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15 Mar 2004

Volume 95, Issue 6, pp. 2947-3233

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Optical studies of metallodielectric photonic crystals: Bismuth and gallium infiltrated opals

V. Kamaev, V. Kozhevnikov, Z. V. Vardeny, P. B. Landon, and A. A. Zakhidov

J. Appl. Phys. 95, 2947 (2004); http://dx.doi.org/10.1063/1.1645676 (5 pages) | Cited 13 times

Online Publication Date: 2 March 2004

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We have fabricated three-dimensional metallodielectric photonic crystals that consist of bismuth and gallium metals infiltrated into porous synthetic opals that have 300 nm diam silica balls. The specular reflectivity was measured in a broad spectral range from 0.3 to 25 μm using a variety of light sources, detectors and spectrometers. In addition to broadening of the original Bragg stop bands in the visible spectral range that give rise to iridescence colors, we also found a dramatic decrease of reflectivity in the visible/near-infrared spectral range. For frequencies below a cut-off frequency in the mid-infrared range the reflectivity increases to its normal bulk value in the respective metal, as predicted by theory and fitted by a model calculation. © 2004 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
78.40.Kc Metals, semimetals, and alloys
78.30.Er Solid metals and alloys
78.66.Bz Metals and metallic alloys

Laser-induced cavitation bubbles for cleaning of solid surfaces

W. D. Song, M. H. Hong, B. Lukyanchuk, and T. C. Chong

J. Appl. Phys. 95, 2952 (2004); http://dx.doi.org/10.1063/1.1650531 (5 pages) | Cited 22 times

Online Publication Date: 2 March 2004

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When a high-power laser beam is focused into liquid, it results in a shock wave emission and cavitation bubble generation. Upon inserting a rigid substrate into the liquid, the bubbles migrate towards the substrate due to the Bjerknes attractive force. Due to bubble–substrate and/or bubble–free-surface interaction, a high-speed liquid jet is formed during bubble collapse, and a collapse shock wave is generated at the moment of bubble collapse near the substrate. These shock waves and liquid jet induce large forces acting on the substrate to remove particles from it. For a substrate several millimeters away from the laser focus point, the collapse shock wave and liquid jet play key roles in removal of particles. The cleaning efficiency increases with an increase of laser fluence and decreases with an increase of distance between substrate surface and laser beam focus point or depth below liquid surface. In a case of bubbles close to substrate and liquid-surface boundaries, implosion of the bubbles will give rise to shock waves and liquid jets oblique to the substrate surface with the parallel and perpendicular components of the forces onto the particles. These oblique liquid jets and shock waves result in high cleaning efficiency. A liquid, such as alcohol and commercial washing solution, as the surrounding medium, rather than air or vacuum, can reduce adhesion force and enhance cleaning efficiency. © 2004 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
62.50.-p High-pressure effects in solids and liquids
47.55.dp Cavitation and boiling
42.62.-b Laser applications
47.40.Nm Shock wave interactions and shock effects

Infrared-laser induced photon avalanche upconversion in Ho3+–Yb3+ codoped fluoroindate glasses

F. Lahoz, I. R. Martín, and A. Briones

J. Appl. Phys. 95, 2957 (2004); http://dx.doi.org/10.1063/1.1649809 (6 pages) | Cited 20 times

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An intense green upconversion emission due to a photon avalanche mechanism has been observed in Ho3+–Yb3+ codoped fluroindate glasses, measured at 200 K, under excitation at around 750 nm. The influence of the Yb3+ concentration on the photon avalanche process has been studied. The pump power threshold of the avalanche mechanism decreases as the Yb3+ concentration is increased. A reduction by about a factor of 3 is observed from the 2.25 mol % Ho3+ single doped glass to the 2.25 mol % Ho3+–2.25 mol % Yb3+ codoped glass. This effect has been related to an extra feeding of the 5I7 intermediate level of Ho3+ ions via Ho3+→Yb3+ and Yb3+→Ho3+ energy transfer and back transfer processes, respectively. © 2004 American Institute of Physics.
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81.05.Kf Glasses (including metallic glasses)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
77.22.Jp Dielectric breakdown and space-charge effects
61.72.S- Impurities in crystals
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Three regimes of growth of a Gaussian ripple on a uniform plane electromagnetic wave front in a plasma

