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1 Dec 1985

Volume 58, Issue 11, pp. 3947-4483

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An electromagnetic microscopic positioning device for the scanning tunneling microscope

B. W. Corb, M. Ringger, and H.‐J. Güntherodt

J. Appl. Phys. 58, 3947 (1985); http://dx.doi.org/10.1063/1.335568 (7 pages) | Cited 17 times

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We have developed a device that is capable of moving with steps as small as 70 Å in any direction over a flat surface. The device that we call the Maggot consists of two permanent magnets attached to the corners of a triangular plate that stands on a flat base with three fixed ball‐bearing feet. The Maggot is propelled across the base by the magnetic fields from two coils that are powered by computer‐controlled current pulses. Steering of the Maggot is made by vector addition of the pulses by the computer. A complete electromagnetic force theory is given in order to find the best magnet and solenoid geometries for maximum performance. The Maggot is UHV compatible, operates from 500 to 4.2 °K, and is most suitable for operation on a vibration‐isolated base. Movement data is measured with both optical and scanning tunneling microscopy.
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06.60.Sx Positioning and alignment; manipulating, remote handling
41.20.Gz Magnetostatics; magnetic shielding, magnetic induction, boundary-value problems
85.70.-w Magnetic devices
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Density sensitive x‐ray line ratios in the Be i, B i, and Ne i isoelectronic sequences

U. Feldman, J. F. Seely, and A. K. Bhatia

J. Appl. Phys. 58, 3954 (1985); http://dx.doi.org/10.1063/1.335569 (5 pages) | Cited 16 times

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The intensities of x‐ray transitions in highly charged ions in the Be i, B i, and Ne i isoelectronic sequences have been calculated as functions of electron density. The intensities of the transitions from the 2sn 2pm 3p configuration, relative to the intensities from the 2sn 2pm 3s and 2sn pm 3d configurations, are strong functions of electron density in high‐density plasmas. The density sensitivity occurs at electron densities between 1016 cm−3 (for Si ions) and 1022 cm−3 (for Kr ions). Opacity is unimportant for plasma dimensions that are characteristic of dense laser‐produced plasmas. These x‐ray line ratios represent a promising new density diagnostic for high‐density plasmas.
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32.30.Rj X-ray spectra
32.70.-n Intensities and shapes of atomic spectral lines
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.La X-ray and γ-ray measurements

Laser optoacoustic measurement of homogeneous linewidth and pump saturation intensity in a CH3I molecule

Ho Seong Lee, Hong Jin Kong, and Sang Soo Lee

J. Appl. Phys. 58, 3959 (1985); http://dx.doi.org/10.1063/1.335570 (4 pages)

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Optoacoustic measurement of the absorption line shape is carried out for the determination of the homogeneous linewidths and the saturation intensities of a CH3I molecule for a 10‐μm P(32) CO2 laser line. By fitting the numerically calculated Voigt function to the experimentally obtained absorption line shape, we find two absorption lines separated by 90 MHz. The measurement of the pressure dependence of the homogeneous linewidth at pressures lower than 0.8 Torr shows that the rate of increase of the homogeneous linewidth is not linear but larger at lower pressure than that at higher pressure. The natural linewidth of 12 MHz is obtained by extrapolating the experimentally obtained linewidth curve toward zero pressure, and also the pump saturation intensities at the line centers of the CH3I absorption line and CO2 laser line are found to be 1.0 and 2.5 W/cm2, respectively.
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07.77.-n Atomic, molecular, and charged-particle sources and detectors
37.20.+j Atomic and molecular beam sources and techniques
33.20.Ea Infrared spectra
33.70.Jg Line and band widths, shapes, and shifts
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques

Surface‐wave propagation along the boundary between sea water and one‐dimensionally anisotropic rock

Wei‐Yan Pan

J. Appl. Phys. 58, 3963 (1985); http://dx.doi.org/10.1063/1.335571 (12 pages) | Cited 10 times

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New formulas for the components of the electromagnetic surface wave propagating along the boundary between sea water (Region 1) and a one‐dimensionally anisotropic rock (Region 2) have been obtained. The conductivity of the rock is taken to be σx=σy=σT, σz=σL, where z is perpendicular to the boundary. Both σL and σT are constant. When σL=σT, the new formulas coincide with those of Wu and King [Radio Sci. 17, 521, 532 (1982); J. Appl. Phys. 54, 507 (1983)] for an isotropic medium. When σL≠σT, the lateral‐wave part of the field is separated into two terms of which the first is of electric type with the wave number k2=kL, and the second is of magnetic type with k2=kT. The new formulas can be used to interpret recent measurements of the oceanic crust.
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03.50.De Classical electromagnetism, Maxwell equations
41.20.Jb Electromagnetic wave propagation; radiowave propagation
92.10.-c Physical oceanography
91.50.Ey Seafloor morphology, geology, and geophysics

