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21 Jul 2003

Volume 83, Issue 3, pp. 407-587

Issue Cover Spotlight Figure

Appl. Phys. Lett. 83, 575 (2003); http://dx.doi.org/10.1063/1.1594830 (3 pages)

P. Yu, M. Mustata, J. J. Turek, P. M. W. French, M. R. Melloch, and D. D. Nolte
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Investigation of a channel-add/drop-filtering device using acceptor-type point defects in a two-dimensional photonic-crystal slab

Takashi Asano, Bong-Shik Song, Yoshinori Tanaka, and Susumu Noda

Appl. Phys. Lett. 83, 407 (2003); http://dx.doi.org/10.1063/1.1592890 (3 pages) | Cited 20 times

Online Publication Date: 16 July 2003

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A channel-drop-filtering device using point and line defects in a two-dimensional photonic-crystal slab is investigated. The efficiency to drop light from a line-defect waveguide to the free space via a point-defect cavity is found to be more than 45%, which is very close to the theoretical maximum of the device. The reverse function of the device (channel-add-filtering) is also demonstrated, where photons incident on a point defect from free space are resonantly trapped and transferred to a line-defect waveguide nearby. The spectrum and polarization characteristic of the add-filtering completely agree with those of the drop-filtering. The results indicate that two-dimensional photonic slabs are very promising for realizing ultrasmall optical functional devices. © 2003 American Institute of Physics.
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42.79.Ci Filters, zone plates, and polarizers
42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials
71.55.-i Impurity and defect levels

Improvement of holographic recording sensitivities in the green in SiO2 nanoparticle-dispersed methacrylate photopolymers doped with pyrromethene dyes

Yasuo Tomita and Hiroshi Nishibiraki

Appl. Phys. Lett. 83, 410 (2003); http://dx.doi.org/10.1063/1.1593816 (3 pages) | Cited 21 times

Online Publication Date: 16 July 2003

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We demonstrate more than one-order-of-magnitude improvement of holographic recording sensitivities in the green by doping pyrromethene dyes into SiO2 nanoparticle-dispersed methacrylate photopolymer films. Holographic recording dynamics are measured for several dye concentrations and writing intensities. It is found that there exists the optimum writing intensity for a given dye concentration to maximize the diffraction efficiency. Noticeable hologram-apodization phenomena caused by the longitudinal refractive-index changes are also observed in the Bragg-angle selectivity curve. © 2003 American Institute of Physics.
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42.70.Ln Holographic recording materials; optical storage media
42.70.Jk Polymers and organics
81.05.Qk Reinforced polymers and polymer-based composites
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.40.Lx Diffraction efficiency, resolution, and other hologram characteristics
42.30.-d Imaging and optical processing
82.35.Ej Nonlinear optics with polymers
82.35.Np Nanoparticles in polymers
81.07.Bc Nanocrystalline materials

Thin film encapsulated flexible organic electroluminescent displays

Anna B. Chwang, Mark A. Rothman, Sokhanno Y. Mao, Richard H. Hewitt, Michael S. Weaver, Jeff A. Silvernail, Kamala Rajan, Michael Hack, Julie J. Brown, Xi Chu, Lorenza Moro, Todd Krajewski, and Nicole Rutherford

Appl. Phys. Lett. 83, 413 (2003); http://dx.doi.org/10.1063/1.1594284 (3 pages) | Cited 54 times

Online Publication Date: 16 July 2003

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We describe encapsulated passive matrix, video rate organic light-emitting diode (OLED) displays on flexible plastic substrates using a multilayer barrier encapsulation technology. The flexible OLED (FOLED™) displays are based on highly efficient electrophosphorescent OLED (PHOLED™) technology deposited on barrier coated plastic (Flexible Glass™ substrate) and are hermetically sealed with an optically transmissive multilayer barrier coating (Barix™ encapsulation). Preliminary lifetime to half initial luminance (L0 ∼ 100 cd/m2) of order 200 h is achieved on the passive matrix driven encapsulated 80 dpi displays; 2500 h lifetime is achieved on a dc tested encapsulated 5 mm2 FOLED test pixel. The encapsulated displays are flexed 1000 times around a 1 in. diameter cylinder and show minimal damage. © 2003 American Institute of Physics.
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85.60.Pg Display systems
85.60.Jb Light-emitting devices

