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Journal of Applied Physics

Issue 1 • Date Jan 1994

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Displaying Results 1 - 25 of 119
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Spectral characteristics of distributed feedback semiconductor lasers and their improvements by corrugation‐pitch‐modulated structure

    Page(s): 1 - 29
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    Semiconductor lasers with stable longitudinal single‐mode operation are essential for optical fiber communication systems. Distributed feedback (DFB) lasers are effective to obtain a stable longitudinal single‐mode operation; however, stability is not enough mainly because of the spatial hole‐burning effect. A corrugation‐pitch‐modulated (CPM) structure was proposed to improve the stability of longitudinal single‐mode operation in distributed feedback lasers. CPM‐DFB lasers have a unique corrugation structure to suppress the spatial hole‐burning effect. This structure was obtained by a newly developed corrugation fabrication method, a photomask self‐interference method. It is confirmed that the CPM‐DFB lasers operate in a stable longitudinal single‐mode by suppressing the spatial hole‐burning effect. This structure is also suitable for narrowing the spectral linewidth for use in coherent optical fiber communication systems. Narrow spectral linewidth lasers with a CPM structure have achieved the narrowest spectral linewidth reported to date. View full abstract»

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  • Dyadic Green’s functions and dipole radiations in layered chiral media

    Page(s): 30 - 35
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    Dyadic Green’s functions in the unbounded chiral medium are expanded by the vector wave functions in unbounded chiral media for Cartesian, cylindrical, and spherical coordinate systems. These expressions are useful to treat the radiation and scattering in planarly, cylindrically, and spherically layered media. Instead of the eigenfunction expansions of the dyadic Green’s functions, the dyadic Green’s functions in isotropic media are used, remarkably simplifying the derivation of dyadic Green’s functions in chiral media. As the first illustrative application, Sommerfeld integral representations of the dyadic Green’s functions and dipole radiations in a planarly layered chiral medium are presented via a novel derivation. As the second application example, by the method of images the closed expression of dyadic Green’s functions are obtained for an isotropic chiral half‐space bounded by a perfectly conducting plane. The established asymptotic and numerical methods for Sommerfeld integrals in isotropic media are therefore applicable to the corresponding problems in multilayer chiral media. View full abstract»

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  • Millimeter wave amplification in a free electron laser with a focusing wiggler

    Page(s): 36 - 42
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    A mm wave amplifier experiment on a free electron laser was performed using an intense, mildly relativistic electron beam (0.7–0.9 MeV) with a combination of a focusing planar wiggler and a weak additional axial magnetic field in the so‐called ‘‘group 1’’ region. A beam transport ratio of over 80%, through the whole wiggler length, was realized. In an amplification experiment, a spatial growth rate of 56 dB/m was obtained at a frequency of 45 GHz, and a power saturation was observed at a level of 6 MW, where the total gain was estimated to be 52 dB. It was shown that the off‐axis component of the beam contributes considerably to the rf amplification in the focusing wiggler. View full abstract»

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  • Intensity‐dependent photorefractive properties in an n‐type BaTiO3

    Page(s): 43 - 48
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    The beam coupling and response time of reduced BaTiO3 are reported. The major carrier changes from hole to electron after reduction. The electro‐optic gain and effective trap density increase with the illumination intensity. Although the electro‐optic gain varies little, the response time τ decreases by a factor of 2.8 after reduction. Experimental results indicate that at least three energy levels including shallow level(s) exist in this BaTiO3. View full abstract»

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  • Solid‐state ultraviolet tunable laser: A Ce3+ doped LiYF4 crystal

    Page(s): 49 - 53
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    A large gain and a wide tunability have been achieved over the Ce3+ (5d‐4f) transition in a LiYF4 crystal. A gain coefficient in excess of 180 cm-1 and a superradiant beam of 2.5 mrad divergence are observed at the laser transition, 325.2 nm, when the crystal is optically excited either at 193 or at 248 nm. Gain measurements indicate that the laser is tunable over a wavelength range of more than 10 nm. View full abstract»

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  • Microwave and millimeter wave generation using nonlinear optical mixing in asymmetric quantum wells

