By Topic

Journal of Applied Physics

Issue 11 • Date Dec 1990

Filter Results

Displaying Results 1 - 25 of 96
  • Two‐dimensional analysis of microbolometer arrays

    Page(s): 5409 - 5414
    Save to Project icon | PDF file iconPDF (1193 KB)  

    A two‐dimensional, time‐dependent analysis is made of array‐compatible bolometers directly deposited onto a single substrate. It applies both to antenna‐coupled and surface‐absorbing configurations. Unlike previous spherically symmetric treatments, it allows analysis of thermal crosstalk between closely neighboring detectors, and of the effects of finite substrate thickness. In a closely packed array of surface‐absorbing detectors, thermal crosstalk generally degrades the array’s resolution more severely than optical (diffractive) crosstalk. Diffraction‐limited resolution with surface‐absorbing detectors is possible only by sacrificing either thermal resistance, and therefore sensitivity, or filling factor. With a minimum substrate thickness of Lmin, a closely packed, diffraction‐limited array is limited to a thermal resistance of Zt≤0.08(κLmin)-1, where κ is the thermal conductivity of the substrate. An array of antenna‐coupled bolometers is not subject to this limitation since the thermally and optically sensitive areas need not be equal. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Thermal energy charge transfer in the Zn‐Ar system

    Page(s): 5415 - 5421
    Save to Project icon | PDF file iconPDF (1199 KB)  

    Charge transfer was predicted in the Zn‐Ar system. We have shown experimentally the validity of this prediction and that in fact Ar+ excites the Zn+2P3/2,1/2 states. Moreover, we find that this process preferentially excites the J= (1)/(2) state in this mixture. This is inferred from the behavior of the intensity ratio of the transition from these two states in correlation with the intensity of the 811.5‐nm line of Ar i, where the latter is a measure for Ar ionization. Our model is based on the molecular states of Zn+Ar and Ar+Zn. The model displays a plausible curve crossings leading to the preference 2P1/2 excitation. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Novel target configurations for selective ionization state studies in molybdenum

    Page(s): 5422 - 5427
    Save to Project icon | PDF file iconPDF (786 KB)  

    Details of experiments aimed at achieving low ionization state selectivity in molybdenum are presented. Targets are excited with a 10 J CO2 laser and the resultant vacuum ultraviolet spectrum (300–700 Å) has been studied. Combinations of focal spot size, target depth, and target geometries are compared. Simple attenuation of energy is shown not to vary ionization stage composition significantly. Experiments conducted with grazing incidence targets result only in a hot plasma. Modular targets with cooling cylinders of various radii demonstrated good selectivity of the ionization states, but with low absolute signals. Finally, results from combinations of focal spot adjustment and radiative cooling illustrate increased control over desired plasma temperature and density for spectroscopic studies of molybdenum. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Energy analysis of neutral atoms in broad oxygen ion beams by Doppler‐shift measurements

    Page(s): 5428 - 5434
    Save to Project icon | PDF file iconPDF (1283 KB)  

    Optical emission spectroscopy has been established as a valuable method for the analysis of broad oxygen ion beams. The ion beams used for reactive ion‐beam etching have been investigated in the energy range of 300–1500 eV. From survey spectra O+2 molecules and neutral O atoms are identified as main emitting species. Concerning the occurrence of emission lines the beam spectrum resembles that obtained from an O2 rf plasma. The intensity ratios however are strongly different within both spectra. Whereas electron impact is the main source for electronic excitation in ordinary etch plasmas, heavy particle collisions are suggested to play an important role in the investigated ion beams. Beam‐induced emissions of atomic oxygen neutrals were recorded at high resolution of 0.1 Å. The O emission lines were found to be triple peaked. One peak at the unshifted wavelength and two Doppler‐shifted peaks could be resolved. The absolute values of the wavelength shifts are well correlated to the energies of the initial ions extracted from the ion source by a grid optics. Besides slow atoms, atoms moving with the full beam energy as defined by the ion extraction conditions and with only half the beam energy are detected. The observed Doppler structure is attributed to charge exchange and dissociative collisions taking place in the gas phase. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Impedance and emission properties of capacitively coupled Hg‐Ar discharges

    Page(s): 5435 - 5446
    Save to Project icon | PDF file iconPDF (2202 KB)  

