bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling spatially extended complex systems from experimental data: Sensitivity to sampling intervals
Authors: Saloma Caesar , Narisma Gemma
Published: July 2002

The reliability of a phenomenological model in describing the profile of a spatially extended complex system is analyzed. An assessment is essential because an observed image of a two-dimensional object is sensitive to increases in sampling intervals. The range of interval values wherein the fractal dimension of the image remains invariant is determined for various kinds of object boundaries. Data sets of the same object that are obtained using sampling intervals that belong within the range contain the same amount of fractal information, and therefore adhere to one phenomenological model. This reliability range is determined for both coherent and incoherent measurement processes. Numerical experiments show that the range is the same for all fractal objects considered, and depends only on the type of measurement process. However, the measurement errors introduced when sampling at intervals beyond the reliability range are highly dependent on the type of fractal structures. Boundaries described by larger fractal dimensions are less sensitive. The existence of a nonzero reliability range implies that object fractal information can be recovered at sampling rates lower than the minimum value imposed by the Nyquist sampling criterion.
Magnetic-field effects on current-generated spatially periodic potentials in p-Ge at 4.2 K
Authors: Liu Shuzheng , Zitter R. N.
Published: July 2002

Voltage-current curves of pure p-type germanium diodes at 4.2 K show sequences of minima which have been attributed to current-generated spatially periodic space-charge distributions along the current path. The effects of applied magnetic fields on the minima, as reported here, are found to be in good agreement with the periodic space-charge model.
Current induced degradation in boron-doped hydrogenated amorphous silicon: A novel investigation technique
Authors: Masini G. , De Cesare G. , Palma F.
Published: July 2002

A novel technique for controllable degradation and monitoring of a boron-doped layer as used in thin film solar cells is presented. The thin p-type layer under investigation is grown embedded in a n-i-n structure. Upon biasing the structure, excess electrons are injected into the layer giving rise to a degradation process. Complete recovery after annealing indicates the metastable nature of the process. The degree of degradation can be monitored by following changes of the forward current flowing into the structure. A simple model enables the interpretation of the experimental curves in terms of doping activation and increased density of defects in the doped layer.
Influence of silicon wafer surface orientation on very thin oxide quality
Authors: Ohmi T. , Matsumoto K. , Nakamura K. , Makihara K. , Takano J. , Yamamoto K.
Published: July 2002

Effects of silicon wafer surface orientation on very thin oxide quality were studied, testing Si(100) and (111) wafers. It has been found that the very thin oxide quality is determined by the silicon wafer surface orientation, and that when Si(111) is oxidized, SiO2/Si(111) interface microroughness increases as oxide becomes thicker than 10 nm, resulting in a degradation of oxide films quality on Si(111). When oxide thickness is decreased less than 10 nm, Si/SiO2 interface smoothness is maintained similar for Si(100) and (111) but SiO2/Si interface for Si(111) exhibits larger interface charges and larger threshold-voltage shift due to hot-electron injection than that for Si(100).
Investigation of the magnetization processes of Nd-Fe-B permanent magnets using a torsion pendulum magnetometer
Authors: von Staa F.
Published: July 2002

Sintered and rapidly quenched permanent magnets based on neodymium-iron-boron alloys are investigated using the torsion pendulum method. The measurement of the magnetic stiffness yields the anisotropy field, the saturation magnetization, and the texture distribution. The determination of the torque leads to the magnetization component perpendicular to the applied field. So the remanence angle can be obtained, which makes a second, independent determination of the texture distribution possible. The damping of the oscillation of the pendulum can be related to magnetic energy losses of the sample due to domain wall motions in small alternating magnetic fields. While such domain wall movements are observed in the demagnetization and virgin curves of sintered magnets, they are never found in rapidly quenched magnets. It is concluded that the torsion pendulum method provides a possibility to distinguish between nucleation and pinning mechanisms experimentally.
Orientational relaxation in cross-linked nonlinear optical polymers
Authors: White K. M. , Cross E. M.
Published: July 2002

Stability of the electro-optic coefficient of a poled and cross-linked nonlinear optical polymer is reported at 85, 100, and 110 °C. The observed decay, which is due to orientational relaxation of the nonlinear optical dyes in the films, is discussed in terms of several proposed models. The introduction of a continuously varying relaxation time, which occurs when considering physical aging during the stability tests, is observed to account for orientational relaxation over a long time period.
The effects of built-in electric field on the performance of compositionally graded P-on-n HgCdTe heterojunction photodiodes
Authors: Rosenfeld D. , Garber V. , Bahir G.
Published: July 2002

The results of a study of the optical and electrical performance of P-on-n HgCdTe heterojunctions, with a linear gradient in composition, are presented. First presented is a solution of the one-dimensional continuity equation which includes the spatial dependencies of the material properties, such as absorption coefficient, band gap, and intrinsic carrier concentration, in the graded layer. Using the above solution, diodes with different grading profiles (and hence different electric fields), but with the same cutoff wavelength, are compared. The advantages of the built-in electric field formed by the grading in composition are presented and discussed. It is shown that the major consequence of the electric field is the reduction of the effects caused by the imperfect CdTe/HgCdTe interface at the backside.
Relation between lattice strain and anomalous oxygen precipitation in a Czochralski-grown silicon
Authors: Kimura Shigeru , Ishikawa Tetsuya
Published: July 2002

