bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical stresses upon crystallization in phase change materials
Authors: Pedersen T. P. Leervad , Kalb J. , Njoroge W. K. , Wamwangi D. , Wuttig M. , Spaepen F.
Published: July 2002

Crystallization processes in different Te alloys, employed in phase change materials for optical data storage, have been investigated by in situ mechanical stress measurements. Upon crystallization a considerable stress buildup is observed, which scales with the volume change upon crystallization. Nevertheless the observed stress change only corresponds to approximately 9% of the stress estimated for a purely elastic transformation. Further evidence of stress relief phenomena comes from the temperature dependence of the stress in the crystalline and amorphous states. Ultrathin dielectric layers have a profound influence on the crystallization process as evidenced by simultaneous optical reflectance and mechanical stress measurements. This observation can be explained by heterogeneous nucleation of crystallites at the interface between the dielectric layer and the phase change film.
Raman spectroscopy and inhomogeneous broadening
Authors: Ricard D.
Published: July 2002

It is generally thought that the various third-order Raman spectroscopic techniques are equivalent to spontaneous Raman scattering, even when inhomogeneous broadening is present. Experimental observations show that certain of these techniques are complementary in certain cases. We give here the simple explanation for this complementarity.
Mechanical properties of layered InSe and GaSe single crystals
Authors: Mosca D. H. , Mattoso N. , Lepienski C. M. , Veiga W. , Mazzaro I. , Etgens V. H. , Eddrief M.
Published: July 2002

The mechanical properties of InSe and GaSe single crystals have been studied by means of nanoindentation tests. Both bulk crystals are well ordered and present a predominant γ-type interlayer stacking sequence as determined by x-ray diffraction and transmission electron microscopy measurements. The course of plastic deformation induced in the crystals by application of a definite shear stress through the penetration of a Berkovich tip indicates that the deformation occurs predominantly by pop-in events along easy slip directions having a fairly elastic character between displacements. Hardness anisotropy along crystal axes is clearly seen and the measured elastic modulus presents a discrepancy smaller than 5% in comparison with theoretical calculations performed using previous experimental values of the elastic constants.
Status report on studies of EBIS in the string mode of operation
Authors: Donets E. D. , Donets D. E. , Donets E. E. , Salnikov V. V. , Shutov, V. B. , Tumanova Yu. A. , Vadeev V. P. , Bjorkhage M. , Lundquist A. , Liljeby L. , Rensfelt K.-G. , Beebe E. , Alessi J. , Pikin A. I.
Published: July 2002

A short description of an EBIS apparatus in the reflex mode of operation, resulting in electron string formation, and recent experimental results are presented. The focus is on experimental studies of electron energy distribution in strings, for which a long tail to high energy was observed and about 30% half width was confirmed by means of spectrometry using the radiative recombination of Ar17+. We have obtained considerable information about the dependency of the number of string electrons versus solenoid magnetic field strength using different EBIS sources and found that it has about 3 in power of B in the region 0–3.5 T. Preparations for the first experiments on the BNL EBIS Test Stand in the reflex mode of operation and for the first test of the JINR Krion-2 source in the string mode at the Nuclotron injector on acceleration of Ar16+ are also described briefly.
Capacitance bridge measurements of magnetostriction
Authors: Boley Mark S. , Shin Won C. , Rigsbee David K. , Franklin Doug A.
Published: July 2002

Magnetostriction effects were investigated for three different materials by using a simple, reproducible, and cost-effective method recently developed in our laboratory. The magnetostriction effects were generated by a large oscillating magnetic field produced by a high current 60 Hz ac welder power supply, capable of reaching saturation levels for the material, and then detected by a change in capacitance between a hollow cylindrical sample and a concentric brass ring. This capacitance change was continuously monitored at a high frequency rate by a standard laboratory capacitance bridge meter. The output voltage of the bridge was fed into a storage cathode-ray oscilloscope and its voltage versus time signals were then analyzed by a computer program. Two ferromagnetic rings, constructed of high-speed steels 4620 and 4340, which have proven applicability for use in magnetoelastic torque sensing, were used as the samples for investigating the magnetostriction effects, while a paramagnetic aluminum ring was used for the control sample. Our study showed that the 4340 ring, which had higher nickel, cobalt, and chromium content than that of the 4620 ring, had the largest magnetostriction effect, and that the aluminum ring displayed no magnetostriction effect, as was expected. We have found this experimental method to be both reproducible and sufficient to rank different ferromagnetic materials by their magnetostriction level, which is a significant consideration in producing effective magnetoelastic torque sensors.
Measurement of debonding in cracked nanocomposite films by ultrasonic force microscopy
Authors: McGuigan A. P. , Huey B. D. , Briggs G. A. D. , Kolosov O. V. , Tsukahara Y. , Yanaka M.
Published: July 2002

