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14 Oct 2002

Volume 81, Issue 16, pp. 2917-3103

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Complete three-dimensional band gap in macroporous silicon photonic crystals

S. W. Leonard

Appl. Phys. Lett. 81, 2917 (2002); http://dx.doi.org/10.1063/1.1513183 (3 pages) | Cited 6 times

Online Publication Date: 7 October 2002

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The prospect of obtaining a complete three-dimensional band gap in macroporous silicon photonic crystals is investigated theoretically. Band structure calculations indicate that a modified form of the simple cubic lattice of air spheres in silicon exhibits a complete band gap, with a bandwidth of up to 4%. It is further shown that this quasispherical crystal may be fabricated using standard etching procedures. These results provide a practical route to obtaining large-scale, high-quality, silicon photonic crystals with a complete band gap. © 2002 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
71.20.Mq Elemental semiconductors
61.43.Gt Powders, porous materials
81.05.Rm Porous materials; granular materials
81.65.Cf Surface cleaning, etching, patterning

Single-photon emission of CdSe quantum dots at temperatures up to 200 K

K. Sebald, P. Michler, T. Passow, D. Hommel, G. Bacher, and A. Forchel

Appl. Phys. Lett. 81, 2920 (2002); http://dx.doi.org/10.1063/1.1515364 (3 pages) | Cited 91 times

Online Publication Date: 7 October 2002

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We report on the generation of triggered single photons obtained from epitaxially grown self-assembled CdSe/Zn(S,Se) quantum dots for temperatures up to 200 K. At low temperatures (T<40 K) photon correlation experiments under pulsed excitation show nearly perfect single-photon emission from an individual CdSe quantum dot. For higher temperatures (T>40 K) an increasing multi-photon emission probability due to spectrally overlapping acoustic phonon sidebands of neighboring quantum dots is observed. We found that the multi-photon emission probability of a bare quantum dot (background subtracted) is strongly suppressed at 200 K if compared to a Poissonian light source of the same average intensity. Our results demonstrate the large potential of self-assembled CdSe/Zn(S,Se) quantum dots for nonclassical light generation at temperatures up to 200 K. © 2002 American Institute of Physics.
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78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
42.50.-p Quantum optics
81.07.Ta Quantum dots
81.16.Dn Self-assembly

Adaptive interferometer based on wave mixing in a photorefractive crystal under alternating electric field

Alexei A. Kamshilin and Alexander I. Grachev

Appl. Phys. Lett. 81, 2923 (2002); http://dx.doi.org/10.1063/1.1515131 (3 pages) | Cited 13 times

Online Publication Date: 7 October 2002

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Coupling of two waves with different polarization states in a photorefractive crystal under an ac electric field allows us to achieve the linear transformation of a small transient phase shift into the intensity modulation without any output polarization filtering. This can lead to design of an adaptive interferometer with sensitivity that reaches the classical homodyne detection limit. © 2002 American Institute of Physics.
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07.60.Ly Interferometers
78.20.Jq Electro-optical effects
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Efficient diode-pumped passively Q-switched laser operation around 1.9 μm and self-frequency Raman conversion of Tm-doped KY(WO4)2

L. E. Batay, A. N. Kuzmin, A. S. Grabtchikov, V. A. Lisinetskii, V. A. Orlovich, A. A. Demidovich, A. N. Titov, V. V. Badikov, S. G. Sheina, V. L. Panyutin, M. Mond, and S. Kück

Appl. Phys. Lett. 81, 2926 (2002); http://dx.doi.org/10.1063/1.1514393 (3 pages) | Cited 19 times