Spatial fluctuations of lattice strain in an as-grown Czochralski-grown silicon wafer, in which a ring-shaped region of densely distributed oxidation-induced stacking faults appears after oxidation thermal treatment, are measured by double-crystal reflection topography with synchrotron radiation. The measured lattice strain is isolated into local variations in lattice dilation and inclination angle from an average plane. The variation profile of the lattice spacing shows a small valley in the ring-shaped region, while showing a peak just outside the ring-shaped region. The relation between the lattice strain and anomalous oxygen precipitation is discussed.
Oxide growth, refractive index, and composition depth profiles of structures formed by 2 MeV oxygen implantation into silicon
Authors: Hatzopoulos N. , Siapkas D. I. , Hemment P. L. F.
Published: July 2002

Single-crystal Si has been implanted with O+ ions at 2 MeV energy, to doses from 0.1 to 2×1018 O+ cm−2 and at substrate temperatures between 90 K and 700 °C. Infrared reflection spectra in the transparent region 1500–7000 cm−1 were measured and interference fringes were observed. A detailed theoretical analysis of the interference fringes yields refractive index profiles which provide accurate measurements of the range and straggle of the implanted ions, the Si overlayer crystallinity, and the oxygen concentration depth profile. The implantation temperature influences the crystallinity of the Si overlayer but not the oxygen distribution. The measured range parameters are in agreement with theory. The 2 MeV results are compared to results from 200 and 90 keV implants, which show that the method is applicable for a wide range of separation by implantation of oxygen structures. Rutherford backscattering spectroscopy and ion channeling results are in good agreement with the infrared results. It is concluded that infrared spectroscopy is the most convenient and inexpensive nondestructive technique to investigate structures formed by MeV and lower-energy O+ implantation.
Purification of diamond films by applying current into the plasma stream in the arc discharge plasma jet chemical vapor deposition technique
Authors: Ito Nobuei , Yamamoto Minoru , Nakamura Satoshi , Hattori Tadashi
Published: July 2002

A synthesis method that provides high-purity diamond films is proposed employing direct current arc discharge plasma jet chemical vapor deposition. In the method, an electric current was supplied to a plasma jet stream by applying a bias voltage between a cathode and the substrate on which diamond films were deposited. The Raman spectral analysis showed that the purity of the synthetic diamond was remarkably improved by the application of the bias voltage during deposition. The alternating current calorimetric method was employed to measure the thermal diffusion coefficient of the synthesized diamond films. The thermal diffusion coefficient greatly increased for films deposited with biasing. This improved thermal diffusion coefficient suggests higher purity diamond films. Emission spectral analysis revealed that the quantity of the dissociated hydrogen contributing to the plasma emission near the substrate is greater when biasing is used. Thus, the dissociated and excited hydrogen atoms are considered to play a key role in removing the carbon allotropes other than diamond.
Theoretical investigations on electron trap generation by fluorine atoms in SiO2 film
Authors: Yokozawa A. , Hirose K. , Ishitani A. , Kamoshida M. , Hillenius S. , Gilmer G. , Raghavachari K.
Published: July 2002

Theoretical investigation on the influence of F atoms incorporated into a thermal SiO2 film is presented. Energetics on the reaction of F atoms with the SiO2 film and the generation of electron traps are discussed using ab initio molecular orbital calculations. The computational result shows that a F atom dissociates a Si—O bond and generates OSi≡ moiety which can trap an electron. This gives a qualitatively appropriate explanation for the experimental result that F incorporated atoms into the SiO2 film generate electron traps.
Influence of hydrogenation on photoluminescence of GaAlAs grown by molecular beam epitaxy
Authors: Mehta S. K. , Srinivasan T. , Dubey G. C. , Jain R. K.
Published: July 2002

The effects of hydrogenation on GaAlAs layer grown by molecular beam epitaxy stored over a long period of time was investigated using photoluminescence (PL) measurement. Upon hydrogenation, the defects in the GaAlAs are passivated and the PL intensity increased many times. Hydrogenation changes the energy of the defect produced on storage of GaAlAs and new features appear in excitonic emissions. On annealing the hydrogenated GaAlAs at temperatures ≳500 °C, the defects are depassivated and the PL intensity degraded. Hydrogenation improves the PL intensity of emission from a stack of GaAs/GaAlAs quantum wells (QW) of different well widths by a factor which varies with the depth of the QW from the surface.
Theory of nonlinear magnetostatic surface wave in a periodically corrugated ferromagnetic slab
Authors: Wang Qi , Shi Jie-long , Bao Jia-shan
Published: July 2002

We present a coupled wave analysis of nonlinear magnetostatic surface waves in ferromagnetic slabs which have double periodically corrugated surfaces. Most relevant are the effects close to the Bragg condition. The nonlinearity of the system shifts downwards and widens the stop bands, however the relative spatial phase difference between the two surface corrugations has significant influence on the widths of stop bands and under certain conditions weakens the nonlinear effects of the system.
Two different micromodels of zinc oxide varistors
Authors: Wang Liangbin , Wu Wenbin , Li Xiao-Guang , Zhang Yuheng
Published: July 2002

