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Journal of Applied Physics

Issue 10 • Date May 1987

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Displaying Results 1 - 25 of 38
  • Atomic force microscope–force mapping and profiling on a sub 100‐Å scale

    Page(s): 4723 - 4729
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    A modified version of the atomic force microscope is introduced that enables a precise measurement of the force between a tip and a sample over a tip‐sample distance range of 30–150 Å. As an application, the force signal is used to maintain the tip‐sample spacing constant, so that profiling can be achieved with a spatial resolution of 50 Å. A second scheme allows the simultaneous measurement of force and surface profile; this scheme has been used to obtain material‐dependent information from surfaces of electronic materials. View full abstract»

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  • Explosive‐driven magnetic flux cumulation by the propagation of shock‐compressed conductive region in highly porous metal powders

    Page(s): 4730 - 4735
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    The explosive‐driven magnetic flux cumulation process by the convergence of high‐pressure shock waves in highly porous metal powders has been studied experimentally. The field‐multiplication ratio depends mainly on the initial density of powder, although the flux compression signal has been detected for all the powders tested. Extremely light aluminum powders of initial density, of about 0.41 g/cm3 is shown to be the most promising within this experiment. The time evolution of flux density, i.e., B(t) for the case of light metal powders (Al and Mg), can be well approximated by the inverse power law. The results are explained by the magnetohydrodynamic theory. View full abstract»

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  • Dispersion compensation for femtosecond pulses using high‐index prisms

    Page(s): 4736 - 4739
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    We have compensated the residual chirp of the pulses emerging from the thick output coupler of our femtosecond dye laser with a sequence of four high‐refraction index prisms. Using the same prisms, we show that it is possible to compensate the great amount of dispersion due to a femtosecond multistage amplifier leading to a compact and low‐loss compensation system. View full abstract»

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  • Improved laser pumping by intense electron beams via a backscattering reflector

    Page(s): 4740 - 4743
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    Experiments demonstrating improved laser media pumping using electron‐beam concentration by means of a backscattering mirror are reported. The backscattering mirror increases the electron pumping density by as much as a factor of 3 at low gas pressures. Use of the concentrator resulted in more than a 50% increase in Ar 2 excimer emission. The N2(C→B) amplified spontaneous emission can be saturated on a gain length of only 10 cm. View full abstract»

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  • Demonstration of optical bistability with a nonlinear prism coupler

    Page(s): 4744 - 4748
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    A guided wave is launched through a nonlinear prism coupler whose prism‐waveguide gap is filled with a liquid crystal. We observed that the intensity of the excited guided wave exhibits optical bistability when the incident intensity is modulated. This result, which is rather surprising when compared to recent theoretical predictions, is shown to arise from a thermal averaging process in the liquid crystal. View full abstract»

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  • Generation of very high‐frequency ultrasonic waves using thin films of vinylidene fluoride‐trifluoroethylene copolymer

    Page(s): 4749 - 4754
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    Electromechanical properties of thin films of vinylidene fluoride‐trifluoroethylene copolymer [P(VDF‐TrFE)] and their application to ultrasonic transducers were studied in the frequency range of 50–250 MHz at room temperature. A 5‐μm‐thick P(VDE‐TrFE) film resonating at 250 MHz in thickness extensional mode exhibited a large electromechanical coupling factor of 0.26. The dielectric and elastic constants were also studied in this frequency region. A transducer using a 3‐μm‐thick film exhibited a large conversion efficiency (6.5 dB at 150 MHz), and good impulse response (30 ns ring‐down time width) in water. A concave transducer transmitted a well‐focused ultrasonic beam (35‐μm beamwidth). View full abstract»

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  • Swirling flow through variable area ducts: Effects of entrance‐flow velocity nonuniformity

    Page(s): 4755 - 4759
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    The effect of nonuniformities in the streamwise‐velocity distribution of a flow which is swirling in rigid‐body motion at the entrance to a (rapid) change in area is analyzed. Experimental data obtained on the flow through a contraction with a rigid‐body swirl are compared to the solution of the inviscid flow equations in which streamwise‐flow nonuniformity is accommodated. At the higher of two imposed swirl rates, comparison between experiment and theory is acceptable, considering the fact that the actual distortion in the entrance streamwise‐velocity profile is unknown. At the lower of the two swirl rates, the analytical solution is used to suggest that a localized boundary layer separation existed near the exit plane of the contraction which resulted in a weak expansion of the core streamtubes. Even the slightest pressure rise is shown to enhance the effect of streamwise‐flow nonuniformities on the classical uniform swirling flow results. View full abstract»

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  • Two‐cavity autoacceleration of an intense relativistic electron beam