Online Publication Date: 7 October 2002

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Passively Q-switched operation of Yb,Tm:KY(WO4)2 and Tm:KY(WO4)2 lasers diode pumped at 805 nm has been investigated. A thin plate of Cr:ZnS was used as a saturable absorber for passive Q switching. A maximum average output power of 116 mW emitted at 1.9 μm in comparison to 160 mW for the free-running regime at the same pumping level has been obtained with a slope efficiency of 26% with respect to the incident pump power. Using a Tm:KYW sample with broadband antireflection coatings and dichroic laser resonator mirror, the first Stokes component of Raman self-frequency conversion was observed at 2365 nm. © 2002 American Institute of Physics.
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42.55.Rz Doped-insulator lasers and other solid state lasers
42.55.Px Semiconductor lasers; laser diodes
42.55.Xi Diode-pumped lasers
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.50.Md Optical transient phenomena: quantum beats, photon echo, free-induction decay, dephasings and revivals, optical nutation, and self-induced transparency

Organic light-emitting devices with extended operating lifetimes on plastic substrates

M. S. Weaver, L. A. Michalski, K. Rajan, M. A. Rothman, J. A. Silvernail, J. J. Brown, P. E. Burrows, G. L. Graff, M. E. Gross, P. M. Martin, M. Hall, E. Mast, C. Bonham, W. Bennett, and M. Zumhoff

Appl. Phys. Lett. 81, 2929 (2002); http://dx.doi.org/10.1063/1.1514831 (3 pages) | Cited 95 times

Online Publication Date: 7 October 2002

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We fabricate long-lived organic light-emitting devices using a 175 μm thick polyethylene terephthalate substrate coated with an organic–inorganic multilayered barrier film and compare the rate of degradation to glass-based devices. The observed permeation rate of water vapor through the plastic substrate was estimated to be 2×10−6 g/m2/day. Driven at 2.5 mA/cm2, we measure a device lifetime of 3800 h from an initial luminance of 425 cd/m2. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices

Wavelength- and duration-tunable soliton source based on a 20-GHz Mach–Zehnder modulator and adiabatic Raman compression

C. J. S. de Matos, D. A. Chestnut, and J. R. Taylor

Appl. Phys. Lett. 81, 2932 (2002); http://dx.doi.org/10.1063/1.1514821 (3 pages) | Cited 3 times

Online Publication Date: 7 October 2002

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Adiabatic Raman compression was employed to obtain wavelength- and duration-tunable solitons from a 20 GHz sinusoidal pulse train generated using a low-cost LiNbO3 Mach–Zehnder amplitude modulator. 25 to 0.8 ps pulse duration tunability was attained under adiabatic compression, while high-quality, low-pedestal solitons as short as 450 fs were still achieved outside of the adiabatic regime. Compressed solitons with similar durations were obtained over the 1540 to 1560 nm wavelength range. © 2002 American Institute of Physics.
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42.65.Tg Optical solitons; nonlinear guided waves
42.81.Dp Propagation, scattering, and losses; solitons
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.55.Ye Raman lasers
42.79.Hp Optical processors, correlators, and modulators
42.55.Wd Fiber lasers

Improvement of efficiency and color purity utilizing two-step energy transfer for red organic light-emitting devices

Jing Feng, Feng Li, Wenbao Gao, Gang Cheng, Wenfa Xie, and Shiyong Liu

Appl. Phys. Lett. 81, 2935 (2002); http://dx.doi.org/10.1063/1.1515884 (3 pages) | Cited 42 times

Online Publication Date: 7 October 2002

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We present organic red light-emitting devices with improved optical and electrical characteristics utilizing the two-step energy transfer. N,N′-diphenyl-N,N′-bis(1-naphthyl)-(1,1′-biphenyl)-4,4′-diamine and tris-(8-hydroxyquinoline) aluminum (Alq) are used as hole and electron-transporting layers, respectively. Quinacridone (QAD) and 4-(dicyanomethylene)-2-t- butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) are codoped into the Alq emitting layer. Compared with devices where the emitting layer is only composed of Alq and DCJTB, the emitting characteristics such as emission efficiency and purity of emission color are greatly improved, and the turn-on voltage is decreased as much as 4 V. We attribute these improvements to the assistant dopant (QAD), which leads to the more efficient energy transfer from Alq to DCJTB. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.66.Qn Polymers; organic compounds
78.60.Fi Electroluminescence
78.55.Kz Solid organic materials
78.40.Me Organic compounds and polymers

