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Journal of Applied Physics

Issue 10 • Date May 1995

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Displaying Results 1 - 25 of 108
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Recent progress in computer‐aided materials design for compound semiconductors

    Page(s): 4845 - 4886
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    Recent progress in computational materials science in the area of semiconductor materials is reviewed. Reliable predictions can now be made for a wide range of problems, such as band structure and structural and thermodynamic properties of various compound semiconductors, using electronic theories such as the pseudopotential method. Further applications are examined by investigating the behavior of various atomic species in semiconductors, including the stability and band structure of heterostructures, superlattices, lattice defects, alloy systems, and surface‐related properties such as surface reconstruction, surface passivation, and adatom migration during thin film growth. The empirical interatomic potentials, pseudopotential, and stochastic Monte Carlo methods are used. An overview of these issues is provided and the latest achievements are presented to illustrate the capability of the theoretical‐computational approach by comparing experimental results. The constituents of the semiconductors that are most applicable to electronic and optical devices, mainly group‐II, ‐III, ‐IV, ‐V, and ‐VI elements, are focused on. These successful applications of the theoretical‐computational approach lead to future prospects for the computer‐aided materials design for semiconductors introduced as ‘‘bond engineering.’’ © 1995 American Institute of Physics. View full abstract»

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  • Collection of athermal phonons into doped Ge thermistors using quasiparticle trapping

    Page(s): 4887 - 4891
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    We have developed a low‐temperature particle detector that uses a novel quasiparticle trapping mechanism to funnel athermal phonon energy from an 80 mg Ge absorber into a 1.6 mg doped Ge thermistor via a superconducting Al film. We report on pulse height spectra obtained at 320 mK by scanning a 241Am alpha source along the device, and show that up to 20% of the energy deposited in the Ge absorber by a 5.5 MeV alpha particle interaction can be collected into a thermistor via quasiparticle trapping. We show that this device is sensitive to the position of an alpha particle interaction in the Ge absorber for interaction distances of up to 5 mm from a quasiparticle trap. © 1995 American Institute of Physics. View full abstract»

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  • Dependence of the absorption of pulsed CO2‐laser radiation by silane on wavenumber, fluence, pulse duration, temperature, optical path length, and pressure of absorbing and nonabsorbing gases

    Page(s): 4892 - 4898
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    The absorption of three lines [P(20), 944.2 cm-1; P(14), 949.2 cm-1; and R(24), 978.5 cm-1] of the pulsed CO2 laser (0001–1000 transition) by SiH4 was measured at various pulse energy, pulse duration, temperature, optical path length, and pressure of the compound and nonabsorbing foreign gases. In addition, low intensity infrared absorption spectrum of silane was compared with high intensity absorption characteristics for all lines of the pulsed CO2 laser. The experimental dependencies show deviations from the phenomenological Beer–Lambert law which can be considered as arising from the high intensity of an incident radiation and collisions of absorbing molecules with surroundings. These effects were included into the expression, being an extended form of the Beer–Lambert law, which reasonably approximates all experimental data. The results, except for extending knowledge on the interaction of a high power laser radiation with matter, can help understanding and planning processes leading to preparation of silicon‐containing technologically important materials. © 1995 American Institute of Physics. View full abstract»

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  • Lifetime measurement of the B2+u level of N+2 by laser‐induced fluorescence

    Page(s): 4899 - 4902
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    The optical diagnostic technique of laser‐induced fluorescence has been applied to a low pressure nitrogen discharge generated by radio frequency waves. The first negative system of N+2 was investigated with the use of a tunable dye laser. The radiative lifetimes of the B2+u(v’=0,1) levels were measured to be 65.1±0.4 and 62.5±0.7 ns, respectively. The obtained lifetimes and transition probabilities agree with the values found in the literature, deduced from electron beam excitation. In addition, rotational constants of the B2+u and X2+g levels were found from the observed spectra. © 1995 American Institute of Physics. View full abstract»

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  • Method of solution of forward problems in eddy‐current testing

