nonequilibrium carrier dynamics in optically excited semiconductor quantum dots, that explicitly accounts for exciton-exciton as well as exciton-carrier interactions. Within this framework, we analyze few-particle effects in the optical spectra and provide a consistent description of additional peaks appearing at high photoexcitation density. We discuss possible applications of such optical nonlinearities in future coherent-control experiments.
Controlling Growth of InAs/GaAs Self-Assembled Quantum Dots to Give 1.3 μm Room Temperature Emission
Authors: Malik Surama , Siverns Philip , Childs David , Roberts Christine , Hartmann Jean-Michel , Murray Ray
Published: April 2011

We have investigated the extent to which the emission wavelength of self-assembled InAs/GaAs quantum dots can be controlled by growth parameters using conventional solid source MBE. Changing from conventionally high growth rates to a very low growth rate (LGR) and a relatively high substrate temperature, tunes the photoluminescence (PL) emission from 1.1 μm to 1.3 μm at room temperature. Atomic force micrographs obtained from uncapped samples reveal that these LGRQDs are larger, lower in density and extremely uniform in size. The improved size uniformity is reflected in the reduction of the PL linewidth from 78 meV to 22 meV. Under conditions of high excitation, emission from the ground and two excited states each separated by ∼70 meV is observed. This implies a parabolic confining potential. Time resolved photoluminescence (TRPL) measurements of dots grown under the various growth conditions yield radiative lifetimes which reflect the depth of the confining potential. A comparison of the decay times measured for the excited states show that the relaxation of carriers within the dots cannot be ascribed to phonon effects.
Morphological Changes to InAs Quantum Dots Caused by GaAs Overgrowth
Authors: Smathers J.B. , Ballet P. , Salamo G.J.
Published: April 2011

We have used in-situ scanning tunneling microscopy (STM) to study the morphological changes to InAs quantum dots (QD's) caused by overgrowth of a GaAs capping layer. We demonstrate that the InAs islands are highly unstable during GaAs overgrowth and that this morphological instability confirms that significant cation intermixing occurs during overgrowth. In particular, the anisotropic nature of the volume redistribution indicates that In surface diffusion is the specific mechanism of In transfer away from the islands. Images taken after 10 monolayers or more of overgrowth reveal that more rapid GaAs overgrowth better preserves the 3D-islands morphology.
Early Stages of Growth of Ge Quantum Dots
Authors: Tognini P. , Patrini M. , Stella A. , Tonova D. , Cheyssac P. , Kofman R. , Bottani C. E. , Gemmi M.
Published: April 2011

The present work is concentrated on the investigation of the initial stages of growth of Ge nanoparticles embedded in an amorphous A1203 matrix on suitable substrates. The growth technique is based on self-organization processes related to the balance of the interface energies involved. Combined data from complementary optical techniques (absorption, Raman scattering, spectroscopic ellipsometry) give evidence of a behaviour which can be ascribed to the existence of a wetting layer, not detectable by conventional transmission microscopy.
Growth by Low Pressure Chemical Vapor Deposition of Silicon Quantum Dots on Insulator for Nanoelectronics Devices
Authors: Baron T. , Martin F. , Mur P. , Wyon C. , Dupuy M. , Busseret C. , Souifi A. , Guillot G.
Published: April 2011

We present the first comparative study of nucleation and growth of Si quantum dots on SiO2, SiOxNy and Si3N4 substrates using silane Low Pressure Chemical Vapor Deposition at low temperature (570–610°C). The samples are investigated by Atomic Force Micoscopy, Scanning Electron Microscopy, High Resolution Transmission Electron Microscopy and Spectroscopic Ellipsometry. We confirm that the chemical nature of the surface and precisely the presence of SiO bonds decreases the Si quantum dot density. By optimising the deposition parameters, a Si dot density of 1012 cm−2 can be obtained below 600°C on a pure Si3N4 surface. The influence of hydrogen, provided by silane decomposition, on the Si nucleation mechanism will be discussed.
The Formation of Close-Packed Two-Dimensional CdSe Colloidal Films by Electric-Field-Induced Deposition
Authors: Xu L. , Huang X.F. , Chen H.M. , Chen W. L. , Liu Z.G. , Chen K.J.
Published: April 2011

