bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffraction by truncated Gaussian apertures: An experimental study
Authors: Horng Jing Shyang , Li Yajun
Published: July 2002

Diffraction of focused truncated Gaussian beams at a circular aperture is investigated experimentally. The beams are obtained from a uniformly illuminated Gaussian transmittance filter. The irradiance along the axis is measured point by point in order to demonstrate the existence of the focal shifts. Diffraction patterns in various planes normal to the axis are presented by photographs. Measured results are compared with theoretical predictions. Close agreement between them has been obtained.
Deuterium implantation in magnetic garnets
Authors: Wilts C. H. , Urai A.
Published: July 2002

The magnetic effects of deuterium implantation and subsequent annealing were measured in Gd, Tm, and Ga-substituted yttrium iron garnet films for comparison with measurements made earlier with hydrogen implantation. Implantation energy was 60 keV and the dose ranged from 0.5 to 3×1016 ions/cm2 for D+2 ions, as compared to an energy of 120 keV and a dose from 0.3 to 4×1016 ions/cm2 for H+2 in the earlier study. Measurements made included x-ray rocking curves and ferromagnetic resonance spectra measured at 9.5 GHz. For all doses the implanted layer remained crystalline. Implanted layer thickness was about 4200 Å and peak strain occured at a depth of 2600 Å. Peak strain increased monotonically, but departed from a linear relation with dose. For the highest dose, the peak strain was 2.5%. Relaxation of strain with annealing was intermediate between that found earlier for hydrogen and neon implantation. As compared to all other implant elements, both deuterium and hydrogen show a large anomalous magnetic anisotropy which can exceed 10 000 Oe for either ion. The absence of this effect for He, Ne, and other ions supports the conjecture that the effect is chemical and related to electronic bonding rather than strain or disorder. The anomalous anisotropy for deuterium decreases and shifts location with annealing. It has largely disappeared at temperatures of 300–350 °C. The shape of the profile is consistent with the hypothesis that the shift in anisotropy is associated with diffusion of the deuterium atoms to the surface of the garnet film. At the highest dose, crystalline damage in the region of highest strain is sufficient to radically alter magnetic properties and in particular reduces even the excess anisotropy so that a two-peak profile results until modified by annealing.
Dissolution pits and Si epitaxial regrowth in the Al/(111)Si system
Authors: Fujimura Norifumi , Kurosaki Hideki , Ito Taichiro , Nakayama Yutaka
Published: July 2002

The reaction between an Al film and a (111) single-crystal Si has been studied by microscopic observation. Dissolution pits were formed on the Si surface due to dissolution of Si into the Al film, by annealing above 300 °C. The shapes of the pits were triangular or hexagonal shaped with a flat bottom. Each side of the pits was parallel to the 〈110〉 directions of the substrate. At the dissolution pits, triangular or hexagonal Si islands regrew epitaxially to the substrate in the Al film. A mechanism for the formation of the dissolution pits and Si epitaxial regrowth is proposed in relation to the strain fields affected by the strain centers in the Si substrate.
Field injection electrostatic spraying of liquid hydrogen
Authors: Woosley J. P. , Turnbull R. J. , Kim K.
Published: July 2002

Uniform charged liquid-hydrogen drops are produced using the method of field injection electrostatic spraying. This method consists of forming a meniscus of liquid hydrogen at the end of a glass nozzle and injecting charge into the liquid using a sharp electrode raised to a high voltage. A small pressure drop across the nozzle results in a constant volume flow rate of liquid through the nozzle allowing a drop to form and drip off. As the amount of charge injection increases with the raised needle electrode voltage, the drop size decreases due to the increased electrostatic forces compensating for the surface tension forces. As a result, the drops drip off at an increased frequency. Eventually a charged jet forms which in turn breaks up into small uniform charged drops. A detailed description of the experimental apparatus is presented. Experimental results are presented and discussed.
Influence of lattice misfit on heterojunction bipolar transistors with lattice-mismatched InGaAs bases
Authors: Ashizawa Y. , Akbar S. , Schaff W. J. , Eastman L. F. , Fitzgerald E. A. , Ast D. G.
Published: July 2002

AlGaAs/InGaAs/GaAs heterojunction bipolar transistors (HBTs) with lattice-mismatched InGaAs bases have been studied for determining the effect of misfit defects on device performance. Defect structures were investigated using scanning cathodoluminescence and transmission electron microscopy. Misfit dislocations were found to form at the bottom interface between n-InGaAs and n-GaAs in the collector. Electrical properties of lattice-misfitted n-GaAs/n-InGaAs heterojunctions were studied using p+-GaAs/n-GaAs/n-InGaAs diode structures. Deep-level transient spectroscopy measurements revealed electron traps (Et=0.49–0.55 eV) and hole traps associated with the lattice-misfitted interface. Devices showed high dc current gains in spite of the presence of misfit dislocations. Poorer saturation of collector current was observed with increasing defect density. HBTS with lattice-mismatched InGaAs bases are considered to be relatively insensitive to the introduction of misfit dislocations in terms of dc characteristics.
An optical demultiplexer using a flexible replica grating, an embedded optical waveguide, and an uneven fiber space array
Authors: Kuzuta Nobuyuki , Hasegawa Eiichi
Published: July 2002