    Page(s): 4903 - 4913
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    An analytical formula for the change in the eddy‐current probe impedance is obtained for the forward problem in the case the conductivities, σ2 and σ1, of the flaw and surrounding medium, respectively, are almost the same. The small parameter ε=1-σ21 is introduced and the vector‐valued solution is expanded in power series in ε. Then, a first‐order approximation to the solution is obtained by a perturbation method. The general procedure is illustrated in detail by two examples where the flaw is not in a symmetric position with respect to the coil axis, namely, a double conductor line above an infinitely long conducting cylinder with a flaw, and a single‐turn coil above a conducting ball with a flaw. It is shown that, in some cases, only one component of the vector potential (or even a part of this component) needs to be known in order to compute the impedance change. © 1995 American Institute of Physics. View full abstract»

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  • Focusing and guiding charged particles by a superconducting tube

    Page(s): 4914 - 4920
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    Electrons traveling through a superconducting tube are studied. Two simple models are proposed to describe the interaction of the magnetic self‐field of the electron stream with the superconducting tube. In the first model A, a complete expulsion of the magnetic flux from the superconductor due to the Meissner effect is assumed. On the contrary, a complete flux penetration through vortices is supposed in the second model B. Both models indicate an electron focusing when the space‐charge effect is compensated. The focusing length is estimated. For electrons traveling in the vicinity of the tube axis, the focusing length determined according to model A is nearly independent on the distance of the electrons from the tube axis, while the focusing length according to model B increases at increasing distance of the electrons from the tube axis. Similar focusing effects are obtained by a superconducting cone. © 1995 American Institute of Physics. View full abstract»

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  • Application of intermixing to p‐type GaAs/AlAs distributed Bragg reflectors for series resistance reduction in vertical cavity devices

    Page(s): 4921 - 4926
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    In this paper we experimentally investigate the application of selective interdiffusion to p‐type (Zn doped) distributed Bragg reflectors, as employed within a range of vertical cavity devices, as a means of lowering the series resistance. Various rapid thermal anneal temperatures and times are studied, both with and without silica encapsulants. The degree of intermixing, and hence series resistance reduction, is found to be cap dependent and this is verified both by secondary ion mass spectrometry and electrical resistance measurements. Both these techniques suggest that the intermixing, due primarily to Zn enhanced interdiffusion, is increased when no encapsulant is used. In this case a series resistance reduction approaching 50% is achieved within the 14 period GaAs/AlAs Bragg reflector. In the silica encapsulated case Ga vacancies are injected into the structure and these suppress the movement of Zn. The resulting Ga diffusion coefficient in this case is found to decrease by a factor of 3 relative to the uncapped case. The effects of interdiffusion on the reflection properties of the reflector, under various anneal conditions, are also described. This has previously been studied theoretically [Floyd et al., J. Appl. Phys. 75, 7666 (1994)] but here we offer experimental evidence on the optical effects of intermixing. We show that the peak reflectivity is found to decrease only slightly with temperature and time, again depending on capping conditions. The major effect contributing to the reflectivity decrease however is surface degradation due to As out‐diffusion. The reflectivity does decrease appreciably (∼10%) when the interdiffusion length of the group III atoms becomes a significant fraction of the quarter‐wave thickness of the GaAs/AlAs layers, as demonstrated in samples annealed at high temperatures and for long times (960 °C/360 s). These issues, along with that of planar integration of vertical cavity lasers a- nd other devices such as modulators and detectors, are of importance for future applications. © 1995 American Institute of Physics. View full abstract»

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  • Gain and current‐density calculation in IV–VI quantum well lasers

    Page(s): 4927 - 4930
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    In this work, a theoretical model is used to study the gain versus current‐density relationship for IV–VI semiconductor quantum well lasers. The model, based on Kane’s two band theory, solves for the anisotropy in the constant energy surfaces and for the strong nonparabolicity of the bands. The system investigated is the EuSe–PbSe0.78Te0.22 quantum well structure at 77 K. The effects of nonparabolicity on the gain versus current‐density relation are a reduction in the current density needed for any given gain and an increase in the gain saturation level. The nonparabolicity of the bands in the growth direction lowers the values of the confinement factor relative to parabolic bands which in turn lowers the modal gain values. Finally, the effects of nonparabolicity on the threshold current are significant for short cavity lasers and decrease with an increase in the cavity length. © 1995 American Institute of Physics. View full abstract»

