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  • American Institute of Physics (AIP)  (31,708)
  • 1985 - 1989  (31,708)
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Years
Year
  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: As a second in a series of theoretical models for the electrical discharge machining (EDM) process, an erosion model for the anode material is presented. As with our point heat-source model in the previous article, the present model also accepts power rather than temperature as the boundary condition at the plasma/anode interface. A constant fraction of the total power supplied to the gap is transferred to the anode. The power supplied is assumed to produce a Gaussian-distributed heat flux on the surface of the anode material. Furthermore, the area upon which the flux is incident is assumed to grow with time. The model is capable of showing, via the determined migrating melt fronts, the rapid melting of the anodic material as well as the subsequent resolidification of the material foation from plasma dynamics modeling could improve substantially our results.
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  • 2
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4112-4122 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Designs are proposed, based on a series of one-dimensional calculations, for layered, hollow cylindrical targets to be placed on the axis of an imploding, hollow Z-pinch plasma that can create the approximate plasma conditions, as well as radiation spectrum, for a photoionization pumped, Ne-like recombination laser. The lasant must reach the Ne-like state and be at the appropriate density at the same time that the photoionizing pump radiation is present, placing severe constraints on designs for such targets. Target designs are further constrained by the fact that the 3s-2p resonance line, which depopulates the lower lasing state, must not be highly trapped and by the fact that the upper lasing state must not be collisionally depopulated. We find that hollow, cylindrical targets consisting of a few-micron-thick CH strongback, coated on the inside with a thin layer of Ni lasant and on the outside with an Al converter layer, can be optimized to achieve appropriate conditions for lasing and modest levels of gain.
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  • 3
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4123-4133 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The nonlinear dynamics of charge transport due to an electric discharge on a dielectric surface is analyzed using a transmission line model. The relation between the resistance per unit length, Rˆ, and the current, I, is assumed to be given by the local arc-welder's ansatz, Rˆ||I||=E*, where E* is a positive constant. The model predicts that a discharge initiated in the vicinity of a charge spot can propagate partway down a current channel and abruptly terminate before transporting charge to the dielectric edge. This behavior is similar to leader phenomena observed in lightning and other electrical discharges. We show that the direction of the current along the current channel is constant throughout such a discharge. The minimum voltage at the charge spot that allows charge to be transported to the dielectric edge is determined. This critical voltage Vl depends on the length l of the current channel. We show that the "average field,'' Vl/l, decreases as l increases. When the charge spot voltage is less than the critical voltage, we obtain upper and lower bounds for both the arc duration time and amount of charge removed from the charge spot.
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  • 4
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An exhaustive experimental investigation of the conditions required to sustain a plasma column through the propagation of the m=1 mode surface wave has been conducted. It reveals that, given a discharge tube radius a, there corresponds a minimum frequency value fm below which the discharge cannot be achieved; conversely, for a given operating frequency f, the tube radius must exceed some minimum value am for the plasma to be sustained. These minimum conditions required to obtain the discharge are observed to obey a scaling law of the form (fa)m(approximately-equal-to)const., where the constant is independent of the gas nature and pressure. Theoretically, the dispersion equation of the m=1 mode wave shows no low-frequency cutoff. However, it is found that the specific dependence of the wave attenuation coefficient on the frequency and on the tube diameter can ultimately account for the observed limitations when the wave is used to sustain a plasma. A discharge stability criterion is proposed that recovers the observed scaling law determining the minimum tube radius and wave frequency values.
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper we report on experiments to investigate the laser-induced breakdown properties of saline solutions of different concentrations and of highly deionized water, using a Q-switched Nd:YAG laser. The observation of the dependence of the breakdown probability on the pulse energy gives information about the influence of the ion concentration on the breakdown occurrence. It has turned out that the generation of initial electrons for the avalanche by the ions determines the breakdown threshold in saline solutions. In extremely pure water, with no ions as electron donors, the first free electrons have to be produced by multiphoton ionization of the water molecules, which leads to a very sharp threshold. The region of pulse energies, where breakdown occurs only with a certain probability, has its minimum width in pure water, shows its maximum extension in low concentrated solutions and is again getting narrower with increasing concentrations.
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  • 6
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4019-4024 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments have shown that transverse conducting foils provide strong focusing for high-current relativistic electron beams. We describe a method to focus and to steer such beams using arrays of wires transverse to the direction of beam propagation. In contrast to foils, the wires have high transparency and can steer the beam in a circular accelerator. We present self-consistent equilibrium models for displaced planar beams in a wire array. The models predict the allowed angular divergence and radius of curvature of high-intensity beams. Wire focusing may be useful for compact accelerators. As an example, a 20-MeV beam with current in the range of 10 kA can be guided through an accelerator with a radius of curvature of about 0.5 m.
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  • 7
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4025-4034 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The electromagnetic field from the current in a circular disk and its Poynting vector off the axis of propagation have been investigated both analytically and experimentally. These studies show that the electromagnetic (EM) missile has the following properties: (1) The waveform of the EM field when propagating remains similar in shape but diminishes in size. (2) The transverse distribution of energy around the axis is stable; i.e., when the longitudinal distance increases, the transverse pattern of the energy remains the same. This "plane-wave beamlike'' property is different from continuous-wave (cw) radiation, in which the energy pattern is like that of a spherical wave. (3) The transverse energy pattern has a cusp on the axis. This property is also different from cw radiation. With cw, the radiation has a flat top on the axis of the main lobe.
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  • 8
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4163-4175 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The trigatron has been in widespread use as a demand-triggered, high-voltage switch for more than 40 years. In spite of the popularity and maturity of the technology, there persists an uncertainty over the basic physical mechanism(s) responsible for triggering breakdown in the devices. We present the results of an empirical study of trigatrons that directly demonstrates that breakdown is initiated by a streamer launched from the trigger pin, independent of the trigger spark. We compare our results with those of previous workers, and discuss the generality of our conclusions.
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  • 9
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Implantations of silicon and silicon fluoride ions into semi-insulating GaAs wafers were performed to compare and evaluate the quality of the n-type layers that were produced. The use of SiFx (x=1,2,3) molecular ion implantations creates n-type active regions and n+ ohmic contact layers employing a higher implant energy than that needed to achieve a similar projected range for silicon ions. The higher energy allows the implanter to operate with a more stable and reproducible ion beam for shallow implant applications. Variables affecting the net electrically active ion distributions, such as the ion beam incidence angle, and the use of furnace or rapid thermal annealing cycles for implantation activation are addressed. Capacitance-voltage profiles were obtained for the n-type regions, and the free carrier distributions for the n+ implantations were obtained by polaron electrolytic profiling. The implanted regions were characterized by Hall-effect measurements, cathodoluminescence, and secondary ion mass spectroscopy.
