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1 Sep 1993

Volume 74, Issue 5, pp. 2999-3623

Page 1 of 5 Pages Next Page | Jump to Page

Synthesis of x‐ray intensity profiles for x‐ray optical systems with curved diffractors

W. Z. Chang and D. B. Wittry

J. Appl. Phys. 74, 2999 (1993); http://dx.doi.org/10.1063/1.354615 (10 pages) | Cited 11 times

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A procedure for synthesizing the x‐ray intensity profile for x‐ray optical systems employing curved diffractors is presented. The synthesis takes account of the effects of misalignment, the solid angle, and the convergence or divergence of the diffracted x rays. Broadening effects due to finite source size, wavelength spread, and presence of polychromatic radiation have also been included. The broadening effects on the intensity profile are demonstrated analytically. By comparing experimental results with results from the synthesis method, curved diffractor’s parameters (rocking curve width and peak reflectivity) were quantitatively evaluated for mica, silicon, graphite, and LiF crystals at three x‐ray wavelengths.
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07.85.-m X- and γ-ray instruments
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
41.50.+h X-ray beams and x-ray optics

Mass spectrometric detection of neutral radicals in a CH4 microwave discharge by use of Li+ ion attachment techniques

Toshihiro Fujii and Ken‐ichi Syouji

J. Appl. Phys. 74, 3009 (1993); http://dx.doi.org/10.1063/1.354616 (4 pages) | Cited 23 times

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The chemical species of the neutral radicals in the methane microwave (MW) discharge plasma were studied by quadrupole mass spectrometry in combination with a Li+ ion attachment technique. The approach is to have a MW discharge flow pass a lithium ion emitter and then to analyze, by quadrupole mass spectrometry, all ions formed by lithium ion attachment. Mainly, radicals such as CnH2n+1 (n=2–11) and CnH2n−1 (n=2–11) were detected. Species such as C4H3, C5H5, and C6H5 may also be produced in the process. Many such species have been identified for the first time. The presence of these species is evaluated by comparison with results from optical spectroscopy and threshold ionization mass spectrometry.
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33.15.Ta Mass spectra
52.80.Pi High-frequency and RF discharges
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)

Behavior of the energy density in the Fresnel region of a conducting circular disk excited by single‐cycle sinusoids

S. N. Samaddar

J. Appl. Phys. 74, 3013 (1993); http://dx.doi.org/10.1063/1.354617 (11 pages) | Cited 7 times

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By comparing the radiated energy densities in the Fresnel’s region due to excitations by a cw (continuous wave) sin ω0t and a single‐cycle sin ω0t, it is shown that the single‐cycle pulse is more efficient in collimating (or focusing) the energy in the vicinity of the disk axis. We have also considered a single‐cycle cos ω0t pulse as an exciting source, which may be more academic than realistic. Nonetheless, the results shed some light in showing clearly that the shorter the rise time of a pulse, the slower is the decay of the radiated energy, and hence, it is highly efficient in focusing the energy in front of the radiating device. It follows then that whenever the transmission of a collimated beam of energy to a large distance along the axis of the radiating aperture is desired, it can be accomplished more efficiently by using a short pulse, instead of a cw source.
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03.50.De Classical electromagnetism, Maxwell equations
41.85.Ew Particle beam profile, beam intensity
42.25.Bs Wave propagation, transmission and absorption
43.20.Px Transient radiation and scattering

Nonlinear Fabry–Perot cavity with chalcogenide glass thin films

M. Bertolotti, V. Chumash, E. Fazio, A. Ferrari, and C. Sibilia

J. Appl. Phys. 74, 3024 (1993); http://dx.doi.org/10.1063/1.354618 (4 pages) | Cited 2 times

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An investigation of a chalcogenide glass thin‐film Fabry–Perot cavity has been performed in picosecond time regime. Nonlinear behavior of the structure derives from both nonlinear absorption of the material and changes in the resonance conditions of the cavity. The conditions to have bistable behavior have been established.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.25.Hz Interference
78.66.Jg Amorphous semiconductors; glasses

