bluuebunny/crossref_metadata_2025 huggingface dataset:
Short-range fluctuations in the Hartree theory of diblock copolymer melts
Authors: Kudlay Alexander , Stepanow Semjon
Published: February 2003

We attempt to develop a fluctuation theory of diblock copolymer melts, which would include short-range fluctuations. The one-loop correction has been found to have an ultraviolet divergence, which is shown to be architecture-dependent. The correlation function S(q) is obtained within the Hartree approach by solving the integral equation. However the solution cannot be related to experiments, because of the architecture-dependence of the divergence. We conclude that construction of the fluctuation theory with the use of the RPA-derived Hamiltonian is impossible.
Critical and dynamical behavior of a driven diffusive lattice gas
Authors: Saracco Gustavo P. , Albano Ezequiel V.
Published: February 2003

In this work, a detailed analysis of the critical behavior of the Katz, Lebowitz, and Spohn (KLS) [Phys. Rev. B 28, 1665 (1983)] model is performed. This model considers a lattice gas of density ρ0 with nearest-neighbor attractive interactions between particles under the influence of an external driven field. The system is in contact with a reservoir at temperature T. The phase diagram of the KLS model is evaluated showing that it exhibits both first- and second-order phase transitions at different temperatures (Tc), depending on particle density. Ordered states are characterized by strips of high particle density running along the direction of the driving field, while disordered states exhibit gas-like behavior. A fit of the phase diagram (i.e., the Tc versus ρ0 curve) near the second-order transition is consistent with an order parameter critical exponent β≈0.33. This exponent is in agreement with an independent measurement performed by studying the dynamic evolution of the system. Furthermore, the strength of the first-order transitions is evaluated by measuring the relaxation of the system starting from both random (T→∞) configurations and well-ordered states (T→0), respectively.
Monte Carlo backbone sampling for polypeptides with variable bond angles and dihedral angles using concerted rotations and a Gaussian bias
Authors: Ulmschneider Jakob P. , Jorgensen William L.
Published: February 2003

An efficient concerted rotation algorithm for use in Monte Carlo statistical mechanics simulations of polypeptides is reported that includes flexible bond and dihedral angles. A Gaussian bias is applied with driver bond and dihedral angles to optimize the sampling efficiency. Jacobian weighting is required in the Metropolis test to correct for imbalances in resultant transition probabilities. Testing of the methodology includes Monte Carlo simulations for polyalanines with 8–14 residues and a 36-residue protein as well as a search to find the lowest-energy conformer of the pentapeptide Met-enkephalin. The results demonstrate the formal correctness and efficiency of the method.
Electrostatic response of hydrophobic surface measured by atomic force microscopy
Authors: Teschke O. , de Souza E. F.
Published: February 2003

The arrangement of water molecules at aqueous interfaces is an important question in material and biological sciences. We have measured the force acting on neutral tips as a function of the distance to hydrophobic silicon surfaces and cetyltrimethylammonium bromide monolayers covering mica surfaces in aqueous solutions. The unusually large magnitude of this force is attributed to an electrostatic response of the aqueous fluid structure (hydration layer) which is generated by the reorientation of water molecular dipoles. The exchange of a volume of this region with a dielectric permittivity (εint) by the tip with a dielectric permittivity (εtip) is responsible for the tip attraction when it is immersed in the polarization (hydration) layer. Variable permittivity profiles starting at ε≈11 at the interface and increasing to ε=80 about 10 nm from hydrophobic silicon surfaces and about 50 nm from cetyltrimethylammonium bromide monolayer covering mica surfaces were measured.
Ga vacancies and grain boundaries in GaN
Authors: Oila J. , Saarinen K. , Wickenden A. E. , Koleske D. D. , Henry R. L. , Twigg M. E.
Published: February 2003

We have applied a low-energy positron beam to study epitaxial Si-doped GaN layers, where the grain size varies from 0.2 to 2–5 μm. Negatively charged Ga vacancies are found in n-type samples. Their concentration is independent of the grain size, suggesting that Ga vacancies exist in the grain interior. Positrons are observed to get trapped also at other negatively charged centers. The positron trapping rate at these defects correlates with the grain-boundary density. We attribute the observed shallow positron traps, which do not contain open volume, to negatively charged edge-type dislocations which define the grain boundaries.
An iterative scheme to derive pair potentials from structure factors and its application to liquid mercury
Authors: Tóth Gergely
Published: February 2003

We developed an iterative scheme to optimize classical mechanical pair-potential parameters of liquids on the basis of diffraction data. An iterative step, similarly as in our previous method, consists of two parts: A classical mechanical simulation with an assumed pair potential and the modification of the potential using the experimental data and quantities calculated in the simulation. The modification part is formulated according to the Gauss–Newton–Marquardt nonlinear parameter fit. The method is used to get tabulated potentials, and seems to be robust also in the case of a fit of few hundred parameters simultaneously. The method keeps the advantages of our previous procedure: The fitted function is the measured structure factor, the Fourier transformation is applied with controllable error, the total functions are determined from the partial ones to avoid the solution of linear equations, and the error of the experiments can be taken into account explicitly. The theoretical justification of the method is the one to one correspondence of the pair potential and the structure factor proved by the inverse theorem of statistical mechanics. We determined effective pair potentials in a tabulated form for liquid mercury at 10 different densities to investigate the structural changes around its metal–nonmetal transition. We found neither a drastic change nor a change in the trends in the structural and pair potential functions. Our results fit well to some of the previous theories about the transition.
Degenerate p-type conductivity in wide-gap LaCuOS1−xSex (x=0–1) epitaxial films
Authors: Hiramatsu Hidenori , Ueda Kazushige , Ohta Hiromichi , Hirano Masahiro , Kamiya Toshio , Hosono Hideo
Published: February 2003