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  • 10
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4184-4187 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A PbTe flux has been used for n-type (Te) doping of GaAs, GaSb, and AlGaSb. The effects of surface accumulation and Te desorption were noticeable in secondary-ion mass spectroscopy profiles of GaAs layers grown at temperatures in excess of 540 °C. Te accumulation was not apparent in GaSb layers grown at temperatures up to 630 °C, but Te desorption occurred from GaSb at temperatures above 540 °C. The donor ionization energy of Te in AlxGa1−xSb is 44 meV for 0.4<X<0.5, i.e., significantly lower than the ionization energies of S or Se in similar material.
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  • 11
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4181-4183 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Reaction kinetics for the direct synthesis process of compound GaSb from Ga and Sb metals was studied by observing viscosity changes of the melt during the reaction process. The mole fraction of Ga (cGa) was obtained during synthesis using the equation; log η=cGa(log ηGa +log ηSb)+(1−2cGa)log ηGaSb, where η is the viscosity of the total system, and ηGa,ηSb, and ηGaSb are the viscosities of molten Ga metal, molten Sb metal, and molten GaSb, respectively. The reaction rate was obtained from the variation of the mole fraction of reactant cGa. Assuming a second-order reaction, the activation energy was estimated to be 15.5 kcal/mol.
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  • 12
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The anomalous scattering of x rays has been used to determine the polarity of single-crystal epitaxial layers, as grown on the substrate material. The method relies on the breakdown of Friedel's law in noncentrosymmetric structures and is particularly effective when there exists a large difference between the values of the imaginary anomalous dispersion correction, f‘, for the respective atomic species. The method is nondestructive and measurements are taken from only one side of the sample (the side with the epitaxial layer).
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  • 13
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4213-4217 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that heat flow is severely decreased in transient phenomena, due to nonlocal effects. The case of phonon transport in a steep temperature gradient is discussed in detail for semiconductors. Fixed end temperatures and an initial heat pulse propagating in a homogeneous sample are considered as boundary conditions. The temperature profile evolves in all cases significantly slower than local theories predict.
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  • 14
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4206-4212 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of growth conditions such as substrate temperature Ts and [H2Se]/[dimethylzinc] ratio on the electrical and luminescence properties has been investigated for undoped ZnSe films grown on GaAs(100) substrates by metalorganic chemical vapor deposition. The observed electrical and luminescence properties are consistent with each other and depend on the deviation from stoichiometry. The properties of the films and the solubility of NSe using N2 gas confirm that at Ts ≤350 °C the deviation from stoichiometry depends on the VI/II ratio. In contrast, it has been difficult to prepare Zn-rich films at Ts ≥375 °C. The VI/II ratio necessary for preparing stoichiometric films decreases rapidly with increasing Ts . The film with the highest mobility maximum of 7600 cm2/V s at ∼40 K has been grown by controlling the stoichiometry. The concentration of acceptors incorporated during growth is lowest in stoichiometric films. It is suggested that the extended lattice defects which reduce the electron mobility are formed more easily as the composition changes from Zn rich to Se rich. The reduction in the deviation from stoichiometry on the Se-rich side is the most important for obtaining low-resistivity n-type ZnSe. The results are consistent with the reported results for bulk crystals.
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  • 15
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4223-4229 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Filament assisted diamond film growth was studied on a clean and highly oriented Ni(100) substrate using x-ray photoelectron spectroscopy (XPS), electron energy loss spectroscopy (EELS), x-ray excited Auger electron spectroscopy (XAES), and low-energy electron diffraction (LEED) to examine the sample at selected intervals in the growth process. The sample was transferred between the growth chamber and the ultrahigh vacuum analytical chamber without exposure to air. Scanning electron microscopy (SEM) was also used to characterize the sample; however, this required exposing the sample to air. Prior to growth the Ni(100) crystal was cleaned and ordered with a combination of Ar-ion bombardment, oxygen/hydrogen treatments, and annealing. After 2 min growth, microcrystalline graphite islands formed on top of a c(2×2) carbon layer. Later, LEED showed a graphite surface with very poor azimuthal orientation. This surface developed into a disordered nondiamond surface that we assign as glassy carbon. Next, EELS and XAES showed new features due to diamond. Growth was stopped when a continuous diamond film was formed. SEM confirmed the presence of well-faceted diamond crystals on a disordered and highly three-dimensional surface. These experiments show that the graphite and glassy carbon layers, formed prior to diamond, are poorly oriented with respect to the Ni(100) surface. Since these intermediate layers are not in registry with the Ni(100) surface, subsequent diamond growth is not epitaxial.
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  • 16
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The small-angle scattered intensity functions I(h) were analyzed for asymmetric bodies of thin disks (TD; R(very-much-greater-than)2L), narrow rods (NR; 2L(very-much-greater-than)R), and prolate (PE; va(very-much-greater-than)a) and oblate ellipsoids of revolution (OE; va(very-much-less-than)a). h, R, and 2L, 2a, and 2av are the magnitude of scattering vectors defined as h=(4π/λ)sin θ, with 2θ and λ being the scattering angle and wavelength of the radiation in the medium, respectively, the radius and length of the disk (or rod), and the lengths of two major axes of the ellipsoid of revolution, respectively. The functions I(h) scale as h−γ (γ=0,1,2,4) and show crossovers between different exponents γ, which depend on the aspect ratio (L/R or v) and the orientation distribution function W(α). When the aspect ratio is much larger or much smaller than unity, the relationship between the intensities at a given direction Ir(h) and that perpendicular to the longest axis of the particle Ip(h) was found to be related by Ir(h)∼h−γL Ip(h), for h(very-much-greater-than)1/max(R,L) or 1/max (va,v), where h−γL is the so-called Lorentz factor or Lorentz correction factor. The criteria for this relationship to be valid were discussed in terms of the aspect ratio and W(α) of the particle.
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  • 17
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4218-4222 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Transverse acoustoelectric voltage (TAV) measurements have been analyzed as a function of incident photon energy, dc bias voltage, temperature, and surface acoustic wave (SAW) frequency of GaAs layer (∼1.4 μm thick) grown on a vicinal Si(100) substrate by molecular-beam epitaxy. The TAV technique is used to show that the band gap and impurity level transitions are of slightly lower energies, compared to the bulk GaAs. This might be due to the residual strain changes in the band structure of GaAs grown on Si. It is also noticed that the presence of an interface considerably changes the shape of the experimental TAV versus bias voltage at low temperatures. Drastic variations of TAV as a function of SAW frequency and temperature are also observed. The cause of variations is not yet clear, but possible explanations are discussed.
