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15 Dec 1996

Volume 80, Issue 12, pp. 6589-7172

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A simple three‐dimensional free electron laser code

G. Dattoli, A. Dipace, E. Sabia, A. Torre, G. K. Voykov, and M. Carpanese

J. Appl. Phys. 80, 6589 (1996); http://dx.doi.org/10.1063/1.363780 (6 pages) | Cited 4 times

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We present a simple and inexpensive computer code for free electron laser (FEL) operation that includes high gain and inhomogeneous broadening effects. The code is based on analytical formulae, obtained within the context of the theory of FEL approximants, requires negligible CPU time, and may run on small computers. © 1996 American Institute of Physics.
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41.60.Cr Free-electron lasers
02.60.Jh Numerical differentiation and integration
07.05.Tp Computer modeling and simulation

Intensity fluctuation of a pulsed planar microcavity laser

Takayuki Enomoto, Takuto Sasaki, Katsumi Sekiguchi, Yoshiko Okada, and Kikuo Ujihara

J. Appl. Phys. 80, 6595 (1996); http://dx.doi.org/10.1063/1.363782 (7 pages) | Cited 8 times

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Probability distributions of the peak output power from planar microcavity dye lasers with pulsed excitation have been studied experimentally. Two microcavities were used, one operating possibly with a single mode and the other possibly with a number of modes. These expectations are based on the relative magnitude of the mode radius and the pump beam radius. In the former cavity an exponential‐like distribution was observed below threshold, which indicates single‐mode operation. In the latter cavity a single‐peaked distribution appeared even below threshold indicating multiple‐mode operation. These results are, respectively, in qualitative agreement with theoretical distributions for steady state. That the observed pulse width is large enough to apply steady state distribution equation is shown by calculating the characteristic transient time for the intensity distribution. © 1996 American Institute of Physics.
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42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.55.Sa Microcavity and microdisk lasers
42.55.Mv Dye lasers
42.60.Fc Modulation, tuning, and mode locking

Dispersion and dipolar orientational effects on the linear electroabsorption and electro‐optic responses in a model guest/host nonlinear optical system

T. Goodson and C. H. Wang

J. Appl. Phys. 80, 6602 (1996); http://dx.doi.org/10.1063/1.363783 (8 pages) | Cited 3 times

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Linear electroabsorption (LEA) and linear electro‐optic (LEO) measurements are demonstrated using a model guest/host system consisting of disperse red 1 (DR1) doped in poly(methyl)methacrylate (PMMA). The LEA response is measured over a wavelength range of 300–700 nm. Electro‐optic measurements of the real and imaginary parts of the electric field‐induced Pockels coefficient are carried out at wavelengths near and far from the resonant absorption. A shift in the absorption maximum and change in the band shape of the LEA spectrum are related to the linear Stark effect and dipolar orientation. Expressions for the real and imaginary parts of the Pockels coefficient derived from the two experiments are provided. Induced dipolar order as a result of the contact poling process is investigated by the LEA measurement. Information concerning the relaxation of the induced dipolar order, investigated by the LEA measurement, is compared to the relaxation results obtained by using the second‐harmonic generation technique. © 1996 American Institute of Physics.
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78.20.Jq Electro-optical effects
42.70.Jk Polymers and organics
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
61.41.+e Polymers, elastomers, and plastics

Population dynamics of the three‐micron emitting level of Er3+ in YAlO3

S. Georgescu, V. Lupei, M. Trifan, R. J. Sherlock, and T. J. Glynn

J. Appl. Phys. 80, 6610 (1996); http://dx.doi.org/10.1063/1.363748 (4 pages) | Cited 5 times

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An analysis of the nonexponential behavior of the kinetics of the initial laser level for three‐micron generation (4I11/2) in an Er3+(45 at. %):YAlO3 crystal under intense pump in the 4S3/2 level is performed. The observed nonexponential 4I11/2 decay can be satisfactorily described by the rate equation model which includes energy transfer processes inside the system of erbium ions, such as up‐conversion from 4I13/2 and 4I11/2 and cross‐relaxation from 4S3/2 and 4I9/2 provided only a small fraction (β21≊0.11) of the excitation from 4I11/2 level reaches the terminal laser level, 4I13/2. The low value of β21 and the observed reduction of the fluorescent lifetime of 4I11/2 with the increasing erbium doping could be related to the presence of accidental impurities. © 1996 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.70.Km Infrared transmitting materials
78.55.Hx Other solid inorganic materials
42.55.Ah General laser theory
78.45.+h Stimulated emission

