By Topic

Journal of Applied Physics

Issue 7 • Date Apr 1991

Filter Results

Displaying Results 1 - 25 of 63
  • Issue Table of Contents

    Page(s): toc1
    Save to Project icon | PDF file iconPDF (328 KB)  
    Freely Available from IEEE
  • Velocity ratio measurements of a gyrotron electron beam

    Page(s): 3789 - 3795
    Save to Project icon | PDF file iconPDF (730 KB)  

    A 140 GHz high‐power gyrotron has recently been operated in a 14 T Bitter magnet to characterize emission as a function of magnetic field and beam current. The velocity ratio (or pitch angle) α=〈v〉/〈v〉 of the beam electrons is a critical parameter for high‐efficiency gyrotron operation and was measured using a capacitive probe located in the beam tunnel before the cavity. The observed velocity ratio decreased as the beam current increased while the beam voltage and magnetic fields were held fixed. This decrease in α partially explains the reduced gyrotron efficiency observed at high‐beam currents. The velocity ratio exhibited saturation effects as a function of both the beam current and the control‐anode voltage, at low cathode magnetic field values. Particle code results show a decrease in α as a function of beam current that is consistent in magnitude with the observed values. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The effect of auxiliary light on the performance of the NaCl:OH- color center laser

    Page(s): 3796 - 3799
    Save to Project icon | PDF file iconPDF (485 KB)  

    Spectroscopic and laser performance data show that the choice of auxiliary light used to optimize the performance of the NaCl F+2:O2- color center laser has little impact on the tuning range or output power of the system. When F‐band auxiliary light is used to process the laser crystal a transient absorption due to F-2 centers occurs, but this feature disappears during laser operation. No such transients appear when other auxiliary light sources are used. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Power extraction studies in a gasdynamic laser

    Page(s): 3800 - 3806
    Save to Project icon | PDF file iconPDF (684 KB)  

    A generalized two‐dimensional flow‐radiation coupled model to extract power from a gasdynamic laser is proposed. The model is used for the study of power extraction from a 9.4‐μm CO2 downstream‐mixing gasdynamic laser, where a cold CO2+H2 stream is mixed with a vibrationally excited N2 stream at the nozzle exits. This model is developed by coupling radiation with the two‐dimensional, unsteady, laminar and viscous flow modeling needed for such systems. The analysis showed that the steady‐state value of 9.4‐μm intensity as high as 5×107 W/m2 can be obtained from the system studied. The role of H2 relaxant in the power extraction process has also been investigated. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Analysis of asymmetric fringe patterns of third‐harmonic generation in a molecular crystal

    Page(s): 3807 - 3810
    Save to Project icon | PDF file iconPDF (439 KB)  

    The asymmetric Maker fringe pattern of third‐harmonic generation in an anisotropic molecular crystal is analyzed to evaluate the third‐order optical susceptibility χ(3). Analysis of a diethyl‐amino‐nitro‐stilbene crystal shows that the molecular axes are not oriented parallel to the crystal surface, but are about 45° relative to the surface. The χ(3) value parallel to the orientation of the molecular axis is estimated to be 1.0×10-11 esu, corresponding to about ten times the χ(3) value perpendicular to that axis. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Electromagnetically generated acoustic determination of delamination

    Page(s): 3811 - 3815
    Save to Project icon | PDF file iconPDF (585 KB)  

    Previous work has demonstrated a technique for acoustically detecting localized delamination of metallized patterns on insulating substrates [W. Imaino, L. Crawforth, A. C. Munce, and A. Julaiana, in Proceedings of the IEEE Ultrasonics Symposium, edited by B. R. McAvoy (IEEE, New York, 1986), p. 1065]. Employing a high‐spatial‐resolution permeable electromagnetic acoustic transducer to preferentially excite the metallization, the acoustic coupling between the metal foil and substrate may be probed. Scanning, then, provides a map of delaminations. To extend and generalize these results, the detailed generation mechanism and acoustic response of the substrate has been studied. A computer program developed previously [W. Imaino, J. Acoust. Soc. Am. Suppl. 1 80, S7 (1986)] was used to model the acoustic source. In this investigation, a finite‐element calculation is used to provide a more detailed description of the acoustic behavior of the delaminated plate. The effects of source size relative to defect dimensions and acoustic properties of the substrate have been studied. The determination of the localized coupling is complicated by structural resonances of the substrate, which make single frequency measurements unfavorable. However, the analysis shows that the spectral acoustic behavior provides an indication of metallization to substrate coupling. A signal‐processing algorithm based on this analysis has been formulated and will be described. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Phonon attenuation and velocity measurements in transparent materials by picosecond acoustic interferometry