This letter reports the application of ultrasonic force microscopy (UFM) to investigate subsurface fracture mechanisms during tensile loading of nanocomposite films consisting of a brittle glass on a ductile polyethylene terephthalate (PET) substrate. Such materials are used in packaging applications where a gas barrier is required to maintain the product quality. Cracking or debonding of the surface glass layer results in destruction of the gas barrier properties of the film. Accurate evaluation of the continuity or discontinuity at the crack edge within the layered material is crucial for the correct characterization of both adhesive failure and crack propagation. Here simultaneous atomic force microscopy and UFM images are compared for a range of tensile strains to identify debonded regions of the glass film from the PET. Debonding occurred for strains greater than 6%. In some films, this debonding increased with applied strain.
Reaction fronts in the oxidation of hydrogen on Pt(111): Scanning tunneling microscopy experiments and reaction–diffusion modeling
Authors: Sachs C. , Hildebrand M. , Völkening S. , Wintterlin J. , Ertl G.
Published: July 2002

Traveling reaction fronts in the oxidation of hydrogen on a Pt(111) surface were investigated by means of scanning tunneling microscopy (STM). The fronts were observed during dosing of the oxygen covered surface with hydrogen at temperatures below 170 K. The fronts represented 10 to 100 nm wide OH-covered regions, separating unreacted O atoms from the reaction product H2O. O atoms were transformed into H2O by the motion of the OH zone. Small scale STM data showed the processes within the fronts on the atomic scale. Experiments on larger scale revealed the velocity and the width of the fronts as a function of temperature. A simple reaction–diffusion model has been constructed, which contains two reaction steps and the surface diffusion of water molecules, and qualitatively reproduces the experimental observations. A lower bound for the front velocity was also derived analytically. For a quantitative comparison between experiment and theory the rate constants of the two reaction steps and the diffusion coefficient of H2O were determined by STM and low energy electron diffraction experiments. With these parameters, the front velocities predicted by the model are approximately one order of magnitude smaller than those determined by STM. The predicted front widths are, depending on the temperature, between two and three orders of magnitude larger than the experimental values. We conclude that these deviations result from the inability of the reaction–diffusion system to describe the complex chemical processes and structure changes within the fronts. The atomically resolved STM data indicate attractive interactions between the particles that in particular affect the diffusion of the H2O molecules.
Stochastic simulations of DNA in flow: Dynamics and the effects of hydrodynamic interactions
Authors: Jendrejack Richard M. , de Pablo Juan J. , Graham Michael D.
Published: July 2002

We present a fully parametrized bead–spring chain model for stained λ-phage DNA. The model accounts for the finite extensibility of the molecule, excluded volume effects, and fluctuating hydrodynamic interactions (HI). Parameters are determined from equilibrium experimental data for 21 μm stained λ-phage DNA, and are shown to quantitatively predict the non-equilibrium behavior of the molecule. The model is then used to predict the equilibrium and nonequilibrium behavior of DNA molecules up to 126 μm. In particular, the HI model gives results that are in quantitative agreement with experimental diffusivity data over a wide range of molecular weights. When the bead friction coefficient is fit to the experimental relaxation time at a particular molecular weight, the stretch in shear and extensional flows is adequately predicted by either a free-draining or HI model at that molecular weight, although the fitted bead friction coefficients for the two models differ significantly. In shear flow, we find two regimes at high shear rate (γ̇) that follow different scaling behavior. In the first, the viscosity and first normal stress coefficient scale roughly as γ̇−6/11 and γ̇−14/11, respectively. At higher shear rates, these become γ̇−2/3 and γ̇−4/3. These regimes are found for both free-draining and HI models and can be understood based on scaling arguments for the diffusion of chain ends.
Ab initio studies on the van der Waals complexes of polycyclic aromatic hydrocarbons. I. Benzene–naphthalene complex
Authors: Lee Nam Ki , Park Soonyong , Kim Seong Keun
Published: July 2002

The stable geometries and binding energies of the benzene–naphthalene complex were studied by the point-by-point method using ab initio calculations at the MP2/6-31G*(0.25) and MP2/6-31+G* levels. Medium-size basis sets were employed not only to save computational time but also to compensate for the tendency of the MP2 method to overestimate the electron correlation energy of aromatic clusters. The use of the 6-31G*(0.25) and 6-31+G* basis sets in the test calculation for the benzene dimer yielded results very similar to those from the CCSD(T) calculation. As for the benzene–naphthalene complex, four stable geometries were found: one parallel-displaced type and three T-shaped ones, with each type similar to the case of the benzene dimer. The global minimum was found to be the parallel-displaced structure whose energy was −4.88 kcal/mol at the MP2/6-31G*(0.25) level and −3.94 kcal/mol at the MP2/6-31+G* level. These values are ∼1.9 times that of the benzene dimer on the same level of calculation. The energy of the most stable T-shaped structure was −4.17 and −3.47 kcal/mol at the MP2/6-31G*(0.25) and MP2/6-31+G* levels, respectively, which are ∼1.8 times that of the corresponding T-shaped structure of the benzene dimer.
Effective thermodynamic elastic constants under finite deformation
Authors: Dunstan D. J. , Bosher S. H. B. , Downes J. R.
Published: July 2002

Nonlinear elasticity is required to account for mechanical and acoustic properties of bodies under finite elastic deformation. R. N. Thurston and K. Brugger gave equations [Phys. Rev. 133, A1604 (1964)] relating experimental acoustic velocities in a strained elastic body to the thermodynamic third-order elastic constants cIJK given in data books. However, no correct and complete set of expressions has been given for the general case, to obtain effective elastic constants from the cIJK to solve mechanical or physical problems. By considering two deformations applied to an elastic body, effective thermodynamic second-order constants cIJ under finite strain are defined thermodynamically and correctly related to the Lagrangian and Eulerian third-order elastic stiffness constants, cIJK.
Temperature dependent structural and transport properties of the type II clathrates A8Na16E136 (A=Cs or Rb and E=Ge or Si)
Authors: Nolas G. S. , Vanderveer D. G. , Wilkinson A. P. , Cohn J. L.
Published: July 2002