Beam propagation algorithms for frequency response of surface acoustic wave directional couplers

I. Haruvi‐Busnach, A. Seidman, and N. Croitoru

J. Appl. Phys. 80, 6614 (1996); http://dx.doi.org/10.1063/1.363784 (5 pages) | Cited 1 time

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Surface acoustic wave directional couplers have long been known in both microwave and integrated acoustic applications. Such couplers are ideal for integration in acoustical signal processing devices, such as modulators or switches. There are, however, very few publications concerning the frequency response of these devices. This article represents both experimental and theoretical studies on the frequency response of directional couplers, with and without a thin strip deposited in the gap between the main channels. The beam propagation method, used in integrated optics, was adapted for acoustical directional couplers. It enabled the analysis and prediction of the frequency response of these types of couplers. Calculations were performed for the channels and interdigital transducers in the frequency range of 50–90 MHz. By using proper dimensions of the couplers’ parameters, coupling efficiency for the higher part of the frequencies, in the receiver channel, was increased. This increase enables the selection of receiver frequencies and, therefore, a frequency channelizer could be developed. A thin strip between the main channels increases the coupling efficiency between the two channels and thereby reduces by about 30% the length of the coupler required for different frequency selections or conventional switches. This reduction makes it possible to obtain more compact devices with reduced losses. © 1996 American Institute of Physics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Boltzmann equation analysis of electron‐molecule collision cross sections in water vapor and ammonia

M. Yousfi and M. D. Benabdessadok

J. Appl. Phys. 80, 6619 (1996); http://dx.doi.org/10.1063/1.363785 (12 pages) | Cited 48 times

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Sets of electron‐molecule collision cross sections for H2O and NH3 have been determined from a classical technique of electron swarm parameter unfolding. This deconvolution method is based on a simplex algorithm using a powerful multiterm Boltzmann equation analysis established in the framework of the classical hydrodynamic approximation. It is well adapted for the simulation of the different classes of swarm experiments (i.e., time resolved, time of flight, and steady state experiments). The sets of collision cross sections that exist in the literature are reviewed and analyzed. Fitted sets of cross sections are determined for H2O and NH3 which exhibit features characteristic of polar molecules such as high rotational excitation collision cross sections. The hydrodynamic swarm parameters (i.e., drift velocity, longitudinal and transverse diffusion coefficients, ionization and attachment coefficients) calculated from the fitted sets are in excellent agreement with the measured ones. These sets are finally used to calculate the transport and reaction coefficients needed for discharge modeling in two cases of typical gas mixtures for which experimental swarm data are very sparse or nonexistent (i.e., flue gas mixtures and gas mixtures for rf plasma surface treatment). © 1996 American Institute of Physics.
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34.80.Gs Molecular excitation and ionization
51.10.+y Kinetic and transport theory of gases

Theoretical and experimental investigation of leakage power in microwave transmit–receive switches

K. Madsén, D. Andersson, M. Lisak, L. Lundgren, and V. Semenov

J. Appl. Phys. 80, 6631 (1996); http://dx.doi.org/10.1063/1.363781 (8 pages)

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A theoretical and experimental investigation is made of the leakage power in microwave transmit–receive switches. The peak leakage power is shown to be independent of incident peak power but to depend on the rise time of the incident pulse. The plateau leakage power through the switch is also estimated and shown to be independent of incident peak power. The theoretical predictions for peak leakage power and plateau leakage power are compared and found to be in good agreement with experimental results. © 1996 American Institute of Physics.
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52.75.Kq Plasma switches (e.g., spark gaps)
84.32.Dd Connectors, relays, and switches

On the radial distribution and nonambipolarity of charged particle fluxes in a nonmagnetized planar inductively coupled plasma

G. Mümken and U. Kortshagen

J. Appl. Phys. 80, 6639 (1996); http://dx.doi.org/10.1063/1.363786 (7 pages) | Cited 18 times

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The radial distribution of electron and ion fluxes to conducting and nonconducting walls in a planar inductively coupled plasma has been studied experimentally and theoretically. Measurements of electron and ion currents have been performed using electrostatic probe arrays. Radially resolved measurements of ion impact energies have been performed using an ion energy analyzer array. For conducting walls it is shown by calculations and measurements that electron and ion currents are not in balance locally but that diffusion is nonambipolar. The ion impact energies measured on a conducting surface show a significant radial variation in accord with our theoretical model. For nonconducting surfaces the ambipolar fluxes of electrons and ions result in the formation of a surface charge potential profile across the surface. Voltages of the order of several volts between the center and the periphery of the surface are measured. © 1996 American Institute of Physics.
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52.70.Ds Electric and magnetic measurements
52.25.Fi Transport properties
52.25.Dg Plasma kinetic equations
52.80.-s Electric discharges

Electron spin resonance identification of a methyl associated organic radical in irradiated amorphous SiO2

Wm. R. Austin and R. G. Leisure

J. Appl. Phys. 80, 6646 (1996); http://dx.doi.org/10.1063/1.363787 (5 pages) | Cited 1 time

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An electron spin resonance (ESR) signal comprised of three resolved lines of equal 19.3 Gauss separation (3×19.3 G), but unequal amplitude, is observed in x‐irradiated amorphous silicon dioxide. The radical appears exclusively in silica samples which also exhibit the methyl radical, a familiar indicator of trace carbon and hydrogen contamination. The 3×19.3 G signal is observed to grow most rapidly versus irradiation dose when methyl radical concentration is near maximum. This evidence suggests that the ESR signal is due to a radiolytic, organic radical which evolves after the methyl radical and, like the methyl radical, is trapped and stabilized in the amorphous silica network. Experimental methods of radical generation are presented, followed by discussion of models for the chemical structure of the 3×19.3 G radical. © 1996 American Institute of Physics.
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76.30.Rn Free radicals
61.80.Cb X-ray effects
61.43.Er Other amorphous solids

Optical properties of LiNbO3 implanted with Ag ions

D. Y. Shang, Y. Saito, R. Kittaka, S. Taniguchi, and A. Kitahara

J. Appl. Phys. 80, 6651 (1996); http://dx.doi.org/10.1063/1.363788 (4 pages) | Cited 9 times

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Ag ions were implanted in LiNbO3 at energies of 25 keV and 3 MeV. Optical absorption spectra were measured in the visible range. A large absorption peak due to small colloidal Ag metal was observed at 460 and 510 nm for the as‐implanted sample at 3 MeV and 25 keV, respectively. Subsequently, the samples were heated in air up to 600 °C. The absorption peak moved toward longer wavelengths up to 560 nm when the sample was heated at high temperature. Small droplets of metallic Ag expelled from the implanted layer formed on the surface of the sample even when the samples were held at room temperature. The number and size of the droplets grew with time and their growth was accelerated when the samples were heated at high temperature. © 1996 American Institute of Physics.
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78.40.Ha Other nonmetallic inorganics
61.72.up Other materials
61.80.Jh Ion radiation effects
82.70.Dd Colloids
81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions

Argon incorporation and surface compositional changes in InP(100) due to low‐energy Ar+ ion bombardment

J. S. Pan, A. T. S. Wee, C. H. A. Huan, H. S. Tan, and K. L. Tan

J. Appl. Phys. 80, 6655 (1996); http://dx.doi.org/10.1063/1.363789 (6 pages) | Cited 12 times

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Angle‐resolved x‐ray photoelectron spectroscopy (ARXPS) has been used to study the Ar incorporation and surface compositional changes in InP(100) after 1–5 keV Ar+ bombardment at various ion fluences. The ARXPS measurements showed that the incorporated Ar concentration achieved saturation at ion bombardment fluences of >1016 cm−2. The surface Ar concentration decreased with increasing bombardment energy. No Ar bubbles were observed by atomic force microscopy, suggesting that Ar bubble formation was not the main Ar trapping mechanism. The altered layers were, on average, In rich up to the sampling depth of the ARXPS technique. However, the altered layers were inhomogeneous as a function of depth and appeared more In rich at the surface than in the subsurface region. The results are compared with those obtained by other authors and discussed in the context of preferential sputtering, radiation‐enhanced diffusion and segregation, and Ar incorporation. Although the altered layers were In rich, a P‐rich phase induced by Ar+ bombardment was identified in the altered layers. © 1996 American Institute of Physics.
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61.80.Jh Ion radiation effects
68.35.Dv Composition, segregation; defects and impurities
68.35.Fx Diffusion; interface formation
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Impurity dependence of oxide defects in Czochralski silicon

