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15 Mar 1998

Volume 83, Issue 6, pp. 2879-3444

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X-ray sensitivity of a-Se for x-ray imaging with electrostatic readout

S. O. Kasap, V. Aiyah, B. Polischuk, and A. Baillie

J. Appl. Phys. 83, 2879 (1998); http://dx.doi.org/10.1063/1.367074 (9 pages) | Cited 7 times

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Currently there is much interest in stabilized amorphous selenium (a-Se alloyed with 0.2–0.3% As and doped with 5–20 ppm Cl) as an x-ray photoconductor in various x-ray imaging systems. Although optical photogeneration in a-Se is well characterized, experiments on its x-ray sensitivity have been limited and, further, have resulted in widely differing conclusions especially for the electron hole pair (EHP) creation energy EEHP. In this work, we first introduce absolute and incremental sensitivity (S and s, respectively) concepts within the electrostatic readout mode of operation and then establish models linking these two sensitivities to the energy EEHP absorbed to create a free EHP. X-ray irradiation induced xerographic discharge experiments have been carried out on vacuum deposited stabilized a-Se x-ray photoconductor films to examine how the sensitivity depends on the charge carrier schubwegs (μτF where μ is the drift mobility, τ is the lifetime, and F is the electric field), the mean photon energy, and the detector thickness L. Experiments indicate that unless both electron and hole schubwegs are much longer than the photoconductor thickness, the sensitivity is reduced. The efficiency of EHP generation per absorbed x-ray photon, i.e., the apparent energy absorbed per free electron hole pair EEHP has been determined as a function of electric field and mean photon energy. EEHP decreases with increasing applied field and energy. By examining EEHP vs 1/F and extrapolating to 1/F = 0, a saturation value EEHP0 for EEHP is predicted and estimated (4 to 6 eV) which, within experimental errors, is close to the theoretical expectation of ∼ 2.2Eg and substantially smaller than previously reported values for EEHP0 (18–29 eV). © 1998 American Institute of Physics.
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73.61.Jc Amorphous semiconductors; glasses
73.50.Pz Photoconduction and photovoltaic effects
85.60.-q Optoelectronic devices
07.85.-m X- and γ-ray instruments

Ellipsometric measurements of the polarizability anisotropies of push–pull molecules in solution

A. Fort, J. Muller, O. Cregut, L. Mager, J. P. Vola, and M. Barzoukas

J. Appl. Phys. 83, 2888 (1998); http://dx.doi.org/10.1063/1.367075 (6 pages) | Cited 2 times

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We have developed an experimental setup for the measurement of the polarizability anisotropy of push–pull molecules in solution. We have used this technique to investigate prototype push–pull molecules that have been incorporated as doping chromophores in low glass transition temperature photorefractive polymers. Results obtained evidence for these compounds that the refractive index modulation is dominated by the orientational birefringence contribution while the electro-optic contribution remains small. © 1998 American Institute of Physics.
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78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Gi Light-sensitive materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Jk Polymers and organics
78.20.Fm Birefringence
78.20.Jq Electro-optical effects
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Ultrafast wide range all-optical switch using complex refractive-index changes in a composite film of silver and polymer containing photochromic dye

Kyoichi Sasaki and Toshihiko Nagamura

J. Appl. Phys. 83, 2894 (1998); http://dx.doi.org/10.1063/1.367076 (7 pages) | Cited 48 times

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An all-optical ultrafast switch which operates at a wide wavelength range has been demonstrated based on photoinduced changes of real and/or imaginary parts of complex refractive index in a composite thin film of silver and polymer containing photochromic spiropyran dye. Very fast switching ON and OFF of a reading beam within 20 ns in a 400–800 nm range was achieved at the incident angle of guided-wave mode using a photochromic spiropyran-doped polystyrene thin film and a ns pulsed UV or visible laser as a writing beam. These responses were caused by the changes of complex refractive index due to photochromism. No applied power was required to hold the switched state. An image was also written to the probe beam by irradiation through a pattern. © 1998 American Institute of Physics.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
78.47.-p Spectroscopy of solid state dynamics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Qn Polymers; organic compounds
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Thermal lensing measurements in line-focus end-pumped neodymium yttrium aluminium garnet using holographic lateral shearing interferometry