Epitaxial films of LaCuOS1−xSex (x=0–1) solid solution were grown on MgO (001) substrates and their electrical and optical properties were examined. Sharp emission due to room-temperature exciton with binding energy of ∼50 meV is observed for all x values. Hall mobility becomes large with an increase in the Se content and it reaches 8.0 cm2V−1s−1 in LaCuOSe, a comparable value to that of p-type GaN:Mg. Doping of Mg2+ ions at La3+ sites enhances a hole concentration up to 2.2×1020 cm−3, while maintaining the Hall mobility as large as 4.0 cm2V−1s−1. Consequently, a degenerate p-type electrical conduction with a conductivity of 140 S cm−1 was achieved.
Solution-processed niobium diselenide as conductor and anode for polymer light-emitting diodes
Authors: Reynolds K. J. , Frey G. L. , Friend R. H.
Published: February 2003

The use of layered transition metal dichalcogenides (LTMDCs) processed from aqueous solution as hole injectors in polymer light-emitting diodes (PLEDs) was recently reported. In this letter, we extend the use of LTMDCs further by using the metallic compounds as semitransparent anodes in PLEDs (in place of indium tin oxide). The LTMDC films have a sheet resistance of ∼1000 Ω/□, and a transmittance of greater than 60% over the range of 400–800 nm. Typical diodes with niobium diselenide anodes show high luminance and power efficiencies of over 1 lm/W, demonstrating the potential to integrate solution-processed LTMDC conducting films in other electronic applications.
Characterization of chemical-vapor-deposited low-k thin films using x-ray porosimetry
Authors: Lee Hae-Jeong , Lin Eric K. , Bauer Barry J. , Wu Wen-li , Hwang Byung Keun , Gray William D.
Published: February 2003

Trimethylsilane-based carbon-doped silica films prepared with varying chemical-vapor-deposition process conditions were characterized using x-ray reflectivity and porosimetry to measure the film thickness, average film density, density depth profile, wall density, and porosity. Samples deposited under single or dual frequency conditions with either N2O or O2 as an oxidant were compared. The structural parameters were correlated with the chemical bond structure measured by Fourier transform infrared spectroscopy. The density profiles of the porous films were uniform with a slight densification at the film surface. The distribution of pores was also uniform through the film. Films prepared under a single frequency and/or N2O atmosphere had the lowest film density, wall density, and dielectric constant. The porosities of the films were similar and the pore sizes were less than 10 Å.
Electronic structure and energetics of RCo5H4 and RCo5 (R=La,Pr)
Authors: Hector L. G. , Herbst J. F.
Published: February 2003

Calculations of the spin-dependent electronic structure and enthalpies of formation, ΔH, of the ternary hydrides LaCo5H4, PrCo5H4, and their parent intermetallics are reported. All four compounds are found to be metallic and ferromagnetic. We obtain ΔH(LaCo5H4)=−45.6 kJ/mole H2, ΔH(PrCo5H4)=−39.8 kJ/mole H2, and ΔH(LaCo5)=−12.6 kJ/LaCo5, values which compare very favorably with experiment. With the assumption of the free-ion 4f moment for Pr, the calculated magnetic moments agree well with available measurements.
ZnO nanowires formed on tungsten substrates and their electron field emission properties
Authors: Dong Lifeng , Jiao Jun , Tuggle David W. , Petty Jeremy M. , Elliff Stephen A. , Coulter Michael
Published: February 2003

Using a vapor transport method, ZnO nanowires were selectively synthesized both on tungsten tips as electron field emitters and on tungsten plates with designed patterns. Control of the growth locations of the nanowires was accomplished by selectively positioning a thin film of Au catalyst. The angular intensity and fluctuation of the field emission current from the ZnO nanowires synthesized on tungsten tips have been demonstrated to be similar to those of carbon nanotubes. A self-destruction limit of ∼0.1 mA/sr for angular intensity was observed, and the power spectra showed a 1/f3/2 characteristic from 1 Hz to 6 kHz.
Nanometer-scale scanning sensors fabricated using stencil lithography
Authors: Champagne A. R. , Couture A. J. , Kuemmeth F. , Ralph D. C.
Published: February 2003

We describe a flexible technique for fabricating 10-nm-scale devices for use as high-resolution scanning sensors and functional probes. Metallic structures are deposited directly onto atomic force microscope tips by evaporation through nanoscale holes fabricated in a stencil mask. We report on the lithographic capabilities of the technique and discuss progress in one initial application, to make high-spatial-resolution magnetic force sensors.
In situ observation of particle-induced desorption from a self-assembled monolayer by laser-ionization mass spectrometry
Authors: Vandeweert E. , Bastiaansen J. , Vervaecke F. , Lievens P. , Silverans R. E. , Cyganik P. , Postawa Z. , Rong H. T. , Buck M.
Published: February 2003