    Page(s): 54 - 57
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    The possibility of microwave and millimeter wave generation using nonlinear difference‐frequency mixing of optical lasers in an asymmetric quantum well (QW) is examined. In principle, this method imposes no limit on the frequency of generated microwave signals. It is shown that these structures are particularly suitable for enhancing the susceptibility of difference‐frequency generation, χ(2)(Ω;ω1,-ω2); this originates from the ability to tune the fundamental photon energies ℏω1 and ℏω2 to valence‐conduction subband transitions, while ℏΩ is tuned to intervalence and interconduction subband transitions. Under such conditions, the existence of a broad resonant enhancement region of χ(2), which is closely associated with the QW band structure is demonstrated. Enhancements of χ(2)xzx and χ(2)zxx exceeding 10 and 104 times over the bulk values are predicted, respectively. View full abstract»

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  • Measurement and theory of the pressure dependence of zero‐dispersion wavelength for communications fibers

    Page(s): 58 - 62
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    The pressure dependencies of the zero‐dispersion wavelength λ0 for dispersion‐shifted fiber on the spool and in a submarine lightwave (SL) cabled sample were measured using pressures P up to 10 kpsi. The spool results showed a mean zero‐dispersion shift dλ0/dP of close to +0.04 nm/kpsi. The corresponding shift for the SL cabled fiber was much smaller (less than 0.01 nm/kpsi) and the results were much less reproducible. This was believed to be due to the pressure‐shielding effect of the cable structure. A theoretical calculation of dλ0/dP has been carried out for the unshielded fiber using a two‐term (electronic and lattice) Sellmeier formalism. Assuming the dominant effect to be of fiber material (rather than waveguide design) origin, we find that the electronic and lattice contributions are of opposite sign with a resultant that agrees with experiment to within the combined accuracy of the experiment and theory. View full abstract»

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  • Structural characterization of II‐VI separate confinement heterostructure lasers with Zn1-xMgxSySe1-y cladding layers

    Page(s): 63 - 67
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    We have investigated the structural characteristics of II‐VI separate confinement heterostructure lasers grown on GaAs substrates and containing Zn1-xMgxSySe1-y quaternary cladding layers, ZnSe or ZnSySe1-y guiding layers and Zn1-zCdzSe quantum well active layers. The study was performed with a combination of transmission electron microscopy and high resolution x‐ray diffraction techniques. We found that the quaternary cladding layers remain pseudomorphic to the GaAs substrate although they can be lattice mismatched up to 0.1%. When the 0.5‐μm‐thick optical guiding layer contains ZnSe, there is partial relaxation of the laser structure by misfit dislocations at the lower cladding‐guiding layer interface and the threading dislocation density in the Zn1-zCdzSe quantum well active region is about 107 cm-2. However, when lattice matched (to GaAs)ZnSySe1-y is used as the guiding layer the entire laser structure is pseudomorphic and the threading dislocation density is ≪106 cm-2. The combination of low defect density and enhanced carrier and optical confinement by using Zn1-xMgxSySe1-y quaternary cladding layers has produced significant improvement in the room temperature threshold current (500 A/cm2) and maximum operating temperature (394 K). View full abstract»

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  • Computations of optical birefringence characteristics of highly eccentric elliptical core fibers under various thermal stress conditions

    Page(s): 68 - 73
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    The birefringence characteristics of optical fibers with a highly eccentric elliptical core are investigated under various thermal stress conditions. A new numerical method for solving the vectorial Maxwell equations is proposed which simultaneously takes into account the effects of ambient temperature and the geometrical distribution of the refractive indices of anisotropic propagation media. To verify the reliability of our numerical procedure, the birefringence characteristics are investigated of a highly birefringent elliptical core fiber used recently in the design of an optical sensor. The birefringence characteristics calculated by this procedure and those obtained from models currently used in the field of fiber‐optic sensing devices are compared with experimental data. For highly birefringent fibers, the numerical method proposed is far more accurate. View full abstract»

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  • Sound velocity in model superlattices with graded profile

    Page(s): 74 - 76
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    We study by means of numerical solution to the wave equation the long‐wavelength sound velocities in model superlattices with a periodic graded profile. The deviations of the sound velocity squares from the uniform limits are observed to be linearly proportional to the squares of the elastic constant modulation amplitude for the small amplitude regime. View full abstract»

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  • Sources of errors in nonlinear constants of crystals and their assessment