Low-temperature operation of AlGaN single-quantum-well light-emitting diodes with deep ultraviolet emission at 285 nm

A. Chitnis, R. Pachipulusu, V. Mandavilli, M. Shatalov, E. Kuokstis, J. P. Zhang, V. Adivarahan, S. Wu, G. Simin, and M. Asif Khan

Appl. Phys. Lett. 81, 2938 (2002); http://dx.doi.org/10.1063/1.1516631 (3 pages) | Cited 18 times

Online Publication Date: 7 October 2002

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We present a study of the electrical and optical characteristics of 285 nm emission deep ultraviolet light-emitting diodes (LED) at temperatures from 10 to 300 K. At low bias, our data show the tunneling carrier transport to be the dominant conduction mechanism. The room-temperature performance is shown to be limited mostly by poor electron confinement in the active region and a pronounced deep level assisted recombination but not by the hole injection into the active region. At temperatures below 100 K, the electroluminescence peak intensity increases by more than one order of magnitude indicating that with a proper device design and improved material quality, milliwatt power 285 nm LED are viable. © 2002 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.67.De Quantum wells
42.72.Bj Visible and ultraviolet sources
07.20.Mc Cryogenics; refrigerators, low-temperature detectors, and other low-temperature equipment
78.60.Fi Electroluminescence
73.21.Fg Quantum wells
73.63.Hs Quantum wells
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

GaAs quantum box cascade lasers

C. Becker, C. Sirtori, O. Drachenko, V. Rylkov, D. Smirnov, and J. Leotin

Appl. Phys. Lett. 81, 2941 (2002); http://dx.doi.org/10.1063/1.1515135 (3 pages) | Cited 38 times

Online Publication Date: 7 October 2002

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Measurements of the light emission under strong magnetic field from quantum cascade lasers emitting at 9 and 11 μm are reported. The laser intensity shows strong oscillations as a function of the magnetic field. This effect is due to changes in the lifetime of the upper state of the laser transition, which is controlled by electron-optical phonon scattering. This process is strongly modified by the extra confinement imposed by a magnetic field applied perpendicular to the plane of the layers, which breaks the electron dispersion into discrete Landau levels. The experimental results are in remarkable agreement with our calculations of the phonon-limited lifetime. We also show that this experiment provides direct indications of the ratio of the scattering rates associated with the two nonradiative transitions in the active region. © 2002 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.)
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
73.21.Fg Quantum wells
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
71.70.Di Landau levels
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Linewidth enhancement factor in 1.3 μm GaAsSb type-II quantum-well lasers

C. Schlichenmaier, S. W. Koch, and W. W. Chow

Appl. Phys. Lett. 81, 2944 (2002); http://dx.doi.org/10.1063/1.1514392 (3 pages) | Cited 3 times

Online Publication Date: 7 October 2002

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The antiguiding or linewidth enhancement factor α is computed microscopically for a series of type-II GaAsSb/GaInAs/GaAs quantum-well structures. The results predict α values below unity at peak gain suggesting highly stable laser operation with excellent linewidth properties. © 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

Polyimide-waveguide-based thermal optical switch using total-internal-reflection effect

Jianyi Yang, Qingjun Zhou, and Ray T. Chen

Appl. Phys. Lett. 81, 2947 (2002); http://dx.doi.org/10.1063/1.1511814 (3 pages) | Cited 26 times

