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11 Nov 2002

Volume 81, Issue 20, pp. 3705-3896

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Dynamic charge-carrier-mobility-mediated holography in thin layers of photoconducting polymers

S. Bartkiewicz, A. Miniewicz, B. Sahraoui, and F. Kajzar

Appl. Phys. Lett. 81, 3705 (2002); http://dx.doi.org/10.1063/1.1512824 (3 pages) | Cited 9 times

Online Publication Date: 4 November 2002

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The dynamic holography technique is proposed for the measurement of the charge-carrier-mobility in thin layers of a photoconducting polymer, used in optically addressed liquid-crystal spatial light modulators. The photorefractive properties of these modulators are studied under short-pulse (20 ps, 532 nm) laser illumination conditions and the charge mobility in the photoconducting polymer (μh = 10−7 cm2/V s) is obtained from the temporal evolution of intensity of the first-order diffracted beam. A mechanism responsible for the grating formation is proposed and discussed. © 2002 American Institute of Physics.
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42.70.Gi Light-sensitive materials
42.70.Jk Polymers and organics
73.61.Ph Polymers; organic compounds
42.40.My Applications
73.50.Pz Photoconduction and photovoltaic effects
42.70.Ln Holographic recording materials; optical storage media
42.40.Eq Holographic optical elements; holographic gratings
42.79.Kr Display devices, liquid-crystal devices
42.79.Hp Optical processors, correlators, and modulators
84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.)

Development of channel waveguide lasers in Nd3+-doped chalcogenide (Ga:La:S) glass through photoinduced material modification

Arshad K. Mairaj, Christos Riziotis, Alain M. Chardon, Peter G. R. Smith, David P. Shepherd, and Daniel W. Hewak

Appl. Phys. Lett. 81, 3708 (2002); http://dx.doi.org/10.1063/1.1520698 (3 pages) | Cited 16 times

Online Publication Date: 4 November 2002

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We report the development of a waveguide laser source in a neodymium-doped chalcogenide (Ga:La:S) glass. Channel waveguide structures were directly written via above band gap (λ=244 nm) illumination provided by a focused UV-laser beam with fluencies 1.5–150 J/cm2. Effects of photoinduced material modification in the form of surface compaction and photodensification were evident. Characterization revealed a low threshold waveguide laser with emission at 1075 nm and slope efficiency of 17%. The active device was spatially single mode and exhibited laser operation with 8.6 mW peak power and attenuation <0.5 dB cm−1. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
81.05.Kf Glasses (including metallic glasses)
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.72.-g Optical sources and standards
42.62.-b Laser applications

Red electrophosphorescence from polymer doped with iridium complex

Xiong Gong, Jacek C. Ostrowski, Guillermo C. Bazan, Daniel Moses, and Alan J. Heeger

Appl. Phys. Lett. 81, 3711 (2002); http://dx.doi.org/10.1063/1.1511283 (3 pages) | Cited 79 times

Online Publication Date: 4 November 2002

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We demonstrate efficient, bright red electrophosphorescent light emitting diodes (LEDs) employing tris (2,5-bis-2′-(9′,9′-dihexylfluorene) pyridine) iridium (III), [Ir(HFP)3], doped into a blend of poly(vinylcarbazole) (PVK) with 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazol (PBD). At a current density of 2.35 mA/cm2 (brightness of 169 cd/m2), the external quantum efficiency (QEext) and luminous efficiency (LE) were 5% ph/el and 7.2 cd/A, respectively. Even at 50 mA/cm2, QEext = 3.4% ph/el and LE = 5.2cd/A. The electroluminescent emission is characteristic of Ir(HFP)3, with maximum at 600 nm. The devices exhibited no emission from either PVK or PBD, even at the lowest concentration of Ir(HFP)3 (0.05 wt %). The results demonstrate that electrophosphorescence with high brightness and efficiency can be achieved from polymer-based LEDs fabricated by processing the active materials from solution. © 2002 American Institute of Physics.
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78.60.Fi Electroluminescence
85.60.Jb Light-emitting devices
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
78.55.Hx Other solid inorganic materials
82.35.Jk Copolymers, phase transitions, structure

