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15 Feb 1990

Volume 67, Issue 4, pp. 1633-2189

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X‐ray optics of doubly curved diffractors

D. B. Wittry and Songquan Sun

J. Appl. Phys. 67, 1633 (1990); http://dx.doi.org/10.1063/1.345629 (6 pages) | Cited 32 times

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Calculations of the x‐ray optics of four types of doubly curved diffractors are described and the results are compared with similar results for singly curved diffractors (Johann and Johansson geometry). In these calculations the locus of points on a curved diffractor’s surface is determined for a given deviation from the Bragg angle when the diffractor is used at Bragg angles ranging from 15 to 75 degrees. The six cases discussed include cylindrical, spherical, and toroidal geometries. The calculations are used as a basis for comparing the collection efficiency and the spectral resolution when these diffractors are used in scanning monochromators. It is shown that doubly curved diffractors are superior to singly curved ones and that a diffractor with spherical planes and toroidal surface provides the best performance of all of the diffractors considered if a wide range of Bragg angles must be covered.
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61.05.cc Theories of x-ray diffraction and scattering

Recommended Bethe–Bloch stopping power parameters for Kapton and Havar

L. E. Porter

J. Appl. Phys. 67, 1639 (1990); http://dx.doi.org/10.1063/1.345630 (4 pages) | Cited 4 times

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Previous measurements of the stopping power of Kapton and Havar for 1.1–4.4‐MeV protons have been analyzed with modified Bethe–Bloch theory in order to extract some of the parameters required in the formalism. Results suggest the possibility of systematic errors, in that the Havar data appear to have been slightly high and the Kapton data quite low when compared with other reported measurements. Currently recommended values of the mean excitation energy and Barkas‐effect parameter are, respectively, 79 eV and 1.34 (Kapton) and 296 eV and 1.36 (Havar). The need for further accurate measurements for Kapton in particular is emphasized.
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61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Three‐dimensional boundary‐element method for analyzing nonrotationally symmetric perturbations in electrostatic lenses

Jiye Ximen and Dayue Li

J. Appl. Phys. 67, 1643 (1990); http://dx.doi.org/10.1063/1.345631 (7 pages)

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The three‐dimensional boundary‐element method (3D BEM) has been discussed in some aspects involving the subdivision of boundary elements, the quadrature of surface charge density integrals, and their singularities. The 3D BEM has been applied to the analysis of nonrotationally symmetric perturbations in electrostatic lenses. The perturbations due to machining defects (including elliptical distortions, inclined end faces, misalignments, and their combinations) have been calculated and also the asymmetric aberrations have been computed. A set of computer programs has been developed. The computed perturbation potential distributions have been compared with the theoretical ones.
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41.75.Fr Electron and positron beams
07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Numerical simulation of collective ion acceleration in an intense electron beam–localized gas cloud system

R. L. Yao and C. D. Striffler

J. Appl. Phys. 67, 1650 (1990); http://dx.doi.org/10.1063/1.345632 (9 pages) | Cited 3 times

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In experiments in which an intense relativistic electron beam is injected into an evacuated drift tube with a localized gas cloud located near the anode, ions with energies several times the electron beam energy have been observed. These experiments have been simulated using a particle‐in‐cell code which realistically models ionization of the gas. It was found that when the injected electron beam current exceeds the space‐charge limiting current, ions are accelerated to energies several times the electron beam energy by coherent motion of the ions and the intense virtual cathode electric fields. The dependence of the peak ion energy on the system parameters as observed in the simulations is also discussed. For the parameter regimes investigated with beam energies up to 3 MV, beam currents up to 35 kA, gas pressures up to 600 mTorr, and gas cloud widths up to 6 cm, peak ion energies of 5–6 times the electron beam energy have been observed.
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41.75.Ht Relativistic electron and positron beams
52.75.Di Ion and plasma propulsion
29.20.-c Accelerators

Thermal model of the catastrophic degradation of high‐power stripe‐geometry GaAs/(AlGa)As double‐heterostructure diode lasers

