bluuebunny/crossref_metadata_2025 huggingface dataset:
Electronic continua in time-resolved photoelectron spectroscopy. II. Corresponding ionization correlations
Authors: Schmitt M. , Lochbrunner S. , Shaffer J. P. , Larsen J. J. , Zgierski M. Z. , Stolow Albert
Published: July 2002

We investigate further the role of ion electronic continua in time-resolved photoelectron spectroscopic measurements of ultrafast nonadiabatic coupling. In the preceding paper [Blanchet, Zgierski, and Stolow, J. Chem. Phys. 114, 1194 (2000)], the limiting case of complementary ionization correlations permitted a disentangling of electronic from vibrational dynamics. Here we examine the other limiting case in which the nonadiabatically coupled sates (e.g., S2 and S1) correlations correspond to the same ionic continua, presumably an unfavorable case. We use ultrafast internal conversion in the polyaromatic hydrocarbons phenanthrene and naphthalene as examples. In this situation, the geometry changes (displacements) upon nonadiabatic crossing and upon ionization will strongly affect the ability to disentangle electronic from vibrational dynamics. Particularly, phenanthrene and naphthalene are both very rigid molecules and have small displacements upon internal conversion and ionization, still allowing for direct monitoring of the S2 state internal conversion rate.
High-spatial-resolution semiconductor characterization using a microwave eddy current probe
Authors: Watson C. C. , Chan Winston K.
Published: July 2002

We report on the design and application of a high-resolution microwave eddy current probe that consists of a microfabricated coil with inner and outer widths of 6 and 20 μm, respectively, integrated with a coplanar waveguide. In addition to improved spatial resolution, we implement a stub-matching technique, which enables us to make high-sensitivity measurements. We demonstrate the utility of our device by measuring the minority-carrier lifetime in a thin In0.53Ga0.47As film. Although our present demonstration does not allow us to reuse the sample, with minor changes this technique can be made noncontact and nondestructive.
Effect of membrane bending stiffness on the axisymmetric deformation of capsules in uniaxial extensional flow
Authors: Kwak Sehoon , Pozrikidis C.
Published: July 2002

The effect of interface bending stiffness on the axisymmetric deformation of liquid capsules enclosed by elastic membranes subject to uniaxial extensional flow is considered. Flow-induced deformation causes the development of membrane in-plane elastic tensions and bending moments due to the noninfinitesimal thickness of the membrane or to a preferred equilibrium configuration of an interfacial molecular network, accompanied by transverse shear tensions. The elastic tensions are related to the surface deformation by means of Mooney’s linear constitutive law for thin elastic sheets, and the bending moments are related to the membrane resting shape and to the instantaneous principal curvatures by means of constitutive equations. Interfacial force and torque balances are used to relate the jump in hydrodynamic traction across the interface to the elastic tensions and bending moments. A numerical procedure is implemented for simulating the capsule deformation in uniaxial extensional Stokes flow based on a boundary-integral method. Results on the transient and asymptotic deformation for capsules with spherical unstressed shapes illustrate the effect of bending stiffness expressed by an interface modulus of bending for a broad range of elasticity capillary numbers. It is shown that bending stiffness, however large, is not able to restrain continued deformation beyond a critical capillary number, and its main effect is to cause highly deformed capsules with pointed shapes to develop instead nearly cylindrical shapes with rounded caps.
Lattice softening and failure in severely deformed molecular crystals
Authors: Coffey C. S. , Sharma J.
Published: July 2002

Atomic force microscope observations have revealed the presence of permanent lattice and molecular distortions in molecular crystals that had undergone plastic deformation by shock or impact. These distortions have led to the suggestion of a deformed lattice potential. Here, the deformed lattice potential is extended to the case of severe plastic deformation in which the lattice softens and may eventually fail. This generalized lattice potential has been incorporated into descriptions of plastic flow and the associated energy dissipation due to dislocation motion by quantum tunneling. The resultant predictions are compared with experiments in which molecular crystals were subjected to severe plastic deformation during impact.
Long-range coupling interactions in ferroelectric sandwich structures
Authors: Shen Jian , Ma Yu-qiang
Published: July 2002

We study the ferroelectric system consisting of the sandwich structure (PbTiO3/BaTiO3/PbTiO3) by using the Ginzburg–Landau phenomenological theory, and emphasize the importance of the long-range coupling interaction to the ferroelectric behavior of the system. We find that after introducing the long-range coupling interaction to the ferroelectric behavior of the sandwich system, the average spontaneous polarization of the interlayer (BaTiO3) increases and a size-driven phase transition disappears. The larger the range of the long-range coupling, the larger the average spontaneous polarization. When the range of the long-range coupling is large enough, the average spontaneous polarization increases gradually with decreasing interlayer thickness, reaches one maximum at a certain finite thickness, and then decreases. The spatial distribution profile of the spontaneous polarization on the range of the coupling interaction for different values of the interlayer thickness is obtained, and the dependence of the averaged polarization on temperature is also examined.
A tutorial on the basic principles of microwave reflectometry applied to fluctuation measurements in fusion plasmas
Authors: Nazikian R. , Kramer G. J. , Valeo E.
Published: July 2002

Microwave reflectometry is now routinely used for probing the structure of magnetohydrodynamic and turbulent fluctuations in fusion plasmas. Conditions specific to the core of tokamak plasmas, such as small amplitude of density irregularities and the uniformity of the background plasma, have enabled progress in the quantitative interpretation of reflectometer signals. In particular the extent of applicability of the one-dimensional (1-D) geometric optics description of the reflected field is investigated by direct comparison to 1-D full wave analysis. Significant advances in laboratory experiments are discussed which are paving the way toward a thorough understanding of this important measurement technique. Data are presented from the Tokamak Fusion Test Reactor [R. Hawryluk, Plasma Phys. Controlled Fusion 33, 1509 (1991)] identifying the validity of the geometric optics description of the scattered field and demonstrating the feasibility of imaging turbulent fluctuations in fusion scale devices.
Micro-optical nonlinearity of a silver oxide layer
Authors: Fukaya Toshio , Büchel Dorothea , Shinbori Shunichiro , Tominaga Junji , Atoda Nobufumi , Tsai Din Ping , Lin Wei Chi
Published: July 2002

We studied the near-field formation mechanism of a silver oxide thin film sandwiched between protective layers using a pump probe with nanosecond laser pulse irradiation and tapping-mode tuning-fork near-field scanning optical microscopy. A multilayer composed of ZnS–SiO2/Ag2O/ZnS–SiO2 showed abnormal optical nonlinear properties compared to ordinary third-order nonlinear materials. The Ag2O layer played a role in generating a strong light scattering center in a reversible chemical reaction in only a small area of the multilayer, and the optical near field produced about the scattering center was 40 times stronger than that produced by an antimony layer instead of Ag2O.
Hydrogen-encapsulated impurity pellet injector for plasma diagnostics
Authors: Viniar I. , Reznichenko P. , Lukin A. , Umov A. , Sudo S.
Published: July 2002

A novel technology is suggested for making solid hydrogen shells around impurity pellets to be injected into plasmas of fusion devices with a view to looking into its transport properties. In proof-of-principle tests, a 3 mm long and 3 mm diameter cylindrical solid hydrogen shell was formed around a 0.2 mm diameter globular pellet at a temperature of 8–11 K within 5 min and accelerated in a pipe-gun barrel up to 1 km/s.
Effects of thermal and hydrogen treatment on indium segregation in InGaN/GaN multiple quantum wells
Authors: Moon Yong-Tae , Kim Dong-Joon , Song Keun-Man , Choi Chel-Jong , Han Sang-Heon , Seong Tae-Yeon , Park Seong-Ju
Published: July 2002

The effects of indium segregation and hydrogen on the optical and structural properties of InGaN/GaN multiple quantum wells, grown by metalorganic chemical vapor deposition were investigated. Photoluminescence and high-resolution transmission electron microscopy analysis showed that two types of indium-rich regions can be formed in the InGaN well layers. Self-assembled quantum dot-like indium-rich regions were found in the well layer grown at a normal growth temperature. These regions behaved as luminescent centers, showing a maximum indium content at the center of indium-rich region. However, randomly-distributed indium-segregated regions, which formed near the upper interface of the InGaN well layers during the subsequent high-temperature annealing process led to the degradation of the optical properties by generating defects such as misfit dislocations. The use of hydrogen during the growth interruption was found to be very effective in suppressing the formation of indium-segregated regions in the InGaN well layers.
Hydrogen induced positive charge generation in gate oxides
Authors: Zhang J. F. , Zhao C. Z. , Groeseneken G. , Degraeve R. , Ellis J. N. , Beech C. D.
Published: July 2002

This article investigates the H2-anneal induced positive charge generation in the gate oxide of metal-oxide-semiconductor field-effect transistors fabricated by a submicron complementary metal-oxide-semiconductor process. A significant number (∼1012 cm−2) of fixed and mobile positive charges are generated at 450 °C. Properties (reactivity, electrical and thermal stability) of these positive charges are compared with the positive charges observed in the buried oxide of silicon-on-insulator devices. The differences in these two are investigated, in terms of their transportation time across the oxide, uniformity and sources of hydrogen. Attention is paid to the role played by boron in the generation and the possible connection between the positive species observed here and the defects responsible for the positive bias temperature instability. Efforts are made to explain the difference in reactivity between the H2-anneal induced positive species and the hydrogenous species released by irradiation or electrical stresses.
Spiral wave drift induced by stimulating wave trains
Authors: Gottwald Georg , Pumir Alain , Krinsky Valentin
Published: July 2002

We investigate the drift of a spiral wave core in a homogeneous excitable medium under the influence of a periodic stimulation by wave trains close to the core. Two important results were found. First, as opposed to existing theories of spiral wave drift, we observe drift induced by wave trains with periods larger than the period of the freely rotating spiral wave. Second, when investigating the drift of meandering spirals we found that the property of meandering of spirals is not robust against periodic stimulations. Simple phenomenological arguments are provided to explain these observations.
Micromagnetic simulations of magnetostatically coupled Nickel nanowires
Authors: Hertel Riccardo
Published: July 2002

Magnetic structures and magnetization processes in arrays of closely packed Ni nanowires (length l=1 μm, diameter d=40 nm, and period: 100 nm) are investigated by means of micromagnetic modelling. The simulations are performed with an algorithm based on the finite element method combined with the boundary element method which allows for the accurate calculation of magnetostatic interactions. Magnetization states of Ni nanowires at zero field are calculated. Only few, simple magnetization configurations result to be stable. Transient states of the magnetization indicate that magnetization reversal occurs by means of nucleation at the ends of the particles and subsequent soliton propagation. Hysteresis loops of up to 16 interacting nanowires are simulated. It turns out that magnetostatic interactions between the wires have a significant influence on the switching field.
Emission spectra and trends for 4fn−15d↔4fn transitions of lanthanide ions: Experiment and theory
Authors: van Pieterson L. , Wegh R. T. , Meijerink A. , Reid M. F.
Published: July 2002

Luminescence spectra of 4fn↔4fn−15d transitions of lanthanide ions in LiYF4 are reported. Some interesting trends are observed. Lifetime measurements for the spin allowed fd emission show that the electric dipole matrix element for the fd transition decreases through the lanthanide series. Also the splitting between the high spin and low spin fd states decreases through the lanthanide series. Both effects are reproduced by calculations using a theoretical model that extends established models for the 4fn configuration by including crystal field and spin–orbit interactions for the 5d electron and the Coulomb interaction between the 4f and 5d electrons.
Dynamics of droplet rebound from a weakly deformable gas–liquid interface
Authors: Gopinath Arvind , Koch Donald L.
Published: July 2002

A droplet of radius a moves with kinetic energy 2πρdUc′2a3/3 in an incompressible, continuum ambient gas and rebounds from an initially planar, weakly deformable interface bounding a half-space of liquid. We study the rebound process in the limit Wed≡ρdUc′2a/σ≪1, where σ is the surface tension of the two liquid–gas interfaces and ρd is the density of the fluid comprising the drop and the planar half-space. When viscous dissipation in both the ambient gas and in the drop is negligible, the flow inside the drop is inviscid and driven by the deformation of the near contact dimple region. The dimple region is approximated as a section of a sphere of radius 2a. Analysis of the motion induced in the liquid phase, coupled with a physically appropriate description of the interfaces, provides a theoretical description of the deformation and flow modes that ensue. Analytical predictions based on a singular perturbation analysis valid in the limit ln(Wed−1/4)≫1 indicate that the time taken by the drop to complete a bounce is aWed1/2Uc′−1π(4/3)1/2 ln1/2(Wed−1/4) and the angular extent of the near contact region which undergoes strong deformation is (4Wedln−1(Wed−1/4)/3)1/4. The asymptotes are compared to numerical solutions to the full governing equations.
Attoliter fluid experiments in individual closed-end carbon nanotubes: Liquid film and fluid interface dynamics
Authors: Megaridis Constantine M. , Güvenç Yazicioglu Almila , Libera Joseph A. , Gogotsi Yury
Published: July 2002

A hydrothermal method of catalytic nanotube synthesis has been shown to produce high-aspect-ratio, multiwall, capped carbon nanotubes, which are hollow and contain a high-pressure encapsulated aqueous multicomponent fluid displaying clearly segregated liquid and gas by means of well-defined curved menisci. Thermal experiments are performed using electron irradiation as a means of heating the contents of individual nanotubes in the high vacuum of a transmission electron microscope (TEM). The experiments clearly demonstrate that TEM can be used to resolve fluid interface motion in nanochannels. Good wettability of the inner carbon walls by the water-based fluid is shown. Fully reversible interface dynamic phenomena are visualized, and an attempt is made to explain the origin of this fine-scale motion. Experimental evidence is presented of nanometer-scale liquid films rapidly moving fluid along the nanochannel walls with velocities 0.5 μm/s or higher.
Oxide phase determination in silicon using infrared spectroscopy and transmission electron microscopy techniques
Authors: Gryse O. De , Clauws P. , Van Landuyt J. , Lebedev O. , Claeys C. , Simoen E. , Vanhellemont J.
Published: July 2002

Infrared absorption spectra of polyhedral and platelet oxygen precipitates in silicon are analyzed using a modified Day–Thorpe approach [J. Phys.: Condens. Matter 11, 2551 (1999)]. The aspect ratio of the precipitates is determined by transmission electron microscopy analysis. The reduced spectral function and the stoichiometry of the precipitate are extracted from the absorption spectra and the amount of precipitated interstitial oxygen. The experimental absorption spectra can be divided in a set with a Fröhlich frequency of around 1100 cm−1 and in a set with a Fröhlich frequency between 1110 and 1120 cm−1. It is shown that the shift in the Fröhlich frequency is not due to a differing stoichiometry, but to the detailed structure of the reduced spectral function. Inverse modeling of the spectra suggests that the oxide precipitates consist of substoichiometric SiOγ with γ=1.17±0.14.
Magnetic screw rod using dual state 0.6C–13Cr–Fe bulk magnetic material
Authors: Mita Masahiro , Hirao Noriyoshi , Kimura Fumio
Published: July 2002

A magnetic screw rod that can replace a mechanical ball screw has been successfully fabricated. This type of device provides linear motion from a rotating motor. The magnetic screw rod is made from dual state 0.6C–13Cr–Fe bulk magnetic rod stock. The material, originally soft magnetically, can be heat treated to obtain a nonmagnetic region which substitutes for the groove of a conventional magnetic screw rod. This method produces a magnetic screw rod with a smooth, round outer shape and a longer, cleaner operational life. This experiment successfully yielded a 300 mm long, 25 mm diameter magnetic rod with 10 mm pitch, 4 mm width, 4 mm depth spiral nonmagnetic region.
Three-dimensional optical memory with rewriteable and ultrahigh density using the valence-state change of samarium ions
Authors: Miura K. , Qiu Jianrong , Fujiwara S. , Sakaguchi S. , Hirao K.
Published: July 2002

We report the recording, readout, and erasure of a three-dimensional optical memory using the valence-state change of samarium ions to represent a bit. A photoreduction bit of 200 nm diam can be recorded with a femtosecond laser and readout clearly by detecting the fluorescence as a signal (excitation at 488 nm, 0.5 mW Ar+ laser). A photoreduction bit that is stable at room temperature can be erased by photo-oxidation with a cw laser (514.5 nm, 10 mW Ar+ laser). Since photoreduction bits can be spaced 150 nm apart in a layer within glass, a multilayer structure with several hundred layers could be used to record data. A memory capacity of as high as 1 Tbit could thus be achieved in a glass piece with dimensions of 10 mm×10 mm×1 mm.
Nanostructured CdS prepared on porous silicon substrate: Structure, electronic, and optical properties
Authors: Zhang P. , Kim P. S. , Sham T. K.
Published: July 2002

Nanostructured CdS was deposited electrochemically on porous silicon (PS) substrate/cathode. The PS-supported CdS deposits were found to be uniformly packed particles of ∼100 nm, each of which is an aggregate of smaller clusters of several nanometers as revealed by scanning electron microscope and confirmed by glancing incidence x-ray powder diffraction. No significant CdS deposition into the pore of porous silicon is found under the reported experimental conditions. X-ray absorption fine structures (XAFS), both extended x-ray absorption fine structure and x-ray absorption near edge structures, across the S and the Si K edge of the samples have been investigated. The structure and electronic properties of the CdS/PS composite are discussed on the basis of the XAFS results obtained using multichannel detection (total electron and x-ray fluorescence yields) from a series of CdS and PS samples. The optical luminescence behavior of CdS/PS was also investigated utilizing a technique often referred to as synchrotron x-ray excited optical luminescence (XEOL). By selecting excitation photon energies near the Si and the S K edge, the luminescence originated from both CdS and PS can be distinguished in the XEOL spectra.
Enhanced tunneling across nanometer-scale metal–semiconductor interfaces
Authors: Smit G. D. J. , Rogge S. , Klapwijk T. M.
Published: July 2002

We have measured electrical transport across epitaxial, nanometer-sized metal–semiconductor interfaces by contacting CoSi2 islands grown on Si(111) with the tip of a scanning tunneling microscope. The conductance per unit area was found to increase with decreasing diode area. Indeed, the zero-bias conductance was found to be ∼104 times larger than expected from downscaling a conventional diode. These observations are explained by a model, which predicts a narrower barrier for small diodes and, therefore, a greatly increased contribution of tunneling to the electrical transport.
Controllable alignment of nematic liquid crystals around microscopic posts: Stabilization of multiple states
Authors: Kitson Stephen , Geisow Adrian
Published: July 2002

Nematic liquid crystal materials are rod-like molecules that align in a locally common direction called the director. This gives rise to anisotropic properties that are used in electro-optical devices such as displays, which usually consist of a sandwich of material between two substrates. The behavior of the director at the substrate surfaces is a critical design consideration, and a wide variety of surface treatments has been reported. Most are dominated by molecular interactions, e.g., high surface energy materials that give homogeneous alignment (the director parallel to substrate). The elastic properties of nematics can also be used to influence alignment by shaping the surface on the micron scale. The potential that this offers to engineer device properties is relatively unexplored; to date, the majority of results reported concentrate on essentially two-dimensional effects. Here we show that the three-dimensional configuration of nematics around microscopic posts results in multiple stable director orientations, and can be used in particular to implement bistable displays with a broad range of control over the optical and switching properties.
Teaching Feynman’s sum-over-paths quantum theory
Authors: Taylor Edwin F. , Vokos Stamatis , O’Meara John M. , Thornber Nora S.
Published: July 2002

We outline an introduction to quantum mechanics based on the sum-over-paths method originated by Richard P. Feynman. Students use software with a graphics interface to model sums associated with multiple paths for photons and electrons, leading to the concepts of electron wavefunction, the propagator, bound states, and stationary states. Material in the first portion of this outline has been tried with an audience of high-school science teachers. These students were enthusiastic about the treatment, and we feel that it has promise for the education of physicists and other scientists, as well as for distribution to a wider audience. © 1998 American Institute of Physics.
Hydrogenated amorphous silicon position sensitive detector
Authors: Arimoto Satoshi , Yamamoto Hidekazu , Ohno Hideo , Hasegawa Hideki
Published: July 2002

The design, fabrication, and characterization of newly developed hydrogenated amorphous silicon position sensitive detectors (a-Si:H PSDs) which employ a tunnel metal-insulator-semiconductor (MIS) structure fabricated by anodic oxidation processes are described. Tunnel MIS structure is chosen as the a-Si:H PSD structure, since it offers high breakdown voltage compared to a-Si:H pin or Schottky-type structures. PSD process includes two-step anodic oxidation of a-Si:H: (1) oxidation in the dark to passivate defects and shunt paths introduced during the growth of a-Si:H layer and (2) oxidation with light to grow thin native oxide to provide barrier between metal and a-Si:H. The fabricated large-area, two-dimensional PSDs, as large as 3 cm×3 cm, show the incident beam position within error of less than 2% of the length of PSD.
Two-beam coupling in photorefractive Bi12SiO20 crystals with moving grating: Theory and experiments
Authors: Refregier Ph. , Solymar L. , Rajbenbach H. , Huignard J. P.
Published: July 2002

Large values of the exponential gain coefficient Γ are obtained (Γ≂8–12 cm−1) when recording with a moving grating in photorefractive BSO crystals (nearly degenerate two-wave mixing; drift recording mode). The resolution of the Kukhtarev’s equations with a moving grating shows a resonance effect which at the optimum velocity makes the modulation of the photoinduced space charge field Esc higher. An optimum of the grating spacing also exists: Λopt:2π(E0/NA)(με/eγR)1/2. In such conditions, the space charge field is phase shifted by π/2 with respect to the incident fringe pattern; this allows an efficient beam coupling between the two recording beams. The dependence of the gain Γ versus the incident beam ratio β of the two interfering waves is interpreted by including the second-order term in the Fourier development of Esc. The conditions allowing one to obtain a reasonable agreement between the theory and experiments are presented and discussed, as well as the adopted values of the crystals’ parameters.
Preparation of amorphous Ti1−xCux (0.10<x≤0.87) by mechanical alloying
Authors: Politis C. , Johnson W. L.
Published: July 2002

We show that amorphous alloy powders of Cu and Ti can be produced over a broad composition range by mechanical alloying of the elemental powders in a high-energy ball mill. The amorphous powders are compared with liquid-quenched amorphous alloys of the same compositions using the techniques of x-ray diffraction and thermal analysis of crystallization. The two types of samples are found to have similar characteristics. Chemical analysis shows that only trace amounts of impurities are introduced in the alloys by the milling process.
Formation of PtSi in the presence of Al
Authors: Chang Chin-An
Published: July 2002

The formation of Pt silicides in the presence of Al is studied using Al/Pt/Si structures with different layer thicknesses of Al. Both the Pt-Si and Pt-Al reactions take place simultaneously, starting around 200 °C, with the formation of PtSi and PtAl2 completed at 400 °C. With an equal layer thickness for all three layers, the two alloys formed stay in contact with each other in a stable form up to about 500 °C. With a layer thickness of Al twice or more that of Pt and Si, the PtSi layer is completely converted to PtAl2 at 450 °C. The released Si from such a reaction is mostly located under the PtAl2 formed. The relation between these results and the unstable PtSi/Al contact in devices is discussed.
Experimental analysis of Ag+-Na+ exchange in glass with Ag film ion sources for planar optical waveguide fabrication
Authors: Honkanen S. , Tervonen A.
Published: July 2002

A detailed experimental analysis of Ag+-Na+ ion exchange in glass using Ag films as ion sources for the fabrication of planar optical waveguides has been performed. The refractive index profiles of the waveguides have been measured and compared to the theoretical Ag+ concentration profiles. The theoretically predicted special characteristics of the process are verified and the material parameters of the used substrate glass (Corning 0211) are evaluated.
Bonding structure of silicon oxide films
Authors: Feldman Albert , Sun Y. N. , Farabaugh E. N.
Published: July 2002

X-ray photoelectron spectroscopy measurements of the O 1s and Si 2p lines in films of the SiOx system have been interpreted on the basis of continuous random network models. Fitting of the spectra to five lines corresponding to five silicon centered tetrahedral configuration yields the relative proportion of each configuration as a function of x. The distributions agree neither with the random mixture model nor with the random bond model (RBM). The total oxygen in the films exceeds the amount of oxygen in the tetrahedral structures indicating the presence of molecular oxygen, water, peroxy bonding, or other forms of oxygen not bonded to silicon. The general features of the distributions can be explained on the basis of silicon clusters, nonbridging oxygen, and the RBM. This conclusion implies that reactive evaporation with oxygen may result in material that is not as fully oxidized as might be expected on the basis of the oxygen content of the film.
Deuterium interactions with ion-implanted oxygen in aluminum
Authors: Myers S. M. , Follstaedt D. M.
Published: July 2002

The trapping of deuterium (D) by ion-implanted oxygen in aluminum was characterized through temperature-ramp experiments which utilized nuclear-reaction profiling. In the presence of γ-Al2O3 precipitates produced by post-implantation annealing at 823 K, two trapping processes were identified: the first, with a binding enthalpy of 0.7 eV relative to D in solution, is attributed to the formation of molecular D2 at the precipitate boundaries; the second process, which exhibits a range of binding enthalpies above 1 eV, is believed to reflect the formation of chemical bonds at oxide defects. These two trapping effects were also observed in the absence of precipitation annealing, but with different saturation concentrations; their occurrence here may reflect O clustering during the room-temperature implantation of O. It is argued that the trapping mechanisms identified in this work may be widely encountered in metals and alloys containing O, with potentially important technological consequences.
Piezo-Hall coefficients of n-type silicon
Authors: Hälg B.
Published: July 2002

The effect of uniaxial mechanical stress on the Hall coefficient of n-type silicon has been measured for various crystallographic orientations, and piezo-Hall coefficients P12 and P11-P44 have been derived for electron concentrations n between 1014 and 1016 cm−3 and temperatures ranging from −80 to +100 °C. In this range the piezo-Hall effect is found to be as important as the piezoresistance effect which is understood in terms of the many-valley band structure of silicon with anisotropic energy minima. For Hall plates in the (100) and the (110) plane of silicon the resulting longitudinal and transverse piezo-Hall coefficients at room temperature are plotted as a function of their orientation in the plane. It turns out that the piezo-Hall as well as the piezoresistance effects are minimized for a Hall plate in the (110) plane with the current flow roughly parallel to 〈11̄1〉.
Crystallographic structure and magnetism of Co-Pd and Co-Pt films with an artificially layered structure
Authors: Sato Noboru
Published: July 2002

Cobalt-noble metal (Co-NM, NM; Pd and Pt) thin films deposited in an alternating multilayer structure by the magnetron dc-sputtering method have an artificial superlattice structure, where Co and NM grow epitaxially on the closest planes of them and a compositionally sharp interface is fabricated. Films with a small periodicity have either a hexagonal closed pack (hcp) structure with the c axis normal to the film plane or a face centered cubic structure (fcc) with the 〈111〉 axis normal to the film plane, depending on the thickness ratio of Co and NM layers. A long-range crystalline order is hardly maintained due to generation of the crystalline phases of Co and NM in films with a large periodicity. The artificial superlattice structure of the films is thermally stable to temperatures up to 500 °C. Many films are ferromagnetic with an easy magnetization direction in the film plane. The perpendicular magnetization hysteresis loop with the coercivities smaller than 1 kOe was obtained in both the Co-Pd films with a Co layer (less than 10 Å) thinner than a Pd layer and the Co-Pt films with a Co layer (less than 15 Å) thinner than a Pt layer. Pd atoms at the interface in the Co-Pd film show the ferromagnetism with an induced magnetization of about 300 G, 0.5 μB per Pd atom.
Free-carrier lifetime and deep-level luminescence in semi-insulating GaAs: The influence of indium doping and growth in a magnetic field
Authors: Leo K. , Rühle W. W. , Nordberg P. , Fujii T.
Published: July 2002

The influence of In doping and/or of growth in a magnetic field on the properties of Czochralski-grown semi-insulating GaAs wafers is investigated. We determine the spatial distribution of the free-carrier lifetime by time-resolved luminescence in the ps regime. The results are compared with the spatial distribution of the near-band-edge and deep-level luminescence. The macroscopical and microscopical homogeneity of the carrier lifetime and the luminescence intensities are improved by the growth in a magnetic field. Indium doping leads to similar improvements and additionally to an increase of the absolute value of the lifetime. The combination of In doping and growth in a magnetic field gives the best results.
Optical properties of electrochromic vanadium pentoxide
Authors: Cogan Stuart F. , Nguyen Nguyet M. , Perrotti Stephen J. , Rauh R. David
Published: July 2002

Electrochemical and spectroscopic measurements were used to characterize the electrochromic behavior of sputtered V2O5 films. In response to lithium intercalation, the fundamental optical absorption edge of V2O5 shifts to high energies by 0.20–0.31 eV as the lithium concentration increases from Li0.0V2O5 to Li0.86V2O5. There is a corresponding increase in the near-infrared absorption that exhibits Beer’s law behavior at low lithium concentrations. The shift in absorption edge results in a large decrease in absorbance in the 350–450 nm wavelength range. This effect is most prevalent in thin films which exhibit a yellow to colorless optical modulation on lithium intercalation. The cathodic coloration in the near infrared is relatively weak with a maximum coloration efficiency of 35 cm2/C.
Monte Carlo simulation of energy dissipation in electron beam lithography including secondary electron generation
Authors: Lee Kang-Yoon , Cho Guang-Sup , Choi Duk-In
Published: July 2002

A new Monte Carlo simulation including secondary electron generation has been performed to study energy dissipation in electron beam lithography. The simulation of inelastic scattering is calculated from the model of the generalized oscillator strength density distribution determined by a set of resonance energies and oscillator strengths. Varying the polymethylmethacrylate film thickness, the energy dissipation profiles for various electron beam energies are evaluated. The effects of backscattered electrons from the silicon substrate and secondary electrons are studied with respect to film thicknesses and electron beam energies. The backscattered electrons from the Si substrate broaden the profile, especially near the bottom layer, and the secondary electrons broaden the profiles over the whole film.
Theoretical and experimental aspects of the thermal dependence of electron capture coefficients
Authors: Goguenheim Didier , Lannoo Michel
Published: July 2002