Ashutosh Sharma, M. P. Verma, Gyan Prakash, and M. S. Sodha

J. Appl. Phys. 95, 2963 (2004); http://dx.doi.org/10.1063/1.1645643 (6 pages) | Cited 9 times

Online Publication Date: 2 March 2004

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Starting with the scalar wave equation and relevant expressions for nonlinear dielectric constant of plasma, the propagation of a Gaussian ripple on a plane wave front of uniform intensity has been studied in the paraxial approximation. In the plane of the ripple width (along the y axis) and the ratio of the electric field intensities of the ripple and the main beam at r=0, z=0, (along the x axis) three distinct regions (for a given intensity of the main beam) can be identified which correspond to steady divergence, oscillatory divergence, and self-focusing of the ripple. The variation of the ripple width with distance of propagation has also been obtained for typical points in the three regions. © 2004 American Institute of Physics.
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52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)

Macroparticle rotation in the vacuum arc plasma jet

E. Gidalevich, S. Goldsmith, and R. L. Boxman

J. Appl. Phys. 95, 2969 (2004); http://dx.doi.org/10.1063/1.1645998 (6 pages)

Online Publication Date: 2 March 2004

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The motion of macroparticles (MPs) emitted from the cathode into the vacuum arc plasma jet is considered taking into account asymmetric ion bombardment of the MP surface. The MP velocity is increased up to 0.17 of the plasma jet velocity for an initial MP radius R0=0.1 μm and up to 0.3 of the plasma jet velocity for R0=0.02 μm. The electric current density distribution within the MP caused by the asymmetric plasma bombardment was calculated assuming homogeneous internal conductivity. The electric potential difference between the apex and antiapex points is ≈10−8 V for an MP radius of R0=0.1 μm, while the average MP electric potential relative to the surrounding plasma is V≈−11.27 V. Interaction between the internal electric current and the magnetic field used to collimate the plasma jet rotates the MPs with a frequency of ≈105 s−1. © 2004 American Institute of Physics.
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52.40.Mj Particle beam interactions in plasmas
52.25.Xz Magnetized plasmas
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Vp Discharge in vacuum
52.65.-y Plasma simulation

Comparative study of soft x-ray emission characteristics in a low energy dense plasma focus device

H. Bhuyan, S. R. Mohanty, N. K. Neog, S. Bujarbarua, and R. K. Rout

J. Appl. Phys. 95, 2975 (2004); http://dx.doi.org/10.1063/1.1647269 (7 pages) | Cited 36 times

Online Publication Date: 2 March 2004

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An investigation on the soft x rays emitted in a 2.2 kJ Mather-type dense plasma focus device using a multichannel diode spectrometer and a simple pinhole camera is reported. Emitted x rays associated with different shapes (hollow, solid, and hemispherical) of anode and in hydrogen/nitrogen gas medium are compared. The structure of x-ray emitting sites as well as x-ray yields were found to be strongly influenced by the shape of the anode and the filling gas pressure. The maximum yield of 2.2 J into 4π sr was obtained in the case of hemispherical anode in hydrogen gas medium. The x-ray pinhole images of the collapsed plasma with the hemispherical anode indicated spot-like structure having 500–800 μm in diameter. On the contrary, other anode shapes showed columnar pinched structure of 8–10 mm in length and 1–2 mm in diameter. Results indicated that an appropriate design of the anode could enhance the x-ray yield by more than tenfold in a conventional low energy dense plasma focus device. © 2004 American Institute of Physics.
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52.75.-d Plasma devices
52.58.Lq Z-pinches, plasma focus, and other pinch devices
52.25.Os Emission, absorption, and scattering of electromagnetic radiation

Analytical fit of the I–V probe characteristic for finite ion temperature values: Justification of the radial model applicability

R. Morales Crespo, J. I. Fernández Palop, M. A. Hernández, and J. Ballesteros

J. Appl. Phys. 95, 2982 (2004); http://dx.doi.org/10.1063/1.1650540 (9 pages) | Cited 14 times

Online Publication Date: 2 March 2004

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This article deals with an extension of the radial model for the sheath that surrounds a cylindrical or spherical Langmuir probe immersed in a plasma in which positive ion thermal motion is taken into account. The dependence of the electric potential profile and of the I–V characteristic on the positive ion temperature is obtained. Moreover, a different parameterization is established from a numerical fit of the I–V characteristic as a function of the probe radius, the biasing potential, and the ratio between the positive ion temperature and the electron temperature. This parameterization allows us to obtain an analytical approximation to the potential profile and the sheath edge. Finally, it also gives us a means of justifying under what conditions the radial model can be applied in plasmas with finite positive ion temperature. © 2004 American Institute of Physics.
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52.40.Kh Plasma sheaths
52.25.Fi Transport properties
52.70.Ds Electric and magnetic measurements
52.65.Vv Perturbative methods
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The yield strength of thin copper films on Kapton

Denis Y. W. Yu and Frans Spaepen

J. Appl. Phys. 95, 2991 (2004); http://dx.doi.org/10.1063/1.1644634 (7 pages) | Cited 81 times

Online Publication Date: 2 March 2004

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Thin films of copper, with thickness between 0.1 and 3 μm, were vapor-deposited on 12.7 or 7.6-μm-thick polyimide (Kapton) substrates. They were tested in a microtensile tester in which the strain is measured by optical diffraction from a microlithographically applied grid. The Young modulus is independent of film thickness and is about 20% below the value calculated from single-crystal elastic constants. The yield stress depends strongly on the film thickness and is fit by σy=116+355(t)−0.473, where t is the thickness in μm and σy is in MPa. The microstructure of the films was studied by focused ion-beam microscopy. The grains are heavily twinned and the microstructural lengths (grain size, twin spacing, twin width) depend only weakly on the film thickness. A substantial part of the yield stress is therefore attributable to an effect of the film thickness, such as that predicted by strain gradient plasticity theory. The lower limit and some estimates of the thickness contribution to the yield stress are calculated. The estimated characteristic length of strain gradient plasticity theory is 0.6 μm for these materials. © 2004 American Institute of Physics.
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81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.60.Wm Other nonelectronic physical properties
61.72.Mm Grain and twin boundaries
81.40.Jj Elasticity and anelasticity, stress-strain relations

Competition between strain-induced and temperature-controlled nucleation of InAs/GaAs quantum dots

P. Howe, E. C. Le Ru, E. Clarke, B. Abbey, R. Murray, and T. S. Jones

J. Appl. Phys. 95, 2998 (2004); http://dx.doi.org/10.1063/1.1645637 (7 pages) | Cited 23 times

Online Publication Date: 2 March 2004

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Atomic force microscopy and photoluminescence spectroscopy (PL) have been used to study asymmetric bilayer InAs quantum dot (QD) structures grown by molecular-beam epitaxy on GaAs(001) substrates. The two QD layers were separated by a GaAs spacer layer (SL) of varying thickness and were grown at different substrate temperatures. Grown independently, these two layers would exhibit a widely different QD number density, and this technique therefore enables us to assess the influence of the strain fields created by the dots in the first layer on the second-layer QD nucleation and characteristics. For very large SLs (>40 nm), total strain relief causes the QD nucleation to be controlled exclusively by the substrate temperature, which influences the migration of In adatoms. In this case, the optical and morphological properties of the second QD layer are identical to a structure with a single QD layer grown at the same temperature. In structures with a much smaller SL, strain effects dominate over the effect of temperature in controlling the nucleation of the QDs, thereby fixing the second-layer QD number density to that of the first (templating effect). There is also evidence that strain relaxation is present in the QDs of the second layer and that this is crucial for extending their emission wavelength. The optimum SL thickness is shown to be 11 nm, for which low-temperature PL emission peaks at 1.26 μm, with a full width at half-maximum of only 15 meV. Intermediate SL thicknesses exhibit broad QD size distributions, with strain effects only partly influencing the QD growth in the second layer. © 2004 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
64.60.Q- Nucleation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.Hc Quantum dots
68.55.A- Nucleation and growth
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
78.55.Cr III-V semiconductors
68.37.Ps Atomic force microscopy (AFM)

Infrared 45° reflectometry of Li doped ZnO films

E. A. Kafadaryan, S. I. Petrosyan, A. G. Hayrapetyan, R. K. Hovsepyan, A. L. Manukyan, E. S. Vardanyan, E. Kh. Goulanian, and A. F. Zerrouk

J. Appl. Phys. 95, 3005 (2004); http://dx.doi.org/10.1063/1.1647268 (5 pages) | Cited 4 times

Online Publication Date: 2 March 2004

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Lithium doped (0–10 at. % Li) ZnO films were grown in the wurtzite structure on sapphire (001) substrates and investigated in the 200–1200 cm−1 frequency range at 300 K by far-infrared reflectivity spectroscopy using polarized oblique (45°) incidence. This technique has enabled us to determine the longitudinal optical phonon frequency E1(LO) at 576 cm−1 of the fundamental lattice vibration at the center of the Brillouin zone, as well as to investigate the LO phonon-plasmon coupling in the low carrier density (N⩽1018 cm−3) ZnO films. The energy shift and halfwidth broadening of the LO phonon band in comparison with the uncoupled mode in high-ohmic ZnO:0.8 at. % Li (ρdc=0.6×106 Ω cm) film have been analyzed to get the concentration and “optical” mobility of charge carriers in the Li doped ZnO films. The results of optical, x-ray diffraction and dc resistivity measurements are discussed. © 2004 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.30.Fs III-V and II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
71.20.Nr Semiconductor compounds
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Ga II-VI semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Optical properties of Cd1−xZnxTe films in a device structure using variable angle spectroscopic ellipsometry

P. D. Paulson, B. E. McCandless, and R. W. Birkmire

J. Appl. Phys. 95, 3010 (2004); http://dx.doi.org/10.1063/1.1646437 (10 pages) | Cited 3 times

Online Publication Date: 2 March 2004

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The optical properties of polycrystalline Cd1−xZnxTe alloy thin films in device structures are reported for energy from 0.8 to 4.6 eV. Cd1−xZnxTe alloy thin films with x from 0 to 1 were deposited on glass/indium-tin-oxide (ITO)/CdS substrates by coevaporation from CdTe and ZnTe sources and were characterized by variable angle spectroscopic ellipsometry, energy dispersive x-ray spectroscopy, and x-ray diffractometry. The Cd1−xZnxTe films are single phase with a zincblende crystal structure over the entire alloy range. The Cd1−xZnxTe optical constants were determined using a multilayer optical model incorporating the optical constants of glass, ITO and CdS, determined independently from glass, glass/ITO, and glass/ITO/CdS specimens. The optical constants of the Cd1−xZnxTe thin films are comparable to literature values reported for single crystals, indicating that the polycrystalline nature of the films does not measurably alter the optical constants. A semiconductor alloy model for determining the composition of CdxZn1−xTe alloy films is developed using the optical data obtained from the analysis. This alloy model can be used to evaluate compositional grading and the effects of Cd1−xZnxTe film processing. © 2004 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.-a Thin film structure and morphology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods

Optical transitions and upconversion luminescence of Er3+/Yb3+-codoped halide modified tellurite glasses

Jianhu Yang, Liyan Zhang, Lei Wen, Shixun Dai, Lili Hu, and Zhonghong Jiang

J. Appl. Phys. 95, 3020 (2004); http://dx.doi.org/10.1063/1.1645642 (7 pages) | Cited 36 times

Online Publication Date: 2 March 2004

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Er3+-doped halide modified tellurite glasses were synthesized by conventional melting and quenching method. The Judd–Ofelt analysis was performed on the absorption spectra and the transition probabilities, excited state lifetimes, and the branching ratios were calculated and discussed. The intense infrared and visible fluorescence spectra under 980 nm excitation were obtained. Strong upconversion signal was observed at pumping power as low as 30 mW in the glasses with halide ions. The upconversion mechanisms and power dependent intensities were discussed, which showed two-photon process are involved for the green and red emissions. The decay times of the emitting states and the corresponding quantum efficiency were determined and explained. © 2004 American Institute of Physics.
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81.05.Kf Glasses (including metallic glasses)
78.55.Qr Amorphous materials; glasses and other disordered solids
64.70.D- Solid-liquid transitions
81.40.Gh Other heat and thermomechanical treatments
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.40.Pg Disordered solids
71.23.Cq Amorphous semiconductors, metallic glasses, glasses

Cathodoluminescence of defects in sintered tin oxide

D. Maestre, A. Cremades, and J. Piqueras

J. Appl. Phys. 95, 3027 (2004); http://dx.doi.org/10.1063/1.1647267 (4 pages) | Cited 14 times

Online Publication Date: 2 March 2004

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Cathodoluminescence (CL) in the scanning electron microscope (SEM) has been used to investigate the luminescence mechanisms in tin oxide. Sintered material prepared from high purity powder has been found to show a strong dependence of the CL emission on the thermal treatments applied during sample preparation. SEM images show the presence of nano and microcrystalline grains. The correlation of the grain size and morphology with the optical emission is analyzed by CL microscopy and spectroscopy. The main emission bands appear centered at about 2.58, 2.25, and 1.94 eV depending on the sintering treatment. CL images reveal that the 2.25 and the 2.58 eV bands are associated at specific crystal faces. The evolution of the luminescence bands with mechanical milling shows a complex evolution of the 1.94 and 2.58 eV emissions which is explained by formation and recovery of defects during milling. © 2004 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
61.72.J- Point defects and defect clusters
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.40.Gh Other heat and thermomechanical treatments
61.66.Bi Elemental solids
61.66.Dk Alloys
81.20.Wk Machining, milling

Organic molecules and nanoparticles in inorganic crystals: Vitamin C in CaCO3 as an ultraviolet absorber

H. Sato and M. Ikeya

J. Appl. Phys. 95, 3031 (2004); http://dx.doi.org/10.1063/1.1650561 (6 pages) | Cited 4 times

Online Publication Date: 2 March 2004

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Organic molecules and nanoparticles embedded in inorganic crystalline lattices have been studied to add different properties and functions to composite materials. Calcium carbonate was precipitated by dropping an aqueous solution of CaCl2 into that of Na2CO3 containing dissolved vitamin C (ascorbic acid). The optical absorption ascribed to divalent ascorbate anions in the lattice was observed in the ultraviolet B (wavelength: 280–315 nm) region, while solid vitamin C exhibited absorption in the ultraviolet C (100–280 nm) region. The divalent ascorbate anion is only stable in CaCO3 due to the absence of oxygen molecules. Doping CaCO3 with nanoparticles of ZnO also enhanced the absorption in the ultraviolet A (315–380 nm) region. These composite materials are suggested for use as UV absorbers. © 2004 American Institute of Physics.
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78.40.Ha Other nonmetallic inorganics
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
64.75.-g Phase equilibria
76.30.Lh Other ions and impurities

Interdiffusion and thermal stability in magnetic tunnel junction ferromagnet/insulator/ferromagnet trilayer structures

Sungkyun Park, David J. Keavney, and Charles M. Falco

J. Appl. Phys. 95, 3037 (2004); http://dx.doi.org/10.1063/1.1650533 (4 pages) | Cited 3 times

Online Publication Date: 2 March 2004

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We used molecular beam epitaxy grown magnetic tunnel junction structures for thermal stability studies using x-ray photoelectron spectroscopy (XPS) and in situ scanning tunneling microscopy (STM). Unannealed trilayers show no oxidation of the bottom magnetic layer for barriers thicker than 1.1 nm. However, upon annealing, we find that the metallic XPS peak of the top layers decrease dramatically, while that of the bottom and barrier layers increases. STM images of the Co top layer on the Al–oxide barrier show that the Co does not agglomerate upon annealing up to 500 °C, which suggests interdiffusion is the most likely explanation for the XPS data. © 2004 American Institute of Physics.
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66.30.Ny Chemical interdiffusion; diffusion barriers
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.65.Ac Multilayers
81.40.Gh Other heat and thermomechanical treatments
81.65.Mq Oxidation
79.60.Jv Interfaces; heterostructures; nanostructures

Epitaxial PbTiO3 thin films grown on (100) MgO by pulsed-laser deposition for optical waveguiding properties

A. Roemer, E. Millon, B. Vincent, A. Boudrioua, O. Pons-Y-Moll, R. M. Defourneau, and W. Seiler

J. Appl. Phys. 95, 3041 (2004); http://dx.doi.org/10.1063/1.1649461 (7 pages) | Cited 10 times

Online Publication Date: 2 March 2004

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Perovskite single phased PbTiO3 thin films have been grown by pulsed-laser deposition on (100) MgO single crystals in order to prepare high quality optical waveguides. The substrate temperature and the oxygen pressure during the deposition have been optimized to improve crystalline quality and to grow epitaxial thin films. The films display two main axis orientations according to the MgO (100) basal plane. The waveguiding properties and the optical losses characterized by using m-lines spectroscopy and charge-coupled device camera measurement, respectively, are correlated to the structural properties of the films. Such textured and epitaxied films display very good optical properties, as the optical losses are found to be lower than 1 dB cm−1. © 2004 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
77.55.-g Dielectric thin films
78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
42.82.Et Waveguides, couplers, and arrays
81.15.Fg Pulsed laser ablation deposition

Dynamic annealing in III-nitrides under ion bombardment

S. O. Kucheyev, J. S. Williams, J. Zou, and C. Jagadish

J. Appl. Phys. 95, 3048 (2004); http://dx.doi.org/10.1063/1.1649459 (7 pages) | Cited 21 times

Online Publication Date: 2 March 2004

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We study the evolution of structural defects in AlxGa1−xN films (with x=0.0–0.6) bombarded with kilo-electron-volt heavy ions at 77 and 300 K. We use a combination of Rutherford backscattering/channeling spectrometry and cross-sectional transmission electron microscopy. Results show that an increase in Al content not only strongly enhances dynamic annealing processes but can also change the main features of the amorphization behavior. In particular, the damage buildup behavior at 300 K is essentially similar for all the AlGaN films studied. Ion-beam-produced disorder at 300 K accumulates preferentially in the crystal bulk region up to a certain saturation level (∼50%–60% relative disorder). Bombardment at 300 K above a critical fluence results in a rapid increase in damage from the saturation level up to complete disordering, with a buried amorphous layer nucleating in the crystal bulk. However, at 77 K, the saturation effect of lattice disorder in the bulk occurs only for x≳0.1. Based on the analysis of these results for AlGaN and previously reported data for InGaN, we discuss physical mechanisms of the susceptibility of group-III nitrides to ion-beam-induced disordering and to the crystalline-to-amorphous phase transition. © 2004 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.72.Cc Kinetics of defect formation and annealing
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
64.60.Q- Nucleation
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Simulating structure and optical response of vacuum evaporated porous rugate filters

Kate Kaminska, Motofumi Suzuki, Kenji Kimura, Yasunori Taga, and Kevin Robbie

J. Appl. Phys. 95, 3055 (2004); http://dx.doi.org/10.1063/1.1649804 (8 pages) | Cited 15 times

Online Publication Date: 2 March 2004

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The drive to develop better thin film devices stimulates great interest in the understanding and control of the properties and morphology of films. In this article we present a study of the optical response of thin film interference filters, utilizing both experimental tools and computer simulation. The filters were deposited onto flat substrates in high vacuum with the technique of glancing angle deposition, which produces complex film structures with nanometer scale pores. A three-dimensional Monte Carlo simulator accurately reproduced this complicated morphology, while also providing information about nucleation, structure evolution, and packing density. Finally, the results of the computer modeling were used to optimize the effects of process parameters to minimize the difference between the design and the observed optical responses, thus providing a powerful tool for improving the performance of optical devices. © 2004 American Institute of Physics.
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42.79.Ci Filters, zone plates, and polarizers
61.43.Bn Structural modeling: serial-addition models, computer simulation
68.35.B- Structure of clean surfaces (and surface reconstruction)
64.60.Q- Nucleation

Growth and charge transfer luminescence of Yb3+-doped YAlO3 single crystals

J. B. Shim, A. Yoshikawa, T. Fukuda, J. Pejchal, M. Nikl, N. Sarukura, and D. H. Yoon

J. Appl. Phys. 95, 3063 (2004); http://dx.doi.org/10.1063/1.1650539 (6 pages) | Cited 6 times

Online Publication Date: 2 March 2004

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Yb3+-doped YAlO3 single crystals have been grown by the Czochralski method with a radio-frequency heating system. Starting melt compositions of Y1−xYbxAlO3 were varied with x=0.02, 0.1, 0.2, 0.3, and 0.45. The best Yb3+-doped YAlO3 single crystals were obtained for a growth rate of 1.0 mm/h. The grown crystals were transparent and almost colorless. To investigate the homogeneity, the effective segregation coefficient of the Yb ion was estimated. The absorption, photoluminescence, and luminescence decay kinetics of Yb3+-doped YAlO3 were investigated for the temperature range 4–300 K. Very fast charge transfer luminescence of Yb3+ from the near ultraviolet to visible spectral range and the high density of the Yb-rich YAlO3 makes this material a promising candidate for fast scintillators. © 2004 American Institute of Physics.
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81.10.Fq Growth from melts; zone melting and refining
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
78.55.Hx Other solid inorganic materials
61.72.up Other materials
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Model of work function of tungsten cathodes with barium oxide coating