    Page(s): 4760 - 4770
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    Three series of experiments have been performed using two 40‐Ω coaxial autoacceleration cavities to accelerate an intense relativistic electron beam. First, conventional magnetic transport was used to propagate a 1.8‐MeV, 11‐kA beam through two 1‐m‐long cavities. An increase of 700±130 keV in kinetic energy was achieved which represents 80% of the maximum theoretical acceleration for an 11‐kA beam passing through two 40‐Ω cavities. Multiple accelerated pulses were generated and no adverse interaction between the cavities was observed. In the second experiment, ion focused transport (IFT) was used to successfully propagate a 9‐kA beam through the accelerator again achieving multipulse operation with both cavities. An energy increase of 560±30 keV was attained which is 78% of the theoretical maximum. Finally, IFT was used to propagate a ≂25‐kA beam through a 1‐m‐long cavity, then a 0.5‐m‐long cavity, demonstrating two stages of temporal energy compression. Gap leakage and current transport losses limited the acceleration to 1.25±0.16 MeV which corresponded to an 84% increase in kinetic energy. View full abstract»

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  • The UV‐visible spectroscopy of laser‐produced aluminum plasmas

    Page(s): 4771 - 4780
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    The optical emission spectra (180–760 nm) of plasmas produced by a flashlamp‐pumped dye laser focused on an aluminum target have been recorded and analyzed. In the incident intensity range from near plasma threshold to 5×107 W/cm2 the electron temperature was calculated from the relative emission intensity of Al(II) states (Te=8.0×103 K). The electron density was determined from Stark broadened linewidths of four Al(II) lines. Both the spatial and temporal dependence of the emission spectra were obtained providing a map of the electron density and temperature. View full abstract»

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  • Measurements of ion transverse‐velocity distribution in the gap of an ion‐beam diode

    Page(s): 4781 - 4785
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    We have measured the distributions of ion transverse velocities in the acceleration gap of a magnetically insulated ion diode. The measurement is based on observing the spectral profile of the Doppler‐broadened spontaneous line emission from accelerating ions. The velocity distributions of C++ and Al++ ions were peaked at zero transverse velocity and symmetric with respect to the directions parallel and antiparallel to the magnetic‐field lines. The mean transverse velocities for both of the ion species corresponded to energies of about 200 eV in experiments with a gap potential difference of 260–330 kV. The divergence angles observed for both of the ion species are significantly smaller than previously observed for protons outside the diode. View full abstract»

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  • Secondary electron emission‐capacitive probes for plasma potential measurements in plasmas with hot electrons

    Page(s): 4786 - 4790
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    It is shown that a secondary electron emission‐capacitive probe can determine the plasma potential when Te ≥50 eV. The probe is wideband (1 Hz to greater than 20 MHz) and relatively simple to operate. The Phaedrus‐B tandem mirror plasma where Te ∼40–60 eV and n≂5×1012 cm-3 is used to verify this technique. View full abstract»

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  • High‐energy ion irradiation effects on the surfaces of silicon carbide and silicon nitride

    Page(s): 4791 - 4794
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    High‐energy ion irradiation effects on the surfaces of α‐silicon carbide (SiC) and hot‐pressed silicon nitride (Si3N4) were studied by optical microscopy, surface profilometry, Auger electron spectroscopy, and transmission electron microscopy (TEM) techniques. Optical microscopy and surface profilometry revealed that 1‐MeV Ni+ ion irradiation at a dose of 1×1016 cm-2 produces swelling and roughness on both SiC and Si3N4. Auger electron spectroscopy in combination with sputtering revealed that the SiC surface becomes C rich, whereas the Si3N4 surface becomes Si rich due to ion irradiation. Cross‐section TEM analysis of the surface layer of irradiated SiC showed that about 1 μm of material at the surface has become amorphous due to irradiation with 1‐MeV Ni+ at a dose of 1×1016 cm-2. Amorphization has also been observed in Si3N4. These results are discussed with reference to the information available in the literature. View full abstract»

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  • Preparation of Ti‐Zr‐B ternary amorphous alloys by a single‐roller melt‐spinning technique and their thermal stability

    Page(s): 4795 - 4799
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    Continuous ribbons of Ti‐Zr‐B ternary alloys, consisting of early transition metal and metalloid elements, were formed by a single‐roller melt‐spinning method. Details of the quenching method employing a modified levitation melting technique are herein described. Amorphous phases were obtained in the composition range of 15 at. %≤B≤25 at. % and 20 at. %≤Zr≤50 at. %. The crystallization of the amorphous alloy took place in two steps. Initially, the amorphous phase changed polymorphously into a boron supersaturated bcc‐like phase, and then this bcc‐like phase decomposed into a bcc phase and a (Ti, Zr)B compound phase. The crystallization temperature was extraordinarily low (∼320 °C) in contrast to the high melting point and the strong chemical bonding between the metal and metalloid elements. View full abstract»

