bluuebunny/crossref_metadata_2025 huggingface dataset:
A photoluminescence study of Cd-related centers in InP
Authors: Swaminathan V. , Donnelly V. M. , Long J.
Published: July 2002

We report detailed studies of the low-temperature photoluminescence of Cd-related centers in InP. The samples consisted of Cd-diffused InP substrates as well as Cd-doped InP epitaxial layers grown by metalorganic chemical vapor deposition. Besides the previously identified 1.365-eV band, a new Cd-related band at a lower photon energy is reported. At 5.5 K, depending upon the excitation intensity, the peak position of this new band lies in the energy range 1.20–1.33 and 1.33–1.34 eV, respectively, in the substrates and in the epitaxial layers and it is broader compared to the 1.365-eV band. The peak position of the bands shifts to higher energy with increasing excitation intensity but the change in the peak energy per decade change in excitation intensity is much larger (50 meV) for the lower-energy band compared to the 1–2 meV shift for the 1.365-eV band. While the excitation dependence of the bands suggests a donor-to-acceptor pair recombination for their origin, we present arguments to show that the larger shift of the peak energy of the lower-energy band with excitation intensity is perhaps a consequence of the involvement of a deep donor in its origin as opposed to a shallow donor in the 1.365-eV band. In the case of InP:Cd substrates both the 1.365-eV band and the 1.20–1.33-eV band exhibit thermal quenching of luminescence above 100 K with an activation energy of 54±4 meV which is comparable to the ionization energy of 56 meV for the substitutional Cd acceptor, CdIn . From this we infer that both bands involve the CdIn acceptor in the recombination process. The identity of the deep donor in the 1.20–1.33-eV band and that of the recombination centers giving rise to the 1.33–1.34-eV band in the InP:Cd epitaxial layers are not known. In a preliminary comparison study on InP:Zn, similar, high- and low-energy Zn-related bands are observed. It is suggested that the deep donor is related to the group II impurity.
Observation of electroluminescence from excitons bound to isoelectronic impurities in crystalline silicon
Authors: Brown T. G. , Hall D. G.
Published: July 2002

We report the observation and characterization of luminescence near the wavelength 1.11 μm resulting from the electrical excitation and radiative decay of excitons bound to isoelectronic impurities in indium-doped crystalline silicon.
Study of the α and β relaxations on a commercial poly(vinyl chloride) by thermally stimulated creep and depolarization current techniques
Authors: del Val J. J. , Alegría A. , Colmenero J. , Lacabanne C.
Published: July 2002

Thermally stimulated creep and depolarization current measurements have been carried out in a temperature range between −180 and 120 °C, on a pure commercial poly(vinyl chloride). Mechanical and dielectric relaxation times involved in α and β relaxations are obtained by fractional stresses/polarizations procedure. The distribution of the Arrhenius-like kinetic parameters, deduced from the relaxation times, is interpreted in terms of compensation laws. From the obtained results, a same molecular origin can be assumed for the mechanical and dielectric behavior in both α and β relaxations. Moreover, the compensation law analysis leads to two different relaxations modes, likely associated to two kinds of thermally activated molecular motions, in β relaxation. In the α region, the values of found kinetic parameters point out a high degree of cooperativeness of the involved molecular motions. Depolarization curve in this region shows a high temperature peak, not found in the mechanical one, whose evolution with the poling field allows us to assign it to a nondipolar process associated to the movement of free charge carriers.
Thermally induced crystallization of amorphous-titania films
Authors: Hsu L. S. , Rujkorakarn R. , Sites J. R. , She C. Y.
Published: July 2002

Three types of amorphous-titania films prepared by ion- and electron-beam techniques have been annealed thermally. An amorphous-crystalline transformation is found in each of these film types at around 350 °C. Its resulting microcrystalline structure and the exact transition temperature appear to be dictated by the rutile microcrystalline seed present in the as-deposited films under different deposition conditions. An amorphous film with a weak rutile seed crystallizes at a lower temperature into the anatase structure, while a film with a relatively strong rutile base crystallizes into the rutile structure at a somewhat higher temperature. It is demonstrated that Raman spectroscopy is a simple and effective tool for characterization of these submicron-thick amorphous films and for the dynamical study of such a phase transformation. Accompanying this amorphous-crystalline transformation, a two-order increase in elastic light scattering is noted implying optical degradation associated with microcrystalline boundaries. In addition, results of the anatase–rutile transformation at a temperature near 900 °C are presented.
Molecular material-based junctions: Formation of a Schottky contact with metallophthalocyanine thin films doped by the cosublimation method
Authors: Maitrot M. , Guillaud G. , Boudjema B. , André J. J. , Simon J.
Published: July 2002

A new method for obtaining thin films of doped molecular materials in a complete absence of oxygen is described. It consists in simultaneously subliming under vacuum the electroactive compound—a metallophthalocyanine—and the electron acceptor or electron donor doping agent. The extent of doping is controlled by the relative rates of sublimation. The ac and dc electrical properties of thin films are determined under high vacuum as to eliminate the influence of oxygen which has been previously shown to be of the utmost importance. Both p- and n-type dopings have been achieved; the increase of conductivity reaches six orders of magnitude for p-type doping with dichlorodicyanoquinone (DDQ). For the first time a rectifying contact between doped phthalocyanine thin films and aluminum has been observed in strict absence of oxygen.
Electron beam deposition studies of the rare gases
Authors: Mandl A. , Salesky E.
Published: July 2002