Justin L. Blows, Judith M. Dawes, and Takashige Omatsu

J. Appl. Phys. 83, 2901 (1998); http://dx.doi.org/10.1063/1.367077 (6 pages) | Cited 12 times

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Thermal lensing in compact neodymium yttrium aluminium garnet slabs and rods end pumped with a beam brought to a line focus has been measured using holographic lateral shearing interferometry. This powerful technique enabled us to directly measure thermal lenses with focal lengths in the range 0.02–12 m with an accuracy of 12% and good spatial resolution. It was found that the line focused pump beam resulted in severe astigmatic thermal lensing. The measured thermal lens strongly deviated from the ideal parabolic profile along both axes, introducing an important additional consideration for laser-diode end-pumped laser resonator design. The degree of longitudinal heat flow was found to strongly influence thermal lens power. It is anticipated that results obtained from the measurement technique presented here will enable optimal design of high-power end-pumped solid-state laser cavities. © 1998 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.40.Kw Holographic interferometry; other holographic techniques
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Material transport during excimer-laser nitriding of iron

C. Illgner, P. Schaaf, K.-P. Lieb, R. Queitsch, and J. Barnikel

J. Appl. Phys. 83, 2907 (1998); http://dx.doi.org/10.1063/1.367116 (8 pages) | Cited 22 times

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The surface topology and nitrogen concentration profiles of iron irradiated with pulses of an excimer laser in a nitrogen atmosphere were studied by means of optical and scanning electron microscopy, surface profilometry, energy-dispersive x-ray spectroscopy, and resonant nuclear reaction analysis. The observations are combined to distinguish several mechanisms contributing to the material transport: ablation, redeposition of nitride from the plasma and pressure-induced lateral flow of the molten iron towards the edges of the laser spot (piston mechanism). Numerical estimates of the time and spatial evolution of temperature and pressure at the surface led to average rates of the material transport in good agreement with the experiment. © 1998 American Institute of Physics.
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81.05.Bx Metals, semimetals, and alloys
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
68.35.Fx Diffusion; interface formation
79.20.Ds Laser-beam impact phenomena
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
82.80.Jp Activation analysis and other radiochemical methods

Second-harmonic generation of femtosecond high-intensity Ti:sapphire laser pulses

Kurumi Mori, Yusuke Tamaki, Minoru Obara, and Katsumi Midorikawa

J. Appl. Phys. 83, 2915 (1998); http://dx.doi.org/10.1063/1.367078 (5 pages) | Cited 7 times

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The second-harmonic generation (SHG) of ultrashort Ti:sapphire laser pulses in potassium dihydrogen phosphate crystal in type-I phase-matching geometry has been investigated theoretically, including the effects of cubic nonlinearity. It is found that the phase mismatch due to the broad bandwidth associated with the short pulse width limits the maximum conversion efficiency to less than 60%, and the temporal shape of the converted pulse has an intensity modulation at an incident intensity of 100 GW/cm2 for a 100 fs pulse. In order to increase the energy conversion efficiency and improve the temporal pulse shape, a new SHG geometry using two antiparallel tilted crystals is discussed. © 1998 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.47.-p Spectroscopy of solid state dynamics
06.60.Jn High-speed techniques (microsecond to femtosecond)
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Investigation of mid-infrared intersubband stimulated gain under optical pumping in GaAs/AlGaAs quantum wells

O. Gauthier-Lafaye, S. Sauvage, P. Boucaud, F. H. Julien, F. Glotin, R. Prazeres, J.-M. Ortega, V. Thierry-Mieg, and R. Planel

J. Appl. Phys. 83, 2920 (1998); http://dx.doi.org/10.1063/1.367079 (7 pages) | Cited 22 times

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We have investigated the mid-infrared intersubband stimulated emission under optical pumping in GaAs/AlGaAs coupled quantum wells. The quantum wells exhibit four levels bound in the conduction band. The energy between the ground and first excited subband is close to the optical phonon energy enabling population inversion. Intersubband stimulated gain between subbands E3 and E2 is observed around 14 μm wavelength by optically pumping the E1−E3 intersubband transition at 10 μm. The gain measurement is performed by time-resolved pump-probe experiments using a two-color picosecond free-electron laser. The dependence of the intersubband stimulated emission is analyzed as a function of the pump intensity, and the pump and probe wavelengths. We show that very large intersubband stimulated gain can be achieved at liquid nitrogen temperature in a 2 mm thick waveguide. The stimulated gain is resonant with the pump wavelength with a broadening ≈25 meV. The experimental results are explained with a nonperturbative matrix density treatment of a three-level system. © 1998 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
78.45.+h Stimulated emission
78.66.Fd III-V semiconductors