Effect of SF6 fluorine donor on the multikilojoule HF chemical laser initiated longitudinally by intense electron beams

Tomoo Fujioka, Fumihiko Kannari, Tadashi Suzuki, and Minoru Obara

J. Appl. Phys. 58, 3975 (1985); http://dx.doi.org/10.1063/1.335572 (9 pages) | Cited 10 times

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The effects of fluorine donor additives and initiation level on the HF laser output characteristics in a strong and short pulse initiation regime are experimentally and theoretically investigated. Typical parameters of the circular e beam used in the experiment are 2 MV, 60 kA, 65 ns FWHM, and 10 cm in diameter, and the e beam is injected longitudinally. The addition of SF6 gas to a mixture of F2/O2/H2 is found to increase not only the specific laser energy but also the electrical laser efficiency. The maximum laser energy obtained from the low‐pressure mixture of F2/SF6/O2/H2=200/84/60/45 (Torr) is 4.4 kJ in a 70 ns FWHM with an electrical laser efficiency of 203% and a chemical laser efficiency of 18.6%. Based on the experimental results, the scaling of the HF laser was established in terms of specific HF laser energy and electrical laser efficiency.
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42.55.Ks Chemical lasers
42.55.Lt Gas lasers including excimer and metal-vapor lasers
78.60.Ps Chemiluminescence

Effect of resonance excitation due to dielectronic capture on the gain coefficients of selected transitions in Fe XVII

G. A. Doschek, U. Feldman, and J. F. Seely

J. Appl. Phys. 58, 3984 (1985); http://dx.doi.org/10.1063/1.335573 (3 pages) | Cited 7 times

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In previous papers, U. Feldman, J. F. Seely, and A. K. Bhatia [J. Appl. Phys. 56, 2475 (1984)] and A. K. Bhatia, U. Feldman, and J. F. Seely [At. Data Nucl. Data Tables (in press)] have calculated atomic data and gain coefficients for ions of the Ne I isoelectronic sequence. Their calculations of electron impact excitation rates were carried out in the distorted wave approximation. They did not include the effect of resonance excitation, i.e., dielectronic capture by a Ne‐like ion followed by autoionization leaving the Ne‐like ion in an excited state. In this paper, we use the recent calculations of this process by B. W. Smith, J. C. Raymond, J. B. Mann, and R. D. Cowan [Astrophys. J. (in press)] to explore the effect of resonance excitation on gain coefficient calculations for the ion Fe XVII. We find substantial differences (factors of about 1.3–3) between gain coefficient calculations with and without the inclusion of resonances at low temperatures. However, these effects are not important at the temperatures considered by Feldman, Seely, and Bhatia for Fe XVII.
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34.80.Dp Atomic excitation and ionization
32.80.Zb Autoionization
32.70.-n Intensities and shapes of atomic spectral lines
42.55.Ah General laser theory

Experimental observation of unstable resonator mode evolution in a high‐power KrF laser

Shingo Izawa, Akira Suda, and Minoru Obara

J. Appl. Phys. 58, 3987 (1985); http://dx.doi.org/10.1063/1.335574 (4 pages) | Cited 6 times

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For a pulsed high‐power laser with unstable resonator, the mode evolution time is important from the viewpoints of beam focusability and laser‐energy usefulness. We observed temporal and spatial behavior of the mode evolution in a several‐tens‐joule KrF laser with a positive branch confocal unstable resonator, which is pumped by electron beams with a pulse width of 65 ns (FWHM). The beam divergence angle was decreased by a factor of 1/M2 (M:magnification) per round trip in the resonator and resulted in a full angle divergence of 0.6 mrad.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Improved performance of a closed‐cycle self‐sustained discharge‐excited cw CO laser

