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1 Dec 1978

Volume 49, Issue 12, pp. 5699-6201

Page 1 of 4 Pages Next Page | Jump to Page

Photochemical enrichment of the chlorine and carbon isotopes induced in Freon (CF2Cl2) by CO2 laser pulses

P. Fettweis and M. Nève de Mévergnies

J. Appl. Phys. 49, 5699 (1978); http://dx.doi.org/10.1063/1.324586 (4 pages) | Cited 16 times

Online Publication Date: 12 August 2008

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Enrichment of the carbon isotopes by photodissociation or photochemical reaction of Freon (CF2Cl2) induced by a TEA‐CO2 laser has been reported recently by several authors. The present work shows that large effects on the chlorine isotopes are also induced. Their laser‐wavelength dependence has been measured, and some complementary information on the carbon isotopic effects has been collected. Excitation around 930 cm−1 yields an enrichment in 37Cl in the residual CF2Cl2, and excitation around 1085 cm−1 has an opposite effect, while 13C enrichment is found around both 1090 and 922 cm−1 and 12C enrichment is found around 1065 cm−1. These effects can be qualitatively explained with the known fundamental vibrations ν1 (922 cm−1, stretching mode) and ν6 (992 cm−1, rocking mode) of CF2Cl2. The efficiency of the photodissociations of CF2Cl2 induced by a CO2 laser is evaluated, and an effective threshold energy density of 3 J/cm2 is found at 1089 cm−1.
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33.80.Rv Multiphoton ionization and excitation to highly excited states (e.g., Rydberg states)
33.80.Wz Other multiphoton processes
82.50.-m Photochemistry
28.60.+s Isotope separation and enrichment

Energy removed from vibration in V‐V collisions between SF6 and helium or argon

J. A. Woodroffe and B. Kivel

J. Appl. Phys. 49, 5703 (1978); http://dx.doi.org/10.1063/1.324587 (7 pages) | Cited 1 time

Online Publication Date: 12 August 2008

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We have measured the amount of vibrational energy transferred to translation in V‐V collisions between SF6 and helium or argon. We used precise mass‐spectrometric measurement of the change in SF6 density in a flow of He or Ar and SF6 through a focused cw CO2 laser beam under conditions where the number of collisions in the beam was much less than the collision number for V‐T deactivation. We have determined the ratio of energy lost Δ? to the number of collisions for V‐V relaxation ZVV to be Z−1VVΔ? =13±6 cm−1/collision for helium and 4±2 cm−1/collision for argon. These values are independent of temperature over the range 150–300 K.
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34.50.Ez Rotational and vibrational energy transfer
82.20.Rp State to state energy transfer

Ionized beam doping in molecular‐beam epitaxy of GaAs and AlxGa1−xAs

Nobutoshi Matsunaga, Toshihisa Suzuki, and Kiyoshi Takahashi

J. Appl. Phys. 49, 5710 (1978); http://dx.doi.org/10.1063/1.324588 (6 pages) | Cited 12 times

Online Publication Date: 12 August 2008

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Molecular‐beam epitaxy (MBE) with ion beams as dopants is proposed, and experiments with Zn ions in GaAs and AlxGa1−xAs are reported. In conventional MBE, impurities with low sticking coefficients have not been used because doping into MBE layers involves simultaneous evaporation. In this paper, a method of ionizing the dopant molecular beam and increasing its effective sticking coefficient is proposed. By means of ionization, an effective sticking coefficient of ∼0.03 for Zn ions in GaAs and AlxGa1−xAs is obtained as compared with a value of ∼10−7 for neutral Zn. This value does not vary even with the mole fraction of AlAs in the system AlxGa1−xAs. A strong ion acceleration is not essential for increasing the sticking coefficient, and ionized dopants arriving at the substrate even without enough kinetic energy for penetration beneath the surface react and bond with the surface atoms sufficiently to prevent reevaporation. Crystallographic characteristics of ion‐doped GaAs and AlxGa1−xAs films are as good as for undoped MBE layers and the Hall mobilities are comparable to those of LPE and VPE p‐type layers. Other electrical and optical characteristics are reported here, and the results show that this modification of MBE can be applied to many other dopants and is a useful method to fabricate various electron devices, especially with complicated structures.
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34.50.-s Scattering of atoms and molecules