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  • Equation‐of‐state parameters for poly(vinyl acetate)

    Page(s): 4800 - 4803
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    The temperature and pressure dependence of the thermal pressure coefficient and internal pressure for poly(vinyl acetate) are discussed on the basis of the equation of state, previously reported. The principle results are as follows: (1) The thermal pressure coefficient of the liquid polymer increases with increasing pressure at constant temperature. (2) The internal pressure of the glassy polymer decreases with increasing pressure at constant temperature. (3) The thermal pressure coefficient of the glassy polymer and the internal pressure of the liquid polymer can be approximated to be independent of pressure. (4) The zero‐pressure thermal expansivity can be approximated to be independent of the glass‐forming pressure. Also, the relationship between the Gruneisen constant and sonic wave velocity is derived and is found to be identical to the Broadhurst–Mopsik equation. View full abstract»

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  • The influence of HCl on the oxidation‐enhanced diffusion of boron and arsenic in silicon

    Page(s): 4804 - 4807
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    The influence of HCl on the oxidation‐enhanced diffusion of boron and arsenic in silicon has been studied. Experimental data at 1000, 1100, and 1150 °C were obtained using secondary ion mass spectrometry (SIMS). A previously proposed empirical model was used in analyzing the impurity profiles, and the parameters of this model were determined by matching the computer simulations of dopant diffusion with the SIMS profiles. The dependence of the model parameters on temperature and HCl concentration is discussed. View full abstract»

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  • Depletion corrections in variable temperature Hall measurements

    Page(s): 4808 - 4811
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    The decrease in the measured Hall free‐electron concentration with decreasing temperature near 300 K is often observed for thin high‐purity GaAs layers. This has previously been interpreted as electron freezeout on deep donor sites. However, it can be quantitatively described by the decrease in carrier concentration per unit area associated with increasing surface and interface depletion region thicknesses. It is shown that when these depletion regions are included in the analysis of the Hall‐effect data, the measured free‐electron freezeout behavior can be accurately described by a simple shallow donor. If necessary, a deep donor may be included in the modeling. The results agree with the observed temperature variation of the capacitance‐voltage (C‐V) profiling data. View full abstract»

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  • Defect‐induced compensation in the bulk of implanted indium phosphide

    Page(s): 4812 - 4815
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    By studying the properties of nondopant impurities (P and In matrix elements, and Fe deep impurity) implanted Zn‐doped p+‐InP (p∼7×1017 holes cm-3) before and after varied annealing treatments (conventional furnace and rapid thermal anneals), we show the following; (i) the implantation‐induced defects lead to electrical compensation in the bulk of InP far beyond the implanted regions; (ii) the compensating centers result from a direct interaction between fast diffusing defects (both during implantation and annealing processes) and Zn atoms. View full abstract»

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  • Improvement in the surface photovoltage method of determining diffusion length in thin films of hydrogenated amorphous silicon

    Page(s): 4816 - 4819
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    Two modifications in the method of determining diffusion length in a‐Si:H films by surface photovoltage are presented; one calculational, the other experimental. In the calculation a known theory together with data at three dc‐bias light levels are used to compute the correct diffusion length, as well as the space‐charge density at all light levels. Experimentally, provision for illuminating a thin sample with blue light from the rear in addition to the normal red and monochromatic light from the front serves to eliminate the disturbing effect of a back surface barrier. The improved results are illustrated. View full abstract»

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  • Effect of annealing atmosphere on the properties of thin‐film CdSe

    Page(s): 4820 - 4828
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    Thin‐film CdSe has been deposited electrochemically from an aqueous solution of selenosulfite. The light‐to‐electric power conversion efficiency depends on the annealing atmosphere with air (oxygen) giving the highest value. The power conversion efficiency correlates with the donor density, the quantum efficiency, and the minority‐carrier diffusion length. Surface analytical techniques have been used to detect the presence of oxygen in the film. Various mechanisms for oxygen activation of the film are considered. View full abstract»

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  • Superconducting AgMo6S8 thin films prepared by reactive sputtering

    Page(s): 4829 - 4834
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    Preferentially oriented thin films of the Chevrel‐phase superconductor AgMo6S8 were prepared by reactive sputtering. Ag and Mo were simultaneously sputtered from separate guns onto sapphire substrates held at about 850 °C with H2S gas injected near the substrate. The films have superconducting critical temperatures up to 9.2 K and narrow‐phase transitions. The reactive sputtering process chosen for the preparation of our films makes it possible to change the superconducting properties and the microstructure of the samples in a systematic way by changing individual preparation parameters and to study which of the preparation conditions are the most crucial for the formation of the Chevrel phase. We find that the superconducting transition temperature of the Chevrel phase is very sensitive to both substrate temperature and to the flow of H2S but insensitive to the background pressure in the chamber before deposition. The microstructure can be changed by controlling the H2S pressure. X‐ray measurements show that the films are preferentially oriented with the rhombohedral 001 planes parallel to the surface of the substrate. View full abstract»