The thermal activation of the capture coefficient c is very often treated in a semiclassical way, resulting from a simple energy barrier. Experimentally, this activation energy Eb is said to be the slope of ln[c(T)] vs 1/T kT. Unfortunately, many experimental evidences deny this analysis and suggest that a single energy barrier is not enough to reproduce the physical behavior of a point defect. Here we propose a more complete approach to the problem of nonradiative carrier capture assisted by phonons, which is based on a less restrictive hypothesis and leads to a compact formulation of the capture coefficient. This formula reproduces the previous asymptotic forms at high temperature in the strong coupling limit, but remains valid over the whole temperature range and for any strength of the coupling between the lattice and the defect. This point is illustrated for typical cases and the accuracy of the new formula is shown in the case of the so-called B level in GaAs, whose capture coefficient does exhibit a nonexponential behavior with temperature. Our wish is to put the theoretical point of view previously developed by Passler under a form allowing more extensive use in order to extract physical parameters from the experimental c(T) curves with better accuracy.
rf modulation of positive-ion energies in low-pressure discharges
Authors: Ingram S. G. , Braithwaite N. St. J.
Published: July 2002

In this work a filament-assisted dc argon discharge is generated between parallel electrodes. A rf signal (<13.56 MHz) is applied to one electrode in order to modulate the plasma potential. The degree of modulation is monitored using an emissive Langmuir probe. The velocity distribution of ions arriving at the earthed electrode is observed to respond to the rf modulation of the local space potential, the effect diminishing as the rf frequency is increased above the ion plasma frequency. A model is developed to describe the behavior of the ions to the rf modulation of the space potential. Good agreement between the simulation and experimental results is observed. The modulation of ion velocities by nonsinusoidal potentials is briefly examined.
Calibration of Sm:YAG as an alternate high-pressure scale
Authors: Bi Q. , Brown J. M. , Sato-Sorensen Y.
Published: July 2002

The pressure-induced wavelength shift of a laser-excited fluorescence in samarium-doped yttrium aluminum garnet (Sm:YAG) was compared with that of ruby to 26 GPa at room temperature. Because the fluorescence wavelength for Sm:YAG has a negligible temperature dependence, it provides a better pressure scale for diamond anvil cell applications than ruby under high-temperature conditions. However, the overall intensity of the Sm:YAG fluorescence is less than that for ruby. A Gaussian–Lorentzian profile was chosen to analyze the fluorescence spectra. The Sm:YAG fluorescence wavelength exhibits an approximately linear pressure dependence (3.07±0.45 Å/GPa) only to 20 GPa at room temperature. A polynomial fit for all data to 26 GPa gives P(GPa)=−10 280(λ/λ0−1)2 +2085(λ/λ0−1), with a rms misfit of 0.14 GPa.
Formation of amorphous Ti-Fe alloys by mechanical alloying
Authors: Chu B.-L. , Lee S.-M. , Perng T.-P.
Published: July 2002

Three amorphous alloy powders in the Ti-Fe system with the ratios of Ti:Fe at 1:2, 1:1, and 2:1 were prepared by mechanical alloying of the elemental powders in a high-energy ball mill. The amorphous powders were characterized by x-ray diffraction and high-resolution transmission electron microscopy. A complete amorphization of Ti1Fe1 was achieved, whereas a remaining crystalline portion besides the amorphous phase was present in Ti2Fe1 and Ti1Fe2. The crystallization temperatures for these alloys detected by differential scanning calorimetry varied from 714 to 791 K, which were corresponding to half of their melting points.
Stress-induced nucleation of voids in narrow aluminum-based metallizations on silicon substrates
Authors: Korhonen M. A. , LaFontaine W. R. , Bo/rgesen P. , Li Che-Yu
Published: July 2002

This work investigates thermal stress-induced voiding, and void nucleation in particular, in narrow, passivated aluminum-based metallizations on silicon substrates. After excursions to a higher temperature, the thermal stress is tensile, and increases during cooldown to room temperature, after which it relaxes with time. Experiments conducted on two aluminum alloy metallizations suggest that stress-induced void nucleation is a one shot phenomenon during cooldown from the heat treatment temperature. Further, the high thermal stresses present, and the strong constraints against deformation provided by the substrate and passivation layer, make void nucleation unique in narrow passivated metallizations. Finally, voids always appear to be connected to grain boundaries. The above experimental evidence and theoretical considerations together suggest that grain boundary sliding is the main mechanism facilitating void nucleation in passivated aluminum alloy metallizations.
Current-stress induced asymmetry in hydrogenated amorphous silicon n-i-n devices
Authors: Nieuwesteeg K. J. B. M. , Boogaard J. , Oversluizen G. , Powell M. J.
Published: July 2002

A novel manifestation of carrier induced degradation of α-Si:H is presented. Amorphous silicon n-i-n devices, which have been subjected to severe constant-current bias stress, show a strongly decreased ohmic conductivity. At the same time, the J–V characteristics in the space-charge limited regime show pronounced asymmetry between the ‘‘forward’’ and ‘‘reverse’’ directions. Annealing the devices, without bias, restores the initial symmetrical characteristics. The decrease in the ohmic conductivity is interpreted as due to an increased density of deep (dangling bond) states in the lower part of the band gap within the i layer, resulting from the thermal equilibration with an increased density of trapped electrons in the conduction band tails. The asymmetry in the J–V characteristics is due to the formation of a spatially inhomogeneous distribution of dangling bond states in the upper half of the gap, induced by the thermal re-equilibration to an inhomogeneous distribution of holes in the valence-band tail states during the bias stress. The density of states is increased in the region next to the electron injecting contact and decreased in the region next to the opposite contact. Model calculations are presented which show how the asymmetric J–V characteristics arise from such an inhomogeneous density of states and indicate the importance of holes for the state-creation process at the electron injecting contact.
A detailed analysis of the optical beam deflection technique for use in atomic force microscopy
Authors: Putman Constant A. J. , De Grooth Bart G. , Van Hulst Niek F. , Greve Jan
Published: July 2002

A Michelson interferometer and an optical beam deflection configuration (both shot noise and diffraction limited) are compared for application in an atomic force microscope. The comparison shows that the optical beam deflection method and the interferometer have essentially the same sensitivity. This remarkable result is explained by indicating the physical equivalence of both methods. Furthermore, various configurations using optical beam deflection are discussed. All the setups are capable of detecting the cantilever displacements with atomic resolution in a 10 kHz bandwidth.
Dielectric properties of CaNdAlO4 at microwave frequencies
Authors: Konopka J. , Wolff I. , Lewandowski S. J.
Published: July 2002

Dielectric properties of CaNdAlO4 monocrystals, a prospective substrate material for the deposition of high-Tc superconductors, were measured with high accuracy at microwave frequencies from 8 to 40 GHz in the temperature range from 10 to 300 K by measuring the resonant frequencies of a completely filled resonant cavity. The material was found to be highly anisotropic. At 300 K it exhibits the dielectric constant along c axis ε′c = 17.68, while the dielectric constant in the a-b plane is ε′=19.62, and loss tangent tan δc ≂ tan δ ≂ 5.1× 10−4. Both ε′c and ε′ depend strongly on temperature and their thermal coefficients have opposite signs, apparently a unique property of CaNdAlO4. Below 160 K microwave losses caused by electric field perpendicular to the optical c axis increase with decreasing temperature, exhibiting a maximum near 65 K followed by a minimum at 30 K. It is suggested that neodymium ions in CaNdAlO4 at lower temperatures become magnetically ordered, causing an increase of magnetic permeability μ′c ≳ 1 and a significant increase of magnetic losses at microwave frequencies. A crystallographic phase transition below 60 K cannot also be excluded.
Nanostructural effects and interface magnetism in Co/Pd multilayers
Authors: He Ping , Shan Z. -S. , Woollam John A. , Sellmyer D. J.
Published: July 2002

A series of Co/Pd multilayers were made by dc magnetron sputter deposition on Al foil substrates. For these multilayered samples, Co layer thicknesses were less than 4 Å and Pd layers were varied from 4 to 22 Å. Sputtering rates were controlled by either sputtering power (10–50 W) or Ar sputtering pressure (3–15 mTorr). In both cases, lower deposition rates yielded higher perpendicular coercivity up to 2.6 kOe. Structures of the samples were studied using conventional θ-2θ x-ray diffractometry (XRD). It has been found that magnetic properties such as coercivity and saturation magnetization are sensitive to interfacial structures. A nanostructural model including interfacial parameters such as alloy layer composition is discussed and compared with the magnetization data. Both XRD and magnetization measurements show that the interfaces become more diffuse at higher sputtering pressures.
Electron emission from ferroelectric materials
Authors: Rosenman G. , Rez I.
Published: July 2002

Ferroelectric materials are a new class of electron emitters. Electron emission occurs due to the appearance of an unscreened charge and an electrostatic field at the polar surfaces of these crystals under pyroelectric, piezoelectric, and anomalous photovoltaic effects as well as during spontaneous polarization reversal. Small external perturbation (for example, a temperature variation of a few degrees or less) is enough for this emission effect to occur. Emission current density up to 103 A cm−2 and electron energy up to about 105 eV have been reported. It is shown that this phenomenon drastically differs from other kinds of electron emissions. The physical nature of this effect is discussed.
Random telegraph signals in silicon-on-insulator metal-oxide- semiconductor transistors
Authors: Simoen E. , Claeys C.
Published: July 2002

Possible physical mechanisms for random telegraph signal (RTS) -like fluctuations in the front-channel drain current of a silicon-on-insulator (SOI) metal-oxide-semiconductor (MOS) transistor are discussed. Particular emphasis is on two RTS mechanisms which are believed to be typical for a SOI MOS transistor. The first one is related to carrier trapping in the Si film, by a deep-level trap in the depletion region. As such, this type of RTS is more or less complementary to the standard behavior, which is caused by carrier trapping through a near-interface oxide trap. Second, it is demonstrated experimentally that by varying the back-gate bias of a thin-film SOI MOS transistor ‘‘new’’ RTSs may be detected.
Spectroscopic study of SiC-like structures formed on polycrystalline silicon sheets during growth
Authors: Pivac B. , Furić K. , Milun M. , Valla T. , Borghesi A. , Sassella A.
Published: July 2002

Edge-defined film-fed grown polycrystalline silicon sheets, grown with one face exposed to oxidizing CO gas added to the inert Ar atmosphere, were studied. Interaction of CO with molten silicon surface during growth produced SiC-like structures in a thin layer on the surface exposed to CO. Infrared spectroscopy results suggest that this layer is constituted of good quality SiC; however, Raman and x-ray photoelectron spectroscopy showed that it consists of Si1−xCx in the form of small crystallites mixed with C- and O-rich silicon.