bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress Effects in 2d Arsenic Diffusion in Silicon
Authors: Rao V. , Zagozdzon-Wosik W.
Published: April 2011

Proximity rapid thermal diffusion (RTD) using arsenic has been used for doping high aspect ratio trench capacitors which may be used in high density dynamic memories. Nonuniformity of doping has been observed in SEM analyses at the trench comers after preferential etching used for junction delineation. Severe thinning was seen at the bottom comers of the junctions produced at low temperatures for long times (90 sec). This non- uniformity was alleviated at high diffusion temperatures for short time resulting in very uniform junctions. We modeled diffusion processes for trench doping using a process simulator, TSUPREM-IV. Default program data produced large discrepancies with experimental results and a new set of parameters was derived. The stress model in the oxide growth was incorporated in our calculations of the diffusion profiles to simulate formation of the dopant glass and obtain match with the experimental results.
Combine Spectroscopic Ellipsometry and Grazing X-ray Reflectance for Fine Characterization of Complex Epitaxial Structures
Authors: Boher P. , Stehle J. L.
Published: April 2011

Spectroscopic Ellipsometry (SE) and Grazing X-ray Reflectance (GXR) techniques are applied on different III-V epitaxial structures in order to extract accurately their structural information. Thickness information are obtained directly from Fourier transformation of the GXR spectra and confirmed by simulation of the reflectance curve. Compositions are deduced from SE regression using GXR thickness as input values. Examples on monolayer and bilayer structures are first remembered. Then the potentiality of the method is demonstrated to more complex systems (multilayer mirrors and HEMT structures).
Use of Advantageous Impurity Effects in Metallization
Authors: Murarka S. P.
Published: April 2011

Impurities control electrical, mechanical, physical, and chemical properties of the materials. We have manipulated their introduction into semiconductors, insulators, and metals to achieve otherwise unattainable properties. More recently, the continued miniaturization of the solid state devices and circuits have challenged the existing interconnection and contact metallization materials and schemes. These have led to an investigation of new multilevel metallization schemes with lower resistivities and higher reliabilities. In addition, efforts are being made to re-examine the use of newer Al-alloys that may satisfy the resistivity and reliability requirements. This paper will briefly review the existing practices, future needs, and current research activities focused to satisfy these future needs.
Interface Stresses in Nanostructured Multilayered Materials
Authors: Cammarata R. C. , Sieradzki K.
Published: April 2011

Surface and interface stresses, which are intrinsic thermodynamic quantities associated with all types of solid surfaces and interfaces are reviewed. A simple model for one type of interface stress is presented. These stresses can strongly influence the structure and mechanical behavior of nanostructured materials such as multilayered materials withultrathin layer thicknesses.
Magnetic Properties of Nanoscale Iron Particles Photodeposited in Glass
Authors: Sunil D. , Gafney H. D. , Tsang C. , Rafailovich M. H. , Sokolov J. , Gambino R. J. , Huang D. M.
Published: April 2011

Transmission Electron Microscopy(TEM) and magnetization measurements were used to study the correlation between size of the iron particles precipitated in glass and their magnetic properties. The iron particles les s than 40 Å in diameter photodeposited in porous Vycor glass(PVG) show superparamagnetic behavior at room temperature. As the size of the particles increases and reaches about 100 Å in diameter, the magnetization curve shows minor hysteresis with a very large coercivity.
High Quality AlGaAs Regrowth on Oxide-Free AlxGa1-xAs (x=0.26) by Metalorganic Chemical Vapor Deposition
Authors: Lee Kun-Jing , Huang Z. C. , Chen J. C.
Published: April 2011

The Al0.13Ga0.87As epilayers were regrown by metalorganic chemical vapor deposition (MOCVD) on different AI0.26Ga0.74As substrate layers. It was found that the quality of regrown A10.13Ga0.87As layers were significantly improved when a Se-doped Al0 26Ga0.74As substrate was used. Electrochemical C-V profile showed that no oxide formation and impurity incorporation at the regwon interface. Low-temperature (14.9 K) photoluminescence showed that the full width of half maximum (FWHM) of the bound exciton peak is as low as 4.51 meV. We attributed this improvement to the Se-passivation effect at the surface of Se-doped A10.26Ga0.74As substrate-layers. Results show that Se will delay the formation of native oxide to achieve the better quality of regrown AlGaAs layers.
Single-Photon Ionization, In Situ Optical Diagnostic Of Molecular Beam Epitaxial Growth Of GaAs
Authors: Ott Adina K. , Casey Sean M. , Alstrin April L. , Leone Stephen R.
Published: April 2011

Single-photon ionization time-of-flight mass spectrometry (SPI-TOFMS) is used in situ to monitor desorbing species and surface reactions during molecular beam epitaxy (MBE) of GaAs. In this method, the 1064 nm fundamental output of a Nd:YAG laser is tripled twice to produce 118 nm (10.5 eV) photons. The pulsed light is passed in front of a growing substrate, giving gaseous scattered molecules sufficient energy to ionize, but not fragment, them. Ionized species are detected with time-of-flight mass spectrometry. Arrangement of the experiment also allows for simultaneous real time monitoring with reflection high-energy electron diffraction (RHEED).