Micromorphology of ZnO varistors made with seed grains shows that there are two kinds of combinations of ZnO grains. Two different micromodels of ZnO varistors are put forward according to their micromorphology. The relation between ZnO grains’ mean diameter and the amount of seed grains has been deduced from the micromodels. The relation between the electric field E1mA/cm2, nonlinear coefficient, and breakdown energy density of ZnO varistors and the amount of ZnO seed grains has been explained by means of micromodels.
Doping effects in zone-melting recrystallization of silicon thin films
Authors: Lee Si-Woo , Joo Seung-Ki
Published: July 2002

Effects of dopant additions on interface stability in zone-melting recrystallization (ZMR) of silicon thin films have been investigated through computer simulation and experiments. The computer simulation has shown that a critical scanning speed V* exists such that the critical wavelength λ* of the solidifying interface increases with scanning speed below V* due to radiative supercooling, while λ* decreases with scanning speed above V* due to constitutional supercooling. Experiments determined that V* decreased with additions of B and P, which was expected from the results of the computer simulation. The primary defect spacings after ZMR was found to increase with the addition of dopants prior to ZMR.
Phenomenological model for the c-axis resistive dissipation in La2−xSrxCuO4 as a function of temperature, magnetic field, and its orientation
Authors: Yuan S. L. , Yang Z. J. , Kadowaki K.
Published: July 2002

The measurement of c-axis resistance in La2−xSrxCuO4 at different temperatures for fields at any orientation shows that the observed dissipation is not dominated by any Lorentz-force-dependent mechanism. To explain the experimental findings, a phenomenological model is developed for c-axis resistance as a function of temperature T, field B, and angle θ between B and ab plane. Excellent agreement between calculated and experimental curves in a wide transition region (5 decades) gives a strong support to the present approach.
Gain and current-density calculation in IV–VI quantum well lasers
Authors: Khodr M. F. , McCann P. J. , Mason B. A.
Published: July 2002

In this work, a theoretical model is used to study the gain versus current-density relationship for IV–VI semiconductor quantum well lasers. The model, based on Kane’s two band theory, solves for the anisotropy in the constant energy surfaces and for the strong nonparabolicity of the bands. The system investigated is the EuSe–PbSe0.78Te0.22 quantum well structure at 77 K. The effects of nonparabolicity on the gain versus current-density relation are a reduction in the current density needed for any given gain and an increase in the gain saturation level. The nonparabolicity of the bands in the growth direction lowers the values of the confinement factor relative to parabolic bands which in turn lowers the modal gain values. Finally, the effects of nonparabolicity on the threshold current are significant for short cavity lasers and decrease with an increase in the cavity length.
Study of deep levels in alpha-irradiated silver-doped p-type silicon
Authors: Ali Akbar , Baber N. , Iqbal M. Zafar
Published: July 2002

Deep-level transient spectroscopy has been employed to study the defects in silver-doped p-type Si, their interaction with radiation-induced defects, and the thermal annealing characteristics of both types of defects. The linearly graded nature of the n+p junctions used allows the acceptor (Ec−0.54 eV) and donor (Ev+0.35 eV) levels associated with silver to be studied simultaneously. The acceptor level is found to be stable against thermal annealing performed up to ∼400 °C, while the donor level shows a decrease beyond 300 °C. Important effects related with rapid thermal quenching of samples are revealed by a comparison of the data with the corresponding data on identical virgin (unquenched) samples. Irradiation by α particles leads to interesting new insights on the interaction of silver-related defects and the radiation-induced defects. New aspects of the kinetics and formation mechanism of the carbon-related defects in Si are brought to light as a result of room-temperature isothermal annealing and isochronal annealing studies on the irradiated samples with and without silver. Irradiation also produces interesting effects on the Ag-related levels—while the acceptor level Ag(A) remains more or less stable, the donor level Ag(D) shows a small but systematic increase in concentration with α-radiation dose. These observations, together with the different annealing behaviors, suggest that the two levels due to silver are not coupled states of the same defect.
Diffusion of boron, lithium, oxygen, hydrogen, and nitrogen in type IIa natural diamond
Authors: Popovici Galina , Wilson R. G. , Sung T. , Prelas M. A. , Khasawinah S.
Published: July 2002

Diffusion of boron, lithium, nitrogen, oxygen, and hydrogen into type IIa natural diamond was studied. The diffusion was performed in two steps. First, diffusion of Li and oxygen was performed in nitrogen atmosphere at 860 °C for one hour. The sample was then placed in a hot filament chemical vapor deposition (CVD) growth reactor and diffusion was performed for two hours in hydrogen atmosphere from a boron solid source placed on the surface of the sample. The condition of diffusion were those used routinely during CVD growth. After diffusion, the concentration of Li was of the order of 2×1016 cm−3 at the depth of 0.5 micrometer, and oxygen, nitrogen, and boron were found to be in the range (1–4)×1020 cm−3 at the same depth. The diffusion of hydrogen under conditions specific to CVD growth has also been studied for the first time and was found to be quite strong.
Annealing behavior of carbon-oxygen complexes in silicon crystals observed by low-temperature infrared absorption
Authors: Shirakawa Yoshimi , Yamada-Kaneta Hiroshi , Mori Haruhisa
Published: July 2002

