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28 Mar 2005

Volume 86, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 131114 (2005); http://dx.doi.org/10.1063/1.1889243 (3 pages)

R. Chan, M. Feng, N. Holonyak, and G. Walter
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Optical control of light in a waveguide by high-Q cavity modulation

Abraham Israel and Aaron Lewis

Appl. Phys. Lett. 86, 131101 (2005); http://dx.doi.org/10.1063/1.1853510 (3 pages) | Cited 2 times

Online Publication Date: 21 March 2005

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High Q factor whispering gallery mode resonators with their ultrahigh selectivity for optical resonances are used to demonstrate switching of cw light with cw light. This switching can result in either higher or lower throughput of a light beam in a waveguide channel and has implications for optical computation and communications. The effect in the present letter is based on small index of refraction alterations induced by a thermo-optic effect. The sign of the effect can be controlled by the relative position of sphere to the waveguide. The geometry used in our demonstration, which has been able to detect an index of refraction alteration of 10−7, is potentially capable of monitoring such changes as small as 10−10 and can be generalized to other means of optical switching and modulation for optical device and computing applications.
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42.81.Qb Fiber waveguides, couplers, and arrays
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
42.60.Fc Modulation, tuning, and mode locking

10 GHz passively mode-locked external-cavity semiconductor laser with 1.4 W average output power

A. Aschwanden, D. Lorenser, H. J. Unold, R. Paschotta, E. Gini, and U. Keller

Appl. Phys. Lett. 86, 131102 (2005); http://dx.doi.org/10.1063/1.1890485 (3 pages) | Cited 10 times

Online Publication Date: 21 March 2005

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We present a 10 GHz passively mode-locked vertical external-cavity surface-emitting semiconductor laser (VECSEL) with 1.4 W average output power in 6.1 ps pulses. The output features a very good pulse quality with a time–bandwidth product of 0.42 in a nearly diffraction-limited beam. This demonstrates that passively mode-locked VECSELs are suitable for generating high powers in high-repetition-rate pulse trains.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings

Cation intermixing at quantum well/barriers interfaces in aged AlGaAs-based high-power laser diodes bars

M. Pommiès, M. Avella, E. Cánovas, J. Jiménez, T. Fillardet, M. Oudart, and J. Nagle

Appl. Phys. Lett. 86, 131103 (2005); http://dx.doi.org/10.1063/1.1891286 (3 pages) | Cited 1 time

Online Publication Date: 21 March 2005

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We report an analysis of quantum well (QW) degradation in high-power AlGaAs-based laser bars emitting at 808 nm. Using low-temperature spectrally resolved cathodoluminescence (LT-SRCL) we evidenced a redshift of the AlGaAs QW luminescence peak in the less degraded regions and a blueshift in the heavily degraded parts. This blueshift is interpreted as an experimental evidence of cation intermixing between the QW and the barriers. A degradation scenario is proposed where locally higher defects concentration at QW interfaces triggers QW degradation assisted by recombination enhanced defect reactions (REDR) leading to cation intermixing as a final product of the degradation.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.60.Hk Cathodoluminescence, ionoluminescence
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Microscope using an x-ray tube and a bubble compound refractive lens

M. A. Piestrup, C. K. Gary, H. Park, J. L. Harris, J. T. Cremer, R. H. Pantell, Y. I. Dudchik, N. N. Kolchevsky, and F. F. Komarov

Appl. Phys. Lett. 86, 131104 (2005); http://dx.doi.org/10.1063/1.1894589 (3 pages) | Cited 5 times

Online Publication Date: 21 March 2005

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We present x-ray images of grid meshes and biological material obtained using an unfiltered x-ray tube and a compound refractive lens composed of microbubbles embedded in epoxy inside a glass capillary. Images obtained using this apparatus are compared with those using a synchrotron source and the same lens. We find that the field of view is larger than that obtained using the synchrotron source, whereas the contrast and resolution are reduced. Geometrical distortion around the edges of the field of view is also reduced. The experiments demonstrate the usefulness of the apparatus in a modest laboratory setting.
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07.85.Tt X-ray microscopes
87.80.-y Biophysical techniques (research methods)
87.59.-e X-ray imaging
42.79.Bh Lenses, prisms and mirrors