Electron scattering cross sections for momentum transfer and inelastic excitation in carbon monoxide

James E. Land

J. Appl. Phys. 49, 5716 (1978); http://dx.doi.org/10.1063/1.324589 (6 pages) | Cited 56 times

Online Publication Date: 12 August 2008

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Cross sections for momentum transfer and for rotational, vibrational, and electronic excitation were obtained from an analysis of experimental data for electron drift velocity, characteristic energy, and ionization coefficient. Recently measured data in the range 1×10−16?E/N?4×10−15 V cm2 were included in the analysis.
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34.80.Gs Molecular excitation and ionization
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)

The Kelvin transformation for a torus

R. Cade

J. Appl. Phys. 49, 5722 (1978); http://dx.doi.org/10.1063/1.324590 (6 pages) | Cited 1 time

Online Publication Date: 12 August 2008

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A perturbation method was given recently for solving electrostatic problems involving a conducting torus which is freely charged or influenced by a uniform field parallel to its axis. It was forseen that one limitation of the method, the fact that no external influence other than the one just mentioned is allowable, could be removed in the case of a circular torus (anchor ring) by means of the Kelvin transformation and superposition, and the present paper develops this aspect. A number of presumably new results are given for a torus influenced by a given charge located on its axis, and it is shown how the procedure can be extended for a very general axisymmetric situation involving a given charge distribution.
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41.20.Cv Electrostatics; Poisson and Laplace equations, boundary-value problems
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems

Guided‐wave acousto‐optic interaction on nonpiezoelectric substrates

S. K. Yao, R. R. August, and D. B. Anderson

J. Appl. Phys. 49, 5728 (1978); http://dx.doi.org/10.1063/1.324591 (3 pages) | Cited 1 time

Online Publication Date: 12 August 2008

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Guided‐wave acousto‐optic diffraction has been demonstrated on a silicon substrate for the first time. The surface acoustic wave is launched from a ZnO/Tab2O5/SiO2/Si multilayered structure, while a Ta2O5/SiO2/Si optical waveguide is used for the acousto‐optic interaction. The measured diffraction efficiency is 3.3% per milliwatt of acoustic power. An order‐better performance is possible with improved transducer geometry. The silicon‐based guided‐wave acousto‐optic technology is preferred for eventual integration of both optical and electronic components for integrated optical applications such as rf spectrum analyzer and fiber‐optical terminals. Experiments with a similar structure on a glass substrate is also reported.
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42.82.-m Integrated optics
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
42.79.Gn Optical waveguides and couplers

Characterization of (Al,Ga)As injection lasers using the luminescence emitted from the substrate

R. L. Hartman and L. A. Koszi

J. Appl. Phys. 49, 5731 (1978); http://dx.doi.org/10.1063/1.324592 (14 pages) | Cited 25 times

Online Publication Date: 12 August 2008

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The spontaneous radiation generated in the active region of (Al,Ga)As double‐heterostructure (DH) proton‐delineated stripe‐geometry lasers has been studied by measuring the luminescence (Ls) emitted from a window fabricated in the metallization on the substrate. Observations of the intensity of this luminescence with an image converter provide an effective means for detecting growth‐, processing‐, and aging‐induced defects. In addition, these measurements provide a simple procedure for separating changes in optical loss from changes in radiative‐recombination efficiency. Thus, Ls observations are useful for quality control and laser‐aging analysis. For lasers with 8% aluminum in the active region, Ls is shown to be principally radiation reemitted from a very thin layer of GaAs substrate at the interface with the n‐type ternary layer. Reasonably high spatial resolution (∼3 μm) of the radiation from the active stripe region is retained in this absorption‐reemission process. For devices with no aluminum added to the active layer, the luminescence is mostly single pass radiation from the active region. Quantitative current and spatial dependences of Ls have been obtained which probe the carrier concentration in the active volume. It has also been shown that the threshold current is easily measured by an abrupt change in dLs/di (saturation) and that this slope also characterized the slope of the intensity of the stimulated emission (L) above threshold. In addition, abrupt changes in dLs/di at threshold current have been measured near the edges of the stripe showing that saturation‐induced effects are observable over the entire stripe width. In the current increment in which near‐field examination of L showed spatial motion of a filament significant spatial changes in Ls were observed (although only for lasers without aluminum in the active layer). Thus, spatial motion of lasing filaments can be correlated with changes in the steady‐state spatial carrier‐concentration profiles. Many lasers exhibited a decrease in Ls above threshold, most pronounced about the central axis of the lasing stripe. This decrease in the steady‐state carrier concentration does not seem to be consistent with a model based on saturable optically absorbing traps.
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42.55.Px Semiconductor lasers; laser diodes