    Page(s): 77 - 83
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    Standard errors of third‐order nonlinear material constants of a crystal, obtained by the least‐squares fit, reflect only the errors from a single source. The source is the random errors in the experimental data used to determine the nonlinear constants. Other, hitherto disregarded, sources of errors are pointed out, namely the linear material constants of the crystal and the orientations of the crystal specimens used to produce the experimental data, and a method to assess their effect is suggested. The case investigated numerically concerns the third‐order nonlinear electromechanical constants of α‐quartz determined by the transit‐time method. To minimize the effect of the errors mentioned, attention must be focused on the linear elastic constants. Standard errors of 1%–2% in the linear constants produce nontrivial errors in the nonlinear constants comparable in size to those due to experimental errors. The standard errors increase the traditionally calculated errors of the nonlinear constants by about 10%–40%, respectively. The errors caused by the remaining linear constants and by the orientation angles seem to be substantially less important. View full abstract»

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  • Strong interaction of arbitrary fields of sound and light: Application to higher‐order Bragg imaging

    Page(s): 84 - 95
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    Small objects positioned in a high‐frequency ultrasonic beam can be imaged by Bragg diffraction of light. The first order contains one image. Using a light beam with a considerable convergence angle and reducing the ultrasonic frequency, one observes that the second diffraction order contains two adjoining images, the third order three, etc., and that the positive orders are the mirror images of the negative ones. These experimental observations are explained by the present theory and general expressions for the angular distribution of the light in the different diffraction orders are presented in the form of a series expansion. Evidence for the multiple images in the higher diffraction orders is found by analyzing the first term in this expansion. The center‐to‐center separation of the images within the higher orders is found to be proportional to the ultrasonic frequency and the interaction width. View full abstract»

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  • On analytic modeling of casing and liner thickness variations in a shaped charge

    Page(s): 96 - 103
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    The jet from a shaped charge is formed by the collapse of its typically conical liner under the high pressures resulting from a detonation front. Nominally the charge is axisymmetric and the jet travels along the axis of symmetry of the charge. However, when asymmetries are present in the shaped charge the velocities imparted to liner elements at a given axial distance from the cone tip will be different. Thus the jet formation process becomes asymmetrical and a nonzero off‐axis component of the jet velocity is generally produced. Such an off‐axis component can cause considerable degradation in the penetration achieved by the jet. In this article a recent novel approach to the modeling of shaped charge liner collapse with constant liner projection velocities in the presence of asymmetries is generalized to include Randers–Pehrson acceleration of the liner elements. The Gurney formula for an asymmetric closed sandwich is used for the limiting liner element speed in the Randers–Pehrson model and it is shown how the required mass elements may be calculated in a shaped charge application. Simple illustrative models are used to describe thickness variations in the shaped charge casing and liner. View full abstract»

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  • Validity of actinometry to monitor oxygen atom concentration in microwave discharges created by surface wave in O2‐N2 mixtures

    Page(s): 104 - 114
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    The validity of actinometry to monitor oxygen atom concentration in O2‐N2 microwave discharges created by surface wave is investigated. The plasma is created with a gas flow in a quartz tube of inner diameter 16 mm at pressures in the Torr range. First, it is shown that the reliability of actinometry can be deduced from the longitudinal profile of the actinometry signal. Second, absolute concentrations of oxygen atoms are estimated from the experimental actinometry signal and agree satisfactorily with concentrations simultaneously measured by vacuum ultraviolet (VUV) absorption downstream from the plasma. Moreover, upon varying the nitrogen percentage (0%–100%), it is evidenced that the actinometry signal is proportional to the concentration measured by VUV absorption. Furthermore, it is evidenced that the oxygen dissociation rate is only 2% in pure oxygen plasmas, while it reaches 15% (433 MHz) or 30% (2450 MHz) for mixtures containing more than 20% of nitrogen. This drastic increase in [O] upon the addition of N2 is extensively discussed and, finally, attributed to a decrease in the recombination frequency of oxygen atoms on the quartz wall, in the presence of nitrogen. View full abstract»

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  • Kinetic‐energy distributions of ions sampled from argon plasmas in a parallel‐plate, radio‐frequency reference cell