Enhancement of third-harmonic generation in absorbing media

G. Veres, S. Matsumoto, Y. Nabekawa, and K. Midorikawa

Appl. Phys. Lett. 81, 3714 (2002); http://dx.doi.org/10.1063/1.1521248 (3 pages) | Cited 9 times

Online Publication Date: 4 November 2002

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The efficiency of third-harmonic generation on glass–air interfaces near the focal point of a tightly focused laser beam is investigated for different material samples. It is found that highly absorbing materials give higher harmonic yield. Moreover, due to the systematic change of the third-harmonic yield with the absorption length, an estimation of the third-order susceptibility χ(3) of absorbing samples can be given from absorption coefficient measurements. © 2002 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.An Optical susceptibility, hyperpolarizability

Ultrafast dynamics of interfacial electric fields in semiconductor heterostructures monitored by pump-probe second-harmonic generation

Yu. D. Glinka, T. V. Shahbazyan, I. E. Perakis, N. H. Tolk, X. Liu, Y. Sasaki, and J. K. Furdyna

Appl. Phys. Lett. 81, 3717 (2002); http://dx.doi.org/10.1063/1.1521573 (3 pages) | Cited 7 times

Online Publication Date: 4 November 2002

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We report measurements of the ultrafast dynamics of interfacial electric fields in semiconductor multilayers using pump-probe second-harmonic generation (SHG). A pump beam was tuned to excite carriers in all the layers in GaAs/GaSb and GaAs/GaSb/InAs heterostructures. The resulting carrier dynamics manifests itself via electric fields created by charge separation due to carrier redistribution at the interfaces. The evolution of interfacial fields is monitored by a probe beam through an eletric-field-induced SHG signal. We distinguish between several stages of dynamics originating from redistribution of carriers between the layers. We also find a strong enhancement of the induced electric field caused by hybridization of the conduction and valence bands at the GaSb/InAs interface. © 2002 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.20.Jq Electro-optical effects
73.21.Ac Multilayers
78.47.-p Spectroscopy of solid state dynamics
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Coefficient determination related to optical gain in erbium-doped silicon-rich silicon oxide waveguide amplifier

Hak-Seung Han, Se-Young Seo, Jung H. Shin, and Namkyoo Park

Appl. Phys. Lett. 81, 3720 (2002); http://dx.doi.org/10.1063/1.1520710 (3 pages) | Cited 3 times

Online Publication Date: 4 November 2002

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Gain-determining coefficients in Er-doped, nanocrystal-Si (nc-Si) sensitized silica waveguide amplifiers are investigated. Single-mode, Er-doped silica waveguides with nc-Si embedded in them were prepared by electron cyclotron resonance plasma-enhanced chemical vapor deposition of Er-doped a-Si:Ox (x<2) followed by a high-temperature anneal to precipitate nc-Si. Exciting the Er ions via nc-Si by pumping the waveguide from the top with the 477 nm line of an Ar laser resulted in an enhancement of the transmitted 1535 nm signal of up to 14 dB/cm, indicating a possible net gain of up to 7 dB/cm. From the dependence of the signal enhancement upon the pump power, an emission cross section of 2×10−19 cm2 at 1535 nm and an effective excitation cross section of ≥ 10−17 cm2 at 477 nm is obtained. © 2002 American Institute of Physics.
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42.82.Et Waveguides, couplers, and arrays
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.55.Rz Doped-insulator lasers and other solid state lasers
42.79.Gn Optical waveguides and couplers

1212 nm pumping of 2 μm Tm–Ho-codoped silica fiber laser

Atsushi Taniguchi, Tetsuro Kuwayama, Akira Shirakawa, Mitsuru Musha, Ken-ichi Ueda, and Mahendra Prabhu

Appl. Phys. Lett. 81, 3723 (2002); http://dx.doi.org/10.1063/1.1521242 (3 pages) | Cited 13 times

Online Publication Date: 4 November 2002

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A Tm–Ho-codoped silica fiber laser pumped by a third-stokes Raman Fiber Laser at 1212 nm is demonstrated. For the 30-cm-long Tm–Ho-codoped fiber, a 400 mW output power is obtained at a wavelength of 1790 nm due to the laser emission from the Tm3+ ions. For the 270-cm-long Tm–Ho-codoped fiber, a 450 mW output power is obtained at 1970 nm due to the laser emission from Ho3+ ions. © 2002 American Institute of Physics.
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42.55.Wd Fiber lasers