The spatial distribution and absolute values of the stopping power of the rare gases Kr, Ar, and Ne were determined in 250-kV electron beam excited gas mixtures. The measured values were compared with 1D and 3D Monte Carlo code calculations. Excellent agreement was found in all cases.
Optimization of the surface impurity concentration of passivated emitter solar cells
Authors: Morales-Acevedo Arturo
Published: July 2002

The optimum emitter surface dopant concentration (Ns) in passivated silicon solar cells is found for different base resistivities with the help of a computer model. The model takes into account not only the band-gap narrowing, Auger and surface recombination effects on the dark saturation current, but it also considers the variation of series resistance as the impurity concentration changes. The results obtained with the model show different behavior for passivated and nonpassivated solar cells. The open-circuit voltage and the conversion efficiency of nonpassivated solar cells is almost independent of the surface impurity concentration when this parameter is greater than 2×1019 cm−3. On the other hand, for passivated solar cells the optimum value is in the range 2.5×1019 cm−3 ≤Ns<5×1019 cm−3 for typical base resistivities. Furthermore, it is confirmed that even when Ns is high (Ns>1×1020 cm−3) there is an advantage in efficiency of passivated solar cells over those which have a high recombination at the surface. However, in order to increase the efficiency appreciably Ns has to be optimized. The model also gives a procedure to optimize the grid design simultaneously with the surface concentration, assuming the other parameters are optimum.
Near-millimeter free electron laser designs based on measured characteristics of small-period electromagnet wigglers
Authors: Destler W. W. , Granatstein V. L. , Mayergoyz I. D. , Segalov Z.
Published: July 2002

The performance characteristics of small-period electromagnet wigglers of novel design are measured and compared with theoretical expectations. Field measurements for wigglers driven by dc, ac, and short-pulse current sources are reported. Fields as high as 1 kG have been readily obtained in a double-sided 3.9-mm-period wiggler. These performance capabilities allow the design of high-power free electron laser oscillators and ‘‘optical klystron’’ amplifiers in the near-millimeter regime using modest electron beam energies in the range 200–400 keV. Oscillator and amplifier designs for operation at 150 and 300 GHz are presented. The generation of 1.2 MW of 150-GHz radiation with >50% efficiency is predicted.
Photoluminescence of Si-doped AlAs grown by molecular-beam epitaxy
Authors: Kudo Kazuhiro , Makita Yunosuke , Nomura Toshio , Tanaka Hideki , Masuda Michiya , Mitsuhashi Yoshinobu , Matsumori Tokue , Izumi Tomio , Kobayashi Toshihiko
Published: July 2002

Low-temperature photoluminescence (PL) spectra for Si-doped AlAs grown by molecular-beam epitaxy is reported for the first time. It is revealed that a sharp emission which is 63 meV below the indirect excitonic band gap Eg,ind(X) is related to the Si-donor level. From the dependence of PL spectra upon Si dosage, it is suggested that a broad emission band which is 135 meV below Eg,ind(X) is due to donor-acceptor (SiAl-SiAs) pair recombinations.
Brillouin light scattering on yttrium iron garnet films in a magnetostatic wave device structure
Authors: Srinivasan G. , Patton C. E. , Emtage P. R.
Published: July 2002

Brillouin light scattering (BLS) has been used for the direct detection of magnetostatic wave (MSW) excitations in a MSW microwave device structure. The results are for a signal-to-noise enhancer device which consists of a yttrium iron garnet (YIG) film on a gadolinium gallium garnet substrate. The YIG film is in contact with a 30-μm-wide stripline and the static magnetic field is parallel to the stripline. MSW excitations were observed over the frequency range 2– 4 GHz. At low power, magnetostatic surface waves (MSSW) were excited with propagation perpendicular to the stripline and field direction. At high power, parametric half-frequency magnons were also observed. The measured magnon dispersion for the MSSW excitations, determined using the wave vector selective capabilities of the BLS spectrometer, is in good agreement with theory. The measured intensity profiles for MSW excitations at low-power levels show strong MSSW excitations over the entire surface wave band. At high power, the scattering intensity for surface MSW excitations saturates and is accompanied by a strong parametric magnon signal.
Cross-sectional transmission electron microscope study of the growth kinetics of hexagonal MoSi2 on (001)Si
Authors: Cheng J. Y. , Cheng H. C. , Chen L. J.
Published: July 2002

Cross-sectional transmission electron microscopy (XTEM) has been applied to the study of the growth kinetics of hexagonal MoSi2 on (001)Si. Growth rates, interface structures, and microstructures in the growth layers were determined for samples annealed at 560–580 °C for various periods of time. The silicide thickness was found to be proportional to the square root of annealing time. The activation energy and the rate constant of the growth were measured to be 2.3 eV and 14 cm2/s, respectively. Growth mechanisms are discussed. The results of the previous studies on the MoSi2 growth are summarized. Advantages of the present approach in the study of the growth kinetics of silicides on silicon, both in sample preparation and in the employment of XTEM technique, are outlined.
Electrical properties of nickel-related deep levels in silicon
Authors: Indusekhar H. , Kumar Vikram
Published: July 2002