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  • Polarization dependence of the absorption coefficient for an array of strained quantum wires

    Page(s): 4931 - 4934
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    The polarization dependence of the absorption coefficient for compressively and tensilely strained quantum wires is investigated as a function of strain, the lateral wire width, and the ratio between the wire and barrier widths. The results are markedly different from the case of an unstrained quantum wire and exhibit a significant variation with the sign and amount of built‐in strain. In the case of compressive strain, absorption of light polarized in the growth direction is considerably suppressed near the band edge, while the ratio between the absorption coefficients for light polarized parallel and perpendicular to the wire is determined by the relative prominence of strain and quantum confinement effects. A discussion of how these results can be applied to characterization of the achieved quantum confinement by polarization‐resolved photoluminescence spectroscopy is given. © 1995 American Institute of Physics.   View full abstract»

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  • Complex electro‐optic constants of dye‐doped polymer films determined with a Mach–Zehnder interferometer

    Page(s): 4935 - 4940
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    The real and imaginary parts of the linear electro‐optic (EO) constants of four dyes, i.e., N,N‐dimethylaminonitrostilbene (DANS), 4‐[N‐(2‐hydroxyethyl)‐N‐ethyl]amino‐4’‐nitroazo‐ benzene [disperse red 1 (DR1)], N,N‐dimentylindoaniline [phenol blue (PB)], and 1,1’,3,3,3’,3’‐hexamethylindotricarbocyanine iodide (HITCI) in polymethylmethacrylate (PMMA) films were determined using a Mach–Zehnder interferometer. The electronic transitions of DANS, DR1, PB, and HITCI are off‐resonant, near‐resonant, and resonant on the higher and lower energy sides with a He‐Ne laser wavelength (632.8 nm), respectively. The different ratios of the real and imaginary parts of the EO constants of four dyes including their signs are successfully explained in terms of detuning energy. © 1995 American Institute of Physics. View full abstract»

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  • Effects of walk‐off and group velocity difference on the optical parametric generation in KTiOPO4 crystals

    Page(s): 4941 - 4947
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    The effects of walk‐off and group velocity difference on the optical parametric generation in KTiOPO4 crystals are numerically revealed. These calculations treat the transverse‐mode profile and the temporal pulse shape of the interaction pulses simultaneously. Combining calculations with experimental results, the values of a second‐order nonlinear coefficient and two‐photon absorption coefficient at 0.6 μm are obtained as d24=4.2 pm/V and 0.35 pm/W, respectively. Due to the back‐conversion, the maximum conversion efficiency with a 5‐mm‐length crystal is limited to about 10%. This is because the beam diameter and the pulse duration of the signal and idler fields become small in the propagation and interaction with the pump field cannot take place at the entire portion of the pump field. The calculation results also indicate that 280 fs output pulses are obtained from a 1 ps pump pulse by the pulse narrowing effect. It is also clarified that the back‐conversion causes depression and splitting of the transverse mode and walk‐off plays an important role in the transformation of the transverse‐mode profile. The depression and splitting can be suppressed by using a short‐length crystal or decreasing pump intensity. © 1995 American Institute of Physics. View full abstract»

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  • Laser oscillation mechanisms of KrF‐laser‐pumped iron vapor plasma

    Page(s): 4948 - 4953
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    In order to study laser oscillation mechanisms of a KrF‐laser‐pumped iron vapor plasma, the population densities of iron atoms, the temperature, and the electron density in iron vapor plasma have been measured. The iron vapor plasma was produced from an iron plate by irradiation with a pulsed YAG laser (2 J/pulse). The population density of the ground‐state iron atoms is about 1014–1015 cm-3, the temperature is about 5000–20 000 K, and the electron density is about 1013–1016 cm-3. When a KrF laser of 34 mJ/pulse irradiates the iron vapor plasma, the absorption cross section of the KrF laser by the iron atom is about 10-16–10-15 cm2. An optical gain has been calculated on the basis of the experimental results, and it is compared with the gain measured experimentally. © 1995 American Institute of Physics. View full abstract»