A low-temperature infrared-absorption study has been performed to investigate the annealing behavior of the carbon-oxygen complexes causing the peaks at 1104 cm−1 (C-OA complex) and 1108 cm−1 (C-OD complex). Upon annealing, the concentrations of the C-OA and C-OD complexes quickly reach the quasithermal-equilibrium values described by the mass-action law. The obtained formulas of this mass-action law indicate that both of these two complexes involve a carbon atom and an oxygen atom. For the annealing temperatures higher than 800 °C, the quasithermal-equilibrium concentration of the C-OA complex increases with increasing temperature. A hypothetical explanation is proposed for this unusual temperature dependence.
Competition between two resonance frequency branches in a waveguide free-electron laser
Authors: Shu X. J. , Kawamura Y. , Tanabe T. , Li D. J. , Toyoda K.
Published: July 2002

One of the problems encountered in designing a waveguide free-electron laser (FEL) is to suppress the lower-frequency branch, which may have a higher gain than the more useful higher-frequency branch. It is shown that the electron pulse length and energy spread strongly influence the competition between the gains at high and low frequency for a waveguide FEL. It is also found that the negative slippage that may take place at the lower-frequency branch results in larger reduction in gain than the positive slippage. The maximum allowable electron energy spread for both resonance frequencies is derived.
High interface recombination velocity caused by spatially indirect quantum well transition in Al0.55In0.45As/InP heteroface solar cells
Authors: Lammasniemi J. , Tappura K. , Smekalin K.
Published: July 2002

The effect of a strained Al0.55In0.45As window layer on p/n InP solar cell performance was studied. In comparison to homojunction InP solar cells, decreased quantum efficiency in the short wavelength region of the spectrum was observed in cells having the window layer. Photoluminescence measurements of the heterojunction and light emission measurements of the solar cell under forward bias revealed an intense radiative transition, which is related to the enhanced recombination of the carriers that are photogenerated in the emitter layer. This recombination occurs between the energy levels of the triangular quantum wells formed at the type II Al0.55In0.45As/InP heterojunction, and prevents effective carrier collection in the solar cell.
Strong room-temperature infrared emission from Er-implanted porous Si
Authors: Namavar Fereydoon , Lu Feng , Perry Clive H. , Cremins Annmarie , Kalkhoran Nader M. , Soref Richard A.
Published: July 2002

This communication demonstrates a strong, room-temperature (RT), infrared (IR) (1.54 μm) emission from Er-implanted red-emitting (peaked at 1.9 eV) porous silicon (Er:PSi). Erbium was implanted into porous Si, bulk Si, and quartz with a dose of 1015/cm2 at 190 keV and annealed for 30 minutes in N2 at temperatures ranging from 500 °C to 900 °C under identical conditions. No RT IR emission was observed from Er implanted quartz and silicon after annealing at 650 °C (although after annealing at 900 °C very weak emission was observed from quartz at 9 K). The highest RT emission intensity at 1.54 μm was from Er:PSi with a peak concentration of 1.5×1020/cm3 and annealed at 650 °C. Even the luminescence intensity from Er:PSi annealed at 500 °C was 26 times higher than that observed from Er-implanted quartz at 400 keV and annealed at 900 °C. A reduction in photoluminescence (PL) intensity of about a factor of two from Er:PSi over the 9 to 300 K temperature range was observed which is consistent with Er in wide band gap materials.
Fabrication and dc, microwave characteristics of submicron Schottky-collector AlAs/In0.53Ga0.47As/InP resonant tunneling diodes
Authors: Reddy M. , Mondry M J. , Rodwell M. J. W. , Martin S. C. , Muller R. E. , Smith R. P. , Chow D. H. , Schulman J. N.
Published: July 2002

We report the fabrication and dc, microwave characteristics of 0.1 μm, Schottky-collector resonant tunnel diodes (SRTDs) in the AlAs/In0.53Ga0.47As/InP material system. Devices with contact areas as small as 0.05 μm2 have been fabricated using electron beam lithography with an interrupted footprint T-gate process. SRTD’s fabricated with 1.4 nm AlAs barriers exhibited a 5×105 A/cm2 peak current density at 0.95 V and a −19 mS/μm2 peak negative conductance. The devices incorporate fully depleted P-doped cap layers to suppress surface leakage currents. From the measured dc and microwave characteristics, a maximum frequency of oscillation fmax=2.2 THz is estimated.
Excess noise, structural properties, and their effects on bolometric performance of thin superconducting films on silicon membranes
Authors: Neff H. , Schaube W. , Laukemper J. , Burnus M. , Heidenblut T. , Hefle G. , Schwierzi B. , Michalke W. , Steinbeiss E.
Published: July 2002

Current induced excess noise, in connection with bolometric performance of thin superconducting GdBa2Cu3O7−x films on silicon membranes, has been investigated as a function of temperature within the transition regime for the first time. The data reveal a strong correlation between structural film properties and the individual noise pattern that clearly indicates three separated coexisting superconducting phases in the film, with transition temperatures of 84.5, 86, and 88.5 K. The latter accounts for the current carrying properties, while the former two have a limiting effect on the sensitivity of the device. Inhomogeneous film growth accounts for high resistance fluctuation noise (flicker noise) at very low frequency. Also, a drastically increased sensitivity against electromagnetic background interference has been observed, in conjunction with nonlinear properties of the device, and at isolated frequencies. The increase in the concentration of microcracks in the film generated upon thermomechanical stress, and through aging, accounts for a drastic increase in the overall noise magnitude and a rapidly degrading bolometric performance, respectively.
Epitaxial growth of AlN thin films on silicon (111) substrates by pulsed laser deposition
Authors: Vispute R. D. , Narayan J. , Wu Hong , Jagannadham K.
Published: July 2002