Angular multiplexing as a technique for short‐pulse amplification in a high‐gain xenon amplifier

Robert P. Sandoval

J. Appl. Phys. 49, 5745 (1978); http://dx.doi.org/10.1063/1.324593 (5 pages) | Cited 2 times

Online Publication Date: 12 August 2008

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It has been proposed that the technique of angular multiplexing could provide an efficient scheme for extracting short pulses from a high‐gain laser with a high degree of spatial and temporal control of the extracted laser beam. The scheme of angular multiplexing proposes to amplify short laser pulses (∼1 nsec) by sequentially passing these pulses through the amplifier at slightly different angles. The intensity of each pulse must be sufficient to control amplified spontaneous emission and to extract a significant fraction of the available energy. The experimental demonstration of this technique on the high‐gain xenon laser is described here. The measurements were made for a two‐pulse train with each pulse width shorter than the amplifier gain period. The results of this experiment indicate that for an optimum pulse separation and input pulse intensity, a major fraction of the available laser energy could be extracted efficiently by the pulse train without significant pulse distortion.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems

The effects of optical absorption in Ba2NaNb5O15 on internal frequency‐doubled operation of Nd : YAG

R. R. Rice, J. R. Teague, and J. E. Jackson

J. Appl. Phys. 49, 5750 (1978); http://dx.doi.org/10.1063/1.324594 (13 pages)

Online Publication Date: 12 August 2008

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Absorption loss in barium sodium niobate (BSN) crystals at both the 1.064‐μm fundamental and 0.532‐μm SH wavelengths perturbs the SHG phase‐matching condition, thereby coupling the circulating and SH power with the nonlinear loss. Discrete transitions in circulating power, hysteresis in the intracavity SHG temperature phase‐matching signature, and bistable operation are the direct result of this absorption loss. Extensive analytical and experimental results were obtained and are reported.
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42.65.-k Nonlinear optics
42.60.-v Laser optical systems: design and operation
42.79.-e Optical elements, devices, and systems

Determination of crack characteristics from the quasistatic approximation for the scattering of elastic waves

S. Teitel

J. Appl. Phys. 49, 5763 (1978); http://dx.doi.org/10.1063/1.324579 (5 pages) | Cited 7 times

Online Publication Date: 12 August 2008

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We extend the work of a previous paper to give a long‐wavelength approximation for elastic wave scattering by an elliptical flat crack. Explicit formulas for the far‐field scattered amplitudes in this approximation are given for various experimental configurations. These formulas are then applied to give a simple inversion procedure. The orientation and eccentricity of the crack are readily determined from unnormalized scattering data. The size may be determined from an absolute intensity measurement.
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43.20.Bi Mathematical theory of wave propagation
62.30.+d Mechanical and elastic waves; vibrations
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Analysis of transient temperature distribution in oil shale due to heat source propagating in retort

H. E. Wilhelm, J. B. DuBow, and S. H. Hong

J. Appl. Phys. 49, 5768 (1978); http://dx.doi.org/10.1063/1.324580 (6 pages) | Cited 1 time

Online Publication Date: 12 August 2008

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The initial‐boundary‐value problem for the transient temperature fields in oil shale, which is heated by a propagating combustion flame in an in situ retort chimney, is formulated and solved analytically. The heat source of the flame is represented by a Gaussian distribution, which models the average statistical variations in radial and axial flame extensions, and is assumed to build up to maximum strength in accordance with a temporal relaxation process. The transient temperature fields in the oil shale surrounding the retort are calculated and discussed with respect to their spatial variations and dependence on the flame relaxation time. The theoretical temperature distributions are shown to be consistent with those observed experimentally. The high‐temperature core extends less than a retort radius into the surrounding shale bed. This result has implications for (i) the in situ retort design and (ii) the environmental impact of in situ retorts. It appears that the spacing between neighboring retorts can be reduced and that the thermal effects of retorts on the environment are less severe than previously anticipated.
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44.10.+i Heat conduction
91.35.Dc Heat flow; geothermy
02.30.Jr Partial differential equations