    Page(s): 115 - 125
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    Kinetic‐energy distributions are presented for ions sampled from 13.56‐MHz discharges in argon in a capacitively‐coupled, parallel‐plate, Gaseous Electronics Conference (GEC) radio‐frequency reference cell. The cell was modified to allow sampling of ions through an orifice in the grounded electrode. Kinetic‐energy distributions are presented for Ar+, Ar++, Ar+2, ArH+, and several trace ions for plasma pressures ranging from 1.3 Pa, where ion‐atom collisions in the plasma sheath are not important, to 33.3 Pa, where collisions are important. Applied peak‐to‐peak radio‐frequency (rf) voltages of 50, 100, and 200 V were used, and the current and voltage waveforms at the powered electrode were measured. Dependences of the ion fluxes, mean energies, and kinetic‐energy distributions on gas pressure and applied rf voltage are interpreted in terms of possible ion‐collision processes. The results agree with previously measured kinetic‐energy distributions of ions sampled from the side of the plasma through a grounded probe for similar discharge conditions, verifying that ion kinetics are characteristic of the plasma sheath independent of where it is formed [J. K. Olthoff, R. J. Van Brunt, and S. B. Radovanov, J. Appl. Phys. 72, 4566 (1992)]. View full abstract»

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  • Backscattering spectrometry and ion channeling studies of heavily implanted As+ in silicon

    Page(s): 126 - 133
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    Backscattering and ion channeling measurements have been carried out on 〈100〉 silicon wafers implanted with a dose of 3×1016 As+/cm2. These samples have been submitted to laser annealing and then to various thermal annealings in the 350–1000 °C temperature range. Three different crystallographic directions, 〈100〉, 〈110〉, and 〈111〉, have been explored. The deactivated As atom displacement with respect to the lattice sites has occurred already by the first stage of electrical deactivation at 350 °C. The average displacement is constant in the considered temperature range and has been found equal to 0.23±0.06 Å making an angle of 23±8° with the [100] direction. By comparing this finding with the local atomic As arrangement, deduced from previously reported extended x‐ray absorption fine structure measurements performed on the same samples, new cluster models are presented. These models consist of As2V and As4V clusters during the very early stage of deactivation, and of several As4V clusters grouped together giving rise to larger AsmVn agglomerates (m up to 12 and n up to 5). In this context, the average As displacement mainly results from the combined displacements of As atoms inside the clusters. The thermal evolution of the As agglomerates at higher temperatures is also discussed.   View full abstract»

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  • Cobalt particles wrapped in graphitic carbon prepared by an arc discharge method

    Page(s): 134 - 137
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    Fine particles of cobalt and cobalt carbide nesting in multilayered graphitic sheets, which were synthesized by an electric arc discharge of carbon rods containing cobalt oxide (CoO), were studied by transmission electron microscopy, including microdiffraction and energy dispersive x‐ray analysis. The size of the wrapped particles was typically in a range from 50 to 200 nm. Three phases of nested materials, hcp(α)‐Co, fcc(β)‐Co, and Co3C, were identified. View full abstract»

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  • High temperature adsorption of nitrogen on a polycrystalline nickel surface

    Page(s): 138 - 142
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    Nickel tetracarbonyl [Ni(CO)4] molecules were used as a probe to investigate the coverage of a heated polycrystalline nickel surface with nitrogen adspecies. For this purpose, the deposition kinetics of nickel (Ni) microstructures from the thermal decomposition of nickel tetracarbonyl was investigated as a function of the partial pressure of nitrogen (N2), used as buffer gas. The laser‐induced chemical vapor deposition technique was used to produce polycrystalline nickel lines in an atmosphere of pure Ni(CO)4 or a [Ni(CO)4+N2] mixture. The deposition process was performed on polysilicon/silicon dioxide/〈100〉 monosilicon substrates. As a heat source, a cw argon‐ion laser was used. The laser‐induced surface temperature was varied in the range 500–850 °C. For Ni(CO)4 partial pressures typically below 0.3 mbar, the nickel deposition rate was found to decrease as the N2 partial pressure increases. For higher Ni(CO)4 partial pressures, the deposition rate was found to be independent of the N2 partial pressure. On the basis of these results, the high temperature adsorption of nitrogen on a polycrystalline nickel surface was investigated. A model which accounts for the dependence of the nickel deposition rate and surface coverage with nitrogen adspecies on the N2 partial pressure was elaborated. View full abstract»

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  • Misfit dislocations and antiphase domain boundaries in GaAs/Si interface

    Page(s): 143 - 152
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    The interaction of the antiphase boundaries that are formed at the early stage of growth with the interfacial misfit dislocations is studied by transmission electron microscopy using contrast criteria. Experimental analysis has shown that the shifting of the misfit dislocation families, by half of their periodicity, is due to their intersection with antiphase boundaries emanating from demisteps on the Si substrate. The observed discontinuity of dislocation lines is attributed to dynamical contrast conditions. The antiphase boundaries do not interrupt the continuity of the network of dislocations. The dichromatic theory of interfacial defects is applied in order to illustrate the geometrical features of the pattern. The disymmetrization mechanism of the pattern obeys the principle of symmetry compensation. A symmetry analysis of the GaAs/Si interface justifies the agreement of the observations with the structural model.   View full abstract»