1.3 μm light amplification in dye-doped hybrid sol-gel channel waveguides

M. Casalboni, F. De Matteis, V. Merlo, P. Prosposito, R. Russo, and S. Schutzmann

Appl. Phys. Lett. 83, 416 (2003); http://dx.doi.org/10.1063/1.1593227 (3 pages) | Cited 11 times

Online Publication Date: 16 July 2003

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We report on light amplification of dye-doped hybrid channel waveguides in the near-infrared region. Films have been grown both on glass and silicon substrates by a spin-coating process that uses a hybrid organic/inorganic sol-gel route. Doped films have been obtained by incorporation of an organic dye (IR1051) emitting in the 1.1–1.3 μm spectral region. Active channel waveguides have been synthesized by photolitographic and ion-milling techniques. An optical gain of about 11 cm−1 was estimated by amplified spontaneous emission measurements. An estimation of the optical losses of the hybrid waveguides is also reported. © 2003 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer
78.45.+h Stimulated emission
42.70.Hj Laser materials

Non-uniform carrier distribution in multi-quantum-well lasers

P. M. Smowton, G. M. Lewis, A. Sobiesierski, P. Blood, J. Lutti, and S. Osbourne

Appl. Phys. Lett. 83, 419 (2003); http://dx.doi.org/10.1063/1.1593818 (3 pages) | Cited 4 times

Online Publication Date: 16 July 2003

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We describe an approach to detect the presence of a nonuniform distribution of carriers between the different wells of multi-quantum-well laser diodes by measuring the gain and spontaneous emission spectra and demonstrate its application to a five-well sample that has a nonuniform carrier distribution at low temperatures. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.67.De Quantum wells
73.21.Fg Quantum wells
73.63.Hs Quantum wells

Electro-tunable laser action in a dye-doped nematic liquid crystal waveguide under holographic excitation

Tatsunosuke Matsui, Masanori Ozaki, and Katsumi Yoshino

Appl. Phys. Lett. 83, 422 (2003); http://dx.doi.org/10.1063/1.1593827 (3 pages) | Cited 7 times

Online Publication Date: 16 July 2003

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Optically pumped distributed feedback lasing has been demonstrated in a dye-doped nematic liquid crystal (NLC) waveguide by holographic excitation. The excitation was performed by two-beam interference using Lloyd mirror configuration. With an applied electric field, continuous tuning of the lasing wavelength was realized due to the change of the effective refractive index of the NLC core layer caused by the reorientation of NLC molecules. © 2003 American Institute of Physics.
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42.55.Mv Dye lasers
42.60.Fc Modulation, tuning, and mode locking
42.79.Kr Display devices, liquid-crystal devices
42.70.Df Liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
42.60.By Design of specific laser systems
42.70.Hj Laser materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Confocal two-photon spectroscopy of red mercuric iodide

X. M. Wen, Paul Xu, Philip B. Lukins, and N. Ohno

Appl. Phys. Lett. 83, 425 (2003); http://dx.doi.org/10.1063/1.1594825 (3 pages)

Online Publication Date: 16 July 2003

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One- and two-photon fluorescence of red mercuric iodide single crystal was studied using confocal laser scanning microscopy and spectroscopy at room temperature. There is a clear difference in the fluorescence spectra for one- and two-photon excitation. With two-photon excitation, a fluorescent band is found at the band gap and its central wavelength shifts toward lower energy with increasing depth below the surface, whereas the fluorescent band for one-photon excitation remains invariant with depth. There is an approximately 70 μm thick defect transition layer near the surface and the defect concentration decreases approximately linearly from the surface to the bulk. The band-gap energy at room temperature is determined as 2.12 eV, which is consistent with previous studies. © 2003 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
07.79.Fc Near-field scanning optical microscopes
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Experimental and computational estimate of bipolar flow parameters in an explosive field emission cathode

D. Shiffler, K. L. Cartwright, Kim Lawrence, M. Ruebush, M. LaCour, K. Golby, and D. Zagar

Appl. Phys. Lett. 83, 428 (2003); http://dx.doi.org/10.1063/1.1589164 (3 pages) | Cited 7 times