We studied particle-stimulated desorption processes of highly ordered, self-assembled monolayers of biphenyl-based thiols covalently bound to Au/mica substrates with laser postionization in combination with mass spectrometry. Direct evidence was obtained that large molecular fragments are removed from these monolayers during impact of electrons with a kinetic energy of 1 keV. The damage that accumulates in the self-assembled monolayer with increasing electron dose was measured using ion-beam, sputter-initiated laser probing. Our results show that electron-induced desorption competes with the gradual erosion of the monolayer by the formation of a carbonaceous residual layer on the substrate.
Passivation of defects in nitrogen-doped polycrystalline Cu2O thin films by crown-ether cyanide treatment
Authors: Okamoto Y. , Ishizuka S. , Kato S. , Sakurai T. , Fujiwara N. , Kobayashi H. , Akimoto K.
Published: February 2003

Crown-ether cyanide treatment, which simply involves immersion in KCN solutions containing 18-crown-6 followed by rinse, is studied in relation to electrical and optical properties of nitrogen-doped, polycrystalline Cu2O thin films, and its effect is compared with that of hydrogen treatment. By the crown-ether cyanide treatment, the luminescence intensity due to the near-band-edge emission of Cu2O at around 680 nm is enhanced, and the hole density is increased from the order of 1016 to 1017 cm−3, analogous to hydrogen treatment. The effects of the passivation by the hydrogen treatment completely disappear after annealing at 350 °C, while those of the crown-ether cyanide treatment stay unchanged after the same annealing treatment. From these results, the crown-ether cyanide treatment for polycrystalline Cu2O thin films can be concluded to be a more suitable method of passivating defects than the hydrogen treatment.
Slowing-down time of energetic ions in solids
Authors: Oen Ordean S. , Robinson Mark T.
Published: February 2003

The average time required for an energetic ion or primary knock-on atom to slow down in a structureless solid has been calculated using a Thomas-Fermi interaction potential and electronic stopping power which is proportional to the velocity. The relevance of this time to radiation damage production is discussed.
High-energy pulsed CO chemical laser
Authors: Tiee J. J. , Quick C. R. , Harper C. D. , Petersen A. B. , Wittig C.
Published: February 2003

A high-energy pulsed CO chemical laser has been constructed. Vibrationally excited CO molecules are produced via the reaction O+CS→CO†+S. A laser output of 240 mJ/pulse is obtained when a mixture of CS2 and O2 is flash photolyzed without any additives. When small amounts of N2O and O3 are introduced, an output energy of 360 mJ/pulse is obtained.
Threshold characteristics of multimode laser oscillators
Authors: Casperson Lee W.
Published: February 2003

The oscillation characteristics of a multimode laser are considered in detail, and for the first time saturation by all of the cavity modes is included. Analytical expressions are obtained for the mode amplitudes, linewidths, and over-all spectral characteristics of lasers operating above and below threshold. It is found that with increasing excitation the spontaneous emission spectrum is gradually resolved into a set of narrow discrete modes. Slightly above threshold the number of modes reduces in a homogeneoulsy broadened laser until only a single mode is oscillating strongly. The theoretical results are in agreement with experimental data that have been reported using semiconductor lasers. With inhomogeneous broadening the spectral width goes through a minimum near threshold.
Transient electromagnetic penetration of a spherical shell
Authors: Dudley D. G. , Quintenz J. P.
Published: February 2003

The transient penetration of an electromagnetic plane wave into the cavity formed by an imperfectly conducting spherical shell is considered. The response at the cavity center to a Gaussian input pulse is compared with other published results. The treatment is then extended to other interior locations. Finally, a ’’band−limited’’ impulse response is determined and numerical results are given at several cavity locations for an aluminum shell of various thicknesses.
First−order treatment of combined effects of space charge and external fields on plane−symmetric beams of charged particles
Authors: Bosi G.
Published: February 2003

First−order equations describing the space−charge spread of charged particle beams under the influence of plane−symmetric external fields are proposed. The present treatment is confined to elliptic cross−section beams and is based upon an earlier work about axially symmetric systems.
Shock and release behavior in porous 1100 aluminum
Authors: Asay J. R.
Published: February 2003

Plate impact techniques were used to determine the dynamic response of 1.60−g/cm3 porous aluminum at energy states approaching incipient melt. Both quartz gauge and laser interferometric techniques were used to measure the shock response of this material over the stress range 0.6−7.3 GPa (6−73 kbar), which is in the region of full compaction. In addition, a nearly complete equilibrium release curve centered at 3.07 GPa (30.7 kbar) was measured using reverberating wave techniques. This is thought to represent the first accurate measurement of a release isentrope through a fully compacted state of a distended material and allows a further test of the equation of state. It is found that both the initial compaction and the release behavior of the compacted aluminum can be accurately predicted using the Mie−Grüneisen equation of state.
Fast decay in a twisted nematic induced by frequency switching
Authors: Bak C. S. , Ko K. , Labes M. M.
Published: February 2003