Variable temperature single-crystal structure analyses for Cs8Na16Si136, Rb8Na16Si136, Cs8Na16Ge136, and Rb8Na16Ge136 are reported along with electrical and thermal transport measurements on two polycrystalline specimens. The strong temperature dependence of the atomic displacement parameters for the alkali-metal atoms is indicative of significant disorder associated with the “rattling” alkali-metal atoms inside the two different polyhedra (sixteen dodecahedra and eight hexakaidecahedra per cubic unit cell) that makeup the type II clathrate hydrate framework. This disorder can lead to low lattice thermal conductivities. Transport measurements show these compounds to be metallic. The potential of type II clathrates for thermoelectric applications is discussed.
Influence of spatially heterogeneous dynamics on physical aging of polystyrene
Authors: Thurau Courtney T. , Ediger M. D.
Published: July 2002

A photobleaching technique has been used to study the segmental dynamics of a polystyrene melt during isothermal physical aging. Both rotational and translational diffusion measurements of dilute tetracene probes dispersed in the polymer matrix were performed. Following a temperature quench from Tg+2 °C into the glass, either rotational relaxation from an induced anisotropic state or translational diffusion across a holographic grating was measured as a function of aging time. Relaxation times for the two observables evolved by nearly a factor of 10 during isothermal aging, and equilibration times ranged from 103 to 106 s at 98.6 to 95.6 °C. Immediately following the temperature jump, probe rotational diffusion has evolved by over half a decade in response to the quench, while probe translational diffusion has been retarded by only 0.2 decades. At longer elapsed times, for aging at 95.6 °C, the translational observable reaches equilibrium before the rotational observable. These differences in aging behavior indicate that the dynamics responsible for physical aging are spatially heterogeneous, and that regions of different mobility age at different rates. Furthermore, the results suggest that these heterogeneous dynamics could be responsible for causing other observables, such as volume and enthalpy, to equilibrate on different time scales—a phenomenon often associated with physical aging.
Solitary holes of negative energy and their possible role in the nonlinear destabilization of plasmas
Authors: Grießmeier J.-M. , Schamel H.
Published: July 2002

A new energy expression for a one-dimensional structured Vlasov–Poisson system is presented. It admits the existence of negative energy states caused by electrons and ions which resonantly interact with the self-consistently excited hole structure. In contrast to earlier energy expressions making use of resonant particle effects the contributions of trapped particles are taken into account rigorously without any reference to linear wave solutions. The main conclusion drawn for current carrying plasmas is that structured states of negative energy exist for drift velocities in the linearly stable range, which may destabilize the plasma nonlinearly already at infinitesimal amplitudes. Two numerical experiments are reconsidered and it is argued that the observed growth of an initial seed-like perturbation may be related to the concept of negative energy waves and the associated release of free energy.
Multiple-component photoluminescence decay caused by carrier transport in InGaN/GaN multiple quantum wells with indium aggregation structures
Authors: Feng Shih-Wei , Cheng Yung-Chen , Chung Yi-Yin , Yang C. C. , Mao Ming-Hua , Lin Yen-Sheng , Ma Kung-Jeng , Chyi Jen-Inn
Published: July 2002

Based on wavelength-dependent and temperature-varying time-resolved photoluminescence (PL) measurements, the mechanism of carrier transport among different levels of localized states (spatially distributed) in an InGaN/GaN quantum well structure was proposed for interpreting the early-stage fast decay, delayed slow rise, and extended slow decay of PL intensity. The process of carrier transport was enhanced with a certain amount of thermal energy for overcoming potential barriers between spatially distributed potential minimums. With carrier supply in the carrier transport process, the extended PL decay time at wavelengths corresponding to deeply localized states can be as large as 80 ns.
On the local stability of limit cycles
Authors: Ali Fathei , Menzinger Michael
Published: July 2002

Orbital stability of limit cycles is the result of the competing local tendencies of perturbations from the cycle to decay (during phases of local stability) and to grow (during phases of local instability), averaged over a cycle. We examine this coexistence of attractive and repulsive phases on limit cycles, including the local rates of expansion and contraction of phase space volumes. This is done in a frame of reference that moves along the orbit, to partially decouple motions tangential and perpendicular to the cycle. Dynamical systems used for illustration are the generalized Bonhoeffer-van-der-Pol and Rössler models, both far from and near to different types of bifurcations. Finally, it is shown that the nonuniformity of local stability in phase space affects the response of limit cycle oscillators to perturbations and gives rise to their phase-dependent response.
Scalar multipole expansions and their dipole equivalents
Authors: Wikswo John P. , Swinney Kenneth R.
Published: July 2002