Plasmonically enhanced diffusive and subdiffusive metal nanoparticle-dye random laser

G. D. Dice, S. Mujumdar, and A. Y. Elezzabi

Appl. Phys. Lett. 86, 131105 (2005); http://dx.doi.org/10.1063/1.1894590 (3 pages) | Cited 42 times

Online Publication Date: 21 March 2005

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We report on surface plasmon (SP)-enhanced random laser emission from a suspension of silver nanoparticles in a laser dye operating at diffusive and subdiffusive scattering strengths. SP resonance enhances the scattering cross section, while the geometrical cross section remains small, thus providing a large gain volume. The localized electromagnetic field near the particle surface leads to enhanced absorption of excitation light and larger amplification of fluorescence. The metal-nanoparticle-based random laser yields larger linewidth narrowing at lower pump fluence threshold than a dielectric-scatterer-based random laser under equivalent conditions. These findings open the door to studies of applications related to light amplification assisted by SP in metallic nanoparticles.
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42.55.Zz Random lasers
42.55.Mv Dye lasers
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.55.Hx Other solid inorganic materials
73.22.Lp Collective excitations

Real-time observation of pulse reshaping using Sr0.61Ba0.39Nb2O6 single crystal fiber in a microwave cavity

Chuanyong Huang, Ruyan Guo, and Amar S. Bhalla

Appl. Phys. Lett. 86, 131106 (2005); http://dx.doi.org/10.1063/1.1890473 (3 pages) | Cited 3 times

Online Publication Date: 22 March 2005

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Ferroelectric single crystal fiber Sr0.61Ba0.39Nb2O6 (SBN) is evaluated for optical pulse engineering in terms of wavelength shifting and pulse compression/expansion through nonlinear optical (Pockels) effect at microwave frequencies. The microwave–photonic interaction was investigated experimentally in a TE103 microwave cavity at 10 GHz. It is shown that the frequency component of an optical pulse can be controlled effectively using the SBN single crystal in a microwave cavity without the need of contact electrodes or any interruption to the optical system. The technique may be utilized in several aspects of optical communications such as channel definition and security encoding of the signal, and shows potential for a range of optoelectronic applications.
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42.81.Wg Other fiber-optical devices
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.81.Dp Propagation, scattering, and losses; solitons
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.60.Fc Modulation, tuning, and mode locking

GaInAs/AlAsSb quantum-cascade lasers operating up to 400 K

Q. Yang, C. Manz, W. Bronner, Ch. Mann, L. Kirste, K. Köhler, and J. Wagner

Appl. Phys. Lett. 86, 131107 (2005); http://dx.doi.org/10.1063/1.1896102 (3 pages) | Cited 22 times

Online Publication Date: 22 March 2005

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Above room-temperature (T ≥ 400 K) operation of GaInAs/AlAsSb-based quantum-cascade lasers has been demonstrated. The lasers are based on vertical-transition active regions and consist of 25 periods of Ga0.47In0.53As/AlAs0.56Sb0.44 active∕injection regions grown lattice-matched on InP substrates by molecular-beam epitaxy. They emit at a wavelength of λ ∼ 4.5 μm. For a device with the size of 18 μm×2.8 mm mounted substrate-side down with as-cleaved facets, a maximum peak power per facet of 750 mW has been achieved at 300 K and remains as high as 30 mW at 400 K. The characteristic temperature T0 of the threshold current density is 171 K in the temperature range between 280 K and 400 K.
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42.55.Px Semiconductor lasers; laser diodes
85.60.Bt Optoelectronic device characterization, design, and modeling
85.30.De Semiconductor-device characterization, design, and modeling

Determination of the piezoelectric field in InGaN quantum wells

I. H. Brown, I. A. Pope, P. M. Smowton, P. Blood, J. D. Thomson, W. W. Chow, D. P. Bour, and M. Kneissl

Appl. Phys. Lett. 86, 131108 (2005); http://dx.doi.org/10.1063/1.1896446 (3 pages) | Cited 25 times