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  • Experimental investigations and analysis for high‐quality Nb/Al‐AlOx/ Nb Josephson junctions

    Page(s): 4835 - 4849
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    We have made a detailed study of the fabrication process of Nb/Al‐AlOx/Nb Josephson junctions with the aim of introducing guiding principles to obtain high‐quality junctions. Junctions were fabricated by a novel process named the self‐aligned contact process. We investigated the deposition conditions of Nb and Al films and optimized them. Oxidation conditions for obtaining target critical current were also investigated. Then composition of the tunneling barrier material and the coverage of the thin Al layer on the base electrode were analyzed by x‐ray photoelectron spectroscopy, Auger electron spectroscopy, etc. We investigated aging and annealing effects on the junctions. We confirmed that the current‐voltage (I‐V) characteristics of the junctions did not change after storage for 450 days at room temperature or when subjected to temperatures of up to 150 °C for shorter periods. Applying the McMillan theory to our experimental results, we explained the characteristics of the junctions. As a result, we have demonstrated that the characteristics are determined by two proximity layers: The first is a double proximity layer composed of an elemental Al layer and Nb/Al alloy layer in the base electrode, and the second is a Nb layer with low transition temperature in the counterelectrode. We have demonstrated that the characteristics are drastically improved by reducing the Nb/Al alloy layer and the Nb layer with low transition temperature and have obtained high‐quality junctions with little leakage current. View full abstract»

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  • Effects of perpendicular stresses on the magnetization processes of polycrystalline magnetic materials

    Page(s): 4850 - 4857
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    Effects of perpendicular stresses on the magnetization mechanisms of polycrystalline ceramics are studied. It is shown that the magnetic behavior depends strongly upon the state of the domain‐wall configuration before the application of the uniaxial stress. To this end, a general study of the magnetization laws is made on two different types of samples according to the well‐established fact that the domain‐wall configuration is first conditioned by the microstructure. The first type, called T, is assigned to samples with a homogeneous structure of very pure grains (without defect). The second type, called D, is assigned to samples with a heterogeneous structure of grains containing apparent defects as micropores, for example. View full abstract»

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  • Angular variation of the coercivity in anisotropic barium and strontium ferrite permanent magnets

    Page(s): 4858 - 4861
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    Room‐temperature measurements have been made of the variation of the intrinsic coercivity Hc of anisotropic barium ferrite and strontium ferrite permanent magnets as a function of the angle θ between the direction of measurement and the preferred axis of magnetization. For the strontium ferrite specimen the angular variation Hc vs θ was also measured at 77, 130, and 230 K. All the results showed a gradual increase in Hc with increase in θ up to a maximum and thereafter a rapid decrease to Hc=0 at θ=90°. The angular variation in coercivity was also measured after saturation parallel to the direction of measurement. An attempt has been made to interpret the results. View full abstract»

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  • Charge‐state changes of substitutional nitrogen impurities in silicon induced by additional impurities and defects

    Page(s): 4862 - 4868
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    Charge states of substitutional N impurities (Ns) in Si are found to be controllable by doping with P, B, and O impurities in N‐ion implanted and subsequently pulsed‐laser annealed Si (Si:N system). Electron‐spin resonance measurements of the Si:N system doped with P, B, or O impurities show that the spin density of neutral Ns (N0s) decreases because of doping with these impurities. Compensation by multiple doping with equal amounts of P and B impurities leaves the density of N0s essentially unchanged. These results yield evidence for charge‐state changes of Ns due to the Fermi level shift. Oxygen doping is found to introduce donors. Three charge states, i.e., positive (N+s) , neutral (N0s) , and negative (N-s) are assigned to off‐center substitutional N in Si. View full abstract»

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  • Band gaps and refractive indices of AlGaAsSb, GaInAsSb, and InPAsSb: Key properties for a variety of the 2–4‐μm optoelectronic device applications

    Page(s): 4869 - 4876
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    The methods for calculation of material parameters in compound alloys are discussed, and the results for AlxGa1-xAsySb1-y, GaxIn1-xAsySb1-y, and InPxAsySb1-x-y quaternaries lattice matched to GaSb and InAs are presented. These quaternary systems may provide the basis for optoelectronic devices operating over the 2–4‐μm wavelength range. The material parameters considered are: the lattice constant, the lowest direct‐ and indirect‐gap energies, and the refractive index. The model used is based on an interpolation scheme, and the effects of compositional variations are properly taken into account in the calculations. Key properties of the material parameters for a variety of optoelectronic device applications are also discussed in detail. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory