bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic properties and microstructures of sprayed SmCo5 magnets exposed to intermediate temperatures
Authors: Kumar K. , Das D.
Published: February 2003

The hysteresis observed in Hci from cycling SmCo5 magnets at temperatures of 650–800 °C has been shown to result from an inability to completely redissolve the precipitated phase (Sm2Co17) at the higher temperature in the short time that has been allowed. It has, therefore, been concluded that the rate of Sm2Co17 precipitation is higher than that of dissolution at these temperatures. Metallographic observations made on plasma-sprayed SmCo5 magnets (after exposing them for time periods of a few hours to several weeks at these temperatures) show that the precipitated phase exists as discrete second-phase particles in the material unlike in sintered magnets where extensive Sm2Co17 precipitation is observed at grain boundaries. It is suggested that the striations observed in micrographs of SmCo5 magnets (after exposure to these temperatures) are the result of strain processes related to thermal-expansion mismatch of neighboring grains.
A micron-size Hall probe for precision magnetic field mapping
Authors: Minden H. T. , Leonard M. F.
Published: February 2003

InSb Hall effect probes have been made with active volumes of about 1 μm3. Successive layers of In and Sb were vacuum evaporated onto microscope cover glasses. The layers were annealed and recrystallized to form low-resistivity InSb. However, before recrystallization, a layer of pure In was evaporated onto the InSb. A hierarchy of photoresist patterns was applied to form the Maltese-cross active area together with long lead stripes. The actual pattern was formed either by sputter etching or by ion milling. The final glass probe was 2 mm wide by 25 mm long with the microscopic active area in the center. In use, the glass strip was placed—with the active area out—on a curved mandril.
Stimulated backscattering from relativistic unmagnetized electron beams
Authors: Sprangle P. , Drobot A. T.
Published: February 2003

Analysis of stimulated scattering of a high-frequency incident pump wave from an unmagnetized relativistic electron beam is presented. The backscattered radiation frequency can be enhanced by the factor 4γ20 over the incident pump frequency, where γ0 is the relativistic factor of the electron beam. The linear growth rates associated with the wave-wave and wave-particle modes of scattering, in the high gain limit, are examined for a number of different pump amplitude regimes. Estimates for the scattering efficiency are presented for the wave-wave scattering process.
Electron- and ion-beam transportation channel formation by laser ionization based on resonance saturation—LIBORS
Authors: Measures R. M. , Drewell N. , Cardinal P.
Published: February 2003

We have been able to show that ’’laser ionization based on resonance saturation’’, LIBORS, represents a powerful new form of laser interaction that can be used to efficiently couple laser energy into either a cold gas or a plasma. In essence, the dense population of resonance-state atoms resulting from laser resonance saturation represents both a reservoir of energy that rapidly provides translation energy to the free electrons through superelastic collisions and a large pool of atoms having an ionization energy reduced by the laser photon energy. We show that over a wide range of conditions LIBORS can be superior to both multiphoton ionization and inverse bremsstrahlung by many orders of magnitude. Indeed, LIBORS appears to be particularly well suited to create long plasma channels needed for electron- or ion-beam transportation in future inertial fusion schemes. We have estimated that a suitably tuned laser pulse of about 0.7 J and 400-nsec duration should be capable of creating a plasma channel with an electron density of close to 1015 cm−3 over an area of 0.2 cm2 for a length of 5 m in sodium vapor of about 0.1 Torr. A similar result should be possible in lithium vapor.
Transient setting of ponderomotive nonlinearity, self-focusing, and plasma-wave excitation
Authors: Sodha M. S. , Singh D. P. , Sharma R. P.
Published: February 2003

This paper presents an investigation of the transient setting of ponderomotive nonlinearity in a collisionless plasma by a Gaussian pulse (in space and time). When the pulse duration is comparable to the diffusion time of carriers across the beam, the modification in the background electron concentration depends not only on the intensity of the pulse at that time but also on the back history of the pulse. Because of the modification of the background electron density, the plasma wave and the EM pulse are nonlinearly coupled and the plasma-wave excitation becomes a transient phenomena. If the initial power of the pulse is more than critical power for self-focusing the pulse is self-focused and the plasma-wave excitation is accordingly modified.
Application of the Langevin method to void growth
Authors: Gurol H.
Published: February 2003

The Langevin method using system-size expansion is applied to the growth of voids in irradiated metals. The evolution of the mean vacancy cluster size is calculated to the first two orders in the ’’system-size’’ inverse ε, for supercritical clusters. The system size is taken to be the vacancy cluster concentration. To the lowest order, the fluctuations of the cluster size are Gaussian and the mean satisfies the growth law used for swelling calculations. The non-Gaussian correction is shown to be negligible except for arrival-rate ratios DiCi/DvCv on the order of unity. The two-time cluster size correlation Φ (t,t′) is then evaluated near the critical size y*, which is an unstable equilibrium point. It is found that Φ (t,t′) is exponentially increasing, with an e-folding time τ*, which is within a numerical factor of the nucleation time-lag estimates using multistate kinetics. This suggests a definition of the time lag based on the cluster-size fluctuations. The supersaturated vapor is also discussed.
First temperature derivatives of the fundamental elastic constants of quartz
Authors: Sinha B. K. , Tiersten H. F.
Published: February 2003