Włodzimierz Nakwaski

J. Appl. Phys. 67, 1659 (1990); http://dx.doi.org/10.1063/1.345633 (10 pages) | Cited 5 times

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In the present work, the three‐dimensional thermal analysis of the process of the catastrophic mirror damage in double‐heterostructure stripe‐geometry GaAs/(AlGa)As diode lasers has been carried out for the case of their high‐power operation. In the analysis, the temperature dependencies of both the thermal conductivity and the thermal diffusivity have been taken into account. The analytical solution has been obtained with the aid of the Green’s function method. The catastrophic mirror damage has been explained from the thermal point of view as a result of a local overheating of the active area close to or at the mirror surface. It has been proved that a determination of an exact value of the critical mirror temperature from the catastrophic degradation point of view is of minor importance because the considered temperature increase is of an avalanche type. The analytical solution obtained in the work has enabled us to show a dependence of a catastrophic‐degradation time, i.e., a permissible length of current pulses from a point of view of the catastrophic mirror damage, on the amplitude of the pulses for the standard stripe diode lasers. Experimentally observed catastrophic mirror damage in diode lasers caused by an increase in their facet reflectivity has been also investigated. It has been confirmed that an increase in the reflectivity of an unprotected mirror may be accompanied by a very rapid facet failure. It has been also shown in which way one can avoid the above phenomenon.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Cavity eigenmodes for a free‐electron laser

S. Riyopoulos and C. M. Tang

J. Appl. Phys. 67, 1669 (1990); http://dx.doi.org/10.1063/1.345634 (7 pages)

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The cavity transfer matrix for the round trip of a light pulse in the optical resonator of the National Institute of Standards and Technology/Naval Research Laboratory free‐electron laser oscillator is derived. The cavity eigenmodes and the corresponding eigenvalues are obtained, using an expansion in Gaussian–Laguerre vacuum modes, by numerical diagonalization. The fractional power loss per eigenmode, caused by the finite sizes of the cavity mirrors and apertures, is determined. It is found that the losses are very small over the entire wavelength regime of operation.
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41.60.Cr Free-electron lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Combinations of the electroelastic and electrostrictive constants of quartz determined using the thickness modes of plates

Carl K. Hruska and Remi Brendel

J. Appl. Phys. 67, 1676 (1990); http://dx.doi.org/10.1063/1.345635 (4 pages) | Cited 4 times

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Ten linear combinations of the fundamental material constants of electroelasticity and electrostriction of quartz have been determined. They were obtained by the least‐squares fit to 134 observations of the change in the resonance frequency of the thickness modes of quartz plates caused by a dc field. With one exception, there is very good agreement between our results and their counterparts obtained independently by the transit‐time method (pulse propagation in bulk quartz). The differences between comparable constants are no longer out of proportion with their standard errors. This work supersedes earlier results [J. Appl. Phys. 65, 715 (1989)].
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77.65.-j Piezoelectricity and electromechanical effects
62.20.D- Elasticity
62.65.+k Acoustical properties of solids

Acoustic microscope using pressurized superfluid 4He

Koichi Karaki, Masaru Suzuki, and Yuichi Okuda

J. Appl. Phys. 67, 1680 (1990); http://dx.doi.org/10.1063/1.345636 (4 pages) | Cited 2 times

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An acoustic microscope has been developed which makes use of pressurized superfluid helium as an acoustic coupling medium. Acoustic micrographs were taken using pure superfluid 4He under saturated vapor pressure at 0.1 K and under 25 atm at 0.1 and 1.9 K, for the frequency of 380 MHz. By pressurizing liquid 4He, the acoustic attenuation decreases, the efficiency of the antireflection coating increases, and the power level of saturation caused by nonlinearity of the superfluid 4He is raised. A good signal‐to‐noise ratio of imaging is thus obtained. The entire imaging instrument set is within a closed cell. The focusing mechanism is composed of two voice coils of superconducting wire. Using a servocontrol mechanism with a sensor and drive coil, Z‐direction stability was better than 0.05 μm. The manipulation sensitivity is 0.5 μm/mV, and the whole stroke is about 2 mm.
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67.25.dt Sound and excitations
43.58.Ls Acoustical lenses and microscopes