Shun‐ichi Sato, Mamoru Kiyota, Tomoo Fujioka, and Hideaki Saito

J. Appl. Phys. 58, 3991 (1985); http://dx.doi.org/10.1063/1.335575 (5 pages) | Cited 7 times

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Detailed performance characteristics of a closed‐cycle subsonic cw CO laser excited by a transverse self‐sustained dc glow discharge are described. Using an electrode configuration which consists of a hollow‐type cathode and a planar anode, the discharge characteristics have been measured under various gas conditions. The measurements show that the discharge instability, and hence the available discharge input, are strongly influenced not only by gas temperature and total static pressure but also by gas composition. From a discharge volume of about 480 cm3, a laser output power of 406 W is extracted with an electrical conversion efficiency of 11.6% for a mixture of CO/N2/He/O2=6/16/78/0.19 at an entrance gas temperature of 156 K. Furthermore, by applying an additional cathode array, the discharge uniformity and the specific input energy have been enhanced. As a result, the maximum extracted laser output reaches as high as 729 W or 1820 W per m of discharge length, with the corresponding conversion efficiency and specific output energy of 16.3% and 125 J/g, respectively. This performance is comparable to or higher than that which has been obtained with an electron‐beam controlled discharge, a pulser‐sustained discharge, etc.
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42.55.Lt Gas lasers including excimer and metal-vapor lasers
42.60.By Design of specific laser systems
52.80.Hc Glow; corona

Catastrophic degradation of InGaAsP/InGaP double‐heterostructure lasers grown on (001) GaAs substrates by liquid‐phase epitaxy

Osamu Ueda, Kiyohide Wakao, Satoshi Komiya, Akio Yamaguchi, Shoji Isozumi, and Itsuo Umebu

J. Appl. Phys. 58, 3996 (1985); http://dx.doi.org/10.1063/1.335576 (7 pages) | Cited 20 times

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Catastrophically degraded InGaAsP/InGaP double‐heterostructure lasers grown on (001) GaAs substrates by liquid‐phase epitaxy, emitting at 727 and 810 nm are investigated by photoluminescence topography, scanning electron microscopy, transmission electron microscopy, and energy dispersive x‐ray spectroscopy. The degradation is mainly due to catastrophic optical damage at the facet, i.e., development of 〈110〉 dark‐line defects from the facet, and rarely due to catastrophic optical damage at some defects, i.e., development of 〈110〉 dark‐line defects from the defects inside the stripe region. These 〈110〉 dark‐line defects correspond to complicated dislocation networks connected with dark knots, and are quite similar to those observed in catastrophically degraded GaAlAs/GaAs double‐heterostructure lasers. The degradation characteristics of the InGaAsP/InGaP double‐heterostructure lasers are rather similar to those in GaAlAs/GaAs double‐heterostructure lasers concerning the catastrophic degradation.
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42.55.Px Semiconductor lasers; laser diodes
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Effect of UV laser preionization on CO2‐laser‐induced optical breakdown

S. Yoshida, J. Sasaki, Y. Arai, and T. Uchiyama

J. Appl. Phys. 58, 4003 (1985); http://dx.doi.org/10.1063/1.335577 (3 pages) | Cited 1 time

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The effect of UV preionization by a KrF laser on CO2‐laser‐induced optical breakdown is studied experimentally. The electron number density as well as the breakdown probability is measured as a function of KrF‐laser energy. The results show that the KrF‐laser preionization is quite effective in initiating the optical breakdown. Once a breakdown is initiated, however, the number of produced electrons is found to be independent of the KrF‐laser energy.
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42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.65.-k Nonlinear optics
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)
52.25.Mq Dielectric properties

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

Md. Salimullah and Md. Ruhul Amin

J. Appl. Phys. 58, 4006 (1985); http://dx.doi.org/10.1063/1.335578 (5 pages)

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In this paper, we have made a theoretical investigation of second harmonic generation from intense p‐polarized laser radiation in an inhomogeneous plasma. The fluid equations have been employed to obtain the nonlinear response of the plasma electrons. The power conversion efficiency of the generated second 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.
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52.38.-r Laser-plasma interactions
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Electron temperature and average density in spherical laser‐produced plasmas: Ultraviolet plasma spectroscopy