A laminated plate theory for high frequency, piezoelectric thin‐film resonators

Y.‐K. Yong, J. T. Stewart, and A. Ballato

J. Appl. Phys. 74, 3028 (1993); http://dx.doi.org/10.1063/1.354619 (19 pages) | Cited 7 times

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A high frequency, piezoelectric, laminated plate theory is developed and presented for the purpose of modeling and analyzing piezoelectric thin‐film resonators and filters. The laminated plate equations are extensions of anisotropic composite plate theories to include piezoelectric effects and capabilities for modeling harmonic overtones of thickness‐shear vibrations. Two‐dimensional equations of motion for piezoelectric laminates were deduced from the three‐dimensional equations of linear piezoelectricity by expanding the mechanical displacements and electric potential in a series of trigonometric function, and obtaining stress resultants by integrating through the plate thickness. Relations for handling the mechanical and electrical effects of platings on the top and bottom surfaces of the laminate are derived. A new matrix method of correcting the cutoff frequencies is presented. This matrix method could also be used to efficiently correct the cutoff frequencies of any nth order plate laminate theories which employ Mindlin’s form of polynomial expansion of mechanical displacements and electric potential through the plate thickness. The first order laminated plate theory with correction factors for cutoff frequencies and slope of the flexural branch at large frequencies was applied to a 2‐layer, zinc oxide‐silicon strip, and a 3‐layer, zinc oxide‐zinc oxide‐silicon strip. Open circuit, dispersion relations were generated for a range of volume fractions and compared to the exact dispersion relations.
Both the 2‐layer and 3‐layer strip show similar qualitative comparison: The present theory compares fairly well with the exact dispersion relation for real wave numbers and nonpropagating (imaginary) wave numbers which are smaller than 0.5i. The extensional branch, and thickness‐shear branches begin to deviate from the exact solution when the nondimensionalized frequency is greater than one. Consequently, to maintain accuracy of solutions when using the present first order laminated plate theory, one should limit the calculation of resonant, nondimensionalized frequencies to less than 1.1. Results for the frequency spectrum in the vicinity of the open circuit, fundamental thickness‐shear frequency, and modes shapes were presented for the 2‐layer strip with fixed edges, and a volume fraction of silicon equal to 0.2. The technically important fundamental thickness‐shear mode is found to have the shear component strongly coupled with extensional component.
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77.65.Fs Electromechanical resonance; quartz resonators
43.35.-c Ultrasonics, quantum acoustics, and physical effects of sound
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Thermal conductivity of the molecular crystal (–)2–(α–methylbenzylamino)‐5‐nitropyridine

R. T. Bailey, F. R. Cruickshank, P. Kerkoc, D. Pugh, and J. N. Sherwood

J. Appl. Phys. 74, 3047 (1993); http://dx.doi.org/10.1063/1.354620 (5 pages) | Cited 9 times

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Thermal diffusivities of high quality (‐)2‐(α‐methylbenzylamino)‐5‐nitropyridine (MBANP) single crystals were measured in different directions by the flash diffusivity method. The complete thermal conductivity tensor at temperatures of 295, 323, and 349 K was then obtained for this monoclinic crystal from the thermal diffusivity, specific heat, and density data. For instance, the thermal conductivity coefficients at 295 K are k1=0.27 W/mK, k2=0.29 W/mK, and k3=0.20 W/mK. The peak melting point of MBANP lies at 357.3 K, whereas the corresponding enthalpy of melting ΔHm has a value 67.2 J/g.  
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66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
05.70.Ce Thermodynamic functions and equations of state

Numerical study of relativistic electron‐beam electrostatic pumping by anode aperture