A three-channel optical demultiplexer has been developed. A flexible replica grating, an embedded optical waveguide, and an uneven fiber space array were used to assemble the demultiplexer. The flexible replica grating showed good demultiplexing characteristics. The uneven fiber space array was used to arrange the center wavelength of each channel to be 1200, 1310, and 1550 nm, respectively. The minimum insertion losses of the channels ranged from 2.0 to 2.4 dB, and the difference between the experimental value of the center wavelength and the designed one was very small within 2 nm.
Radiated power from short period undulators with a large magnet gap
Authors: Csonka Paul L. , Watanabe Hiroshi , Tatchyn Roman O. , Toor Art
Published: July 2002

The total power Ptot radiated by an electron beam passing through an undulator is studied as a function of the undulator wavelength λu, while the magnet gap g remains fixed. As expected, for λu≫g, the Ptot falls off exponentially for decreasing λu, but for smaller λu the falloff is less steep and, in particular, for λu→0, Ptot is asymptotically proportional to λu.
120-ps duration pulses by active mode locking of an XeCl laser
Authors: Shay T. M. , Sze R. C. , Maloney M. , Figueira J. F.
Published: July 2002

A short actively mode-locked XeCl oscillator has produced 120-ps duration pulses for the first time. The pulses have an energy of 15 μJ and a modulation depth of >95%. The evolution of the pulsewidth during the mode-locked pulse train was also measured.
Electron-density distribution in a laser tube with a hyperboloid of revolution boundary: Nonisothermal case
Authors: Young Mary R. , Demas Nicholas G. , Ventrice Carl A.
Published: July 2002

The electron density is determined in a laser tube that is formed by a hyperboloid of revolution and spherical-end surfaces. The electron temperature variation is accounted for by allowing the ratio of the free-electron production factor α to the diffusion coefficient Da to be a function of the local tube radius. Calculations are made assuming different symmetrical optical resonator configurations ranging from near planar to near confocal. The tube geometry is specified in terms of the optical resonator parameters: resonator length L, mirror radius of curvature Rm, and optical spot size at the mirror surface d. The active medium is assumed to be low-temperature, weakly ionized plasma. Schottky boundary conditions are assumed and the particle-diffusion equation is solved using oblate spheroidal coordinates. The oblate spheroidal angular dependence (which in the cylindrical limit corresponds to the variation perpendicular to the axis of the cylinder) of the density is found to be that of a zero-order Bessel function. The oblate spheroidal radial dependence (which in the cylindrical limit corresponds to the axial dependence) is obtained by means of numerical methods. Radial density profiles are calculated, assuming L=1.0 m, for various Rm /L ratios. The peak radial density is found to remain at the center of the tube (Z=0) for all values of Rm /L>0.5.
Theoretical transient currents from two-component unipolar space-charge swarms in fields in media
Authors: Henson Bob L.
Published: July 2002

Using an arbitrary initial unipolar space-charge distribution consisting of two species of charge carriers of different but constant mobilities in a medium, relations for the electric fields and charge-carrier densities are derived as functions of positions and time. The highly nonlinear, one-dimensional equations, which are derived for swarms of charge carriers between parallel plane electrodes with a fixed potential difference, include the effects of the space-charge fields. A general method is outlined which, in principle, can be used to generate a second order differential equation whose solution predicts the time-dependent current caused by the drifting space-charge swarm. The general equations are applied to the special case where the initial space-charge distributions are uniform in a solid or fluid medium. Although the resulting differential equation is complicated, the equation is in a form such that its solutions could be computer generated.
Infrared laser beam positioning with an inexpensive pyroelectric detector
Authors: Küttel Olivier M.
Published: July 2002

A Philips pyroelectric detector is used as a precise infrared beam positioner (λ=6.5–14 μm). The accuracy in X and Y direction is ≤±10 μm (≤±40 μm) for beam diameters of 2w=0.3–10 mm (10–35 mm). Furthermore, this detector allows the determination of beam diameters exceeding 4 mm.
Annealing temperature dependence of T
C of thin-film Gd grown on a glass substrate
Authors: Nakamura O. , Baba K. , Ishii H. , Takeda T.
Published: July 2002

Thin films of Gd were grown on a glass substrate with a sputtering technique. Measurements of x-ray diffraction, magnetization, and electrical resistance were carried out for different samples that were annealed at various temperatures after the deposition. The deposited films are polycrystalline of hcp structure with preferred orientation, with the (100) plane parallel to the sample surface. The estimated Curie temperature TC of these films changes between 273 and 293 K, depending on the annealing temperature. It is found that this variation of TC is correlated with the relaxation of lattice imperfections.
Some remarks on excitation spectra versus photoluminescence spectra for the evaluation of quantum wells
Authors: Miller Robert C. , Bhat Rajaram
Published: July 2002

Several GaAs/AlxGa1−xAs single-quantum-well samples are examined via photoluminescence and excitation spectra to emphasize that in many cases there is a poor correlation between the perceived qualities of quantum wells as deduced from each of the two different kinds of spectra.
Magnetic properties and media noise of Co-Ni-P plated disks
Authors: Yoshida Kazuetsu , Yamashita Takeo , Saito Makoto
Published: July 2002

Magnetic properties and read-write characteristics of Co-Ni-P plated disks are examined. In-plane coercive force and squareness increase with increasing the thickness of an Ni-P layer which is formed between the substrate layer (Cu-Sn) and Co-Ni-P film. However, media noise increases with thickening of the Ni-P layer. The relationships between magnetic properties and media noise are investigated by measuring rotational hysteresis (Wr) and its integral (RH). As a result, it is found that media noise closely correlates RH values: smaller RH values cause less media noise. This result shows that media noise is dominated by the magnetization process, and magnetic thin film in which the magnetization process occurs through coherent rotation is desirable for magnetic recording media.
Measurements on standing waves in GaAs coplanar waveguide at frequencies up to 20.1 GHz by electro-optic probing
Authors: Zhu Z. H. , Wu M. C. , Lo Y. H. , Pan C. L. , Wang S. Y. , Wang S.
Published: July 2002

We report the experimental results of the standing waves in GaAs coplanar waveguides at frequencies up to 20.10 GHz with different terminations (open, short, and 50 Ω) by a new electro-optic probing technique. The effective refractive indices from 4.11 to 20.10 GHz are presented and compared with theoretical values. Dispersion of coplanar waveguide in that frequency range is shown to be negligible.
A moving dislocation kink as the soliton on a background of quasiperiodic process in unbounded sine-Gordon system
Authors: Pawel/ek A. , Jaworski M.
Published: July 2002

This paper deals with an extension of the well-known case of the harmonic oscillation of a nonkinked dislocation line to the case of both harmonic and anharmonic oscillations of a dislocation line in the presence of a moving kink. The one-kinked dislocation is considered as the unbounded, nondissipative sine-Gordon system, and the mixed, one-soliton one-periodic solutions of the sine-Gordon equation, recently obtained by applying the method of Riemann theta function, are used for this purpose.
Solid-state nucleation at the interfaces of thin Ni films on CdTe and Hg0.8Cd0.2Te
Authors: Ehsani H. , Bené R. W.
Published: July 2002

The interfacial reaction between thin Ni film (deposited by either e beam evaporation or sputtering) and (Cd, Hg0.8Cd0.2)Te has been investigated using transmission electron microscopy and diffraction. Auger depth profiles have been used to determine the distribution of Te, Cd, Hg, and Ni with respect to the interface of Ni-Hg1−x CdxTe. In the Ni-Hg0.8Cd0.2Te system, we observed the δ-phase (NiTe-NiTe2) formation upon deposition of 40- and 80-Å Ni films with either deposition system at the as-deposited temperature. The electron diffraction patterns of the δ phase and some Ni were observed, with the formation of the δ phase located at the interface. The electron diffraction of both the Ni film and δ phase were partially ordered with respect to the substrates. The Auger depth profile indicated that the excess of Te appeared mostly at the interface. Annealing of the Ni-Hg0.8 Cd0.2 Te system in a vacuum and at 100, 200, and 300 °C shows growth of the crystal and increased ordering of the δ phase. In the Ni-CdTe system the generation of Te was observed for both sputter deposition and e beam evaporation. Auger profiling indicated that the amount of Te generated by sputtering was approximately three times the amount of Te generated by e beam evaporation. The generated Te was mostly accumulated at the interface of Ni-CdTe. We observed δ-phase formation upon annealing at 250 °C after sputter deposition, and at 300 °C after e beam evaporation of Ni on CdTe substrates, but the crystallites did not have the orientational relation with CdTe substrates (texturing), as was seen in the Ni-Hg0.8 Cd0.2 Te system.
Electrical characterization of epitaxial layers of In0.71Ga0.29As0.63P0.37
Authors: Shibli̇ S. M. , Garcia de Carvalho M. M.
Published: July 2002

We have performed measurements of carrier concentration and Hall mobility, between 4.2 K and room temperature, in InGaAsP (energy gap of 0.96 eV) epitaxial layers grown on semi-insulating InP. It is shown that for this kind of material in the range of concentration studied (2.0×1016–1.6×1018 cm−3), alloy scattering has to be taken into account as a mechanism limiting the mobility even at low temperatures. Also, in the entire range of temperature and concentration studied, Fermi-Dirac statistics are better suited than Boltzmann statistics for theoretical calculations of Fermi energy, because even for concentrations as low as 2.0×1016 cm−3, the material is degenerated at low temperatures. Following these assumptions, we have calculated the alloy scattering potential as being between 0.52 and 0.62 eV.
Bonding configuration of fluorine in fluorinated silicon nitride films
Authors: Fujita Shizuo , Toyoshima Hideo , Sasaki Akio
Published: July 2002

Bonding configuration of constituent elements in fluorinated silicon nitride insulating films prepared by reactive plasma of SiF4 (or SiF2), N2, and H2 gas mixture is investigated by means of optical absorption analysis and electron-spin resonance study. Fluorine is bonded to silicon rather than to nitrogen. Slight variations of spin density and optical gap with chemical composition are attributed to the complemental increase of fluorine with decrease of nitrogen, and to the passivation of silicon dangling bonds by fluorine atoms.
Reexamination of recent experimental results in surface-wave-produced argon plasmas at 2.45 GHz: Comparison with the diffusion-recombination model results
Authors: Sola A. , Gamero A. , Cotrino J. , Colomer V.
Published: July 2002

In this paper we comment on recently reported experimental data about some characteristic magnitudes of plasma columns produced and maintained by surface microwaves. We then compare them with theoretical values obtained from the diffusion-recombination model of Mateev, Zhelyazkov, and Atanassov [J. Appl. Phys. 54, 3049 (1988)] and Zhelyazkov, Benova, and Atanassov [J. Appl. Phys. 59, 1466 (1986)] for the same magnitudes, in a wide range of operating conditions. Such a comparison allows us to make conclusions about the results of the model and its hypothesis.
Emission distribution, brightness, and mechanical stability of the LaB6 triode electron gun
Authors: Gesley Mark , Hohn Fritz
Published: July 2002

Experiments have characterized the operation of a LaB6 triode gun in a standard three-lens column of the type used for Gaussian electron-beam lithography and scanning electron microscopy. A series of images representing cross sections of the three-dimensional spatial distribution of current emitted from the gun is obtained by configuring the electron optics as a scanning confocal microscope. The gun acts as an immersion objective whose image is scanned by deflection coils and focused by the condenser lenses onto a pinhole transmission detector. Characteristics of the emission distribution include an emission image of the cathode surface situated between two distinct beam crossovers whose origin is either the apex (001) and {310} planes or the large {110} planes on the machined 90° cone angle of the cathode surface. Virtual objects are imaged when the back focal plane of the condensers falls inside the high-field region of the gun. The target axial brightness is dependent on gun excitation and angular acceptance angle. The temperature-dependent brightness of the cathode is used to determine its effective emission area, work function, and surface electric field. Beam positional stability of three-carbon-mounted LaB6 directly heated cathodes is measured. However, for measurement times ≤100 h the drift rate is found to be limited by thermal expansion of the movable anode assembly and not the particular cathode mounting technique.
The ultimate frequency response and time evolution of resonant tunneling in double-barrier structures
Authors: Kan S. C. , Yariv A.
Published: July 2002

A new approach to treating the problem of the frequency response of tunneling barriers is demonstrated. The Schrödinger equation for an incident monoenergetic electron is solved in the case of a double-barrier structure with an applied potential oscillating at an arbitrary frequency. The details of the tunneling in the transient stage and the following steady state, as well as the charging and discharging processes around the structure, are revealed in the high-frequency modulation regime. We find that the linear frequency response for a typical fast structure rolls off above 1.5 THz with a 1/f dependence. An enhancement in the nonlinear frequency response at 770 GHz is observed for a single electron tunneling. From the motion of the wave front in the structure, we find that the phase transit time across the structure ranges from 140 to 40 fs decreasing with frequency. Generation of the transmitted pulses with an energy spread about ℏω where ω is the angular modulation frequency is observed. This corresponds to an emission and absorption of a quantum of ℏω.
Inequality of surface potential of specimen in plasma anodization
Authors: Matsumura Koki
Published: July 2002

In plasma anodization the oxide growth rate decreases with time during constant current anodization. This phenomenon has been studied noting that the surface potential of specimens is closely related to the current efficiency. The oxide growth rate during the plasma anodization of aluminum wires or films is observed to vary depending on the dimensions of specimens and also on the thickness of a wet-anodic Al2O3 film previously grown on the specimen surface. It turns out that the surface potential changes not only because the plasma-anodic Al2O3 film itself is not uniform in thickness but also because the surface potential of the oxide film is floating in a plasma. The change of the surface potential was observed using a sounding probe. It is concluded that a difference in the surface potential exists between the central part and the peripheral part of the specimen, and that the difference increases with the increase of the forming voltage. The change of the surface potential may be the cause of the rate-limiting process in the oxide growth during the plasma anodization.
Low-temperature SOI (Si-on-insulator) formation by lateral solid-phase epitaxy
Authors: Miyao M. , Moniwa M. , Kusukawa K. , Sinke W.
Published: July 2002

Low-temperature (550–600 °C) formation of a Si-on-insulator structure by a solid-phase process is investigated. A microprobe (μ) reflection high-energy electron diffraction observation reveals that oriented crystal growth propagates from the seeding area in solid-phase epitaxy (SPE). The effects of random nucleation, epitaxial alignment, and local doping on lateral (L)-SPE are examined. As a result, a relatively large L-SPE area, 14 μm from the seeding area, is achieved on insulating regions. Crystal quality and electrical properties of L-SPE layers are examined using μ-Raman spectroscopy and field-effect transistor fabrication. A small stress field, 2.5×109 dyn/cm2, and high electron mobility, 720 cm2/V s, comparable to that of bulk Si are obtained.
Preparation and electrical properties of LaCr1−xCuxO3
Authors: Hirai Y. , Kubota K.
Published: July 2002

The perovskite-type ceramic LaCr1−xCuxO3 was prepared by the solid-state reaction or the coprecipitation method in the range of 0≤x≤0.5. X-ray diffraction, and electrical and some optical measurements were performed to examine the crystal structure and other physical properties. In this range, all samples show p-type semiconducting properties, and the transport mechanism is attributed to a hopping of a small polaron. The conductivity increases and the activation energy decreases as the concentration of Cu increases. At low temperatures, electrical properties show a variable range hopping caused by the Anderson localization mechanism. According to the activation energy dependence of the Cu concentration, we suggest that the virtual insulator-metal transition occurs at the critical concentration xc=0.77.
Excitation of leaky guided waves in infinite cylinders by obliquely incident acoustic waves
Authors: Molinero I. , de Billy M.
Published: July 2002

The scattering of a bounded acoustic beam by elastic infinite cylinders is investigated for oblique incidence. The nonspecular effects and the frequency analysis confirm the existence of dispersive leaky guided waves propagating along the axis of the cylinder. In the present work the nongeometrical effects and the resonance phenomena are used to measure the phase velocity dispersion curves. The experimental measurements obtained with a stainless-steel cylinder immersed in water are in good agreement with the theoretical calculations. The experiments are limited to the values of ka<16 (k is the wave vector and a designates the radius of the cylinder).
Dielectric composites incorporating enthalpy stabilization for NbTi windings
Authors: Lawless W. N. , Clark C. F.
Published: July 2002

Composites of ceramic powders in epoxies appropriate for both insulating and impregnating NbTi windings are studied. Specific heat, thermal conductivity, thermal contraction, and magnetocaloric measurements on composites are presented. Thermal contractions well matched to copper are found, and thermal shock resistance is greatly enhanced. Enthalpies, 4.2–6 K, range up to 80 mJ cm−3 and are 20–50 times larger than that of the pure epoxies. The thermal group parameter, η=(κρC)1/2, is 2 1/2 –4 times larger than that for epoxy (data are given for magnetic field strengths up to 8 T). An interesting magnetocaloric stabilization mechanism is found: on up-ramp, a magnetocaloric enthalpy ≤7.6 mJ cm−3 is available for stabilization via adiabatic-magnetization cooling. Results are not specific to the epoxies used but apply to composites with any amorphous matrices.
Time resolved plasma photoemission of myocardium with excimer laser excitation
Authors: Gauthier T. D. , Clarke R. H. , Isner J. M.
Published: July 2002

Time resolved emission spectra of myocardium irradiated with 193- and 308-nm excimer laser radiation were recorded as a function of laser fluence. The laser fluence impinging on the sample varied from 0.48 to 2.0 J/cm2. It was found that the recorded emission spectra depend greatly on the incident laser fluence and time delay. At a laser fluence of 2.0 J/cm2 and short delay, the emission spectra are dominated by nitrogen ion emission lines. At longer delays and lower laser fluences C2 and CN radical emission spectra are recorded. The sequence in which the emission from these species is seen, as a function of laser fluence and time delay, suggests that at high fluence a plasma is formed in the plume above the ablation site and that excited-state nitrogen species may play an important role in the generation of radical fragments commonly seen in the laser induced plasma emission of organic materials. It is not clear to what extent these fragments may be generated as direct ablation products.
‘‘Regular’’ supercurrent nonuniformities in Josephson junctions by ion implantation
Authors: Camerlingo C. , Russo M. , Tosello C.
Published: July 2002

Nitrogen ion implantation in niobium thin films has been used to get local inhomogeneities in the critical current density of niobium-based Josephson tunnel junctions. A technique to obtain ‘‘regular’’ supercurrent nonuniformities in Nb-Nbx Oy -Pb structures is reported. The dependence of the maximum Josephson current on the external magnetic field has been measured to investigate the actual critical current density profile. Preliminary results on small (L< λj ) overlap junctions show a good agreement with the theoretical behavior computed in the framework of a steplike current density distribution.
Nonequilibrium electron transport in an AlGaAs/GaAs double-heterojunction bipolar transistor
Authors: Taira K. , Kawai H. , Kaneko K.
Published: July 2002

A 100-Å base double-heterojunction bipolar transistor was grown by metalorganic chemical vapor deposition with p+ layers epitaxially embedded in an extrinsic base. Hot electron spectroscopy was used to study electron transport in the narrow base. The spectra indicate nonequilibrium electron transport in the p+ GaAs base.
A simple method for monolithic fabrication of InGaAsP/GaAs lasers
Authors: Ito Toshio , Ishikawa Joji , Aramaki Takashi , Machida Toyotoshi , Takahashi N. Shin-ichi , Kurita Shoichi
Published: July 2002

A simple method for the fabrication of Fabry–Perot mirrors of InGaAsP/GaAs lasers is presented. The vertical and smooth wall etching is done for active layers only (not for both active and cladding layers), by an H2SO4:H2O2:H2O=3:1:1 etchant for 2–5 s. Since the active layers are much thinner than the cladding layers, the etching becomes much easier. The threshold current density of the etched mirror laser is ∼4.4 kA/cm2, about 1.1 times that of the cleaved laser, and the mirror reflectivity is evaluated as 29.4% (cleaved 31.4%).
Effect of substrate photoexcitation on channel conduction in a modulation-doped AlxGa1−xAs/GaAs heterostructure
Authors: Jiang P. H. , Huang Y. J. , Ge W. K. , Sun D. Z. , Zeng Y. P.
Published: July 2002

If a modulation-doped AlGaAs/GaAs heterostructure is illuminated by light, photoexcitation of deep levels in the GaAs substrate leads to some interesting effects. Below 100 K, the heterostructure shows a persistent photoconductivity effect. Moreover, a strong persistent channel depletion is observed at low temperatures when a small negative voltage is applied to the substrate contact (backgate). The latter effect is explained by a double-layer model of GaAs where the GaAs side of the heterostructure consists of (1) a buffer layer and (2) a semi-insulating substrate. Under illumination, most of the applied negative voltage drops across the very thin buffer layer, and the enhanced electric field in the layer exerts a very strong influence on the conducting channel.
Effective Richardson constant of sputtered Pt-Si Schottky contacts
Authors: Tōyama Naotake
Published: July 2002

The effective Richardson constant A* of a sputtered Pt-Si Schottky diode shows a large change with the thickness of a Pt-electrode film. For the purpose of investigating the cause of the change in A* with the Pt-film thickness, a 1000-Å-thick Pt film has been deposited by rf sputtering onto Si substrates which have been heated to various temperatures between room temperature and 500 °C. The barrier height ΦB and the effective Richardson constant A* for these Pt-Si contacts have been investigated photoelectrically. As a result, it has been found that the change in A* with the thickness of a sputtered Pt film is due to the rise of temperature at the Pt-Si interface during sputtering. From the concentration profiles of Pt and Si atoms near the Pt-Si interface by using Auger electron spectroscopy, we can attribute the dramatic change in A* to the formation of a Pt silicide layer during sputtering.
A critique of contact charge spectroscopy: A response
Authors: Fabish T. J. , Duke C. B.
Published: July 2002

Comparison of the experimental parameters used in a recent set of contact charge exchange measurements by Lowell, Rose-Innes, and El-Kazzaz with those used earlier by Fabish, Saltsburg, and Hair reveals that the former correspond to the shallow injection (d∼1 nm) of small amounts of charge and the latter to the deeper (d∼2 μm) injection of larger amounts of charge. These differences suggest that the former results should be interpreted in terms of rapid charge sharing after injection (i.e., nonadditive transfer) whereas the latter should yield results characteristic of noncommunicating, nonequilibrium injected charges (i.e., additive transfer under certain conditions). They also reveal the importance of a careful analysis of the noise inherent in contact charge exchange measurements.
Nonlinear large signal admittance in n-GaAs diodes at terahertz frequencies based upon transport analysis
Authors: Krowne Clifford M.
Published: July 2002

Previous simulations of the transport in a n-GaAs n+nn+ diode structure using both moments of the Boltzmann equation and a Monte Carlo particle-field self-consistent approach suggest that submillimeter-wave generation may be possible only at cryogenic temperatures. These simulations employed only modest ac signal levels compared to the dc value. Here the terminal admittance behavior is examined for truly large signal levels, up to 100% of the dc value. It seems that such large signal conditions suppress the appearance of negative conductance in the submicron diode.
Structural studies of the effects of silver and gold on the YBaCuO superconducting films formed from layer structures
Authors: Chang Chin-An
Published: July 2002

Superconducting YBaCuO films have recently been formed using both Ag/Cu/BaO/Y2O3/MgO and Au/Cu/BaO/Y2O3/MgO structures, where MgO is the substrate. The addition of a silver layer in the starting structure improves the film resistances from those using the Cu/BaO/Y2 O3 /MgO structure, especially at lower annealing temperatures. This allows the formation of superconducting films between annealing temperatures of 750 and 900 °C, all with an onset above 85 K. The transition into full superconductive state, however, broadens with decreasing annealing temperatures, with zero resistance between 80 and 60 K. This dependence on annealing temperatures is studied by x-ray diffraction, which shows the diminishing signals of the superconducting YBa2 Cu3 O7 phase at reduced annealing temperatures. A study of the surface morphology provides further information regarding the roles of silver and gold on the superconducting films formed.
Damage of silicon induced in low-energy CF4 discharges
Authors: Chen F. Y. , I Lin
Published: July 2002

The damage of silicon induced by low-energy (30 eV) CF4 discharges in a rf hollow oval magnetron system has been studied. The damage level was evaluated by the surface trap density measured by the high-low frequency capacitance-voltage method. By comparison with the results obtained using low-energy Ar discharges and other high-energy (450 eV) CF4 and Ar discharges, the involatile reaction residue was inferred as the major cause of damage in the low-energy CF4 discharges.
Generation of pure ion beams by field ionization of laser-excited Rydberg atoms
Authors: Oomori T. , Ono K. , Murai Y.
Published: July 2002

Sodium atoms (108–1011 cm−3) effused from an oven were stepwise excited from their ground state to a Rydberg state ns or nd (20≤n≤26) by two pulsed dye lasers (∼5–10 ns, ∼100 μJ, ∼1.6-mm-diam spot). The laser energy density necessary to saturate the excitation processes from the ground state to the Rydberg state is ∼ several mJ/cm2. About 50 ns after the laser irradiation, a pulsed electric field (0.5–5.5 kV/cm) was applied to the Rydberg atoms to ionize them and accelerate the resulting ions. Thus, a pulsed sodium ion beam of purity >99.99% was obtained with a maximum total electric charge of ∼5 pC and a pulse width of ∼120 ns full width at half maximum. The total electric charge of the ion beam is estimated including the effect of space-charge field of the beam ions, and is in good agreement with the experimental values.
Inherent peculiarities in nuclear reaction analysis
Authors: Arafah D.-E. , Meyer J. D.
Published: July 2002