The rise and decay times of the light transmission in a twisted nematic mixture of phenyl benzoates were measured under an ac electric field while switching from one frequency to another. Decay times were drastically reduced by applying a high−frequency electric field at which the dielectric anisotropy has changed sign. A threshold voltage exists for the decay process where the normal oscillation in the light transmission is suddenly and completely suppressed, resulting in a monotonic decay.
Cavitation in gas−supersaturated solutions
Authors: Hemmingsen Edvard A.
Published: February 2003

Water equilibrated with gas at high pressures and contained in glass tubes (0.01−0.25−cm inside diameter) was able to sustain very high supersaturations without any occurrence of gas bubbles on decompression to atmospheric pressure. Interference from cavitation nuclear was minimized by their dissolution under pressure prior to saturation of the water. The maximum supersaturation tensions without cavitation, which represent the lowest possible limit of spontaneous bubble formation, were 140 atm for O2 and Ar, 190 atm for N2, and 300 atm for He. Massive cavitation occurred at 20−30 atm higher supersaturations. The onset of cavitation was slightly affected by large changes in the surface tension and in the solubilities of the gases in the liquids (by addition of ethanol) and was only significantly affected by temperature over a narrow range at about 1 °C. The bubbles arose primarily or exclusively at the water−glass interface. The data indicate that their formation was spontaneous rather than a result of preexisting nuclei.
Electromechanical response of PZT 65/35 subjected to axial shock loading
Authors: Lysne P. C. , Bartel L. C.
Published: February 2003

This theoretical and experimental investigation deals with the electromechanical response of a shock−loaded ferroelectric ceramic material. Quartz gauge and voltage−mode techniques were used to characterize the mechanical and electrical responses, respectively, of PZT 65/35 to ≈80 kbar. Below ≈20 kbar the wave propagation was dispersive, whereas step shocks were steady between ≈20 kbar and the ≈36−kbar Hugoniot elastic limit. Above 36 kbar the final stress states were reached asymptotically and are believed to be steady. The electrical response was complicated by the ferroelectric−to−paraelectric phase transformation at 60±3 kbar and the kinetics of the change in polarization. To investigate this latter effect, a kinetic model is developed which gives good agreement with experimentally determined voltage responses.
Field effect conductance modulation in vacuum−evaporated amorphous silicon films
Authors: Neudeck G. W. , Malhotra A. K.
Published: February 2003

Electron−beam vacuum−deposited amorphous silicon films were deposited at controlled rates from 3.1 to 5.6 Å/sec onto Si−SiO2 substrates followed by a 4−h 400 °C in situ anneal. The high−temperature activation energy for these films has an average value of 0.79 eV and is relatively independent of the deposition rate. The room−temperature resistivity varies from 3×107 Ω cm at a 5.6 Å/sec rate to 5.7×107 Ω cm at 3.1 Å/sec. The preexponential factor has an average value of 7×10−5 Ω cm and is independent of the deposition rate. A change in source−drain current due to a transverse electric field was observed at room and elevated temperatures for both positive and negative gate voltages. The results indicate that the Fermi level is not pinned near midgap and that the density of localized states near the Fermi level is nearly uniform for ±0.40 above and below midgap. Calculations indicate that the density of localized states near the Fermi level is about 1020/cm3 eV and decreases slightly as the rate is decreased.
Thermal expansion and Grüneisen parameters of InBi
Authors: White T. J. , Davis Jack Hayne , Walter H. U.
Published: February 2003

Thermal expansion of InBi single crystals was measured over the temperature range 4.2−350 °K by dilatometry and x−ray diffraction. Unusually high anisotropy was observed; upon cooling, the samples expand in the c direction and contract perpendicular to c. α∥ is an order of magnitude more negative than the negative thermal expansion coefficients noted for other materials. The 300 °K thermal expansion coefficients (α⊥=60±5×10−6/ °K, α∥=−86±5×10−6/ °K) were used to calculate the following Grüneisen parameters for room temperature: γ∥=0.5±0.1, γ⊥ =1.5±0.2, and γ=0.7±0.1.
Study of electrode products emitted by vacuum arcs in form of molten metal particles
Authors: Utsumi T. , English J. H.
Published: February 2003

The electrode products emitted by vacuum arcs in the form of molten metal particles were studied for Au, Pd, and Mg in the current range 2−6 A. The study includes the size distribution of these molten metal particles, the volume carried by these particles versus the volume carried by the metal vapor, and the velocity distribution of these particles. It was found that the ratio of volumes carried by the particles and the vapor is greatly dependent on the cathode material.
Momentum modulation of a free electron beam with a laser
Authors: Piestrup M. A. , Rothbart G. B. , Fleming R. N. , Pantell R. H.
Published: February 2003

A Nd : YAG laser has been used to modulate the energy of a free electron beam. With a single pass of the 2−MW laser light through the 100−MeV electrons we have measured a 37−keV increase in the width of the energy spectrum for the particles. The interaction occurred in helium at standard temperature and pressure over a distance corresponding to 105 optical wavelengths, and a phase synchronism condition was maintained by means of the inverse Cerenkov effect. That is, along the direction of motion of the electrons the phase velocity of the electromagnetic wave equaled the electron velocity. Therefore, the electrons remained in an electric field of constant phase, resulting in significant energy exchange.
Determination of transition probabilities through stimulated emission in rare gas ions
Authors: Karatsu Osamu , Ogura Iwao
Published: February 2003