Aluminum nitride thin films have been grown epitaxially on Si(111) substrates, for the first time, by pulsed laser ablation of sintered AlN target. The influence of process parameters such as laser energy density, substrate temperature, pulse repetition rate, nitrogen partial pressure, etc. on epitaxial growth has been investigated to obtain high quality AlN films. These films were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, x-ray diffraction (Θ and ω scans) technique, high resolution transmission electron microscopy, and scanning electron microscopy. The films deposited at laser energy density in the range of 2–3 J/cm2, substrate temperature of 750 °C, and base pressure of 3×10−7 Torr are single phase and highly oriented along c axis normal to the Si(111) planes. The results of x-ray diffraction and electron microscopy on these films clearly show the epitaxial growth of the AlN films with an orientational relationship of AlN[0001] ∥ Si[111] and AlN[21̄1̄0] ∥ Si[011̄]. The AlN/Si interface was found to be quite sharp without any indication of interfacial reaction. Laser physical vapor deposition is shown to produce high quality epitaxial AlN films with smooth surface morphology when deposited under optimized conditions.
Fourth order elastic moduli of diamond structure materials
Authors: Gerlich D.
Published: July 2002

The values of the fourth order elastic moduli (FOEM) for the diamond structure elements, silicon and germanium, have been calculated. The derivation utilizes the Keating model, assuming that both the third and fourth order terms in the interaction potential are composed of a bond-stretch, an angle-bend, and a mixed bond-stretch angle-bend term. The three force constants in the fourth order interaction potential are evaluated from the measurements of the sound velocity under pressure, hence, numerical values for all 11 FOEM may be obtained. The set of FOEM thus calculated shows markedly different characteristics than the analogous quantities for other materials, e.g., the alkali halides.
In situ observation of the strain in GaP on Si during cooling step after growth by Raman spectroscopy
Authors: Sugiura Masayuki , Kishi Masato , Katoda Takashi
Published: July 2002

A new Raman measurement system with which it is possible to characterize various properties of semiconductors being grown in an atmosphere of flowing gas at a high temperature was developed. As an example of application of the system, the characterization of gallium phosphide (GaP) grown on a silicon (Si) substrate by chloride vapor phase epitaxy at 700 °C was done. The Raman spectra indicated that almost all the strain in a GaP layer with a thickness of 1 μm on a Si(111) substrate due to the difference of lattice constants is relaxed at the growth temperature while tensile strain due to the difference of thermal expansion coefficients exists at room temperature. The results of Raman spectra measured at every hundred degrees during the cooling process have good agreement with the calculated results based on the bimetal model. This means that thermal stress is stored gradually at the early stage of the cooling process.
Mössbauer study of HhpfSn in the Heusler alloy Co2MnSn under pressure
Authors: Gavriliuk A. G. , Stepanov G. N. , Irkaev S. M.
Published: July 2002

The pressure dependence of the ‘‘hyperfine magnetic field’’- Hhpf at the nuclei of the diamagnetic atoms 119Sn was investigated in the Heusler alloy Co2MnSn using Mössbauer absorption spectroscopy with pressures up to 10 GPa at room temperature. The dependence can be fitted by the linear function HhpfSn(P)/HhpfSn(0)=1+k1⋅P with coefficient k1=−0.023 ±0.002 GPa−1, where HhpfSn(0)=10.5±0.3 T. Diamond anvil cells were used for the high pressure generation. A drop of HhpfSn in the pressure range 0–10 GPa can be explained on the basis of empirical theory developed by Delyagin, Krylov, and Nesterov [JETP 76, 8, 1050 (1980)].
Comment on ‘‘Temperature limits on infrared detectivities of InAs/InxGa1−xSb superlattices and bulk HgxCd1−xTe’’ [J. Appl. Phys. 74, 4774 (1993)]
Authors: Williams G. M.
Published: July 2002

Theoretical calculations [P. M. Young, C. H. Grein, H. Ehrenreich, and R. H. Miles, J. Appl. Phys. 74, 4774 (1993)] comparing optimized InAs/InxGa1−xSb superlattice (SL) to bulk HgxCd1−xTe (MCT) detectors claim that the SL detector is superior to MCT for 11 μm operation. The referenced analysis is incomplete for three reasons: first, radiative recombination is ignored, resulting in unrealistically high SL performance predictions; second, the Auger-7 (chlh) mechanism is assumed to limit lifetime in p-type MCT, while longer radiatively limited lifetime has been observed experimentally; and finally, optimized MCT devices are routinely fabricated in thin epitaxial layers, which give higher performance than is obtained in bulk material. A more complete theory for SL detectors is unlikely to predict higher performance than that of MCT detectors, since MCT detectors are theoretically limited by radiative processes. Measured MCT detector performance in near agreement with the radiative limit has been observed.
Transverse susceptibility of particulate recording media in different remanence states
Authors: Zimmermann G.
Published: July 2002

Transverse susceptibility measurements were performed on isotropic and aligned γ-Fe2O3 and ZnTi-doped barium-ferrite powder samples in different remanence states. Measurement results obtained on a sintered NdFeB sample are given for comparison. Deviations of the experimental result from the Stoner–Wohlfarth theory are ascribed to inhomogeneous magnetization states and particle–particle interactions. The remanent reversible transverse susceptibility appears to be much more sensitive to these influences than standard remanence-curve analysis and thus provides a new experimental approach to the interaction problem.
Interface structure modified by plasma-surface interaction and its effect on ablative hole opening process in a bilayer system of TeSeF film and a fluorocarbon subbing layer
Authors: Horie M. , Tamura T.
Published: July 2002