Scattering birefringence polarizers based on oriented blends of poly(ethylene terephthalate) and core–shell particles

Y. Dirix, H. Jagt, R. Hikmet, and C. Bastiaansen

J. Appl. Phys. 83, 2927 (1998); http://dx.doi.org/10.1063/1.367080 (7 pages) | Cited 18 times

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Here, we present the results on the optical characteristics of polymeric, linear polarizers produced from oriented, two-component, polymer blends. By a proper selection of materials and drawing conditions, the refractive index of the dispersed phase of the blend is matched with the ordinary refractive index of the birefringent continuous phase while, at the same time, a large refractive index mismatch is generated in the perpendicular direction. The films are, therefore, transparent or opaque, dependent on the polarization direction of the incident light and act as linear polarizers with a high contrast ratio (≈1000) between the transparent and opaque state. These polarizers are all-polymer-based linear polarizers that operate on the anisotropic scattering of light, instead of anisotropic absorption, which offers some unique features and advantages. © 1998 American Institute of Physics.
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78.20.Fm Birefringence
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Experimental and computational study of copper–gadolinium alloy evaporation

S. Chatain, C. Gonella, and P. Roblin

J. Appl. Phys. 83, 2934 (1998); http://dx.doi.org/10.1063/1.367081 (6 pages) | Cited 1 time

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We report an experimental study of the expansion of a gadolinium–copper atomic vapor mixture in vacuum and the comparison with a test-particle Monte Carlo simulation. This simulation gives a description of collision relaxation in the binary case, taking account of excited metastable levels. The metal alloy was evaporated by a focused electron gun. We measured the net mass flow rate, radial velocities, and angular flux profiles. These data show the occurrence of aerodynamic phenomena in these mixtures: the velocity increase and the narrowing of the angular flux profile of a heavy element with a light element present, the decrease in the velocity, and broadening of the angular flux profile of the light element with a heavy element present. There is good agreement between the experimental results and the computations. © 1998 American Institute of Physics.
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64.70.F- Liquid-vapor transitions
02.50.Ng Distribution theory and Monte Carlo studies
02.70.Rr General statistical methods
61.80.Fe Electron and positron radiation effects

Optimized performance of a powerful hollow-cathode rf oscillator

J. Felsteiner, S. Ish-Shalom, and Ya. Z. Slutsker

J. Appl. Phys. 83, 2940 (1998); http://dx.doi.org/10.1063/1.367082 (4 pages) | Cited 7 times

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We have studied the power, efficiency, and frequency ranges achievable for a hollow-cathode based rf oscillator. We have found that the rf component of the discharge current can be much larger (up to ∼ 4.5 times) than its dc component. In the achievable frequency range of 15–120 MHz, this very simple cold cathode device produces up to 40 kW of rf power with efficiency of up to 25%. The internal resistance of this device always remained within a convenient range of 20–40 Ω. The rf pulse duration could be prolonged up to tens of μs. The physical processes governing the oscillator parameters are discussed. © 1998 American Institute of Physics.
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84.47.+w Vacuum tubes
84.30.Ng Oscillators, pulse generators, and function generators

H− laser photodetachment at 1064, 532, and 355 nm in plasma

M. Nishiura, M. Sasao, and M. Bacal

J. Appl. Phys. 83, 2944 (1998); http://dx.doi.org/10.1063/1.367083 (6 pages) | Cited 19 times

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The fundamental frequency (1064 nm), the second harmonic (532 nm), and the third harmonic (355 nm) of a Nd yttrium aluminum garnet laser have been used to investigate the influence of the energies of photodetached electrons upon the determination of the H− density and the H− drift velocity in a hydrogen plasma, where the electron density and temperature range from 1010 cm−3 to 1011 cm−3 and from 0.5 to 3 eV, respectively, with the n−/ne ratio less than 2%. From the δIp−Vp characteristics, where δIp is the photodetachment current and Vp is the probe voltage, it is found that there is no dependence of the energies of photodetached electrons on the photon energies. The effective temperature of photodetached electrons Teff is close, within 40%, to that of background electrons. As a result the H− density and the H− drift velocity are not affected by photon energies. © 1998 American Institute of Physics.
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52.70.Ds Electric and magnetic measurements
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
32.80.Gc Photodetachment of atomic negative ions
52.27.Jt Nonneutral plasmas
34.50.Fa Electronic excitation and ionization of atoms (including beam-foil excitation and ionization)

Experimental and theoretical study of a glow discharge at atmospheric pressure controlled by dielectric barrier

Françoise Massines, Ahmed Rabehi, Philippe Decomps, Rami Ben Gadri, Pierre Ségur, and Christian Mayoux

J. Appl. Phys. 83, 2950 (1998); http://dx.doi.org/10.1063/1.367051 (8 pages) | Cited 381 times

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The aim of this paper is to confirm the existence of atmospheric pressure dielectric controlled glow discharge and to describe its main behavior. Electrical measurements, short time exposure photographs, and numerical modeling were used to achieve this task. Experimental observations and numerical simulation are in good agreement. Therefore, the analysis of the calculated space and time variations of the electric field together with the ion and electron densities helps to explain the discharge mechanisms involved, showing the main role played by the electron as well as helium metastable density just before the discharge is turned on. © 1998 American Institute of Physics.
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52.80.Hc Glow; corona
02.60.-x Numerical approximation and analysis
07.68.+m Photography, photographic instruments; xerography

Hysteresis and self-sustained oscillations in space charge limited currents

Yu. N. Gartstein and P. S. Ramesh

J. Appl. Phys. 83, 2958 (1998); http://dx.doi.org/10.1063/1.367983 (7 pages) | Cited 6 times

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A problem of charged particle flow between parallel plate electrodes with arbitrary injection velocities is revisited. A steady-state analysis is advanced by the kinetic simulations which show that the system under consideration can exhibit features characteristic of nonlinear dynamical systems. In particular, a hysteresis between supply limited and space charge limited currents is demonstrated as well as the existence of self-sustained oscillations in the space charge limited regime. These phenomena are most sharply pronounced for narrow distributions of the initial injection energies. © 1998 American Institute of Physics.
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52.80.-s Electric discharges
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)

Influence of gas pressure and cathode composition on ion energy distributions in filtered cathodic vacuum arcs

M. M. M. Bilek, P. J. Martin, and D. R. McKenzie

J. Appl. Phys. 83, 2965 (1998); http://dx.doi.org/10.1063/1.367052 (6 pages) | Cited 43 times

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We report measurements of ion energy distributions of ionized species in titanium and aluminium filtered cathodic vacuum arcs operating in oxygen and nitrogen gas atmospheres. The ion energy distributions were recorded using a Hiden mass selected ion energy analyzer. The results show that a significant reduction in ion energies and a change in the shape of ion energy distributions occurs as the gas pressure is increased. The degree of the energy reduction depends on both the type of gas and the metal ions making up the arc plasma. This has important implications for the deposition of thin films, such as titanium nitride, commonly produced using vacuum arcs in reactive gas atmospheres. The ion energy distributions of the cathode ion species in the absence of background gas and at low gas pressures are well fitted by shifted Maxwellian distributions. As the gas pressure rises the distributions consist of a progressively increasing thermalized Maxwellian component and a decreasing shifted Maxwellian. An investigation of energy distributions of species in arcs triggered on alloyed cathodes showed that the relative abundance of ions of different charge states and their energy distributions varied as alloy metals were introduced. This indicates that the electron temperature in the cathode spot and hence the cathode spot dynamics is affected by the presence of the alloy metal. © 1998 American Institute of Physics.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Argon metastables in a high density processing plasma

D. Leonhardt, C. R. Eddy, V. A. Shamamian, R. F. Fernsler, and J. E. Butler

J. Appl. Phys. 83, 2971 (1998); http://dx.doi.org/10.1063/1.367123 (9 pages) | Cited 22 times

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Absolute densities of metastable argon atoms (Paschen 1s5, 1s3) and the intermediate resonant state (1s4) were measured in a high density plasma etching environment. Excited species densities were measured ranging from 108 to 3×109 cm−3, depending on the particular atomic state. A straightforward reaction rate formalism consisting of only two competing electron-atom collision rates accurately predicts such densities. Because of the low densities of these long-lived excited state species, all excited argon species need to be considered only as energy loss channels in modeling high density (1011–1012 cm−3), low pressure ( ∼ 1 mTorr) plasma sources. Metastable production rates were also used to identify energy transfer mechanisms under etching conditions of Cl2/Ar mixtures and substrate biasing in the reactor.
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31.50.Df Potential energy surfaces for excited electronic states
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
52.25.-b Plasma properties
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Effects of MeV ion irradiation of thin cubic boron nitride films

J. Ullmann, J. E. E. Baglin, and A. J. Kellock

J. Appl. Phys. 83, 2980 (1998); http://dx.doi.org/10.1063/1.367053 (8 pages) | Cited 20 times

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Adherent boron nitride thin films with a high cubic phase content (up to about 90%) were synthesized over large areas by means of ion assisted evaporation. Besides the well known superior properties of cubic boron nitride (c-BN) nearly nothing is known about the behavior of c-BN under MeV ion irradiation where the ions penetrate through the thin film and come to rest far away in the substrate. Therefore, exploratory MeV ion implantation experiments into as-deposited c-BN rich films were conducted at room temperature. Ions with different masses were chosen to study the effect of the nuclear and electronic stopping processes on the highly cubic BN films. Furthermore the influence of various ion doses (3.5×1013–2.0×1017 ions/cm2) on the cubic structure was investigated. To get an insight into the effects of the different post-deposition treatments, the as-deposited and ion implanted films were analyzed by Fourier transformed infrared spectroscopy, Rutherford backscattering, x-ray diffraction, and Auger electron spectroscopy. Depending on the ion dose, the heavy Xe ion implantation results in four different regimes for the resulting material. The implantation induced the total number of displacements per unit volume as an essential measure of the effect of the postdeposition treatment. Depending on the total number of displacements per unit volume the cubic BN structure can be transformed into a hexagonal BN dominated network. © 1998 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.82.Ms Insulators
61.72.up Other materials
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators

Hydrogen–oxygen interaction in silicon at around 50 °C

V. P. Markevich and M. Suezawa

J. Appl. Phys. 83, 2988 (1998); http://dx.doi.org/10.1063/1.367054 (6 pages) | Cited 51 times

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Formation kinetics of oxygen–hydrogen (O–H) complexes which give rise to an infrared absorption line at 1075.1 cm−1 have been studied in Czochralski-grown silicon crystals in the temperature range of 30–150 °C. Hydrogen was incorporated into the crystals by high temperature (1200 °C) in diffusion from H2 gas. It was found that the observed kinetics can be explained as being due to an interaction of mobile neutral hydrogen-related species with bond-centered oxygen atoms. The binding energy of the O–H complex was determined to be 0.28±0.02 eV. An activation energy for migration of hydrogen-related species responsible for the formation of the O–H complexes was found to be 0.78±0.05 eV. It was shown that atomic hydrogen and H2∗, a complex containing two hydrogen atoms, one at bond-centered site and another one at antibonding site, cannot account for the hydrogen–oxygen interaction considered. Hydrogen molecules (H2) located at tetrahedral interstitial site are suggested to be the species which interact with interstitial oxygen atoms and form the complex giving rise to the absorption line at 1075.1 cm−1. © 1998 American Institute of Physics.
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78.30.Am Elemental semiconductors and insulators
61.72.J- Point defects and defect clusters
61.72.uf Ge and Si

Modelling of kinetics of creation and passivation of interface traps in metal-oxide-semiconductor transistors during postirradiation annealing

Goran S. Ristić, Momčilo M. Pejović, and Aleksandar B. Jakšić

J. Appl. Phys. 83, 2994 (1998); http://dx.doi.org/10.1063/1.367055 (7 pages) | Cited 11 times

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The dependencies of creation–passivation processes of interface traps in irradiated n-channel metal-oxide-semiconductor transistors on the temperature and gate bias during annealing have been investigated. The experimental results, which are explained by the hydrogen–water (H–W) model, show the influence of both the annealing temperature and gate bias on these processes. The modelling of creation–passivation kinetics of interface traps, based on bimolecular theory and numerical analysis, is also performed. Numerical modelling shows that the H–W model can include the temperature and gate bias dependencies of creation of interface traps, latent interface trap buildup and the decrease of interface trap density. © 1998 American Institute of Physics.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
81.65.Rv Passivation
61.72.Cc Kinetics of defect formation and annealing
85.30.Tv Field effect devices

Theory of nonlinear optical properties of C60-derived nanotubes

Rui-Hua Xie and Jie Jiang

J. Appl. Phys. 83, 3001 (1998); http://dx.doi.org/10.1063/1.367124 (7 pages) | Cited 18 times

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We study the third-order optical nonlinearities (characterized by the second-order hyperpolarizabilities γ) of C60-derived nanotubes. It is found that the static γ magnitudes of armchair (C60+i×10) and zigzag (C60+i×18) nanotubes obey their own exponent laws given by γ/γ60 = (1+i×10/60)3.15 and γ/γ60 = (1+i×18/60)2.98, respectively, where γ60 is the static γ magnitude of C60 and i is a positive integer. Also, the dynamical nonlinear optical responses of armchair and zigzag nanotubes are studied in detail. It is found that the symmetry and caps of these nanotubes have a large effect on their third-order optical nonlinearities. By these detailed studies, we find that armchair and zigzag nanotubes can compete with polymeric materials for photonic applications due to their large nonresonant and resonant third-order optical nonlinearities. © 1998 American Institute of Physics.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
36.40.Mr Spectroscopy and geometrical structure of clusters
42.65.An Optical susceptibility, hyperpolarizability
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Ostwald ripening of end-of-range defects in silicon

C. Bonafos, D. Mathiot, and A. Claverie

J. Appl. Phys. 83, 3008 (1998); http://dx.doi.org/10.1063/1.367056 (10 pages) | Cited 69 times

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End-of-range (EOR) defects are interstitial type dislocation loops which nucleate just beneath the crystalline/amorphous (c/a) interface formed by ion implantation in Si, after the preamorphization of the substrate, and during the ramping-up of the anneal. They originate from the presence of a high supersaturation of “excess” Si self-interstitial atoms located just beneath the c/a interface. Upon annealing, the mean radius of the defects increases while their density decreases through the exchange of Si self-interstitial atoms between the loops. The number of interstitials stored in the loops stays constant. For sufficiently high thermal budgets, when the nucleation is finished, and when the local equilibrium between extended and point defects is established, the coarsening of the EOR defects can be modeled through the Ostwald ripening theory applied to the dislocation loops geometry. Indeed, and as expected from the theory, the square of the mean radius of the loop population increases with time while the loop density decreases proportional to 1/t. Furthermore, the theoretical function describing the size distributions perfectly matches the time evolution of the experimental stack histograms, for different annealing temperatures. During the asymptotic steady-state coarsening regime, the activation energy for the loop coarsening is 4.4 eV, which is in the range of values given in the literature for self-diffusion in Si. Nevertheless, an activation energy of about 1–2 eV is found during the transient period preceding the local equilibrium, i.e., in the range of the migration energy of self-interstitials. The limiting phenomenon for the loop growth appears to be diffusion, since it is the hypothesis that leads to the best fit between theory and experiment. An estimate of DiCi∗ has been derived from the growth laws of the EOR defects. A value of about 1.8×107 cm−1 s−1 at 1000 °C is obtained and compares well with the values given in the literature. © 1998 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.)
61.72.uf Ge and Si
61.80.Jh Ion radiation effects
61.72.Cc Kinetics of defect formation and annealing
61.72.Lk Linear defects: dislocations, disclinations
61.72.J- Point defects and defect clusters

Elastic constants of α-GeO2

M. Grimsditch, A. Polian, V. Brazhkin, and D. Balitskii

J. Appl. Phys. 83, 3018 (1998); http://dx.doi.org/10.1063/1.367117 (3 pages) | Cited 14 times

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The elastic constants of α-GeO2, the quartzlike polymorph of germanium dioxide, have been determined using Brillouin scattering. The data were obtained using a high quality single crystal of α-GeO2. When compared with existing data on α-SiO2, our results show that the shear constants are considerably softened in GeO2. This could be an indication that the observed pressure induced phase change is related to a shear instability. © 1998 American Institute of Physics.
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62.20.D- Elasticity
78.35.+c Brillouin and Rayleigh scattering; other light scattering
62.50.-p High-pressure effects in solids and liquids
64.70.K- Solid-solid transitions