Online Publication Date: 22 March 2005

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In many studies, the value of the experimentally determined internal piezoelectric field has been reported to be significantly smaller than theoretical values. We believe this is due to an inappropriate approximation for the electric field within the depletion region, which is used in the analysis of experimental data, and we propose an alternative method. Using this alternative, we have measured the strength of the internal field of InGaN p-i-n structures, using reverse bias photocurrent absorption spectroscopy and by fitting the bias dependent peak energy using microscopic theory based on the screened Hartree-Fock approximation. The results agree with those using material constants interpolated from binary values.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.65.Bn Piezoelectric and electrostrictive constants
73.50.Pz Photoconduction and photovoltaic effects

GaInAs∕AlGaAsSb quantum-cascade lasers

Q. Yang, C. Manz, W. Bronner, L. Kirste, K. Köhler, and J. Wagner

Appl. Phys. Lett. 86, 131109 (2005); http://dx.doi.org/10.1063/1.1896447 (3 pages) | Cited 8 times

Online Publication Date: 22 March 2005

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Quaternary-barrier-containing GaInAs∕AlGaAsSb quantum-cascade lasers, motivated by reducing the barrier height compared to that in GaInAs∕AlAsSb quantum-cascade lasers, have been demonstrated. The design of these quaternary-barrier-containing lasers is based on triple-quantum-well vertical-transition active regions, and their fabrication relies on molecular-beam-epitaxial growth of Ga0.47In0.53As∕AlGaAs1−xSbx (x close to 0.45) heterostructures on n-InP substrates. Including twenty-five periods of active regions and injection regions, the quantum-cascade lasers operate up to T ≥ 400 K in pulsed mode, with an emission wavelength of about 4.9 μm at room temperature. The characteristic temperature T0 of the threshold current density is 169 K in the temperature range between 280 and 400 K.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Direct observation of a pure focused evanescent field of a high numerical aperture objective lens by scanning near-field optical microscopy

Baohua Jia, Xiaosong Gan, and Min Gu

Appl. Phys. Lett. 86, 131110 (2005); http://dx.doi.org/10.1063/1.1886250 (3 pages) | Cited 16 times

Online Publication Date: 22 March 2005

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Intensity distributions of a tightly focused evanescent field generated by a center blocked high numerical aperture (1.65) objective lens are investigated by a scanning near-field optical microscope. The pure focused evanescent field is mapped and a splitting phenomenon of the focal spot along the direction of polarization, caused by depolarization, is observed not only on the interface, where the evanescent field is generated, but also in the parallel planes away from the interface. The decaying nature of the focused evanescent field shows good agreement with the theoretical predication, indicating that the field is purely evanescent and does not contain a significant contribution from the propagating component. It is found in our experiment that the light coupling efficiencies of the longitudinal polarization component Ez and the transverse polarization component Ex to the fiber probe differ by a factor of 3.
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42.79.Bh Lenses, prisms and mirrors
68.37.Uv Near-field scanning microscopy and spectroscopy
42.79.Fm Reflectors, beam splitters, and deflectors

Far-infrared optical and dielectric response of ZnS measured by terahertz time-domain spectroscopy

L. Thamizhmani, A. K. Azad, Jianming Dai, and W. Zhang

Appl. Phys. Lett. 86, 131111 (2005); http://dx.doi.org/10.1063/1.1896451 (3 pages) | Cited 12 times

Online Publication Date: 23 March 2005

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The optoelectronic technique of terahertz time-domain spectroscopy (THz-TDS) has been applied to measure the frequency-dependent optical and dielectric properties of ZnS in the frequency range extending from 0.3 to 3.5 THz. THz-TDS clearly reveals the low-frequency phonon resonance features in both the single- and polycrystalline ZnS. These phonons account for the increased absorption as indicated by the resonance lines in the spectra. The measured index of refraction is found to be dominated by the transverse optical-phonon resonance, which is verified by a theoretical fit using the relation for the dielectric response of the damped harmonic oscillator.
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78.70.Gq Microwave and radio-frequency interactions
78.30.Fs III-V and II-VI semiconductors
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.47.-p Spectroscopy of solid state dynamics

Dynamics of nonlinear photonic crystal atoms characterized by numerical simulations in a pump-probe scheme

Sheng Lan, Xiong-Wen Chen, Jing-Dong Chen, Xu-Sheng Lin, and Achanta Venu Gopal

Appl. Phys. Lett. 86, 131112 (2005); http://dx.doi.org/10.1063/1.1894612 (3 pages) | Cited 1 time

Online Publication Date: 24 March 2005

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We investigate the dynamics of nonlinear photonic crystal (PC) atoms by use of numerical simulations in a pump-probe scheme based on a finite-difference time-domain technique. A two-dimensional nonlinear PC atom with multimode is intentionally employed for the numerical simulations. The use of the multimode PC atom makes it possible that the pump and probe waves are set at different frequencies, ensuring the clear identification of the dynamics of the nonlinear PC atom. The physical model for the dynamics of nonlinear PC atoms has been established and very good agreement between the analytical and simulation results has been achieved.
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42.70.Qs Photonic bandgap materials
42.70.Mp Nonlinear optical crystals
42.65.Sf Dynamics of nonlinear optical systems; optical instabilities, optical chaos and complexity, and optical spatio-temporal dynamics

Optical microfabrication of highly reflective volume Bragg gratings

Vincent K. S. Hsiao, Tzu-Chau Lin, Guang S. He, Alexander N. Cartwright, Paras N. Prasad, Lalgudi V. Natarajan, Vincent P. Tondiglia, and Timothy J. Bunning

Appl. Phys. Lett. 86, 131113 (2005); http://dx.doi.org/10.1063/1.1880435 (3 pages) | Cited 20 times

Online Publication Date: 24 March 2005

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An approach for fabricating wide-bandwidth and highly reflective Bragg grating structures with the technique of holographic photopolymerization of a liquid crystal (LC) polymer composite is presented. The key to this fabrication method that distinguishes it from previous methods is the use of a nonreactive solvent, acetone, to dissolve the photoinitiator and coinitiator in an acrylate monomer/LC mixture. The addition of acetone results in the creation of controllable periodic voids inside the thin film after the acetone evaporates. Peak reflectivity as high as 80% and a broad reflection bandwidth of 80 nm were observed in the reflection gratings formed with acetone present in the starting mixture. It was estimated from a fit to the experimental data that the resulting index mismatch was approximately 0.2; consistent with the presence of air voids. It is determined that tunable wavelength, diffraction efficiency, and bandwidth of reflection notches can be achieved by backfilling with fluids of different refractive indices.
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42.40.Eq Holographic optical elements; holographic gratings
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.70.Df Liquid crystals
42.70.Jk Polymers and organics

Microwave operation and modulation of a transistor laser

R. Chan, M. Feng, N. Holonyak, and G. Walter

Appl. Phys. Lett. 86, 131114 (2005); http://dx.doi.org/10.1063/1.1889243 (3 pages) | Cited 17 times

Online Publication Date: 25 March 2005

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The microwave operation and modulation (3 GHz) of an InGaP/GaAs heterojunction bipolar transistor (HBT) laser is reported. The HBT layer structure is in the form of an optical waveguide (with cleaved ends) that also includes an InGaAs recombination quantum well in the p-type base region to improve the recombination radiation properties. The shift in HBT laser operation from spontaneous to stimulated emission is manifest as a distinct change in the HBT current–voltage characteristics, specifically a decrease in the common-emitter current gain (βdc = IC/IB) and the occurrence of even a more striking peak in the small signal (ac) gain βac = ΔIC/ΔIB.
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42.50.Pq Cavity quantum electrodynamics; micromasers
42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Fc Modulation, tuning, and mode locking
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.30.Pq Bipolar transistors

Resonantly diode laser pumped 1.6-μm-erbium-doped yttrium aluminum garnet solid-state laser

Dmitri Garbuzov, Igor Kudryashov, and Mark Dubinskii

Appl. Phys. Lett. 86, 131115 (2005); http://dx.doi.org/10.1063/1.1898427 (3 pages) | Cited 7 times

Online Publication Date: 25 March 2005

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We report direct resonant diode pumping of a 1.6-μm-Er3+-doped bulk solid-state laser. Using a 1470-nm-single-mode diode laser module to pump the Er:YAG rod, an absorbed photon conversion efficiency of 26% has been obtained in this initial experiment. Analysis of the diode-pumped solid-state laser input–output characteristics suggests that the obtained slope efficiency can be doubled through the reduction of intracavity losses and pumping efficiency improvement.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.55.Xi Diode-pumped lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Harmonic generation from chromium plasma

R. A. Ganeev, M. Suzuki, M. Baba, and H. Kuroda

Appl. Phys. Lett. 86, 131116 (2005); http://dx.doi.org/10.1063/1.1898428 (3 pages) | Cited 19 times

Online Publication Date: 25 March 2005

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The generation of up to the 33rd harmonic (λ = 24.12 nm) of a Ti:sapphire laser pulse using prepulse-produced chromium plasma as a nonlinear medium was demonstrated. A steep decrease of intensity for low-order harmonics (up to the 15th order) was followed by a plateau. A considerable restriction of 27th harmonic generation was observed in different focusing conditions.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
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Single-crystalline polytetrafluoroethylene-like nanotubes prepared from atmospheric plasma discharge

J. Zhang, Y. Guo, J. Z. Xu, X. S. Fang, H. K. Xie, D. L. Shi, P. He, and W. J. van Ooij

Appl. Phys. Lett. 86, 131501 (2005); http://dx.doi.org/10.1063/1.1894598 (3 pages) | Cited 11 times

Online Publication Date: 21 March 2005

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Atmospheric plasma polymerization of perfluorohexane was investigated in this letter. A large quantity of single-crystalline polytetrafluoroethylene (PTFE)-like nanotubes were formed on a simultaneously deposited film at room temperature without any catalysts or templates. The outer diameter of the nanotubes varied from 60 to 1200 nm with a maximum aspect ratio up to 100:1. Transmission electron microscopy and x-ray diffraction results indicated a single crystal close-packed hexagonal (cph) structure in the nanotubes. Polarization optical micrographs of the nanotubes showed their thermal stability comparable to PTFE. It is suggested that the plasma filament played a key role in the rapid formation of the nanotubes. This atmospheric plasma discharge synthesis can serve as a common method for nanofabrication of many other single-crystalline polymer systems.
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81.07.De Nanotubes
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
61.46.-w Structure of nanoscale materials
61.41.+e Polymers, elastomers, and plastics
52.77.-j Plasma applications
68.37.Lp Transmission electron microscopy (TEM)

Effect of triggered discharge using an excimer laser with high-repetition-rate of the order of kilohertz

Michiteru Yamaura, Takashi Watanabe, Nobuya Hayashi, and Satoshi Ihara

Appl. Phys. Lett. 86, 131502 (2005); http://dx.doi.org/10.1063/1.1896104 (3 pages) | Cited 2 times

Online Publication Date: 22 March 2005

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The triggering ability of the laser-triggered lightning method is improved by using a KrF excimer laser with a high-repetition-rate of the order of kHz order. It is clarified that the effect of a triggered discharge is considerably enhanced when the plasma density is greater than 1013 cm−3. Thus far, the laser-triggered lightning method has not been expected to display a triggering ability since one pulse of an excimer laser possesses energy of less than 1 J, and the produced plasma has a low density of 1012 cm−3, its plasma density is one order lower than that required for its application in the triggering and guiding of lightning discharge. The enhancement of plasma density achieved by utilizing the accumulation effect of charged particles generated by the high-repetition-rate laser was 1013 cm−3. This led to an effective a 50% reduction in the self-breakdown voltage.
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52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.80.Pi High-frequency and RF discharges
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.Jm Ionization of plasmas
52.77.-j Plasma applications
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Growth and thermal stability of Ga(1−X)CrXN films

G. T. Thaler, R. M. Frazier, C. R. Abernathy, and S. J. Pearton

Appl. Phys. Lett. 86, 131901 (2005); http://dx.doi.org/10.1063/1.1895479 (2 pages) | Cited 4 times

Online Publication Date: 21 March 2005

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GaCrN thin films were synthesized using gas-source molecular beam epitaxy. No evidence of second-phase formation was observed by powder x-ray diffraction. Magnetic characterization performed using a superconducting quantum interference device magnetometer showed evidence of ferromagnetic ordering at room temperature for all samples. In agreement with theoretical predictions, material with 3% Cr showed the highest degree of ordering. No evidence of segregation was found from secondary ion mass spectroscopy analysis. The oxygen content of the film was found to be ∼ 1019 cm−3. After rapid thermal annealing at temperatures up to 700 °C in a nitrogen ambient for 1 min, the room temperature saturation magnetization of the GaCrN films remained virtually unchanged, in contrast to similarly prepared GaMnN films.
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75.50.Pp Magnetic semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.60.Dv Thermal stability; thermal effects
75.50.Dd Nonmetallic ferromagnetic materials
68.55.A- Nucleation and growth
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Cc Kinetics of defect formation and annealing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Low dose ionizing radiation detection using conjugated polymers

E. A. B. Silva, J. F. Borin, P. Nicolucci, C. F. O. Graeff, T. Ghilardi Netto, and R. F. Bianchi

Appl. Phys. Lett. 86, 131902 (2005); http://dx.doi.org/10.1063/1.1891300 (3 pages) | Cited 22 times

Online Publication Date: 21 March 2005

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In this work, the effect of gamma radiation on the optical properties of poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) is studied. The samples were irradiated at room temperature with different doses from 0 Gy to 152 Gy using a math gamma ray source. For thin films, significant changes in the UV-visible spectra were only observed at high doses (>1 kGy). In solution, shifts in absorption peaks are observed at low doses (<10 Gy), linearly dependent on dose. The shifts are explained by conjugation reduction, and possible causes are discussed. Our results indicate that MEH-PPV solution can be used as a dosimeter adequate for medical applications.
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78.66.Qn Polymers; organic compounds
61.82.Pv Polymers, organic compounds
61.80.Ed γ-ray effects
87.56.Da Ancillary equipment
61.82.Fk Semiconductors
78.40.Me Organic compounds and polymers
78.40.Fy Semiconductors

Optical properties of transparent Li2O–Ga2O3–SiO2 glass-ceramics embedding Ni-doped nanocrystals

Takenobu Suzuki, Ganapathy Senthil Murugan, and Yasutake Ohishi

Appl. Phys. Lett. 86, 131903 (2005); http://dx.doi.org/10.1063/1.1891272 (3 pages) | Cited 39 times

Online Publication Date: 21 March 2005

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Transparent Li2O–Ga2O3–SiO2 (LGS) glass-ceramics embedding Ni:LiGa5O8 nanocrystals were fabricated. An intense emission centered around 1300 nm with the width of more than 300 nm was observed by 976 nm photoexcitation of the glass-ceramics. The lifetime was more than 900 μs at 5 K and 500 μs at 300 K. The emission could be attributed to the math(math)→math(math) transition of Ni2+ in distorted octahedral sites in LiGa5O8. The product of stimulated emission cross section and lifetime for the emission was about 3.7×10−24 cm2 s and was a sufficiently practical value.
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81.05.Pj Glass-based composites, vitroceramics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.43.Fs Glasses
78.35.+c Brillouin and Rayleigh scattering; other light scattering
78.45.+h Stimulated emission

Orientation-dependent phonon observation in single-crystalline aluminum nitride

M. Bickermann, B. M. Epelbaum, P. Heimann, Z. G. Herro, and A. Winnacker

Appl. Phys. Lett. 86, 131904 (2005); http://dx.doi.org/10.1063/1.1894610 (3 pages) | Cited 15 times

Online Publication Date: 21 March 2005

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In this study, we present a microspectroscopic investigation performed on different facets of a self-nucleated aluminum nitride (AlN) single crystal. We show that, apart from evaluating crystalline quality, Raman and Fourier transform infrared spectroscopy can provide means to detect the orientation of any AlN facet. Such local, nondestructive technique is very useful for selecting and evaluating samples of single crystalline AlN.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.30.Fs III-V and II-VI semiconductors
81.70.Fy Nondestructive testing: optical methods

White-light emission from organics-capped ZnSe quantum dots and application in white-light-emitting diodes