The probabilities of four radiative transitions of argon ion and three of krypton ion are determined through stimulated emission phenomena in rare gas ion lasers. Perturbation spectroscopic study is applied to the rare gas ion lasers, and the rate equations of Lamb are used to calculate the transition probabilities. Measured values of argon ion are compared with published values and found to be in good agreement with them. Measured values of krypton ion are compared with the data of spontaneous emission intensity, and are considered to be reasonable.
Nitrogen−implanted silicon. II. Electrical properties
Authors: Mitchell J. B. , Shewchun J. , Thompson D. A. , Davies J. A.
Published: February 2003

This paper presents measurements of capacitance−voltage, Hall−effect, and diode characteristics on nitrogen−implanted silicon as a function of anneal temperature. The results of these three types of electrical measurements are consistent and show that less than 1% of the implanted nitrogen exhibits donor effects following anneals in the temperature range ∼700−900 °C. Hall−effect measurements performed as a function of temperature indicate that nitrogen in silicon has an ionization energy of 0.017±0.002 eV. Room−temperature Hall−effect measurements combined with stripping techniques have shown that the distribution of electrically active nitrogen is constant as a function of implantation depth. These results are believed to be due to a donor (substitutional) position involving <1% of the implanted nitrogen ions; this interpretation is consistent with the lattice location and damage results presented in Paper I.
Modification of the particle−model theory of diffuse reflectance properties of powdered samples
Authors: Simmons E. L.
Published: February 2003

Equations are derived which describe the diffuse reflectance of a powdered sample in terms of its fundamental optical parameters on the basis of the rough−surfaced spherical particle model for a powdered sample. The major difference in the derivation compared with previous particle−model theories is that the assumption that a particle in a powdered sample scatters light equally in all directions is not used. The equations obtained are compared with those obtained from Melamed’s theory and with experimental results.
Anomalous capacitance of Schottky barriers on strontium titanate
Authors: Neville R. C. , Hoeneisen B.
Published: February 2003

An anomalous capacitance−vs−voltage characteristic of Schottky barriers on n−type single−crystal perovskite strontium titanate is described. This anomalous phenomenon is assigned to a heavily doped buried layer which forms during the evaporation of the metal contact.
Self−focusing of electromagnetic beams in bismuth
Authors: Tewari D. P. , Kumar Awdhesh
Published: February 2003

An intense Gaussian electromagnetic beam propagating through bismuth gives rise to the heating and redistribution of electrons and holes and hence self−induced focusing occurs. At upper microwave frequencies (∼5000 GHz), the critical power for self−focusing is 0.02 W. At a beam power of 1 W, the focusing length is ∼10 cm. The absorption of the beam in intrinsic bismuth is very small. At strong static magnetic fields (≳102 kG), mode−dependent effects are important.
Investigation of tellurium−implanted silicon
Authors: Lee T. F. , Pashley R. D. , McGill T. C. , Mayer J. W.
Published: February 2003

Hall and sheet−resistivity measurements as a function of temperature combined with layer removal have been used to study Si implanted with Te at energies up to 220 keV. At low doses (≲4×1012 cm−2), Te has a donor level with a 140−meV activation energy. The activation energy decreases at higher Te doses and is approximately equal to zero for Te doses ≳1015 cm−2. At high dose levels, the number of conduction electrons per unit area Ns is more than an order of magnitude below the number of Te per unit area. High−temperature anneal treatments followed by quenching did not produce a substantial increase in Ns, suggesting that the formation of Te clusters was not responsible for the low value of Ns. Also, channeling measurements indicated a high substitutional fraction. Based on differential Hall measurements on samples implanted with phosphorus, with and without Si predamage, we conclude that residual radiation damage is not a major factor. A theoretical calculation, which includes the effect of decrease of activation energy with increasing impurity concentrations, indicated that the number of conduction electrons could be much less than the number of implanted Te even though the apparent activation energy is almost zero. Although the results of theoretical calculation do not give quantitative agreement with the experimental results, they do confirm the changes in apparent activation energy with concentration.
Effect of intervalley transfer on microwave Faraday effect in n−GaSb
Authors: Srivastava G. P. , Mathur P. C. , Shyam Radhey , Kataria N. D.
Published: February 2003

A theoretical and experimental study is performed on free−charge−carrier Faraday effect in n−GaSb, on the basis of a two−band model. The expression of magnetoconductance derived earlier by Bordure and Savelli are generalized to high frequency and the theory of Faraday effect in n−GaSb is formulated. The theoretical study indicates that GaSb would produce Faraday rotation which depends very much on intervalley scattering. Rotation and ellipticity has been studied as a function of magnetic field and it has been found that the intervalley scattering has a predominant effect, as compared to intravalley scattering, on the transport mechanisms in GaSb. Also this effect increases with the decrease of temperature. Experimental measurement of microwave Faraday rotation has been made using the straight through transmission technique at 23.6 GHz, and at temperatures of 300 °K and 100 °K.
Lorentz electron microscopy of domain walls in single−crystal evaporated iron films
Authors: Proto George R. , Lawless Kenneth R.
Published: February 2003