Mass spectra are examined and analyzed to quantify fluxes and relative ionization cross sections of growth species. The real time behavior of arsenic and gallium mass signals during epitaxy is presented as a function of substrate temperature and incident gallium flux. Surface reactions are proposed to elucidate mechanisms of arsenic incorporation and compared to measured RHEED results.
In-Situ Monitoring Of Mocvd Grown Inall_ As/Gaas Epitaxial Layers By Two Laser Beams Reflectometry
Authors: Baek Jong-Hyeob , Lee Bun , Choi Sung Woo , Lee Jin Hong , Lee El-Hang
Published: April 2011

We report application of in-situ laser reflectometry in monitoring InAl1−xAs (0 ≤ x ≤1) epitaxial layers grown on a GaAs substrate by low pressure metal-organic chemical vapor deposition. Two different lasers were used simultaneously: One was a He-Ne laser operating at 0.6328 μm and the other was a diode laser operating at 1.53 μm. The two laser beams were incident on the growing layer at an angle of 71° from the surface normal, and the reflected beams were detected by Si and Ge photovoltaic detectors, respectively. Since the epitaxial layer of InxAl1−xAs (0 ≤ x ≤1) has a wide range of index of refraction, the reflected signals showed a variety of patterns. The optical constants of the InxAl1−xAs epitaxial layers were obtained for the entire range of composition.
Single-Crystal Fine-Positioning Devices for Scanned-Probe Microscopies
Authors: Kleiman R. N.
Published: April 2011

We have developed a novel fine-positioning device for scanned-probe microscopies. Instead of the conventional scanner tube made of ceramic PZT material, we have constructed analogous structures from single-crystal piezoelectric wafers. Single-crystal materials, in particular Lithium Niobate, are available which solve many of the problems inherent with PZT. In addition, their superior thermal and mechanical properties lead to improved performance in a number of significant ways. We discuss the actual implementation of this idea in the construction of a scanner, possible applications for this design, and briefly discuss results obtained.
Double Modulation and Selective Excitation Photoreflectance for Characterizing Highly Luminescent Semiconductor Structures and Samples with Poor Surface Morphology
Authors: Amirtharaj P. M. , Chandler-Horowitz D. , Bour D. P.
Published: April 2011

Photoreflectance (PR) is a powerful, contactless, and nondestructive technique capable of probing interband electronic transitions and built-in electric-fields at the surface and in interface regions in semiconductor materials and microstructures. It has been widely used as a characterization tool. However, its application to highly luminescent systems, such as quantum-well (QW) lasers and samples with poor surface morphology has been limited because of the difficulty in minimizing the interference from the luminescence and the pump beam that is scattered from the surface. We present a double modulation procedure where both the probe and pump beams are modulated which allows the PR component to be completely separated from the luminescence and scattered contributions. The separation is achieved through the appropriate choice of modulation frequencies and specially designed tuned amplifiers. A complete PR system, along with the necessary circuits, is presented. In addition, we have also exploited the freedom provided by the system to choose any pump wavelength to selectively modulate specific regions of the multilayer structure (QW, barrier, and cladding layer) and extract detailed information regarding the properties of each layer. The applicability of the procedure is demonstrated by fully characterizing a GaInP based QW laser structure used for visible emitters and by measurements on a saw-cut and chemically etched back surface of a commercial GaAs wafer. Finally, procedures attempted in the past to overcome difficulties with the luminescence and surface scattering are discussed and compared to the double modulation PR technique.
Characterization of AlGaAs/GaAs Heterojunction Bipolar Transistors Using Photoreflectance and Spectral Ellipsometry
Authors: Smith Patricia B. , Kim Tae S. , Magel Lissa K. , Duncan Walter M. , Ley A. Vance , Brette Nick A.
Published: April 2011

Photoreflectance spectroscopy (PR) and spectral ellipsometry (SE) have been used to characterize the doping and structure of heterojunction bipolar transistors (HBT). This information provides a more complete description of the epitaxial HBT structure than is possible by relying solely on electrical characterization of specially processed test structures. Additional benefit is derived from the nondestructive nature of both SE and PR. The measurements are fast enough to be implemented on all production-bound HBT material. We describe our recent results comparing capacitance-voltage measurements with PRderived doping levels in the emitter layer of the HBT. We also describe some work comparing SE fit results with Auger electron spectroscopy depth profiles for InGaAs contact layer composition and thickness.
Exciton Dynamics in Ultrathin InAs/GaAs Quantum-Wells
Authors: Brübach J. , Haverkort J. E. M. , Wolter J. H. , Wang P. D. , Ledentsov N. N. , Torres C. M. Sotomayor
Published: April 2011

We have studied the transient behaviour of a sharp emission line, which emerges close to the heavy-hole (hh) exciton photoluminescence line in a 1.6 monolayer thick InAs layer embedded in a GaAs matrix, when the light-hole (lh) exciton transition is excited. We find, that the decaytime of the sharp line is equal to the lh-exciton lifetime for excitation on resonance, but it strongly decreases for excitation off resonance. Since in our structure the energy separation between the hhand lh-exciton transitions amount to one GaAs LO phonon we conclude, that the sharp line originates from double resonant Raman scattering for off resonant excitation, whereas it is predominantly due to resonant luminescence for excitation on resonance. The strong decrease of the intensity of the sharp line due to a temperature rise from 4 to 18K proves the existence of a well confined lh-exciton state. In addition, we performed carrier capture measurements on this structure. We find a constant capture time of 20ps at the lh-exciton transition, whereas the capture time decreases step-like from 55ps to 22ps within the hh-exciton transition. This provides clear evidence for a two-step capture process, where the lh-level acts as an intermediate capture state.
Optical Characterization of Hydrogenated Silicon Films in the Extended Energy Range
Authors: Globus T. , Fonash S. J. , Gildenblat G.
Published: April 2011

This work introduces a new interference technique for the diagnostic characterization of hydrogenated silicon thin films. The interference technique is based on new self-consistent data analysis algorithms for simultaneous optical transmission and specular reflection using exact interference equations for the system of a film on a substrate. It provides a quick non-destructive optical measurement of absorption coefficient and refractive index spectra of amorphous silicon (a-Si:H) and polycrystalline silicon (poly-Si:H) thin films in a wide range of the incident photon energies (0.5–3.5 eV). This non-contacting, high sensitivity method is a powerful probe of various material properties including thickness, refractive index and absorption spectra, hydrogen content, alloy fraction, energies of localized defect states and their concentrations. Experimental results for optical study of hydrogenated Si films indicate that the proposed method makes possible high precision measurements of the absorption in the region near the fundamental edge. In this region the absorption coefficient varies over several orders of magnitude. Also, the absorption related to impurities and defects in the subgap energy region at least from 102 cm−1 can be detected. As a result, the interference technique shows promise in providing feedback for monitoring film growth and device fabrication processes.
In Situ Multi-Wavelength Ellipsometric Control of Thickness and Composition For Bragg Reflector Structures
Authors: Herzinger Craig , Johs Blaine , Chow Peter , Reich Dave , Carpenter Greg , Croswell Dan , Hove Jim Van
Published: April 2011

We have demonstrated real-time feedback control of thickness and composition for Bragg reflector structures using in situ multi-wavelength ellipsometry. This demonstration was performed under conditions which were not ideal for ellipsometric measurements: the angle of incidence for the ellipsometric measurement beam was far away from the Brewster angle, substrate rotation was enabled (which caused an angular wobble in the measurement beam), and strain effects were present in the ellipsometer windows. Furthermore, to simulate drift in the MBE system (and test the effectiveness of the ellipsometer control), the Ga effusion cell was ramped to change the Ga flux by 50% during two of the growth runs. Results of the growth control precision and accuracy are presented; the influence of the non-ideal measurement conditions on the ellipsometer growth control capability is also discussed.
Non-Destructive Characterisation of Rapid Thermally Annealed N+-Doped Polysilicon Using Spectroscopic Ellipsometry
Authors: Carline R. T. , Leong W. Y. , Cullis A. G. , Houlton M. R. , Hope D. A.
Published: April 2011

The use of spectroscopic ellipsometry (SE) to characterise the effects of rapid thermal annealing on Si implanted with phosphorous and phosphorous with fluorine are presented. Variations in the measured SE spectra with anneal temperature and presence/absence of fluorine are clearly observed. Spectra are successfully modelled using refractive indices which are graded with depth. Comparison with cross-sectional transmission-electron microscopy and secondary ion mass spectroscopy show that the results can be correlated with both the crystallinity and impurity distribution in the poly-Si.
Influence of Ohmic Contacts on Semi-Insulating GaAs Detector Performances
Authors: Castaldini A. , Cavallini A. , Canali C. , Chiossit C. , Papa C. Del , Nava F. , Lanzieri C.
Published: April 2011

Ohmic contact has been observed to play an important role in the performances ofLiquid Encapsulated Czochralski gallium arsenide particle detectors since it is possible to control the injection of charge carriers which determines the device performances. Alloyed and implanted contacts characteristics have been compared to relate the presence of electrically active defects induced during contact preparation to the final detector efficiency. In-situ optical probing investigations have been carried out to analyze the electric field distribution. Spectroscopic investigations show that the contact fabrication process significantly influences the trap density, whilst it does not change their type.
Acoustic Emission for The Diagnostic of Semiconductor Structures
Authors: Lyashenko O. V. , Perga V. M.
Published: April 2011

Acoustic emission (AE), electric current fluctuation, as well as luminescence intensity fluctuations in lightemitting semiconductor structures have been investigated. The authors examined the hypothesis about the origin of nonelectronic acoustic low frequency noise that is observed in electronic systems. The various sets of AE's sources allow one to understand the various dynamics of the AE in the structures on the A3B5 compound base and p-n germanium diodes.
Study of Periodic Surface Nanostructures Using Coherent Grating X-Ray Diffraction (CGXD)
Authors: Shen Qun
Published: April 2011

It is shown that an x-ray interference phenomenon, Coherent Grating X-ray Diffraction (CGXD), can be used to study lateral nanostructure arrays on crystal surfaces and interfaces. Compared to Fraunhofer grating diffraction of visible light, x-ray grating diffraction contains information not only about geometric profiles of a surface, but also about the internal crystalline structures and lattice strain distributions in grating features. Grating diffraction patterns can also be measured in a white-beam Laue method using highly collimated polychromatic synchrotron radiation. This provides a way for parallel data collection and is useful inin-situstudies of structural evolution of nanostructure arrays.
Transmission Electron Diffraction Techniques for NM Scale Strain Measurement in Semiconductors
Authors: Vanhellemont J. , Janssens K. G. F. , Frabboni S. , Smeys P. , Balboni R. , Armigliato A.
Published: April 2011

An overview is given of transmission electron microscopy techniques to address strain with nm scale spatial resolution. In particular the possibilities and limitations of (large angle) convergent beam electron diffraction ((LA)CBED) and electron diffraction contrast imaging (EDCI) techniques are discussed in detail. It will be shown by a few case studies that unique and quantitative information on local strain distributions can be obtained by the combined use of both (LA)CBED and EDCI in correlation with three dimensional finite element simulations of the strain distributions in the thinned specimen.
Optical and Structural Characterization of Arsenide/Phosphide Interfaces Formed by Flow Modulation Epitaxy
Authors: Emerson D. T. , Smart J. A. , Whittingham K. L. , Chumbes E. M. , Shealy J. R.
Published: April 2011

Bulk GaAsP, 20Å–500Å GaAsP/GaInP single quantum wells and 70 Å period GaAsP/GaInP superlattices were deposited on GaAs substrates by Flow Modulation Epitaxy. In these structures, the disordered GaInP is lattice matched while the GaAsP is in tension with the As mole fraction varying from 0.6 to 1. The structures were studied using asymmetric x-ray diffraction, 1K photoluminescence, Raman scattering, transmission electron microscopy and atomic force microscopy. Raman and x-ray diffraction are used to assess the structural quality of the superlattices, especially with regard to the presence/absence of superlattice x-ray satellites and disorder activated longitudinal acoustic phonons. A model including the effects of composition, strain, and confinement on longitudinal optic phonons is described and used to estimate the composition, using Raman scattering, in the thin, pseudomorphic GaAsP layers in the superlattices. Photoluminescence is used to assess the composition of the interfacial layers in the single quantum wells and to determine transition energies in the superlattices. In addition, analysis of the heterostructure luminescence, including prediction of the energy band alignment as calculated with the model solid theory corrected for strain, is found to suggest the presence of a type II band alignment in the heterostructures for some values of GaAsP composition. Finally, Raman scattering and x-ray diffraction are used to compare arsenide to phosphide interfaces in GaAs and InP-based heterostructures.
Characterization Of Nitrogen Species For P-Type Doping Of Znse
Authors: Kimura K. , Kajiyama H. , Miwa S. , Asuda T. Y , Kuo L. H. , Jin C. G. , Tanaka K. , Yao T.
Published: April 2011

Laser-induced fluorescence(LIF) spectroscopy has been applied to the detection of excited nitrogen molecules coming out of a plasma source used for p-type doping of ZnSe. With the use of a fluorescence-photon-counting system, the fluorescence of nitrogen molecules in the A3 Σ u+ (v=0) state was observed even in a high vacuum condition ˜ 10−4 Pa. The correlation between LIF intensity of nitrogen molecules in the A3 Σ u+(v=0) state and the net acceptor concentration of nitrogen doped ZnSe epitaxial layers was investigated.
Combine spectroscopic ellipsometry and grazing x-ray reflectance for fine characterization of complex epitaxial structures
Authors: Boher P. , Stehle J. L.
Published: April 2011

AbstractM

Spectroscopic Ellipsometry (SE) and Grazing X-ray Reflectance (GXR) techniques are applied on different III-V epitaxial structures in order to extract accurately their structural information. Thickness information are obtained directly from Fourier transformation of the GXR spectra and confirmed by simulation of the reflectance curve. Compositions are deduced from SE regression using GXR thickness as input values. Examples on monolayer and bilayer structures are first remembered. Then the potentiality of the method is demonstrated to more complex systems (multilayer mirrors and HEMT structures).
Ge-Related Interfacial Defects In SiGe Alloy Structures
Authors: Macfarlane Patricia J. , Zvanut M. E. , Carlos W. E. , Twigg M. E. , Thompson P. E.
Published: April 2011

This paper reports etching results supporting the identification of the SG1 center as a germanium dangling bond defect at the interface between an oxide and crystalline SiGe. The presence of this defect is significant because, like an analogous center in Si-based systems, it may alter the operation of any microelectronic or micro-optical device which incorporates an interface between SiGe and an overlying oxide. The samples examined are oxygen implanted SiGe layers in which the SG 1 center is believed to occur at the interface between oxide precipitates and SiGe. Because of the center's apparent relation to the oxide precipitates distributed through layers of the sample, a depth profile assists in confirming the interfacial nature of the defect. We obtain a depth profile by comparing electron paramagnetic resonance (EPR) spectra of samples etched to decreasing thickness. EPR spectra indicate that the SG1 center decreases with depth in a manner that when correlated to a cross sectional transmission electron micrograph confirms the association with Si0 2 and supports its location at the SiGe/SiO2 precipitate interface.
Process Diagnostics For Remote Plasma-Enhanced Chemicalvapor Deposition (Pecvd) Of Silicon Nitrides
Authors: Banerjee A. , Lucovsky G.
Published: April 2011

Hydrogenated silicon nitride films were deposited in a remote plasma reactor using a plasmaexcited NH3/He mixture, and with downstream injection of SiH4. An electrically biased grid placed between the plasma tube and the deposition region was used to control the extent of the plasma afterglow into the deposition region. In situ monitoring by mass spectrometry (MS) indicated that the Si content of the film was increased when charged species were transported from the plasma region to the deposition region of the chamber, and that the properties of the resulting films could be understood in terms of two different deposition pathways, driven respectively by neutral, and a combination of neutral and charged precursor species.
Simultaneous Spatially Resolved Multispectral Optical Emission Of Sputter Processes
Authors: Klein J. D. , Clauso S. L.
Published: April 2011

An optical spectroscopy system was configured to monitor several plasma positions at the same time. The system allows monitoring of several points within a single plasma. Magnetron sputtering of YBa2Cu3O7 (YBCO) in a reduction-oxidation (redox) environment provided a process in which both cation and gas species are vital in determining the quality of the product film. Spatial sampling of the sputter plasma defined a disparity in the manner in which Ba and Cu emissions respond to changes in chamber gas composition. Oxygen emissions were found to respond quickly to inlet gas composition while Cu emissions were notably sluggish.
Non-Classical Reaction Kinetics: Experiments
Authors: Kopelman Raoul , Lin Anna L.
Published: April 2011

It has been well established by theory and simulations that the reaction rates of diffusion-limited reactions can be affected by the spatial dimension in which they occur. The types of reactions A + B → C, A + A → A, and A + C→, C have been shown, theoretically and/or by simulation, to exhibit non-classical reaction kinetics in low and fractal dimensions. We present here experimental results from several 1D and fractal systems.

An A+B → C type reaction was experimentally investigated in a long, thin capillary tube in which the reactants, A and B, are initially segregated. This initial segregation of reactants means that the net diffusion is along the length of the capillary only, making the system effectively 1D and allowing some of the properties of the resulting reaction front to be studied. The reaction rate of excitonic fusion, A + A →A, as well as trapping, A + C→ C, reactions were observed via phosphorescence(P) and delayed fluorescence(F) of naphthalene within the channels of Vycor glass, in isotopically mixed naphthalene crystals and in the isolated chains of dilute polymer blends. In these experiments, the non-classical kinetics are measured in terms of the heterogeneity exponent, h, from the equation: Rate ∼ F =; kt-hpn,, which gives the time dependence of the rate coefficient. Classically h =; 0, while h =; 1/2 in 1D, as well as in the fractal dimensions discussed here, for A + A → A as well as A + C →C type reactions.
Dynamic Light Scattering in 5CB Confined in Disordered Porous Media
Authors: Aliev Fouad M. , Nadtotchi Vladimir V.
Published: April 2011

We performed dynamic and static light scattering measurements in nematic LC (5CB) confined in silica porous glasses with average pore sizes of 1000 A˚ (volume fraction of pores 40%) and 100 A˚ (27%). The experiments show significant changes in physical properties of confined LC. Nematic-isotropic phase transition temperature TNIis depressed by 0.6°C in 1000 A˚ pores compared to that bulk value and this phase transition was not detected at all in 100 A˚ pores. We found that even about 20°C below bulk melting temperature the relaxational processes in confined LC were not frozen. Slow relaxation process which does not exist in the bulk LC and wide spectrum of relaxation times (10−8–)s appear in both 100 A˚ and 1000 A˚. In 100 A˚ pores slow relaxation exists even at T corresponding to the bulk isotropic phase. Our data can not be described using the standard form of dynamical scaling variable (t/r) but they obey activated dynamical scaling with the scaling variablex= lnt/lnr.
Relaxational Dynamics and Strength in Supercooled Liquids from Impulsive Stimulated Thermal Scattering
Authors: Yang Yongwu , Muller Laura J. , Nelson Keith A.
Published: April 2011

Impulsive stimulated thermal scattering (ISTS), a time-domain light scattering technique, provides a more than 6-decade time range from sub-ns to many ms. It permits characterization of the structural relaxation dynamics and determination of the relaxation strength or Debye-Waller factor in supercooled liquids, and thus allows testing of the mode coupling theory of the liquidglass transition. ISTS experiments were performed on glass formers salol, butylbenzene, and the molten salt [Ca(N03)]0.4[KNO3]0.6. The relaxational dynamics and the Debye-Waller factorfq=0 were obtained. A square-root anomaly was observed in fq=0 (T) at a crossover temperature Tc for all three materials, consistent with the prediction of mode coupling theory.
Simulation of Dynamics of Liquid-Glass Transition
Authors: Kogure Y. , Kunitomi K. , Nakamura Y. , Doyama M.
Published: April 2011

Glass transition of of copper is simulated by the molecular dynamics method. Embedded atom method potential is used. The glass state was produced by quenching the liquid sample, which was produced by melting a crystal. The split second peak in RDF was observed in the glass state.
Enthalpy Relaxation Near the Glass Transition of a Supercooled Liquid [Ca(NO 3) 2]0.4[KNO3]0.6
Authors: Moon I. K. , Jeong Yoon-Hee
Published: April 2011

We have investigated the slow dynamics in the glass transition region of a supercooled liquid [Ca(NO3)2]0.4[KN3]0.6 by measuring the dynamic specific heat in the frequency range from 0.01 Hz to 5 kHz. The equilibrium dynamics of the system in this range is well described by the stretched exponential function, exp[-(t/τ)β], and the Vogel-Fulcher type relaxation time, τ = τ0exp[Δ/(T − T0)].
Variation of the Structural Unit in Tellurite Glasses
Authors: Suehara Shigeru , Yamamoto Kazuo , Hishita Shunichi , Aizawa Takashi , Inoue Satoru , Nukui Akihiko
Published: April 2011

We show that the variation of the structural unit in tellurite glasses is due to the charge transfer from modifier atoms to TeO6 octahedra with use of first-principles molecular orbital calculations. Orbital overlap population analysis reveals that the transferred electrons to the Te- O antibonding orbital cause breaking Te-O bonds and lead to reducing the coordination number of the Te atom.
Localization of Electrons and Acoustical Phonons in Irregular or Fractal Crystallites
Authors: Sapoval B. , Russ S.
Published: April 2011

The behavior of electron and phonon excitations in systems with irregular boundaries is discussed on the specific example of prefractal shapes. We show that both electron states and acoustical phonons exhibit localization properties. This effect is stronger when the fractality of the shape is increased. In consequence the electron-phonon interaction in small crystallites should be strongly dependent on their shape or roughness. This localization could play a role in the thermal properties of glasses where internal partial crytallization has no reason to build pseudo-crytalline entities which should be smooth.
A Model for Ion-Sputtering: from Pattern Formation to Rough Surfaces
Authors: Cuerno R. , Makse H. A. , Tomassone S. , Harrington S. T. , Tanley H. E.
Published: April 2011

Many surfaces eroded by ion-sputtering have been observed to develop morphologies which are either periodic, or rough and non-periodic. We have introduced a discrete stochastic model that allows to interpret these experimental observations within a unified framework. A simple periodic pattern characterizes the initial stages of the surface evolution, whereas the later time regime is consistent with self-affine scaling. The continuum equation describing the surface height is a noisy version of the Kuramoto-Sivashinsky equation.
A Growth Model For Ramified Electrochemical Deposition
Authors: Marshall Guillermo , Mocskos Pablo , Olivella Martin
Published: April 2011

We introduce a macroscopic model for the description of growth pattern formation in ramified electrochemical deposition. The theoretical model is formulated as a 2D time-dependent problem consisting in the Nernst-Planck equations for the concentration of the solute (cations and anions), coupled to a Poisson equation for the electrostatic potential and the Navier-Stokes equations for the solvent, with a moving boundary. A dimensional analysis is performed and a new set of dimensionless numbers governing the flow regime is derived. A 2D discrete version of these equations in a DBM scheme with a random moving boundary constitutes the computational model. We present numerical results which show that our growth model, with a proper variation of the set of dimensionless numbers, gives a reasonable picture of the interplay of the electroconvective, migration and diffusive motion of the ions near the growing tips.
Dehydration of Fractal Particles of Iron (III) and Aluminum Hydroxides
Authors: Vertegel A. A. , Kalinin S. V. , Oleynikov N. N. , Tretyakov Yu. D.
Published: April 2011

The kinetic behavior of Fe(OH)3 and AI(OH)3 powders during thermal dehydration is investigated. It has been shown that the dehydration rate is governed by the value of fractal dimension of the sample without any respect to the nature of metal atom in hydroxide. The quantitative model for dehydration of fractal particles with particular value of fractal dimension is suggested. Theoretical predictions are in a good agreement with experimental data.
Influence of Spatial Correlations on Permeability and Connectivity of Sandstone
Authors: Makse Hernan A. , Havlin Shlomo , King Peter R. , Stanley H. Eugene
Published: April 2011

Sedimentary rocks have complicated permeability patterns arising from the geological processes that formed them. Here we address the longstanding question of how such patterns are generated. We also analize data on two sandstone samples from different geological environments, and find that the permeability fluctuations display long-range power-law correlations characterized by an exponent H. For both samples, we find H ≈ 0.82 – 0.90. These permeability fluctuations significantly affect the flow of fluids through the rocks.
Microhydrodynamics with Dissipative Particle Dynamics
Authors: Español Pep , Zúñiga Ignacio
Published: April 2011

Dissipative particle dynamics is essentially a coarse-grained molecular dynamic simulation technique that captures the essential physics with considerably less computer effort. We have given a sound theoretical foundation to the technique with respect to the equilibrium and hydrodynamic properties. In this paper we further explore the connection of the model parameters of DPD with the underlying microscopic dynamics for the case of a simple model of a solid. This provides some insight into the difficulties of interpretation of DPD simulations.
Critical Behavior in the Ultrasonic Properties of Suspensions
Authors: Esquivel-Sirvent R. , Green D. H.
Published: April 2011

Velocity and attenuation measurements of compressional waves at 3 and 5 MHz are presented for suspensions made of 1μm size particles of kaolinite or glass beads in water or light oil. At a critical concentration of 40%, the attenuation shows a sharp peak in attenuation as well as a sudden change in velocity. This behavior is observed in all suspensions and is independent of frequency or particle geometry. The observed behavior is consistent, with the excess attenuation induced by the fluid-shearing between particles. This behavior is the first experimental evidence for the existance of the freezing point, predicted by computer simulations.
Microstructure and Phase Characterization of the Surface of a-C:H Films by Means of Scanning Tunneling Microscopy and Spectroscopy
Authors: Rusman I. , Klibanov L. , Ben-Jacob E. , Croitoru N.
Published: April 2011