    Page(s): 3816 - 3822
    Save to Project icon | PDF file iconPDF (802 KB)  

    A detailed analysis of the method of picosecond acoustic interferometry to study attenuation and velocity of longitudinal acoustic phonons in transparent materials in the Brillouin frequency range with picosecond laser pulses is presented. Experimental results for fused quartz from 90 to 300 K show good agreement with previous Brillouin scattering data. Measurements on a borosilicate glass (Corning 7059) and sapphire have also been made. This method makes these measurements possible under conditions where conventional approaches are not applicable. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Sheath voltage ratio for asymmetric rf discharges

    Page(s): 3823 - 3829
    Save to Project icon | PDF file iconPDF (689 KB)  

    Spherical and cylindrical many‐particle models are used to simulate rf (radio frequency) discharges in which the rf powered and the grounded electrodes have different areas. This asymmetry determines the magnitude of the average plasma‐to‐electrode voltage Va (the ion bombarding energy) at the smaller powered electrode, which is a critical process parameter. A collisionless uniform ionization discharge model predicts that the voltage ratio Va/Vb scales as the fourth power of the electrode area ratio Ab/Aa, where Vb is the potential drop at the other electrode. However, measurements indicate a much weaker dependence of Va/Vb on the area ratio, which is also observed in our simulations. Over a limited range of area ratios it was found that the power dependence was close to one, in agreement with a local ionization discharge model. The simulation codes used are PDC1 (plasma device cylindrical one‐dimensional) and PDS1 (plasma device spherical one‐dimensional). View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Characterization of a dual‐segment cylindrical surface discharge

    Page(s): 3830 - 3834
    Save to Project icon | PDF file iconPDF (532 KB)  

    A cylindrical surface‐discharge device was developed to study photolytically pumped and photoinitiated gas laser schemes. The discharge plasma plasma produces intense ultraviolet and vaccum‐ultraviolet (vuv) broadband irradiation of a 3‐l active volume. Homogeneous, large‐area (≥103 cm2) plasma shells are formed adjacent to the interior surfaces of dielectric cylinders by an electric discharge. Although the device resembles a Z‐pinch, the plasma shells do not collapse to the axis and operation with various gases at high pressure (≤2× 105 Pa) is possible. Initial experiments have emphasized electrical, gasdynamic, and radiative characterization of the device. Current wave forms are oscillatory, indicating an impedance mismatch between the surface‐discharge source and capacitor‐bank driver. A radially converging shock wave is launched by the discharge while the expanding plasma shells remain tightly pressed against the dielectric surfaces. Operation at a peak current of 94 kA produced approximately 45 J of radiated energy within the vuv spectral band from 170 to 210 nm in a 1.7‐μs full‐width‐at‐half‐maximum pulse, which represents a conversion efficiency for stored electrical energy into radiation of 2.7% and an equivalent brightness temperature of ≂13 500 K. The effective optical pulse width decreases as one moves from the visible into the vuv spectral regions. vuv radiation is only efficiently produced during the initial current half‐period, i.e., during the gap breakdown process. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Influence of partial ionization on the energy loss of fast ions in high‐Z material

    Page(s): 3835 - 3841
    Save to Project icon | PDF file iconPDF (817 KB)  

    Analytical and simple numerical calculations of the stopping power of partially ionized high‐Z targets are presented. Up to now such calculations are difficult, mainly because of lacking precise average ionization potentials of the target ions. The aim of this paper is both to clarify the importance of a suitable treatment of target ions in different ionization stages and to show by means of general scaling laws and explicit examples, that high‐Z plasmas of high density and low ionization degree may have smaller stopping powers than cold matter. The resulting range lengthening of the projectile ions might be of crucial importance for a proper design of pellets in inertial confinement fusion. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Influence of excited states on the energy loss of fast ions in a hydrogen plasma

    Page(s): 3842 - 3848
    Save to Project icon | PDF file iconPDF (839 KB)  

    Stopping power calculations of fast ions penetrating a hydrogen plasma target in local thermodynamic equilibrium at arbitrary temperatures are performed. Excited state contributions to the energy loss are included in the framework of the Bethe formalism. Average ionization potentials for the excited ions are given in a quasiclassical approximation. It is shown that the net effect is an enhancement of the stopping power compared to the energy loss when assuming all atoms to be in their ground state. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Effect of laser annealing on electrical and optical properties of n‐mercury cadmium telluride

    Page(s): 3849 - 3852
    Save to Project icon | PDF file iconPDF (394 KB)  