If the source of a field that satisfies Poisson’s equation can be written as the divergence of a vector s, then a scalar multipole expansion of the source can be evaluated in terms of s, which is a dipole density. A multipole expansion in terms of the dipole density can be computed about different origins. This allows us to evaluate the expansion of a dipole displaced from the origin and find a method of approximating some multipole expansions by displaced dipoles. In many physical applications it is known that the source is a displaced dipole, and we can find its location from a multipole expansion at some convenient location. It is possible to derive pictures in terms of dipole densities that in the proper limit become the individual multipoles. There are, however, ambiguities in that for some multipoles more than one picture gives the proper field.
Measurements of deep levels in high-purity molecular beam epitaxial GaAs
Authors: DeJule R. Y. , Haase M. A. , Stillman G. E. , Palmateer S. C. , Hwang J. C. M.
Published: July 2002

Constant capacitance deep-level transient spectroscopy measurements are performed on molecular beam epitaxially grown GaAs layers with net carrier concentrations of 3.3–6.5×1014 cm−3. Four trap levels are detected, three of which are usually detected in molecular beam epitaxial layers, and the fourth, a very shallow trap at 30 meV, has not been previously reported. Determination of the concentrations for this new level dispute the accepted interpretation of Hall measurements near and above room temperature.
Effect of annealing on the microstructure of sintered Nd-Fe-B magnets
Authors: Mishra Raja K. , Chen J. K. , Thomas G.
Published: July 2002

A transmission electron microscopy study of sintered Nd-Fe-B magnets after annealing above 650 °C shows the formation of a thin intergranular Nd-rich layer extending to pockets of polycrystalline fcc Nd crystals. The grain boundary phase acts as a pinning site for the magnetic domain walls and is necessary for good magnetic hardening. On the other hand, the Nd1+εFe4B4 phase is an unavoidable product of the sintering process but need not be present for good coercivity.
Ionized impurity scattering in Monte Carlo calculations
Authors: Van de Roer T. G. , Widdershoven F. P.
Published: July 2002

A method to represent the effect of ionized impurity scattering in Monte Carlo calculations is presented. It is based on a model of B. K. Ridley [J. Phys. C 10, 1589 (1977)] and does not have the computational disadvantages of the Brooks–Herring and Conwell–Weisskopf models.
Molecular-beam epitaxy of GaSb/AlSb optical device layers on Si(100)
Authors: Malik R. J. , van der Ziel J. P. , Levine B. F. , Bethea C. G. , Walker J.
Published: July 2002

We report for the first time the growth of GaSb/AlSb multilayers and alloys on Si(100) by molecular-beam epitaxy. High-quality films were achieved in spite of the large lattice constant mismatch of 12%. Room temperature, optically pumped pulsed lasers emitting at 1.8 μm have been demonstrated. Lateral photoconductive detectors with responsivities of 0.18 A/W have also been made. The film nucleation on the Si substrate was observed in situ by reflection high-energy electron diffraction. Characterization of the grown epilayers and preliminary optical device results are described.
Model for ion-assisted thin-film densification
Authors: Müller Karl-Heinz
Published: July 2002

A theoretical model to explain the densification of thin films by ion assistance is described. The model takes advantage of previously developed fast methods for three-dimensional Monte Carlo cascade computations and assumes a low thermal adatom mobility. It is shown that ion incorporation and recoil implantation of surface atoms lead to a film densification slightly below the surface of a growing film and that the density enhancement depends on the ability of vapor atoms to refill surface vacancies which are created by sputtering and driven-in atoms. In particular, the time-dependent mass density profiles evolving during the growth of a 600-eV, oxygen-assisted, vapor-deposited ZrO2 film has been determined and good agreement with experiment is obtained.
Impact of Clarence Zener upon metallurgy
Authors: Hillert Mats
Published: July 2002

A review is given of Clarence Zener’s impact on physical metallurgy, based upon his famous paper on the kinetics of the decomposition of austenite. He demonstrated how basic physical principles could be applied to explain the general features of this complicated reaction. However, his models were general and many of them have been accepted for general use and are still being further developed. Zener also demonstrated the usefulness of simple mathematical treatments based upon dimensional arguments or dilute solution thermodynamics and he thus inspired the following generation of metallurgists to investigate the fundamental principles behind complicated phenomena.
A generalized theory for determining the field-enhanced thermal emission rate by the reverse pulsed deep-level transient spectroscopy
Authors: Choi Ghung G. , Li Sheng S.
Published: July 2002

A generalized theory for determining the field-enhanced thermal emission rates and carrier capture cross section of deep-level defects at very high field and for large trap density by the reverse pulsed deep-level transient spectroscopy technique has been developed in this paper. Using this new theory the field-enhanced emission rates for the DX center in a liquid-phase-epitaxial grown Sn-doped Al0.2Ga0.8As were determined for field strength up to 7×105 V/cm.
A two-dimensional theory for high-frequency vibrations of piezoelectric crystal plates with or without electrodes
Authors: Lee P. C. Y. , Syngellakis S. , Hou J. P.
Published: July 2002

Two-dimensional equations of motion of successively higher-order approximations for piezoelectric crystal plates with triclinic symmetry are deduced from the three-dimensional equations of linear piezoelectricity by expansion in series of trigonometric functions of the thickness coordinate of the plate. These equations, complemented by two additional relations: one, the usual relation of face tractions to the mass of electrodes, and the other relating face charges to face potentials and face displacements, can accommodate either the traction and charge boundary conditions at the faces of the plate without electrodes or the traction and potential boundary conditions at the faces of the plate with electrodes. Dispersion curves are obtained from the first- to fourth-order approximate plate equations for a rotated 45° Y-cut lithium tantalate plate without electrodes, and these curves are compared with those from the frequency equation of the three-dimensional equations with close agreement. Solutions of forced vibrations of an AT-cut quartz plate with electrodes are obtained from the first-order plate equations complemented by the two additional relations. It is shown that cutoff frequencies of the fundamental thickness-shear vibrations from the approximate equations are identical to the ‘‘exact’’ ones obtained from the three-dimensional equations.
Catastrophic breakdown in silicon oxides: The effect of Fe impurities at the SiO2-Si interface
Authors: Honda Kouichirou , Nakanishi Toshirou , Ohsawa Akira , Toyokura Nobuo
Published: July 2002

The behaviors of Fe impurities at the SiO2-Si interface of metal-oxide-semiconductor (MOS) capacitors was studied with electrical measurements and transmission electron microscopy. The MOS capacitors were fabricated on silicon wafers which had been intentionally contaminated by Fe+ ion implantation. It is confirmed that Fe impurities either scattered uniformly, or nucleated at the interface of SiO2-Si. Uniformly scattered Fe impurities lower the barrier height of the SiO2-Si interface. The nucleated Fe precipitates are in a metallic α-FeSi2 phase, penetrating both the silicon oxide and the silicon substrate. They degrade the MOS capacitors not only by reducing the barrier height of the SiO2-Si interface, but also by inducing weak spots in the silicon oxide where the electric field is strengthened and local tunneling currents are enhanced.
The study of charge carrier kinetics in semiconductors by microwave conductivity measurements. II.
Authors: Kunst M. , Beck G.
Published: July 2002

In previous work [J. Appl. Phys. 60, 3558 (1986)] an introduction was given to the study of charge carrier kinetics in semiconductors by microwave conductivity measurements. This paper compares quantitatively our experimental results to theoretical calculations for single-crystalline Si wafers, taking into account the dependence on the microwave frequency and the dark conductivity of the sample, which ranged from σ=0.2 to 400 Ω−1 m−1. In particular, difficulties arising from experimental conditions that cannot easily be treated by theory are discussed. It is shown that quantitative measurements of samples with low dark conductivity can be performed even in a very simple configuration, which permits determination of the sum of charge carrier mobilities.
Ultrasonic measurement of the surface area of porous materials
Authors: Warner K. L. , Beamish J. R.
Published: July 2002

We have developed a technique to measure the amount of gas adsorbed on a porous solid using ultrasonic velocity measurements. This allows us to determine both the specific surface area and the porosity of the material. The technique has several advantages over conventional methods of determining absorption isotherms. No calibrated volumes or delicate balances are needed; the only measurements being of gas pressure and sound velocity. There is no need to know the mass of the sample or the dead volume of its container. Continuous and automatic measurements are possible, both during adsorption and desorption. We have demonstrated the usefulness and accuracy of this technique for two samples with very different surface areas (about 100 and 3 m2/g). In both cases, the results agree well with conventional volumetric measurements.
Shock-induced melting and shear banding in single-crystal NaCl
Authors: Schmitt Douglas R. , Ahrens Thomas J. , Svendsen Bob
Published: July 2002

Radiative color temperatures were measured in single-crystal sodium chloride under shock compression parallel to [100] over a pressure range from 20 to 35 GPa. Color temperatures from 2500 to 4500 K and emittances from 0.003 to 0.3 were determined by fitting observed spectra (450–850 nm) to the Planck greybody radiation law. These data support a heterogeneous shock deformation model of shocked halite in this pressure range. A 2500-K temperature rise, of unknown origin, is observed over the B1–B2 mixed phase region from 25 to 30 GPa. Assuming that shock deformation occurs via yielding in localized planar zones which become melt and the melting temperature at high pressure controls the temperature, we infer that the temperature of the B2 fusion curve from 30 to 35 GPa rises from 3200 to 3300 K. The B1–B2-liquid triple point is predicted to be at a temperature of 2250 K and 23.5 GPa.
Computerized analysis of glow curves from thermally activated processes
Authors: Hoogenboom J. E. , de Vries W. , Dielhof J. B. , Bos A. J. J.
Published: July 2002

A method is presented to analyze complex glow curves composed of several, possibly overlapping, peaks from thermally stimulated processes of general kinetic order and is applicable when the process studied is activated using any arbitrary temperature profile. A theoretical analysis is given to determine the properties of a single glow curve peak. Several new results are presented, among which is an expression for the peak temperature for general kinetic order and temperature profile. From the theoretical analysis of the asymmetry of a glow peak a method is described to determine the kinetic order of a peak and to obtain an initial estimate of the peak parameters sufficiently accurate to start a least-squares minimization procedure to determine the actual parameters of all peaks present in the total glow curve. The method is demonstrated for a synthetic glow curve and for two measured glow curves from a thermoluminescence experiment and a thermal gas desorption experiment.
A clarification of the index of refraction of beta-iron disilicide
Authors: Bost M. C. , Mahan John E.
Published: July 2002

Previously published values of the index of refraction of beta-iron disilicide are corrected. Based on improved measurements and analysis, the undispersed value of the refractive index is 5.6. The previously published analysis of the absorption coefficient showed that the material possesses a direct forbidden energy gap of approximately 0.87 eV. The type of the transition is unchanged, but the band-gap value is slightly shifted to 0.89 eV.
Characterization of yttria-stabilized zirconium oxide buffer layers for high-temperature superconductor thin films
Authors: Lee J-W. , Schlesinger T. E. , Stamper A. K. , Migliuolo M. , Greve D. W. , Laughlin D. E.
Published: July 2002

We have employed transmission electron microscopy and x-ray diffraction to investigate the properties of yttria-stabilized zirconium oxide (YSZ) sputter deposited on silicon. It is shown that the as-deposited YSZ films are polycrystalline (grain size 7–20 nm) with microvoids between grains. Anneals of these films at temperatures of 800, 950, and 1100 °C for 1 h eliminate the microvoids and cause the grain size to increase from 20 to 50 nm at the higher anneal temperatures. Particular texture of the YSZ film is controlled by the details of the deposition conditions. Resistivity measurements of superconducting films deposited on silicon using these buffer layers are also presented.
Theoretical treatment of ferroelectric composites using Monte Carlo calculations
Authors: Pardo L. , Mendiola J. , Alemany C.
Published: July 2002

Measurements of ferroelectric composites made from lead zirconate titauate (PZT) ceramic particles and an epoxy resin as matrix have allowed one to establish the constitutional parameters of the composite that characterize the pyroelectric and piezoelectric properties of these materials. The concept of the degree of heterogeneity is introduced to complete the description of these composites, which do not present a defined connectivity. A model is proposed based on consideration of the randomness of the particle distribution in the matrix by using the Monte Carlo method in the calculation of the active volumetric fraction of ceramic. An equivalent circuit of the composites is used to describe their dielectric properties. The model allows one to estimate the effect of the degree of heterogeneity on the properties of the composite. The results of the calculations compare well with the experimental values. Thus the model opens possibilities for the prediction of the properties and design of two-phase ferroelectric composites made from a randomly disperse phase in a matrix.
Velocity profile on quartz crystals oscillating in liquids
Authors: Martin B. A. , Hager H. E.
Published: July 2002

The particle velocity distribution on the surface of AT-cut quartz crystals oscillating in liquid is investigated. The distribution, amplitude, and direction of surface motion are determined. This study improves the understanding of the oscillation characteristics of quartz crystals in solution.
Electroluminescence of doped organic thin films
Authors: Tang C. W. , VanSlyke S. A. , Chen C. H.
Published: July 2002

Electroluminescent (EL) devices are constructed using multilayer organic thin films. The basic structure consists of a hole-transport layer and a luminescent layer. The hole-transport layer is an amorphous diamine film in which the only mobile carrier is the hole. The luminescent layer consists of a host material, 8-hydroxyquinoline aluminum (Alq), which predominantly transports electrons. High radiance has been achieved at an operating voltage of less than 10 V. By doping the Alq layer with highly fluorescent molecules, the EL efficiency has been improved by about a factor of 2 in comparison with the undoped cell. Representative dopants are coumarins and DCMs. The EL quantum efficiency of the doped system is about 2.5%, photon/electron. The EL colors can be readily tuned from the blue-green to orange-red by a suitable choice of dopants as well as by changing the concentration of the dopant. In the doped system the electron-hole recombination and emission zones can be confined to about 50 Å near the hole-transport interface. In the undoped Alq, the EL emission zone is considerably larger due to exciton diffusion. The multilayer doped EL structure offers a simple means for the direct determination of exciton diffusion length.
Quantitative description of a very high critical current density Nb-Ti superconductor during its final optimization strain. II. Flux pinning mechanisms
Authors: Meingast C. , Larbalestier D. C.
Published: July 2002

Flux pinning by α-Ti precipitates has been studied in a carefully made Nb 48 wt. % Ti composite having very high critical current density and a macroscopically rather uniform precipitate array. The pinning was studied as a function of field (0–15 T) and temperature (2.3 K—Tc) for a ratio of the precipitate thickness (tppt) and the coherence length (ξ) which was varied between 10 and 0.1 by a large drawing strain. Surprisingly, the maximum bulk pinning force (Fp) occurred for tppt/2ξ≂0.1 and a precipitate spacing about one-eighth the fluxon spacing, suggesting that the flux pinning occurs at clusters of precipitates. In contrast to earlier studies, strict temperature scaling of Fp was not observed; the peak of the pinning force shifted to lower reduced fields as the temperature increased. The effect was largest for the finest scale microstructure. This nonscaling is interpreted in terms of two pinning mechanisms having different field and temperature dependencies. At low reduced fields, and at temperatures close to Tc, the core interaction (δHc) dominates. At higher reduced fields and low reduced temperatures, pinning due to variations in κ also contributes to Fp. Clusters of very fine α-Ti ribbon precipitates give rise to these variations in Hc and κ. A comparison of the specific pinning force with the core interaction model was made close to Tc, where the δHc pinning mechanism dominates. Good agreement was obtained for all precipitate thicknesses, indicating that the pinning can be quantitatively described by the core interaction and the direct summation models. No significant proximity effect suppression of the pinning force at fine precipitate dimensions was observed.
Generation, growth, and collapse of vapor bubbles in hydrocarbon liquids under a high divergent electric field
Authors: Kattan R. , Denat A. , Lesaint O.
Published: July 2002