Online Publication Date: 7 October 2002

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A total-internal-reflection waveguide switch with an X junction was designed and fabricated by using the thermo-optic effect of polyimide materials. Experimental results show that the crosstalk is below −28 dB at the wavelength of 1.55 μm. The switching power with the current electrode is 132 mW, which can be reduced to 20–30 mW with an optimized design together with electroplating to form a thick conducting path. © 2002 American Institute of Physics.
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42.65.Pc Optical bistability, multistability, and switching, including local field effects
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
42.70.Jk Polymers and organics
42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
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Depth profiling InGaN/GaN multiple quantum wells by Rutherford backscattering: The role of intermixing

S. Pereira, E. Pereira, E. Alves, N. P. Barradas, K. P. O’Donnell, C. Liu, C. J. Deatcher, and I. M. Watson

Appl. Phys. Lett. 81, 2950 (2002); http://dx.doi.org/10.1063/1.1513661 (3 pages) | Cited 6 times

Online Publication Date: 7 October 2002

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We report a detailed compositional analysis of InxGa1−xN/GaN multiple quantum wells (MQWs) grown by metalorganic chemical vapor deposition. Depth profiles of the InN fraction, x, in the MQWs were determined from grazing incidence Rutherford backscattering spectroscopy (RBS) analysis. Simulation of the RBS spectra provides precise estimations of individual well compositions, thickness, and the extent of In/Ga intermixing. It is ascertained that intermixing, and In segregation to the GaN cap layer, strongly increase with the value of x in the wells and with the number of periods in the MQW stack. Deleterious effects of intermixing on the spectral properties are apparent when comparing the photoluminescence spectra of two MQW structures with 8 and 18 wells, grown under the same nominal conditions. © 2002 American Institute of Physics.
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68.65.Fg Quantum wells
78.67.De Quantum wells
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis
78.55.Cr III-V semiconductors

Optical and structural properties of InAsP ternary self-assembled quantum dots embedded in GaAs

E. Ribeiro, R. L. Maltez, W. Carvalho, D. Ugarte, and G. Medeiros-Ribeiro

Appl. Phys. Lett. 81, 2953 (2002); http://dx.doi.org/10.1063/1.1513215 (3 pages) | Cited 10 times

Online Publication Date: 7 October 2002

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We report on the growth of self-assembled ternary InAsP quantum dots embedded into GaAs. A comparison between average sizes and recombination energies for different dot species (InAs, InAsP, and InP) confirms the formation of the ternary alloy islands. By carefully changing the growth conditions, we determined a global growth map for InAs, InAsP, and InP dots, showing that it is possible to tailor the optical characteristics of the InAsP species, thus covering the energy range between InAs and InP quantum dot emission. © 2002 American Institute of Physics.
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78.67.Hc Quantum dots
81.07.Ta Quantum dots
68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology

High temperature stability of Al2O3 dielectrics on Si: Interfacial metal diffusion and mobility degradation

S. Guha, E. P. Gusev, H. Okorn-Schmidt, M. Copel, L.-Å Ragnarsson, N. A. Bojarczuk, and P. Ronsheim

Appl. Phys. Lett. 81, 2956 (2002); http://dx.doi.org/10.1063/1.1513662 (3 pages) | Cited 38 times

Online Publication Date: 7 October 2002

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We have examined the stability of Al2O3/Si heterostructures and show that significant Al diffusion occurs into the silicon for temperatures of 1000 °C and more. This may be caused by dissociation of small quantities of Al2O3 and subsequent dissolution of the Al into the silicon. Such diffusion may be reduced, though not eliminated via an interfacial silicon oxynitride diffusion barrier. Using long channel metal gate Al2O3/Si n field effect transistor data, we show that anneals at 1000 °C result in a degradation of the electron mobility by a factor of 2. © 2002 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.35.Fx Diffusion; interface formation
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
64.75.-g Phase equilibria
61.72.Cc Kinetics of defect formation and annealing

Direct determination of free exciton binding energy from phonon-assisted luminescence spectra in GaN epilayers

S. J. Xu, W. Liu, and M. F. Li

Appl. Phys. Lett. 81, 2959 (2002); http://dx.doi.org/10.1063/1.1514391 (3 pages) | Cited 15 times