Monodispersed CdSe nanocrystals with average diameter of ∼5 nm were synthesized from SeSO32− and rich Cd2+ ionic reagents in aqueous solution. Two-dimensional (2D) close-packed colloidal CdSe films were formed on the electrode surface by electric-field induced deposition method. Transmission electron microscopy (TEM) images show that colloidal CdSe films exhibit different states, named “gas”, “liquid” and “solid” states, which can be transformed by adjusting applied field (E) or deposition time (T). The experimental results demonstrate that the average nearest-neighbor distance of clusters on the electrode surface is inversely proportional to the ET product.
Electron Beam Induced Current Imaging of Ferroelectric Thin Films
Authors: Lubomirsky Igor , Wang Tzu Yu , Gartsman Konstantin , Stafsudd Oscar M.
Published: April 2011

We have observed Electron Beam Induced Current imaging of thin film ferroelectrics. The Electron beam irradiation of a thin ferroelectric film creates a local temperature gradient that induces a polarization gradient and therefore a local electric field. Although the temperature difference is small the gradient is on the order of thousands K/cm and results in a corresponding electric field of a few MV/cm. The thermally induced electric field drives the electron beam created carriers toward an electrode thus inducing an externally measurable current. Despite the very small carrier life time (<1 ns) in ferroelectrics, the induced electric field is strong enough to collect carriers from a few hundred nm depth before recombination. An EBIC gain of 5 to 20 was measured experimentally with BaTiO3 and LiTaO3 films on silicon substrates. This method is insensitive to charge traps and provides a resolution better than 1 μm.
Lattice Defects in SrRuO3 Thin Films and Their Contribution to film Resistivity
Authors: Zakharov N. D. , Satyalakshmi K. M. , Koren G. , Hesse D.
Published: April 2011

Lattice defects present in PLD-grown, epitaxial SrRuO3 thin films on (001) SrTiO3 substrates are analyzed by high resolution transmission electron microscopy (HRTEM). Before the preparation of TEM samples, the electrical resistivity of films grown at different substrate temperatures was determined. Films grown at 775 °C exhibited a low electrical resistivity of only 200 μΩcm. They were found to be of orthorhombic structure and contained only few lattice defects. Films grown at 700 °C showed a high electrical resistivity of 1400 μΩcm. They were of cubic lattice symmetry, while films grown at temperatures above 800 °C showed resistivities between 300 and 900 μΩcm. The latter films mainly consist of an orthorhombic-cubic phase mix and involve lattice defects of high density, such as twins and antiphase boundaries (APBs). These defects are mainly located in between the islands and obviously contribute to the high film resistivity observed. For example, the APBs contain an extra single SrO layer, which is certainly insulating. Moreover, Ru vacancies are present in these films.
Transparent Conducting Coatings Made from Redispersable Crystalline Nanoscaled Powders
Authors: Goebbert C. , Bisht H. , Nonninger R. , Aegerter M. A. , Schmidt H.
Published: April 2011

A new wet chemical concept is presented for the preparation of electrically conducting SnO2:Sb (ATO) and In2O3:Sn (ITO) coatings. It is based on the deposition by spin, dip or spray techniques of a solution containing crystalline nanoscaled particles fully redispersable in a solvent. The particle synthesis is carried out in a solution at temperatures < 200 °C by a controlled growth reaction using SnCl4 and InCl3 as precursors and SbCl3 and SnCl4 as dopant, respectively. The aggregation of the particles is avoided by in-situ surface modification with bifunctional organic molecules. After drying the nanocrystalline particles can be fully redispersed in ethanol at pH < 6 (for ITO) or water at pH > 8 (for ATO) with solid contents up to 8.8 vol. %. Single layers with thickness up to 200 nm (ATO) and 400 nm (ITO) have been fabricated. Their sheet resistance decrease with the sintering temperature. Typical lowest values are 430 Ω□ (550 °C) for ATO and 90 Ω□ (900 °C) for reduced ITO. The resistivity of as fired ATO and ITO coatings is stable but it slightly increases with time for ITO in the reduced state. All coatings have a transmission in the visible range of about 90 %. Anti-glare conducting coatings on glass with 70 GU as well as antistatic coatings (R□ ≈ 1 MΩ□) on polycarbonate substrates have been obtained with chemically modified ITO suspensions.
High Energy Density Capacitors Fabricated by Thin Film Technology
Authors: Wagner Andrew V. , Johnson Gary W. , Barbee Troy W.
Published: April 2011