A detailed description of the kinematics governing a nuclear reaction analysis is presented for exothermic reactions. In particular, the peculiar behavior demonstrated when the emitted particle energy decreases with increasing bombarding energy is emphasized. The method is applied to 16O(d,p)17O and D(d,p)T reactions from SiO2 and D2O targets, respectively. Moreover, an algorithm was written to compute reaction cross sections as a function of energy or concentration as a function of depth from the measured reaction yields.
Effects of Zn to Te ratio on the molecular-beam epitaxial growth of ZnTe on GaAs
Authors: Feldman R. D. , Austin R. F. , Bridenbaugh P. M. , Johnson A. M. , Simpson W. M. , Wilson B. A. , Bonner C. E.
Published: July 2002

ZnTe films have been grown with Zn:Te flux ratios ranging from 1 to 3.2. The highest quality films have been grown with flux ratios between 2 and 3, substrate temperatures between 300 and 325 °C, and a surface reconstruction that is a combination of c(2×2) and (2×1). Films grown under these conditions have x-ray rocking curve half-widths between 125 and 225 arcsec. Photoluminescence spectra show that the relative intensity of emission related to Zn vacancies decreases with increasing Zn:Te ratio. Picosecond photoconductivity measurements show an initial decay rate for photoexcited carriers that correlates well with other material parameters. After several hundred picoseconds, the decay rates for different samples show exponential behavior with a lifetime of approximately 675 ps.
Nonlinear electroacoustic interaction between a bias electric field and acoustic Lamb modes in LiNbO3 plates
Authors: Palmieri L. , Socino G. , Verona E. , Tran H. T. , Marini A.
Published: July 2002

The change in phase velocity produced by a bias electric field on Lamb acoustic waves propagating along yz- and zy-LiNbO3 plates is analyzed here. This effect is interpreted theoretically in terms of the modifications produced by the bias field on the second-order material constants, under the approximation of small-amplitude acoustic waves superposed on a bias. According to this theory, these modifications are linked to the components of the bias field through combinations of second- and third-order material constants. Measurements performed on several Lamb modes lead to the determination of the effective second-order material constants in the presence of a bias field. The results obtained allow the evaluation of the electroelastic effect for acoustic propagation along any direction in the yz plane of the crystal, provided that the bias electric field lies in the same plane. In addition, these results give useful information on the nonlinear properties of the medium.
Deposition chemistry and structure of plasma-deposited silicon nitride films from 1,1,3,3,5,5-hexamethylcyclotrisilazane
Authors: Brooks T. A. , Hess D. W.
Published: July 2002

Silicon nitride films were deposited in an rf glow discharge from various mixtures of NH3, H2, and N2 with 1,1,3,3,5,5-hexamethylcyclotrisilazane (HMCTSZN). Fourier transform infrared spectroscopy, Rutherford backscattering spectroscopy, and proton magnetic resonance spectroscopy, indicate that the films deposited with NH3 are essentially silicon nitride (<4 at. % C) and contain 25 at. % H , when deposited from dilute HMCTSZN mixtures at elevated rf power. Gas phase neutral mass spectroscopy indicates a relative abundance of NHx radicals produced under these conditions, which actively remove carbon and enhance Si-NH-Si bonding. Films deposited in NH3 /H2 mixtures result in still greater Si–N bonding, since NH3/H2 plasmas are more NHx radical rich than NH3 discharges. Films deposited from H2/HMCTSZN plasmas contain significant carbon concentrations (30–40 at. %), but those formed from dilute HMCTSZN mixtures at elevated rf power are low in H content (21 at. %) and are highly cross-linked due to H abstraction from radicals produced in the discharge.
Dynamic response of crystalline solids with microcavities
Authors: Hori Muneo , Nemat-Nasser Siavouche
Published: July 2002

Based on an approximate method by the authors for calculating void deformation in crystalline solids, the global response of a small continuum material element which contains microcavities is studied. A rate-dependent power-law plastic flow by double-slip is assumed to govern the local inelastic deformation. The local field variables are analytically calculated in an incremental manner. The average stress and strain are then computed by the integration of the local stress and strain over the continuum element. These average variables are used to describe the overall response of the material element under high loading rates. Several illustrative examples are given. It is shown that the global response of the material is significantly affected by the loading rate: the material response becomes tougher as the loading rate increases, but once the entire matrix becomes plastic, a strong ductility develops. It is observed that the large overall plastic deformation of crystalline solids stems not only from a uniform plastic flow in the entire matrix but also from the slip caused by the stress concentration near cavities; even under all-around uniform compression or tension, significant plastic deformations can take place in the vicinity of preexisting cavities, and affect the overall response of the material. The global material response, in general, is anisotropic, being induced by local flow on geometric slip systems. In addition, it is shown that the overall material response under compression is not, in general, the reverse of that under tension. The overall failure of crystalline solids, caused by void collapse or void growth, is investigated under compressive and tensile loads applied at various rates.
Relative ion expansion velocity in laser-produced plasmas
Authors: Goldsmith S. , Moreno J. C. , Griem H. R. , Cohen Leonard , Richardson M. C.
Published: July 2002