Electrically active deep levels related to nickel in silicon are studied under different diffusion conditions, quenching modes, and annealing conditions. The main nickel-related level is at Ev+0.32 eV. Levels at Ev+0.15 and Ev+0.54 eV are not related to nickel while those at Ev+0.50 and Ev+0.28 eV may be nickel related. Their concentrations depend on the quenching mode. There is no nickel-related level in the upper half of the band gap. The complicated annealing behavior of the main nickel-related level is explained on the basis of the formation and dissociation of a nickel-vacany complex.
Thermodynamics of Nitinol
Authors: McNichols J. L. , Cory J. S.
Published: July 2002

A self-consistent macroscopic thermodynamics is developed for the calculation of work, heat, and dissipation for thermodynamic paths of the shape memory alloy, Nitinol. The thermodynamic system analyzed is a Nitinol helix for which extensive force–length–temperature (FLT) equation of state measurements have been made. The Nitinol system exhibits significant hysteresis and is determined to be a nonequilibrium thermostatic system. A set of equations of state are provided which correlate all reversible and irreversible Nitinol thermodynamic paths to both the set of helix (FLT) thermodynamic state variables and to new ‘‘history’’ state variables. It is shown that these equations predict observed cyclic behaviors not previously interpreted. In the absence of calorimetric measurements for the Nitinol helix system, a physical assumption is made that reversible paths are of constant phase. This assumption is used to estimate the reversible path thermal and mechanical heat capacities for the Nitinol system. With the state equations and the estimated reversible path heat capacities, the nonequilibrium thermostatic formalism is employed to derive expressions for the heat flow for any Nitinol thermodynamic path. It is shown that predicted calorimetric quantities are in good qualitative agreement with measurements. It is also shown that the calorimetric quantities are sensitive to state equation coefficients, which in turn are sensitive to cold-working or ‘‘conditioning’’ of the material. The large heat of transformation, ∼2.4 cal/g, an estimated isentropic temperature change of 22 °C and the large dimensional changes associated with the shape memory effect, imply that Nitinol may be useful for many applications, including use as a working medium for low-grade thermal-energy conversion (i.e., heat engines).
Electronic structure of an AlN film produced by ion implantation, studied by electron spectroscopy
Authors: Gautier M. , Duraud J. P. , Le Gressus C.
Published: July 2002

N+ ion implantation in a pure Al (111) monocrystal triggers a crystalline and stoichiometric thin AlN film. A complete description of the electronic states of the film is obtained by combining different spectroscopies carried out in situ. The density of electronic states in the valence band is given by x ray and UV photoemission spectroscopy; excitation of a core level (Al2p) by electrons provides information on the density of unoccupied states in the conduction band. Low-electron energy-loss spectroscopy allows one to study transitions between occupied and unoccupied states, as well as localized levels in the band gap, due to the presence of structural defects.
Consistent perturbation expansion for phase-changing material in a finite domain
Authors: Kahn Peter B. , Zarmi Yair
Published: July 2002

A self-consistent perturbation expansion is developed for the case of a finite slab of phase-changing material with constant boundary conditions corresponding to a ‘‘two-phase’’ problem. Consistency is achieved by a power-series expansion in functions of both solid and liquid Stefan numbers. Terms through third order are calculated.
Light scattering study on surface magnons in permalloy films
Authors: Srinivasan G. , Patton C. E.
Published: July 2002

Brillouin light scattering has been used to study the critical angle behavior for magnetostatic surface waves (MSSW) in thin permalloy films on silicon substrates. The measured magnon frequency versus wave number for various MSSW propagation angles with respect to the applied in-plane static field show that (i) for propagation perpendicular to the applied field, there is good agreement between the experimental and theoretical dispersion; (ii) for propagation away from perpendicular, the experimental frequencies are smaller than the theoretical values; and (iii) the surface mode merges with the zero-order bulk spin wave mode at a propagation angle well above the theoretical critical angle. These results demonstrate a significant departure from existing theories.
Mixed rare-earth iron garnet (TbY)IG for magnetic field sensors
Authors: Kamada O. , Minemoto H. , Ishizuka S.
Published: July 2002

Temperature dependence of sensitivity constants, corresponding to Verdet constant, of dodecahedrally substituted (TbxY1−x)IG crystals grown by a conventional flux method and liquid-phase epitaxy method are studied. By measuring the variation of the sensitivity constant with temperature, it was found that crystals with X=0.19 show a minimum value of ±1% between 300 and 400 K. The temperature dependence of sensitivity constants on Tb concentration was explained by a simple theoretical calculation.
A semiempirical model for the laser-induced molten zone in the laser recrystallization process
Authors: Willems G. J. , Poortmans J. J. , Maes H. E.
Published: July 2002

In this paper a semiempirical model is presented which describes the amount of silicon that is molten in laser recrystallization of polycrystalline silicon layers. The model is based on the fitting of rather simple, physically meaningful expressions to experimentally obtained values for the width of the molten zone induced by a scanning laser beam. The influence of laser power, scan velocity, preheating temperature, and capping layer structure can be described.
Deposition of silicon films from SiCl4 glow discharges: A kinetic model of the surface process
Authors: Bruno G. , Capezzuto P. , Cicala G. , Cramarossa F.
Published: July 2002