K. C. Mishra, R. Garner, and P. C. Schmidt

J. Appl. Phys. 95, 3069 (2004); http://dx.doi.org/10.1063/1.1646451 (6 pages) | Cited 10 times

Online Publication Date: 2 March 2004

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Using a full-potential band structure approach, we have investigated the work function of barium oxide coated tungsten cathodes in low pressure discharge lamps. The main objective of this work is to understand why the work function for such cathodes is lower than that of the uncoated tungsten. The model studied in this work is based on a well known supposition that the source of thermionic electrons is the barium atoms released from the barium oxide coating due to a chemical reaction with the underlying metallic tungsten. For the unrelaxed seven-layer model of (100) surface of barium on barium oxide, the work function is calculated to be 2.22 eV, which is lower than that of BaO, Ba, and W metals separately. For a fully relaxed nine-layer surface, it becomes 1.36 eV. Although this value of the work function is lower than those estimated for the fluorescent cathodes by electrical measurements, which averages contributions from surfaces in all possible random orientations, this model provides a satisfactory explanation of the lowering of the work function of tungsten based cathodes in low pressure fluorescent lamps. © 2004 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
79.40.+z Thermionic emission
42.72.Bj Visible and ultraviolet sources

Spectroscopic, topological, and electronic characterization of ultrathin a-CdTe:O tunnel barriers

Ivan Dolog, Robert R. Mallik, Dan Malz, and Anthony Mozynski

J. Appl. Phys. 95, 3075 (2004); http://dx.doi.org/10.1063/1.1647259 (6 pages) | Cited 1 time

Online Publication Date: 2 March 2004

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Ultrathin oxygenated amorphous CdTe (a-CdTe:O) films are prepared by rf sputtering of CdTe in a background of argon or argon/nitrogen/oxygen mixtures. Atomic force microscopy (AFM) is used to characterize the films and shows that they have an island structure typical of most sputtered thin films. However, when sufficiently low powers and deposition rates are employed during sputtering, the resulting films are remarkably smooth and sufficiently thin for use as barrier layers in inelastic electron tunneling (IET) junctions. Four terminal current–voltage data are recorded for Al/a-CdTe:O/Pb tunnel junctions and conductance–voltage curves are derived numerically. WKB fits to the conductance–voltage curves are obtained using a two-component trapezoidal plus square (TRAPSQR) model barrier potential to determine values for the tunnel barrier parameters (height, shape, and width); these parameters are consistent with AFM topological measurements and values from similar devices reported in the literature. IET spectra are presented which confirm that electrons tunnel through ultrathin regions of the a-CdTe:O films, which contain aluminum oxide subregions in a manner consistent with the TRAPSQR barrier model. Because tunneling occurs predominantly through these ultrathin regions, IET spectroscopic data obtained are representative of states at, or within a few tenths of nanometers from, the surface and confirm that the a-CdTe:O surface stoichiometry is very sensitive to changes in the argon/oxygen/nitrogen concentration ratios during film growth. Full IET spectra, current–voltage, and conductance–voltage data are presented together with tunnel barrier parameters derived from (WKB) fits to the data. The results presented here indicate that inelastic electron tunneling spectroscopy is a useful tool for characterizing the surface states of a-CdTe:O and possibly other photovoltaic materials. © 2004 American Institute of Physics.
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73.61.Ga II-VI semiconductors
73.61.Jc Amorphous semiconductors; glasses
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
68.35.B- Structure of clean surfaces (and surface reconstruction)
73.20.-r Electron states at surfaces and interfaces
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
68.37.Ps Atomic force microscopy (AFM)
73.40.Gk Tunneling

The Schrödinger–Poisson self-consistency in layered quantum semiconductor structures

L. R. Ram-Mohan, K. H. Yoo, and J. Moussa

J. Appl. Phys. 95, 3081 (2004); http://dx.doi.org/10.1063/1.1649458 (12 pages) | Cited 9 times

Online Publication Date: 2 March 2004

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We develop a self-consistent solution of the Schrödinger and Poisson equations in semiconductor heterostructures with arbitrary doping profiles and layer geometries. An algorithm for this non-linear problem is presented in a multiband k⋅P framework for the electronic band structure using the finite element method. The discretized functional integrals associated with the Schrödinger and Poisson equations are used in a variational approach. The finite element formulation allows us to evaluate functional derivatives needed to linearize Poisson’s equation in a natural manner. Illustrative examples are presented using a number of heterostructures including single quantum wells, an asymmetric double quantum well, p-i-n-i superlattices, and trilayer superlattices. © 2004 American Institute of Physics.
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61.72.S- Impurities in crystals
71.15.-m Methods of electronic structure calculations
71.20.Ps Other inorganic compounds
02.70.Dh Finite-element and Galerkin methods
73.21.Fg Quantum wells
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An active tunneling model for the magnetotransport in mixed-phase polycrystalline manganites

Sheng Ju and Zhen-Ya Li

J. Appl. Phys. 95, 3093 (2004); http://dx.doi.org/10.1063/1.1649462 (6 pages) | Cited 10 times

Online Publication Date: 2 March 2004

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Based on phase separation between metallic and insulating domains, the evolution of magnetoresistance in mixed-phase polycrystalline manganites, as a function of temperature, has been modeled via a bond-disordered random resistor network. The tunneling bond is introduced in the resistor network to account for the contribution from grain boundaries, where the energy barrier is formed. The model is analytically worked out by means of the effective-medium approximation. Compared with the transport in single-phase ferromagnetic-ordered polycrystal, the transport in mixed-phase polycrystal is governed by not only the properties of grain boundaries but also the competing metallic and insulating phases. The fraction of tunneling bonds strongly depends on the temperature and external magnetic field. An active tunneling model is thus established in mixed-phase polycrystalline manganites. Within our model, the effect of crystallinity on the temperature dependence of magnetoresistance in mixed-phase polycrystalline manganites is well explained. © 2004 American Institute of Physics.
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75.47.Lx Magnetic oxides
75.47.Gk Colossal magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials

Permeability dependence of the effective magnetostriction of magnetostrictive composites

Y. P. Wan, Z. Zhong, and D. N. Fang

J. Appl. Phys. 95, 3099 (2004); http://dx.doi.org/10.1063/1.1650532 (12 pages) | Cited 4 times

Online Publication Date: 2 March 2004

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A model is presented in this article to investigate the dependence of effective magnetostriction of the magnetostrictive composites on the parameters of components including the elastic modulus, permeability, and volume fraction, etc. Concentrating on the two-component magnetostrictive composites and choosing the two components to be general magnetostrictive materials, this model yields, analytically, the effective magnetostriction of composites by means of the method of complex potential. In terms of the analysis of this model, the magnetostrictive composites can be roughly divided into two kinds. One kind is that the matrix material is nonmagnetic or a material with very low magnetostriction, in which the effective magnetostriction is independent of the permeability of components. Another kind is the case in which the two components have close magnetostriction, and the effective magnetostriction of the composites generally depends on the elastic and the magnetic parameters of both components and the volume fraction. Unlike the first kind of composite, in a certain range, effective magnetostriction of this kind of composite can be improved by increasing the permeability of matrix. In addition, dependence of the effective magnetostriction on the other parameters of the components has also been discussed systematically. To evaluate the accuracy of this model, comparisons are made between the theoretical values and the experimental results published in the literature, which indicate that predictions of this model agree qualitatively with the experimental data. © 2004 American Institute of Physics.
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75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Mg Numerical simulation studies
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Composition and orientation dependence of electrical properties of epitaxial Pb(ZrxTi1−x)O3 thin films grown using metalorganic chemical vapor deposition

Takahiro Oikawa, Masanori Aratani, Hiroshi Funakubo, Keisuke Saito, and Manabu Mizuhira

J. Appl. Phys. 95, 3111 (2004); http://dx.doi.org/10.1063/1.1645646 (5 pages) | Cited 20 times

Online Publication Date: 2 March 2004

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The composition dependence and orientation anisotropy of the dielectric and ferroelectric properties of epitaxial Pb(ZrxTi1−x)O3 (PZT) thin films grown using metalorganic chemical vapor deposition were investigated. {100}-, {110}-, and {111}-oriented PZT films were ascertained to have been grown on (100)c, (110)c, and (111)cSrRuO3//SrTiO3 substrates, respectively. The relative dielectric constant reached a maximum near x=0.5, around the morphotropic phase boundary (MPB) composition, irrespective of film orientation, with the {111}-oriented film showing the largest value. Well-saturated hysteresis loops were observed for all films, and abrupt saturation of the remanent polarization (Pr) and coercive field (Ec) values were observed when the value of x was small, irrespective of film orientation. The Ec value reached a minimum around the composition for {110}- and {111}-oriented films but not for {100}-oriented ones. The saturated polarization (Psat) and Pr values for the {111}-oriented film reached a maximum around the MPB composition, while attaining a minimum for films with other orientations. The ratio of Pr to Psat decreased near the MPB composition regardless of film orientation. These results suggest that the electrical properties of epitaxial PZT thin films strongly depend on both of the composition and orientation of the films. © 2004 American Institute of Physics.
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77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
61.66.Bi Elemental solids
61.66.Dk Alloys
68.55.Nq Composition and phase identification
81.15.Kk Vapor phase epitaxy; growth from vapor phase
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