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  • Radiation‐induced segregation of nitrogen implanted into iron

    Page(s): 153 - 160
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    Nitrogen redistribution toward the sample surface during the implantation processes performed at temperatures ranging from room temperature to 250 °C was studied for pure iron by means of nuclear reaction analysis and secondary‐ion‐mass spectrometry. The role of carbon and radiation defects was investigated. The results reveal the importance of radiation defects on nitrogen migration and trapping. The migration mechanism was identified as a radiation‐induced segregation. View full abstract»

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  • High‐speed scanning tunneling microscopy: Principles and applications

    Page(s): 161 - 168
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    A fast scanning tunneling microscope (STM) for scanning micron‐sized areas of atomically rough surfaces has been developed. The response time of the feedback loop controlling the tip‐sample spacing is roughly 5 μs, and the maximum scan velocity is 1 mm/s. The instrument uses fast electronics and a novel mechanical design to achieve the high bandwidth. The high bandwidth makes the STM capable of nearly real‐time panning and zooming, allowing for rapid searches over the surface of the sample. The instrument has been used in air to study wear of atomic layers, and also to perform nanowriting while scanning. In the case of the wear study, it was found that step edges not only can retreat during wear, but can also advance. View full abstract»

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  • Positive identification of the ubiquitous triangular defect on the (100) faces of vapor‐grown diamond

    Page(s): 169 - 172
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    Scanning tunneling microscopy and atomic force microscopy were used to index the faces and orientation of the sloping triangular defect which often appears on the {100} surfaces of chemical‐vapor‐deposited diamond. These features were confirmed to be 〈111〉 penetration twins which appear as sections of cubo‐octahedra oriented with a 〈221〉’ direction parallel to the ‘‘parent’’ crystal’s {100} surface normal. Multiple twins of this type can give rise to the pentagonal structures usually attributed to simpler combinations of ordinary 〈111〉 twins. The ability to suppress this twin by proper choice of growth conditions is a major factor in controlling the morphology of vapor‐grown diamond. View full abstract»

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  • Optical and structural properties of MeV erbium‐implanted LiNbO3

    Page(s): 173 - 180
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    LiNbO3 single crystals have been implanted with 2.0 or 3.5 MeV Er ions with fluences between 2.0×1014 and 7.5×1015 cm-2 and annealed at temperatures between 500 and 1060 °C in a wet oxygen atmosphere. Photoluminescence spectroscopy, Rutherford backscattering spectroscopy, and secondary‐ion‐mass spectrometry have been used to study the influence of the annealing treatment on the optical activity of the Er ions, the crystal structure of the implanted LiNbO3 layer, and the depth distribution of the Er ions, respectively. The as‐implanted, amorphized LiNbO3 already emits the characteristic photoluminescence (PL) of Er3+ around 1.53 μm. Annealing for 1 min at 500 °C causes recrystallization of the amorphized layer by columnar solid‐phase epitaxial regrowth from the substrate. The PL intensity increases by more than one order of magnitude on annealing at 500 °C and the PL lifetime rises from 1.65 to 2.85 ms. In contrast, much longer annealing times and a much higher temperature are necessary to remove the columns and restore the perfect lattice but do not further improve the optical properties. Up to an Er concentration of 0.12 at. % no concentration quenching effects are noticed. MeV implantation‐doped samples show the same optical spectra as those doped during growth from the melt. View full abstract»

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  • Amorphous phase formation by ion bombardment: Direct comparison between ion implantation and ion‐beam mixing

    Page(s): 181 - 185
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    A direct comparison between ion implantation and ion‐beam‐mixing experiments for the formation of an amorphous phase in metals is provided. The system investigated is Ni‐Zr and the technique used to monitor amorphization is Rutherford backscattering and channeling. It is demonstrated that the crystalline‐to‐amorphous phase transformation results from the introduction of a threshold concentration of foreign atoms into the surface layer of the bombarded target in both cases. However the onset and spatial development of the amorphization process are shown to strongly depend on the type of experiments performed. 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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Meet Our Editors

Editor
P. James Viccaro
Argonne National Laboratory