I. G. Yovchev, I. P. Spassovsky, N. A. Nikolov, K. G. Kostov, and V. A. Spassov

J. Appl. Phys. 74, 3052 (1993); http://dx.doi.org/10.1063/1.355320 (5 pages) | Cited 3 times

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Quality and pumping of an electron beam by means of the inhomogeneous electrostatic field at an anode aperture are investigated using numerical simulation. A specially developed relativistic particle‐in‐cell code, described here, is employed. The longitudinal velocity spread and the pitch ratio of the beam electrons are derived for different aperture radii and cathode‐aperture distances. The presented results could be practically useful for operation of high‐power cyclotron resonance masers with a sharpened cathode and an anode aperture. The beam pumping in such devices is typically achieved by more complicated systems (pumping magnet, adiabatically changing magnetic field, etc.). The numerical simulations show a significant pumping effect coming from the anode aperture itself.
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52.75.-d Plasma devices
84.40.Ik Masers; gyrotrons (cyclotron-resonance masers)

Microwave/millimeter‐wave generation in a counterstreaming‐beam‐plasma system

R. W. Schumacher, J. Santoru, M. Rosenberg, and N. A. Krall

J. Appl. Phys. 74, 3057 (1993); http://dx.doi.org/10.1063/1.354621 (4 pages)

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Radiation from 8 to 60 GHz is generated by injecting counterstreaming, high‐power (up to 50 keV and 4 A) electron beams into an unmagnetized, plasma‐loaded waveguide. The radiation is emitted at twice the plasma frequency and is amplitude modulated on the ion plasma frequency time scale. The beam‐to‐millimeter‐wave power conversion efficiency at 31 GHz is ≳0.04%. A turbulence theory model is consistent with the radiation characteristics and power scalings.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.40.Mj Particle beam interactions in plasmas

Plasma edge and its application to infrared measurement and detection

Dingrong Qian

J. Appl. Phys. 74, 3061 (1993); http://dx.doi.org/10.1063/1.354622 (4 pages)

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A steep plasma edge in infrared reflectivity spectra of Hg1−xCdxTe and HgSe:Fe has been observed. It is predicted that the edge is sensitive to the variation of carrier concentration, which indicates the possibility of developing a fast light‐controlled switch for infrared radiation as well as a new approach of infrared modulation and detection. The modulation gain in power and detectivity limited by the generation‐recombination process has been calculated and compared with the photoconductive counterpart.
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78.30.Fs III-V and II-VI semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
85.60.Gz Photodetectors (including infrared and CCD detectors)

Mathematical modeling of a free‐burning arc in the presence of metal vapor

J. J. Gonzalez, A. Gleizes, P. Proulx, and M. Boulos

J. Appl. Phys. 74, 3065 (1993); http://dx.doi.org/10.1063/1.354624 (6 pages) | Cited 46 times

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The transfer of energy between the plasma and the iron anode and the evaporation of metal were taken into account in modeling a short free‐burning arc in argon at atmospheric pressure. The presence of metal vapor in the plasma modifies the electrical conductivity and the radiated power and leads to arc cooling in the anode region. In return, the arc cooling modifies the rate of vaporization of the anode and thus the calculated concentration of iron vapor in the arc.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity

Influence of irradiation conditions on plasma evolution in laser‐surface interaction

J. Hermann, C. Boulmer‐Leborgne, B. Dubreuil, and I. N. Mihailescu

J. Appl. Phys. 74, 3071 (1993); http://dx.doi.org/10.1063/1.354594 (9 pages) | Cited 15 times

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The plasma plume induced by pulsed CO2 laser irradiation of a Ti target at power densities up to 4×108 W cm−2 was studied by emission spectroscopy. Time‐ and space‐resolved measurements were performed by varying laser intensity, laser temporal pulse shape, ambient gas pressure, and the nature of the ambient gas. Experimental results are discussed by comparison with usual models. We show that shock wave and plasma propagation depend critically on the ratio Ivap/Ii, Ivap being the intensity threshold for surface vaporization and Ii the plasma ignition threshold of the ambient gas. Spectroscopic diagnostics of the helium breakdown plasma show maximum values of electron temperature and electron density in the order of kTe∼10 eV and ne=1018 cm−3, respectively. The plasma cannot be described by local thermodynamic equilibrium modeling. Nevertheless, excited metal atoms appear to be in equilibrium with electrons, hence, they can be used like a probe to measure the electron temperature. In order to get information on the role of the plasma in the laser‐surface interaction, Ti surfaces were investigated by microscopy after irradiation. Thus an enhanced momentum transfer from the plasma to the target due to the recoil pressure of the breakdown plasma could be evidenced.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
79.20.Ds Laser-beam impact phenomena

The defect structure of congruently melting lithium niobate

A. P. Wilkinson, A. K. Cheetham, and R. H. Jarman

J. Appl. Phys. 74, 3080 (1993); http://dx.doi.org/10.1063/1.354572 (4 pages) | Cited 27 times

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Six samples of congruently melting lithium niobate (∼Li0.95Nb1.01O3) have been examined by powder x‐ray diffraction for the occurrence of niobium antisite defects (niobium on lithium sites). Contrary to current thinking, we have found no evidence for the occurrence of high concentrations of such defects, which also require the presence of Nb site vacancies. Rather, it was found that the number of antisite defects is close to the minimum that is required to sustain charge neutrality in a model of the type ([Li1−xNbx/5][Nb]O3), where the Nb site is fully occupied.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Crystallization of arsenic‐doped hydrogenated amorphous silicon deposited on gallium arsenide

Katsuhiro Yokota, Masanori Sakaguchi, Daidou Uchida, Takafumi Kuroda, and Susumu Tamura

J. Appl. Phys. 74, 3084 (1993); http://dx.doi.org/10.1063/1.354573 (7 pages) | Cited 2 times

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Crystallization temperatures of a‐Si:H films deposited on GaAs substrates by a glow‐discharge method increased with an increase in the concentration of As doped into the a‐Si:H films. Crystallization of a‐Si:H films with an As concentration of 2×1020 cm−3 started at a temperature of about 1050 °C. These a‐Si:H films also had a large amounts of H and SiH3.  
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61.43.Dq Amorphous semiconductors, metals, and alloys
68.55.-a Thin film structure and morphology
61.50.Ks Crystallographic aspects of phase transformations; pressure effects

Observation of ion‐implantation‐damage‐created n‐type conductivity in InP after high‐temperature annealing

B. Molnar, T. A. Kennedy, E. R. Glaser, and H. B. Dietrich

J. Appl. Phys. 74, 3091 (1993); http://dx.doi.org/10.1063/1.354574 (8 pages) | Cited 8 times

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The conductivity and the impurity profiles of InP implanted with dopant ions (Si,Be) or non dopant ions (B,H,N,O,P) have been investigated. Experiments have been done in substrates with and without Fe doping. Low‐temperature, short‐time annealing of implanted Si and Be reveals an n‐type distribution of carriers which cannot be accounted for on the basis of implant activation. In order to examine the contribution without the carriers originating from the dopant ions, the behavior of electrically inactive B, H, N, O, and P, implants was investigated. Implantation of these ions into semi‐insulating InP introduced n‐type doping in the 1×1016 cm3 range after an anneal above 450 °C. For H, O, N, and P ions, the n‐type conductivity could be eliminated by annealing at higher temperatures. However, boron anneals up to 750 °C did not eliminate the n‐type conductivity. The n‐type carrier profiles tracked the ion profiles. The carrier profile is influenced by the redistribution of the Fe during annealing; however, the Fe motion cannot explain the n‐type conductivity. This conductivity may be due to a complex formed above 450 °C.
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61.72.uj III-V and II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
76.70.Hb Optically detected magnetic resonance (ODMR)

Proton implantation intermixing of GaAs/AlGaAs quantum wells

Gregory F. Redinbo, Harold G. Craighead, and J. Minghuang Hong

J. Appl. Phys. 74, 3099 (1993); http://dx.doi.org/10.1063/1.354575 (4 pages) | Cited 14 times

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We have investigated proton implantation enhanced intermixing of GaAs/AlGaAs quantum wells for H+ doses ranging from 5×1013 to 1×1016 ions/cm2. Implantation of 20 keV H+ followed by a high temperature rapid thermal anneal leads to enhanced diffusion of Al into the GaAs quantum well. Shifts of electron–heavy hole recombination energies due to compositional changes were observed using room temperature cathodoluminescence. Diffusion lengths of longer than 2 nm were calculated from energy shifts in a 5 nm well and were found to vary with both implanted dose and anneal time, as expected if the enhanced interdiffusion is caused by implantation introduced defects.
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61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
78.60.Hk Cathodoluminescence, ionoluminescence

The barrier to misfit dislocation glide in continuous, strained, epitaxial layers on patterned substrates

G. Patrick Watson, Dieter G. Ast, Timothy J. Anderson, and Balu Pathangey

J. Appl. Phys. 74, 3103 (1993); http://dx.doi.org/10.1063/1.354576 (8 pages) | Cited 3 times

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In a previous report [G. P. Watson, D. G. Ast, T. J. Anderson, and Y. Hayakawa, Appl. Phys. Lett. 58, 2517 (1991)] we demonstrated that the motion of misfit dislocations in InGaAs, grown by organometallic vapor phase epitaxy on patterned GaAs substrates, can be impeded even if the strained epitaxial layer is continuous. Trenches etched into GaAs before growth are known to act as a barrier to misfit dislocation propagation [E. A. Fitzgerald, G. P. Watson, R. E. Proano, D. G. Ast, P. D. Kirchner, G. D. Pettit, and J. M. Woodall, J. Appl. Phys. 65, 2220 (1989)] when those trenches create discontinuities in the epitaxial layers; but even shallow trenches, with continuous strained layers following the surface features, can act as barriers. By considering the strain energy required to change the length of the dislocation glide segments that stretch from the interface to the free surface, a simple model is developed that explains the major features of the unique blocking action observed at the trench edges. The trench wall angle is found to be an important parameter in determining whether or not a trench will block dislocation glide. The predicted blocking angles are consistent with observations made on continuous 300 and 600 nm thick In0.04Ga0.96As films on patterned GaAs. Based on the model, a structure is proposed that may be used as a filter to yield misfit dislocations with identical Burgers vectors or dislocations which slip in only one glide plane.
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61.72.Lk Linear defects: dislocations, disclinations
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Effect of rubbing on the molecular orientation within polyimide orienting layers of liquid‐crystal displays

N. A. J. M. van Aerle, M. Barmentlo, and R. W. J. Hollering

J. Appl. Phys. 74, 3111 (1993); http://dx.doi.org/10.1063/1.354577 (10 pages) | Cited 70 times

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The influence of various rubbing parameters on the molecular reorientation of thin polyimide orienting layers, used to align liquid‐crystal (LC) molecules within liquid‐crystal displays, has been studied. For this purpose the optical phase retardation in the polymer layer, explicitly induced during the rubbing treatment, was determined. The observed rubbing‐induced phase retardation can directly be related to a molecular orientation within the polymer orienting layer, as could be shown by infrared dichroism studies. Furthermore, it is found that the top of the polymer layer, directly contacting the rubbing cloth during the actual rubbing process, is almost instantaneously oriented to a certain maximum value as soon as the rubbing is started. Additional or stronger rubbing has no detectable influence on the orientation within the top layer. Increasing the rubbing density or the rubbing pressure only results in an increase of the penetration depth of the rubbing process, i.e., molecular reorientation occurs deeper within the layer. Experiments show that the penetration depth can be varied from less than 10 nm to more than 60 nm by variation in rubbing conditions. These findings are supported by surface second‐harmonic‐generation studies of LC monolayers deposited onto rubbed orienting layers and by infrared dichroism studies.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
78.66.Qn Polymers; organic compounds
85.60.Pg Display systems

Determining the lattice relaxation in semiconductor layer systems by x‐ray diffraction

Paul F. Fewster and Norman L. Andrew

J. Appl. Phys. 74, 3121 (1993); http://dx.doi.org/10.1063/1.354578 (5 pages) | Cited 36 times

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This paper illustrates the procedure for extracting structural information available from x‐ray diffraction space mapping and topography. The methods of measuring, the residual strain, macroscopic tilts, microscopic tilts and their lateral dimensions, and the strain field disruption emanating from the interfacial defects are presented. Partially relaxed thick InGaAs layers on GaAs substrates were studied and it was concluded that the relaxation and macroscopic tilting were anisotropic, the microscopic tilting reduced with thickness, and the interfacial disruption did not continue to increase with increasing relaxation. A ‘‘mosaic grain growth’’ model is postulated to account for the diminishing microscopic tilt spread and increasing topographic contrast with layer thickness.
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61.05.C- X-ray diffraction and scattering
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology

Near‐surface region characterization by extremely asymmetric Bragg reflection topography

Dachao Gao, Stephen W. Wilkins, Andrew W. Stevenson, and Geoff N. Pain

J. Appl. Phys. 74, 3126 (1993); http://dx.doi.org/10.1063/1.354579 (5 pages) | Cited 2 times

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Near‐surface regions of Cd1−xMnxTe and Hg1−xCdxTe epilayers (down to tens of angstroms) on (001) GaAs substrates have been characterized by extremely asymmetric Bragg reflection topography (EABRT) with the laboratory x‐ray source condition and a Lang camera, using x‐ray grazing incidence angles less than the critical angle for total external reflection. The experimental topographs obtained in the present work illustrate the potential of the EABRT technique for nondestructive characterization of near‐surface regions of crystals. The resolution of an image in EABRT is discussed in detail.
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61.05.cf X-ray scattering (including small-angle scattering)
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
68.55.-a Thin film structure and morphology
07.85.-m X- and γ-ray instruments

Cooperative behavior during ferroelectric transitions in KNO3 powder

M. J. Westphal

J. Appl. Phys. 74, 3131 (1993); http://dx.doi.org/10.1063/1.354580 (6 pages) | Cited 5 times

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Experimental evidence of cooperative behavior during the ferroelectric phase transitions in granular and powder KNO3 at atmospheric pressure is presented. Three different experimental studies were performed in which phase transitions were detected and characterized by heat flow calorimetry: (1) the distribution of SiC powder in granular KNO3 was varied; (2) the volume fraction of SiC in powdered KNO3 was varied; and (3) pure KNO3 powder was thermally cycled. All three studies provided evidence of cooperative behavior between the KNO3 particles during the III‐II phase transition. The cooperative behavior reduced the temperature range of phase III stability from ∼97–124 °C to that characteristic of bulk material (∼110–124 °C). Separate KNO3 particles behaved as individual ferroelectric domains, with each particle making the phase transition independently near the expected Curie temperature. Particles of KNO3 in intimate physical contact tended to behave cooperatively as a single large ferroelectric domain leading to sharper phase transitions more characteristic of single crystals. The degree of cooperative behavior was dependent upon the extent to which the individual particles were in physical contact. The absence of the III‐II phase transition in KNO3 powder that has been reported in the literature can be understood from the results obtained using SiC powder to separate KNO3 particles during heat flow calorimetry measurements.
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77.80.B- Phase transitions and Curie point
64.70.K- Solid-solid transitions
81.05.Rm Porous materials; granular materials

Kinetics of the amorphous‐to‐nanocrystalline transformation in Fe73.5Cu1Nb3Si13.5B9

P. Allia, M. Baricco, P. Tiberto, and F. Vinai

J. Appl. Phys. 74, 3137 (1993); http://dx.doi.org/10.1063/1.354581 (7 pages) | Cited 21 times

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Isothermal measurements of the electrical resistance R were performed in samples of the alloy Fe73.5Cu1Nb3Si13.5B9 at temperatures where the nanocrystalline phase develops. At each temperature, nanocrystallization is associated to a very slow decrease of R(t) compared to conventional crystallization processes. X‐ray‐diffraction data were obtained on similar samples annealed at the same temperatures for selected times. The evolving nanocrystalline fraction turns out to be essentially proportional to the variation in the electrical resistance. The form of the kinetic law describing the R(t) decays is obtained by making use of a novel procedure, developed to analyze time‐dependent properties characterized by a complex behavior. Nanocrystallization in the considered alloy appears as initially described by a Johnson–Mehl–Avrami kinetics with exponent n≂4, suggesting that the early stages of the process involve homogeneous nucleation and three‐dimensional grain growth. For longer times, corresponding to the hearth of the nanocrystallization process, and at all temperatures, the functional form of the kinetic law drastically changes to a much slower power law of the type R∼At−α. The exponent α turns out to be essentially independent of temperature. Such a change presumably reflects a reduction in the grain growth velocity and/or in the nucleation rate.
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64.70.K- Solid-solid transitions
61.43.-j Disordered solids
81.40.Rs Electrical and magnetic properties related to treatment conditions

Thermodynamic properties of metastable Ag‐Cu alloys

R. Najafabadi, D. J. Srolovitz, E. Ma, and M. Atzmon

J. Appl. Phys. 74, 3144 (1993); http://dx.doi.org/10.1063/1.354582 (6 pages) | Cited 49 times

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The enthalpies of formation of metastable fcc Ag‐Cu solid solutions, produced by ball milling of elemental powders, were determined by differential scanning calorimetry. Experimental thermodynamic data for these metastable alloys and for the equilibrium phases are compared with both calculation of phase diagrams (CALPHAD) and atomistic simulation predictions. The atomistic simulations were performed using the free‐energy minimization method (FEMM). The FEMM determination of the equilibrium Ag‐Cu phase diagram and the enthalpy of formation and lattice parameters of the metastable solid solutions are in good agreement with the experimental measurements. CALPHAD calculations made in the same metastable regime, however, significantly overestimate the enthalpy of formation. Thus, the FEMM is a viable alternative approach for the calculation of thermodynamic properties of equilibrium and metastable phases, provided reliable interatomic potentials are available. The FEMM is also capable of determining such properties as the lattice parameter which are not available from CALPHAD calculations.  
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64.60.My Metastable phases
65.20.-w Thermal properties of liquids
65.40.gd Entropy
81.30.Bx Phase diagrams of metals, alloys, and oxides
64.75.-g Phase equilibria

Diffusion of dopants in B‐ and Sb‐delta‐doped Si films grown by solid‐phase epitaxy

H.‐J. Gossmann, A. M. Vredenberg, C. S. Rafferty, H. S. Luftman, F. C. Unterwald, D. C. Jacobson, T. Boone, and J. M. Poate

J. Appl. Phys. 74, 3150 (1993); http://dx.doi.org/10.1063/1.354583 (6 pages) | Cited 32 times

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The diffusion of δ‐function‐shaped B‐ and Sb‐dopant spikes in thin Si films grown by solid‐phase‐epitaxy [(SPE), growth of amorphous film by molecular‐beam epitaxy (MBE) at room temperature and subsequent regrowth in situ] during annealing in vacuum is compared to diffusion in films grown by low‐temperature (LT) MBE. Diffusion temperatures from 750 to 900 °C, and two‐dimensional concentrations of 0.7–1.6×1014 cm−2 have been investigated. The diffusive behavior of dopants in SPE films is found to be qualitatively different from that in films grown by LTMBE. This is related to the vacancylike defects that are intrinsic to growth by SPE but not to growth by LTMBE. Dopant profiles widen significantly during SPE regrowth, making the achievement of δ‐function dopant spikes impossible. After a vacuum anneal the diffusion coefficients for both n‐ and p‐type dopants are lower in SPE films than the corresponding values in films grown by LTMBE by up to one order of magnitude. The diffused depth profile of the dopant in LTMBE films shows the characteristic deviation from a pure Gaussian that is expected due to the concentration dependence of diffusion, i.e., a flat top and steep shoulders. In contrast, dopant depth profiles of SPE‐grown material show after diffusion a central spike and relatively flat shoulders. The width of the central spike is, after an initial transient that it was not possible to resolve, independent of diffusion time and temperature. This indicates that the SPE material is defective, with the defects acting as traps during diffusion.
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66.30.J- Diffusion of impurities
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.uf Ge and Si

Epitaxial growth of CoSi2 on Si wafer using Co/Ta bilayer

Jeong Soo Byun, Sug Bong Kang, Hyeong Joon Kim, Cha Yeon Kim, and Kyo Ho Park

J. Appl. Phys. 74, 3156 (1993); http://dx.doi.org/10.1063/1.354584 (6 pages) | Cited 8 times

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A CoSi2 epitaxial layer was grown by thermal annealing of Co/Ta bilayer on a Si(100) wafer in the NH3 ambient. During thermal annealing an intermediate Ta layer between a Co layer and a Si wafer played two important roles for epitaxial growth of CoSi2. One was a reduction of a native oxide on a Si substrate, which resulted in an atomically clean Si surface. The other was a limitation of a flux of Co atoms to the Si surface, which made CoSi2 the most stable phase among several cobalt silicide ones. Both roles of the Ta layer made it possible to produce an epitaxial layer of CoSi2 with a coherent interface with a Si substrate, even at the early stage of thermal annealing.
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81.15.Np Solid phase epitaxy; growth from solid phases

GaAs free‐standing quantum‐size wires

Kenji Hiruma, Masamitsu Yazawa, Keiichi Haraguchi, Kensuke Ogawa, Toshio Katsuyama, Masanari Koguchi, and Hiroshi Kakibayashi

J. Appl. Phys. 74, 3162 (1993); http://dx.doi.org/10.1063/1.354585 (10 pages) | Cited 71 times

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Ultrathin GaAs wires as thin as 15–40 nm and about 2 μm long have been grown on a GaAs substrate by metal‐organic vapor‐phase epitaxy. The wires, which consist of whiskers, are grown between 380 and 550 °C using trimethylgallium and arsine (AsH3) as source materials. It is found that the wire growth direction is parallel to the [111] arsenic dangling‐bond direction and can be perfectly controlled by the crystallographic orientation of the GaAs substrate surface. From transmission electron microscopic analysis it is revealed that the crystal structure of the wire coincides with the zinc‐blende type for the growth temperature range of 460–500 °C, but it changes to the wurtzite type at 420 °C and temperatures higher than 500 °C. It is also found that the wires have a twin‐type structure around the [111] growth axis for zinc blende and [0001] growth axis for wurtzite. Photoluminescence study of these wires shows that the luminescence peak energy shifts to a higher energy as the wire width decreases from 100 to about 35 nm. In terms of luminescence polarization it is confirmed that the luminescence intensity parallel to the wires is four times greater than that perpendicular to the wires. These results clearly indicate the quantum‐size effect of carriers confined in the wire. As a preliminary application to devices, a p‐n junction has been formed along the GaAs wire. Light emission by current injection to the p‐n junction wires has been observed in continuous operation at room temperature.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.55.Cr III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
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