Scanning Tunneling Microscopy and Spectroscopy (STM/STS) are used for obtaining nano-scale information on morphological and electronic properties of the surface of diamond-like amorphous hydrogenated carbon (a-C:H) filns. The films are prepared by rf plasma decomposition of methane CH4.A two phase model of a-C:H is suggested - sp3 bonded matrix in which sp2 clusters are embedded. A novel method of mapping graphite-like clusters over a-C:H surface is proposed. Tunneling I/V characteristics with a gap acquired on indium tin oxide (ITO) deposited on a-C:H indicate location of sp2 regions at the surface of a-C:H below an ITO overlayer
Complex Impedance Analysis of Silica Surface Film on Molybdenum Disilicide
Authors: Lin Wen-Yi , Gerhardt Rosario A. , Speyer Robert F.
Published: April 2011

The exposure of molybdenum disilicide to combustion products at 1370° and 1600°C for 1 and 60 hours led to the formation of a silica surface film. The thickness of this protective layer, ranging from 4.4–18.2 μm, increased with temperature and exposure time. However, the dielectric constant (3.16) of the thin film was independent of ac field frequency, exposure time, and temperature, according to complex impedance analysis in the frequency range of 500 Hz to 1 MHz. MoSi2 specimens with a silica coating on one side resembled, in impedance spectroscopy terms, a resistor of low resistivity (MoSi2, 10−4 Ω·cm) in series with a parallel RC circuit of high resistivity (SiO2, 3.0×1010 Ω·cm). From this analysis, a calibration curve was generated for converting measured capacitance to silica film thickness. Relaxation time (on the order of 0.1 sec) and relaxation frequency (on the order of 1–10 Hz) were also derived, with the aid of semicircular regression of the complex impedance curves.
Numerical Impedance Analysis of Groove Electrodes In Aconducting Solution
Authors: Matsui H. , Kunugi A.
Published: April 2011

The effect of electrode surface unevenness on electrode impedance was examined at rectangular groove electrodes by numerically solving the Laplace equation. CPE behavior appeared for the double-layer charging at considerably large groove electrodes in the absence of outer solution layer at high frequencies. This behavior originated from the current concentration to the upper portions of the groove. In the presence of an outer solution layer, the current concentration was greatly weakened by the series connection of solution resistance, resulting in the disappearance of CPE behavior. The real part of the impedance at high frequencies was not additive in the presence of exposed electrode surfaces outside the groove. The origin of no impedance additivity was discussed based on equipotential-amplitude data.
Quartz Crystal Microbalance for the Transient Study of Electrode Processes
Authors: Daujotis V. , Raudonis R , Kubilius V. , Gaidamauskas E. , Sližys R.
Published: April 2011

A technique for the measurement of quartz supported electrode oscillation frequency with special reference to transient electrochemical experiments was prepared. Due to changes in solution viscosity and density and in surface roughness during potential step experiments, the error in calculation of mass changes from frequency responses can reach 3–5 %. Initial deviation of electron numbers from unity by 30–60% during pulse electroreduction of dicyanoargentate shows that this process is not a simple faradaic reaction.
Characteristics of Ni/Nd-Doped Ceria Anode For Solid Oxide Fuel Cell
Authors: Nagamoto H. , Kumagai K. , Murayama H.
Published: April 2011

A fuel electrode consisting of particles of Ni and mixed conductor, Nd-doped ceria (NDC) has been developed. The electrode resistance decreased with decreasing the oxygen partial pressure lower than 10−11 atm, where the electronic conduction is predominant for NDC. This decrease in the resistance could be attributed to an increase in the triple phase boundary caused by an increase in electronic conductivity of NDC.
Experimental Limitations In Impedance Spectroscopy of Materials Systems
Authors: Hsieh G. , Edwards D. D. , Ford S. J. , Hwang J.-H. , Shane J. , Garboczi E. J. , Mason T. O.
Published: April 2011

Using resistor-capacitor networks, sources of experimental artifacts in impedance spectroscopy were investigated, such sources include machine limitations, rig/cabling contributions at high frequencies, and artifacts due to high impedance reference electrodes and their geometrical placement. In the instance of electrode placement, computer simulations with a pixel-based model were in agreement with the experimental observations. Remedies for these artifacts such as rig shielding/grounding, geometrical adjustments, and null corrections are also discussed.
Evaluating the Microstructure of Conductor-Insulator Composites using Effective Media and Percolation Theories
Authors: McLachlan David S.
Published: April 2011

The widely used Bruggeman symmetric and asymmetric media equations and the Clausius-Mossetti approximation are presented, and the idealized microstructures characterizing these media are examined.

The percolation equations for the conductivity (σm) and complex dielectric constant (ɛm = ɛrm + iɛim) for ideal perfect conductor–conductor and conductor–perfect insulator continuum media (and lattices) are then introduced. The parameters characterizing the microstructure in the percolation equations are a critical volume fraction or percolation threshold (φc) and two exponents (t&s). The equations characterizing the crossover region, which occurs whenever the ratio of the conductivities of the two components is finite, or dielectric measurements are made, are also introduced. A general effective media equation, which has the same parameters as the percolation equations is noted, and its success in obtaining φc, when the ratio of the conductivities is finite, examined.