Samuel Goldsmith, J. F. Seely, U. Feldman, W. E. Behring, and Leonard Cohen

J. Appl. Phys. 58, 4011 (1985); http://dx.doi.org/10.1063/1.336288 (4 pages) | Cited 6 times

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The average values of the electron temperature Te and the electron density Ne in the corona plasmas of spherically irradiated high‐Z targets have been estimated. Targets composed of the elements Cu through Br, Rb, and Mo were irradiated using the fundamental (1.06 μm) and the frequency‐tripled (351 nm) output of the Omega laser system. Spectra were recorded in the wavelength region 15–200 Å. Using various extreme ultraviolet spectroscopic techniques, it is found that for the case of a Mo plasma produced by frequency‐tripled laser irradiation, Te=2600±600 eV and Ne>6×1020 cm−3. This is consistent with a ‘‘flux limit’’ smaller than 0.1. The estimated values of Te and Ne are lower in the corona plasmas produced using the fundamental (1.06 μm) irradiation.
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52.38.-r Laser-plasma interactions
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
32.30.Jc Visible and ultraviolet spectra

Dual channel formation in a laser‐triggered spark gap

M. J. Kushner, W. D. Kimura, D. H. Ford, and S. R. Byron

J. Appl. Phys. 58, 4015 (1985); http://dx.doi.org/10.1063/1.335579 (9 pages) | Cited 4 times

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During self‐break in spark‐gap switches, multiple streamers can form in close proximity to one another. The rate of expansion of these streamers is sufficiently fast that they can interact during the current pulse. To help understand how these closely spaced, expanding spark columns interact, a laser‐triggered spark gap has been studied in which two parallel columns (separation 1.3 mm) are simultaneously preionized, resulting in a pair of nearly identical, axisymmetric spark columns. The spark gap (electrode separation 1.2 cm) switches a 100 ns, 40–60 kV, 12‐20 kA, 1.5 Ω waterline. Interferograms of the expanding arc channels are obtained with a laser interferometer having a time and spatial resolution of 5 ns and 10 μm, respectively. Voltage and current were measured with an internal capacitive‐voltage divider and a current viewing resistor. The interferograms show that for initially identical axisymmetric columns, the individual channels do not merge into a single larger axisymmetric spark column. Instead, regions of high gas density remain inside the combined column long into the recovery period. The columns also do not remain axisymmetric as they grow, indicating a long‐range interaction between the channels. The voltage drop and resistance of the dual channel spark gaps changes by less than 15% from that of a single spark channel. A scaling model is presented to explain the resistance measurements and to predict the change in resistance for multichannel spark gaps.
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52.75.Kq Plasma switches (e.g., spark gaps)
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Distribution of ion energies incident on electrodes in capacitively coupled rf discharges

M. J. Kushner

J. Appl. Phys. 58, 4024 (1985); http://dx.doi.org/10.1063/1.335580 (8 pages) | Cited 117 times

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The energy and angular distribution of ions striking the electrodes in rf discharges are of interest with respect to the application of such discharges to the processing of semiconductor materials. The ability to fabricate small (< 1 μm) semiconductor features using the plasma etching process results, in part, from the energetic and anisotropic flux of ions which strike the semiconductor surface. In this paper the energy and angular distribution of ions striking the electrodes in low‐pressure capacitively coupled rf discharges are studied using a Monte Carlo model for ion trajectories and a parametric model for the time‐dependent electric field within the sheath. Energy and angular distributions are discussed as a function of rf frequency, ion mass, and the mean‐free path between charge exchange collisions within the sheath. The ion energy distribution is found to be characterized by a scaling parameter proportional to (rf frequency × sheath thickness)2 × ion mass/(sheath voltage); small values of this parameter yield bimodal distributions, intermediate values yield distributions peaked at the maximum sheath potential, and high values yield distributions peaked at the average sheath potential. The ion energy distribution is also examined for different values of the dc and rf components of the sheath potential and for different models for the electric field within the sheaths. When the dc component of the sheath potential is small compared to the rf amplitude, a large thermal component to the ion energy distribution results. The implication of this result and that for the angular distribution of ions incident on the electrodes is discussed with respect to the isotropy of the etch obtained during plasma etching of semiconductor materials.
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52.80.Pi High-frequency and RF discharges
52.40.Hf Plasma-material interactions; boundary layer effects
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
52.20.Dq Particle orbits

Ion trapping in the emitter sheath in thermionic converters

Lennart Lundgren

J. Appl. Phys. 58, 4032 (1985); http://dx.doi.org/10.1063/1.335581 (4 pages)

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The effect of ion trapping in the emitter sheath in ignited thermionic converters is studied. The ion trapping prevents the emitter‐sheath barrier from being higher than approximately 0.1 eV, when the current decreases in the converter. This gives a condition for the constriction of the arc. I‐V curves are calculated for an ignited thermionic converter with a hydrodynamic plasma theory that takes into account the effect of Coulomb scattering and volume recombination, but assumes that the electron temperature is constant in the plasma.
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52.75.Fk Magnetohydrodynamic generators and thermionic convertors; plasma diodes
52.40.Hf Plasma-material interactions; boundary layer effects
84.60.Rb Thermoelectric, electrogasdynamic and other direct energy conversion

Analysis of polycrystalline silicon diffusion sources by secondary ion mass spectrometry

H. Schaber, R. v. Criegern, and I. Weitzel

J. Appl. Phys. 58, 4036 (1985); http://dx.doi.org/10.1063/1.335582 (7 pages) | Cited 41 times

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Polycrystalline silicon diffusion sources have been analyzed using secondary ion mass spectrometry. Polysilicon films were grown by standard low‐pressure chemical vapor deposition and doped with As, P, or B by ion implantation. Although dopant segregation at the poly‐Si/single‐crystal‐silicon interface occurred and has been analyzed quantitatively, no diffusion barrier has been observed at this interface. Diffusion profiles in the single‐crystal substrate have been measured for diffusion temperatures between 800 and 1000 °C. It is shown by comparison to numerical simulations that these profiles obey standard diffusion theory. Proper boundary conditions to be used for such calculations are deduced for the different dopant species. Furthermore, the saturation concentration of boron in silicon over the temperature range given above has been reliably determined.
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66.30.J- Diffusion of impurities
61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.sm Impurity gradients
61.72.U- Doping and impurity implantation

Influence of P and As implantation of the formation of MoSi2

A. H. van Ommen and R. A. M. Wolters

J. Appl. Phys. 58, 4043 (1985); http://dx.doi.org/10.1063/1.335583 (6 pages) | Cited 5 times

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Molybdenum disilicide films have been formed by a reaction of Mo with polycrystalline silicon. Implantation of phosphorus or arsenic prior to reaction has been shown to have a large effect on the silicidation process. The object of implantation was to enhance the silicide reaction by creating damage at the metal‐silicon interface. This, then, results in silicide films with less surface roughness (and a lower electrical resistivity). Molecular P+2 ions were found to be more effective in creating damage than single P+ ions, due to the fact that for P+2 ions two simultaneous collision cascades occur which overlap. Apart from the beneficial effect of implantation damage, the introduction of phosphorus has a deleterious effect on the properties of the silicide films. This phenomenon is explained by the presence of a thin and nonuniform native oxide layer which hinders the silicide reaction. Without addition of phosphorus, new nuclei for the silicide reaction can be formed due to stress introduced by the formation of the silicide, which will act upon the oxide and cause it to break up at some weak spot. The effect of phosphorus is proposed to be that it renders the oxide more viscous which prevents this process from taking place. The x‐ray diffraction spectra revealed that the orientation of the grains in the polycrystalline MoSi2 films is influenced by the method of preparation.
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68.55.-a Thin film structure and morphology
61.80.Jh Ion radiation effects
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties
64.75.-g Phase equilibria

Clustering of oxygen atoms around carbon in silicon

P. Fraundorf, G. K. Fraundorf, and F. Shimura

J. Appl. Phys. 58, 4049 (1985); http://dx.doi.org/10.1063/1.335584 (7 pages) | Cited 20 times

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Transmission electron microscope studies of carbon‐doped Czochralski silicon, when combined with previous infrared data on the same specimens, reveal a double peak in the carbon‐sited oxygen‐cluster size distribution after 64 h at 750 °C. The first peak, which represents most of the carbon and oxygen in the specimen, is comprised of clusters with an average of two oxygens per carbon atom. These clusters can survive 64 h at 1000 °C although they are not created by such an anneal, suggesting that carbon atoms have difficulty trapping a first oxygen atom at 1000 °C. The second peak in the distribution near 104 oxygen atoms in size is populated with regular {111}‐octahedral precipitates having large dilatational strain fields. The two peaks in the size distribution, and their dependences on heat treatment, indicate roles for both seeding (creation of metastable clusters below critical size) and nucleation (achievement of energetic stability) in the formation of carbon‐sited precipitates. The observations confirm a trend toward octahedral precipitate morphologies in carbon‐doped specimens. However, the trend may result not from site differences but from effects of carbon or point defects on strain energy during precritical cluster growth. Finally, differences between secondary defects associated with precipitation in low‐ and high‐carbon specimens suggest that substitutional carbon atoms at 1000 °C act as sites for silicon self‐interstitial condensation near precipitates.
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61.72.Nn Stacking faults and other planar or extended defects
61.72.U- Doping and impurity implantation
81.40.Gh Other heat and thermomechanical treatments
81.30.Mh Solid-phase precipitation

Lattice parameters of Zn1−xMnxSe and tetrahedral bond lengths in AII1−xMnxBVI alloys

D. R. Yoder‐Short, U. Debska, and J. K. Furdyna

J. Appl. Phys. 58, 4056 (1985); http://dx.doi.org/10.1063/1.335585 (5 pages) | Cited 83 times

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This paper reports the results of lattice parameter measurements on the ternary semiconductor alloy Zn1−xMnxSe over the range 0≤x≤0.57. We find that the mean cation‐cation distance increases linearly with manganese concentration x according to Vegard’s Law. It is also noted that this linear dependence occurs across the region in which the alloy changes crystal structure from zinc blende (x≤0.30) to wurtzite (0.33≤x). These observations are compared with the behavior of the crystal lattice as a function of composition in other AII1−xMnxBVI alloys. A fairly unifed pattern of behavior emerges, relating the lattice parameters and bond lengths for the entire family of these materials. In addition, this analysis provides an experimentally determined value of the tetrahedral radius of manganese.
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61.66.Dk Alloys
64.70.K- Solid-solid transitions

Ion‐beam‐mixed iron boron films

B. M. Clemens and J. J. Neumeier

J. Appl. Phys. 58, 4061 (1985); http://dx.doi.org/10.1063/1.335586 (4 pages) | Cited 9 times

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Ion beam mixing of layered iron‐boron films with 200‐keV Ar ions is investigated by x‐ray diffraction, Auger depth profiling, and high‐temperature resistivity. Samples consisting of alternating layers of electron beam deposited polycrystalline iron (25 nm thick) and boron (50 nm thick) were irradiated to doses from 5×1015 to 1×1016 ions/cm2, at rates ranging from 0.3 to 3.3 μA cm2. The mixing extends to a depth of 150 nm and increases with dose rate. This dependence is due to beam heating of the sample. The structure of the mixed material is amorphous iron boron.
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61.80.Jh Ion radiation effects
64.75.-g Phase equilibria
66.30.-h Diffusion in solids

Dislocation motion in GaAs/AlxGa1−xAs structures

K.‐H. Kuesters, B. C. De Cooman, and C. B. Carter

J. Appl. Phys. 58, 4065 (1985); http://dx.doi.org/10.1063/1.335587 (9 pages) | Cited 10 times

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Dislocations have been made to move through different compound semiconductor epilayer structures by deformation at 320 °C and have then been examined by transmission electron microscopy. The interaction between the dislocations and the GaAs/AlxGa1−xAs interface is shown to depend on the thickness of the AlxGa1−xAs layer. Dislocations are pinned at the interface and, for the MOCVD‐grown material, within the AlxGa1−xAs layer. Dislocation dipoles, some of which are faulted dipoles, are then pulled out and lie preferentially along the heterojunction. It is emphasized that these dipoles, which may be important in device degradation, form as a result of dislocation glide and not dislocation climb.
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61.72.Yx Interaction between different crystal defects; gettering effect
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Characterization of microvoids in carbon fibers by absolute small‐angle x‐ray measurements on a fiber bundle

M. Shioya and A. Takaku

J. Appl. Phys. 58, 4074 (1985); http://dx.doi.org/10.1063/1.335588 (9 pages) | Cited 12 times

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A method has been developed to characterize the voids in a fibrous material by using the small‐angle x‐ray scattering from a unidirectionally aligned fiber bundle, and the parameters evaluating the sizes, volume fraction, and number of the voids have been deduced. The distribution of cross‐section size of voids has also been considered in relation to the size parameters deduced. The method developed has been applied to a commercial carbon fiber. The values of the size parameters of the carbon fiber, evaluated experimentally by the method developed here, are in good agreement with those calculated by assuming that the distribution of the cross‐section size of voids obeys a Maxwellian distribution. A convenient method for determining the primary beam power by comparing the observed and theoretically calculated scattering intensities of air has also been developed in order to measure the scattering intensity of a specimen in absolute units.
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61.05.cc Theories of x-ray diffraction and scattering
61.05.C- X-ray diffraction and scattering
61.72.jd Vacancies
61.72.jj Interstitials

Substrate‐dependent electrical properties of low‐dose Si implants in GaAs

Y. K. Yeo, R. L. Hengehold, Yong Yun Kim, A. Ezis, Y. S. Park, and J. E. Ehret

J. Appl. Phys. 58, 4083 (1985); http://dx.doi.org/10.1063/1.335589 (6 pages) | Cited 14 times

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A comprehensive electrical study of low‐dose (1012−1013 cm−2) Si implants in both liquid‐encapsulated Czochralski (LEC) grown undoped and horizontal Bridgman grown Cr‐doped semi‐insulating GaAs has been made using Hall measurements. The optimum annealing temperature is 850 °C, and an apparent electrical activation efficiency of 90% has been achieved with room‐temperature implantation for both substrates. The carrier depth profiles are much broader and the peak concentrations are much lower than those expected according to the Lindhard–Scharff–Schiott (LSS) theory. Although the carrier profiles for both substrates agree with each other relatively well, the mobilities for the undoped substrates are significantly higher than those for the Cr‐doped substrates at all low doses.
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72.80.Ey III-V and II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
61.72.U- Doping and impurity implantation
61.72.sd Impurity concentration
61.72.sh Impurity distribution
61.72.sm Impurity gradients

Transmission electron microscopy investigation of laser‐induced defects in (Al, Ga) As

B. Zysset, R. P. Salathé, J. L. Martin, R. Gotthardt, and F. K. Reinhart

J. Appl. Phys. 58, 4089 (1985); http://dx.doi.org/10.1063/1.335538 (6 pages)

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In their luminescence appearance three different defects induced in (Al, Ga) As heterostructures through highly focused cw Kr‐ion laser irradiation have been investigated by transmission electron microscopy (TEM). Two of them, a luminescent defect and a nonradiative defect are only revealed by TEM through thickness variations due to the chemical thinning process. They probably consist of point defects or point‐defect complexes. A third type of defect consisting of extended dislocation networks was also occasionally found. These networks seem to originate from native defects and are very similar to formerly described dark‐line defects.
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61.80.-x Physical radiation effects, radiation damage
61.72.J- Point defects and defect clusters
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Static and computer‐simulated dynamic model approaches to effective elastic properties of noncubic polycrystals

T. R. Middya, Mala Paul, and A. N. Basu

J. Appl. Phys. 58, 4095 (1985); http://dx.doi.org/10.1063/1.335539 (7 pages) | Cited 7 times

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Based on the static deformation scheme envisaged by the effective medium theory developed by Zeller and Dederichs [Phys. Status Solidi B 55, 831 (1973)] formally similar to that of the quantum mechanical multiple scattering method, we have deduced a general expression for determining the effective elastic properties of any single component polycrystalline substance. From these general formulas using appropriate symmetry for the component crystallite the expressions for cubic, hexagonal, tetragonal, trigonal, and orthorhombic polycrystals may be easily derived. Two sets of approximate formulae are given and their ranges of validity discussed. For comparison with this static approach, we have also calculated the same quantities by simulating the polycrystal on a computer using the dynamic model developed by Middya, Basu, and Sengupta [J. Appl. Phys. 57, 1844 (1985)]. The results obtained by these two approaches based on entirely different assumptions are remarkably close to each other and to experiment for twenty‐four different noncubic polycrystalline specimens considered in the present investigation. In fact, for the effective rigidity modulus, the agreement between the two methods is within 1% in all cases except for two specimens. The reasons for this discrepancy are discussed. However, while the computer simulation provides a very simple method for evaluating the effective elastic properties of polycrystals with high accuracy, it raises a question regarding the relation between the apparently contradictory assumptions on which the static and the dynamic methods are based. Finally, an experiment is suggested that may be helpful in resolving this difficulty.
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62.20.D- Elasticity
46.25.-y Static elasticity
62.20.F- Deformation and plasticity
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