Size effects in surface segregation

Cs. Cserháti, I. A. Szabó, and D. L. Beke

J. Appl. Phys. 83, 3021 (1998); http://dx.doi.org/10.1063/1.367125 (7 pages) | Cited 8 times

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The effect of the slab thickness (d) on the segregation behavior has been investigated for a phase separating system in a slab consisting of atomic planes parallel to the free surfaces. The calculations were carried out using the Fowler–Guggenheim approximation in the monolayer limit. It is shown, that by varying the surface fraction ξ, a surface phase transition can occur, similar to a semi-infinite system where a change in temperature can lead to a phase transition (S-shaped segregation isotherm). Furthermore, the existence of a minimum on the free energy curve versus d was examined. It was demonstrated that such a minimum can exist in the nanocrystalline region. © 1998 American Institute of Physics.
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68.35.Fx Diffusion; interface formation
68.35.Rh Phase transitions and critical phenomena
61.46.-w Structure of nanoscale materials

Nonequilibrium solidification of hypercooled Co–Pd melts

T. Volkmann, G. Wilde, R. Willnecker, and D. M. Herlach

J. Appl. Phys. 83, 3028 (1998); http://dx.doi.org/10.1063/1.367057 (7 pages) | Cited 24 times

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Co–Pd alloy melts are characterized by a low heat of fusion and, as a consequence, by a comparably small critical undercooling for the hypercooling limit ΔThyp of the order of 300 K. It is shown that containerless processing of bulk melts by electromagnetic levitation offers undercooling levels of ΔT ≈ 350 K thus exceeding the hypercooling limit considerably. Solidification of undercooled melts from the hypercooling regime leads to rapid crystallization of the entire sample under nonequilibrium conditions. The electromagnetic levitation technique in combination with time-resolved recalescence detection was used to measure the growth velocity of Co–Pd alloy melts as a function of undercooling prior to solidification. The growth velocities of undercooled metallic melts were measured in an undercooling range exceeding the hypercooling limit. The experimental results are discussed within current theory of dendritic growth. © 1998 American Institute of Physics.
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64.70.D- Solid-liquid transitions
81.30.Fb Solidification
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)

Measurement of the lattice thermal expansion coefficients of thin metal films on substrates

O. Kraft and W. D. Nix

J. Appl. Phys. 83, 3035 (1998); http://dx.doi.org/10.1063/1.367118 (4 pages) | Cited 13 times

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A difference in thermal expansion between a thin film and its substrate causes mechanical stresses in the film. Therefore, knowledge of the thermal expansion coefficients of thin films are important for their technological applications. In this article, we present an analysis which can be used to extract the thermal expansion coefficient of a thin film material using a commonly used x-ray technique. The major advantage of our approach is that it is not necessary to remove the film from the substrate. The knowledge of the elastic constants of the thin film material and their temperature dependence is not required, which is particularly useful when thin film alloys are studied whose thermal and elastic properties are not available. For verification of the method, we investigated thin Al films because the thermal and elastic properties of bulk Al are well known. The comparison of our results with the bulk properties shows a reasonable agreement, indicating the validity of the new method. © 1998 American Institute of Physics.
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68.60.Dv Thermal stability; thermal effects
65.40.De Thermal expansion; thermomechanical effects

Diffusion with multiple kinds of trapping sites

Tadashi Kasuya and Masao Fuji

J. Appl. Phys. 83, 3039 (1998); http://dx.doi.org/10.1063/1.367058 (10 pages) | Cited 4 times

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Since diffusion in solid is influenced by trapping sites which have different binding energies, analytic solutions to describe diffusion with multiple kinds of trapping sites have been derived for dilute systems without using the assumption of local equilibrium. Numerical comparisons with the local equilibrium treatment show that the transport of free atoms evaluated by the present solutions is faster at short times than that of the local equilibrium treatment. As time passes, the difference becomes small. The present solutions also show that the transport of free atoms is influenced by the initial concentrations at trapping sites, and that the apparent transport is accelerated in some cases. Using the present solutions, systematic investigations of diffusion phenomena with many kinds of trapping sites become possible. © 1998 American Institute of Physics.
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66.30.Dn Theory of diffusion and ionic conduction in solids
61.50.Lt Crystal binding; cohesive energy
05.60.-k Transport processes
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