Online Publication Date: 16 July 2003

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Explosive field emission cathodes constitute an important class of cathodes for high power microwave tubes. These cathodes have the advantages of being light weight and the capability of operating cold. In the past, this class of cathodes suffered from large amounts of outgassing, nonuniform emission, and very high emittance. These effects tended to dominate the diode performance, masking effects due to the anode. However, a type of carbon cathode has enabled the role of the anode in the diode to be better determined. In this letter, we compare experimental results with simulated diode performance, allowing an estimate of the bounds on the secondary emission coefficient from the anode surface as well as the amount of neutral gas liberated from this surface. In general, secondary electrons and neutral atoms lead to plasma formation in high power microwave devices, which in turn deleteriously affect the tube performance. Hence, an estimate of such quantities for use in particle-in-cell codes can prove pivotal for accurate modeling of experimental devices. © 2003 American Institute of Physics.
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85.45.Db Field emitters and arrays, cold electron emitters
84.40.Fe Microwave tubes (e.g., klystrons, magnetrons, traveling-wave, backward-wave tubes, etc.)

Ion characteristics of laser-produced plasma using a pair of collinear femtosecond laser pulses

Z. Zhang, P. A. Van Rompay, and P. P. Pronko

Appl. Phys. Lett. 83, 431 (2003); http://dx.doi.org/10.1063/1.1592616 (3 pages) | Cited 7 times

Online Publication Date: 16 July 2003

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Femtosecond laser-pulse absorption is studied in silicon ablation plasmas by means of a pair of identical 1016 W/cm2 collinear pulses separated on a picosecond time scale. The second laser-pulse modifies ionic characteristics of the preformed plasma, such as ion yield, ion energy, and average charge state. Resonance absorption is demonstrated to be the dominant mechanism by comparing results of s and p polarization. It is shown that maximum effects occur when a well defined critical density surface of the initial plasma forms together with an optimum density gradient scale length of kL = 1.5. The optimal enhancement of ion yield, which occurs at 5 ps delay, is a factor of 2 greater than that produced by a single pulse with twice the energy of each individual double pulse. Applications are identified in regard to cluster beam formation and plasma isotope enrichment in ultrafast ablation plumes. © 2003 American Institute of Physics.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.38.Mf Laser ablation
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.-b Plasma properties
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Location control of crystal grains in excimer laser crystallization of silicon thin films

Hideya Kumomi

Appl. Phys. Lett. 83, 434 (2003); http://dx.doi.org/10.1063/1.1591998 (3 pages) | Cited 11 times

Online Publication Date: 16 July 2003

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Location of crystal grains in polycrystalline Si thin films formed by excimer-laser crystallization is controlled by manipulating the superlateral-growth phenomenon. The superlateral growth of a single grain occurs preferentially at an artificial site where nanometer-sized crystallites are embedded in the precursory amorphous thin films. Only a part of the crystallites embedded in the site could survive the melting and grow to serve as the seed crystal in the subsequent recrystallization. Such grain-location control provides a basis for two-dimensional control of the grain-boundary location in low-temperature polycrystalline Si thin films, which is essential to the device-to-device uniformity of high-performance thin-film transistors. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
64.70.K- Solid-solid transitions
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.46.-w Structure of nanoscale materials
61.82.Fk Semiconductors
81.10.Jt Growth from solid phases (including multiphase diffusion and recrystallization)

Negative-U property of the oxygen vacancy defect in SiO2 and its implication for the E1′ center in α-quartz

D. J. Chadi

Appl. Phys. Lett. 83, 437 (2003); http://dx.doi.org/10.1063/1.1592003 (3 pages) | Cited 6 times

Online Publication Date: 16 July 2003

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The +1 charged state of an oxygen vacancy V(O)+ in α-quartz is found to be unstable with respect to the reaction 2V(O)+→V(O)0+V(O)2+, which lowers the total energy by 2.9 eV, making it highly unlikely that V(O)+ is the source of the electron-paramagnetic-resonance (EPR) active E1′ center in α-quartz. Results from ab initio total energy calculations indicate that V(SiO3)+ and V(SiO4)+ are the smallest EPR active vacancy complexes. The atomic and electronic structures of these two multivacancy clusters are surprisingly similar to those of V(O)+. © 2003 American Institute of Physics.
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76.30.Mi Color centers and other defects
61.72.J- Point defects and defect clusters
71.55.Ht Other nonmetals
71.15.-m Methods of electronic structure calculations