A method for measuring the width of domain walls by Lorentz electron microscopy is presented and applied to the case of a single−crystal iron film. The method consists of measuring the domain wall image width at a number of defocusing distances and fitting the resulting curve to a theoretical curve of image width versus defocusing distance using the wall width and a parameter which is a function of the deviation of the beam as variables. The appearance of the wall images and the measured wall widths indicate that domain walls in single−crystal iron films around 1000 Å thick are 180 ° asymmetric and 90 ° symmetric or asymmetric types.
Forces at low− and high−speed limits in magnetic levitation systems
Authors: Lee S. W. , Menendez R.
Published: February 2003

We consider the lift and drag forces on dc current coils moving over an infinitely large conducting slab (track). With respect to the dominant Fourier component of the current, simple analytical expressions for several limiting cases in both repulsive and attractive systems are derived. These results are compared with those in the literature and we delineate the precise conditions under which the approximations are valid.
A study of the formation conditions of electrets
Authors: Latour Dr. Mireille
Published: February 2003

The role played by resistivity and the importance of this variable in electret formation is demonstrated; measurements of this quantity during formation enable one to control the resulting electret characteristics and to predict future behavior. This study is concerned principally with dielectrics of moderately low (?1015 Ω cm) resistivity. It is shown that the application of the electric field during either polymerization of the monomer or evaporation of the solvent of a polymer solution results in a greater and more stable charge than was the case in normal thermoelectret formation. The effect of a number of important parameters on the maximum charges attainable and their stability is determined. These include the addition of varying amounts of plasticizers and ionic impurities to polymers, as well as polarizing field and temperature cooling speed and ageing. We show that knowledge of the polarizing field and resistivity alone are sufficient to predict a priori whether the resulting electret will be heterocharged or homocharged.
Thermionic emission from negative electron affinity silicon
Authors: Howorth J. R. , Sheppard C. J. R. , Holtom R. , Harmer A. L.
Published: February 2003

Thermionic emission from negative electron affinity surfaces on silicon has been studied. The value is dependent on the state of activation of the surface, and dark currents in the range 10−11−10−13 A/cm2 may be obtained. These values agree with those measured on sealed−off tubes. The dark current is thought to originate from surface states acting as traps for the generation of electrons. The density of surface states is estimated from the measurement of the variation of dark current during oxygenation. Field enhancement of dark current and photoemission has been observed.
High current efficiency accelerating lens system of field emission scanning electron microscope
Authors: Kuroda Katsuhiro , Suzuki Tatsuro
Published: February 2003

The current efficiency of the lens system for an accelerating lens composed of three anodes combined with an auxiliary magnetic lens in a field emission scanning electron microscope is described. In this system the spot size for the needed primary beam current can satisfactorily be minimized since the working distance can freely be changed and the auxiliary magnetic lens can be operated under the optimum condition. Current efficiency of one order higher than that of the accelerating lens composed of two anodes is obtained.
Ion currents at the cathode in a Ne−Ar abnormal glow discharge
Authors: Courville G. E. , Mahler David S.
Published: February 2003

A method for studying properties of the ion current to the cathode in mixed−gas cold−cathode discharges is discussed. Retarding potential measurements of the current through a small aperture in the cathode enables one to distinguish between currents due to different ion species provided the energy distribution of each ion species is different. This technique is applied to an abnormal glow discharge in Ne−Ar Penning mixtures. It is found that at saturation of the Penning effect (at about 0.6% argon in the mixture) nearly 70% of the ion current to the cathode is due to Ar+ ions.
Improved calculations of secondary electron energy distributions of metals
Authors: Chung M. S.
Published: February 2003

Some recent theoretical calculations of secondary electron energy distributions have been modified by including the effects of quantum−mechanical reflections at the solid−vacuum interface. The shapes and important characteristics of the secondary electron energy distribution curves are altered significantly, bringing them into
Composition dependence of stacking−fault parameter of binary and ternary copper systems
Authors: Chatterjee S. C. , Gupta M. P.
Published: February 2003

The straight−line relationship, proposed by Liu and Gallagher to correlate the stacking−fault probability α with the solute concentration factor [C/(1+C)] in the binary silver systems has been applied to copper alloys. The relationship appears to be obeyed well. An attempt has been made to widen the scope of this approach to include the ternary copper systems as well.
Detection of low−mass impurities in thin films using MeV heavy−ion elastic scattering and coincidence detection techniques
Authors: Moore J. A. , Mitchell I. V. , Hollis M. J. , Davies J. A. , Howe L. M.
Published: February 2003

The usefulness of heavy−ion forward scattering coincidence measurements is demonstrated for the detection of low−mass impurity atoms in thin self−supporting nickel and gold films. Oxygen beams of 15−20 MeV have been used to detect 16O and 24Mg atoms in nickel films ?200 μg cm−2 thick and chlorine beams of 40 MeV to detect 39K and 63Cu atoms in gold films ?350 μg cm−2 thick. The detection sensitivity and mass discrimination are functions of the angle of acceptance of the detectors. Impurity atom concentrations of the order 1014 atoms cm−2 are detectable. Depth information is available from the energy spectra. Possible application of the detection technique to the determination of the lattice site of low−mass impurities, by channeling in thin single crystals, is considered.
An improved method for measuring the order parameter in nematic liquid crystals
Authors: Boilini E. , Ghosh S. K.
Published: February 2003