Low energy density in conventional capacitors severely limits efforts to miniaturize power electronics and imposes design limitations on electronics in general. We have successfully applied physical vapor deposition technology to greatly increase capacitor energy density. The high dielectric breakdown strength we have achieved in alumina thin films allows high energy density to be achieved with this moderately low dielectric constant material. The small temperature dependence of the dielectric constant, and the high reliability, high resistivity, and low dielectric loss of Al2O3, make it even more appealing. We have constructed single dielectric layer thin film capacitors and shown that they can be stacked to form multilayered structures with no loss in yield for a given capacitance. Control of film growth morphology is critical for achieving the smooth, high quality interfaces between metal and dielectric necessary for device operation at high electric fields. Most importantly, high rate deposition with extremely low particle generation is essential for achieving high energy storage at a reasonable cost. This has been achieved by reactive magnetron sputtering in which the reaction to form the dielectric oxide has been confined to the deposition surface. By this technique we have achieved a yield of over 50% for 1 cm2 devices with an energy density of 14 J per cubic centimeter of Al2O3 dielectric material in 1.2 kV, 4 nF devices. By further reducing defect density and increasing the dielectric constant of the material, we will be able to increase capacitance and construct high energy density devices to meet the requirements of applications in power electronics.
Dielectric Response of free Standing Strontium Titanate Thin Films from 10 Khz to 1 Ghz as A Function of Temperature and Applied Voltage
Authors: Dalberth M. J. , Price J. C. , Rogers C. T.
Published: April 2011

Using pulsed laser ablation, we have grown epitaxial bilayers of strontium titanate (STO) and yttrium barium copper oxide (YBCO) on (110) neodymium gallate (NGO) substrates. Using a selective acid etch, we have removed the YBCO from the middle of the bilayer and lifted off the STO films from their parent substrates. Using coplanar interdigital capacitors patterned on the surface of the films, we have measured the capacitance and loss as a function of frequency (from 10 kHz to 1 GHz), temperature (from 300 K to 4 K), and applied electric field (up to roughly 2 V/μm). We have seen frequency dependent loss peaks in the films that indicate thermally activated behavior, and an improvement in the tuning quality.
Oxygen Diffusion in Tantalum Oxide Metal-Oxide-Metal Capacitor Structures
Authors: Chang J. P. , Steigerwald M. L. , Fleming R. M. , Opila R. L. , Alers G. B.
Published: April 2011

We have studied structures used in MOM capacitors including Ta2O5/TiN/Ti, Ta2O5/Ti, Ta2O5/TaN/Ti, Ta2O5/WN/Ti, and Ta2O5/M where M = Ta, Pt, W, Al, and Si using X-Ray Photoelectron Spectroscopy. We find that Ti and Al are able to reduce the Ta2O5 to Ta, forming oxides of Ti and Al, respectively. The diffusion barrier TiN hampers the diffusion of oxygen and therefore postpone the reduction of Ta2O5 to higher temperatures. The oxygen migrates from the Ta2O5 layer and through the TIN layer to the Ti layer during the heat treatment. As judged by the temperatures at which the reduction of Ta2O5 occurs, TaN and WN are more effective oxygendiffusion barriers than TiN. Leakage current observed in AI/Ta2O5/TaN/Ta capacitors is one to two orders of magnitude lower than that observed in Al/Ta2O5/TiN/Ti capacitors.
Electrical Noise in Ultra Thin Giant Magnetoresistors
Authors: Lisauskas A. , Khartsev S. I. , Grishin A. M. , Palenskis V.
Published: April 2011

We report measurements of low frequency 1/f excess noise for the series of La0.75Sr0.25MnO3 (LSMO) giant magnetoresistive thin epitaxial films with thickness of 42, 50, 100, and 600 Å. Fabricated manganite films experience semiconductor-normal metal (paramagnetic-ferromagnetic) phase transition with the temperature change. The transition manifests itself by the sharp change of resistivity and characteristic peak of magnetoresistivity. Thickness decrease results in lowering the transition temperature and increasing of resistivity. The noise spectra has 1/fa behavior with a ≈ 1± 0.2. The voltage fluctuations spectral density shows quadratic dependence on current indicating that observed noise is caused by the resistance fluctuations. Noise level, temperature coefficient of resisistvity and magnetoresistance increase for thin films. Therefore, the operation point (transition temperature) can be tailored from 330 K to 220 K by changing only the film thickness while the performance of temperature and magnetic field LSMO sensors can be maintained almost constant in thickness range down to 100 Å.
Critical Microscopic Processes in Semiconductor Lasers
Authors: Hybertsen Mark S. , Alam M. A. , Baraff G. A. , Smith R. K.
Published: April 2011

The cascade of microscopic processes relevant to semiconductor laser operation is outlined. An integrated laser simulator which encapsulates these processes is applied to illustrate the connection between an accurate model of the optical gain in the quantum wells and measured characteristics of representative 1.3 μm InGaAsP/InP lasers. These results highlight the impact of carrier transport effects on the observed optical gain and the modulation response of semiconductor lasers.
Silicon Crystal Growth on a Ni Silicide Seeding Layer by DC Magnetron Sputtering
Authors: Guliants E. , Anderson W.A.
Published: April 2011

Direct current (d.c.) magnetron sputtering was applied to polycrystalline Si growth and yielded a uniform Si film at a deposition temperature below the glass softening point. The approach involved the deposition of a thin Ni film over SiO2 prior to Si sputtering. The interaction of a fine-grained metallic Ni with an atomic Si provided by a sputtering gun resulted in the formation of Ni silicide at the Ni-Si interface immediately after the onset of Si deposition. The phase composition of the nickel silicide was controlled by the temperature of deposition and the Si-to-Ni concentration ratio. The silicide region exhibited a layered structure where the bottom layer consisted of the mixture of several NixSiy phases and the top layer represented the pure NiSi2 phase. This Ni disilicide layer provided the nucleation sites for the epitaxial Si crystal growth. As a result, the polycrystalline silicon film consisted of 0.1-0.5µm grains with preferred (11) or (110) orientation without an indication of an amorphous phase. The carrier lifetime of 11 µs indicated good electrical properties which make the film potentially applicable to fabrication of thin film transistors and solar cells. The Ni prelayer thickness in the 5-100nm range dramatically influenced the crystal size and preferential crystal orientation. Possible mechanisms responsible for the nickel silicide induced grain growth of silicon and the correlation between the Ni silicide and silicon microstructure is discussed.
Characterization of Epitaxial Growth of Semiconducting Rhenium “Disilicide” Films
Authors: Misra A. , Verdier M. , Mahan J.E. , Mitchell T.E.
Published: April 2011

We have characterized, through transmission electron microscopy (TEM), the ReSi2−x thin films grown by reactive deposition on (001) Si. ReSi2−x thin films exhibit a distorted body-centered tetragonal MoSi2-type structure, and have excellent epitaxy on (001) Si since the face diagonal of the Si unit cell is equal to the c lattice parameter of silicide. The Si-deficient composition in the “disilicide” may be accommodated by collapse and shear of missing Si planes to form planar faults. Kirkendall voids are also observed at the film-substrate interface. The engineering of the defect and interface structures of these complex, non-stoichiometric silicides for optimized optoelectronic properties are discussed.