The generation, growth, and collapse of vapor bubbles in purified cyclohexane under a high divergent electric field was studied as a function of hydrostatic pressure (105–1.2×107 Pa). In these experimental conditions a very fast and localized energy injection (10−10–10−8 J) occurs as a consequence of electron avalanches, and the liquid is raised to a supercritical state. Below the critical pressure of the liquid, a vapor bubble is created. In this paper we present a time-resolved optical study of its dynamics which is shown to be controlled by inertial forces. The transition to a streamer phenomenon is also investigated and discussed.
Novel second-order nonlinear optical polymers via chemical cross-linking-induced vitrification under electric field
Authors: Eich Manfred , Reck Bernd , Yoon Do Y. , Willson C. Grant , Bjorklund Gary C.
Published: July 2002

We present a novel method of preparing highly efficient and stable second-order nonlinear optical (NLO) polymers via chemical cross-linking induced vitrification under electric field. In this method a soluble prepolymer is first prepared that contains cross-linking sites attached to the NLO-active groups. Upon preparing samples of desired thicknesses, the prepolymer is heated (precured) to enable some chemical cross-linking and thus to increase the glass transition temperature (Tg) to an optimum for poling. The precured polymer is then heated above its Tg and subjected to a high electric field to obtain the desired alignment of NLO moieties. Subsequent chemical cross-linking (curing) under electric field continues to advance the Tg and hence leads to in situ vitrification of the polymer that stabilizes the electric-field-induced orientation of the NLO moieties. Detailed results of thermal, linear optical, poling kinetics, and NLO properties are described for the polymer system prepared from tetrafunctional 4-nitro 1,2-phenylenediamine and bifunctional Bisphenol-A diglycidylether as the starting monomers. The polymer which has been cured finally at 140 °C under a very high corona field exhibits d33≂14 and d31≂3 pm/V, determined from the Maker-fringe experiments. Most significant, however, is the fact that this polymer shows no detectable decay in second harmonic generation for over 500 h under ambient conditions and no tendency of relaxation even at 85 °C.
Model of plasma immersion ion implantation
Authors: Lieberman M. A.
Published: July 2002

In plasma immersion ion implantation, a target is immersed in a plasma and a series of negative high-voltage pulses are applied to implant plasma ions into the target. We develop an approximate analytical model to determine the time-varying implantation current, the total dose, and the energy distribution of the implanted ions.
Thermal expansion and pressure effect on magnetic transition of Mn2−xCoxSb
Authors: Suzuki T. , Kanomata T. , Yoshida H. , Kaneko T.
Published: July 2002

Pressure dependence of the magnetic phase transition temperatures of Mn1.8Co0.2Sb were obtained by measuring temperature variation of initial permeability at various pressure. Both the transition temperature (Tt) from antiferromagnetic (AF) to ferrimagnetic (FM) states and the Curie temperature (Tc) increase with increasing pressure. Temperature variations of the lattice parameters of the sample were also measured by using the powder x-ray diffraction method. The discontinuous change of a and c axes and the changes of the thermal expansion coefficients were observed at Tt and Tc, respectively. It is found that the negative exchange striction below Tc and the sign of volume change at Tt are consistent with the results of pressure dependence of Tc and Tt. On the basis of these results, the relation between the effects of alloying and of pressure on the magnetic transitions of Mn2−xCoxSb system is discussed.
Interfacial reactions in the Ir/GaAs system
Authors: Schulz K. J. , Musbah O. A. , Chang Y. A.
Published: July 2002

Interfacial reactions between iridium and gallium arsenide in both the thin-film and bulk forms have been investigated in the temperature range 400 to 1000 °C using transmission electron microscopy, energy dispersive x-ray analysis, and electron probe microanalysis. The diffusion path for Ir/GaAs has been determined to be Ir/IrGa/IrAs2 /GaAs and is consistent with the phase diagram between the initial stages of reaction (thin-film) and long-term annealing (bulk). In the thin film case where the Ir supply is limited, the final configuration is Ir3 Ga5/ IrAs2 /GaAs. The diffusion path and reaction morphology has been rationalized using the phase diagram, kinetic observations, and growth mechanisms observed during the reactions.
Theory of magnetic superlattices: Interlayer exchange coupling and magnetoresistance of transition metal structures (invited)
Authors: Levy P. M. , Ounadjela K. , Zhang S. , Wang Y. , Sommers C. B. , Fert A.
Published: July 2002

Theoretical calculations and models to explain two unusual features of Fe/Cr magnetically layered structures are presented: (1) Strong antiferromagnetic (AF) couplings between Fe layers separated by Cr layers have been found in Fe/Cr/Fe sandwiches and Fe/Cr superlattices. These AF couplings are too strong to be accounted for by dipolar interactions and have to be ascribed to exchange interactions through the Cr layers. The interlayer exchange coupling from numerical calculations of the electronic structure of Fe/Cr superlattices based on the local density approximation is derived. (2) Recently, giant magnetoresistance effects have been found in Fe/Cr magnetically layered structures for currents in the plane of the layers. The spin-dependent scattering at the Fe/Cr interfaces that comes from interface roughness, as well as that in the bulk of the layers are considered. The resistivity of these magnetic superlattices are calculated by adapting the quantum treatment of the electrical conductivity of ultrathin metallic films. We find the resistivity when the Fe moments in adjacent layers are parallel and antiparallel, and compare the results with experimental data.
Granular Nix (SiO2)100−x thin films as low temperature thermometers
Authors: Unruh K. M. , Patterson B. M. , Beamish J. R. , Mulders N. , Shah S. I.
Published: July 2002

A series of granular Nix (SiO2)100−x thin films have been prepared by rf sputtering with nickel concentrations between 60 and 90 at. %. The temperature dependence of the resistance is strongly composition dependent. In films with Ni concentrations below 70%, the resistance increases as the temperature decreases, but shows a crossover to a weaker temperature dependence below about 1 K. The magnetoresistance of these materials is small and negative in applied magnetic fields up to 6 T. The temperature dependence of the resistance and the small magnetoresistance indicate that films with Ni concentrations near 66% may be useful for thermometry over a wide range of temperatures.
Use of temporally coincident ultraviolet laser pulses of two different wavelengths to ablate organic polymers
Authors: Srinivasan R. , Braren Bodil
Published: July 2002

The etching of polymethyl methacrylate (PMMA), by pulsed ultraviolet laser radiation [20-ns full width at half maximum (FWHM), 193 nm] can be increased more than threefold by overlapping both spatially and temporally laser pulses of 308 nm (20 ns FWHM) along with the 193 nm pulses. At a constant fluence of 193 nm, increasing the fluence of the 308 nm pulses progressively increases the etch depth/pair of pulses even though the fluence of the 308 nm radiation is kept below the value at which it would etch the polymer by itself at 1 Hz repetition rate. When a time delay of +300 to −400 ns is introduced between the two pulses, the 193 nm pulse being set as time zero, the enhancement due to pairing the pulses is found to be a maximum at nearly total overlap. A similar enhancement in the etching of PMMA by pulsed 248-nm laser radiation can be achieved by mixing 308 nm pulses with the 248 nm, and in the etching of polyethylene terephthalate, by mixing 351-nm laser pulses with 308-nm laser pulses. Chemical analysis of the solid polymeric product from the laser ablation of PMMA by 248 and 308 nm alone, and by a mixture of 248 and 308 nm laser radiation shows that the mixed laser radiation etches in a way that is chemically similar to pulsed 248-nm laser light and the effect can probably be attributed to an enhancement of the photoablation process.
Laser-excited luminescence in Ti-doped MgAl2O4 spinel
Authors: Bausá L. E. , Vergara I. , García-Solé J. , Strek W. , Deren P. J.
Published: July 2002

The photoluminescence (excitation, emission, and fluorescence decay time) spectra of spinel (Ti:MgAl2O4) excited by pulsed Nd:YAG and dye lasers have been systematically investigated. Excitation into the T2g→Eg crystal-field transition of Ti3+ produces a broad infrared emission band at 805 nm which could, in principle, be used for tunable laser applications. Two different Ti3+ centers with lifetimes of 4.2 and 41 μs contribute to this emission. At the same time this IR band can also be observed under high-intensity excitation in the ultraviolet region (266 nm) via a two-photon process.
Implantation and diffusion of noble gas atoms during ion-beam etching of silicon
Authors: Sawyer W. D. , Weber J. , Nabert G. , Schmälzlin J. , Habermeier H.-U.
Published: July 2002

The excessive damage and high defect density generated during ion-beam etching of crystalline Si is characterized by Rutherford backscattering, photoluminescence, and transmission electron microscopy. In samples etched at room temperature, a highly damaged surface layer (d≊5 nm) with a large concentration of noble gas atoms is detected and analyzed using Rutherford backscattering in axial channeling geometry. Point defects due to the low-energy noble gas ion implantation are produced within a depth of 100 nm and deeper, and are monitored by their characteristic photoluminescence. The intensity of the noble-gas-defect photoluminescence is studied for different ion-beam energies (200–2000 eV) and crystal orientations. A threshold to produce the defects can then be determined, leading to an estimate of the number of vacancies contained in the noble gas defect. Annealing of etched samples at 650 °C causes the formation of different new photoluminescent centers. Although little is known about the structure of these defects, it is observed that the defects effectively getter copper. Further annealing of the Ar-etched samples at 1050 °C causes the formation of Ar bubbles with an average diameter of about 5 nm.
Raman spectra of Si-implanted GaSb
Authors: Su Y. K. , Gan K. J. , Hwang J. S. , Tyan S. L.
Published: July 2002

The variations of Raman spectra for Si-implanted (100) GaSb with various doses and energies were investigated. Samples implanted at room temperature showed disorder or amorphous layer. In order to heal the damage layer, furnace annealing as well as rapid thermal annealing were used. We got a better structural recovery with increasing the annealing temperature or time, and rapid thermal annealing showed better results in comparison with conventional furnace annealing. The relative intensities of longitudinal optical phonons from Raman spectra by rapid thermal annealing samples were compared with those of unimplanted GaSb. It is found that a better recovery of damage layer is formed comparable to an unimplanted wafer when the annealing temperature is 600 °C for 30 s.