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  • Thermal conductivity of metal‐matrix composites

    Page(s): 4954 - 4960
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    The thermal conductivity of metal‐matrix composites, which are potential electronic packaging materials, is calculated using effective medium theory and finite‐element techniques. The thermal boundary resistance, which occurs at the interface between the metal and the included phase (typically ceramic particles), has a large effect for small particle sizes. It is found that SiC particles in Al must have radii in excess of 10 μm to obtain the full benefit of the ceramic phase on the thermal conductivity. Bimodal distributions of particle size are considered, since these are often used to fabricate high‐volume fraction composites. It is found that if the small particles (in a bimodal distribution) have a radius less than 2.5 μm in SiC/Al their addition reduces the thermal conductivity of the composite. Diamond‐containing composites, which have large thermal boundary resistance effects, are analyzed. Comparison of the effective medium theory results to finite‐element calculations for axisymmetric unit‐cell models in three dimensions and to simulation results on disordered arrays of particles in two dimensions confirms the validity of the theory. © 1995 American Institute of Physics. View full abstract»

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  • Study of C2F6 overetch induced damage and the effects of overetch on subsequent SiCl4 etch of GaAs/AlGaAs

    Page(s): 4961 - 4966
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    A quantum well intermixing probe system has been used to study the damage in GaAs/AlGaAs due to exposure to C2F6 plasmas as a function of rf power. At an etching power of ≤80 W, the photoluminescence energy shift after rapid thermal processing is rf power dependent. The etch rate selectivities between SiO2 and GaAs, and between GaAs and AlGaAs were found to increase with decreasing power, while the etching of AlGaAs was inhibited at an rf power of 10 W and below. In situ reflectometry measurements during subsequent SiCl4 etching suggest that fluorocarbon contaminants are deposited on the GaAs surface during the C2F6 etch, that these contaminants protect the surface from oxidation in the air, and therefore the GaAs induction time in SiCl4 is reduced. However, during a SiCl4 etch of a GaAs/AlGaAs layered structure, these contaminants are redeposited on the AlGaAs surface resulting in an increased AlGaAs induction time, a nonconstant etch rate and surface roughening. © 1995 American Institute of Physics. View full abstract»

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  • Collisional sheath dynamics

    Page(s): 4967 - 4972
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    Using a collisional fluid model, we investigate the dynamics of the collisional sheath following the application of a large, negative, finite‐rise‐time, voltage pulse to a planar target. For a moderate amount of collisionallity, we find that the ion impact energy decreases significantly, while the sheath width and ion flux (i.e., the ion current) are not greatly reduced. The theory shows fair agreement with experimental measurements. © 1995 American Institute of Physics. View full abstract»

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  • X‐ray diagnostics of plasma focus DPF‐78 discharge with heavy‐gas admixtures

    Page(s): 4973 - 4978
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    The x‐ray structure (λ≪10 Å) of the DPF‐78 discharge was investigated with different heavy‐gas admixtures to a basic D2 filling. A possible classification of plasma features is proposed. Micropinches with an unusual high aspect ratio of about 10:1 were found. Soft x‐ray spectra of single micropinches were registered on film. The use of x‐ray spectroscopic methods by means of spectra simulation codes allowed us to estimate the parameters of particular types of pinches with axial size of 0.5 mm and full radial size of 0.05 mm. In the He‐like ionization state we obtained ne≊3×1021 cm-3 and Te≊0.8 keV. The electron temperature determined in the H‐like ionization stage was considerably higher, Te≊2 keV, indicating a strong ionizing plasma. Possible deviations from the Bennett condition are discussed in connection with the spectroscopic results. © 1995 American Institute of Physics.   View full abstract»