We present here an improved method for measuring the order parameter S in nematic liquid cyrstals. The mehtod is based on measuring the centers of gravity (CG) of two groups of lines, generally unresolved or partially resolved, of the magnetic resonance spectrum of ring protons. The CG are defined from the spectral center and the separation between them is used to obtain S. The method is applied to measure S in para−azoxyanisole at different temperatures and the results are compared with earlier ones. In obtaining the spectrum, use has been made of the Fourier transform of the proton free−precession signal. The advantages of using this procedure over the commonly used continuous−wave technique are also discussed.
Further consideration of the track−interaction model for thermoluminescence in LiF(TLD−100)
Authors: Attix Frank H.
Published: February 2003

At the Second International Conference on Luminescence Dosimetry in Gatlinburg in 1968 Claffy, Klick, and Attix introduced the track−interaction model in an attempt to explain the phenomena of supralinearity and sensitization generally observed in the thermoluminescence of LiF(TLD−100). Their proposal in general terms was that the electron−hole traps are located near the paths of the energetic charged particles (primary or secondary) which traversed the crystal during ionizing irradiation, and that this nonrandom spatial distribution affects the thermoluminescence process both with respect to its dependence upon dose and upon linear energy transfer. Moreover the observed sensitization of the phosphor, after receiving a large radiation dose followed by a partial annealing, was attributed to the survival of luminescence centers. In the present work a very simplistic model has been adopted for purposes of estimating how the average distance between luminescence centers along a charged−particle track compares with the average distance between tracks. Magnesium centers, occurring at ?68−Å intervals, are assumed to provide trapping sites both for electrons and holes. The luminescence centers are taken to be F centers associated in some way with the titanium centers which occur at ?127−Å intervals. For the Compton secondary electrons resulting from 60Co γ−ray interactions, the average separation of ionizing events along the track is ?350 Å, and the average separation of F centers is ?2300 Å, resulting from about every seventh ionizing event. The average separation of tracks for a γ−ray exposure of 103 R is ?660 Å, which is roughly the same as the average separation of trapped charge carriers along a given track from their nearest F center in the same track. This is the same exposure level at which supralinearity of TL response vs exposure begins to appear for 60Co γ irradiation. The more densely ionizing tracks of heavy charged particles are shown to be much more widely separated relative to the luminescence center intervals in each track; thus supralinearity should not be expected in that case, in agreement with observations. An important feature of this paper is the estimation of an energy budget for LiF(TLD−100), beginning with the deposition of 60Co γ−ray dose in the crystal, and terminating in the emission of 0.04% of that energy as thermoluminescence. Reasonable avenues are suggested by which the energy losses may occur, and estimates are made of the energy fraction in each category, based on available evidence.
Short−range order in Au−Fe radiation−enhanced diffusion and the effectiveness of 14−MeV neutrons
Authors: Borg R. J. , Dienes G. J.
Published: February 2003

Solute clustering in a Au−Fe (17% Fe) alloy has been demonstrated by Mössbauer effect measurements of the magnetic ordering temperature. Neutron irradiation at room temperature produces clustering by means of radiation−enhanced diffusion, while annealing at high temperatures is required to produce clustering thermally. The radiation−enhanced diffusion effect was used to compare directly the efficiency of mobile defect production by 14−MeV fusion neutrons and reactor neutrons. The 14−MeV neutrons are more effective by about a factor of 10 than the reactor neutrons (E≳0.1 MeV) in producing mobile lattice defects. Other compositions failed to respond to radiation−induced clustering, suggesting that Au−17−Fe is in a critical composition region regarding the response of the magnetic ordering temperature to variations in short−range order.
GaAs double heterostructure lasing behavior along the junction plane
Authors: Hakki B. W.
Published: February 2003

Properties along the junction plane of GaAs double heterostructure (DH) injection lasers are studied in a self−consistent analytical model which takes into account the effect of lasing action in the active region. Solutions are obtained for the distribution of current under the stripe, and profiles of carrier concentration and gain in the active region, all as functions of lasing intensity. The results of the analysis are applied to practical situations in which the stripe width is varied from 10 to 20 μm, and the distance between the active region and the metallic stripe is varied between 0.5 and 3 μm. For these situations it is found that lasing action in the active region can exert a strong influence on the spatial distribution of the gain component of junction current. This influence increases as a function of increase in stripe width, increase in resistivity in the layer separating the active region from the stripe contact, and reduction of carrier diffusion length. In particular, it is found that as the power in the fundamental lasing mode increases the local gain decreases at the center of the stripe and increases towards the edges, thus favoring excitation of a first−order mode along the junction plane. For a 10−μm stripe width the fundamental mode is the dominant mode up to fairly large lasing power outputs, whereas for a 20−μm−wide stripe geometry a first−order mode can be excited soon after exceeding threshold. In addition, when the internal radiative differential quantum efficiency is 100%, the analysis yields a structure internal efficiency of 80%, for typical geometries used in practice. Part of the reduction in device efficiency is due to increased junction current flow, outside the lasing region, above threshold. The other part is associated with the increase in total gain current component as the lasing intensity increases. The increase in gain current is required to compensate for changes in its spatial distribution that are caused by the stimulated recombination.
Pressure dependence of thermal conductivity in polyethylene
Authors: Frost R. S. , Chen R. Y. S. , Barker R. E.
Published: February 2003