The deposition of amorphous silicon films from plasma-chemical reduction of silicon tetrachloride has been studied using optical emission spectroscopy, mass spectrometry, and laser interferometry as diagnostic techniques. The experimental results have been examined using a kinetic model of the surface processes. In the model, silicon tetrachloride (SiCl4) and silicon dichloride (SiCl2), chemisorbed on the growing surface, interact with hydrogen atoms to give free bond silicon species (−SiClx), which are reactive intermediates for the silicon-to-silicon bond formation on the surface. The temperature dependence of the deposition rate in the kinetic region has been also investigated. It has been established that the apparent activation energy for the silicon plasma deposition depends on the electronic character of the material (i.e., undoped, n, and p doped). As the surface becomes boron or phosphorus doped, the value of the apparent activation energy changes with respect to the undoped surface, as a result of the different chemisorption heat on the different surfaces.
Fluorinated chemistry for high-quality, low hydrogen plasma-deposited silicon nitride films
Authors: Chang Chorng-Ping , Flamm Daniel L. , Ibbotson Dale E. , Mucha John A.
Published: July 2002

We have developed a low-temperature (≲300 °C) plasma deposition process to prepare novel fluorine-containing silicon nitride films (p-SiN:F) using SiH4–NF3–N2 discharge mixtures at 14 MHz rf applied frequency. The deposition rate can be extremely high, up to 1600 Å/min. Data indicate p-SiN:F has electrical properties (dielectric constant, breakdown strength, resistivity, etc.) which compare favorably to high-temperature, chemical-vapor-deposited silicon nitride. By controlling the feed chemistry and physical variables of the discharge, a wide variety of film compositions are achieved. Moreover, this chemistry is superior to the only other p-SiN:F which was prepared from a SiF2/SiF4-H2-N2 feed. Two classes of films were identified as stable or unstable to air exposure and the instability of the films correlated with the atom fraction of fluorine initially incorporated. Infrared, Auger electron, and Rutherford backscattering spectroscopy measurements show that low hydrogen concentrations are produced by the introduction of fluorine in the silicon nitride films. More importantly, the concentration of Si–H is extremely low because strong Si–F bonding replaces the weak Si–H bonds that satisfy free Si orbitals found in conventional plasma nitride, and the hydrogen remaining in the film is present as stable N–H bonds. We believe this substitution of silicon-bound hydrogen, caused by the gas phase and surface-driven reactions, is a source of superior film properties. The mechanism for this novel discharge chemistry is discussed.
Role of sulfur atoms in microwave plasma etching of silicon
Authors: Ninomiya Ken , Suzuki Keizo , Nishimatsu Shigeru , Okada Osami
Published: July 2002

The Si etch rate in an (F2+O2) microwave plasma has been measured as a function of O2 mixing ratio at a fixed total pressure of 5.3×10−2 Pa. The etch rate significantly decreases with the mixing ratio. This etch rate decrease is due primarily to surface oxidation. When sulfur is added to the (F2+O2) plasma, the Si surface is much less oxidized and the etch rate increases by about a factor of 4. Such sulfur-containing species as S atoms react with O atoms or ions in the plasma and form O atom-containing species, such as SO2, SO+, SOF+, and SOF+2, thereby reducing the O atom and O+ ion concentrations in the plasma. As a result, the Si surface is scarcely oxidized, so that the etching reaction can easily proceed. Sulfur atoms inhibit surface oxidation and promote Si etching. Sulfur atoms contained in SF6, which is usually used in microwave plasma etching of Si, are expected to have the same role.
Behavior of SiNx films as masks for Zn diffusion
Authors: Zou W. X. , Vawter G. A. , Merz J. L. , Coldren L. A.
Published: July 2002

The detailed behavior of SiNx films as masks for Zn diffusion into GaAs at both low and high temperatures has been investigated. It is found that the film behavior as a mask is a function of the refractive index of the SiNx mask film and that a film with index n=2.06 shows optimum performance at both 650 and 950 °C. The experimental results suggest that the film with n=2.06 is nearly stoichiometric. Possible reasons for this optimized masking behavior are discussed.
Damage to shallow n+/p and p+/n junctions by CHF3+CO2 reactive ion etching
Authors: Wu I.-W. , Street R.A. , Mikkelsen J.C.
Published: July 2002

The damage incurred during contact etch is studied, with emphasis on determining those defects responsible for leakage current of shallow junctions. Shallow p+/n and n+/p junctions have been prepared with depths of 160–180 nm. Junction leakage and contact resistance measurements have been made for various amounts of silicon loss up to within 20 nm of the junctions during contact etch through a 300 nm of SiO2 film by using a CHF3+CO2 plasma. For p+/n junctions, the leakage current density was found to depend strongly on contact area and increase rapidly with etch depth after the etched surface has extended to within 80 nm of the junction boundary. On the other hand, the leakage current stays constant even when the etched surface approaches within 40 nm of the junction boundary for n+/p junctions. Further etching of the n+/p junction only induces punch-through. Contact resistance was found to increase with etch depth for the p+ junctions after 50 nm of silicon was removed from the surface, and stays constant for all etched n+ junctions. Etching induces a prominent feature at 970–975 meV in photoluminescence (PL) spectra. The occurrence and peak height of this luminescence, which is associated with H and independent of C concentrations, are found to correlate directly with leakage current of as-etched junctions. The annealing behavior of reactive ion etching (RIE) damage is somewhat more complicated, with a change in defect PL before there is a noticeable change in the leakage current. A transmission electron microscopic study showed no evidence of defects.
Effects of peening on magnetic-flux density in a metallic glass
Authors: Nishi Yoshitake , Harano Hidehiko
Published: July 2002

The change of the saturated magnetic-flux density, Bs, with peening is studied for a Fe-Ni-Si-B glass. The peened glass shows the large Bs. Taking the driving force of the peening to be the collision energy, a rate process theory is applied for the glass. The parameter of X [(Bs−B0s)/(Bms−B0s)] is used, where Bms and B0s are Bs of the peened glass at an extremely long period of time and the minimum value of Bs, respectively. Based on the rate process, X is expressed by the following equation: log10[−ln(1−X)]=n log10 t+log10 k. Bs approaches Bms with peening. Bms is 9.51 kG, when the correlation coefficient is maximum. The faster the cooling rate, the smaller the n and log k become. Thus, Bs can be obtained by controlling the cooling rate and peening time according to our discretion.
Disordered intermixing at the platinum:silicon interface demonstrated by high-resolution cross-sectional transmission electron microscopy, Auger electron spectroscopy, and MeV ion channeling
Authors: Abelson John R. , Kim Ki Bum , Mercer Douglas E. , Helms C. Robert , Sinclair Robert , Sigmon Thomas W.
Published: July 2002

The metallurgical interaction at the interface between single-crystal silicon substrates and thin films of elemental platinum has been examined using the complementary techniques of high-resolution cross-sectional transmission electron microscopy (HRXTEM), Auger sputter profiling, and MeV ion channeling. We identify the existence of a 30-Å-thick layer of intermixed platinum and silicon which forms at the metal-silicide interface when 50 Å of Pt is electron beam evaporated onto room-temperature Si. The interfacial layer is evident in the HRXTEM as a uniform band of dark and noncrystalline contrast. In Auger sputter profiling, the evolution of the Si LVV line shape indicates the presence of a platinum silicide region adjacent to the film/Si interface but not at the surface of the Pt film. MeV ion channeling reveals that ∼1.5×1016 Si atoms/cm2 are displaced from their substrate lattice sites upon Pt deposition. In addition, the HRXTEM reveals islands of unreacted Pt and occasional grains of Pt2Si on top of the intermixed layer of Pt and Si.
Structures and magnetic properties of Fe/Ag multilayer films prepared by sputtering and ultrahigh-vacuum depositions
Authors: Kozono Y. , Komuro M. , Narishige S. , Hanazono M. , Sugita Y.
Published: July 2002

Fe/Ag multilayer films were prepared by rf-magnetron sputtering and ultrahigh-vacuum (UHV) depositions. The Ag layer thickness dAg was 2 nm constant, and the Fe layer thickness dFe was changed from 1 to 40 nm. The relationships between film structures and magnetic properties were investigated. The periodicity of multilayer films by UHV deposition is superior to that of sputtered films. The crystal orientation of sputtered films is Fe(110)∥Ag(111) for dFe less than 7.3 nm, and Fe(110)∥Ag(200) for dFe more than 14.7 nm. The critical thickness of dFe corresponds to the continuity of the Fe layer. When the crystal orientation is Fe(110)∥Ag(200), the saturation magnetic flux density Bs(T) is about 2.1 T, and the coercive force Hc is less than 2 Oe. When the films are Fe(110)∥Ag(111), Bs sharply decreases and Hc increases with decreasing dFe. The crystal orientation of UHV deposition films is Fe(110)∥Ag(200) in the range of dFe=2–40 nm. Bs of UHV deposition films is about 2.0 T constant and Hc decreases with decreasing dFe.
Pulsed-laser optogalvanic spectroscopy of sodium and scandium in a high-pressure metal halide discharge
Authors: Kramer Jerry
Published: July 2002

Pulsed-laser irradiation of a high-pressure metal halide discharge tuned to excite Hg and the metal additives, sodium and scandium, produced negative optogalvanic voltage signals and positive optogalvanic current signals. The optogalvanic signals resulted from excitation of ground-state sodium atoms at 589 and 589.6 nm, from excitation of both ground- and excited-state scandium atoms throughout the visible, and from excited states of Hg. The optogalvanic spectrum was very similar to the emission spectrum, except for the absence of self-reversal in the optogalvanic spectrum. The nonlinear dependence of the optogalvanic signals on laser energy for ground-state Na and Sc and the excited states of Hg was attributed to stimulated emission. Vertical segregation of Na and Sc was evident from the axial variation of the optogalvanic signals. Increasing the envelope temperature, and hence the vapor pressures of the additives (by raising the input power to the discharge), increased the optogalvanic signals from ground-state Na and Sc.
System effects in double-channel gated-integrator-based deep-level transient spectroscopy
Authors: Balasubramanyam N. , Kumar Vikram
Published: July 2002

The effects of the two sampling gate positions, and their widths and the integrator response times on the position, height, and shape of the peaks obtained in a double-channel gated-integrator-based deep-level transient spectroscopy (DLTS) system are evaluated. The best compromise between the sensitivity and the resolution of the DLTS system is shown to be obtained when the ratio of the two sampling gate positions is about 20. An integrator response time of about 100 ms is shown to be suitable for practical values of emission time constants and heating rates generally used.
Interdependence of magnetic properties and intrinsic stress in mono- and polycrystalline thin nickel films
Authors: Shih C. Y. , Bauer C. L. , Artman J. O.
Published: July 2002

Mono- and polycrystalline Ni films, ranging in thickness from 19 to 382 nm, have been produced by vacuum deposition on (001) monocrystalline Ag/NaCl and on glass substrates, respectively. Subsequently, saturation magnetization Ms, magnetogyric factor γ/2π, and effective uniaxial anisotropy Hk were measured by a combination of vibrating sample magnetometer and ferromagnetic resonance (FMR), and corresponding internal stress σ was measured by a levered optical beam reflection technique. In addition, the microstructure of both mono- and polycrystalline films has been characterized by conventional and cross-section transmission electron microscopy. Saturation magnetization can be interpreted by the presence of a magnetic dead layer of about 9 nm and a constant value of 434 emu/cm3, thereafter. Results from FMR can be described by contributions from shape and stress-induced anisotropy. Corresponding values of σ, as computed from Hk, are in satisfactory agreement with values measured by the optical beam reflection technique and yield values of about 1010 dyn/cm2; σ generally decreases with increasing film thickness and annealing time and temperature. Finally, monocrystalline films are characterized by a single FMR peak; polycrystalline films thicker than about 200 nm are characterized by multiple peaks. Occurrence of these multiple peaks is attributed to variation in the effective magnetoelastic constant as a result of a change from equiaxed to columnar grain morphology.
Barkhausen effect and discontinuous magnetostriction in Terfenol-D
Authors: Jiles D. C. , Ostenson J. E. , Owen C. V. , Chang T. T.
Published: July 2002

Measurements of magnetostriction λ, magnetic Barkhausen effect (MBE), and magnetic induction B have been made as a function of magnetic field H in a number of specimens of Tb0.3Dy0.7Fe1.9 prepared recently at Ames Laboratory. These results showed marked variations in properties from specimen to specimen. For example, the saturation magnetostriction of the materials under a compressive load of 14 MPa (2000 psi) varied from 1500 to 2200×10−6. However, it was noticed that in the high-performance, high-magnetostriction specimens a common feature was a very rapid change in magnetostriction with field in the range 400–500 Oe. Barkhausen measurements taken on two extreme specimens from the group also revealed very different signals, in particular the high-performance material was found to have a distinctive double peak in Barkhausen activity, one peak of which corresponded to the rapid change in magnetostriction, while the other occurred at the flat region of the magnetostriction versus field curve, corresponding to little or no change in magnetostriction.
Mechanism of surface-limited release of hydrogen from oxidized metals
Authors: Richards P. M. , Myers S. M. , Wampler W. R. , Follstaedt D. M.
Published: July 2002

Analysis has been made of the time dependence of surface recombination and release of deuterium from helium-bubble traps in iron with both clean and oxidized surfaces. In both cases second-order kinetics are obeyed over a large range of time scales, including short times when the traps are saturated. We show this is possible only if, in both cases, release is limited by escape from surface sites which have the same energy as the traps. We therefore propose that the oxide represents an additional barrier, but does not alter the energies of sites from which recombination takes place relative to solution sites. We further show that for both iron and stainless steel the prefactor for the recombination rate is about the same for a bare surface and for an oxide layer. Thus effects of the barrier are mostly on the activation enthalpy of release.
The etching mechanism of titanium polycide in a mixture of SF6 and O2
Authors: Manenschijn A. , Janssen G. C. A. M. , van der Drift E. , Radelaar S.
Published: July 2002

Reactive ion etching of titanium disilicide films on top of undoped polycrystalline silicon has been investigated in order to determine the etching mechanism of the silicide in a fluorine plasma. Mixtures of SF6 and O2 and of CF4 and O2 were used. Vertical and lateral etch rates have been determined as a function of pressure and the amount of oxygen addition. The density of fluorine atoms and positive ions in the plasma has been determined from optical emission spectroscopy and electric probe measurements, respectively. From these results, the fluxes of fluorine to and away from the sample and the ion flux towards the sample have been calculated. With x-ray photoelectron and Auger electron spectroscopy, the surface constitution after etching has been studied. The TiSi2 layer is etched anisotropically, independent of pressure and the addition of oxygen. A relation between the etch rate and the density of fluorine atoms in the plasma is not found, in contrast with results obtained elsewhere [K. C. Cadien, S. Sivaram, and C. D. Reintsema, J. Vac. Sci. Technol. A 4, 739 (1986)]. From our results it is shown that the etch rate of TiSi2 in a low-pressure fluorine plasma is not limited by the supply of reactive fluorine to the surface. It is limited by ion-induced desorption or ion-induced formation of volatile titanium fluoride compounds. The magnitude of the observed vertical and lateral etch rate of silicon are described by means of the reaction probability of fluorine at the silicon surface and the density of fluorine atoms in the plasma. Anisotropic etching of the polysilicon layer in a SF6/He/O2 plasma occurs when more than 10% oxygen is added. The effect of oxygen on etch rates and anisotropy is due to a surface reaction and not to gas-phase reactions. It is argued that an oxyfluoride layer is formed on the silicon surface that hinders the formation of saturated silicon fluoride species.
Magnetization curling in a finite cylinder
Authors: Ishii Y. , Sato M.
Published: July 2002

In order to see the variation of the magnetization state in a finite cylinder, it is assumed that the magnetization changes its direction by the magnetization curling mode in which θ is given by θ=λ(z/L)2+ν, where θ is the deviation of the magnetization in the cylinder from the z axis which is the axis of the cylinder, L is half of the cylinder length, and λ and ν are the coefficients which specify the magnetization state. Finding λ and ν which minimize the total energy ε of the cylinder, we obtain the hysteresis loops and the coercive force. The coercive force obtained in this work agrees well with the experimental results for a cylinder 2.5 μm long and a diameter from about 50 to about 130 nm. It is also found that the configurations can be stable in which the magnetizations are not along the z axis, and the hysteresis loops are not rectangular, even though an applied field is along the z axis.
Glass transition in an elastohydrodynamic lubrication: A quasielastic light scattering approach
Authors: Bezot P. , Hesse-Bezot C.
Published: July 2002

A study of the infinite frequency longitudinal modulus M∞ of 5P4E [m-bis(m-phenoxyphenoxy) benzene] as a function of pressure, by means of the Brillouin light scattering technique, through the glass transition, is presented. To make measurements in different compression kinetics, the analysis system has been modified to reduce significantly the measuring time without lowering the signal-to-noise ratio. It is observed that the M∞ value depends on the pressure histories and consequently contains information on the nonequilibrium structural state of the fluid. For example, when the compression rate for a step pressure from 0.17 to 0.245 GPa is divided by 30, the Brillouin shift decreases by 200 MHz, which is much larger than the experimental errors. The experimental results, obtained in various dynamic conditions similar to those encountered in an elastohydrodynamic (EHD) contact, are in relatively good agreement with computed values using a fictive pressure model. The computed structural relaxation time of the fluid is found to be strongly dependent on the compression rate. This behavior is in agreement with the large viscosity variation as a function of the transit time in an EHD contact.
Differential and total cross sections for the elastic scattering of 1–1000-eV electrons from silicon using the optical model
Authors: Srivastava R. , Williamson W.
Published: July 2002

Differential and total cross sections for the elastic scattering of electrons from gound-state silicon atoms have been calculated using the optical model. The optical potential includes the static potential, and the effects of exchange and polarization. The results are compared with the first Born approximation and screened Rutherford differential cross sections which are often used in electron Monte Carlo transport codes. It is found that the screened Rutherford differential cross sections differ considerably from the optical model calculations for the entire energy range considered. The first Born differential cross sections merge with the optical model results at about 500 eV.
Monte Carlo studies of steady-state electronic transport in compensated In0.53Ga0.47As
Authors: Costa Julio , Peczalski Andrzej , Shur Michael
Published: July 2002

The steady-state velocity-field characteristics of n-type In0.53Ga0.47As are obtained through a Monte Carlo calculation for temperatures between 77 and 400 K, and for compensation ratios Na/Nd between 0 and 0.9. Alloy scattering is found to play a significant role in the low-temperature regime. Low-field electron drift mobilities are extracted from the velocity-field curves. We conclude by suggesting empirical relationships which model the velocity-field characteristics as a function of low-field electron drift mobility.
An analysis of the in-plane acceleration sensitivity of quartz surface-wave resonators rigidly supported along the edges
Authors: Shick D. V. , Zhou Y. S. , Tiersten H. F.
Published: July 2002

An analysis of the in-plane acceleration sensitivity of grooved ST- and SST-cut-quartz surface-wave resonators rigidly supported along the edges is performed. The biasing deformation fields are obtained using a new variational approximation procedure which is very accurate, computationally efficient, and convenient to use. The calculated extensional biasing states are employed in an existing perturbation equation along with the proper continuous representation of the acoustic surface-wave mode shape for arrays of reflecting grooves to calculate the in-plane acceleration sensitivity for both cuts. The calculations reveal that the ST cut is slightly less sensitive than the SST cut and that both are a few parts in 1011 per g.
Solving the spatially dependent Boltzmann’s equation for the electron-velocity distribution using flux corrected transport
Authors: DiCarlo John V. , Kushner Mark J.
Published: July 2002

Boltzmann’s equation(BE) for the electron-velocity distribution (EVD) in partially ionized plasmas is not usually directly integrated as an initial value problem using finite differences. This circumstance is a result of numerical effects which blur sharp density boundaries in the position-velocity plane. To address this issue, we have applied flux corrected transport (FCT) to solving BE and demonstrated the method by calculating the EVD in the cathode fall of a He glow discharge by direct integration. Unidirectional and bidirectional EVDs are considered, and comparisons are made to conventional multibeam and Monte Carlo simulations to validate our method. We find that using FCT to solve BE is a significant improvement over conventional finite difference methods, being both more accurate and computationally faster.
Disorder effects on optical spectra and band structure of Si induced by ion implantation
Authors: He Xing-Fei , Jiang Ren-Rong , Chen Rui-Xiang , Mo Dang
Published: July 2002

We have studied the effects of both structural and substitutional disorder in As+-implanted Si at doses from 3×1012 to 1×1016 ions cm−2 on interband optical spectra, particularly on an E1 structure at 3.4 eV. Increasing the implant dose results in a structural order-disorder transition, found to be well described by the peak-to-peak height of the E1 derivative spectra. The damage rate is defined as being based on the E1 spectral structure and is related to the fractional strength of interband optical response, in good agreement with that in effective-medium theory. The relationships between interband optical properties and electronic structure in the implanted region are discussed. After annealing, there is a red shift of the E1 threshold together with a decrease in optical response. This is attributed to substitutional impurities and screening of free carriers, which was observed and compared with previous results.
Dynamic writing of magnetic domains in GdTbFe: Observations made by Lorentz microscopy
Authors: Greidanus F. J. A. M. , Jacobs B. A. J. , den Broeder F. J. A. , Spruit J. H. M. , Rosenkranz M.
Published: July 2002

In this paper the sizes and shapes of thermally written magnetic domains in a GdTbFe layer are discussed. The magneto-optical layer is deposited on a specially prepared silicon wafer disk, provided with Si3N4 windows. This allows dynamic writing of domains under realistic recording conditions on a rotating substrate and direct observation of the magnetization patterns in the transmission electron microscope, using Lorentz microscopy. Domain patterns were written in two different ways: With the first method, laser modulation (LM), the laser beam was modulated while applying a fixed field. In the second method, magnetic field modulation (MFM), the laser was on continuously and the applied magnetic field was modulated. With LM it was observed that both size and shape are closely dependent on the magnitude of the applied field. This behavior is in good agreement with observations made with optical readout of similar magneto-optical disks. Domains written with MFM have somewhat irregular contours. The degree of irregularity depends on the magnitude of the applied magnetic field and its switching time. Reduction of these irregularities can be achieved by simultaneously modulating the laser beam.
Effective minority-carrier hole confinement of Si-doped, n+-n GaAs homojunction barriers
Authors: Chuang H. L. , Klausmeier-Brown M. E. , Melloch M. R. , Lundstrom M. S.
Published: July 2002

The electrical performance of Si-doped n+-n GaAs homojunction barriers grown by molecular-beam epitaxy (MBE) is characterized and analyzed. We employed a successive etch technique to study hole injection currents in GaAs n+-n-p+ solar cells. The results of the analysis show that minority-carrier holes in our MBE-grown material have a mobility of 293 cm2/V s for an n-type Si-doping level of 1.5×1016 cm−3 at 300 K. The interface recombination velocity for these homojunction barriers is estimated to be less than 1×103 cm/s, and it appears to be comparable to that recently observed for Si-doped n+-n GaAs homojunction barriers grown by metalorganic chemical vapor deposition. We present evidence that these n+-n GaAs homojunctions, unlike p+-p GaAs homojunctions, are almost as effective as AlGaAs heterojunctions in minority-carrier confinement, and that their electrical performance is not degraded by heavy doping effects.
The effect of electron-hole plasmas on the density of states of silicon and GaAs
Authors: Lowney Jeremiah R.
Published: July 2002

The densities of states of the conduction and valence bands of silicon and GaAs have been calculated at 300 K for the case of an electron-hole plasma, which can occur at high-injection levels in bipolar devices or in bulk material under intense optical excitation. The results show considerable narrowing of the band gap, which needs to be included in the analysis of device measurements or the interpretation of photoluminescence data. Furthermore, the band-gap narrowing that results from dopant ions is reduced by excess carriers because of the reduced free-carrier screening radius.
Temperature dependence of the dark conductivity and photoconductivity in evaporated thin films of 1,4-dithioketo-3,6-diphenyl-pyrrolo- [3,4-c]-pyrrole under a high vacuum or in the atmosphere of oxygen or hydrogen
Authors: Mizuguchi Jin
Published: July 2002

The temperature dependence of dark conductivity and photoconductivity has been investigated in evaporated thin films of 1,4-dithioketo-3,6-diphenyl-pyrrolo-[3,4-c]-pyrrole (DTPP) under a high vacuum or in the atmosphere of oxygen or of hydrogen. This investigation aims at examining the influence of an electron-accepting impurity (O2 ) or of an electron-donating impurity (H2 ) on the photoconductive properties of DTPP under practical conditions for electrophotographic photoreceptors. The dark conductivity and photoconductivity are found to be scarcely affected by these gases at room temperature. Although some influence appears at elevated temperatures, it is well within the tolerance acceptance in practical operations of electrophotographic photoreceptors.
Charged point defects in GaAs crystals evaluated by nuclear-magnetic-resonance spin echo
Authors: Suemitsu Maki , Nakajo Naoki
Published: July 2002

Separation of the quadrupolar interaction in GaAs is of practical importance since the interaction magnitude is proportional to the density of charged point defects in the crystal. For this purpose, nuclear-magnetic-resonance spin-echo experiments were carried out and the results were analyzed with a theory extended from a conventional spin-echo theory. Spin echoes were obtained for 75As under a static magnetic field H0=11.7 T at room temperature. The analysis included effects of incoherent spins which are not in phase at the formation of echoes. With a combination of a Gaussian-type relaxation function for the dipolar interaction and an exp(−Kt3/2) type for the quadrupolar interaction, the theoretical fitting in the analysis showed an excellent agreement with the experiment. A pair of fitting parameters thus obtained corresponded to the strengths of the above two interactions. Each of the two parameters showed consistent orientation dependence with theoretical predictions: A+Bf(θ) for the dipolar parameter and A+Bf(θ)3/4 for the quadrupolar parameter, where  f(θ)=4 cos2 θ−3 cos4 θ with θ the angle between H0 and the [110] direction of the crystal. Considering that the anisotropic amplitude B in the quadrupolar parameter represents the virtual strength of the quadrupolar interaction, the charged point-defect density in the crystal was obtained and compared with the values of optical measurements.