Stresses generated by the thermomigration of liquid inclusions in silicon

T. R. Anthony and H. E. Cline

J. Appl. Phys. 49, 5774 (1978); http://dx.doi.org/10.1063/1.324581 (9 pages) | Cited 8 times

Online Publication Date: 12 August 2008

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Estimates of the stresses generated in a silicon wafer by thermomigration processing indicate the potential presence of stresses ranging from 1.7×10−1 to 7×103 MPa. The causes of these stresses include the heating and cooling of the wafer, the partial infrared transparency of silicon, thermal edge losses from the periphery of the wafer, the increasing solubility of silicon in the inclusion with increasing temperature, the difference in thermal conductivity between the liquid inclusion and the silicon matrix, the lattice expansion induced by impurity atoms in the dopant trials, the mismatch in thermal expansion coefficients in the Al‐Si sandwich at the completion of processing, and inclusions frozen in the wafer. Various ways of decreasing or eliminating these stresses are suggested so that the performance and yield of devices made by thermomigration will be optimized.
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46.40.-f Vibrations and mechanical waves
83.50.-v Deformation and flow
62.10.+s Mechanical properties of liquids
62.20.-x Mechanical properties of solids

Transformation of coordinates associated with linearized supersonic motions

T. S. Shankara and Kamal Kanti Nandi

J. Appl. Phys. 49, 5783 (1978); http://dx.doi.org/10.1063/1.324582 (7 pages) | Cited 2 times

Online Publication Date: 12 August 2008

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A Lorentz‐like transformation (LLT) is introduced in the supersonic regime which keeps the wave equation invariant and simultaneously fixes the coordinate system to the body, producing small disturbances. Its implications, which appear to be far reaching, are briefly discussed.
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47.40.Ki Supersonic and hypersonic flows
43.20.Bi Mathematical theory of wave propagation

The evaporation rate from the cathode spot on base metal electrodes in vacuum arcs

Takayoshi Kubono

J. Appl. Phys. 49, 5790 (1978); http://dx.doi.org/10.1063/1.324583 (4 pages) | Cited 4 times

Online Publication Date: 12 August 2008

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The rate of metal evaporation from the cathode spot in a vacuum arc is calculated and expressed in approximate formulas as a function of arc current by use of estimated values of its radius and temperature on the basis of the cathode mechanism theory proposed recently. As the evaporation rate is in good agreement with the experimental erosion rate, these formulas for the radius, temperature, and rate of evaporation on the cathode spot as a function of arc current are very useful in the industrial field.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
81.90.+c Other topics in materials science (restricted to new topics in section 81)
84.32.Dd Connectors, relays, and switches

Generation of a plasma wave and second harmonic in a magnetoplasma

A. K. S. Thakur and R. P. Sharma

J. Appl. Phys. 49, 5794 (1978); http://dx.doi.org/10.1063/1.324584 (7 pages)

Online Publication Date: 12 August 2008

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This paper presents an investigation of the generation of a plasma wave and a second‐harmonic electromagnetic wave in a collilsionless hot magnetoplasma by a Gaussian EM beam (pump wave) propagating perpendicular to a static magnetic field in the ordinary mode. Because of the Gaussian intensity distribution of the EM wave, the ponderomotive force becomes finite and the electrons become redistributed; the electron density gradient (so created) and the intensity gradient of the EM wave lead to the generation of a plasma wave at the pump‐wave frequency. The intensity of the magnetic field significantly affects the plasma‐wave generation. When the pump‐wave frequency is equal to the upper‐hybrid frequency, resonant excitation of the plasma wave occurs. The plasma wave interacting with the pump wave leads to the generation of a second‐harmonic electromagnetic wave. Moreover, as the pump wave propagates in the plasma, its self‐focusing occurs; consequently, the plasma‐wave and the second‐harmonic generation become drastically affected.
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52.25.Fi Transport properties
52.35.Hr Electromagnetic waves (e.g., electron-cyclotron, Whistler, Bernstein, upper hybrid, lower hybrid)