Online Publication Date: 7 October 2002

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Investigation of variable-temperature longitudinal optical (LO) phonon-assisted luminescence spectra of free excitons and free electrons in heteroepitaxial GaN thin films has been conducted. It is found that thermal broadening of the LO phonon-assisted photoluminescence peaks is much slower than those of the peaks of their parents so that the first-order LO peaks of the free exciton transition and the band-to-band transition can be well resolved even at room temperature, leading to a direct determination of the band A free exciton binding energy as 25.4±0.9 meV. At the same time, we demonstrate that the simple hydrogenlike model still is a good approximation to describe the energy level structure of free excitons in GaN. © 2002 American Institute of Physics.
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71.35.Cc Intrinsic properties of excitons; optical absorption spectra
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
63.20.kk Phonon interactions with other quasiparticles

Cathodoluminescence of Cu diffusion in CdTe thin films for CdTe/CdS solar cells

Manuel J. Romero, David S. Albin, Mowafak M. Al-Jassim, Xuanzhi Wu, Helio R. Moutinho, and Ramesh G. Dhere

Appl. Phys. Lett. 81, 2962 (2002); http://dx.doi.org/10.1063/1.1515119 (3 pages) | Cited 10 times

Online Publication Date: 7 October 2002

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We investigate the distribution of Cu acceptor states in CdTe thin films used in high-efficiency solar cells. These states are CuCd and Cui+–VCd− complexes, which are relatively deep and shallow acceptors, respectively. Cathodoluminescence spectroscopy and imaging show that, first, CuCd and Cui+–VCd− do not coexist and, second, the primary diffuser is represented by Cui+–VCd− complexes. Our results are used to discuss the effect of grain boundaries on Cu diffusion. © 2002 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
71.55.Gs II-VI semiconductors
66.30.J- Diffusion of impurities
84.60.Jt Photoelectric conversion
78.66.Hf II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Mm Grain and twin boundaries

GaAs(311) templates for molecular beam epitaxy growth: surface morphologies and reconstruction

Z. M. Wang, V. R. Yazdanpanah, J. L. Shultz, and G. J. Salamo

Appl. Phys. Lett. 81, 2965 (2002); http://dx.doi.org/10.1063/1.1514822 (3 pages) | Cited 12 times

Online Publication Date: 7 October 2002

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Morphologies of GaAs(311) surfaces grown by molecular beam epitaxy were investigated by in situ reflection high-energy electron diffraction and scanning tunnelling microscope. In addition to the (8×1) reconstruction, two surface phases, GaAs(311)A-(4×1) and GaAs(311)B-(2×1) were observed. Both of these surfaces are characterized by wider, atomically smooth terraces with much lower structural anisotropy, when compared to the (8×1) reconstructed GaAs(311) surfaces. The observed surfaces have potential as templates for the growth of organized quantum dots, wires, and wells. © 2002 American Institute of Physics.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Structural disorder and loss of piezoelectric properties in α-quartz at high temperature

J. Haines, O. Cambon, D. A. Keen, M. G. Tucker, and M. T. Dove

Appl. Phys. Lett. 81, 2968 (2002); http://dx.doi.org/10.1063/1.1515363 (3 pages) | Cited 10 times

Online Publication Date: 7 October 2002

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The piezoelectric properties of α-quartz-based resonators, characterized by the mechanical quality factor, Q, are found to degrade beginning above 300 °C. This is well below the transition at 573 °C to the β phase, which in principle limits the piezoelectric response of this material. This gradual loss of piezoelectric response can be linked to the increase in structural disorder in α-quartz found in total neutron scattering measurements. Analysis of these data by reverse Monte Carlo modeling indicates that between 200 and 400 °C, the local disorder in the instantaneous structure of α-quartz becomes comparable to that of β-quartz. © 2002 American Institute of Physics.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.65.Fs Electromechanical resonance; quartz resonators
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
61.43.Bn Structural modeling: serial-addition models, computer simulation
64.70.K- Solid-solid transitions

Temporal and thermal studies of charge transportation in self-assembly organic photovoltaic devices

F. Ghebremichael

Appl. Phys. Lett. 81, 2971 (2002); http://dx.doi.org/10.1063/1.1514398 (3 pages) | Cited 3 times

Online Publication Date: 7 October 2002

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The charge transport of holes injected into organic nanostructure photovoltaic devices using the third harmonic of a pulsed infrared laser was studied. The devices were fabricated using the electrostatic self-assembly technique. From temporal and thermal time-of-flight studies, we determined the drift mobility to be in the range of 10−7–10−6 cm2/(V s) in 120 nm thick films. A model was adopted that accounts for the Pool–Freknel type effects to characterize the devices, including the electric-field coefficient and the activation energy. Using similar techniques, fill factor of 0.34±0.02 at 1 mW/cm2 intensity was determined for the devices. © 2002 American Institute of Physics.
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85.60.-q Optoelectronic devices
85.30.-z Semiconductor devices
72.20.Fr Low-field transport and mobility; piezoresistance
72.20.Ht High-field and nonlinear effects

Influence of stacking faults on the performance of 4H–SiC Schottky barrier diodes fabricated on (11math0) face

K. Kojima, T. Ohno, T. Fujimoto, M. Katsuno, N. Ohtani, J. Nishio, T. Suzuki, T. Tanaka, Y. Ishida, T. Takahashi, and K. Arai

Appl. Phys. Lett. 81, 2974 (2002); http://dx.doi.org/10.1063/1.1512956 (3 pages) | Cited 13 times

Online Publication Date: 7 October 2002

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The influence of stacking faults (SFs) on the performance of 4H–SiC (11math0) Schottky barrier diodes fabricated on the epilayer grown on the substrate which was grown in [11math0] direction by the sublimation method was investigated. The number of SFs under the Schottky electrode was determined by KOH etching of (1math00) face cross section. SFs were found to have a severe influence on the leakage current of reverse characteristic and Schottky barrier height. The leakage current is increased even though a few SFs exist under the electrode. The Schottky barrier height is also affected by the SF under the electrode. © 2002 American Institute of Physics.
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85.30.Kk Junction diodes
61.72.Nn Stacking faults and other planar or extended defects
85.30.Hi Surface barrier, boundary, and point contact devices
81.65.Cf Surface cleaning, etching, patterning

Relationship between the Li ionic conduction and the local structures in B-site substituted perovskite compounds, (Li0.1La0.3)1+xMxNb1−xO3 (M = Zr, Ti; x = 0, 0.05)

Masanobu Nakayama, Hiromasa Ikuta, Yoshiharu Uchimoto, Masataka Wakihara, and Yasuko Terada

Appl. Phys. Lett. 81, 2977 (2002); http://dx.doi.org/10.1063/1.1515366 (3 pages) | Cited 5 times

Online Publication Date: 7 October 2002

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Generally, it is known that the activation energy for the Li+ conduction in the perovskite-type oxides such as (Li,La)NbO3 decreases with the expansion of the lattice. However, our previous results showed an increase in the activation energy with Zr doping at B site in spite of lattice expansion. In the present study, the local structure of B site substituted perovskite oxides, (Li0.1La0.3)1+xMxNb1−xO3 (M = Zr, Ti; x = 0, 0.05), has been investigated using the extended x-ray absorption fine structure (EXAFS) technique with a view to explore the divergence exerted by Zr-doped perovskites. The EXAFS measurement revealed that the Li+ migration pathway in the Zr-doped samples is subjected to contract due to the local lattice distortion around the Zr-doped site. © 2002 American Institute of Physics.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
78.70.Dm X-ray absorption spectra
61.66.Bi Elemental solids
61.66.Dk Alloys
61.66.Fn Inorganic compounds