The effect of a plasma-surface interaction on the adhesion force of a thin metal film was investigated using a bilayer system consisting of a TeSeF film and a fluorocarbon subbing layer. The change in an ablative hole opening process with a focused laser beam in this bilayer system was also affected by the modification of the adhesion force due to the plasma-surface interaction. An Ar plasma treatment of the fluorocarbon subbing layers prior to the TeSeF film deposition increased the adhesion force and the threshold energy for the ablative hole opening. Even without such intentional plasma treatment, the interface chemical structure depended on the plasma-surface interaction during the TeSeF active layer deposition, where the active layer was deposited by the rf or dc reactive sputtering of TeSe in a SeF6/Ar gaseous mixture. The rf sputtered TeSeF film required larger threshold energy for hole opening than the dc sputtered one. The modified interface chemical structure by the plasma-surface interaction was analyzed using x-ray photoelectron spectroscopy. The increase in the threshold energy for hole opening for the plasma-treated subbing layer and for the rf sputtered TeSeF film was due to the increase in the cross-linking density in the fluorocarbon polymer, unsaturated bonds, and dangling bonds at the interface in the bilayer system.
Overwrite repeatability of magneto-optical exchange-coupled multilayer
Authors: Miyamoto Harukazu , Andoo Keikichi , Niihara Toshio , Ojima Masahiro
Published: July 2002

Overwrite repeatability of exchange-coupled multilayer for light-intensity-modulated overwrite (OW) was studied by using Arrhenius analysis. A computer simulation showed that typical OW disks and a conventional nonoverwrite (NOW) disk have similar maximum temperature during recording. Nevertheless, the overwrite repeatability of the OW disks was smaller than that of the NOW disk. The degradation mode characteristic to the OW disks was found to have lower activation energy than the conventional NOW single-layer disk. The degradation mode was caused by initialization noise resulting from domain-wall fluctuations under a large initializing field, and was reduced by using a transition-metal dominant memory layer with high-domain-wall coercivity. An overwrite repeatability of more than 106 was achieved.
Effect of hydrogen termination and electron irradiation on the sticking probability of Sb on Si(100) surfaces exposed to Sb4
Authors: Mills A. P. , Gossmann H.-J.
Published: July 2002

The controlled placement of dopant atoms in all three dimensions of a host semiconductor would enable production of a variety of novel devices. We investigate the use of hydrogen adsorption and electron-beam irradiation to achieve selective deposition of Sb on Si. The retention of Sb after annealing to 570 K on a hydrogen-terminated Si(100) surface is enhanced in those areas that have been electron irradiated either before or after exposure to Sb4. The maximum contrast ratio is ≊2:1 for an electron dose of 0.05 C/cm−2.
Piezoelectric properties of bidomain LiNbO3 crystals
Authors: Kugel V. D. , Rosenman G. , Shur D.
Published: July 2002

Our studies of piezoelectric properties of bidomain (‘‘head-to-head’’) Z-cut plates of LiNbO3 formed by diffusion treatment show that the spectrum of excited vibrations differs from that of monodomain crystals. We found that the length- and width-longitudinal vibrations are suppressed and bending vibrations appear to be maximal for an inverted layer thickness equal to one-half of the sample thickness. The amplitude of the fundamental frequency and its overtones for the thickness vibrations depend on the thickness of the inverted layer. A model explaining these properties is proposed.
Comparative study of critical thicknesses of strained epitaxial layers based on the zero-energy criterion of dislocation half-loops
Authors: Shintani K. , Yonezawa H.
Published: July 2002

Considering nucleation of dislocation half-loops from the crystal growth surface as a mechanism of generation of misfit dislocations between an epitaxial film and a substrate, critical thicknesses can be determined by calculating the zero of free energy of the system according to van de Leur et al.’s model [J. Appl. Phys. 64, 3043(1988)]. On estimating the free energy, two analytical methods are adopted; one is the whole-space approximation and another treats surface half-loops in the half-space by the image stress construction. In both of the methods, interaction between the two dislocation glide loops either lying in the identical slip plane or lying in the parallel slip planes are incorporated into the analysis. It is shown that half-loop correction reduces critical thickness, the former interaction reduces and the latter interaction increases it, and the interaction effects become smaller by the half-space correction. Finally, it is also shown that the effect of anisotropy in the whole-space approximation tends to increase critical thickness.
Laser direct writing of gold tracks from decomposition of organometallic screen ink
Authors: Tonneau D. , Bouree J. E. , Correia A. , Roche G. , Pelous G. , Verdeyme S.
Published: July 2002

Direct writing of micronscale gold tracks on alumina samples is possible by local thermal decomposition of a metallopolymer spread all over the substrate surface, induced by a tightly focused cw Ar+ laser beam. The polymer decomposition occurs at low laser powers and leads to the formation of very pure deposits as shown by SEM+EDS analyses. The influence of laser scan speed and laser power on the carbon contamination and the resistivity of the deposits has been investigated. Line profiles have also been studied as a function of laser scan speed and laser power.
Time-resolved shock-wave experiments on granite and numerical simulations using dynamic phase mixing
Authors: Boettger J. C. , Furnish M. D. , Dey T. N. , Grady D. E.
Published: July 2002

A recently developed model for simulating the dynamic behavior of silicate materials is applied to the loading and unloading properties of granite. Four time-resolved wave profile measurements on granite are presented and used to supplement Hugoniot data to constrain the model. This model is based on a dynamic process-dependent description of phase mixing. In the solid–solid mixed-phase region, the loading states are determined from a simple two-parameter constraint equation which relates the mass fraction of the high pressure phase λ to the Gibbs free-energy difference between the phases ΔG. On release, the reverse phase transition is modeled as a two-stage transition with each stage described by a two-parameter equation with the same form as the loading equation. In all four of the simulations, the loading behavior of the shock-wave experiment is well represented. For three of the experiments the release behavior is accurately simulated up to the point at which the measured interface speed reaches its first minimum. For the remaining experiment the simulation matches only the earliest release behavior and then rapidly deviates from the measured data.
Tensile strength of synthetic chemical-vapor-deposited diamond
Authors: Olson D. S. , Reynolds G. J. , Virshup G. F. , Friedlander F. I. , James B. G. , Partain L. D.
Published: July 2002

Pressure burst tests gave measured tensile strengths between 230 and 410 MPa for a total of six chemical-vapor-deposited (CVD) diamond disks in both transparent ‘‘white’’ and opaque ‘‘black’’ forms obtained from three different sources. The disks were nominally 0.635 cm in diameter and 254 μm thick. These strengths are explained by a theoretical model using a Young’s modulus of 1.05×106 MPa and a fracture surface energy of 5.3 J/m2, appropriate for natural diamond, and with critical crack lengths between 33 and 105 μm. The latter lengths can fit, either on or inside, the tapered columnar crystal grains that grow vertically in synthetic CVD diamond films. The model is consistent with the observed inverse dependence of measured tensile strength on film thickness and with tensile strengths between 180 and 5190 MPa reported by other workers for synthetic CVD diamond.
Lattice sites of arsenic ions implanted in diamond
Authors: Bharuth-Ram K. , Quintel H. , Restle M. , Ronning C. , Hofsäss H. , Jahn S. G.
Published: July 2002

The lattice sites of As ions implanted in diamond and the annealing of implantation damage were investigated in emission channeling measurements. A dose of 1.0×1013 cm−2 73Se ions was implanted into IIa diamond at 300 K with an energy of 60 keV. 73Se (t12=7.1 h) decays to 73As (t1/2=80 d), which in turn decays to excited states in 73Ge. Channeling effects were measured on conversion electrons emitted in the 73Ge decay. Annealing studies in the range 873–1673 K showed an annealing stage of the implantation damage setting in at 1100 K. Comparison of the measured effects with simulations based on the dynamical theory of electron diffraction showed that after annealing at temperatures above 1100 K, 55(5)% of the implanted ions were located on substitutional lattice sites.
Optically pumped ZnSe-based vertical cavity surface emitter with SiO2/TiO2 multilayer reflector
Authors: Honda T , Sakaguchi T. , Koyama F. , Iga K. , Yanashima K. , Inoue K. , Munekata H. , Kukimoto H.
Published: July 2002

We have fabricated a SiO2/TiO2 high-reflectivity dielectric multilayer mirror specifically suitable for ZnSe-based vertical cavity surface-emitting lasers operating in the green-to-blue spectral region. In the fabrication process, the thickness of each layer has been precisely controlled by using an in situ optical monitoring system. A photo-pumped ZnCdSe/ZnSe/ZnSSe surface-emitting laser has also been demonstrated using the SiO2/TiO2 dielectric multilayer mirrors stacked with the ZnCdSe/ZnSe/ZnSSe structures. Cavity mode emission with a linear polarization has been observed in the direction normal to the surface at 20 K.
On Brewster’s angle of metals
Authors: Hüttner Bernd
Published: July 2002

We derive an elementary relation for the determination of the pseudo-Brewster angle of metals as a function of frequency. The pseudo-Brewster angle is defined as the angle where the reflection is minimal, i.e., the absorption is maximal. A comparison of the approximated values with the exact ones shows that the former are very accurate for photon energies below the Drude plasma frequency. Additionally we give two very simple expressions for a fast and surprisingly good estimate at low and high photon energies.
Comment on ‘‘Transient nucleation in solid-state crystallization of a-Si films’’ [J. Appl. Phys. 75, 2884 (1994)]
Authors: Shneidman Vitaly A.
Published: July 2002

In the experimental study of amorphous silicon films by H. Kumomi and T. Yonehara [J. Appl. Phys. 75, 2884 (1994)] the role of transient nucleation in formation of distribution of overcritical grains was emphasized. The corresponding analytical expression was previously obtained by V. Shneidman [Sov. Phys. Technol. Phys. 32, 76 (1987); 33, 1338 (1988)]. This solution is presented and its relation to the work of Kumomi and Yonehara is discussed.
Diffraction efficiency analysis in hologram gratings recorded by counterpropagating-type geometry
Authors: Nonaka Koutarou
Published: July 2002

This article gives formulas for calculating the diffraction efficiency of gratings with modulation that varies along the direction perpendicular to the grating vector. The analysis uses coupled-wave theory for mixed (phase and absorption) hologram gratings. General solutions for diffracted (signal) and undiffracted (reference) waves are given. The diffraction efficiency calculated for some special cases is compared with that for a uniform grating. Angle and wavelength mismatch from the Bragg condition is also discussed.
Dispersive transport of carriers under nonuniform electric field
Authors: Talwalkar N. , Das A. , Vasi J.
Published: July 2002

We have presented in this paper a semi-numerical simulation of dispersive transport under one-dimensional nonuniform electric field which could be used to study dispersive transport of carriers in the oxide. Our simulation is based on continuous time random walk principles (CTRW). Previous formulations using CTRW were derived under the assumption of uniform electric field. Comparison of our simulation results with the equivalent uniform field case shows that the treatment of nonuniform electric field is necessary to correctly predict events linked to dispersive transport, such as the growth of trapped oxide charge due to hole trapping or interface states due to H+ ions reaching oxide semiconductor interface of metal-oxide-semiconductor devices.
Modulation of excitonic reflectance at GaAs/GaAs interfaces
Authors: Novikov A. B. , Röppischer H. , Stein N. , Novikov B. V.
Published: July 2002

We have studied photoreflectance (PR) and reflectance spectra of undoped molecular-beam-epitaxy GaAs films on semi-insulating GaAs substrates at low temperature. In the PR spectra a sharp structure near the band-gap energy was observed which is sensitive to pump and probe light intensity. The origin of this structure was investigated by combining time-resolved and depth-resolved measurements. It is shown that the sharp PR structure arises from the superposition of a fast and a slow component of the modulated spectra. The slow PR signal originates from the epilayer–substrate interface. Both components are attributed to the modulation of exitonic transitions centered at slightly different energies.
Study of Ag/oxide interface of Bi-2223 silver-sheathed superconducting composite
Authors: Hua L. , Yao Q. Z. , Jiang M. , Wang Y. Z. , Tang H. , Li Z. R. , Qiao G. W.
Published: July 2002

The composition and microstructure of the Ag/Bi-2223 oxide interface in the silver-sheathed superconducting composite have been analyzed by Auger electron spectroscopy, electron probe microanalysis, x-ray-diffraction analysis, scanning electron microscopy, and energy-dispersive analysis x-ray spectroscopy. The results reveal that a diffusion layer exists in the Ag/oxide interface, and the width of the diffusion layer is greater in high-Jc samples than in low ones. It is also found that bismuth oxide may vaporize through the silver cladding at high temperature, and the deficiency of bismuth brings about the formation of nonsuperconducting phase.
Spatial and temporal beam reshaping effects using bulk CdTe
Authors: Hamad A. Y. , Wicksted J. P. , Wang S. Y. , Cantwell G.
Published: July 2002

Reshaping effects of ns pulses were theoretically and experimentally investigated using bulk CdTe. The experiments were performed using a 1.064 μm Nd:YAG laser with pulse duration of 10 ns. We observed that the laser pulses emerging from the sample experienced temporal compression and modulation which were found to be dependent on the input irradiance, the distance from the exit surface of the sample, and the cross sectional area detected. Self-defocusing and the formation of ring structures were also observed in the transmitted spatial profile and were found to be dependent on the input irradiance and the position of the detector from the sample. In our model we assumed that the free carriers generated by the two-photon absorption process were responsible for the induced nonlinear change in the index of refraction. As a result, the temporally and radially dependent phase shift encoded to the field that emerged from the sample was the cause of the reshaping effect. The results of our model, for both the spatial and the temporal profiles, are in good agreement with the experimental results. Moreover, the nonlinear parameters deduced from the fitting are in good agreement with previous experimental and theoretical results.
Interface fluctuations in Czochralski crystal growth
Authors: Miyano Takaya , Shintani Akira , Kanda Tadashi , Hourai Masataka
Published: July 2002

We construct a mathematical model of interface fluctuations in Czochralski crystal growth based on the thermal balance across the growing interface. The model describes time-dependent growth rate in relation to fluctuations in crystal pull rate and melt flow viewed as external perturbations. Complexities in the flow of a silicon melt are characterized in terms of time series forecast about melt thermal fluctuations actually observed beneath a growing crystal. The melt exhibits self-affine random motion with spatial and temporal structure specific to crucible rotation rate. The influence of the complex flow to crystal growth is discussed on the basis of the model proposed.
Stimulated emission and laser oscillation from light-hole excitonic state in a ZnSe-Zn0.8Cd0.2Se superlattice
Authors: Guan Z. P. , Zheng Z. H. , Fan X. W.
Published: July 2002

At 77 K, stimulated emission from n=1 light-hole excitons in a ZnSe-Zn0.8Cd0.2Se superlattice is observed and the oscillation mode properties of n=1 light-hole and heavy-hole excitons are analyzed. It is noticed that the ZnSe-Zn0.8Cd0.2Se superlattice with the shorter Fabry–Pérot cavity length d has the larger threshold excitation. The threshold of each mode has been determined using its time delay curve.
Current-voltage characteristics of unbalanced superconducting Wheatstone bridges
Authors: Cahay M. , Qian G. , Kothari R.
Published: July 2002

We compute the current-voltage characteristics of unbalanced superconducting Wheatstone bridges biased with constant and radio frequency current sources. An analytical expression for the critical supercurrent at which a nonzero voltage appears across the transverse junction of the bridge is derived. Analytical expressions of the first three Shapiro steps are also given and found to be in good agreement with numerical simulations.