The spectra of highly ionized titanium, Tixiii through Tixxi, and Cvi Lyman lines were excited in laser-produced plasmas. The plasma was produced by uniformly irradiating spherical glass microballoons coated with thin layers of titanium and parylene. The 24-beam Omega laser system produced short, 0.6 ns, and high intensity, 4×1014 W/cm,2 laser pulses at a wavelength of 351 nm. The measured wavelength for the 2p-3s Tixiii resonance lines had an average shift of +0.023 Å relative to the Cvi and Tixx spectral lines. No shift was found between the Cvi, Tixix, and Tixx lines. The shift is attributed to a Doppler effect, resulting from a difference of (2.6±0.2)×107 cm/s in the expansion velocities of Tixix and Tixx ions compared to Tixiii ions.
Propagation of a picosecond-duration, relativistic electron beam through hydrogen at atmospheric pressures
Authors: Fisher A. S. , Pantell R. H. , Feinstein J. , Deloney T. L. , Reid M. B.
Published: July 2002

An experiment demonstrating the propagation of a 42-MeV electron beam from an rf linear accelerator through 1 m of H2 at pressures from 10−3 to 1.25 atm is reported. Measurements were made of the transmitted current and the beam’s radius, transverse position, and angular divergence along the path. The beam current was fully transmitted at all pressures, without the often detrimental plasma interactions (space-charge neutralization, magnetic neutralization, and various plasma instabilities) seen in previous studies. The observed beam expansion was consistent with calculations of multiple scattering. The propagation can be attributed to the 4-ps duration of the accelerator’s electron bunches. This time is three to four orders of magnitude shorter than that used in the earlier work and is shorter than the growth times for the beam-plasma interactions. Such a beam should prove suitable for a gas-loaded free-electron laser.
Correction of charged particle beam optics by a programmed electrostatic wire array
Authors: Humphries S. , Terry R. L.
Published: July 2002

Theoretical and experimental results are reported on a method for the correction of aberrations in optical elements for high-power ion beams. The approach involves the use of arrays of wires immersed in large diameter beams. Individually controlled voltages are applied to the wires, resulting in local transverse deflections of beam particles. With regard to wire survivability and voltage requirements, the method appears feasible for application to high-intensity negative ion beams. A formalism is described for the calculation of optimum wire voltages to achieve a specified beam angular correction in a Cartesian geometry. The results of the calculations were tested in modeling experiments using an 8-keV electron beam. The experimental array consisted of 46 wires and boundary plates with independent applied voltages up to 3 kV. Voltage profiles for one-dimensional focusing, two-dimensional focusing, and beam steering were studied. The observed particle deflections and beam emittance growth due to the facet lens effect are in agreement with predictions.
The contrastive behavior of Fe and Cr during the intrinsic gettering of silicon
Authors: Goorsky M. S. , Lagowski J. , Gatos H. C.
Published: July 2002

We found that Fe and Cr exhibit significantly different characteristics in being gettered during a high (1150 °C), low (750 °C), and medium (1000 °C) temperature cycle in Czochralski silicon. The behavior of Fe and Cr was monitored using deep level transient spectroscopy. Although Si was highly supersaturated with respect to both species throughout the low temperature step, Fe was gettered but Cr was not. This behavior indicated that a barrier to bulk silicide formation on oxide precipitates existed for Cr, but not for Fe at this temperature. We attribute the gettering of Cr at 1000 °C to the production of strain and Si interstitials during oxide precipitate growth. Since the differences in gettering behavior cannot be explained in terms of diffusivity and supersaturation, we propose a model which considers additional physical and chemical interactions.
Temperature dependence of photoconductivity and recombination in hydrogenated amorphous silicon
Authors: Yoon Jung-Kee , Jang Jin , Lee Choochon
Published: July 2002

The recombination processes in undoped hydrogenated amorphous silicon under steady-state illumination have been studied in order to explain the temperature dependences of photoconductivity. The recombinations of free carriers through the exponential tail states and through the Gaussian distributed dangling bond states were calculated in terms of the Shockley–Read theory and the occupation statistics of correlated defects. An additional recombination of trapped electrons and holes in the tail states through the dangling bonds by tunneling should be included in order to explain the experimental data of the activated photoconductivity at low temperatures.
High gain metal grating free-electron laser
Authors: Garate E. , Cherry R. , Fisher A. , Phillips P.
Published: July 2002

The small signal gain is calculated for a metal grating free-electron laser consisting of a planar metallic grating and an opposing planar metal boundary. The TM01 mode of the metal grating waveguide interacts with a cold, dense, mildly relativistic electron beam which is constrained to move along the axis of the waveguide. Since the interaction fields evanesce away from the slow wave supporting structure, a beam-grating gap is included in the analysis. Results indicate appreciable gain at lower mm wavelengths over a 30-cm interaction length at electron accelerating voltages as low as 20 kV. Interaction between the forward wave region of the n=0 space harmonic and the electron beam slow-space-charge wave could result in output wavelengths as low as 400-μm at 250-kV accelerating voltages.
Retardation-related anisotropy in the optical behavior of a periodic cermet: The concept of depolarizing field revisited
Authors: Bosi G. , Truong V.-V.
Published: July 2002

An earlier dipolar treatment, including retardation and predicting an anisotropic behavior for a periodic cermet, has been applied to a suitable model. This has pointed out the need for carefully handling the concept of depolarizing field in the presence of retarded dipole-dipole interactions. Calculations have been performed to carry out the effective permittivity tensor of the given model. The results show a certain amount of anisotropy but do not agree with a very recent experiment. Possible implications are briefly discussed.