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  • 18
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The solid phase crystallization of amorphized Si films on quartz substances is studied by means of the transmission electron microscope observation of grain growth. The amorphous Si films are prepared by Si ion implantation into polycrystalline Si films deposited by low-pressure chemical vapor deposition. It has been found that the twin formation in grains at the early stage of the crystallization accelerates the growth rate preferentially in a 〈112〉 direction. During the twin growth about a given 〈112〉 direction, other twins also grow from the twin boundary dendritically in some other 〈112〉 directions, leading to the formation of a large grain of dendritic structure.
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  • 19
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4252-4257 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: InSb thin films were evaporated and deposited on mica substrates by a simple vacuum evaporation method. A recrystallization of the deposit was observed at the last stage of the thin-film deposition. The recrystallization showed a dendritic crystal regrowth and the recrystallized area obtained one order of magnitude higher electron mobility than that of the as-deposited area. The maximum electron mobility obtained at room temperature was 6.0×104 cm2 /V s with impurity concentration of 5.8×1015 cm−3 . The crystal regrowth was found to be due to the melting-solidification process through the vapor-liquid-solid mechanism.
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  • 20
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4258-4261 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A three-dimensional image of the surface roughness of four conducting iron-oxide Fe3O4 thin films was obtained using a scanning tunneling microscope. We obtain grain size and surface roughness of films deposited on Si(100) by reactive sputtering at different substrate temperatures. The apparent grain size lies between 10 and 50 nm, and depends on the substrate temperature and film thickness. We have also determined the scanning tunneling microscopy parameters (tip size and shape) to obtain "real'' images (i.e., images without artifacts) of the films.
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  • 21
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A direct reading thermal comparator has been used to measure the thermal conductivity of dielectric thin-film coatings. In the past, the thermal comparator has been used extensively to measure the thermal conductivity of bulk solids, liquids, and gases. The technique has been extended to thin-film materials by making experimental improvements and by the application of an analytical heat flow model. Our technique also allows an estimation of the thermal resistance of the film/substrate interface which is shown to depend on the method of film deposition. The thermal conductivity of most thin films was found to be several orders of magnitude lower than that of the material in bulk form. This difference is attributed to structural disorder of materials deposited in thin-film form. The experimentation to date has primarily centered on optical coating materials. These coatings, used to enhance the optical properties of components such as lenses and mirrors, are damaged by thermal loads applied in high-power laser applications. It has been widely postulated that there may be a correlation between the thermal conductivity and the damage threshold of these materials.
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  • 22
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: For the first time, atomic force microscope measurements on the (111) and (100) surfaces of AgBr crystals are reported. We could image steps of varying sizes ranging from 0.9 nm to several nm. The lateral orientation of these steps could be determined by comparison with x-ray measurements. On the (100) surface, steps with the low index orientations 〈011¯〉 and 〈011〉 were observed. On the (111), surface steps were mainly oriented in the 〈12¯1〉 and 〈11¯0〉 directions. The most evident difference between these surfaces was that on the (111) surface no crossing steps occurred. This observation will be discussed in relation to the adsorption of dye aggregates on these crystals, which is of great importance for photographic emulsion technology.
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  • 23
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The concentration of occupied deep centers in Si-doped AlxGa1−xAs for x≥0.2 has been calculated from a three-level donor model, in which the shallow levels are treated as excited states of the deep (DX) ground state. The deep level is assumed to be tied to the L valley, and the shallow levels to the Γ and X valleys. The behavior of the free-electron density and the thermal activation energy as function of composition is in good agreement with experimental results reported in the literature. In this model of dependent donor levels the deep-level occupancy can be directly calculated without needing deep-level transient spectroscopy measurements. A two-level donor model is used to calculate the pressure dependence of the deep level from a hydrostatic pressure experiment on a GaAs/Al0.3Ga0.7As heterostructure reported in the literature. We assume a shallow level tied to the Γ valley and an arbitrary deep level which is not coupled to any of the conduction bands. The calculation of the position of the deep level relative to the Γ valley as a function of pressure confirms the coupling of the deep level to the L valley. In this dependent donor model no large compensation is needed to fit the experimental data.
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  • 24
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4262-4268 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The applicability in various circumstances of the classical equation relating substrate curvature to film stress for the case of a thin film on a plate substrate is examined. Theoretical treatments, based on elementary plate-bending theory and general elasticity theory, are given of the effects of gravity, substrate shape, film nonuniformity, and substrate crystallinity on substrate curvature. Formulas describing the effect of gravity and of film nonuniformity are confirmed experimentally using a laser-beam reflection technique. It is shown that gravity effects can cause significant errors in stress calculations based on the classical curvature versus stress equation, but these effects are largely avoidable or subtractable. Within limits, curvature is independent of substrate shape. For a film of nonuniform thickness, the classical equation does not apply, but in certain cases a simple analog does. Appropriate interpretation of elastic moduli appearing in the classical equation allows the equation to apply when the substrate is elastically anisotropic (e.g., a single crystal) with third-order or higher symmetry about its z axis. These studies augment thin-film stress measurement experimental technique.
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  • 25
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4279-4283 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
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  • 26
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4275-4278 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Two absorption peaks at 2663 and 2692 cm−1 are reported which were observed by Fourier transform infrared at a temperature below 77 K in all fast-neutron-irradiated samples investigated. These peaks are very weak and obscured by the nearby divacancy 3.61-μm band in most cases. However, they are obviously enhanced by the presence of impurity hydrogen. They anneal out at about 200 °C. It is proposed that a single defect center, which may be the di-interstitial, gives rise to the two peaks.
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  • 27
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report electrical characterization of a series of ZnSe samples which are planar doped by a new approach to doping involving periodic deposition of sheets of Ga on Zn- or Se-rich surfaces. For samples planar doped on Zn-rich surfaces, the mobility could be described by ionized-impurity scattering and polar optical-phonon scattering mechanisms, while planar-doped samples on Se-rich surfaces and uniformly doped samples require additional scattering mechanisms to describe their mobilities. The latter two cases give higher mobilities than the first, a result which is in conflict with the fact that the latter have higher total ionized-impurity concentrations and compensation. These results of higher mobilities along with higher total ionized-impurity concentrations are interpreted as evidence of donor-acceptor pair formation.
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  • 28
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Data obtained on a set of GaAs/AlGaAs double-barrier quantum-well resonant tunneling structures are compared with model calculations of the ideal case where scattering is negligible and tunneling is coherent throughout the entire structure. The comparison points to interface roughness in the well as the most likely cause for the observed large valley currents. The currents at low biases, before resonance sets in, are also studied. Their magnitude is found to be consistent also with the sequential tunneling picture.
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  • 29
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4325-4328 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Isothermal anneal experiments have been conducted over a wide temperature range from 300 to 900 °C for polycrystalline YBa2 Cu3 O7−x samples in air. The phase transformation and oxygen contents of the annealed samples were studied and determined by x-ray diffraction and iodine titration. Oxygen diffusion coefficients at different temperatures were determined by a novel technique based on direct observation of the oxygen diffusion fronts by polarized light microscopy. The activation energy for the diffusion of oxygen in YBa2 Cu3 O7−x was obtained by an Arrhenius plot of the diffusion coefficients at different temperatures. The tetragonal-to-orthorhombic phase transformation controlled by oxygen diffusion is discussed.
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  • 30
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4329-4337 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the limit of negligible exchange and anisotropy (except uniaxial), certain shapes of magnetic samples in certain subsaturating field configurations can be analyzed analytically to obtain magnetization and domain wall patterns. Here we consider two cases: (1) generalized cylindrical objects of arbitrary cross section (with several specific examples given) and (2) a general ellipsoid. We also discuss a "tipping instability'' which might occur in an ellipsoid with uniaxial anisotropy, resulting in a sudden transition from a "curling'' state to a "transverse vortex'' state.
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  • 31
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4284-4287 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The low-frequency excess electrical noise has been measured on carbon fibers with a wide range of crystalline perfection and corresponding electrical and mechanical properties. Fibers include those prepared from ex-PAN and ex-pitch polymers, and a catalytic-chemical vapor deposited filament. The extensional (Young's) moduli of these fibers varied from about 220 to 890 GPa (35–130 Msi), while the electrical resistivities varied from about 19 to 1 μΩ m. The low-frequency electrical noise of each fiber was found to be proportional to I2 and to vary as 1/f α, where f is the frequency and α is about 1.15. The most striking feature of the results was the strong dependence of the normalized noise power on the degree of crystalline perfection.
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  • 32
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4338-4344 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fe multilayered films with various intermediate layers are formed. Their magnetic properties and film structures are examined to understand the mechanism originating soft magnetic properties. The soft magnetic properties change with the lattice mismatches between Fe and intermediate layers, showing low coercive force and high relative permeability at lattice mismatches from 0.4 to 1.2%. It is thought that the lattice mismatches above 0.4% decrease Fe crystallite size and improve soft magnetic properties. Although Fe crystallite size is small at the lattice mismatches above 1.2%, the soft magnetic properties are poor. This is because the large lattice mismatch increases internal stress and magnetic anisotropy energy. This report indicates that the good soft magnetic properties are obtained when both Fe crystallite size and internal stress are small.
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  • 33
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4350-4359 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper we study the dielectric response of materials which display a dc conductivity at low frequencies. A framework based on the generalized Master equation and time dependent transition rates is argued to be applicable to disordered materials and exhibits an interesting fractal dynamics. The relationship of this framework to the "Distribution of transition rates'' theory and the models put forward by Ngai [Comments Solid State Phys. 9, 141 (1980] and by Dissado and Hill [J. Chem. Soc. Faraday Trans. 2, 80, 291 (1984)] is discussed. Model calculations of the dielectric response by means of the above-mentioned three theories are carried out and are compared to experimental results on Al2O3 and SiOxNy thin films. The theories can be distinguished only when the exponent of the power law at high frequencies is close to unity. The Dissado–Hill model is in better agreement with experiments than the other theories, but important discrepancies can easily be seen.
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  • 34
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The optical behavior near the fundamental absorption edge (4.1–6.6 eV) of sputter-deposited microcrystalline aluminum nitride grown on unheated fused silica substrates is studied here. The absorption coefficient α shows three types of behavior with incident photon energy E: (1) a high-energy region (>6.06 eV) in which α slowly varies with E, (2) a middle-energy region (∼5.6–6.06 eV) in which α varies directly with exp E, and (3) a low-energy shoulder. High- and medium-energy absorption is modeled in terms of a disordered semiconductor, using a coherent potential approximation with Gaussian site disorder in the valence and conduction bands. α is expressed in terms of three interrelated energy parameters: the energy-band gap of the virtual crystal (6.18 eV), the energy gap of the disordered crystal (5.50–5.64 eV), and the inverse slope of the exponential dependence of α on E (0.24–0.29 eV). Enhancement of α at low energy is explained in terms of a discrete absorption band whose strength is ∼6×1020/cm3.
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  • 35
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The advantage of a film with high saturation magnetic flux density for perpendicular magnetic recording is investigated through computer simulations and read/write measurements. A single-pole head using Fe-C/Ni-Fe multilayered film with a saturation magnetic flux density of 2.0 T is fabricated. Read/write tests are performed with the Co-Cr double-layer media. It is shown that the recording ability of this head is very high and does not change with increasing Co-Cr layer coercivity. Computer simulations show that the recording ability also increases when using film with high saturation magnetic flux density for the back layer of a double-layer medium. The upper limit of saturation magnetization of the recording layer can be extended by increasing coercivity. Thus, the higher saturation magnetization medium, which offers higher output voltage and resolution, can be used by applying film with high saturation magnetic flux density for the main pole and the back layer.
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  • 36
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The total yield spectra of combinations of rare-earth trifluorides were measured in the 30–250-eV photon energy range to investigate their value as high-efficiency, customizeable photocathode materials. The yield spectra resemble the weighted sum of the absorption spectra of the constituent rare earths, but the amplitude of the yield spectra were compressed relative to the absorption coefficient data due to the large electron escape depths in these materials.
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  • 37
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4372-4380 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The steady-state photoconductance and the transient photoresponse of boron-doped polycrystalline silicon films have been measured as a function of intensity at photon energies above and below the band gap applying several semiconductor lasers. The intensity dependence of the dc photosignal and the transient behavior are distinctly different for interband and subgap excitation. A kinetic model taking into account grain boundary as well as bulk carrier generation and recombination has been developed describing the observed nonlinear and transient effects consistently. The experimental results yield the density of occupied and unoccupied trap states, absolute values for the optical absorption cross section and thermal capture cross sections and relaxation time constants.