Effective conductivity of two‐phase materials consisting of long parallel cylinders

Yee C. Chiew

J. Appl. Phys. 67, 1684 (1990); http://dx.doi.org/10.1063/1.345637 (5 pages) | Cited 3 times

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The effective conductivity σe of a dispersion of long, parallel cylinders (or two‐dimensional systems), distributed in a second continuous matrix phase, is determined as a function of its microscopic structure. We obtained an expression for the effective conductivity of two‐dimensional systems (based on an approximate scheme) that includes the one‐body and two‐body terms in the cluster expansion for σe. The effective conductivities of two‐dimensional hard disks and square‐well particles are computed. It is found that this expression yields excellent estimates for the effective conductivity over a wide range of cylinder volume fractions, and for cases in which the cylinder to matrix phase conductivity ratios are high.
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44.30.+v Heat flow in porous media

Breakdown voltage enhancement by wall charges in repetitively pulsed discharge tubes

F. L. Curzon, M. Suzuki, and S. Mikoshiba

J. Appl. Phys. 67, 1689 (1990); http://dx.doi.org/10.1063/1.345638 (5 pages) | Cited 5 times

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It is shown that, over a narrow range of amplitudes, applied voltage pulses can deposit wall charges inside a discharge tube without causing breakdown of the interelectrode gas: these charges enhance the breakdown voltage of the interelectrode gas for subsequent pulses, and the enhancement decays exponentially with the pulse interval. The enhancement decays more rapidly when the temperature of the discharge tube is increased so as to reduce its surface resistance, which furnishes the main leakage path of the wall charges. It is suggested that breakdown voltages of closely packed, repetitively pulsed discharge tubes are frequently enhanced by wall charges.
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52.80.-s Electric discharges

X‐ray tomography of hot electrons in the barrier region of the tandem mirror GAMMA 10

T. Kondoh, T. Cho, M. Hirata, N. Yamaguchi, T. Saito, Y. Kiwamoto, and S. Miyoshi

J. Appl. Phys. 67, 1694 (1990); http://dx.doi.org/10.1063/1.345639 (6 pages) | Cited 9 times

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Tomographic reconstructions of x‐ray emission from hot electrons have been carried out in the thermal barrier region of the GAMMA 10 plasmas. Here, the first application of two sets of the 50‐channel microchannel plates have been performed using their detailed calibration data as a function of x‐ray energy and incident angle [Rev. Sci. Instrum. 59, 256 (1988); 59, 2453 (1988); 60, 368 (1989)]. The x‐ray reconstructed signals under standard thermal barrier operating conditions indicate a good axisymmetric radial profile peaked on the magnetic axis. This symmetric profile is important for preventing the formation of a local anisotropic electric field, which may cause particle confinement degradation, and its peaking profile is desirable for thermal barrier potential formation in the core plasma region. When we have relocated the second‐harmonic electron cyclotron layers (ω=2Ωe) in two different ways (moving them out radially, or axially away from the midplane), tomographic reconstructions show hollow x‐ray profiles in both cases. These may be formed due to the E×B rotations of the hot electrons produced near ω=2Ωe . These applications of x‐ray tomography to two‐dimensional radial profile observations along with the axial x‐ray profile measurement give information that the production mechanism of these hot electrons is ascribed to second‐harmonic electron cyclotron heating.
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28.52.Av Theory, design, and computerized simulation
52.55.-s Magnetic confinement and equilibrium
52.70.La X-ray and γ-ray measurements

Dynamics of electron flow in extended planar‐anode diode operating at 19 MV and 700 kA

T. W. L. Sanford, J. A. Halbleib, J. W. Poukey, G. T. Baldwin, G. A. Carlson, W. A. Stygar, G. A. Mastin, T. Sheridan, R. Mock, J. A. Alexander, E. R. Brock, and C. O. Landron

J. Appl. Phys. 67, 1700 (1990); http://dx.doi.org/10.1063/1.345640 (12 pages) | Cited 12 times

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The electron flow in a planar‐anode diode having an extended anode‐cathode gap operating on the HERMES III accelerator is characterized and compared with predictions of a computational model. The model combines a particle‐in‐cell code with Monte Carlo radiation transport. The comparisons confirm the model and show that the diode provides both a matched load and a versatile large‐area source of γ rays for the study of nuclear radiation effects. Electrical and spatial parameters of the beam at the diode and the downstream radiation fields from a graphite target are presented as a function of the anode‐cathode gap.
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52.80.Pi High-frequency and RF discharges
41.75.Ht Relativistic electron and positron beams
84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables

Effects of convection and electric field on thermofluid transport in horizontal high‐pressure mercury arcs

Wei Shyy and Peggy Y. Chang

J. Appl. Phys. 67, 1712 (1990); http://dx.doi.org/10.1063/1.346097 (8 pages) | Cited 7 times

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A three‐dimensional theoretical model based on first principles has been developed to predict the characteristics of mass, momentum, energy, and electrostatic potential transport in high‐pressure mercury arcs confined in a quartz arctube. The model is utilized to systematically investigate the impact of convection on the transport process by including and excluding the gravity effect. Strong three‐dimensional convection flows with multiple contrarotating vortices have been identified. These vortices substantially change the energy balance within the arc, causing highly nonuniform gas temperature distribution and lowering the maximum gas temperature. Geometrical modifications of the arctube such as wall contour curvature and electrode offsets do not change the strength of convection but can produce better overall temperature uniformity within the arctube by accommodating the upward‐moving tendency of temperature contours caused by convection. In agreement with the experimental measurement, the model predicts that the arctube curvature can cause large differences of wall temperature profiles, including shape, level, and locations of peak values.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)

Cathode‐ and anode‐spot tracks in a closed magnetic field

P. D. Swift

J. Appl. Phys. 67, 1720 (1990); http://dx.doi.org/10.1063/1.345641 (5 pages) | Cited 3 times

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The velocity of cathode spots with nonretrograde motion in a closed magnetic field has been found to have a component normal to the direction of j×B, and the trajectory of the cathode spots in this field configuration is not stable, in contrast to the trajectory for retrograde motion. This component of the spot motion can be understood, as has been predicted, by consideration of the Lorentz force acting on a positive space charge, which has been proposed to be associated with cathode spots. The behavior of the motion normal to j×B of cathode spots with retrograde velocities can be explained by the same model. Further results presented are consistent with a positive space charge also being associated with anode spots.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
29.27.-a Beams in particle accelerators

Basic considerations for scaling Z‐pinch x‐ray emission with atomic number

K. G. Whitney, J. W. Thornhill, J. P. Apruzese, and J. Davis

J. Appl. Phys. 67, 1725 (1990); http://dx.doi.org/10.1063/1.345642 (11 pages) | Cited 70 times

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Two energies are identified that define the x‐ray emission characteristics of Z‐pinch array implosions. One, the kinetic energy per ion, is intensive, and the other, the kinetic energy per centimeter, is extensive. From a series of one‐dimensional axisymmetric hydrodynamic calculations, we have calculated the dependence of the x‐ray emission from aluminum implosions above 1 keV on these energies. These calculations are carried out for a specially chosen theoretical case where the kinetic energy that is generated during implosion is converted to thermal energy and x rays during the plasma collision on axis in the absence of current. In this case, we determine the I4 to I2 transition of the scaling of emission with peak current, I, as a parametric function of the kinetic energy per ion. We also determine a functional dependence of the emission on this energy when the mass of the imploded aluminum array is held fixed. It is seen that the ability of the plasma to radiate large amounts of energy in either I4 or I2 regimes is strongly dependent on the mass loading. Finally, some arguments are presented on how the breakpoint between I4 and I2 scaling is expected to scale when the atomic number of the array load is varied.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.55.Ez Theta pinch
52.30.-q Plasma dynamics and flow

Conductivity enhancement of poly‐ether‐ether‐ketone by ion implantation

C. J. Bedell, C. J. Sofield, L. B. Bridwell, and I. M. Brown

J. Appl. Phys. 67, 1736 (1990); http://dx.doi.org/10.1063/1.345622 (4 pages) | Cited 9 times

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Amorphous poly‐ether‐ether‐ketone (PEEK) films have been implanted with a variety of ions (He, N, F, As, Xe and I) in the energy range 50 keV to 32 MeV. At the lower end of this range, the dependence of the electrical conductivity of the PEEK on the dose and ion species has been explained in terms of a simple model of electronic and nuclear excitation effects. Implantations in the MeV energy range yielded a surface layer on the PEEK with a high conductivity [up to 2.5 (Ω cm)−1] and a moderate hardness (320 knoop, 1‐g load). Evidence for diffusion of iodine implanted at the highest energy has been found. The role of the uniform iodine concentration throughout the implanted layer in the prevalent conduction mechanism is not known at present.
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61.72.up Other materials
81.40.Rs Electrical and magnetic properties related to treatment conditions

A comparison of electrical and chemical profiling of doping superlattices in silicon

A. Casel, H. Jorke, M. Pawlik, R. Groves, and E. Frenzel

J. Appl. Phys. 67, 1740 (1990); http://dx.doi.org/10.1063/1.345623 (4 pages) | Cited 1 time

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Molecular‐beam epitaxy was used to grow vertical silicon structures with extremely sharp doping transitions. Hereby a series of modulation‐doped multilayer structures was prepared which had successively reduced period lengths from 100 down to 4 nm. These test samples are appropriate to study the depth resolution of standard electrical and chemical profiling techniques. Secondary ion mass spectrometry is able to resolve doping modulations down to 4 nm. Electrical measurement techniques are fundamentally limited by the out‐diffusion of carriers from the highly to the lowly doped layers. Such effects become of increased importance in small period superlattices. Spreading resistance is only able to resolve the doping modulations of the test sample with the largest period length (100 nm).
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61.72.uf Ge and Si
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.61.Cw Elemental semiconductors
73.61.Jc Amorphous semiconductors; glasses
73.61.Le Other inorganic semiconductors
66.30.-h Diffusion in solids

Metastable phase formation in the Zr‐Al binary system induced by mechanical alloying

H. J. Fecht, G. Han, Z. Fu, and W. L. Johnson

J. Appl. Phys. 67, 1744 (1990); http://dx.doi.org/10.1063/1.345624 (5 pages) | Cited 72 times

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We have studied the sequence of phase transformations induced in the Zr‐Al binary system by mechanical alloying of mixed Zr and Al powders. The structure of these materials has been studied by transmission electron microscopy and by x‐ray diffraction measurements. Three different metastable phases have been found experimentally with variation of the initial composition xAl: (1) a nanocrystalline supersaturated solid solution of α‐Zr for xAl≤0.15, (2) an amorphous phase for 0.15<xAl≤0.4, and (3) a metastable face‐centered‐cubic phase for xAl=0.5 with a grain size of 4 nm. The crystallization reaction of the amorphous phase was monitored by differential scanning calorimetry, and the kinetics of the reaction have been examined as well. A possible explanation based on thermodynamic arguments is given for the defect‐driven vitrification of the crystalline Zr phase.
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64.70.K- Solid-solid transitions
61.66.Dk Alloys
65.20.-w Thermal properties of liquids
65.40.gd Entropy

Surface modification and atomic resolution on a vacuum‐annealed gold foil in air by scanning tunneling microscopy