The existing temperature derivatives of the effective elastic constants of quartz are referred to the variable temperature-dependent intermediate position of material points rather than the fixed reference position, to which the fundamental elastic constants are referred. Since the existing temperature derivatives are not with respect to the fundamental elastic constants, they cannot conveniently be employed in calculations of thermally induced frequency changes in electroded quartz resonators. This is essentially a result of the fact that a knowledge of temperature-induced biasing strains and the third-order elastic constants cannot be used in the existing linearly based formalism, but requires a proper nonlinearly based formalism. In order to remedy the existing situation, the derivatives with respect to temperature of the fundamental elastic constants of quartz are determined from the original data from which the existing temperature derivatives of the effective elastic constants were obtained. As usual in such work, the electric field and piezoelectric effect are completely ignored in the analytical treatment.
Axial-current-mode shock depoling of PZT 56/44 ferroelectric ceramic disks
Authors: Mock Willis , Holt William H.
Published: February 2003

Gas-gun impact techniques have been used to investigate the electrical response of shock-depoled PZT 56/44 ferroelectric ceramic disks in the stress range rom 0.7 to 8.8 GPa. External short-circuit current pulses were measured as the shock wave propagated axially through the disk in a direction either parallel or antiparallel to the remanent polarization vector. Complete charge release was not observed in any of the shots. About 82% of the available charge was released for both orientations in the stress range from about 1.5 to 5.6 GPa. At stress levels of 6.8 and 8.8 GPa the charge release for the antiparallel orientation shots was less than for the parallel orientation shots. A series of electrical polarization reversal measurements was performed under nonshock conditions on PZT disks to estimate the electrical properties in the region ahead of the shock front. Maximum electric fields for the regions ahead of and behind the shock front were estimated to be 1–6 and 4–24 kV/mm, respectively, as the shock stress was increased.
Analysis of resistance-versus-pressure relations for the diamond indentor-anvil system
Authors: Ruoff Arthur L.
Published: February 2003

Pressures in excess of 1.4 Mbars have been attained by Ruoff and Wanagel1 by pressing tiny spherical diamond indentors (tip radius of 2 μm or less) against a diamond anvil. This system has been used for resistance-vs-pressure measurements as follows. A thin (200 Å) coherent layer of a conductor, e.g., palladium, can be sputtered on the tip and on the anvil and electrical leads can then be attached to these at points remote from the contact area. Then a thin layer of the sample to be studied can be evaporated, sputtered, or placed on the anvil. When the indentor is pressed against the sample, the resistance changes as the pressure increases and as the contact radius increases. This paper analyzes the resistance-vs-pressure relationship for three different types of resistivity-vs-pressure behavior.
The compressive strength of perfect diamond
Authors: Nelson David A. , Ruoff Arthur L.
Published: February 2003

This paper extends the earlier work on the theoretical compressive strength of perfect-diamond cubic crystals under [100] loading to the case of [111] loading for which they are found to be much stronger. From this it is inferred that the compressive strength of perfect diamond loaded in the [111] direction is 4.1 Mbars.
An organic crystal with an exceptionally large optical second-harmonic coefficient: 2-methyl-4-nitroaniline
Authors: Levine B. F. , Bethea C. G. , Thurmond C. D. , Lynch R. T. , Bernstein J. L.
Published: February 2003

We have grown and measured the optical second-harmonic coefficient dijk of the new nonlinear crystal 2-methyl-4-nitroaniline (MNA). We find that the dijk are very large with d12 being 5.8 times larger than d31 of LiNbO3 giving a birefringence phase-matching figure of merit d2/n3 which is 45 times larger than LiNbO3. The other coefficient d11 is 40 times larger than LiNbO3, giving a huge figure of merit which is 2000 larger than LiNbO3.
Tripling of CO2 laser frequency in deuterium chloride gas
Authors: Kung R. T. V. , Mani S. A.
Published: February 2003

The generation of third-harmonic radiation from the 9.6-μm P (22) CO2 laser line was investigated in DCl (deuterium chloride). A total of 11 conversion efficiency maxima were observed up to a pressure of 28 atm. The measured index mismatch (n3−n1) between the third harmonic and the fundamental frequencies is 4×10−6/atm. This compares favorably with the calculated index mismatch of 3.6×10−6/atm. It is found that the major contribution to n3−n1 arises from the far-infrared pure rotational transitions. The measured χ(3) was deduced from experimental results and shown to agree with calculated values to a factor of 2.
Excitation of horizontally polarized shear elastic waves by electromagnetic transducers with periodic permanent magnets
Authors: Vasile C. F. , Thompson R. B.
Published: February 2003

Theoretical and experimental results obtained with a new type of noncontact electromagnetic transducer are presented. The transducer differs from previous configurations in that a periodic permanent magnet and an axially wound coil are combined to produce a transversely directed periodic surface stress. It is demonstrated that this configuration can be used to generate horizontally polarized shear waves traveling along, or at a predetermined angle to, the surface of a thick metal object, horizontally polarized shear modes of a thin plate, or torsional waves in a tube. A model is presented for the radiation resistance of the transducer in semi-infinite samples and plates and supporting experiments are reported. Some advantages of this transducer in ultrasonic nondestructive evaluation of structural materials are summarized.
Low-temperature thermal conductivity of a reticulated glassy carbon
Authors: Gardner J. W. , Anderson A. C.
Published: February 2003