Laser fluorescence spectroscopy of three‐level systems

K. G. Müller and M. Stania

J. Appl. Phys. 49, 5801 (1978); http://dx.doi.org/10.1063/1.324585 (5 pages) | Cited 7 times

Online Publication Date: 12 August 2008

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In common laser fluorescence spectroscopy a quasi‐instantaneous distribution of the laser‐coupled levels according to their statistical weights is assumed. This saturation case can only be achieved by a fast rising laser pulse of sufficient intensity. Otherwise, losses from the laser‐pumped levels and the time dependence of the laser pulse have to be taken into account. In this paper a model including losses is investigated. Normalized fluorescence curves result which are characterized by one fit parameter. Into this parameter the rise time of the laser pulse, the overlap of the laser line and of the corresponding atomic line and its oscillator strength enter. The influence of the loss processes on the peak of the fluorescence curve can be shown. The model is applied to measurements at a nonthermal neon plasma of a microwave discharge. Transitions from the levels 2p5 3s 3P0, 3P1, 3P2 to a common upper level 2p5 3p 3P1 have been pumped. Evaluation of the fluorescence signal (2p5 3p 3P1→2p5 3s 1P1) leads to relative populations of the lower levels. The agreement between the theoretical and the experimental fluorescence curve proves the applicability of our model. By this method the range of applicability of laser fluorescence spectroscopy can be extended to nonsaturation cases.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.70.Nc Particle measurements
33.50.Dq Fluorescence and phosphorescence spectra
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques
07.60.Rd Visible and ultraviolet spectrometers

Effect of radial expansion in the laser heating of short plasma columns

C. S. Lai

J. Appl. Phys. 49, 5806 (1978); http://dx.doi.org/10.1063/1.324595 (3 pages)

Online Publication Date: 12 August 2008

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Plasmas heated uniformly by inverse bremsstrahlung are found to approach a constant electron‐ion temperature difference as a function of only the laser intensity and wavelength. A quasistatic model is employed to account for the radial expansion of plasmas. Analytic solutions up to the first order in β are obtained for the electron and ion temperatures.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Low‐frequency instabilities in the high‐pressure regime of Penning discharges

S. K. Guharay, S. N. SenGupta, and M. R. Gupta

J. Appl. Phys. 49, 5809 (1978); http://dx.doi.org/10.1063/1.324596 (7 pages) | Cited 1 time

Online Publication Date: 12 August 2008

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See Also: Erratum

Show Abstract
A general dispersion relation for the rotationally symmetric (m=0) and asymmetric (m≠0) low‐frequency waves has been delineated, utilizing a dimensional treatment as done by Hoh, for a high‐pressure (p∼10−2 Torr) Penning discharge having gradients (radial) of ion density, plasma potential, and electron temperature. The present analysis is found to be very helpful for investigating the role of the temperature gradient in exciting various modes; here, a positive temperature gradient has been found to have a destabilizing influence in general. The theoretical predictions of the growth condition and the frequency of the instability have been found to agree well with the present experimental observation of an m=0 mode. Further, an experiment on the suppression of this instability has been carried out for understanding the excitation mechanism.
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52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.80.Sm Magnetoactive discharges (e.g., Penning discharges)
52.25.Kn Thermodynamics of plasmas
52.70.Ds Electric and magnetic measurements

Crystalline and magnetic properties of an ion‐implanted layer in bubble garnet films

K. Komenou, I. Hirai, K. Asama, and M. Sakai

J. Appl. Phys. 49, 5816 (1978); http://dx.doi.org/10.1063/1.324597 (7 pages) | Cited 31 times

Online Publication Date: 12 August 2008

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Crystalline properties of Ne+‐implanted garnet films with varying implantation energies and dosages have been studied by means of the double‐crystal x‐ray‐diffraction method, and it was found that when implantation‐induced damage was low, Pendellösung interference was observed which is directly related to crystal perfection, and a layer with large microscopic strain was found to become amorphous. The damage profiles were determined by measuring changes in x‐ray rocking curves after etching the implanted layers. Based on these experimental results, an implanted layer model was derived. The influences of the crystalline properties on the magnetic properties were also investigated from the viewpoints of the flux keeper and hard‐bubble‐suppression effects. For high implantation dosage the amorphous layer becomes magnetically inactive. This phenomenon is ascribed to randomly oriented micro‐magnetic‐domains with zero net magnetization caused by large microscopic strain in the amorphous layer. The effect of annealing is also discussed.
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61.72.U- Doping and impurity implantation
61.05.C- X-ray diffraction and scattering
75.70.Kw Domain structure (including magnetic bubbles and vortices)

Crystal structure and compression of ruby to 46 kbar

Larry W. Finger and Robert M. Hazen

J. Appl. Phys. 49, 5823 (1978); http://dx.doi.org/10.1063/1.324598 (4 pages) | Cited 50 times

Online Publication Date: 12 August 2008

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Crystal structures and lattice constants have been determined for ruby at hydrostatic pressures up to 46 kbar using a gasketed opposed‐anvil diamond cell on a four‐circle diffractometer. The measured compressibility is slightly anisotropic, having a value of 1.36±0.03×10−4 kbar−1 parallel to c and 1.22±0.03×10−4 kbar−1 perpendicular to c. If a Birch‐Murnaghan equation of state is used and K′0 is assumed to be 4, the isothermal bulk modulus is 2.57±0.06 Mbar. Refined atomic coordinates do not change with pressure; therefore, the structure compresses in a uniform manner. This study demonstrates that crystal structures may be determined at high pressure on single crystals with a precision approaching that of room‐pressure results.
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61.66.Fn Inorganic compounds
62.50.-p High-pressure effects in solids and liquids

The redistribution of implanted dopants after metal‐silicide formation

M. Wittmer and T. E. Seidel

J. Appl. Phys. 49, 5827 (1978); http://dx.doi.org/10.1063/1.324599 (8 pages) | Cited 61 times

Online Publication Date: 12 August 2008

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The redistribution of implanted As and Sb following metal‐silicide formation of Pt, Pd, and Ni has been studied. The phases of the silicides used were PtSi, Pd2Si, and NiSi. Investigations with Rutherford backscattering analysis showed that after the formation of the silicides, the Sb was always found in the silicide layer near the surface of the samples, whereas PtSi and Pd2Si caused a partial rejection of As for implanted doses of 2×1015 cm−2 and higher. No rejection of As was found after the formation of NiSi. The results are discussed in terms of solid solubilities and impurity‐metal compound formation. The data presented has implications in the fabrication of Ohmic contacts and the adjustments of the heights of Schottky barriers on silicon.
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61.72.U- Doping and impurity implantation
85.30.Hi Surface barrier, boundary, and point contact devices
61.80.Jh Ion radiation effects
66.30.J- Diffusion of impurities

Distorted twisted nematic liquid‐crystal structures in zero field

T. J. Scheffer

J. Appl. Phys. 49, 5835 (1978); http://dx.doi.org/10.1063/1.324600 (8 pages) | Cited 8 times

Online Publication Date: 12 August 2008

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Leslie’s differential equations describing the orientation of the optic axis through a twisted nematic layer are solved for the case where there is a nonzero tilt bias angle. Three classes of solutions are investigated: the simple solution of constant tilt angle through the layer with uniform twist, symmetric solutions where the tilt angle in the middle of the layer has an extreme value, and antisymmetric solutions where the tilt angle in the middle of the layer is identically zero. These solutions and their corresponding elastic deformation energies are compared for typical values of the splay, twist, and bend elastic constants of nematic liquid crystals. For 90° twisted nematic layers the antisymmetric solution always has a higher elastic energy than the symmetric solution. This result explains why regions of reverse twist are suppressed in twisted nematic display devices which have finite tilt bias angles at both boundaries. Reverse‐twisted domains can also be avoided by adding chiral dopants to the nematic mixture and by making layers having total twist angles of less than 90°. The effectiveness of these three techniques is discussed in terms of a comparison of the elastic energy difference between the oppositely twisted configurations.
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61.30.Cz Molecular and microscopic models and theories of liquid crystal structure
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order