Britta Hoffmann‐Millack, Clive J. Roberts, and William S. Steer

J. Appl. Phys. 67, 1749 (1990); http://dx.doi.org/10.1063/1.345598 (4 pages) | Cited 12 times

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Scanning tunneling microscopy has been used to investigate changes in a vacuum‐annealed gold surface induced by the application of voltage pulses to the tip. After a 2‐V 1.5‐s pulse a hole several hundreds of angstroms wide and of similar depth was generated, the responsibility being ascribed to ion arcing. We present a time‐lapse sequence showing its decay process, from which surface‐diffusion velocities between 4 and 0.1 Å s−1 have been determined. From the new surface, a scan showing atomic resolution has been obtained, giving different interatomic spacings (S) and atomic diameters (D) in two lattice directions at an angle of 60°. These are S=2.1 Å and D=2.0 Å for the short axis and S=3.1 and 3.8 Å and D=2.7 Å for the long axis.
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68.35.Fx Diffusion; interface formation
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination
81.05.Bx Metals, semimetals, and alloys

Structure of amorphous carbon in amorphous C/Ge multilayers

N. J. Long and H. J. Trodahl

J. Appl. Phys. 67, 1753 (1990); http://dx.doi.org/10.1063/1.345599 (4 pages) | Cited 3 times

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Amorphous C‐Ge multilayers have been produced with periods varying from 2.6 to 12.5 nm. We have studied the multilayers using Raman spectroscopy and dc conductivity measurements and found that their properties change significantly when the carbon sublayer thickness is smaller than 2.5 nm. This value corresponds to the proposed dimension of sp2 bonded carbon islands within a‐C and we find that our results can be understood in terms of the carbon forming these islands, but the islands becoming disconnected as the nominal carbon layer thickness decreases. The conductivity shows a percolation behavior for the thinnest layers.
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72.60.+g Mixed conductivity and conductivity transitions
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
72.80.Ng Disordered solids

Mechanism of the growth of amorphous and microcrystalline silicon from silicon tetrafluoride and hydrogen

Y. Okada, J. Chen, I. H. Campbell, P. M. Fauchet, and S. Wagner

J. Appl. Phys. 67, 1757 (1990); http://dx.doi.org/10.1063/1.345600 (4 pages) | Cited 9 times

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We study the growth of amorphous (a‐Si:H,F) and of microcrystalline (μc‐Si) silicon over trench patterns in crystalline silicon substrates. We vary the conditions of the SiF4‐H2 glow discharge from deposition to etching. All deposited films form lips at the trench mouth and are uniformly thick on the trench walls. Therefore, surface diffusion is not important. The results of a Monte Carlo simulation suggest that film growth is governed by a single growth species with a low (∼0.2) sticking coefficient, in combination with a highly reactive etching species.
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61.43.Fs Glasses
61.43.-j Disordered solids
61.44.Br Quasicrystals
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Be+/P+, Be+/Ar+, and Be+/N+ coimplantations into InP:Fe

Mulpuri V. Rao and Ravi K. Nadella

J. Appl. Phys. 67, 1761 (1990); http://dx.doi.org/10.1063/1.345601 (6 pages) | Cited 23 times

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Single‐ and multiple‐energy Be+/P+, Be+/Ar+, and Be+/N+ coimplantations were performed into semi‐insulating InP:Fe. Significantly higher Be dopant activations were obtained for Be+/P+ and Be+/Ar+ coimplantations compared to Be+ implantation. Sharp hole‐concentration depth profiles were obtained for Be+/P+ and Be+/Ar+ coimplantations in contrast to the deep diffusion fronts for Be+ implantation. A high degree of crystalline lattice damage in coimplanted material is believed to be responsible for the improved electrical characteristics of the material. A poor Be dopant electrical activation was observed for Be+/N+ coimplantation.
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61.72.U- Doping and impurity implantation
78.30.Fs III-V and II-VI semiconductors
81.20.-n Methods of materials synthesis and materials processing

Ion beam synthesis of heteroepitaxial Si/CoSi2/Si structures

A. H. Van Ommen, C. W. T. Bulle‐Lieuwma, J. J. M. Ottenheim, and A. M. L. Theunissen

J. Appl. Phys. 67, 1767 (1990); http://dx.doi.org/10.1063/1.345602 (12 pages) | Cited 35 times

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The formation of buried single crystalline CoSi2 layers within a monocrystalline Si substrate by high‐dose ion implantation of Co has been studied. Comparison of measured Co distributions with profiles obtained from Monte Carlo calculations has revealed the two basic phenomena that are responsible for the formation of buried layers. The enhanced stopping due to the incorporation of high concentrations of Co into Si has been identified as the dominant effect in the ion beam synthesis of buried layers. The high stopping near the top of the implanted distribution causes accumulation of Co at this point, which promotes buried layer formation. Sputtering brings the entire Co profile closer to the surface. After implantation at a temperature of 450 °C, Co is present in the form of coherent CoSi2 precipitates. Precipitates occur both in a twinned and an aligned orientation and are highly strained due to the lattice mismatch with Si. For high doses a buried monocrystalline and aligned CoSi2 layer forms within the Si lattice, during implantation. Annealing of the implanted structures results in the formation of a buried layer when, near the top of the implanted distribution, more than 50% of the Si is converted into CoSi2. These layers too are monocrystalline and have on aligned orientation. Cobalt diffusion in the Si lattice has been suggested to be the rate‐determining step in the growth process of the buried layers. Finally, the electrical properties of these ion beam synthesized structures exhibit some unique features.
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73.40.Vz Semiconductor-metal-semiconductor structures
61.72.uf Ge and Si
81.15.Np Solid phase epitaxy; growth from solid phases
07.79.Cz Scanning tunneling microscopes
61.05.-a Techniques for structure determination

Dopant incorporation in Si‐implanted and thermally annealed GaAs

J. Wagner, H. Seelewind, and W. Jantz

J. Appl. Phys. 67, 1779 (1990); http://dx.doi.org/10.1063/1.345603 (5 pages) | Cited 5 times

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The incorporation of Si in ion‐implanted and thermally annealed GaAs has been studied by local vibrational mode spectroscopy. Raman scattering and Fourier transform IR absorption have been used to analyze the Si site distribution both in the near surface region and averaged over the whole implanted layer, respectively. The samples implanted with doses of 5×1014 –1016 cm−2 were annealed with various techniques using different capping layers. The Si site distribution is found to depend strongly on the details of the annealing. In particular, capping with SiO2 leads to the formation of the so‐called Si‐X defect complex in addition to the incorporation of Si on both lattice sites and the formation of nearest‐neighbor Si pairs.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
63.20.Pw Localized modes
78.30.Fs III-V and II-VI semiconductors

Analysis of thermal stress, fracture strength, and the effect of ion exchange on high average power phosphate glass slab lasers

John C. Lambropoulos

J. Appl. Phys. 67, 1784 (1990); http://dx.doi.org/10.1063/1.345604 (9 pages)

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It has been recently demonstrated that it is possible to significantly alter the maximum power input required for mechanical failure of glass used for high average power laser applications by employing an ion exchange process that does not alter the optical properties of the strengthened glass. We present the analysis of the thermal stresses, fracture, and strengthening for the experimental geometry used. From this analysis the fracture strength of the untreated and treated glass can be estimated. Some suggestions for the control of thermal stresses during the operation of solid‐state lasers using glass slab geometries are presented. The second part of this report presents a micromechanical analysis of the strengthening effect due to the ion exchange process in which the enhancement in fracture strength is correlated to the depth of the zone in which ion exchange has occurred, to the length of microscopic flaws present on the surface of the glass, and to the magnitude of the microscopic volume expansion due to the ion exchange process. In particular, we consider the cases where the depth of the treated zone is much smaller or much greater than the depth of surface flaws. The magnitude of the enhancement in fracture strength is calculated in terms of these microscopic quantities for some material properties typical of phosphate glasses.
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62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
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