    The impedance and emission properties of capacitively coupled Hg‐Ar discharges have been studied in order to determine the limitations of efficiency and radiance of the Hg UV radiation. The background is an application in electrodeless discharge lamps. The Ar pressure was varied between 40 and 1330 Pa, the frequency range was 10–400 MHz. The radiation efficiency generally increases with frequency, in particular at low Ar pressure and high rf power. It is correlated with the variation of the resistive impedance component with rf current and frequency. The results are discussed in terms of a discharge structure consisting of a positive column‐like bulk plasma and two rf sheaths. The frequency dependence is mainly caused by the power dissipation in the non‐luminous sheaths. The power share between bulk plasma and sheaths is determined by a suitable impedance analysis. At high power densities, the efficiency is additionally limited by saturation phenomena. Efficiencies comparable to those known from conventional, electroded discharges can be obtained by a proper choice of parameters such as discharge current and operating frequency. The measurements of the Hg UV radiation are supplemented by a spatially resolved spectroscopy of the Ar excitation. The extension of the dark spaces corresponds to the sheath thickness ds as derived from the impedance data. ds varies with Ar pressure pAr and frequency  f approximately as (pAr)-1/3f-1/2. A recently described model for the power dissipation in the sheath of capacitively coupled rf discharges in Ar is also in good agreement with the impedance data of Hg‐Ar discharges. The complex sheath impedance is represented by a semi‐empirical, analytical expression over a wide range of Ar pressures and frequencies. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Experimental study of optical waveguides with absorption induced by metallic electrodes

    Page(s): 5447 - 5450
    Save to Project icon | PDF file iconPDF (596 KB)  

    We have experimentally studied the influence of metallic slabs deposited in the vicinity of an optical waveguide on its guided propagation properties. The observed induced optical absorption is well described by the theory of the azimuthal effective‐index method recently proposed by Marcatili and Hardy [IEEE J. Quantum Electron. QE‐24, 766 (1988)]. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A computational model of a dual‐wavelength solid‐state laser

    Page(s): 5451 - 5455
    Save to Project icon | PDF file iconPDF (731 KB)  

    A rate equation model of a Y‐cavity solid‐state laser with a single active medium operating simultaneously on two laser lines having a common upper level is described. Application is made to Nd3+ : YAG, where the 1.06‐μm and 1.32‐μm infrared lines can be sum‐frequency mixed to produce 0.589‐μm yellow radiation. The model is used to optimize cavity design with respect to efficiency of sum‐frequency mixing. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Fractal surface scattering: A generalized Rayleigh solution

    Page(s): 5456 - 5462
    Save to Project icon | PDF file iconPDF (1147 KB)  

    We consider the scattering of electromagnetic waves from perfectly conducting fractal surfaces. The surface is modeled by a multiscaled bandlimited continuous fractal function. We analytically develop a generalized Rayleigh solution for electromagnetic wave scattering from such fractal surfaces. After an examination of the convergence of the Rayleigh systems, we numerically calculate the coupling strengths and relate the angular scattering energy distribution to the fractal descriptors of the surface. We find that the slope of the coupling strengths as a function of their corresponding spatial frequencies on a logarithmic scale depends monotonically on the fractal dimension of the scattering surface. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Fabrication of low‐loss zinc‐selenide coated silver hollow waveguides for CO2 laser light

    Page(s): 5463 - 5466
    Save to Project icon | PDF file iconPDF (566 KB)  

    ZnSe coated Ag hollow waveguides transmitting CO2 laser light were developed. An inner ZnSe coating of good quality was obtained with high rf power and high translating speed in deposition by rf sputtering. The inner ZnSe layer was found to be amorphous by x‐ray diffraction analysis; A layer structure (ZnSe‐Ag) was observed by Auger electron spectroscopy analysis. Transmission properties of the short waveguides with 25 cm length were evaluated by measurements of loss spectra in the mid‐IR region. As a result, ZnSe coated Ag waveguides showed lower loss than the Ge coated one fabricated previously, and the loss for CO2 laser light was predicted to be 0.021 dB/m. Furthermore, it was found that a ZnSe coated Ag waveguide is durable in practical use. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Comparison of YAG:Er and YAlO3:Er laser crystals emitting near 2.9 μm

    Page(s): 5467 - 5471
    Save to Project icon | PDF file iconPDF (698 KB)  

    Four different erbium laser crystals, two YAG:Er (40 at. %) and two YAlO3:Er (30 at. % and 50 at. %), have been compared with respect to their laser thresholds and slope efficiencies. The performance of these laser crystals was further compared with a YSGG:Cr:Er (Y3Sc2Ga3O12) (3.6 at. % Cr3+ and 4 at. % Er3+). The experimental results are explained with up‐conversion processes in the crystals. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Temperature variation of elastic nonlinearity of NaCl

    Page(s): 5472 - 5477
    Save to Project icon | PDF file iconPDF (1035 KB)  

    The second harmonic generation technique has been used to evaluate combinations of third‐order elastic constants (TOEC) of NaCl between room temperature and liquid‐nitrogen temperature. TOEC data at room temperature are compared both with theory and other experimental results. The temperature variation of C111 is somewhat larger than predicted by theory. The temperature behavior suggests that a noncentral force and other exchange interactions predominate at 0 K. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Hyperbolic heat conduction due to axisymmetric continuous or pulsed surface heat sources

    Page(s): 5478 - 5485
    Save to Project icon | PDF file iconPDF (1178 KB)  

    Irradiation of metals with laser pulses in the nanosecond to picosecond range may give rise to temperature fields which are significantly different from those predicted by the classical Fourier heat conduction model. In this work we examine the very short‐time temperature response of a semi‐infinite region to an axisymmetric laser surface source, which is either continuous or activated for a period Δt and has a spatial profile which is Gaussian, doughnut, or a combination of the Gaussian and doughnut modes. The material properties are assumed constant, and radiation and convection from the irradiated surface are neglected. The non‐Fourier temperature responses are compared with their diffusive counterparts and shown to give rise to steep local temperature concentrations. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Effective conductivity of hard‐sphere dispersions

    Page(s): 5486 - 5493
    Save to Project icon | PDF file iconPDF (1425 KB)  

    Three‐point bounds on the effective conductivity σe of isotropic two‐phase composites, that improve upon the well‐known two‐point Hashin–Shtrikman bounds [J. Appl. Phys. 23, 779 (1962)], depend upon a key microstructural parameter ζ2. A highly accurate approximation for σe developed by Torquato [J. Appl. Phys. 58, 3790 (1985)] also depends upon ζ2. This paper reports a new and accurate algorithm to compute the three‐point parameter ζ2 for dispersions of hard spheres by Monte Carlo simulation. Data are reported up to values of the sphere volume fraction ϕ2 near random close‐packing and are used to assess the accuracy of previous analytical calculations of ζ2. A major finding is that the exact expansion of ζ2 through second order in ϕ2 provides excellent agreement with the simulation data for the range 0≤ϕ2 ≤0.5, i.e., this low‐volume‐fraction expansion is virtually exact, even in the high‐density region. For ϕ2 ≫0.5, this simple quadratic formula is still more accurate than other more sophisticated calculations of ζ2. The linear term of the quadratic formula is the dominant one. Using our simulation data for ζ2, we compute three‐point bounds on the conductivity σe and Torquato’s approximation for σe . View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multiple scattering of electrons in the reflex triode

    Page(s): 5494 - 5506
    Save to Project icon | PDF file iconPDF (1816 KB)  

    Analytical theories and Monte Carlo calculations are used to treat the scattering and energy loss of electrons in the anode of a reflex triode. The solution of this scattering problem is combined with the equations for particle flow in vacuum to give a quantitative theory of triode operation. It is now possible to calculate several important properties of this device. These include the operating voltage in the constant voltage mode, the ratio of ion‐to‐electron current and the ion transit time. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Investigation of the creation process in dc pulsed discharges

    Page(s): 5507 - 5510
    Save to Project icon | PDF file iconPDF (528 KB)  

    In this paper we study the creation process of a cylindrical pulsed argon plasma. A new numerical model to simulate the plasma evolution during the creation process has been developed. This model is based on the solution of the continuity equations for ions and electrons together with the Poisson’s equation. The good agreement obtained between numerical and experimental results of electron density as a function of the time confirms the validity of the hypothesis made in the model proposed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An extreme ultraviolet spectroscopic diagnostic for fluctuations of electron density and temperature in tokamak plasmas

    Page(s): 5511 - 5518
    Save to Project icon | PDF file iconPDF (1502 KB)  

    Extreme ultraviolet (XUV) spectral line emissivities, originating from resonant transitions with upper states excited mainly from ground or both ground and lowest metastable states by electron collisional excitations of highly ionized intrinsic impurities in tokamak plasmas, are linear functions of both electron density and temperature fluctuations, ñe and T~e, when the fluctuations are small and at high frequency. Correlations between measured intensities of spectral lines can thus provide localized measurements of the fluctuations. Newly developed XUV monochromators of high throughput enable accurate and fast diagnostics of ñe and T~e for the study of the tokamak plasma microturbulence. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • rf modulation of positive‐ion energies in low‐pressure discharges

    Page(s): 5519 - 5527
    Save to Project icon | PDF file iconPDF (1578 KB)  

    In this work a filament‐assisted dc argon discharge is generated between parallel electrodes. A rf signal (≪13.56 MHz) is applied to one electrode in order to modulate the plasma potential. The degree of modulation is monitored using an emissive Langmuir probe. The velocity distribution of ions arriving at the earthed electrode is observed to respond to the rf modulation of the local space potential, the effect diminishing as the rf frequency is increased above the ion plasma frequency. A model is developed to describe the behavior of the ions to the rf modulation of the space potential. Good agreement between the simulation and experimental results is observed. The modulation of ion velocities by nonsinusoidal potentials is briefly examined. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Theoretical treatment of rf discharges in CO2 waveguide lasers

    Page(s): 5528 - 5531
    Save to Project icon | PDF file iconPDF (685 KB)  

    Theoretical investigations have been performed to describe the discharges in rf‐excited CO2 waveguide lasers. Especially, the formation of boundary layers has been considered as these regions are not yet understood completely. As characterization of the plasma, the spatial distributions of electron density and electric field have been calculated as these two quantities are suitable to describe the electrical properties of the discharge as well as the optical behavior. The electric‐field strength is split up into the rf field and a static field which forms as a consequence of ambipolar diffusion. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Study of the structure in rf glow discharges in SiH4/H2 by spatiotemporal optical emission spectroscopy: Influence of negative ions

    Page(s): 5532 - 5539
    Save to Project icon | PDF file iconPDF (1442 KB)  

    Radio frequency glow discharges in SiH4(50%)/H2 at 13.56 MHz and 100 kHz have been investigated by using time‐ and space‐resolved optical emission spectroscopy. The relative net‐excitation rate is obtained by deconvolving the spatiotemporal emission profile considering the influence of the radiative lifetime. From the results, we infer the behavior of electrons with energy greater than the threshold energy for the dissociative excitation and we discuss the discharge structure. Lines of SiI(4s 11P0→3p 21D), SiH(A2Δ;v’=0→X2Π;v‘=0), Hα, and H2(d 3Πu→a 3Σ+g) are selected for observation. It is concluded that there exists a considerable population of negative ions compared with positive ions, which has not been previously proposed in high‐frequency discharges in SiH4 because of the small degree of electron attachment. At 13.56 MHz, the optical emission oscillates at 2ω in the bulk plasma region, in addition to the emissions at the plasma‐sheath boundaries. It implies that the field in the bulk is strengthened by the external sinusoidal field to make up for the loss of electrons by electron attachment. The bulk field is estimated at 69 sin(ωt) V cm-1 from V‐I characteristics. The existence of a double layer by the modulation of electrons is strongly suggested even in a high frequency at 13.56 MHz. At low frequency (100 kHz), a double layer is observed, which is formed by the large modulation of negative and positive ions. Consequently, excitation by electrons accelerated in the field at the double layer is observed in addition to excitation by secondary electrons from ion bombardment. Consideration of the role of negative ions i- n high‐frequency SiH4 discharges at 13.56 MHz is necessary to understand the discharge structure of the silane plasma and the deposition of the hydrogenated amorphous silicon. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Internal energy distributions in a shielded plasma device

    Page(s): 5540 - 5548
    Save to Project icon | PDF file iconPDF (1517 KB)  

    A shielded plasma device has been used extensively in plasma synthesis and plasma processing. In order to optimize these processes, optical diagnostics were used to study the device operated at 545 kHz and pressures between 2.5 and 580 Torr. Plasma‐induced emission for Ar, N2, and N+2 suggested that a local thermodynamic equilibrium point of view was inappropriate. Spatially resolved laser‐induced fluorescence and laser absorption measurements were performed on the metastable argon state 3P2 and the radiative state 3P1. The metastable profiles were described in terms of a kinetic model dominated by electron‐atom kinetics. The model was used to determine the electron temperature Te as a function of axial position and total gas pressure. These temperatures were found to lie in the range of 5000 K at 580 Torr to 11 000 K at 25 Torr. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Surface order transition in nematic liquid crystals induced by the flexoelectric polarization

    Page(s): 5549 - 5554
    Save to Project icon | PDF file iconPDF (749 KB)  

    The influence of the flexoelectric polarization on the nematic surface energy is analyzed. It is shown that if the dielectric constant of the substrate is lower than a critical value the undistorted orientation is no more the one corresponding to lowest energy. The presence of a conducting substrate is also considered. In this case it is shown that by changing the thickness of the dielectric material deposited over the conducting material, a surface order transition is expected. Furthermore, the influence of a finite anchoring energy between nematic and substrate on the critical value of the dielectric constant is discussed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Annealing characteristics and electrical properties of 1‐MeV arsenic‐ion‐implanted layers in silicon

    Page(s): 5555 - 5563
    Save to Project icon | PDF file iconPDF (2048 KB)  

    Arsenic ions have been implanted in (100)Si at an incident energy of 1 MeV to a dose of 1×1015/cm2. Rutherford backscattering measurements with a 1.5‐MeV He‐ion beam have shown that a buried amorphous layer is formed in the Si substrate which is implanted at a low ion‐beam current of 0.8 μA and that considerable annealing occurs when implantation is carried out at a high ion‐beam current of 2 μA. The implantation‐induced amorphous layer recrystallizes after annealing above 550 °C, but a high density of lattice defects still remains in the substrate even after annealing at 1000 °C. Defect observations using a cross‐sectional transmission electron microscope have revealed that those defects are located at the two depths corresponding to the initial transition regions where the crystallinity is changed from the amorphous to nonamorphized states in the substrate. In addition, secondary defects also exist in a particular region inside the initial buried amorphous layer. The recrystallization of the buried amorphous layer during post‐implant annealing is initiated not only from the deeper part of the substrate but also from the nonamorphized surface layer. From a series of isothermal annealing studies, it has been shown that the recrystallization rates at 550 °C are 140 and 180 Å/min on the frontside and backside of the buried amorphous layer, respectively. Electrical profile measurements, using the differential Hall method, have shown that a highly doped, buried conductive layer with a peak carrier concentration of around 2×1019/cm3 can be formed by annealing above 800 °C. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Boron ion implantation in p‐type Hg0.8Cd0.2Te

    Page(s): 5564 - 5566
    Save to Project icon | PDF file iconPDF (382 KB)  

    Differential Hall measurements at 77 K were done on 150‐keV boron implanted p‐type mercury‐cadmium‐telluride (HgCdTe). n+ layers formed as a result of implantation with various doses were very sharp and thicknesses of the n+ layers were found to depend on boron dose. The sheet carrier concentration tends to saturate above the dose 1×1013 cm-2. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Properties of polycrystalline ZnSe thin films grown by ion‐beam deposition

    Page(s): 5567 - 5570
    Save to Project icon | PDF file iconPDF (611 KB)  

    Polycrystalline ZnSe thin films were grown by ion‐beam deposition on glass substrates. The crystallinity of ZnSe films grown by ion‐beam deposition is affected by ionization. In particular, at a substrate temperature of 200 °C, there is an abrupt increase in the number of (311) oriented grains. Without ionization, the (111) oriented grains predominate. Transmittance of ZnSe films is improved by ion‐beam deposition at substrate temperatures below 200 °C, in the wavelength range of 460–550 nm near the interband absorption edge. Ion‐beam deposition has a heating effect on the film surface during deposition by ion bombardment, which controls the crystallinity and the optical properties of ZnSe films at low substrate temperature on noncrystalline substrates. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Impurity effect on the creation of Ga vacancies in a Si‐doped layer grown on Be‐doped GaAs by molecular‐beam epitaxy

    Page(s): 5571 - 5575
    Save to Project icon | PDF file iconPDF (945 KB)  

    The impurity effects on the creation of Ga vacancies in Si‐doped GaAs grown on a Be‐doped epilayer by molecular‐beam epitaxy were investigated through slow positron beam measurements. Doping of Si impurities enhances the creation of Ga vacancies in GaAs. The experimental results support the theoretical prediction of the creation of Ga vacancies in terms of the change in the Fermi‐level position by the Si doping into GaAs, and also suggest that a Si atom diffuses in GaAs as a neutral complex of SiGa‐VGa rather than that of SiGa‐SiAs. The change in the S parameter distribution at the interface between Si and Be‐doped regions is explained by the Be carryforward phenomenon which occurs during the growth of Si‐doped GaAs on a Be‐doped epilayer. 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