Nanoshell tubes of ferroelectric lead zirconate titanate and barium titanate

Yun Luo, Izabela Szafraniak, Nikolai D. Zakharov, Valanoor Nagarajan, Martin Steinhart, Ralf B. Wehrspohn, Joachim H. Wendorff, Ramamoorthy Ramesh, and Marin Alexe

Appl. Phys. Lett. 83, 440 (2003); http://dx.doi.org/10.1063/1.1592013 (3 pages) | Cited 77 times

Online Publication Date: 16 July 2003

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Wafer-scale fabrication of ferroelectric oxide nanoshell tubes as well as ordered nanotube arrays have been accomplished using a simple and convenient fabrication method that allows full tailoring of tube dimensions as well as array pattern and size. Using different silicon and alumina templates, barium titanate and lead zirconate titanate tubes with diameters ranging from 50 nm up to several micrometers meter and lengths of more 100 μm have been fabricated. Ferroelectric switching of submicrometer tubes has been shown using piezoresponse scanning probe microscopy. © 2003 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
77.80.Fm Switching phenomena
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
77.65.Bn Piezoelectric and electrostrictive constants

Wavelength selective charge storage in self-assembled InGaAs/GaAs quantum dots

M. Kroutvar, Y. Ducommun, J. J. Finley, M. Bichler, G. Abstreiter, and A. Zrenner

Appl. Phys. Lett. 83, 443 (2003); http://dx.doi.org/10.1063/1.1588368 (3 pages) | Cited 26 times

Online Publication Date: 16 July 2003

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We present a wavelength selective optical memory device based on optically-induced charge storage in an inhomogeneously broadened ensemble of InGaAs quantum dots. We show that electrons and holes can be efficiently and resonantly stored without thermal redistribution of charge between dots over timescales much longer than 25 μs at 10 K. Direct information on the absorption mechanisms are obtained for self-assembled dots. The maximum efficiency of the charge storage process is estimated to be close to unity. © 2003 American Institute of Physics.
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78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

In situ lateral growth control of optically efficient quantum structures

T. Schallenberg, W. Faschinger, G. Karczewski, L. W. Molenkamp, V. Türck, S. Rodt, R. Heitz, D. Bimberg, M. Obert, G. Bacher, and A. Forchel

Appl. Phys. Lett. 83, 446 (2003); http://dx.doi.org/10.1063/1.1592894 (3 pages) | Cited 7 times

Online Publication Date: 16 July 2003

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We present a versatile method for in situ lateral growth control of optically efficient quantum structures. The method is based on molecular-beam epitaxy through an epitaxial shadow mask. Lateral control is achieved by selective area growth of short period superlattices. We demonstrate how the method can be applied to both lattice-matched and unmatched material systems. In the former, selective growth is employed in the formation of quantum wires. In the latter, this growth concept was also successfully applied to control the self-assembly of quantum dots within selected areas. The excellent quality of the quantum structures is demonstrated by their bright cathodoluminescence at room temperature. © 2003 American Institute of Physics.
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81.07.Ta Quantum dots
78.67.Hc Quantum dots
78.60.Hk Cathodoluminescence, ionoluminescence
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Photostimulated luminescence in Eu-doped fluorochlorozirconate glass ceramics

Stefan Schweizer, Linn W. Hobbs, Mihail Secu, Johann-Martin Spaeth, Andrew Edgar, and Grant V. M. Williams

Appl. Phys. Lett. 83, 449 (2003); http://dx.doi.org/10.1063/1.1593228 (3 pages) | Cited 41 times

Online Publication Date: 16 July 2003

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We report the synthesis of Eu2+- and chlorine-doped fluorozirconate glass-ceramics that show an intense photostimulated luminescence (PSL) after x-ray irradiation at room temperature. The PSL efficiency is up to 80% of that found in the well-known crystalline x-ray storage phosphor BaFBr:Eu2+, and it is the largest thus far reported for a glass-ceramic. We attribute the PSL to crystallites of orthorhombic BaCl2 that are formed after annealing above the glass temperature. Hexagonal BaCl2 crystallites are also observed after short annealing times, but they do not provide a measurable PSL signal. The photoluminescence peak from glass-ceramics containing orthorhombic BaCl2 crystallites occurs at 402 nm, and the stimulation band is centered at about 560 nm. © 2003 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
81.40.Gh Other heat and thermomechanical treatments
61.72.Cc Kinetics of defect formation and annealing

Near-surface characterization of amorphous carbon films by neutron reflectivity

J. A. Johnson, J. B. Woodford, A. Erdemir, and G. R. Fenske

Appl. Phys. Lett. 83, 452 (2003); http://dx.doi.org/10.1063/1.1590731 (3 pages) | Cited 17 times

Online Publication Date: 16 July 2003

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A high-density top-surface layer of approximately 30 Å was found in a form of diamondlike carbon, “near-frictionless carbon,” developed at Argonne National Laboratory. Three diamondlike-carbon films were prepared by plasma-enhanced chemical vapor deposition with different hydrogen-to-methane ratios in the plasma. Complementary films were prepared with deuterated methane and deuterium, in the same ratios. Results from neutron relectivity experiments are presented, along with model comparisons, and a hypothesis is postulated. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.U- Carbon/carbon-based materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness

Abnormal electrical resistivity in γ-TiAl thin films deposited by magnetron sputtering

T. L. Alford, K. S. Gadre, H. C. Kim, and S. C. Deevi

Appl. Phys. Lett. 83, 455 (2003); http://dx.doi.org/10.1063/1.1593826 (3 pages) | Cited 3 times

Online Publication Date: 16 July 2003

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Thin films of γ-TiAl are being considered as a potential conductor and/or diffusion barrier for high temperature electronics because of their high melting points and high oxidation resistance. However, it is not possible to form pure γ-TiAl thin films by thermal annealing of Al/Ti bilayers. This study, however, demonstrates the formation of γ-TiAl thin films by dc magnetron sputtering of a compound target. X-ray diffractometry and Rutherford backscattering spectrometry analyses confirm the γ-TiAl phase formation, composition, and thermal stability in vacuum (up to 700 °C, 1 h) on SiO2. Four-point probe resistivity measurements in vacuum show an initial increase in the resistivity with temperature up to transition temperature for the γ-TiAl thin films. At higher temperatures a decrease in resistivity with additional heating (i.e., negative temperature coefficient of resistivity, TCR) is seen. The values of dρ/dT are typically on the order of −0.32 μΩ cm/°C between 200 and 550 °C. At the highest temperature, a minimum value of resistivity of ∼ 13 μΩ cm is obtained; this value is about one half the value of bulk TiAl at room temperatures. The negative TCR, low resistivity values at high temperatures, and temperature stability are not typically seen in bulk TiAl. This abnormal electrical property is explained using a modified model for a thermally activated polaron-hopping mechanism. © 2003 American Institute of Physics.
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73.61.At Metal and metallic alloys
81.15.Cd Deposition by sputtering
81.05.Bx Metals, semimetals, and alloys
68.55.Nq Composition and phase identification
68.60.Dv Thermal stability; thermal effects
72.60.+g Mixed conductivity and conductivity transitions

Irradiation-induced recovery of disorder in gallium nitride

W. Jiang and W. J. Weber

Appl. Phys. Lett. 83, 458 (2003); http://dx.doi.org/10.1063/1.1594282 (3 pages) | Cited 8 times

Online Publication Date: 16 July 2003

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Gallium nitride has been irradiated to two fluences with energetic Au2+ ions at 300 K. Two different damage levels and depth profiles were produced that are characterized by near-surface damage accumulation and deeper-regime damage saturation. Thermal annealing at 873 K resulted in disorder recovery only in the near-surface region at low fluence. However, simultaneous irradiation with 5.4 MeV Si2+ ions during annealing at 873 K induced significant recovery over the entire damage profile at both low and high fluences. The irradiation-enhanced recovery is primarily attributed to defect-stimulated recovery and epitaxial recrystallization processes due to the creation of mobile Frenkel pairs. © 2003 American Institute of Physics.
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61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing

Short-period SinGem strained-layer superlattices grown from gas sources by synchrotron-radiation-excited chemical-beam epitaxy

Housei Akazawa

Appl. Phys. Lett. 83, 461 (2003); http://dx.doi.org/10.1063/1.1593795 (3 pages)