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  • 38
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4364-4367 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Tungstic oxide film is prepared from a W metal target by the rf sputtering method and its electrochromic characteristics are compared with that from WO3 target. Maximum coloration efficiency found for both kinds of films are equal and about 0.06 cm2 /mC at the wavelength of 600 nm, which is higher than that of typical evaporated films. Films from the W metal target, for the maximum coloration efficiency, can be prepared at a broader oxygen range of sputtering atmosphere than that of a WO3 target. It is found that films from a W metal target can be prepared at higher input power than that of a WO3 target. Therefore, the W metal target is suitable to get films with required thickness and EC characteristics.
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  • 39
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4387-4392 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We propose that short-period doping superlattices are suitable for the enhancement of a third-order susceptibility arising from free carriers in nonparabolic energy subbands. The inherent advantage lies in the ability to simply engineer the superlattice potential profile, yielding control of miniband energy dispersion. We consider short-period GaAs doping superlattices composed of uniformly doped donor and acceptor layers, and planar-doped n- and p-type monolayers separated by intrinsic regions. Calculations of the electronic structure of compensated and n-type noncompensated n-i-p-i superlattices incorporating miniband dispersion at nonzero temperature are reported. We show that small modulations of the superlattice potential lead to large subband nonparabolicities and we calculate a twentyfold improvement in the third-order susceptibility over bulk GaAs at room temperature, comparable to that predicted for GaAs/AlGaAs compositional superlattices.
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  • 40
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Band-gap narrowing of GaAs as a function of doping concentration has been measured using photoluminescence spectroscopy on samples grown by molecular beam epitaxy. Both n- (Si) and p- (Be) doped samples with concentrations varying from 3×1017 to 3×1018 cm−3 have been measured. The experimental results obtained from a line-shape analysis of the spectra taking tailing effects into account are in good agreement with recent theoretical calculations. A simple expression for the band-gap narrowing as a function of concentration for both n-and p-doped GaAs is given.
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  • 41
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The intrinsic magneto-optical readout performance in reflection is calculated for bismuth and cobalt-substituted iron-garnet films on a multilayer interference mirror at 800-, 633-, 488-, and 420-nm wavelengths and is compared with that of a trilayer medium composed of an antireflection layer, a rare-earth transition-metal film, and a metallic mirror. It is found, when disregarding inhomogeneities, like irregular domain shape, ripple of the magnetic anisotropy, and surface roughness, that iron garnets are superior to rare-earth transition-metal films at blue to near-ultraviolet wavelengths if operated at thicknesses where optical interference occurs in the magnetic layer. Optical transmittance at these thicknesses is sufficiently high so that multilevel recording media can be conceived. In contrast, the optical absorption of rare-earth transition-metal alloys is much higher so that only thicknesses much above interference conditions are feasible, thus precluding them from multilevel recording.This comparative study is supplemented by calculating the magneto-optical performance in reflection of a recently reported multilayer medium composed of an antireflection coating and a periodically repeated sandwich of 4-A(ring) Co and 9-A(ring) Pt layers. In contrast to conventional rare-earth transition-metal films, the magneto-optical Kerr effects of this material do not degrade when decreasing the wavelength from 800 to 400 nm, but still do not reach the performance of bismuth-iron garnets in the green to ultraviolet spectrum. For the garnet system Y3−xBixFe5O12 the spectra of the real and imaginary parts of the diagonal and off-diagonal component of the dielectric tensor εij are reported in the range of photon energies between 1 and 5 eV, i.e., 1240- and 248-nm wavelengths and a bismuth concentration up x=1.4 Bi3+ atoms per garnet formula. In addition, the off-diagonal components ε'12 and ε(large-closed-square)12 are parametrized in terms of paramagnetic optical transitions, taking the spectra for x=1.25 as a typical example. Furthermore, optical and magneto-optical spectra are presented for Co2+- and Co3+- substituted iron garnets and barium hexaferrite BaFe12O19.Finally, the spectral dependence of the magneto-optical figure of merit 2aitch-thetaF/α of (Y,Bi)3Fe5O12 and amorphous TbFe is compared. Furthermore, high-resolution transmission electron micrographs and x-ray double-crystal diffractograms are presented that elucidate the perfect epitaxial alignment of single-crystalline iron-garnet films and the columnar morphology of polycrystalline iron-garnet films prepared by rf magnetron sputtering. The initial nucleation period of polycrystalline garnet films can be influenced by low-energy ion bombardment for improving the film texture. Under favorable sputtering conditions single- and polycrystalline bismuth-iron garnet films develop a perpendicular magnetic anisotopy. It is not yet clear whether sputtered iron-garnet films can meet the critical requirements on magnetic wall coercivity and magnetic remanence.
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  • 42
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4418-4424 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The physical mechanism of photostimulated luminescence (PSL) of RbBr:Tl, resulting from x-ray irradiation, has been investigated. Spectroscopic methods have been utilized to identify the bromine F center as the occupied electron trap. By means of absorption studies the charge state of the dopant Tl was found to be monovalent. The spectral emission showed the characteristic Jahn–Teller splitting of the 3P1 state of the Tl+ and its known temperature dependence. PSL lifetime and efficiency experiments have been conducted in the temperature regime from liquid helium to 500 K to understand the charge transport from the F center to the activator and have been compared with corresponding data obtained from direct optical excitation into the A band of the Tl+. The observed temperature dependencies of both lifetimes could be explained by the properties of the s2 ion Tl+. As a resulting model for the PSL process a tunneling from the relaxed excited state of the F center to an excited state of the Tl2+ ion following photostimulation is suggested. The temporal, thermal, and spectral behavior of the subsequent radiative fraction of the deexcitation process is solely determined by the properties of the Tl+ ion in the RbBr matrix.
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  • 43
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The absorption coefficient (α) and fundamental transition energies of thin-film CuInSe2 were determined by spectrophotometry in the near-infrared (NIR) and visible wavelength regions from 500 to 2000 nm for a wide range of compositions. The results suggest a relationship between the constituent specie fluxes and substrate temperature, and the resulting polycrystalline nature of the film which dominates the optical properties. Near-stoichiometric and Cu-rich films appear to crystallize in larger grain sizes in comparison with Cu-poor films, with a Cu2−δ Se secondary phase at grain boundaries and free surfaces. Correspondingly, significant variations in the absorption coefficient among different film compositions exist in the neighborhood of the band edge. At energies well above the gap, all films behave similarly with α's of (1–2)×105 cm−1 at 500 nm. Similarly, continuous dispersion curves for the index of refraction have only been derived for single phase Cu-poor material by an iterative technique. The absorption data are substantiated through spectral response simulations that accurately reproduce measured device data. The range of primary and secondary transition energies, respectively, is 0.95–1.01 and 1.17–1.22 eV. These values indicate a valence-band splitting of 0.20–0.24 eV, in good agreement with single-crystal values.
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  • 44
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4431-4434 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The distribution of Si oxidation states in 1.7-, 2.0-, and 3.0-nm-thick downstream plasma enhanced chemical vapor deposited SiO2 film upon Si has been studied by soft x-ray photoemission, using synchrotron radiation. The spectra from the as-deposited 3.0-nm-thick oxide show two prominent Si oxidation states, the Si4+ and the Si3+, with the Si3+ oxidation state preferentially located at the oxide vacuum interface. The Si3+ state is considerably larger than that observed in thermal SiO2 and is radiation and thermally sensitive, partially converting to the Si4+ state during annealing and extended irradiation. The analysis of the photoinduced conversion from the Si3+ to the Si4+ oxidation state suggests that the paramagnetic component of the Si3+ structure matrix can be correlated with the structure of the E' defect center, as measured by electron spin resonance. A model is proposed for the SiO2 deposition mechanism whereby a temperature activated surface oxidation of the Si3+ structure is taking place.
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  • 45
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4425-4430 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments were conducted in which a high-power CO2 TEA laser interacted with metallic cathode in a high-vacuum (10−8 Torr) diode. For power densities lower than 5×107 W/cm2, no current was detected. For power densities in the range of 5×107–5×108 W/cm2, the Cu cathode emitted a maximum current of 40 mA. At a higher power density level, a circuit-limited current of 8 A was detected. The jump of a few orders of magnitude in the current is attributed to breakdown of the diode gap. The experimental results are similar to those of a triggered vacuum gap, and a thorough comparison is presented in this paper. The influence of the pressure in the vacuum chamber on the current magnitude shows the active role that adsorbed gas molecules have in the initial breakdown. When the cathode material was changed from metal to metal oxide, much lower laser power densities were required to reach the breakdown current region.
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  • 46
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4435-4440 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time-resolved measurements of optical emission from the ablation plume of ArF excimer-laser-irradiated Cu, CuO, Bi1.7Sr1.3Ca2Cu3Ox, and Y1Ba1.7Cu2.7Oy are reported. Data were collected on several emission lines for a variety of neutral and ionic species, including Cu+, Cu, Sr+, Sr, Ca+, Ca, and Y. The time dependence of the emission intensity is analyzed to obtain effective particle velocities. The results indicate most probable velocities of (3–10)×105 cm/s for the neutral species and (1–2)×106 cm/s for the ions, in qualitative agreement with previous work. However, the time dependence of the optical emission intensity can be influenced by radiation trapping and the detailed mechanisms of species excitation. These effects are shown to complicate the quantitative relationship between the emission intensity versus time and the particle velocity.
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  • 47
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4444-4455 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The formation of pits during laser recrystallization of silicon-on-insulator films has been studied in detail. Hydrogen originating from the decomposition of hydrogen bonds in the capping material or in the insulating layer is identified as being the cause of the formation of pits in the recrystallized silicon. These pits are the result of the formation of hydrogen gas bubbles in the molten zone near the solidification interface. A mechanism for the formation of the pits is presented. The dependence of the pit formation on capping layer material composition, annealing conditions, layer thickness, preheating temperature, scan velocity, and silicon film thickness is studied. Also hydrogen-containing insulating layers are discussed. Some recommendations are made to prevent pit formation.
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  • 48
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4441-4443 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Chemical analysis of the surface of an oxidized silicon-germanium mixture by Rutherford backscattering reported recently showed that the silicon is oxidized, but not the germanium. This result provides evidence that the effective oxygen concentration at the silica-silicon interface is low, which is contrary to a slow interface reaction. Strain in the oxide film can result in linear-parabolic oxidation kinetics without a slow interface reaction.
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  • 49
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimentally determined solar cell parameters of a large number of metal-insulator-semiconductor cells on damaged p-type silicon are compared with the dislocation conductivity model [J. Appl. Phys. 60, 406 (1986)]. Cell behavior is explained in terms of conducting dislocations. The variation of major cell parameters with the density of dislocations is calculated using the model. It is predicted that silicon with mild surface damage where dislocation density is less than about 105 cm−2 can produce solar cells of almost equal quality as dislocation-free Si.
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  • 50
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4466-4473 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Image sensors made from amorphous silicon ( a-Si:H ) are under development. Their elements consist of back-to-back Schottky diodes. For practical operation, long-term stability is of great importance. We investigated dark conductivity and photoconductivity, capacitance-voltage characteristics, and response behavior after switching off illumination. Even after light soaking for many hours, no change in photocurrent occurred, whereas dark current, capacitance, and response time increased. These changes are metastable and can be reversed by annealing above 200 °C. Contrary to the Staebler–Wronski effect, [Appl. Phys. Lett. 31, 292 (1977)], the dark-current increase disappears at room temperature after several hours. We investigated the time dependence of this relaxation and calculated the energetic depth of the states involved. The contact between a-Si:H and indium-tin-oxide is described as a Schottky–Bardeen-metal-insulator-semiconductor junction. Its properties are strongly dependent on interface states, in particular on the position of the neutrality energy of the interface states with respect to the Fermi energy. We show that besides the well-known Staebler–Wronski effect, a new degradation process is observed. We suggest a model where holes are trapped in interface states about 1.0–1.4 eV above the valence band. Their thermal emission governs the relaxation behavior of the dark current.
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  • 51
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4456-4461 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The thickness of gold thin films of 0.1–100 nm on Si substrates has been measured with an electron probe microanalyzer. The analysis process is as follows. k ratio versus thickness calibration curves are produced through use of a Monte Carlo simulation of electron scattering based on the Mott cross sections for elastic scattering, where the exact film/substrate boundary condition is included. Then the thickness can be determined, corresponding to an observed k ratio from the samples. Prior to the analysis, the ionization cross sections for Au Mα and Lα x rays required in the simulation are obtained by measuring the x-ray intensity from very thin gold films as a function of incident electron energy. The measured thickness results agree very well with experimental ones, which are obtained with a quartz balance apparatus. The simulation model is discussed in comparison between theory and experiment. Also it is shown that the thickness detection limit of the present method can reach submonolayer films.
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  • 52
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4474-4480 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A comprehensive bipolar transistor model based on the Gummel–Poon model [Bell Syst. Tech. J. 49, 827 (1970)] for low-temperature circuit simulation is presented. Relevant low-temperature physics such as doping-dependent dielectric permittivity, temperature-dependent free-carrier mobility and intrinsic carrier density, and de-ionization of impurity dopants are included in the model. Consequently, the model does not require temperature fitting parameters as does the Gummel–Poon model. Comparisons of the present model with the Gummel–Poon model, with experimental data, and with simulation from a two-dimensional device simulator (pisces) are included.
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  • 53
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4488-4495 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report transient effects in amorphous silicon thin-film transistors occurring upon switch-on and switch-off, which are controlled by trapping and emission from the deep states in the amorphous silicon. We develop a unifying theoretical description which is applicable to both switch-on and switch-off. The model is based on carrier thermalization to the deep states and includes the spatial dependence of the thermalization process in the band-bending region. The model is able to explain the experimentally observed switch-on and switch-off behavior. In the case of switch-on, electrons are progressively trapped into the deep states in the bulk a-Si:H throughout the entire thickness of the layer. The range of trapping times is large and this leads to a dynamic threshold votage shift and a time dependence of the source-drain current extending between 1 μs and 1 s. In the case of switch-off, two processes occur sequentially. First, there is emission of electrons from the bulk a-Si:H deep states, which leads to a uniform space charge throughout the thickness of the layer. After that, a redistribution of the space charge occurs, leading to the eventual thermal equilibrium space-charge distribution. These processes give rise to two different time constants in the measured decay of the total charge stored in the transistor. Full thermal equilibrium can take several hours to reach.
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  • 54
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4481-4487 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We describe resonant refractive index lithography (RRIL), a new technique to enhance the resolution of optical lithography. RRIL utilizes a highly refractive layer between the mask and the photosensitive layer to increase optical resolution. The refractive index of this layer is enhanced by a resonant absorption near the wavelength of the exposing radiation. In this work GaAs, which has a large resonant refractive index increase conveniently centered around the mercury spectral g line, is used as the refractive layer. It is shown that the large reduction in wavelength, which is more than a factor of 5 at 431 nm, enables this technique to increase resolution by as much as 226%. In addition, the absorption associated with the increased refractive index significantly attenuates the diffracted light and virtually eliminates standing waves that would be produced by reflections between the mask and the substrate. Furthermore, the refractive medium enhances the collimation of the exposing radiation. We demonstrate the RRIL technique by fabricating an opposed gate-source transistor with a sub-quarter-micrometer source electrode. The dimensions and alignment precision achieved were less than one-half the wavelength of the incident radiation. In this paper RRIL is introduced, experimental results are presented and compared with a model of the diffraction effects, and finally the RRIL technique is applied to planar lithography and microscopy.
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  • 55
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The influence of 60-keV N+2 ion implantation on the aqueous degradation of the Y1Ba2Cu3O7−x high-Tc superconductor is studied by the small-angle x-ray diffraction technique. Structural depth profiling is performed by registering the x-ray data at several small angles of incidence between 0.3° and 10.0° within Seeman–Bohlin geometry. Examination of samples implanted at a dose value of 3×1017 ions/cm2 and subjected to different aqueous treatments reveals that implantation arrests the degradation process and imparts structural stability to the superconductor. Resistivity temperature data are also provided for specific cases of interest.
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  • 56
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method is presented for dealing with numerical problems in calculations of potential fields using expansions in modified Bessel functions. Using this method, problems in mathematical physics with cylindrical symmetry, e.g., volume conductor problems, can be solved with high accuracy.
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  • 57
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4496-4503 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Laser cutting of biological matter is explained by a combined action of evaporation and ejection of liquid. It is shown that when the depth of the incision is larger than its diameter and when a certain critical value of the intensity is exceeded, a new effect, a turbulent flow of the liquid layer, emerges as a result of the increased vapor pressure gradient. This turbulent flow is accompanied by the appearance of a number of additional effects. These are the occurrence of a local minimum in the dependence of the normalized recoil momentum as a function of the position of the beam focus, the formation of bumps and, connected with this, a change in the extent and velocity of the ejection. These effects are experimentally studied in the present investigation. In addition, it is shown that for cutting soft tissue the accuracy of focusing has a crucial influence on the depth of the generated incision and the extension of the created thermal damage zone.
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  • 58
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4514-4516 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to understand the mechanisms which determine the I-V characteristics of granular bridges, a model was established treating the granular bridge as a network of Josephson junctions. Calculations of many diverse configurations of such networks show that only certain superpositions of voltages of single junctions lead to Shapiro steps in the overall I-V curves of the network. These steps can be obtained when the granular bridge consists of a few grains only and when the ac current is applied with not too high a frequency. Then, characteristics of single junctions determine the behavior of the network, and Shapiro steps probably will appear.
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  • 59
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    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4519-4521 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have shown that high-purity Cu films can be deposited on the Si substrate at room temperature in a conventional vacuum condition using the partially ionized beam technique. The beam contains about 2% of Cu self-ions and a bias potential of 1 kV is applied to the substrate during deposition. By using the secondary ion mass spectrometry technique we show that the Cu/Si interface is free of contaminants such as oxygen, carbon, and hydrogen, despite the fact that no in situ surface cleaning has been performed on the substrate prior to deposition. These phenomena are attributed to the self-cleaning effect induced by the energetic Cu ions bombardment during deposition.
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  • 60
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4529-4531 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron-irradiation-induced defects in epitaxially grown 3C-SiC crystals have been studied by electron-spin-resonance (ESR) measurements. The results indicate the presence of an isotropic ESR center that consists of five lines equally spaced at about 1.5 G and has a g value of 2.0029±0.0001. Isochronal and isothermal annealing of electron-irradiated 3C-SiC showed that this center was annealed at three stages (150, 350, and 750 °C) and that the 750 °C stage exhibited first-order reaction with an activation energy of 2.2±0.3 eV.
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  • 61
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have studied the effects of a polymer matrix on charge acceptance and retention of polymers doped with hole-transport molecules in order to understand the nature of traps in molecularly doped polymers (MDPs). Prolonged illumination decreases charge acceptance and retention of MDPs. A light-induced change in charge acceptance depends on the kind of polymer binder. A remarkable change is observed in acidic polymer binders or basic polymer binders exhibiting broad absorption spectra. In MDPs manifesting a remarkable light-induced change, the transient photocurrent pulse shape becomes dispersive after prolonged light exposure. The experimental results show that the shallow charge emission centers increase during light exposure. These shallow charge emission centers are metastable states formed by charge transfer between the transport molecule and the polymer matrix during light exposure.
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  • 62
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4535-4537 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: β-SiC is grown on a Si (100) substrate by the chemical vapor deposition method using the SiH2Cl2/C3H8/H2/HCl/ gas system. The addition of HCl to the SiH2Cl2/C3H8/H2 gas system makes it possible to grow stoichiometric β-SiC at the low temperature of 1000 °C. Moreover, β-SiC selective deposition on a Si (100) surface, with no nucelation on a SiO2 surface, is achieved in more than 1.5% HCl concentration. The mechanism of low-temperature selective β-SiC growth due to HCl addition is discussed.
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  • 63
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4539-4541 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Low energy inelastic electron tunneling spectra are presented for thermally formed oxides on copper films. Thinner oxide tunnel barriers are observed to contain interfacial gradients as evidenced by spectral intensity asymmetries between forward and reverse bias, whereas thicker oxides appear to be more uniform in composition. Spectral results are in good qualitative agreement with reported studies of bulk cuprous oxides, and the semiconducting nature of the oxide layers is reflected in a negative temperature coefficient of resistivity of the tunnel junctions.
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  • 64
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Reflection and transmission of a stepwise pressure wave incident to a partially water-saturated porous medium is investigated. The strongly dispersive character of the phase velocities and damping due to air bubble resonance causes pressure over- and undershoot in reflection and a fast oscillatory disturbance propagating into the porous medium. Theoretical results are compared with new results from shock tube experiments. A qualitative agreement is found.
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  • 65
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 4542-4544 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new type of radioluminescent light source has been demonstrated. This all-organic system consists of covalently bound tritium within a solid, optically clear polymeric matrix. The matrix contains a set of organic luminophores that capture excitation energy from beta decay and red shift the energy in a stepwise fashion, after which a chosen wavelength is emitted as fluorescence. Both blue and orange lights have been fabricated. Unlike currently available tritium gas tube lights or radioluminescent paints, the brightness of these new systems is, in principle, scalable because self-attenuation and absorption effects are minimized.
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  • 66
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Infrared absorption spectroscopy was used to study the oxidation of hydrogenated amorphous silicon carbide (a-Si:C:H) films prepared by the glow-discharge decomposition of gaseous mixtures of silane and methane. It has been found that carbon-rich samples incorporate oxygen when exposed to air, as detected by an increased absorption of the Si-O-Si stretching vibration band. The analysis of the infrared spectra of samples annealed in air at room temperature and at 200 °C indicates that, except for their oxidation rate, no appreciable difference exists in the mechanisms of oxygen incorporation in the films at the two temperatures. The oxidation kinetics suggests an open porous structure for these carbon-rich films. On the contrary, samples having a low carbon content appear to oxidize on the surface only, in a way similar to amorphous silicon.
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  • 67
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 3173-3177 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The deviation in saturation magnetization (Ms ) from the Slater-Pauling curve for Co-Cr films was confirmed from several points of view, and was clarified not to be caused by some experimental imperfection, such as the use of a composite target or residual oxygen. There existed a critical value of Cr content, 13 at. %, where the films changed their homogeneity. This critical value was interpreted as corresponding to the Cr solubility limit in the hexagonal close-packed (hcp) solid solution on the phase diagram reported by Hansen [Constitution of Binary Alloys (McGraw-Hill, New York, 1958), p. 466], which has 13 at. % Cr solubility limit and two-phase-mixture area from 13 to 57 at. % Cr contents below 500 °C. The temperature dependence of Ms was also consistent with the tendency of the Hansen phase diagram.
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  • 68
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 3178-3186 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
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  • 69
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 3187-3191 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An expression for the ac susceptibility of a ferro or ferrimagnet, including damping resulting from various microscopic proceses, is derived microscopically. The two-magnon case can be derived from the equations of motion methods given in Lax and Button [Microwave Ferrites and Ferrimagnetics (McGraw–Hill, New York, 1962), pp. 172–180], but other processes require many-body perturbation theory.
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  • 70
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 3192-3201 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An in situ method based on interfacial electrical impendance measurements is described for following the time-dependent intrusion of water in an adhesive interface that is exposed to a humid environment. Water ingress is measured by its effect on bulk and interfacial conductivity, while regions of liquid water are identified by the presence of aqueous double-layer capacitances. Preliminary measurements are made using aluminum triple-track electrodes to study the environmental stability of adhesion between oxidized silicon (SiO2, 4% P) substrates and three coating materials (RTV silicone, amine-cured epoxy, and mercaptan-cured novolac epoxy) at 80 °C and 94% relative humidity. Moisture-induced changes in conductivity of all coatings are measured, and the presence of condensed water in the mercaptan-cured epoxy interface is clearly identified. Based on static potential field calculations, a modified experimental procedure is outlined that can be used to quantitatively isolate interfacial conduction processes from ac conduction in bulk substrate and coating phases. By indicating the state and quantity of interfacial moisture, capacitance and conductance measurements will allow interface displacement processes to be monitored.
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  • 71
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 3202-3206 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Environmental effects in the intraimpurity emission of Yb3+(2F5/2-2F7/2 intracenter transition) in GaxIn1−xP (0<x<0.3) bulk crystals are reported. Cationic disorder manifests itself in the appearance of line splittings and substantial broadening of all the emission lines with increasing Ga contents. Spectra of the crystals with small Ga contents are dominated by emission from two types of centers. One, typical of InP:Yb, corresponds to Td symmetry, while the second is most likely due to a Yb center perturbed by the presence of a single Ga atom in the next-nearest-neighbor position (Yb-P4-In11-Ga).
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  • 72
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    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 3074-3081 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A simple model for photoconductivity in a-Si:H is shown to be capable of describing the variations of photoconductivity observed both with doping and with optical degradation. The model consists of a trivalent recombination center with consideration only of transitions connecting the centers and extended states, and of exponential conduction and valence-edge tail states with occupancy described simply by the locations of the dark or quasi-Fermi levels. The model describes the changes in the magnitude of photoconductivity with doping or optical degradation as arising primarily from changes in the density of effective recombination centers caused by shifts in the location of the dark Fermi level, and only secondarily from changes in the total density of dangling bonds. The model also describes the change in the exponent for the variation of photoconductivity as a power of the excitation rate; this exponent changes from a value of 0.50, when the density of electrons trapped in conduction tail states is proportional to the density of neutral recombination centers, to a value of 1.0 when an appreciable density of neutral recombination centers exists in thermal equilibrium. Both qualitative and semiquantitative agreement are demonstrated between the predictions of the model and published experimental data on doping and optical degradation.
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  • 73
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The absorption and luminescence spectra of yttrium aluminum garnet single crystals doped with iron have been studied. At low levels of iron doping, the intensity of the defect photoluminesence at 320 nm decreases with increasing iron concentration, as a result of energy transfer to Fe+3 ions which luminesce at 800 nm. Further increases in iron concentrations eliminate luminescence at all wavelengths. Differences between the absorption bands of iron in octahedral and tetrahedral sites, and inter-ion charge tra