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  • Measurements of reduced‐density air channels produced by a double‐pulsed electron beam

    Page(s): 4979 - 4983
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    Single‐pulse and noncollinear double‐pulse channels formed by intense relativistic electron beams were studied by using a laser deflection probe for times up to 100 ms. The first of two pulsed electron beams propagating in a 30‐cm‐diam tube was magnetically deflected to generate an off‐axis neutral‐density channel of ∼40% depth in moist air at 250 Torr. Subsequently after a time delay of 1.36 ms, a similar electron beam pulse (1.2 MeV, 13 kA, 10 ns full width at half maximum) was injected along the tube axis. After injection of the second pulse, the rate of channel decay was enhanced, and a large‐scale convective motion of the hot channel gas toward the second pulse ensued. Measurements of the channel motion are compared with the predictions of a simple hydrodynamic model. © 1995 American Institute of Physics.   View full abstract»

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  • Photoconductivity evolution due to carrier trapping by defects in 17 MeV‐proton irradiated silicon

    Page(s): 4984 - 4992
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    Damage concentration dependence of dark and photoconductivity has been studied in crystalline Si, irradiated with 17 MeV proton. The photoconductivity spectra consist of a broad peak due to a band‐to‐band transition and a tail spectrum on the lower energy side. Two kinds of tail spectra are observed in impurity‐doped and/or damaged specimens, and the latter threshold is deeper than the former. While the main peak of the doped specimen does not greatly change up to a certain irradiation fluence ϕC, it steeply decreases beyond the ϕC, which depends on the shallow‐impurity concentration. The tail spectrum of the shallow impurity simultaneously vanishes at the ϕC and another tail spectrum grows above the ϕC. As compared to fluence dependence of photocurrent decay time, it is clarified that the drastic decrease in the main peak results from a drop in the decay time or the carrier density, not in the carrier mobility. The defect density for the critical fluence ϕC has good correlation with the dopant concentration. It is concluded from these results that a competitive process between shallow impurities and deep defects dominates the optical transition and transport, and that the critical fluence ϕC corresponds to the damage concentration required to capture all the doped carriers. Mechanisms for the photoconductivity evolution and defect trapping efficiency are discussed as is a comparison with electron‐induced damage. © 1995 American Institute of Physics. View full abstract»

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  • Partial and perfect dislocation nucleation at the onset of stress relaxation in In0.60Ga0.40As active layers of high mobility transistors grown on InP

    Page(s): 4993 - 4996
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    The morphology of compressive InxGa1-xAs/In0.52Al0.48As layers grown on (100)‐InP substrates by molecular beam epitaxy was observed by transmission electron microscopy. A preliminary analysis of the network of misfit dislocations at the interface in layers with a thickness of 0.5 μm and xIn between 54% and 63% led to a further study of the onset of stress relaxation for layers with composition xIn=60% and thickness ranging from 5 to 25 nm. A critical thickness was found for plastic relaxation at 20 nm≪tc≪25 nm. Following a model of excess stress, a mechanism for the nucleation of dislocations according to the sequence 90°partial→60°perfect→30°partial is proposed. © 1995 American Institute of Physics. View full abstract»

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  • Amorphous alloy formation by mechanical alloying and consecutive heat treatment in Fe50B50 powder mixture

    Page(s): 4997 - 5003
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    Equiatomic composition powder mixture of pure Fe and B was mechanically alloyed in a controlled atmosphere vibration mill. Amorphous alloy phase formation was established by Mössbauer spectroscopy and by transmission electron microscopy. The variation of the average boron concentration and the homogeneity of the amorphous phase during the alloying process was followed by Mössbauer spectroscopy. At the early stage of the milling process a broad concentration distribution (from 20 to 50 at. % B) was observed. Upon further milling the average B concentration of the amorphous component was gradually enhanced and the concentration heterogeneity decreased. The B concentration of the amorphous phase could be further enhanced by heat treating the milled powder mixture. The highest boron content alloy attained in this study is Fe60B40. © 1995 American Institute of Physics. View full abstract»