    Single crystals of n‐Hg1-xCdxTe (x=0.18) were grown by the Bridgman technique. The bulk single crystals were irradiated with laser pulses of various energy densities. A pulsed laser (Nd:YAG) capable of producing 10‐ns pulses of 0.53‐μm wavelength (frequency doubled) with varying energy densities (2–50 mJ/cm2) was employed. dc conductivity and Hall coefficient measurements were made on the single crystal using the van der Pauw technique in the temperature range 77–300 K, for both as‐grown and laser‐irradiated samples. Also, transmission measurements of the samples were taken at room temperature. Both electrical and optical studies showed that laser irradiation introduces additional defects in mercury cadmium telluride (MCT), and its quality deteriorates instead of improving as observed in many other semiconductor materials. We found that laser irradiation increases free‐carrier concentration and decreases the band gap of MCT. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dynamics of picosecond laser‐induced density, temperature, and flow‐reorientation effects in the mesophases of liquid crystals

    Page(s): 3853 - 3859
    Save to Project icon | PDF file iconPDF (854 KB)  

    A detailed theoretical and experimental study of laser‐induced density and temperature changes, and flow‐reorientation effects in the nematic and smectic phases of liquid crystals is presented. Using picosecond lasers, the initial nanosecond dynamics of the photoinduced density waves, temperature buildup, and relaxations are temporally resolved. The experimentally observed relaxation phenomena and time scales are in good agreement with the theoretical expressions obtained by analytical solutions of the coupled hydrodynamical equations describing these fundamental mechanisms. Our new measurement and theory provide a quantitative account of the relative contribution from the electrostrictive and thermoelastic contributions that had not been presented in previous studies. Our study of the smectic phase has conclusively established the mechanism for the formation of erasable and permanent grating effects under short‐laser‐pulse excitation as laser‐induced electrostrictive and thermoelastic effects. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Study of the influence of the phosphorus pressure on the preparation of nominally undoped semi‐insulating InP wafers

    Page(s): 3860 - 3864
    Save to Project icon | PDF file iconPDF (492 KB)  

    The conditions for the preparation of nominally undoped semi‐insulating (SI) InP wafers by annealing under controlled phosphorus pressure are described. It is demonstrated by the results of electrical profile measurements (differential Hall effect) and by photoluminescence that diffusion effects in a thin peripheral layer (≊20 μm) can be correlated to a phosphorus in‐ and indium out‐diffusion. But diffusion of these species is correlated to a donor behavior and relatively slow. It can, therefore, not be used to explain the SI bulk property which seems not to depend on the phosphorus overpressure during annealing. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Analysis of the effects of oxygen migration on dislocation motion in silicon

    Page(s): 3865 - 3877
    Save to Project icon | PDF file iconPDF (1367 KB)  

    A systematic theory is presented for the prediction of oxygen migration near a 60° dislocation and for the resulting retardation of dislocation motion. Quantitative predictions are based on the solution of the macroscopic equation for transport of oxygen in the elastic stress field created by the dislocation. The link between the microscopic dynamics of interstitial oxygen within the diamond lattice and macroscopic transport is established by a constitutive model for the dependence of the drift velocity band diffusivity of oxygen on the elastic interaction of oxygen atoms and dislocations and on temperature. The transport equation is solved numerically assuming that the dislocation core is fully saturated with oxygen. The drag force on the gliding dislocation caused by the surrounding oxygen is computed from linear elasticity theory, combined with the phenomenological model of Alexander and Haasen [Solid State Phys. 22, 27 (1968)] for the dependence on the applied stress of the velocity of a dislocation in pure silicon. The predicted dependence of the dislocation velocity on the applied stress at specific temperatures and oxygen concentrations is in qualitative agreement with the experimental data of Imai and Sumino [Philos. Mag. A 47, 599 (1983)]. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Solubility enhancement of metallic impurities in silicon by rapid thermal annealing

    Page(s): 3878 - 3881
    Save to Project icon | PDF file iconPDF (521 KB)  

    We report on the results of a study of the influence of rapid thermal annealing (RTA) on the diffusivity and solubility limit of titanium and chromium in silicon. It is shown that RTA has no influence on the diffusion of the metal atoms as long as the treatment is performed with the metal silicide as the boundary phase, but that the diffusivity is decreased if silicidation occurs during RTA. On the other hand, a strong solubility enhancement is found to occur during RTA. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Low‐power pulsed‐laser annealing of implanted GaAs

    Page(s): 3882 - 3885
    Save to Project icon | PDF file iconPDF (443 KB)  

    Low‐power annealing by a pulsed laser is used to recover the structure of low‐dose implanted (100) GaAs crystals. Reflection high‐energy electron diffraction with variable glancing incidence is employed to detect the structural changes at different depths in the specimens. The depth dependence of the damage is studied in more detail by Rutherford backscattering analysis. The annealing results depend on the irradiation conditions. A laser energy window below the melting threshold is found within which the structure can be restored to about as high degree of crystallinity as the virgin one, without any visible surface damage. A simple theoretical estimate shows that the temperature rise of the material is far below the melting threshold. This rise is too short in time to cause substantial dopant diffusion; however, it can enhance well the point‐defect mobility. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Properties of curved x‐ray diffractors with stepped surfaces

    Page(s): 3886 - 3892
    Save to Project icon | PDF file iconPDF (823 KB)  

    Problems in the practical fabrication of high‐efficiency x‐ray diffractors are discussed and a diffractor with a stepped surface is proposed to overcome these problems. The effects of the diffracting materials’ rocking curve width and x‐ray penetration on the performance of diffractors with simple geometry are evaluated to determine when diffractor geometries involving doubly curved surface and planes are more advantageous than simple geometries. An example calculation of the performance of a stepped diffractor approximating the Wittry geometry (J. Appl. Phys. 68, 387, 1990) is given and experimental results are presented for the performance of a six‐step diffractor using mica as the diffracting material and the fifth‐order reflection of CuKα radiation produced by a microfocus x‐ray source. It is concluded that the stepped diffractor geometry is a viable solution to the problem of fabricating high‐efficiency x‐ray diffractors. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Theoretical equation of state for aluminized nitromethane

    Page(s): 3893 - 3900
    Save to Project icon | PDF file iconPDF (868 KB)  

    The simple fluid constituents of the reaction products of an aluminized nitromethane explosive are described by a perturbation technique based on their intermolecular interactions. Liquid metal constituents are treated with a Grover scaling model. Standard solid‐state approaches are applied to the solid components of the reaction products. Calculated detonation velocities compared favorably with experimental data. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dopant diffusion in silicon in the presence of other dopants: A new predictive approach based on modeling boron and phosphorous diffusion in germanium‐rich regions of silicon

    Page(s): 3901 - 3906
    Save to Project icon | PDF file iconPDF (562 KB)  

    The effect of dopant‐dopant interaction on diffusion in silicon for a specific set of impurities is modeled. The first step in the modeling process involved quantum chemical calculations. The connection between the atomic scale results and macroscopic behavior was made through the medium for transmission of interactions between dopants. The molecular orbitals of the lattice system comprise that medium; consequently, interactions can be transmitted, with minimal reduction in magnitude, over separations of hundreds of lattice spacings. Macroscopically, additional flux components are generated that modify the conventional expression of Fick’s second law. Detailed simulation of boron and phosphorous diffusion in germanium‐rich regions of silicon illustrate the power of this approach to successfully model and predict the complex behavior exhibited by a particular set of interacting dopant species. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The thermal stability of Al/Ti‐Ta metallization on Si

    Page(s): 3907 - 3914
    Save to Project icon | PDF file iconPDF (944 KB)  

    The thermal stability and the interfacial reactions in the metallization system of Al/Ti‐Ta/Si for T≤550 °C were studied by x‐ray diffraction, transmission electron microscopy, and Auger electron spectroscopy. The analysis of this complex system was made possible by a systematic study of its subsystems. Bilayers of Al/Ti and Al/Ta, tri‐layers of Al/Ti/Ta and Al/Ta/Ti, and finally Al on alloy films of Ti‐Ta were deposited on Si(100) and studied. The refractory metals interactions with Al started at much lower temperatures than those with Si. In the case of the bilayer systems, Al/Ti/Si and Al/Ta/Si, the onset of interaction with Al was at 300 and 350 °C for Ti and Ta, respectively, resulting in the formation of Al3Ti and Al3Ta. The corresponding temperatures for silicide formation were 500 and 700 °C. For the tri‐layer systems the Al overlayer reacted with the top refractory metal at 300–350 °C, while the lower metal reacted with the Si substrate at the corresponding temperature for silicide formation. For the alloy samples, reactions at the Al/refractory alloy interface at 300–350 °C resulted in a mixture of Al3Ti and Al3Ta. The majority of the Ti‐Ta film, and especially its interface with Si, remained intact at annealing temperatures lower than 500 °C. For the Ta‐rich compositions studied (Ti20Ta80 and Ti50Ta50) at 500 °C Si diffused through the Ti‐Ta alloy to the outer region of the contact forming Ti and Ta disilicides, while Al penetrated deeply into the Si substrate. Most of the Ti‐rich alloy, Ti80Ta20, however, remained essentially intact even after 500 °C 30‐min anneal. At this stage a shallow contact was obtained by the formation of a ver- y thin silicide layer at the substrate interface, while penetration of Al to the substrate was prevented by a limited interaction of Al with Ti and Ta to form the corresponding aluminides. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Polycrystalline silicon carbide films deposited by low‐power radio‐frequency plasma decomposition of SiF4‐CF4‐H2 gas mixtures

    Page(s): 3915 - 3923
    Save to Project icon | PDF file iconPDF (1130 KB)  

    Polycrystalline silicon carbide thin films have been deposited on amorphous substrates by radio‐frequency plasma‐assisted decomposition of tetrafluoro silane, tetrafluoro methane, and hydrogen gas mixtures using low‐power density and deposition temperatures. The material is shown to possess the α‐SiC structure using transmission electron microscopy. It has highly visible transmittance and exhibits bands due to silicon carbide as well as fluorine bonded to carbon and silicon in the infrared transmission spectra. It is easily doped, both types showing high conductivity (∼10 S/cm) and Hall mobility [∼10 cm2/(V s)] for either carrier type. The conductivity is seen to be independent of thickness down to ∼10 nm when deposited on glass. This behavior and the dependence of both structural and electronic properties on deposition parameters is discussed in terms of the chemical reactions in gas phase and on the growth surface. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Simultaneous Sb doping and formation of self‐aligned TiSi2 by codeposition of Ti and Sb

    Page(s): 3924 - 3928
    Save to Project icon | PDF file iconPDF (642 KB)  

    Thin Ti films containing Sb were deposited on silicon by electron‐beam evaporation. The films were annealed in three steps at different temperatures in order to achieve simultaneous Sb doping and self‐aligned TiSi2 formation. Sb behavior during the Ti silicide formation and silicide structures were investigated with Auger electron spectroscopy, transmission electron microscopy, and secondary ion mass spectroscopy. Shallow n+‐p junctions have been obtained by using a modified self‐aligned TiSi2 process. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Abnormal grain growth in aluminum alloy thin films

    Page(s): 3929 - 3940
    Save to Project icon | PDF file iconPDF (1555 KB)  

    Abnormal grain growth in 0.75‐μm‐thick aluminum alloy thin films has been studied using x‐ray diffractometry, plan‐view and cross‐sectional transmission electron microscopy, scanning transmission electron microscopy, and energy dispersive x‐ray analysis. Transmission electron microscopy was used with preannealed samples as well as with samples annealed in situ. By varying the deposition temperatures, compositions, and annealing conditions, we have determined the roles of alloying elements in the formation of second‐phase precipitates and in promoting abnormal grain growth. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Molecular‐beam epitaxial growth of InAs/GaAs superlattices on GaAs substrates and its application to a superlattice channel modulation‐doped field‐effect transistor

    Page(s): 3941 - 3949
    Save to Project icon | PDF file iconPDF (1062 KB)  

    The molecular‐beam epitaxial growth conditions for (InAs)m(GaAs)n short period superlattices (SPSs) on GaAs substrates have been optimized by monitoring reflection high‐energy electron diffraction (RHEED) intensity oscillations. The RHEED oscillation measurements enable understanding InAs growth behavior on a 7% lattice‐mismatch GaAs substrate. Within one monolayer InAs deposition with lower than 560 °C growth temperature can give high SPS crystalline quality. The SPS periodic structure and the monolayer InAs formation, embedded in GaAs layers, have been confirmed by x‐ray diffraction and transmission electron microscopy measurements. The obtained thickness controllability for the SPSs is less than±6% for InAs and ±3% for GaAs. The electron Hall mobilities for modulation‐doped structures having an (InAs)1(GaAs)n SPS as an electron channel, whose layer index of n varied from 3 to 6, have been compared with those with a pseudomorphic InGaAs random alloy channel which has the equivalent In composition. The SPS channel samples have shown up to 15% higher electron Hall mobilities than the InGaAs alloy channel samples at 77 K. A 0.2‐μm‐gate (InAs)1(GaAs)6 superlattice channel modulation‐doped field‐effect transistor (FET) has exhibited a maximum extrinsic transconductance of as high as 450 mS/mm with a 70‐GHz cut‐off frequency at room temperature. The best noise figure of 0.58 dB with an associated gain of 11.15 dB has been attained. The obtained device characteristics are comparable or superior to those for the corresponding InGaAs alloy channel FETs. These results demonstrate, for the first time, the (InAs)m(GaAs)n SPS potentialities as an ordered counterpart for InGaAs random alloy for high‐speed device applications. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

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

Full Aims & Scope

Meet Our Editors

Editor
P. James Viccaro
Argonne National Laboratory