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Journal of Applied Physics

Issue 5 • Date Mar 1986

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Displaying Results 1 - 25 of 69
  • On the motion of dust particles in a gas

    Page(s): 1415 - 1417
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    It is pointed out that the use of the usual equations relating to particle motion in a gas in the presence of diffusion and drift can lead to certain paradoxes. Modified equations are derived which resolve these paradoxes and which (among other things) lead to a modification in the form of the equilibrium distribution for particles in a gravitational field. This modification becomes of importance when the particle sedimentation velocity approaches its thermal velocity. View full abstract»

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  • Some considerations on the electric field induced in insulators by electron bombardment

    Page(s): 1418 - 1430
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    Starting from a simple model of the distributions of charge created in an insulator by bombardment with electrons, the components of the electric field are evaluated by using Maxwell’s equations and image effects. The results are applied to the most common experimental situations: a semi‐infinite sample (i) bounded by a vacuum or (ii) covered by a conducting film, and a sample in the form of a film (iii) unsupported or (iv) covering a conducting substrate. The results are compared to some experimental data concerning, for instance, electromigration and electron‐stimulated desorption. In surface analysis the decay of the Auger signal from ions of opposite charges and the opposite behavior of ions of the same charge are explained. Similar effects observed in electron‐probe microanalysis of glasses are also elucidated. The results concern scanning electron microscopy, transmission electron microscopy, and electron‐beam lithography applied to biological objects, polymers, ceramics, minerals, glasses, and electronic devices. With slight modifications, the same model can be applied to cases of irradiation with ions or x rays. The evolution of the trapped charges with time is suggested, and the need to indicate the electric parameters (ϵ and γ) of the investigated samples is outlined. View full abstract»

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  • Spectroscopy of tetracene submonolayers using phonon emission

    Page(s): 1431 - 1434
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    A new technique for the optical spectroscopy of adsorbed molecules is introduced. It is based on the detection of the phonons emitted during nonradiative relaxation. A high sensitivity was achieved by using superconducting tunnel junctions as detectors. A light power of the order of 1 μW was sufficient for the spectroscopy of submonolayers of tetracene. Molecules deposited on a cold substrate had a spectrum similar to the one of isolated molecules in a solvent. Deposition, or annealing, at room temperature, however, yielded spectra like those of single crystals. View full abstract»

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  • ArF short‐pulse extraction studies

    Page(s): 1435 - 1445
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    A series of measurements characterizing an e‐beam pumped ArF* laser was carried out using a 200‐ns e‐beam pulse having a rise time of 25 ns at currents up to 50 A/cm2. These pump conditions are relevant for inertial confinement fusion laser drivers. Intrinsic laser efficiencies up to 7.7% and power efficiencies up to 10% were observed. At high pressures (2 atm≪P≪5 atm) F2/Ar/Ne mixtures performed significantly better than F2/Ar mixtures. Absorption measurements were performed in Ne‐buffered mixtures as a function of pressure, wavelength, and time. It appears that the background absorption peaks at a wavelength of 220 nm and is significantly smaller near 193 nm. View full abstract»

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  • Fabrication of high‐purity chalcogenide glasses by chemical vapor deposition

    Page(s): 1446 - 1449
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    High‐purity Ge–Se chalcogenide glasses were fabricated using chemical vapor deposition. Gas‐phase GeCl4 and SeCl2 were used together with H2 for the reaction. High transparency was observed over a wide IR region of 2–10 μm. In addition, it is reported that heat treatment under NH3 and CO gas flow has been found to be effective for eliminating oxygen impurities. Using this technique, the oxygen content was reduced to below 1 wt. ppm. These glass compounds are applicable for infrared‐transmitting windows as well as infrared optical fibers. View full abstract»

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  • Teflon‐clad As‐S glass infrared fiber with low‐absorption loss

    Page(s): 1450 - 1452
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    An As‐S glass fiber with Teflon Fluorinated Ethylene Propylene (FEP) cladding has been fabricated. The transmission range of this fiber was 1–7 μm with two pronounced absorption peaks at 2.8 and 4.1 μm. It was found that these absorptions were caused by moisture adsorbed on the surface of the As‐S glass as well as the hydrogen impurity due to the silica ampule. By removing these impurities the absorption loss was reduced and a minimum optical loss of 0.15 dB/m was obtained for this infrared fiber. View full abstract»

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  • Anisotropic optical scatter from moisture patches in thin films deposited obliquely

    Page(s): 1453 - 1455
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    Moisture adsorption patches in magnesium‐fluoride spacer layers of metal‐dielectric‐metal interference filters deposited obliquely are known to possess elliptical symmetry. The spatial distribution of light scattered from these patches at normal incidence is shown to exhibit the same elliptical symmetry with the major and minor axes interchanged. View full abstract»