The microstructures that allow φc to have values between a few percent and over 60%, as well as the occurrence of non–universal values of t, will also be discussed.
Dielectric Relaxation in Composite Systems
Authors: Mopsik Frederick I.
Published: April 2011

Dielectric relaxation phenomena have contributions from both the internal reorientation modes of the molecules comprising a material as well as the details of how those modes couple together to form the material. This behavior can change quite sensitively with changes in the composition of material. For a composite material that has more than one phase, the presence of phase boundaries and even shape can play an additional and large role in the observed relaxation behavior. Analysis of the relaxation spectra can be used to study these effects. Examples are shown, primarily of polymeric materials, ranging from liquid solutions to phase separated mixtures to show how dielectric relaxation over a wide frequency range can be used to characterize and study composite materials.
Evaluation of 0-3 Ceramic/Ceramic Piezoelectric Composites by Dielectric Methods
Authors: Sayer M. , Mcintyre D. S. , Beckett J. , Barrow D. A. , Tandon R.
Published: April 2011

Piezoelectric composites prepared by firing ceramic lead zirconate titanate (PZT) powders within a PZT sol gel have a two phase structure in which both phases have high permittivity. Dielectric measurements reflect the presence of the two phases and of interfacial layers between the phases and at the electrodes. The system has been modelled as a) a composite dielectric and b) a multi-layer capacitor with some complex components. The frequency dependent response of composites, sol gel derived films and a bulk ceramic is compared.
Impedance Spectroscopy Of Biological Cells
Authors: Schmukler Robert E.
Published: April 2011

A six-electrode impedance chamber is used to perform wide-bandwidth (10 Hz − 3 MHz), sensitive impedance measurements to evaluate the electrical properties of living cells under normal physiologic conditions. The high sensitivity in these measurements, compared to cell suspension techniques, is accomplished by embedding the cells into the pores of a filter, creating a “pseudoepithelium” and markedly reducing the current shunt pathways around the cells. The shunt resistance for each cell is between 6 − 7 × 107 Ω. The cellular geometry and the portion of cell membrane under measurement are precisely controlled in this method. This technique produces a multi-parallel, whole-cell, patch-clamp like structure for 3.3 × 105 cells. The advantages of this technique, general insights, and improvements in impedance measurements will be discussed. Effects of bandwidth mismatch between high-input impedance amplifiers, reference point drift due to solution resistivity changes, and the use of porous electrodes will be covered. Lastly, the ability to electroporate the cell membrane contributes another unique way to study the impedance of living cells.
The Dynamics of Interacting Systems: Glassy Ionic Conductors and Glass-Forming Materials
Authors: Ngai K. L. , Rizos A. K.
Published: April 2011

The dynamics of densely packed interacting systems including glass-forming materials and glassy ionic conductors of various chemical and micro structures have been investigated experimentally by many workers, covering an immense time range from microscopic times shorter than 10−12 s to macroscopic times as long as 104 s. The short time dynamics is fundamental because it can directly reveal the microscopic mechanism of the relaxation. Several experimental investigations of structural relaxation in glass-forming substances have found that the short time dynamics shows exponential relaxation with a correlation function well described by exp(−t/τo) for ttc. The relaxation times τ and τo are related by the expression τ = [tc−(1−β)τo]1/β. In this work, we focus on glassy ionic conductors and ionic glass-forming materials and experiments that employ dielectric spectroscopic and conductivity relaxation techniques, the theme of this Symposium. We show that these experimental data exhibit the same feature as described above for structural relaxation and are in accord with the predictions of the coupling model proposed by one of the authors.
Radionuclide Content of Simulated and Fully Radioactive SRL Waste Glasses: Comparison of Results from ICP-MS, Gamma Spectrometry, and Alpha Spectrometry
Authors: Wolf S. F. , Bates J. K.
Published: April 2011

We have measured the transuranic content of two transuranic-doped, simulated waste glasses, using inductively coupled plasma-mass spectrometry (ICP-MS), γ-spectrometry, and α-spectrometry. Average concentrations measured by each technique were within ±10% of the as-doped concentrations. We also report the transuranic content of three fully radioactive SRL waste glasses that were determined using γ- and α-spectrometry measurements to deconvolute isobaric interferences present in the ICP-MS analyses.
Kinetics of Phase Separation in Lithium Bearing HLW Alkaliborosilicate Glasses
Authors: GÖttlicher J. , Pentinghaus H. J.
Published: April 2011

A TEM study on the kinetics of metastable phase separation in a lithium bearing HLW glass frit is presented. As nothing was known about the kinetics of metastable phase separation below the glass transformation temperature we had to carry out annealing experiments just above and below the transformation temperature, in order to achieve phase separation on a laboratory time scale- Particle growth in the WAKID5 HLW glass frit at 550 °C occurs by a diffusion controlled Ostwald ripening process (about 40 °C above Tg). Metastable phase separation in the lithium bearing glasses even at lower temperatures cannot be excluded from the present study. In NaBSi3O8 glass (Tg ≈ 580 °C) phase separation could be detected at 500 °C well below Tg after about 160 days.
Instantaneous Formation of Synroc-B Phases at Ambient Pressure
Authors: Mchale J. M. , Coppa N. V.
Published: April 2011

The titanate based nuclear waste immobilization medium, Synroc-B, has been synthesized at atmospheric pressure from freeze dried nitrate precursors. Complete formation of the phase assemblage (CaTiO3, CaZrTi2O7, and BaAl2Ti5O14) occurred upon calcination of the nitrate precursor after only 10 minutes at 1100°C. This improvement in the preparation conditions may lead to practical application of the material in the safe disposal of high level nuclear waste and the immobilization of other strategic nuclear materials.