Manabu Itsumi, Hideo Akiya, Masato Tomita, Takemi Ueki, and Masataka Yamawaki

J. Appl. Phys. 80, 6661 (1996); http://dx.doi.org/10.1063/1.363790 (5 pages) | Cited 1 time

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Octahedral cavities have recently been found in the Czochralski silicon (CZ‐Si) substrate surface layer just under oxide defects. We investigate the effect that adding HCl to oxygen during oxidation has on the oxide defect density. The effect of intentionally introducing impurities onto a Si surface on the oxide defect density is also examined. Our experimental results suggest that impurities are closely related to the generation of oxide defects. A model is presented in which impurities are incorporated into the growing octahedral cavities during Si crystal growth, and then introduced into the growing oxides during thermal oxidation. These impurities in the oxides then act as a conductive path (oxide defects) in the insulator on the CZ‐Si. © 1996 American Institute of Physics.
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81.65.Mq Oxidation
61.72.uf Ge and Si

Thermal properties of the nonlinear optical crystal zinc tris (thiourea) sulphate

P. Kerkoc, V. Venkataramanan, S. Lochran, R. T. Bailey, F. R. Cruickshank, D. Pugh, J. N. Sherwood, R. Moseley, A. E. Goeta, C. W. Lehmann, and J. A. K. Howard

J. Appl. Phys. 80, 6666 (1996); http://dx.doi.org/10.1063/1.363791 (4 pages) | Cited 14 times

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The heat capacity of crystalline zinc tris (thiourea) sulphate, has been measured in the range from 220 to 500 K by differential scanning calorimetry, and was found to obey the relationship Cp(T)=2.76×10−3 T+0.366 J g−1 K−1. Thermal expansion data have been measured in the range from 150 to 473 K. From these data, the principal thermal expansion coefficients were found to be α1=6.41×10−5 K−1, α2=4.52×10−5 K−1, and α3=−4.32×10−6 K−1. The thermal conductivity tensor of this orthorhombic crystal was calculated from values of the thermal diffusivity in the directions normal to the (100), (010), and (001) crystal planes by the laser flash method. The thermal conductivity coefficients at 295 K are k1=0.27 W m−1 K−1, k2=0.34 W m−1 K−1, and k3=0.54 W m−1 K−1. © 1996 American Institute of Physics.
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42.70.Mp Nonlinear optical crystals
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
65.40.-b Thermal properties of crystalline solids
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
65.40.De Thermal expansion; thermomechanical effects

Grain‐boundary slit propagation in an electric field

L. M. Klinger, X. Chu, W. W. Mullins, and C. L. Bauer

J. Appl. Phys. 80, 6670 (1996); http://dx.doi.org/10.1063/1.363792 (7 pages) | Cited 11 times

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Advancement of a fine slit along a planar grain boundary in an electric field E0, applied parallel to the slit, is investigated by considering electromigration along both the grain boundary and the slit surface. Electrically induced flux in the grain boundary Igb (+ toward the slit tip) and both electrically and curvature‐induced fluxes on the slit surfaces are considered assuming 2Is>Igb, where Is is the flux (+ away from the slit tip) on each of the parallel slit surfaces far removed from the tip. Steady‐state solutions of the transport equations are classified according to the value of a parameter β=tan−1 (2Is/Igb) which, under reasonable assumptions, depends on material parameters only. For 5π/4≥β≥β2, unique steady‐state solutions exist; for β2>β>β1, multiple steady‐state solutions occur; below β1≥π/4, no steady‐state solution is possible. Since β1<π/2, Igb>0 (flux exiting the grain boundary into the slit) for all cases in which no steady‐state solution is possible. In the case of multiple solutions, those corresponding to smallest width (and hence largest velocity) are determined. For all steady‐state solutions, slit width and tip velocity scale as E−1/20 and E3/20, respectively. Results also apply to the propagation of a slit within a grain or along a passivation layer. Generally, tip velocities can approach 1 nm/s (3.6 μm/h), thereby representing a likely failure mechanism in fine‐line (near bamboo structure) interconnects. © 1996 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
61.72.Mm Grain and twin boundaries
66.30.Qa Electromigration
66.30.Lw Diffusion of other defects
85.40.Qx Microcircuit quality, noise, performance, and failure analysis

Bulk solidification and recalescence phenomena in amorphous Ge films upon picosecond pulsed laser irradiation

J. Siegel, J. Solis, C. N. Afonso, and C. García

J. Appl. Phys. 80, 6677 (1996); http://dx.doi.org/10.1063/1.363815 (6 pages) | Cited 17 times

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Melting and rapid solidification are induced in amorphous Ge films upon irradiation with 10 ps laser pulses at 583 nm. The role of heat flow during the solidification process was investigated by comparing the behavior of films grown on substrates with different thermal properties. The melting and solidification kinetics are followed in real time by reflectivity measurements in the nanosecond time scale and the induced structural changes are analyzed by means of Raman spectroscopy in micro‐Raman configuration. If the thermal diffusivity of the substrate is high enough, the film reamorphizes via bulk nucleation of the amorphous phase from the melt. When the thermal diffusivity of the substrate is reduced, the initial nucleation of the solid phase leads to an increase in the liquid temperature (recalescence) and in the melt duration, thus promoting the formation of the crystalline phase. © 1996 American Institute of Physics.
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64.70.D- Solid-liquid transitions
81.30.Fb Solidification
81.05.Cy Elemental semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators
68.55.-a Thin film structure and morphology
68.60.Wm Other nonelectronic physical properties

Unambiguous determination of crystal‐lattice strains in epitaxially grown SiGe/Si multilayers

A. Yu. Nikulin, P. Zaumseil, and P. V. Petrashen’

J. Appl. Phys. 80, 6683 (1996); http://dx.doi.org/10.1063/1.363793 (6 pages) | Cited 14 times

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A new method for unambiguous reconstruction of crystal‐lattice strains in epitaxially grown layers from high‐resolution x‐ray diffraction data is proposed. The technique uses x‐ray diffracted intensity profiles collected for two different radiation wavelengths. We enhance the theory for the previously developed algorithm for model‐independent determination of crystal‐lattice strain profiles in single crystals with epitaxially grown top‐surface layers. The method relies on the retrieval of the scattered x‐ray wave phase from its intensity profile via a logarithmic Hilbert transform. This phase‐retrieval technique is always associated with the problem of complex polynomial root finding. A practical procedure for the mapping of complex polynomial roots is proposed to distinguish true and virtual zeros. This allows the phase of the diffracted x‐ray wave to be retrieved unambiguously. The method was applied to determine physical dimensions and concentration composition of a Si/Si1−xGex/Si alloy multilayer structure typical for SiGe heterobipolar transistor device. © 1996 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
61.05.cp X-ray diffraction

The early stages of solid‐state reactions in Ni/Al multilayer films

C. Michaelsen, G. Lucadamo, and K. Barmak

J. Appl. Phys. 80, 6689 (1996); http://dx.doi.org/10.1063/1.363794 (10 pages) | Cited 52 times

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Ni/Al multilayer films with pair thicknesses of 10 and 20 nm and with overall compositions in the range 48–88 at. % Al were prepared by sputtering. For comparison, Ni‐Al alloy films in the same concentration range were prepared by co‐deposition of the elements. The films were studied by x‐ray diffraction, electron diffraction, and differential scanning calorimetry. It was found that the B2 NiAl phase with a metastable concentration of approximately 63 at. % Al was the first phase to grow upon annealing of the multilayer films. The growth of this phase could be described by Johnson–Mehl–Avrami kinetics with an activation energy of 0.8 eV and an Avrami exponent of 0.5. This low activation energy was consistent with the observation that the phase had formed during deposition and continued to grow upon annealing at low temperatures to thicknesses of a few nanometers. If the reactant phases were not fully consumed by the B2 phase growth, the subsequent reaction was the formation of NiAl3, previously thought to be the first product phase in the Ni‐Al system. The reduction of driving force by the preceding B2 phase growth explains why the formation of NiAl3 takes place by a nucleation‐and‐growth process, an observation that has been discussed controversially in the recent literature. The nucleation and growth of NiAl3 had an activation energy of 1.5 eV in agreement with previous studies. © 1996 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.40.Gh Other heat and thermomechanical treatments
68.35.Fx Diffusion; interface formation
68.35.Ct Interface structure and roughness
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Morphology and microstructure of epitaxial Cu(001) films grown by primary ion deposition on Si and Ge substrates

Brian W. Karr, Y. W. Kim, I. Petrov, D. B. Bergstrom, David G. Cahill, J. E. Greene, L. D. Madsen, and J.‐E. Sundgren

J. Appl. Phys. 80, 6699 (1996); http://dx.doi.org/10.1063/1.363795 (7 pages) | Cited 20 times

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A low‐energy, high‐brightness, broad beam Cu ion source is used to study the effects of self‐ion energy Ei on the deposition of epitaxial Cu films in ultrahigh vacuum. Atomically flat Ge(001) and Si(001) substrates are verified by in situ scanning tunneling microscopy (STM) prior to deposition of 300 nm Cu films with Ei ranging from 20 to 100 eV. Film microstructure, texture, and morphology are characterized using x‐ray diffraction ω‐rocking curves, pole figure analyses, and STM. Primary ion deposition produces significant improvements in both the surface morphology and mosaic spread of the films: At Ei>37 eV the surface roughness decreases by nearly a factor of 2 relative to evaporated Cu films, and at Ei≂35 eV the mosaic spread of Cu films grown on Si substrates is only ≂2°, nearly a factor of 2 smaller than that of evaporated Cu. During deposition with Ei≂25 eV on Ge substrates, the film coherently relaxes the 10% misfit strain by formation of a tilt boundary which is fourfold symmetric toward 〈111〉. The films have essentially bulk resistivity with ρ=1.9±0.1 μΩ cm at room temperature but the residual resistance at 10 K, ρ0, shows a broad maximum as a function of Ei, e.g., at Ei≂30 eV, ρ0=0.5 μΩ cm. © 1996 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.50.-h Electronic transport phenomena in thin films
73.61.At Metal and metallic alloys
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Mm Grain and twin boundaries

A refined scheme for the reduction of threading dislocation densities in InxGa1−xAs/GaAs epitaxial layers

G. MacPherson and P. J. Goodhew

J. Appl. Phys. 80, 6706 (1996); http://dx.doi.org/10.1063/1.363796 (5 pages) | Cited 4 times

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A scheme is presented for the reduction of threading dislocation densities in InxGa1−xAs/GaAs epitaxial single layers by accurate control of layer thickness. The model developed differs from previous models since the InxGa1−xAs growth is restricted to less than ten times the Matthews and Blakeslee critical thickness (hc) where the asymmetry in the [110] and [110] dislocation densities is the greatest. Beyond this thickness it is shown that the removal or annihilation of threading dislocations in the epilayer is more than offset by the introduction of new threading dislocations from spiral and Frank–Read‐type sources. Maintaining epilayer thickness below this thickness ensures that the majority of misfit dislocations generated lie predominantly in only one of the 〈110〉 directions, reducing the likelihood of blocking with orthogonal dislocations, thereby increasing the mean free path from that expected in higher density dislocation arrays. Etch pit densities show that the threading dislocation density can be reduced by up to a factor of 10 below that found in the substrate, with the added benefit of reducing the inhomogenities in the distribution of threading dislocations. Atomic force microscopy shows that the surface quality of these layers remains high with an absence of striations. © 1996 American Institute of Physics.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.35.B- Structure of clean surfaces (and surface reconstruction)

Substitutional versus interstitial carbon incorporation during pseudomorphic growth of Si1−yCy on Si(001)

H. J. Osten, Myeongcheol Kim, K. Pressel, and P. Zaumseil

J. Appl. Phys. 80, 6711 (1996); http://dx.doi.org/10.1063/1.363797 (5 pages) | Cited 57 times

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Molecular beam epitaxial growth of Si1−yCy alloys pseudomorphically strained on the (2×1) reconstructed Si(001) has been investigated as a function of growth conditions. An important question concerns the relation between substitutional and interstitial carbon incorporation, which has a large impact on electrical and optical properties of these layers. We show that the interstitial‐to‐substitutional carbon ratio is strongly influenced by the growth conditions, such as growth temperature and Si growth rate. Both reduction in growth temperature and increase of the overall growth rate lead to an increase in the substitutional‐to‐interstitial carbon ratio. However, these changes in growth conditions can also cause some deterioration in crystal quality. The carbon incorporation behavior is well described by first order kinetics. © 1996 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.J- Point defects and defect clusters
78.30.Hv Other nonmetallic inorganics
81.05.Hd Other semiconductors
78.66.Li Other semiconductors

Composition dependence of activation energy in solid phase epitaxial growth of Si1−xGex alloys

K. Y. Suh and Hong H. Lee

J. Appl. Phys. 80, 6716 (1996); http://dx.doi.org/10.1063/1.363745 (4 pages) | Cited 2 times

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A theoretical model called the ‘‘multibody model’’ is developed for the composition dependence of the activation energy. The model that is based on the diffusion required of the recrystallization for the solid phase epitaxy does not involve any adjustable parameters and is shown to represent experimental data satisfactorily. For the Si1−xGex alloys that are of diamond structure, the most logical choice is the ‘‘five‐body model’’ involving five atoms. The model is equally applicable to any other binary alloy. © 1996 American Institute of Physics.
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81.15.Np Solid phase epitaxy; growth from solid phases
81.05.Hd Other semiconductors

Heteroepitaxial structures of SrTiO3/TiN on Si(100) by in situ pulsed laser deposition

R. D. Vispute, J. Narayan, K. Dovidenko, K. Jagannadham, N. Parikh, A. Suvkhanov, and J. D. Budai

J. Appl. Phys. 80, 6720 (1996); http://dx.doi.org/10.1063/1.363798 (5 pages) | Cited 24 times

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High‐quality ceramics based heteroepitaxial structures of oxide‐nitride‐semiconductors, i.e., SrTiO3/TiN/Si(100) have been fabricated by in situ pulsed laser deposition. The dependence of substrate temperature and oxygen partial pressure on the crystalline quality of the SrTiO3 films on Si with epitaxial TiN template has been examined. We found that epitaxial growth occurs on TiN/Si(100) above 500 °C, initially at a reduced O2 pressure (10−6 Torr), and followed by a deposition in the range of 5–10×10−4 Torr. X‐ray diffraction (Θ, ω, and Φ scans) and transmission electron microscope (TEM) results revealed an excellent alignment of SrTiO3 and TiN films on Si(100) with a cube‐on‐cube epitaxy. Rutherford backscattering and ion channeling results show a channeling minimum yield (χmin) of ∼13% for the SrTiO3 films. High‐resolution TEM results on the SrTiO3/TiN interface show that the epitaxial SrTiO3 film is separated from the TiN by an uniform 80–90 Å crystalline interposing layer presumably of TiNxO1−x (oxy‐nitride). The SrTiO3 film fabricated at 700 °C showed a high relative dielectric constant of 312 at the frequency of 1 MHz. The electrical resistivity and the breakdown field of the SrTiO3 films were more than 5×1012 Ω cm and 6×105 V cm−1, respectively. An estimated leakage current density measured at an electric field of 5×105 V/cm−1 was less than 10−7 A/cm2. © 1996 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.80.Jh Ion radiation effects
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
77.22.Ch Permittivity (dielectric function)
77.22.Jp Dielectric breakdown and space-charge effects

Nanoindentation studies of single‐crystal (001)‐, (011)‐, and (111)‐oriented TiN layers on MgO

H. Ljungcrantz, M. Odén, L. Hultman, J. E. Greene, and J.‐E. Sundgren

J. Appl. Phys. 80, 6725 (1996); http://dx.doi.org/10.1063/1.363799 (9 pages) | Cited 88 times

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The mechanical properties of (001)‐, (011)‐, and (111)‐oriented MgO wafers and 1‐μm‐thick TiN overlayers, grown simultaneously by dc magnetron sputter deposition at 700 °C in a mixed N2 and Ar discharge, were investigated using nanoindentation. A combination of x‐ray‐diffraction (XRD) pole figures, high‐resolution XRD analyses, and Auger electron spectroscopy was used to show that all TiN films were single crystals with N/Ti ratios of 1.0±0.05. The nanoindentation measurements were carried out using a three‐sided pyramidal Berkovich diamond indentor tip operated at loads ranging from 0.4 to 40 mN. All three orientations of MgO substrates, as‐received, exhibited identical hardness values as determined using the Oliver and Pharr method. After a 1 h anneal at 800 °C, corresponding to the thermal treatment received prior to film growth, the measured hardness of MgO(001) was 9.0±0.3 GPa. All TiN films displayed a completely elastic response at low loads. Measured hardness values, which decreased with increasing loads, increased in the order (011)<(001)<(111). After a 30 s postdeposition anneal at 1000 °C, however, hardness was found to be independent of load except at displacements >100 nm where substrate effects were apparent. TiN(001) and (111) films had hardnesses of 20±0.8 and 21±1 GPa, respectively, while data obtained from (011) layers exhibited large scatter due to surface roughness effects. Young’s moduli for annealed samples, calculated from the elastic unloading curves, were found to be 307±15 GPa for MgO (001) and 445±38 and 449±28 GPa for TiN (001) and TiN (111), respectively. © 1996 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
62.20.Qp Friction, tribology, and hardness
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

Annealing behavior of silver, copper, and silver–copper nanoclusters in a silica matrix synthesized by the sol‐gel technique

G. De, M. Gusso, L. Tapfer, M. Catalano, F. Gonella, G. Mattei, P. Mazzoldi, and G. Battaglin

J. Appl. Phys. 80, 6734 (1996); http://dx.doi.org/10.1063/1.363800 (6 pages) | Cited 40 times

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Silver, copper, and mixed silver–copper nanocluster‐doped silica thin layers were prepared by the sol‐gel process. Samples were heat treated in different annealing atmospheres (air, argon, or 5%H2–95%N2) in the temperature range 500–1100 °C. Specimens were characterized by optical absorption spectroscopy, Rutherford backscattering spectrometry, x‐ray diffraction, and transmission electron microscopy. Cluster growth and dissolution, as well as migration of metal atoms towards the sample surface, with a subsequent evaporation, were observed to occur at temperatures that depend on the annealing atmosphere. In the mixed silver–copper system, the formation of Ag–Cu phase‐separated clusters was observed. © 1996 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.05.Bx Metals, semimetals, and alloys
81.40.Gh Other heat and thermomechanical treatments
61.72.Cc Kinetics of defect formation and annealing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Isothermal capacitance transient spectroscopy study of deep electron traps in low resistivity melt‐grown ZnSe single crystals

H. Okada

J. Appl. Phys. 80, 6740 (1996); http://dx.doi.org/10.1063/1.363801 (9 pages) | Cited 6 times

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Deep electron traps in ZnSe crystals grown by the vertical gradient freezing method using a sealed molybdenum capsule were studied by isothermal capacitance transient spectroscopy. These crystals have electron concentrations of 1015–1017 cm−3 in the as‐grown state. Besides the deep traps caused by isolated impurities, two characteristic traps were found. One is the most dominant trap in almost all samples studied, with an apparent activation enthalpy of ∼0.3 eV accompanied by an electron capture barrier of 0.05–0.29 eV. The concentration of this trap is less than 3×1015 cm−3. By a deconvolution of its highly broadened spectrum, the nontheoretical emission behavior was recognized as an overlapped emission of a number of different traps with similar emission time constants. That probably corresponds to the difference of the impurity species combined with the native defect in this trap. The other trap has an activation enthalpy of 1.03–1.1 eV and the concentrations of electrons captured by the trap are found to depend logarithmically on the duration of the filling pulse. The origin of this trap is assumed to be an impurity atom associated with extended defects such as dislocations. © 1996 American Institute of Physics.
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71.55.Gs II-VI semiconductors
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
65.20.-w Thermal properties of liquids
65.40.gd Entropy
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