The thermal conductivity of an interconnected filamentary (reticulated) glassy carbon has been measured between 0.1 and 100 K. The conductivity of the reticulated structure at 4 K is a factor of 1000 smaller than other rigid construction materials typically used for cryogenic thermal isolation. However, the intrinsic thermal conductivity of the individual filaments of the reticulated structure is identical to that of other glassy carbons, depending only on the temperature of pyrolysis.
Propagation of power pulses in magnetically insulated vacuum transmission lines
Authors: Di Capua Marco S. , Pellinen Donald G.
Published: February 2003

The propagation of a 1.8-MV 80-kA power pulse in a 10-m-long 41.6-Ω impedance coaxial vacuum transmission line has been investigated experimentally. The onset of magnetic insulation has been correlated to attainment of the critical current. Measurements of boundary (cathode) current suggest that 50–60% of the current flows in space charge in the axial direction between the conductors. The pulse sharpens as it propagates and attains a stationary shape. Pulse rise times of 4 ns were observed. Propagation velocities equal to 0.7c have been measured. Power and energy transports as high as 90 and 70% have been observed. The peak power density in the transmission line was 2×109 W cm−2.
The Gurney equations for multilayered fragments
Authors: Jones Gordon E.
Published: February 2003

The Gurney approach is used to obtain a relationship betweeen the speeds of multiple layers of metal deployed by high explosives. When used with equations describing shock interactions, the derived relationship will be useful in predicting the speeds of the various layers so that the approximate distribution of fragments can be determined analytically.
a-Si : H produced by high-temperature thermal decomposition of silane
Authors: Wiesmann H. , Ghosh A. K. , McMahon T. , Strongin Myron
Published: February 2003

Hydrogenated amorphous silicon has been deposited by a new technique of thermal decomposition of silane from a hot tungsten or carbon foil heated to about 1600 °C. Initial measurements indicate that the resulting films have a fairly high photoresponse. Introduction of ammonia along with silane is seen to enhance the photoconductivity quite significantly.
Lifetimes of the 4F3/2 state in Nd : YVO4
Authors: Sliney J. G. , Leung K. M. , Birnbaum Milton , Tucker A. W.
Published: February 2003

The fluorescence lifetime of the 4F3/2 state of Nd3+ in YVO4 crystals has been determined as a function of temperature and concentration. Over the temperature range 90–300 °K the lifetime is approximately 100 μsec and decreases to 87 μsec at 453 °K. The lifetime at 300 °K is found to depend on the Nd3+ concentration decreasing from 100 μsec at 0.4 at.% to 60 μsec at 1.6 at.%.
Laser-annealing behavior of a phosphorus-implanted silicon substrate covered with a SiO2 film
Authors: Tamura H. , Miyao M. , Tokuyama T.
Published: February 2003

Laser-annealing behavior of phosphorus-implanted silicon substrates is investigated as a function of the SiO2 film thickness formed on implanted surfaces. Surface-carrier concentration after laser irradiation through the SiO2 layers shows periodic enhancement in relation to SiO2 thickness. Calculation of laser energy transferred into the silicon surface through various SiO2 film thicknesses is carried out and the results agree well with the experiments.
Barkhausen discontinuities, nucleation, and pinning of domain walls in etched microparticles of SmCo5
Authors: McCurrie R. A. , Willmore L. E.
Published: February 2003

A study has been made of the effects of etching on the magnetic hysteresis of single SmCo5 particles. It has been shown that the domain-wall nucleation and pinning fields are substantially increased by etching in 0.5% HNO3 for various times up to 6.5 min. After further etching, these fields decreased. The use of a vibrating-reed magnetometer has enabled the observation of individual Barkhausen discontinuities in the motion of the domain walls which in turn can be used to characterize the coercivities of individual particles.
Magnetic anisotropy from dipolar interactions in amorphous ferrimagnetic alloys
Authors: Mizoguchi T. , Cargill III G. S.
Published: February 2003

Classical magnetic dipolar interactions can make significant contributions to magnetic anisotropy in amorphous ferrimagnetic alloys with slight structural anisotropies on either atomic or microstructural scales. Simple expressions have been derived for this magnetic anisotropy in terms of structural anisotropy parameters, p, V, and Δx. For an alloy with atomic-scale structural anisotropy (pair ordering), p is a measure of alignment of unlike nearest-neighbor pairs. For an alloy with aligned elongated composition inhomogeneities, V is the volume fraction of inhomogeneities and Δx is the composition difference (atom fraction) between the inhomogeneities and their surroundings. Accounting for magnetic anisotropy observed experimentally in bias-sputtered GdCo-based alloy films solely in terms of pair ordering and classical dipolar interactions requires p∼0.015. Accounting for the anisotropy solely in terms of composition inhomogeneities requires Δx∼0.1 for V=0.5. Although such atomic-scale structural anisotropy will be very difficult to detect with currently available experimental techniques, composition inhomogeneities of this magnitude should be easily detectible in x-ray, electron, or neutron small-angle scattering experiments. Results of small-angle x-ray scattering experiments on micron-thick sputtered GdCo-based films indicate that occurrence and characteristics of microstructural inhomogeneities depend critically on substrate bias. Although intense anisotropic small-angle scattering is present for nonbiased films, scattering from biased magnetically anisotropic films is weak and isotropic and can be attributed to formation of small Gd-oxide clusters during film growth, apparently unrelated to magnetic anisotropy. Although no evidence for anisotropic composition inhomogeneities is seen in x-ray scattering experiments on micron-thick bias-sputtered GdCo-based films, such inhomogeneities may be present in oxygen-doped evaporated Gd-Co films and in some annealed Gd-Co films prepared by evaporation and by zero-bias sputtering. Magnetic anisotropy in GdCo-based films probably involves spin-orbit interactions as well as classical magnetic dipolar interactions.
Magnetic properties of the system GdC2-DyC2
Authors: Sakai Tetsuo , Adachi Gin-ya , Shiokawa Jiro
Published: February 2003