The effect of pressure on the thermal conductivity of polyethylene is treated theoretically. Borrowing from the quasilattice theory of liquids, a general expression for the volumetric response of a polymeric system to pressure is derived. By formulating a theory of thermal conduction in terms of the quasilattice model, it is shown that anharmonic contributions to the quasilattice vibrations lead to a very simple pressure dependence for the conductivity. The results of the theory are found to be in good agreement with observed thermal-conductivity–pressure data.
Measurement and calculation of absolute intensities of x-ray spectra
Authors: Brown D. B. , Gilfrich J. V. , Peckerar M. C.
Published: February 2003

Calculations and measurement of the continuum spectra of Cr and W x-ray tubes operated at 45 kV are compared. The calculation is based on the Boltzmann transport equation and the bremsstrahlung cross sections of Kirkpatrick and Wiedmann. The measurements use a crystal spectrometer whose efficiency is well known. The calculations and experimental data are in agreement within ±5% on a relative basis and within ±30% on an absolute basis.
Single laser beam of spatial coherence from an array of GaAs lasers: Free-running mode
Authors: Philipp-Rutz Elisabeth M.
Published: February 2003

Spatially coherent radiation from a monolythic array of three GaAs lasers in a free-running mode is reported. The lasers, with their mirror faces antireflection coated, are operated in an external optical cavity built of spherical lenses and plane mirrors. The spatially coherent beam formation makes use of the Fourier transformation property of the internal lenses. The transverse mode control is accomplished by a spatial filter. The optical cavity is similar to that used for the phase-controlled mode of spatially coherent beam formation, which had been reported; only the spatial filters are different. The spatial filter in the free-running mode controls the fields of the lasers to be in the lowest-order transverse mode, but it does not control their phase angles. Random amplitude and phase variations of the longitudinal modes prevent the formation of a stationary interference waveform. In the far field (when restored by an external lens), the intensities of the lasers in the array are concentrated in a single laser beam of spatial coherence, without any grating lobes. The far-field distribution is not influenced by the spacings among the lasers. The far-field distribution of the laser array in the free-running mode differs significantly from the interference pattern of the phase-controlled mode. The modulation characteristics of the optical waveforms of the two modes are also quite different. This is because the modulation is related to the interaction of the spatial filter with the longitudinal modes of the laser array with the optical cavity. The modulation of the optical waveform of the free-running mode is nonperiodic, confirming that the fluctuations of the optical fields of the lasers are random. Experiments were performed at room temperature using a monolythic array of three GaAs lasers. The far-field distribution of the laser array and the optical waveform were investigated.
Hole photocurrents and electron tunnel injection induced by trapped holes in SiO2 films
Authors: Powell Richard J.
Published: February 2003

The transport and trapping of holes generated by strongly absorbed uv light has been observed in SiO2. Hole photocurrents decay with time under small applied fields because the accumulation of trapped holes in the light-absorbing region counteracts the applied field. However, with increasing applied fields a steady-state hole photocurrent has been observed for the first time. The quantum efficiency for hole collection saturates at 100% as the applied field is increased. A new mechanism for radiation-induced currents has been observed: The trapping of holes near the Si-SiO2 interface enhances Fowler-Nordheim tunneling, producing electron-injection currents nearly two orders of magnitude larger than the photocurrent. Upon cessation of the radiation, these field-induced currents decay slowly with time as trapped holes are gradually annihilated, giving the appearance of very slow carriers being swept out of the oxide. Hole photocurrents increase with field, saturating at about 3 MV/cm. This is interpreted as a decrease in electron-hole pair recombination with increasing field. A qualitative model involving hole transport and trapping near both interfaces satisfactorily explains the experimental results.
The anisotropy of H
c2 and its implications to grain-boundary flux pinning in V3Si
Authors: Kramer Edward J. , Knapp G. S.
Published: February 2003

We report that V3Si has an extremely large anisotropy in Hc2. This anisotropy is large enough to account for the observed strength of grain-boundary pinning observed in polycrystalline V3Si.
Inferring mechanical relaxation spectra as an ill-posed problem
Authors: Wiff D. R. , Gehatia Matatiahu
Published: February 2003

Inferring a relaxation spectrum from mechanical test data was approached as a mathematically ill-posed or incorrectly formulated problem in the Tikhonov sense. A compound technique presented previously by the authors, which incorporates Tikhonov’s regularization ideas into quadratic programming, was successfully applied to the inversion of the Fredholm integral equations of the first kind encountered in the theory of linear viscoelasticity. Very good results were obtained when computer-simulated data from initially assumed unimodal and symmetrical bimodal distributions were used.
An attempt to rationalize the apparent incompatibility between the random coil and the folded chain crystal
Authors: Lindenmeyer P. H.
Published: February 2003

Arguments are given which suggest that polymer materials in theta solvents and melts do not interpenetrate to the extent suggested by random-coil statistics.