Hsueh Shih Chen, Shian Jy Jassy Wang, Chun Jeu Lo, and Jim Yong Chi

Appl. Phys. Lett. 86, 131905 (2005); http://dx.doi.org/10.1063/1.1886894 (3 pages) | Cited 47 times

Online Publication Date: 21 March 2005

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Organics-capped ZnSe quantum dots were synthesized by a colloidal chemical approach using ZnO and Se powder as precursors. The photoluminescence of the specimens showed strong white emission ( ∼ 200 nm full width at half maximum) in the visible range under ambient conditions. The white emission was attributed to the mixing of blue emission of ZnSe nanocrystals exhibiting quantum confinement effect with green-red emission of radiative deep levels from ZnSe surface strained lattice. Based on organic-capped ZnSe quantum dots, the white-light-emitting diodes were fabricated using a near-UV InGaN chip as the excitation source. The diodes emitted white light with CIE chromaticity coordinates of (0.38 and 0.41) and show great potential for use in lighting applications.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.16.Be Chemical synthesis methods
78.55.Et II-VI semiconductors
78.67.Hc Quantum dots
71.55.Gs II-VI semiconductors

Nanoscale effects on ion conductance of layer-by-layer structures of gadolinia-doped ceria and zirconia

S. Azad, O. A. Marina, C. M. Wang, L. Saraf, V. Shutthanandan, D. E. McCready, A. El-Azab, J. E. Jaffe, M. H. Engelhard, C. H. F. Peden, and S. Thevuthasan

Appl. Phys. Lett. 86, 131906 (2005); http://dx.doi.org/10.1063/1.1894615 (3 pages) | Cited 46 times

Online Publication Date: 21 March 2005

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Layer-by-layer structures of gadolinia-doped ceria and zirconia have been synthesized on Al2O3(0001) using oxygen plasma-assisted molecular beam epitaxy. Oxygen ion conductivity greatly increased with an increasing number of layers compared to bulk polycrystalline yttria-stabilized zirconia and gadolinia-doped ceria electrolytes. The conductivity enhancement in this layered electrolyte is interesting, yet the exact cause for the enhancement remains unknown. For example, the space charge effects that are responsible for analogous conductivity increases in undoped layered halides are suppressed by the much shorter Debye screening length in layered oxides. Therefore, it appears that a combination of lattice strain and extended defects due to lattice mismatch between the heterogeneous structures may contribute to the enhancement of oxygen ionic conductivity in this layered oxide system.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
82.45.Gj Electrolytes
82.47.Ed Solid-oxide fuel cells (SOFC)
82.45.Mp Thin layers, films, monolayers, membranes
61.72.Nn Stacking faults and other planar or extended defects
77.22.Jp Dielectric breakdown and space-charge effects
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Evidence for nanoindentation-induced phase transformations in germanium

Jae-il Jang, M. J. Lance, Songqing Wen, and G. M. Pharr

Appl. Phys. Lett. 86, 131907 (2005); http://dx.doi.org/10.1063/1.1894588 (3 pages) | Cited 23 times

Online Publication Date: 21 March 2005

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Nanoindentation experiments were performed using Berkovich and cube-corner indenters to investigate whether nanoindentation-induced phase transformations, such as those observed in silicon, also occur in germanium. Although the indentation load-displacement curves for germanium do not show the unloading pop-out or elbow phenomena observed in silicon, clear evidence for phase transformations was obtained by scanning electron microscopy (SEM) and micro-Raman spectroscopy. SEM showed that there is extruded material around the contact periphery of cube-corner hardness impressions that is metalliclike in its flow characteristics, just as in silicon. Micro-Raman spectroscopy revealed more direct evidence by identifying amorphous and what may be the crystalline BC8 (Ge-IV) phase. The fact that these phenomena are observed primarily and reproducibly only for the cube-corner indenter suggests that the contact geometry significantly affects the transformation behavior. Results are discussed in terms of possible deformation mechanisms and how they may be influenced by the indenter geometry.
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81.05.Cy Elemental semiconductors
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.35.Gy Mechanical properties; surface strains
64.70.K- Solid-solid transitions
62.20.Qp Friction, tribology, and hardness
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
62.20.M- Structural failure of materials
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
78.30.Er Solid metals and alloys
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