Magnetic susceptibilities of GdC2, DyC2, and their solid solutions (GdxDy1−xC2; x=0.20, 0.42, 0.51, 0.62, 0.82) have been measured from 4.2 K to room temperature. The dicarbides, DyC2 and GdC2, exhibit antiferromagnetic ordering at 61 and 42 K, respectively. The solid solutions, GdxDy1−xC2, show two cusps on the χ-vs-T curves at TN1 and TN2 suggesting successive antiferromagnetic ordering of spins of the component metal ions. The values of TN1 and TN2 of the solid solutions have been plotted as a function of the average value of the de Gennes factor [?= (g−1)2J (J+1)]. With increasing Gd ion concentration the values of TN1 decrease linearly, whereas the values of TN2 increase. TN1 and TN2 exhibit similar variations with ?. The results have been discussed in the light of the RKKY theory.
Piezoelectric relaxation in polyvinylidene fluoride
Authors: Furukawa T. , Aiba J. , Fukada E.
Published: February 2003

The piezoelectric and related properties have been measured for stretched polyvinylidene fluoride as a function of temperature. The piezoelectric relaxation observed around the glass transition temperature Tg is discussed taking the two-phase structure into consideration. The piezoelectric constant e31 (polarization/strain) is positive and increases with temperature. This increase is ascribed to the increase of the electrostrictive constant in noncrystalline regions which couples with the residual polarization located in crystalline and/or noncrystalline regions. The electrostrictive constant changes its sign below Tg from negative to positive with temperature. The piezoelectric activity below Tg is considered to be originated from the intrinsic piezoelectricity, i.e., the rotation of oriented molecular dipoles caused by strain. The residual polarization in the sample due to the dipoles is estimated to be 0.9×10−2 C/m2. The piezoelectric increment around Tg is accounted for by assuming the spatial distribution of the residual polarization due to both dipoles and space charges.
Depolarized light scattering from a phase-separated glass
Authors: Tomozawa M. , Kerwawycz J. P.
Published: February 2003

The depolarized light scattering from a phase-separated borosilicate glass was experimentally measured. The theory predicts that the internal stress field around the second-phase particles gives rise to a depolarized four-leaf-clover scattered-intensity pattern. The phase-separated and annealed specimen showed practically no scattered intensity when viewed in the crossed polarizer and analyzer arrangement, while quenched specimens showed a small four-leaf-clover pattern in the same experimental arrangement, indicating that this depolarized scattered intensity is not due to the internal stress field. Instead, it is explained in terms of the Rayleigh-Gans scattering theory from an anisotropic material.
Hydrogen content and density of plasma-deposited amorphous silicon-hydrogen
Authors: Fritzsche H. , Tanielian M. , Tsai C. C. , Gaczi P. J.
Published: February 2003

The hydrogen concentration and density of amorphous semiconducting films prepared by glow-discharge decomposition of silane have been measured as a function of deposition temperature. An inductively coupled as well as a capacitively coupled plasma-decomposition system was used. For samples prepared by the capacitively coupled system, the hydrogen content decreased from 26 to 8 at.% and the density increased from 1.9 to 2.27 g/cm3 as the substrate temperature was increased from 25 to 450 °C.
Surface acoustic waves in periodic structures
Authors: Datta Supriyo , Hunsinger Bill J.
Published: February 2003

A noniterative technique is described for obtaining surface-wave solutions in periodic layered media by expanding the field quantities in an orthonormal series of Laguerre functions perpendicular to the surface and in a Fourier series in the propagation direction. The principle is illustrated with uniform layered media, thin and thick metallic gratings, and grooved arrays. The technique is general and applicable to arbitrary periodic structures.
Formation of superconducting Nb3Si by explosive compression
Authors: Dew-Hughes D. , Linse V. D.
Published: February 2003

The claim that the high-temperature equilibium tetragonal Nb3Si phase can be transformed, by explosive compression, into a superconducting phase has been confirmed. After being subjected to shock compression with peak pressure close to 1 Mbar, the resulting material is superconducting, with an onset Tc of 18 K. The structure of this superconducting phase is ambiguous, but it could have the A15 structure with a lattice parameter of 5.12 Å.
Estimation of wave-number spectrum parameters from fixed probe-pair data
Authors: Iwama Naofumi , Ohba Yasuo , Tsukishima Takashige
Published: February 2003