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  • Causality and the Keller approximation for acoustic waves

    Page(s): 1456 - 1457
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    A method is presented for specifying the physically meaningful high‐frequency wave velocity (the geometric limit) in the context of the Keller approximation, which describes wave propagation in a weakly inhomogeneous medium. The root regularly chosen is shown to violate causality of the coherent wave. View full abstract»

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  • Third harmonic generation of p‐polarized laser radiation in an inhomogeneous laser‐produced plasma

    Page(s): 1458 - 1465
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    In this paper, we have made a theoretical investigation of third harmonic generation from intense p‐polarized laser radiation in an inhomogeneous laser‐produced plasma. The fluid equations have been employed to obtain the nonlinear response of the plasma electrons. The power conversion efficiency of the generated third harmonic wave depends drastically on the scale length of the plasma inhomogeneity and the angle of incidence of the laser radiation with the density gradient of the plasma. View full abstract»

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  • Axial structure of a plasma column produced by a large‐amplitude electromagnetic surface wave

    Page(s): 1466 - 1472
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    Electromagnetic surface waves in the rf and microwave frequency range can be used to produce long large/small‐diameter plasma columns. We propose a theory of surface‐wave‐produced plasmas at two different low‐pressure gas‐discharge regimes, diffusion and recombination, respectively. For a given regime the axial plasma density profile is specified by two quantities: a numerical parameter σ=ωR/c (ω being the wave frequency, R the tube radius, and c denoting the speed of light) and the collision frequency ν (ν≪ω). Our theory predicts the magnitude of the axial electron number density gradient. The very good agreement between the experimentally measured plasma density gradients and the theoretically calculated ones for diffusion‐controlled surface‐wave‐produced plasma columns confirms the adequacy of the proposed model. View full abstract»

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  • Intense magnetization generated by standing waves in a plasma

    Page(s): 1473 - 1476
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    Nonlinear increments of displacements of electrons in a cold unmagnetized electron plasma due to two strong elliptically polarized electromagnetic waves have been studied. These results have been used to find the induced magnetization due to standing waves formed by the two counterpropagating elliptically polarized electromagnetic waves. The induced magnetization has been found to be strong enough for interest in the investigation of laser‐plasma interaction. For an Nd‐glass laser (λ=1.06 μm, power flux∼1016 W/cm2) interacting with a plasma (N∼1017/cm3), the induced magnetic field is found to be in the megagauss region. The principal effect of the high magnetic field is on the electron thermal conduction. The heat transport is inhibited due to the generated field. View full abstract»

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  • Characterization of disorder and annealing behavior of Si‐implanted Ga1-xAlx As with laser Raman spectroscopy

    Page(s): 1477 - 1481
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    Effects of aluminum in Ga1-xAlx As on damage introduced by Si implantation and annealing behavior were studied based on Raman spectra. Increase in aluminum content suppresses the introduction of damage. However, aluminum in Ga1-xAlxAs reduced the concentration of Si in lattice site after annealing. View full abstract»

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  • Direct evidence for an order/disorder phase transition at x≂0.3 in single‐crystal metastable (GaSb)(1-x)(Ge2)x alloys: High‐resolution x‐ray diffraction measurements

    Page(s): 1482 - 1487
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    High‐resolution triple‐crystal x‐ray diffractometry has been used to investigate long‐range order in single‐crystal (100)‐oriented metastable (GaSb)(1-x)(Ge2)x alloys. Measurements of the integrated intensities of superstructure and fundamental reflections provide the first direct evidence of an order/disorder, zinc blende to diamond, structural transition in (III‐V)(1-x)(IV2) x alloys. The transition in (GaSb)(1-x)(Ge2)x was found to occur at x≂0.3. The long‐range order parameter S and the probability r that a Ga or Sb atom will occupy a site on its corresponding sublattice were determined as a function of composition from the normalized ratio of the integrated intensities of the (200) superstructure to the (400) fundamental reflections. S(x), which is unity for pure zinc blende structure GaSb, initially decreased slowly with increasing Ge concentration, but decreased ever more rapidly as x approached 0.3. S(x) was essentially zero for alloys with x≫0.3, indicating a ‘‘disordered’’ diamond structure. Correspondingly, r decreased from 1 at x=0 to 0.5 at x≥0.3. View full abstract»

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  • Real‐time measurement of crystallization process of polymers by pulsed nuclear magnetic resonance

    Page(s): 1488 - 1492
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    Real‐time measurement of the crystallization process of polymers [poly(ϵ‐caprolactone) and its blend with poly(vinyl methyl ether) and polystyrene] by pulsed nuclear magnetic resonance has been made. The measurements on both the spin‐spin relaxation time T2 and the spin‐lattice relaxation time in the rotating frame T 1 ρ have been performed for the first time. From the data, we can obtain information on the temporal change of the crystallinity as well as the change of the mobility in each phase. Furthermore, the temporal change of the intermediate phase corresponding to the interface between crystalline and amorphous part has been successfully detected. View full abstract»

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  • Contribution of small dislocation loops to the precursor decay of a longitudinal plane pulse

    Page(s): 1493 - 1499
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    The precursor decay relation in plate impact experiments by a longitudinal wave is studied on the basis of the elastodynamics of dislocations. The material is modeled as an elastic continuum containing a distribution of dislocation loops. The waves radiated from the dislocations as they are hit by the incident wave result in the decay of the latter at the wave front. The response of the instruments is considered finite, so that the decay is calculated at a time Δt behind the front. The loops are assumed small, i.e., of radius α0∼0 (c1Δt) so that the wavelets emanated from the whole loop have the time to contribute to the decay. The loops are assumed to lie on a plane which makes an angle with the direction of propagation of the incident front and they are set in motion of uniform radial expansion by the incident front. The fundamental solution from each loop is obtained asymptotically and the precursor decay is obtained by superposition of all the loops that had the time to contribute. The obtained precursor decay relation is a modified Orowan’s relation since it is of the same form as that obtained by using Orowan’s formula but with a correction factor which depends on the dislocation velocity and configuration (curvature and orientation). View full abstract»

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  • Atomic migration and surface evaporation of Hg in Hg1-x CdxTe crystals observed by 40‐MeV O5+ ion backscattering method

    Page(s): 1500 - 1503
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    Dissociation and evaporation of Hg from the near‐surface region of Hg1-xCdxTe crystals was investigated, up to several microns, by means of 40‐MeV O5+ backscattering. Samples with x=0.18 and 0.32 were heat treated in a vacuum for 60 min at various temperatures up to 320 and 340 °C, respectively. The change of the backscattering spectra with the temperature of heat treatment indicated that the Hg atoms outdiffused partly from the near‐surface region of the crystals at higher temperatures than 280 and 320 °C for x=0.18 and 0.32, respectively. This behavior of outdiffusion is in contrast to the case of HgTe crystal. View full abstract»

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  • The effect of interface roughness on the intensity profiles of Bragg peaks from superlattices

    Page(s): 1504 - 1507
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    We have derived an expression for the structure factor of a superlattice with ‘‘rough’’ interfaces, i.e., with random variations in the thicknesses of the layers. Our expression allows the determination of x‐ray diffraction profiles in both radial (θ‐2θ) and rocking scans. We have shown that the rocking curve of the central peak is essentially unaffected by this kind of disorder; and we have calculated the rocking curve widths of the satellites as a function of roughness. The implications of our model for the use of satellite/central peak intensity ratios as a measure of superlattice perfection are discussed. View full abstract»

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  • Properties of AlxGa1-xAs (xAl≂0.3) grown by molecular‐beam epitaxy on misoriented substrates

    Page(s): 1508 - 1512
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    The effects of substrate misorientation on the morphological and optical properties of AlxGa1-xAs (xAl≂0.3) grown by molecular‐beam epitaxy (MBE) have been studied. The substrate temperatures and V/III beam‐flux ratios used were such that layers grown on nominally (100) substrates typically exhibited rough morphologies and poor 4.2 K PL characteristics. By intentionally misorienting the substrate slightly from (100), smooth layers can be grown at 620 and 650 °C at typical MBE growth rates (≂1 μm/h). These smooth layers also exhibited sharp, exciton‐related emission peaks at 4.2 K with half‐widths as narrow as 5 meV. Since rough surfaces may lead to poor interfaces between GaAs and (Al,Ga)As and in turn to degraded performance in heterojunction devices, the present results may have significant implications for the performance of such structures grown by MBE. View full abstract»

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  • Channeling dependence of ion‐beam‐induced epitaxial recrystallization in silicon

    Page(s): 1513 - 1517
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    Buried amorphous layers in silicon, formed by self‐ion‐implantation, have been regrown using 300‐keV neon and nitrogen ion beams in the temperature range 200–400 °C. When the beams were aligned with the 〈100〉 axis in the crystal, the regrowth rate at the shallower amorphous/crystalline interface was reduced, while the deeper regrowth front proceeded with the same rate as that for a random beam direction. The observed channeling effect is attributed to a decreased nuclear energy deposition for the channeled ions, which suggests that the annealing mechanism involves point‐defect migration in the crystalline material. View full abstract»

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  • Localized epitaxial growth of MoSi2 on silicon

    Page(s): 1518 - 1524
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    Epitaxial tetragonal and hexagonal MoSi2 (t‐MoSi2 and h‐MoSi2) were grown locally in (001), (111), and (011)Si. Five different epitaxial modes, referring to sets of definite orientation relationships between silicides and the substrate Si, were identified for t‐MoSi2, whereas three distinct modes were found for h‐MoSi2. Variants of epitaxy, required by the symmetry consideration, were also observed. It is conceived that ample thermal energy was supplied during high‐temperature annealings to cause various modes of epitaxy which presumably correspond to low‐energy states that occur. The reactive nature of the silicide formation is suggested to facilitate the growth of epitaxial silicides on silicon. View full abstract»

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  • Variation of the nucleated products in ultrathin films of Ti‐Co on Si substrates with processing changes

    Page(s): 1525 - 1535
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    The purpose of this study is to investigate solid‐state nucleation and growth in Ti/Co/Si and Co/Ti/Si thin‐film ternary systems, and to compare results under a variety of preparation conditions. The deposition methods used were rf sputtering and e‐beam evaporation. The nucleated compounds are determined by transmission electron microscopy and diffraction. CoTi2 is the first nucleated compound in the Ti/Co/Si ternary systems prepared by e‐beam evaporation irrespective of substrate temperature, thickness, or other factors. This is in contrast to the films produced by rf sputtering where this phase was not observed. Experimental findings also show that in thin‐film ternary systems, the first‐phase nucleation temperature and subsequent compounds could be altered as the intermediate metal layer becomes less than 20 Å. This is an indication that interference between interfaces begins to play a significant role at about this thickness, so that the reaction paths and the first nucleated phases are determined not only by internal binary kinetics, but also by intermediate transition metal layer restrictions in the interfacial region. In addition, a phase previously reported on Ti/Si system was also found in the Ti/Co/Si and Co/Ti/Si systems, and is labeled the (TiSi)N (metastable) phase. This phase occurs in the form of coherent precipitates of a nonequilibrium metastable structure. View full abstract»

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  • A study of deep levels by transient spectroscopy on p‐type liquid‐phase‐epitaxial GaxIn1-xAsyP1-y grown on semi‐insulating InP

    Page(s): 1536 - 1543
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    p‐type layers of InP, Ga0.28In0.72As0.6P0.4 (λ=1.3 μm) and Ga0.47In0.53As (λ=1.65 μm) grown by liquid ‐phase epitaxy on semi‐insulating InP:Fe substrates have been investigated by deep level transient spectroscopy. In InP, we have found near the surface a majority‐carrier trap which is located at 0.22 eV above the top of the valence band. A very similar trap (capture cross section and energy) appears with about the same concentration in the quaternary layer but is not present in the ternary layer. Thus, we suggest that this trap could be related to the phosphorus sublattice (e.g., a complex, a vacancy, or a substitutional impurity), caused by a phosphorus depletion produced at the end of the epilayer growth. Other traps have been found in quaternary and ternary layers but are not identified. View full abstract»

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  • S‐vacancy energy levels in AgInS2

    Page(s): 1544 - 1547
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    A luminescence study of energy levels due to lattice defects in AgInS2, which belongs to the I‐III‐VI2 compounds, is reported in this article. As‐grown and annealed crystals under maximum or minimum sulfur pressure have been used. We have found a donor level at 70 meV, an acceptor level at 70 meV, and a level (acceptor or donor) at 100 meV. Two of these levels (at least) are attributed to the sulfur vacancy. View full abstract»

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  • Thermally stimulated current in p‐type CuInSe2 thin films

    Page(s): 1548 - 1551
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    We observe a strong thermally stimulated current (TSC) in p‐type CuInSe2 thin films at temperatures from 100 to 350 K. Annealing in air appears to passivate this TSC activity. The passivation is reversible, and the spectra may be partially recovered by reduction. We attribute the three dominant TSC structures to three energy levels, 35, 45, and 100 meV, and we believe that they are associated with intrinsic defects, i.e., vacancies and antisites which are also observed in photoluminescence. We identify oxygen compensation of donors as the cause of the improved transport in CuInSe2 after air annealing. View full abstract»

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  • Transport properties of high purity, polycrystalline titanium diboride

    Page(s): 1552 - 1556
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    Thermal conductivity data for several TiB2 samples are presented and the results for one sample extend from 80 to 400 K. These results show that the thermal conductivity attains a maximum value of about 130 W/m K at 140 K. An analysis of the results shows that this is caused by the electronic component of the thermal conductivity and that phonon conduction is also probably significant. Seebeck coefficient values agreed with the results of previous studies. The electrical resistivity of one sample was also determined to 1800 K. These results can be described by the Bloch–Grüneisen equation if the effect of thermal expansion is included. View full abstract»

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Aims & Scope

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

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Editor
P. James Viccaro
Argonne National Laboratory