Dynamic etching of silicon for broadband antireflection applications

C. C. Striemer and P. M. Fauchet

Appl. Phys. Lett. 81, 2980 (2002); http://dx.doi.org/10.1063/1.1514832 (3 pages) | Cited 58 times

Online Publication Date: 7 October 2002

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An electrochemical etching technique has been developed that provides continuous control over the porosity of a porous silicon layer as a function of etching depth. Thin films with engineered porosity gradients, and thus a controllable gradient in the index of refraction, have been used to demonstrate broadband antireflection properties on silicon wafer and solar cell substrates. A simulation was also developed to examine the effects of specific porosity profiles on film reflectivity. © 2002 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
42.79.Wc Optical coatings
42.70.-a Optical materials
84.60.Jt Photoelectric conversion
78.66.Db Elemental semiconductors and insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Physical aging in a hyperquenched glass

Y. Z. Yue, S. L. Jensen, and J. deC. Christiansen

Appl. Phys. Lett. 81, 2983 (2002); http://dx.doi.org/10.1063/1.1514386 (3 pages) | Cited 20 times

Online Publication Date: 7 October 2002

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We report experimental data on the enthalpy relaxation of a hyperquenched silicate glass subjected to long-time aging (annealing) below the glass-transition temperature (Tg). The relaxation of a hyperquenched glass substantially differs from that of a normally cooled glass. Two mechanisms govern the relaxation of a hyperquenched glass. During relaxation of the first hyperquenched, and afterward aged glass, a relaxation endotherm occurs followed by an exotherm. This is reflected by the occurrence of crossover. By increasing the aging temperature and time, the endotherm becomes more pronounced, while the exotherm gradually disappears. The consequence of this is the shift of the crossover point to higher temperature. The relaxation of the hyperquenched glass at 0.66Tg with the aging time is highly nonexponential. © 2002 American Institute of Physics.
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65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
81.40.Gh Other heat and thermomechanical treatments
81.05.Kf Glasses (including metallic glasses)

Virtual surfaces, director domains, and the Fréedericksz transition in polymer-stabilized nematic liquid crystals

Pavel A. Kossyrev, Jun Qi, Nikolai V. Priezjev, Robert A. Pelcovits, and Gregory P. Crawford

Appl. Phys. Lett. 81, 2986 (2002); http://dx.doi.org/10.1063/1.1515136 (3 pages) | Cited 16 times

Online Publication Date: 7 October 2002

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The critical field of the Fréedericksz transition and switching dynamics are investigated for polymer-stabilized nematic liquid crystals as a function of polymer concentration. A simple phenomenological model is proposed to describe the observed critical field and dynamic response time behaviors as a function of concentration. In this model, the polymer fibrils form director domains, which are bounded by “virtual surfaces” with a finite anchoring energy. © 2002 American Institute of Physics.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
64.70.M- Transitions in liquid crystals
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
42.70.Df Liquid crystals

Theoretical evidence for the kick-out mechanism for B diffusion in SiC

R. Rurali, P. Godignon, J. Rebollo, P. Ordejón, and E. Hernández

Appl. Phys. Lett. 81, 2989 (2002); http://dx.doi.org/10.1063/1.1515369 (3 pages) | Cited 15 times

Online Publication Date: 7 October 2002

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In this letter, we analyze by means of first-principles electronic structure calculations the diffusion of B impurities in 3C-SiC. We find, through molecular dynamics, that substitutional B at a Si lattice site is readily displaced by a nearby Si interstitial by the process known as a kick-out mechanism, in agreement with recent experimental results. This is in contrast to the situation in Si, where B has recently been shown to diffuse via an interstitialcy mechanism. © 2002 American Institute of Physics.
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66.30.J- Diffusion of impurities
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
71.20.Nr Semiconductor compounds
71.55.Ht Other nonmetals
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