Spectrum parameter estimation concerning a stationary and homogeneous random field is examined in terms of quantities obtainable from a pair of fixed probes. The estimators of the mean wave number and the wave-number spectral width are derived by relating wave-number spectral moments to spatial derivatives of the complex covariance of the field, the effect of finite probe size being taken into account. The estimate biases associated with the probe separation can be greatly reduced by employing an algorithm based on the polar-form representation of the complex covariance, while the variances of the estimates have a tendency to be enhanced with the decrease of the probe separation. An optimum range of the probe separation is theoretically determined.
Fuel preconditioning studies for e-beam fusion targets
Authors: Olsen J. N. , Widner M. M. , Chang J. , Baker L.
Published: February 2003

Fuel temperature and density conditions, achieved during the preheat phase of electron-beam fusion compression experiments, must be accurately known to understand experimental results via numerical simulations. We present studies of discharge preheating in a simplified cylindrical geometry which compare measured quantities with results from the one-dimensional Lagrangian CHARTB magnetohydrodynamic code. Experimental measurements included schlieren photography and ultraviolet through visible time- and space-resolved spectroscopy in various configurations. It is seen that an 8-kA 500-ns heating pulse in 100 Torr of D2+10% O2 produces 10–12 eV temperatures, 1018 cm−3 electron densities, and 7×105 cm/s expansion velocities in the heated discharge channel. These results are consistent with previous claims for neutron-producing targets, although the target geometry is different.
Deuterium-ion-beam impurities produced by a gas-discharge ion source (duopigatron)
Authors: Bickes R. W. , O’Hagan J. B.
Published: February 2003

Mass-spectroscopic analyses of dc deuterium-ion beams produced by a duopigatron ion source were carried out. These analyses showed that under normal operating conditions the beams contained less than 1% of impurities and consisted primarily of masses 12, 14, 16, 18, 20, and 22 and some metal ions. The source of the metal contaminants was the secondary cathode. Several cathode materials including Mo, Al, Al2O3, BN, and TiB2 were tested.
Simplifications in the x-ray line-shape analysis
Authors: Adler T. , Houska C. R.
Published: February 2003

It is shown that a Fourier series associated with the Warren-Averbach line-shape analysis can be fitted with only five parameters to a pair of peaks. These interrelate the Fourier coefficients and thereby provide a simplified series which has been applied to the study of a Mo film on a Si crystal. The parameters include the average particle size, the first neighbor rms strain, a term which gives the variation in rms strain with cell separation, and two instrumental broadening coefficients. Although considerable simplification is possible, equivalent information can be obtained as compared with the original analysis and the ’’hook effect’’ is eliminated in the fitted coefficients.
On the correlation of blister diameter and blister skin thickness in helium-ion-irradiated Nb
Authors: Das S. K. , Kaminsky M. , Fenske G.
Published: February 2003

A systematic study of the correlation between blister diameter and blister skin thickness has been performed for helium-ion irradiation of monocrystalline and polycrystalline Nb for ion energies ranging from 20 to 500 keV. The results indicate that a relationship Dmp∝t1.50 between the most probable blister diameter, Dmp, and blister skin thickness, t, which has been suggested by other authors, does not exist for the various types of Nb targets studied. For example, for room-temperature irradiation of annealed polycrystalline Nb the experimentally determined relationship is Dmp=10.3t1.22. Furthermore, the D-t relationship was found to depend on the irradiation temperature in contrast to theoretical predictions by the lateral stress model of blister formation. These results do not appear to support the lateral stress model which predicts the relationship D∝t1.5. However, the experimentally determined relationships can be explained in part by the gas pressure model of blister formation.
Interpretation of elastic-wave scattering theory for analysis and design of flaw-characterization experiments: The long-wavelength limit
Authors: Gubernatis J. E. , Krumhansl J. A. , Thomson R. M.
Published: February 2003

Recently, the results of a general theory of the scattering of elastic waves from a flaw embedded in an isotropic medium were shown in the far-field limit to be compactly represented by a single vector, the f vector. Studying the f vector is thus a way to investigate systematically the dependence of the scattering on the polarization of the incident mode, scattering angle, changes in material parameters, and shape. In the long-wavelength limit the f vector is exactly determinable and exhibits significant features of the flaw. We discuss long-wavelength scattering results for volume flaws and idealized cracks and compare some of the results with those of the Born approximation, which has already been calibrated by comparison to exact calculations and experiment.
On the yield strength of diamond
Authors: Ruoff Arthur L.
Published: February 2003

This paper describes how the yield stress of strong single crystals can be estimated from the Hugoniot elastic limit and the second- and third-order elastic constants. Data on germanium and silicon are analyzed. The dynamic yield stresses obtained are compared with a directly measured static value for silicon and for values obtained from Knoop hardness tests. The dynamic results for silicon and germanium are used along with a scaling law to estimate the yield stress for diamonds. This, in turn, is found to compare favorably with the values deduced from Knoop hardness tests and a directly measured static yield stress. The yield stress of diamond is approximately 35 GPa.
Scattering of low-energy electrons on micron-size pinholes
Authors: Spears D. P. , Allen J. D. , Anderson V. E. , Becker R. S. , Hubbell H. H. , Ferrell T. L. , Ritchie R. H. , Birkhoff R. D.
Published: February 2003