Surface inhomogeneities on arsenic‐implanted silicon

R. Vale and P. S. Dobson

J. Appl. Phys. 49, 5843 (1978); http://dx.doi.org/10.1063/1.324601 (3 pages)

Online Publication Date: 12 August 2008

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Patterns have been observed on the surfaces of silicon epitaxial layers grown on annealed‐silicon substrates which had been implanted with arsenic at high doses and high dose rates. The patterns take the form of bands which lie parallel to the scanning direction of the ion beam and which contain a large density of pits. X‐ray topography reveals that the bands are present immediately after the slice had been annealed and the band contrast is sensitive to the diffraction conditions employed. Transmission electron microscopy shows that the bands contain a high density of dislocation loops, as well as the pits which always contain a small precipitate at their center. These results are discussed in terms of temperature variations in the slice during the implantation process which lead to inhomogeneities in the damage and impurity distribution.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.U- Doping and impurity implantation

Pulse charging of nanofarad capacitors from the shock depoling of PZT 56/44 and PZT 95/5 ferroelectric ceramics

Willis Mock and William H. Holt

J. Appl. Phys. 49, 5846 (1978); http://dx.doi.org/10.1063/1.324602 (9 pages) | Cited 8 times

Online Publication Date: 12 August 2008

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Gas‐gun impact techniques have been used to pulse charge nanofarad capacitors from the shock depoling of PZT 56/44 and PZT 95/5 ferroelectric ceramics. The PZT materials were depoled in the normal mode. Pulse powers of hundreds of kilowatts were produced in a few microseconds. The PZT 56/44 material was impacted in the stress range from 4.4 to 11.8 GPa. A maximum load voltage of 55 kV was produced at 7.9 GPa, resulting in a charge release of about 78%. Shock‐induced electrical breakdown in the PZT material occurred at 11.8 GPa. The PZT 95/5 material was impacted at 1.4 and 2.9 GPa stress levels. A maximum load voltage of 81 kV was produced at the higher stress, resulting in a charge release of about 74% before electrical breakdown occurred in the PZT material.
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62.50.-p High-pressure effects in solids and liquids
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ej Polarization and depolarization
77.22.Jp Dielectric breakdown and space-charge effects

The viscosity and structural relaxation rate of evaporated amorphous selenium

R. B. Stephens

J. Appl. Phys. 49, 5855 (1978); http://dx.doi.org/10.1063/1.324603 (10 pages) | Cited 52 times

Online Publication Date: 12 August 2008

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Certain properties of vacuum‐deposited thin films of a‐Se were measured and compared with those of melt‐quenched Se glass. After annealing in the temperature range 25–50 °C, the creep, heat capacities, and far‐infrared behaviors of the vapor‐deposited films were indistinguishable from those of melt‐quenched specimens. The shear‐viscosity η measurements on the films were extended into a temperature range well below that where such data on melt‐quenched samples are available. Over this temperature range, 25–35 °C, the T dependence of η of the equilibrated films was well fit by an Arrhenius relation with an activation energy of 130 kcal/mole. The stress and thermal‐relaxation rates for annealed films were also measured as functions of T. They are controlled by different sets of relaxation processes and are not directly proportional to the equilibrium η. However, they are in good agreement with each other, except that the thermal‐relaxation times are more widely dispersed over a span of about two orders of magnitude. The isothermal relaxation of the films to their equilibrium creep rates, though not a simple exponential decay with a single time constant, can be simply described by a relaxation time τ (t), which is proportional to the instantaneous viscosity η (t). As deposited, the films exhibited glass‐transition temperatures as much as 10 °C below those of annealed films. Also they showed a broad exothermic peak at about 50 °C. These results, on annealed and as‐deposited films, are consistent with the hypothesis that the various molecular constituents, presumably eight‐membered rings and polymeric chains of a‐Se, readily interconvert to an equilibrium distribution at temperatures as low as 30 °C. This distribution is temperature dependent and the same in vapor‐deposited and melt‐quenched a‐Se.
Show PACS
62.20.Hg Creep
65.40.-b Thermal properties of crystalline solids
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
81.05.Kf Glasses (including metallic glasses)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
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