Generation of bright low-divergence high-order harmonics in a long gas jet

D. G. Lee, H. T. Kim, K. H. Hong, C. H. Nam, I. W. Choi, A. Bartnik, and H. Fiedorowicz

Appl. Phys. Lett. 81, 3726 (2002); http://dx.doi.org/10.1063/1.1521241 (3 pages) | Cited 10 times

Online Publication Date: 4 November 2002

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Guided propagation of intense 28 fs laser pulses through a long gas jet made it feasible to produce a bright 27th harmonic from argon with a divergence of 0.5 mrad. This harmonic saturated an x-ray charge-coupled device of an extreme ultraviolet spectrometer in a single laser shot of 5 mJ. The low-divergence harmonic generation resulted from a well-guided pumping laser pulse, achieved by balancing diffraction and plasma defocusing with nonlinear self-focusing, and a large harmonic-generation cross section. © 2002 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
52.38.-r Laser-plasma interactions
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Analysis of coupling between two-dimensional photonic crystal waveguide and external waveguide

Eiji Miyai, Makoto Okano, Masamitsu Mochizuki, and Susumu Noda

Appl. Phys. Lett. 81, 3729 (2002); http://dx.doi.org/10.1063/1.1521586 (3 pages) | Cited 24 times

Online Publication Date: 4 November 2002

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Coupling between conventional wire waveguide and two-dimensional photonic crystal waveguide was analyzed by means of a three-dimensional finite difference time domain method. We evaluated the transmittance corresponding to the coupling efficiency between two waveguides. By using SiO2 clad below the wire and setting the width of the wire to be an appropriate value, we obtained single mode guiding and a coupling efficiency over 80% for the wave length around 1.55 μm. © 2002 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers

Sum frequency generation of synchronously-seeded, high-power Yb and Er fiber amplifiers in periodically poled KTP

P. A. Champert, S. V. Popov, A. V. Avdokhin, and J. R. Taylor

Appl. Phys. Lett. 81, 3732 (2002); http://dx.doi.org/10.1063/1.1521582 (3 pages) | Cited 1 time

Online Publication Date: 4 November 2002

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Synchronous temporal seeding of single-mode, high-peak, and average-power Yb and Er fiber amplifiers allowed efficient, single-pass, sum frequency generation in periodically poled KTP. 3.5 W average power in the red, at 630 nm, is generated with Gaussian spatial beam quality. © 2002 American Institute of Physics.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.55.Wd Fiber lasers

Ultralow threshold powers for optical pumping of homoepitaxial InGaN/GaN/AlGaN lasers

V. Yu. Ivanov, M. Godlewski, H. Teisseyre, P. Perlin, R. Czernecki, P. Prystawko, M. Leszczynski, I. Grzegory, T. Suski, and S. Porowski

Appl. Phys. Lett. 81, 3735 (2002); http://dx.doi.org/10.1063/1.1521243 (3 pages) | Cited 5 times

Online Publication Date: 4 November 2002

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We report ultralow threshold powers for optically pumped laser emission from InGaN/GaN/AlGaN laser structures grown on bulk GaN substrates. The threshold powers at room temperature (for excitation with 355 nm third harmonic of Nd:YAG laser) are between 2.4 and 5.8 kW/cm2, depending on a cavity length. We believe that this is the consequence of a significant reduction of concentration of nonradiative centers in the active layer of homoepitaxial structures. We report also that spacing of the longitudinal laser modes exceeds by a factor of 6–7 the values predicted from the standard calculations. © 2002 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)

Electro-optic modulation at 1.5 GHz using single-crystal film of an organic molecular salt

M. Thakur, A. Mishra, J. Titus, and A. C. Ahyi

Appl. Phys. Lett. 81, 3738 (2002); http://dx.doi.org/10.1063/1.1520713 (3 pages) | Cited 4 times

Online Publication Date: 4 November 2002

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Electro-optic modulation using single-crystal film of an organic molecular salt with light propagating perpendicular to the film (transverse configuration) has been recently reported. In this letter, we report results of measurements at high speed (up to 1.5 GHz) using such films in the same configuration. Excellent signal-to-noise ratio has been observed even at a low applied voltage (1 V across 15 μm gap) for a 3 μm thick film. The magnitudes of the electro-optic coefficients are: r11 = 445 pm/V and r21 = 148 pm/V at 750 nm. A wide range of applications of these films are predicted. © 2002 American Institute of Physics.
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42.79.Hp Optical processors, correlators, and modulators
78.47.-p Spectroscopy of solid state dynamics
78.66.Qn Polymers; organic compounds
78.20.Jq Electro-optical effects

Flexible mirrorless laser based on a free-standing film of photopolymerized cholesteric liquid crystal

Tatsunosuke Matsui, Ryotaro Ozaki, Kazuhiro Funamoto, Masanori Ozaki, and Katsumi Yoshino

Appl. Phys. Lett. 81, 3741 (2002); http://dx.doi.org/10.1063/1.1522498 (3 pages) | Cited 73 times

Online Publication Date: 4 November 2002

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Optically pumped mirrorless laser action has been observed in a dye-doped flexible free-standing film of photopolymerized cholesteric liquid crystal (PCLC). In the PCLC film, self-organized helical structure acts as one-dimensional (1D) photonic crystal. At high excitation intensity above the threshold, a laser action is observed at an edge of the 1D photonic band of the PCLC helical structure. This PCLC film laser possesses an excellent mechanical flexibility, and the laser action is also observed in a bent film of PCLC. This implies that the one-dimensional periodic structure for the laser action is maintained even in the deformed film. Using such flexibility of the PCLC film, a focusing effect of laser emission is demonstrated in a circularly deformed film. Moreover, the helical pitch of the PCLC has no temperature dependence in contrast to that of unpolymerized cholesteric liquid crystal. This means that the operation wavelength of laser action is thermally stable, which is the great advantage for the device application. © 2002 American Institute of Physics.
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42.55.Mv Dye lasers
42.70.Qs Photonic bandgap materials
42.70.Df Liquid crystals
42.70.Hj Laser materials
82.35.-x Polymers: properties; reactions; polymerization
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Multiple ion-focusing effects in plasma immersion ion implantation

X. B. Tian and Paul. K. Chu

Appl. Phys. Lett. 81, 3744 (2002); http://dx.doi.org/10.1063/1.1520716 (3 pages) | Cited 9 times

Online Publication Date: 4 November 2002

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In plasma immersion ion implantation, the sample is negatively biased and a plasma sheath forms. Ions are accelerated to the sample surface through this sheath. The electric field contours dictate the shape of the plasma sheath that wraps around corners and tends to be smoother and rounder than the surface topography, for instance, at a sharp corner. Our theoretical and experimental studies reveal ion flux focusing effects leading to lateral nonuniformity of the incident ion dose. Ion focusing occurs not only at the sample edge but also in the central region even for a planar sample (wafer). In this work, we numerically and experimentally investigate this ion focusing effect and ion dose nonuniformity. A simple geometric model is also presented in this letter to understand the mechanism. The results demonstrate that ion focusing originates from plasma sheath convergence that is time and space dependent. Consequently, multiple ion focusing may occur at different local sites when the target shape and processing parameters vary, and a small plasma sheath relative to the target is of paramount importance for uniform implantation. © 2002 American Institute of Physics.
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52.77.Dq Plasma-based ion implantation and deposition
52.40.Kh Plasma sheaths
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Influence of low-energy electron beam irradiation on defects in activated Mg-doped GaN

O. Gelhausen, H. N. Klein, M. R. Phillips, and E. M. Goldys

Appl. Phys. Lett. 81, 3747 (2002); http://dx.doi.org/10.1063/1.1519358 (3 pages) | Cited 11 times

Online Publication Date: 4 November 2002

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The effect of low-energy electron beam irradiation (LEEBI) on residual hydrogen impurities and native defects in activated metalorganic vapor phase epitaxy-grown Mg-doped (p-type) GaN layers was studied by cathodoluminescence (CL) microanalysis and spectroscopy at temperatures between 80 and 300 K. The LEEBI treatment dissociates (Mg–H)0 complexes producing (i) at 300 K, a significant increase in a free-to-bound transition (e,Mg0) centered at 3.26 eV and (ii) at 80 K, a substantial decrease in a H–Mg donor–acceptor pair emission at 3.27 eV. In-plane and depth-resolved CL imaging reveals a direct correlation between the spatial distribution of the injected carriers and the depth and lateral distribution of activated Mg acceptors. This finding strongly suggests that hydrogen dissociation results from electron-hole recombination at hydrogen defect complexes rather than heating by the electron beam. The results at 80 K indicate that the process of dissociation of hydrogen from (Mg–H)0 complexes is accompanied by a generation of additional defect centers. It is proposed that following LEEBI hydrogen does not leave the specimen, but instead associates with nitrogen vacancies, generating additional recombination channels. © 2002 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
61.82.Fk Semiconductors
71.55.Eq III-V semiconductors

Enhancement of the activation energy in coupled CdTe/ZnTe quantum dots and quantum-well structures with a ZnTe thin separation barrier

H. S. Lee, K. H. Lee, J. C. Choi, H. L. Park, T. W. Kim, and D. C. Choo

Appl. Phys. Lett. 81, 3750 (2002); http://dx.doi.org/10.1063/1.1517716 (3 pages) | Cited 17 times

Online Publication Date: 4 November 2002

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Temperature-dependent photoluminescence measurements showed that the activation energy of CdTe/ZnTe quantum dots (QDs) coupled with a quantum well is much larger than that of the QDs alone, This behavior is attributed to the tunneling of carriers via a thin separation layer from the quantum well to the QDs. The present observations can help improve understanding of the enhancement of the activation energy in coupled CdTe/ZnTe nanostructures. © 2002 American Institute of Physics.
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73.21.La Quantum dots
73.21.Fg Quantum wells
68.65.Fg Quantum wells
68.65.Hb Quantum dots (patterned in quantum wells)
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
78.67.Hc Quantum dots
78.67.De Quantum wells
73.40.Gk Tunneling
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Second-order luminescent saturation effects in SrGa2S4:Eu

P. Manigault, C. J. Summers, and C. Stoffers

Appl. Phys. Lett. 81, 3753 (2002); http://dx.doi.org/10.1063/1.1490398 (3 pages) | Cited 2 times

Online Publication Date: 4 November 2002

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This study identified a quadratic energy loss process in europium-doped strontium thiogallate using luminescent decay time analysis. The role of activator–activator cross relaxation in producing the nonlinearity in the luminescent efficiency for SrGa2S4:Eu was assessed. Ground-state depletion did not contribute to the observed saturation, which instead was attributed to interionic energy transfer (cross relaxation). This work provides a deeper understanding of the factors contributing to luminescent saturation. The understanding of these mechanisms will contribute to the optimization of phosphors for cathodoluminescent applications. © 2002 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.60.Hk Cathodoluminescence, ionoluminescence

Influence of crystal growth atmosphere on the formation of color centers in PbWO4 single crystals

Tae Hoon Kim, Shinuk Cho, Kwanghee Lee, Min Su Jang, and Ji Hyun Ro

Appl. Phys. Lett. 81, 3756 (2002); http://dx.doi.org/10.1063/1.1520708 (3 pages) | Cited 12 times

Online Publication Date: 4 November 2002

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We report optical and steady-state photoconductivity spectra of two kinds of lead tungstate (PbWO4) crystals each grown in different atmosphere. When the crystals were grown in air by Czochralski method, they exhibit a yellowish tint with additional spectral responses around 2.9 and 3.5 eV as compared with the colorless crystals grown in argon. We attribute such additional features to a stoichiometric deficiency of Pb ions, resulting in the formation of two defect states of Pb3+ and O−. Those states act as color centers and also as trap sources for the exciton dissociation, thereby contributing to the photocurrent response in the visible-UV range. © 2002 American Institute of Physics.
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61.72.J- Point defects and defect clusters
81.10.Fq Growth from melts; zone melting and refining
72.40.+w Photoconduction and photovoltaic effects
78.40.Ha Other nonmetallic inorganics
61.66.Bi Elemental solids
61.66.Dk Alloys
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Stacking fault formation in highly doped 4H-SiC epilayers during annealing

H. J. Chung, J. Q. Liu, and M. Skowronski

Appl. Phys. Lett. 81, 3759 (2002); http://dx.doi.org/10.1063/1.1519961 (3 pages) | Cited 17 times

Online Publication Date: 4 November 2002

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Stacking fault formation in n+ 4H-SiC epilayers (n = 9×1019 cm−3) deposited on the 4H-SiC substrates (n = 5×1018 cm−3) has been observed by conventional and high-resolution transmission electron microscopy (HRTEM). Formation of faults occurred during annealing in Ar at 1150 °C for 90 min. All faults were identical double layer Shockley faults formed by the glide of partial dislocations on two neighboring basal planes. The sign of the Burgers vector for several of the partial dislocations bounding the faults at the epilayer/substrate interface has been determined by HRTEM. Approximately half the dislocations had a sign corresponding to the extra half-plane inserted into the epilayer, while the other half resulted in the removal of the same half-plane from the film. In one case, two faults bounded by opposite sign dislocations were separated by only 80 nm. This result is inconsistent with mechanical stress due to the doping difference between the epilayer and the substrate as a driving force of fault expansion. © 2002 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Nn Stacking faults and other planar or extended defects
61.72.Cc Kinetics of defect formation and annealing
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

High temperature efficient deuterium permeation and oxidation (Al,Ti)N barriers deposited on stainless steel

N. Bazzanella, R. Checchetto, A. Miotello, B. Patton, A. N. Kale, and D. C. Kothari

Appl. Phys. Lett. 81, 3762 (2002); http://dx.doi.org/10.1063/1.1521576 (3 pages)

Online Publication Date: 4 November 2002

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We have shown that reduction of deuterium permeation through AISI 316L stainless steel can be obtained by the deposition of an (Al,Ti)N coating: a 1.7-μm-thick coating was able to reduce the deuterium permeation flux by a factor 100–1000 in the 473–873 K temperature range. This result is related to the very low diffusivity of the deuterium migrating species in the nitride: in the examined temperature range the evaluated values of the deuterium diffusion coefficient are on the order of 10−12–10−11 cm2/s with an activation energy as low as 0.37±0.03 eV: this activation energy may be related to the defect microstructure of the sample. The (Al,Ti)N layer, which is produced on an industrial scale as an anticorrosive and wear resistant coating, has shown good properties as an oxidation barrier during thermal treatment in air at temperatures up to 873 K. © 2002 American Institute of Physics.
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66.30.J- Diffusion of impurities
81.65.Mq Oxidation
81.65.Kn Corrosion protection
84.60.-h Direct energy conversion and storage
81.40.Gh Other heat and thermomechanical treatments

Optical spectroscopy of bulk GaN crystals grown from a Na–Ga melt

B. J. Skromme, K. C. Palle, C. D. Poweleit, H. Yamane, M. Aoki, and F. J. DiSalvo

Appl. Phys. Lett. 81, 3765 (2002); http://dx.doi.org/10.1063/1.1521575 (3 pages) | Cited 16 times

Online Publication Date: 4 November 2002

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Colorless transparent platelet and prismatic GaN crystals up to 3–4 mm, grown from a Na–Ga melt (0.6–0.7 mol fraction of Na) at temperatures of 700–800 °C in a modest (5 MPa) pressure of N2, are characterized using Raman scattering, room and low temperature photoluminescence, and reflectance. They exhibit sharp free and bound exciton luminescence features (down to 0.22 meV full width at half maximum), including multiple excited states. Residual Mg and Zn acceptors and a 33.6 meV donor (possibly ON) are identified. Raman spectra suggest free carrier concentrations down to the low to mid 1016 cm−3 range. © 2002 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.10.Fq Growth from melts; zone melting and refining
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
71.55.Eq III-V semiconductors

Structural characteristics and magnetic properties of chemically synthesized CoPt nanoparticles

Andrew C. C. Yu, M. Mizuno, Y. Sasaki, H. Kondo, and K. Hiraga

Appl. Phys. Lett. 81, 3768 (2002); http://dx.doi.org/10.1063/1.1521569 (3 pages) | Cited 48 times

Online Publication Date: 4 November 2002

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CoxPt100−x nanoparticles with dimensions from approximately 2 to 5 nm were synthesized using the reverse micelle method. High-resolution electron microscopy revealed single- and poly-crystalline nanoparticle structures. Twin boundary is a common feature in the polycrystals. As-grown nanoparticles did not show any coercivity at room temperature. However, the nanoparticles became ferromagnetic after annealing at 550 °C for 4 h. Face-centered-cubic to face-centered-tetragonal phase transformation of the nanoparticles that occurred at annealing temperatures above 550 °C was confirmed by electron diffraction patterns and x-ray diffractometry. Coercivity of the annealed nanoparticles were found depending on the nanoparticle chemical compositions. Composition atomic ratio of Co to Pt at around unity gives the highest coercivity of 5500 Oe at room temperature. © 2002 American Institute of Physics.
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61.46.-w Structure of nanoscale materials
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Cc Other ferromagnetic metals and alloys
81.07.Bc Nanocrystalline materials
81.05.Bx Metals, semimetals, and alloys
61.72.Mm Grain and twin boundaries
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related 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

Coherent longitudinal optical phonon and plasmon coupling in GaAs

Y.-M. Chang and N.-A. Chang

Appl. Phys. Lett. 81, 3771 (2002); http://dx.doi.org/10.1063/1.1521246 (3 pages) | Cited 3 times

Online Publication Date: 4 November 2002

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The coupling between femtosecond laser-excited coherent LO phonons and plasmon in GaAs was investigated in real time via two-pump time-resolved second-harmonic generation. The coherent LO phonon–plasmon coupling mode dominated the lattice oscillation when the photoexcited plasma density exceeded 3×1018/cm3. Its oscillation intensity showed sinusoidal dependence on the separation time between the two pumps and a phase shift from the initial LO phonon oscillation. These observations reveal the formation time of photoexcited plasmon and its coherent coupling with LO phonon in femtosecond time scale. © 2002 American Institute of Physics.
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63.20.kk Phonon interactions with other quasiparticles
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.47.-p Spectroscopy of solid state dynamics
78.66.Fd III-V semiconductors

Microstructure evolution and abnormal grain growth during copper wafer bonding

K. N. Chen, A. Fan, C. S. Tan, R. Reif, and C. Y. Wen

Appl. Phys. Lett. 81, 3774 (2002); http://dx.doi.org/10.1063/1.1521240 (3 pages) | Cited 22 times

Online Publication Date: 4 November 2002

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Evolution of microstructure morphologies and grain orientations of Cu–Cu bonded wafers during bonding and annealing were studied by means of transmission electron microscopy, electron diffraction, and x-ray diffraction. The bonded Cu grain structure reaches steady state after post-bonding anneal. An abnormal (220) grain growth was observed during the initial bonding process. Upon annealing, the preferred grain orientation of the whole film shifts from (111) to (220). The effects of yielding and energy minimization are possible reasons for the evolution of the preferred grain orientation. © 2002 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
68.55.-a Thin film structure and morphology
68.35.Np Adhesion
61.72.Cc Kinetics of defect formation and annealing

Thickness dependent phase separation in La0.7Ca0.3MnO3 films

R. Rauer, J. Bäckström, D. Budelmann, M. Kurfiß, M. Schilling, M. Rübhausen, T. Walter, K. Dörr, and S. L. Cooper

Appl. Phys. Lett. 81, 3777 (2002); http://dx.doi.org/10.1063/1.1520705 (3 pages) | Cited 7 times

Online Publication Date: 4 November 2002

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The complex dielectric function of La0.7Ca0.3MnO3 films with various thicknesses and on different substrates was determined by the analysis of measured ellipsometric parameters. The temperature-dependent redistribution of low-energy spectral weight shows that the metallicity is developed gradually below an onset temperature that is found to depend strongly on global and local strain properties, not on film thickness alone. Importantly, the 2 nm film shows no metallic conduction but an optical charge-carrier response below 240 K. This suggests that ultrathin films are characterized by phase separation and a percolation-type transition. © 2002 American Institute of Physics.
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64.75.-g Phase equilibria
71.30.+h Metal-insulator transitions and other electronic transitions
68.55.Nq Composition and phase identification
78.66.Nk Insulators
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