In exploring forces between charged particles and surfaces, we have sent a beam of low-energy (0.5–40 eV) electrons through two (laser drilled) micron-size pinholes in thin films of gold spaced 10 cm apart. Image forces associated with the solid around the second pinhole cause the beam to diverge into an angular distribution which is scanned with a movable slit and Channeltron detector. Distributions have widths which depend inversely on electron energy as expected from transit time considerations. The paraxial portion of the distribution appears to diverge as though from a weak negative electron lens. The impulse approximation for the radial component of the electron motion is used to derive a radial potential averaged along a line parallel to the pinhole axis. This potential approximately equals the expected value e/4x at x=10 Å from the pinhole edge but deviates from this function at greater distances. This deviation may be due to geometric effects, to the impulse collision model employed, or to geometric irregularities at the edge. The results are useful in estimating efficiencies of filters for charged aerosol collection.
Spherical aberration coefficients of double-cylinder electrostatic lenses over wide magnification ranges
Authors: Saito Tsunenari , Sovers Ojars J.
Published: February 2003

Focal properties and spherical aberration coefficients of double-cylinder bipotential electron lenses are calculated by numerical solution of Laplace’s equation and the electron trajectory equations. A wide range of electrode gap sizes is investigated. The variation of focal and aberration properties with lens geometry, magnification, and focus voltages is represented by analytic functions. These describe the entire family of lenses to a high degree of approximation, and are expected to be useful in practical lens design problems. At a fixed focal length, it is possible to decrease the spherical aberration coefficient substantially by increasing the electrode gap size.
Electron-beam-controlled transmission of 10-μm radiation in semiconductors
Authors: Corkum P. B. , Alcock A. J. , Leopold K. E.
Published: February 2003

An electron beam has been used to control the transmission of 10.6-μm radiation in Ge, ZnSe, and CdTe samples. With an ∼2.5-A/cm2 20-ns pulse of ∼110-keV electrons incident on the semiconductor, the transmission falls abruptly, recovering in approximately the recombination time of the semiconductor. Carrier-absorption cross sections at 10.6 μm have been determined for CdTe and ZnSe. Semiconductor transmission switching provides a broad-bandwidth active isolator which may find applications in high-gain CO2 laser systems.
Optical properties of single-crystalline ZnO film smoothly chemical-vapor deposited on intermediately sputtered thin ZnO film on sapphire
Authors: Shiosaki T. , Ohnishi S. , Kawabata A.
Published: February 2003

ZnO-Br2-O2, ZnCl2-O2, and ZnO-H2-H2O-O2 chemical-vapor-deposition (CVD) systems are studied to obtain as-grown optical waveguides of single-crystalline ZnO on sapphire. The waveguide is made on a very thin sputter-deposited epitaxial layer of ZnO on sapphire by using the ZnO-H2-H2O-O2 isothermal CVD system. The minimum loss obtained for the TE0 mode propagating perpendicular to the c axis in a (112̄0) ZnO film is 0.7 dB/cm. This chemical-vapor deposition of ZnO on a thin-sputtered ZnO film gives a method for the fabrication of strip waveguides on sapphire due to the selective growth of the ZnO films on sputter-deposited ZnO strips.
Performance characteristics of a Pr-based infrared quantum-counter imaging system
Authors: Krasutsky N. J. , Case W. E. , Chivian Jay S.
Published: February 2003

We have evaluated the resolution and sensitivity of a Pr3+ infrared quantum counter near 4.5 μm under the conditions required for operation as an imaging detector. Our measurements indicate center-to-center spacing of resolution cells in the crystal to be (conservatively) 75 μm. Further, fluorescence collected from a 75-μm-diam cell on the crystal yields a detectivity value comparable to that obtained with an earlier nonimaging system.
Be doping of liquid-phase-epitaxial InP
Authors: Abrams E. B. , Sumski S. , Bonner W. A. , Coleman J. J.
Published: February 2003

The distribution coefficient for Be-doped liquid-phase-epitaxial InP is determined to be kBe?0.1. Comparison is made with other p-type and n-type impurities with regard to suitability for use in GaInPAs-InP double heterostructures.
Corrections to proximity effects in electron beam lithography. II. Implementation
Authors: Parikh Mihir
Published: February 2003

Mathematical formulations for the correction of proximity effects in electron beam lithography have been developed in the preceding paper. The implementation of these techniques to practical electron lithographic patterns involves (1) an efficient evaluation of the proximity interaction between every pair of shapes in the pattern. This interaction can be computed explicitly in limited cases; an algorithm for general cases is described. (2) The solution of the linear equations that yield the corrections to proximity effect. This is accomplished via a series of algorithms that involve dissecting the data into overlapping zones of different types. Pattern data manipulation is reduced by an algorithm involving generation of additional data, tagging, and sorting.
Corrections to proximity effects in electron beam lithograhy. III. Experiments
Authors: Parikh Mihir
Published: February 2003

Satisfactory corrections to intershape and intrashape proximity effects in electron lithography have been experimentally obtained for a variety of patterns and geometries. The self-consistent formulation and the algorithms for computation described in the two preceeding papers have been used. The computer program used for the automatic computation of corrections to the incident electron exposure for an arbitrary pattern is described. Pattern delineation depends on the proximity function and its parameters. They are found to be not critical in practical lithography until submicron dimensions are reached.
Ion-beam deposition of thin films of ferroelectric lead zirconate titanate (PZT)
Authors: Castellano R. N. , Feinstein L. G.
Published: February 2003

Lead zirconate titanate is a solid solution with nominal composition Pb(ZrxTi1−x)O3. Ferroelectric thin films of this material have been successfully deposited by a focused ion-beam sputtering technique in an O2 atmosphere. These films were characterized according to composition, crystal structure, and dielectric and ferroelectric properties. The effects of deposition temperature, heat treatment after deposition, and substrate and target material were investigated. The composition of the films was within 1 at.% of the composition of the multicomponent PZT target for substrate temperatures up to 200 °C. The Pb concentration decreased for substrate temperatures above 200 °C. Films deposited at substrate temperatures below 250 °C were microcrystalline. At 300 °C, the pyrochlore phase was obtained. Films with the ferroelectric perovskite structure were deposited above 400 °C, which is the lowest deposition temperature ever reported for this phase. O2 losses during postdeposition annealing resulted in a collapse of the perovskite structure. Ferroelectric hysteresis loop measurements indicated a saturation remanent polarization of 4.9 μC/cm2 and a coercive field of 25.2 kV/cm.
The emissivity of LaB6 at 650 nm
Authors: Storms Edmund K.
Published: February 2003

The emissivity of LaB6 at 650 nm between 1600 and 2100 K can be described by the equation e=1.2144−2.467×10−4Ts, where Ts is the observed surface temperature.
Valence alternation pair model of charge storage in MNOS memory devices
Authors: Kirk C. T.
Published: February 2003

Certain point defects in amorphous silicon nitride called valence alternation pairs (VAP) appear to be able to account not only for the charge storage and decay characteristics of MNOS memory devices but also for the fatigue phenomena that occur in these devices after undergoing a sufficiently large number of write-erase operations. The theory and properties of VAP defects in the nitride are described. A model for the MNOS memory device based on the existence of VAP defects in the nitride is proposed. Charge storage, decay, and fatigue characteristics of MNOS devices are explained in terms of the model.
High-temperature electron mobility in ZnSe : Al and ZnSe : As
Authors: Ray A. K. , Kröger F. A.
Published: February 2003

Experimental values of high-temperature Hall mobility in ZnSe : Al and ZnSe : As are compared with theoretical values calculated taking into account lattice scattering and ionized impurity scattering. It is seen that the latter has a marked effect on the mobility up to 1000 °C in samples with dopant concentrations of 5×1017 cm−3. The Conwell-Weisskopf theory for impurity scattering describes the results slightly better than the Brooks theory.
Imaging of thin intergranular phases by high-resolution electron microscopy
Authors: Krivanek O. L. , Shaw T. M. , Thomas G.
Published: February 2003

We discuss the imaging of thin amorphous intergranular films by high-resolution electron microscopy. The thin films can either be imaged indirectly as gaps between two crystalline grains, or directly by dark-field imaging of the diffuse scattering due to the amorphous phase. The new direct method is shown to be much less dependent on defocus and boundary orientation than previous methods. It is also capable of precise determination of the boundary film thickness, and is much easier experimentally than other methods.
Fe80B20−xSix glasses: A study of some physical properties as depending on metalloid content
Authors: den Broeder F. J. A. , van der Borst J.
Published: February 2003

It is found that the formation of Fe80B20−xSix metallic glasses and their thermal stability improve considerably upon substituting silicon for boron in the range 0<x<5, but diminish again at higher concentration. This behavior is suggested to be of structural origin. The dependence of the magnetic moment and Curie temperature on x is relatively small. The variation of the magnetic properties, being different from those of corresponding cobalt glasses, is discussed in terms of change in the band shape through electron hybridization and of charge transfer which occurs when transition metals are alloyed with metalloid elements. The microhardness decreases continuously as boron is replaced by silicon. With a simple model, by treating atoms as macroscopic pieces of material, it is shown that this effect is due to variations of the molar volume and compressibility of the different metalloid elements.
Inhomogeneities in horizontally dipped LPE (La,Ga): YIG films studied by spin wave resonance
Authors: Algra H. A. , Robertson J. M.
Published: February 2003

A series of films with different dipping times were grown using the LPE method. The [111] GGG substrates were horizontally dipped with a rotation rate of 41 rpm. The saturation magnetization and the lattice mismatch were measured. The uniaxial anisotropy, as determined by the spin wave resonance technique, of both the transient layer and the bulk of each of these films, shows a typical behavior. These phenomena can be interpreted such that when a film grows not only the outside layer changes, but also the bulk of the film changes its properties. Further information has been obtained by a chemical etching experiment. The experimentally obtained spin wave resonance spectra are compared with numerically calculated resonance spectra and reveal that our films are homogeneous throughout the film thickness except for a very small region of 0.5 μm thickness next to the substrate-film interface, which can be understood from the growth kinetics.
Piezoelectric coupling and dislocations in III-V compounds
Authors: Booyens H. , Vermaak J. S.
Published: February 2003

By considering the coupling effect between the direct and converse piezoelectric effects, general expressions are derived for the polarization charge distribution and electric field due to a general dislocation with its line along a 〈110〉 direction in undoped crystals of the sphalerite structure. It is found that there exists a line charge on the dislocation which is in general different from the dangling bond charge. Furthermore, there exists a critical value of this charge for which the dislocation attains a minimum energy configuration in which the radial component of the electric field disappears. The equilibrium polarization charge distributions associated with pure edge and 60° dislocations in undoped GaAs are determined numerically. The effects of these charge distributions on the free carriers in crystals are discussed.
Characterization of 31P+-implanted Si layers by ellipsometry
Authors: Nakamura Kunio , Gotoh Tsuyoshi , Kamoshida Mototaka
Published: February 2003

Ellipsometry has been used to investigate damage in 1013-1016/cm2 31P+-implanted Si and crystallinity recovery by subsequent annealing. Implantation-induced changes in optical constants, calculated from measured ellipsometric data, become prominent for implantation over the critical dose for amorphization. The refractive index increases with increasing implant dose, except when the implant dose exceeds 1015/cm2. The extinction coefficient increases monotonically with increasing implant dose and decreasing implant temperature. The dose dependence of the change in reflectivity shows a good agreement with the results by channeling effect analysis. For a sample implanted over the critical dose, optical constants and sheet resistances rapidly recover after annealing at around 500 °C, corresponding to epitaxial regrowths of implantation-induced amorphous layers.
Resistance to shock-front propagation in solids
Authors: Gilman J. J.
Published: February 2003

The structure of a strong shock front is modeled using a wall of dislocations. Motion of these dislocations changes the density of the solid medium and simultaneously relaxes the shear strains that would otherwise exist behind the front. The dislocation motion is highly dissipative because it requires atoms in intimate contact to slide over one another. This transports momentum down the velocity gradient. It is shown that the energy dissipation rate associated with dislocation motion is larger than for any other general mechanism in the system, including electron-electron, electron-phonon, and phonon-phonon interactions. The reason for this is that electrons are not effective in transporting momentum, and atomic thermal velocities are substantially smaller than the velocities of the dislocations which move with the shock front. The viscosity coefficient associated with the dislocations is propertional to the shock velocity, so the viscous drag stress is proportional to the square of the shock velocity. This can lead to large drag pressures.
Tritium diffusion in rutile (TiO2)
Authors: Cathcart J. V. , Perkins R. A. , Bates J. B. , Manley L. C.
Published: February 2003

The diffusivity of tritium in rutile single crystals has been measured parallel to the a and c axes in the temperature range 250–900 °C. Raman-scattering measurements were also made to aid in identifying a nonpolar tritium species involved in the diffusion process. Two species, OT− ions and T2 molecules, are involved in tritium migration. The OT− ions dissociate preceding each tritium jump. Along the a axis the T2 molecules diffuse four orders of magnitude slower than the T+ ions associated with OT−. No dependency of the tritium diffusivity upon the rutile defect structure was observed.
Parametric mixing of surface acoustic waves
Authors: Adamou A. , Alippi A. , Palma A. , Palmieri L. , Socino G.
Published: February 2003

A simple approximate theory for the explanation of the parametric mixing of collinear surface acoustic waves (SAW) is proposed. The proposed theory considers only the transverse elastic displacement of the waves and neglects piezoelectricity. The effect of the quasiexponential wave profiles on the interaction is described by two factors of form, one for the up, F312, and one for the down, F412, conversion. Using an optical method, the nonlinear coupling coefficients for the up and down conversions have been measured as a function of the fundamental-frequency ratio f2/f1. This was performed for YZ LiNbO3 in the 20–100-MHz range of frequencies. The observed variations of the magnitudes of the coupling coefficients were found to be in good agreement with those predicted theoretically. Notably, the magnitude of the coupling coefficient for the up conversion was found to be nearly constant and twice as large as that of second-harmonic generation, whereas that of the down conversion decays almost linearly with f2/f1 according to ∼ (1−f2/f1).
A fracture model of radiation blistering
Authors: Kamada K. , Higashida Y.
Published: February 2003

The formation process of blisters is interpreted by a fracture model on the basis of the stress fields around a lenticular bubble calculated in a previous paper. This model implicitly presumes a microcrack nucleated at a depth near the projected range of the ions. Two factors are separated theoretically to explain the blister formation: One is a geometrical factor which depends only on the ratio of size to depth, from a free surface, and the other factor is proportional to the square of the ratio between the internal gas pressure of the bubble to plastic yield stress of the target materials, depending entirely on the physical and chemical properties of the materials and gas atoms. The relation between the blister diameter and the cover thickness must be basically linear as expected from the first factor, but is modulated by the second factor, giving a slight departure from linearity as observed by experiment. The ratio of the gas pressure to the yield stress must be 0.02–0.2 in magnitude and depends on the ion energy and the target materials. This value leads to an estimation that the amount of gas atoms contained in the blister is about 10% of the injected ions. Griffith’s criterion for the crack propagation in the subsurface layer with taking into account of ductility of the materials near the crack tip was derived, and showed that the estimated internal pressure of the blister is far smaller than the necessary pressure to satisfy the criterion. The objections against the gas-pressure model were criticized on the basis of the present model.