Online Publication Date: 16 July 2003

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Short-period SinGem strained-layer superlattices were successfully grown on Si (100) substrate from gas sources by synchrotron-radiation-excited chemical-beam epitaxy at 250 °C. Atomically sharp interfaces between the Si and Ge layers and two-dimensional morphology were obtained. With thinner Ge layers, the misfit strain is relieved by atomic-scale roughness at the interfaces; as the Ge layers become thicker, misfit dislocations become the main relief mechanism. The thickness of Si and Ge layers as derived from spectroscopic ellipsometry agreed nicely with images of the lattices. The dielectric constants of the growing Si and Ge top layers were much lower than those of Si and Ge bulk crystals, which is consistent with the mechanism of photoepitaxy, that is, the formation of a hydrogenated network as the precursor state followed by photolytic crystallization. © 2003 American Institute of Physics.
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68.65.Cd Superlattices
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.82.Fk Semiconductors
61.80.Cb X-ray effects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)

Elastic–stiffness mapping by resonance-ultrasound microscopy with isolated piezoelectric oscillator

Hirotsugu Ogi, Jiayong Tian, Toyokazu Tada, and Masahiko Hirao

Appl. Phys. Lett. 83, 464 (2003); http://dx.doi.org/10.1063/1.1593819 (3 pages) | Cited 10 times

Online Publication Date: 16 July 2003

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A resonance-ultrasound microscopy has been developed for mapping a material’s elastic constant in a localized surface region. It detects the effective elastic modulus through a resonance frequency of free vibrations of a solid probe touching the specimen via a small tungsten-carbide bearing. Langasite (La3Ga5SiO14) crystal is used as a probe because of the low sensitivity of its elastic constants to temperature and its high piezoelectric coefficients. The vibration of the probe is excited and detected with a surrounding solenoid coil. This noncontacting acoustic coupling isolates the probe vibration and measures the resonance frequency with an accuracy better than one part in 105. This microscopic method is applied to a composite material consisting of silicon-carbide (SiC) fibers in titanium-alloy matrix. The stiffness distribution inside a single fiber was determined. © 2003 American Institute of Physics.
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81.70.Cv Nondestructive testing: ultrasonic testing, photoacoustic testing
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
81.40.Jj Elasticity and anelasticity, stress-strain relations
43.35.Yb Ultrasonic instrumentation and measurement techniques
62.20.D- Elasticity
46.80.+j Measurement methods and techniques in continuum mechanics of solids
43.58.Ls Acoustical lenses and microscopes
07.10.Fq Vibration isolation

Structure of the nanocrystals in oxyfluoride glass ceramics

M. Beggiora, I. M. Reaney, and M. S. Islam

Appl. Phys. Lett. 83, 467 (2003); http://dx.doi.org/10.1063/1.1594842 (3 pages) | Cited 9 times

Online Publication Date: 16 July 2003

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The crystallization of fluoro-silicate glasses obtained using high-purity SiO2, AlO1.5, CdF2, PbF2, ZnF2, and ErF3 has been investigated. Upon heat treatment, PbF2 nanocrystals form which host most of the Er3+ ions. The major peaks obtained by x-ray diffraction suggest that the nanocrystals are fluorite structured, but the low volume fraction of nanocrystals and line broadening due to their small size mean that unambiguous identification of the crystal structure is impossible. Therefore, atomistic simulation techniques have been performed to investigate the mechanism of incorporation of Er3+ in the PbF2 nanocrystals and polycrystalline (1−x)PbF2–xErF3 ceramics have been fabricated to study the expected phase assemblage. © 2003 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
81.05.Pj Glass-based composites, vitroceramics
81.07.Bc Nanocrystalline materials
81.10.Aj Theory and models of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
61.43.Fs Glasses
81.05.Kf Glasses (including metallic glasses)
81.40.Gh Other heat and thermomechanical treatments
61.66.Fn Inorganic compounds

Photoreflectance evidence of the N-induced increase of the exciton binding energy in an InxGa1−xAs1−yNy alloy

M. Geddo, G. Guizzetti, M. Capizzi, A. Polimeni, D. Gollub, and A. Forchel

Appl. Phys. Lett. 83, 470 (2003); http://dx.doi.org/10.1063/1.1594279 (3 pages) | Cited 10 times

Online Publication Date: 16 July 2003

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The binding energy of the heavy-hole ground-state exciton in In0.25Ga0.75As1−yNy/GaAs single quantum wells (y = 0, 0.011) was experimentally derived by photoreflectance measurements. We measured a binding energy of 6.6 and 8.5 meV for the N-free and the N-containing sample, respectively. The observed increase of the exciton binding energy can be accounted for by an increase of the exciton reduced mass of about 30% upon N introduction into the InxGa1−xAs lattice, consistently with recent experimental results and in agreement with earlier theoretical predictions. © 2003 American Institute of Physics.
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73.21.Fg Quantum wells
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.67.De Quantum wells
71.15.Nc Total energy and cohesive energy calculations

Measurement of the elastic constants of textured anisotropic thin films from x-ray diffraction data

P.-O. Renault, E. Le Bourhis, P. Villain, Ph. Goudeau, K. F. Badawi, and D. Faurie

Appl. Phys. Lett. 83, 473 (2003); http://dx.doi.org/10.1063/1.1594280 (3 pages) | Cited 24 times

Online Publication Date: 16 July 2003

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The elastic constants (compliances sij) of a textured anisotropic thin film deposited on a substrate have been determined. Using x-ray diffraction to measure the intragranular strain and a tensile machine to deform in situ the samples, an analytical method is described and has been developed for fiber textured thin films. The determination of thin film compliances only requires the knowledge of the substrate elastic constants. In the case of a 260-nm-thin gold film, the compliances were found to be slightly different from the corresponding bulk material ones. © 2003 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
62.20.D- Elasticity

Growth of InP quantum dots on vicinal GaAs (100) substrates by metalorganic chemical vapor deposition

X. B. Zhang, R. D. Heller, M. S. Noh, R. D. Dupuis, G. Walter, and N. Holonyak

Appl. Phys. Lett. 83, 476 (2003); http://dx.doi.org/10.1063/1.1595152 (3 pages) | Cited 5 times

Online Publication Date: 16 July 2003

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We report the growth of InP self-assembled quantum dots (QDs) on In0.5Al0.5P and In0.5(Al0.6Ga0.4)0.5P matrices, lattice matched on 0°, 2°, 6°, and 25° off-axis (100) GaAs substrates by metalorganic chemical vapor deposition. The influence of the substrate misorientation on the morphology and cathodoluminescence (CL) properties of the InP QDs was investigated. We find that the density of QDs grown on both In0.5Al0.5P and In0.5(Al0.6Ga0.4)0.5P matrices increases with the misorientation angle up to 6° off (100). At the same time, the dispersion of the QD size is getting larger for the growth on an In0.5Al0.5P matrix, but not for the growth on an In0.5(Al0.6Ga0.4)0.5P matrix. The InP QDs grown on In0.5(Al0.6Ga0.4)0.5P on 25° off-axis substrates are two-dimensionally well ordered. Moreover, the ordering improves and the density of QDs increases with an increase in the deposition of InP. The room-temperature CL intensity of InP QDs grown on a 25° off In0.5(Al0.6Ga0.4)0.5P is much stronger than that for InP QDs grown on a 25°-off In0.5Al0.5P matrix. © 2003 American Institute of Physics.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.67.Hc Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
78.60.Hk Cathodoluminescence, ionoluminescence
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Highly low resistance and transparent Ni/ZnO ohmic contacts to p-type GaN

June O Song, Kyoung-Kook Kim, Seong-Ju Park, and Tae-Yeon Seong

Appl. Phys. Lett. 83, 479 (2003); http://dx.doi.org/10.1063/1.1591236 (3 pages) | Cited 44 times

Online Publication Date: 16 July 2003

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We report on a promising Ni (5 nm)/Al-doped ZnO (AZO) (450 nm) metallization scheme for low resistance and transparent ohmic contacts to p-GaN (5×1017 cm−3). It is shown that the as-deposited Ni/AZO contact shows a nonohmic characteristic due to the insulating nature of the as-deposited AZO. However, annealing the contacts at 450 and 550 °C for 2 min in air ambient results in linear current–voltage characteristics, giving a specific contact resistance of 1.01×10−5 and 8.46×10−6 Ω cm2, respectively. It is further shown that annealing the contact at 550 °C for 5 min produces a specific contact resistance of 6.23×10−6 Ω cm2. The light transmittance of the contacts annealed at 550 °C for 2 min is measured to be higher than 76% at wavelengths in the range of 400–550 nm. It is shown that the Ni/AZO contact could be a suitable scheme for high-performance optical devices. © 2003 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
85.40.Ls Metallization, contacts, interconnects; device isolation
73.40.Cg Contact resistance, contact potential
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.Cc Kinetics of defect formation and annealing
78.40.-q Absorption and reflection spectra: visible and ultraviolet
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