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  • X‐ray study of elastic and plastic strains in Na+‐implanted (001) monocrystalline MgO

    Page(s): 5004 - 5007
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    The morphological, plastic, and elastic strains in Na+‐implanted MgO have been determined by measuring the swelling of the surface with a profilometer and in‐plane lattice parameters by x‐ray diffraction at glancing incidence. The high value of the stress (∼9 GPa) is related to a high dislocation density with very low mobility leading to weak plastic flow (∼0.2%). © 1995 American Institute of Physics. View full abstract»

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  • Radiation hardening of pure‐silica‐core optical fibers by ultra‐high‐dose γ‐ray pre‐irradiation

    Page(s): 5008 - 5013
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    Induced optical absorption in three SiO2‐core/SiO2:F‐clad fibers (two high‐OH, one low‐OH) and one SiO2:Ge‐core fiber was investigated in situ in the range 415–1100 nm during repeated 60Co γ‐ray exposures to doses ≳1 MGy(Si). Injected visible light (∼5 μW) was maintained during the first and second irradiations at ∼27 °C and an intervening period out of the source; an additional irradiation and subsequent out‐of‐source period were monitored with the light off. Bleaching effects due to radiation alone, light alone, and the synergism of light plus irradiation were independently observed. All visible‐range damage in the pure‐silica‐core fibers in excess of a few tens of dB/km was deduced to arise from activation of precursor states including chloride impurities and process‐induced defects. These extrinsic color centers were eventually eradicated and the fibers permanently rad hardened after a cumulative radiation dose of 8.3×106 Gy and a visible light fluence of ∼1.4 mW h. The hardening mechanism is here ascribed to radio‐ or photostimulated complexing of the extrinsic centers with radiolytically derived interstitial oxygens. View full abstract»

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  • Gettering effects in BF2‐implanted Si(100) by ion‐beam defect engineering

    Page(s): 5014 - 5019
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    The gettering effects of ion‐beam defect engineering (IBDE) in BF2‐implanted silicon have been studied. It has been shown that the IBDE technique may be useful in the improvement of the properties of BF2‐implanted silicon. The gettering layer introduced by MeV Si ion irradiation and formed during the process of thermal annealing collects not only impurities but also simple defects. Thus, it effected (1) reductions of secondary defects and F impurity accumulation in the BF2‐doped region; (2) reduction of the anomalous diffusion of B atoms; and (3) enhancement of the electrical activation of B atoms. © 1995 American Institute of Physics. View full abstract»

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  • Nucleation of crystalline phases in plastically deformed amorphous NiZr

    Page(s): 5020 - 5025
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    The thermodynamic and kinetic aspects of the nucleation of crystalline phases in plastically deformed a‐NiZr layers have been examined considering the effect of a concentration gradient and of an advancing interface on the suppression of both the homogeneous and heterogeneous nucleation process. In establishing the effect of a concentration gradient, the possibility of limited atomic mobility has been explicitly taken into account. An extension to the case of plastic deformation of the concept of a critical velocity of the advancing interface has allowed us to derive a simple expression for the critical thickness of the amorphous layer which can be tested experimentally. Contrary to the case of thermally induced growth of the amorphous layer it is shown that in the case of plastic deformation, because of the combined effect of thermodynamic and kinetic constraints, there is only a finite range of thickness of the amorphous phase which allows heterogeneous nucleation of a crystalline phase. The theoretical predictions on the critical thickness of the amorphous layer and on the critical size of the crystalline nuclei have been compared with the experimental observation that, during plastic deformation, homogeneous nucleation of a metastable crystalline phase is followed at a slightly higher thickness of the amorphous phase by heterogeneous nucleation of a different crystalline compound at the a‐NiZr/Zr interface. The theoretical predictions are compatible with the experimental observations and allow us to interpret both the observed sequence of nucleation events and the different growth behavior of the crystalline phases formed by homogeneous and heterogeneous nucleation. © 1995 American Institute of Physics. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory