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21 Feb 2005

Volume 86, Issue 8, Articles (08xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 86, 083106 (2005); http://dx.doi.org/10.1063/1.1866504 (3 pages)

L. Liao, J. C. Li, D. H. Liu, C. Liu, D. F. Wang, W. Z. Song, and Q. Fu
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High-Q optical resonators in silicon-on-insulator-based slot waveguides

Tom Baehr-Jones, Michael Hochberg, Chris Walker, and Axel Scherer

Appl. Phys. Lett. 86, 081101 (2005); http://dx.doi.org/10.1063/1.1871360 (3 pages) | Cited 70 times

Online Publication Date: 14 February 2005

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This letter describes the design, fabrication and characterization of high-Q oval resonators based on slot waveguide geometries in thin silicon-on-insulator material. Optical quality factors of up to 27 000 were measured in such filters, and we estimate losses of −10 dB/cm in the slotted waveguides on the basis of our resonator measurements. Such waveguides enable the concentration of light to very high optical fields within nanoscale dimensions, and show promise for the confinement of light in low-index material with potential applications for optical modulation, nonlinear optics and optical sensing.
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42.79.Gn Optical waveguides and couplers
42.65.Wi Nonlinear waveguides

Single-layer multiband infrared metallodielectric photonic crystals designed by genetic algorithm optimization

Robert P. Drupp, Jeremy A. Bossard, Douglas H. Werner, and Theresa S. Mayer

Appl. Phys. Lett. 86, 081102 (2005); http://dx.doi.org/10.1063/1.1868884 (3 pages) | Cited 8 times

Online Publication Date: 14 February 2005

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Metallodielectric photonic crystals (MDPCs) consisting of a planar periodic array of metallic patch elements designed by genetic algorithm (GA) optimization were patterned on flexible dielectric substrates and exhibit strong mid- and far-infrared (IR) dual-band response. The GA uses biological principles of natural selection to evolve nonintuitive geometries by optimizing the MDPC scattering response based on a user-defined fitness function. The transmission spectra measured on two different MDPCs optimized for optically thin and thick substrates have two strong stop bands with attenuation greater than 10 dB, which agree well with those predicted by full-wave periodic method of moments (PMM) modeling. This versatile GA optimization approach will facilitate design of scaled mid- and near-IR MDPCs with user-defined scattering response.
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42.70.Qs Photonic bandgap materials
42.15.Eq Optical system design

Using proton-transfer laser dyes for organic laser diodes

Ken-ichi Sakai, Takeo Tsuzuki, Yoshihiro Itoh, Musubu Ichikawa, and Yoshio Taniguchi

Appl. Phys. Lett. 86, 081103 (2005); http://dx.doi.org/10.1063/1.1868885 (3 pages) | Cited 21 times

Online Publication Date: 14 February 2005

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Photopumping measurements for the dilute thin films of the representative proton-transfer laser dye, 2-(2-hydroxyphenyl)benzothiazole (HBT) revealed that it exhibited better stimulated-emission performance, especially at the high doping level of 26 wt %. This suggests that HBT has an ability to form high gain media, in addition to an inherent potential for widely tuning gain wavelength. Both are advantageous for overcoming the polaron-absorption problem that is a major obstacle to making organic laser diodes.
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42.55.Px Semiconductor lasers; laser diodes
42.55.Mv Dye lasers
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.70.Hj Laser materials
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)

Effects of epitaxial lift-off on interface recombination and laser cooling in GaInP/GaAs heterostructures

Babak Imangholi, Michael P. Hasselbeck, Mansoor Sheik-Bahae, Richard I. Epstein, and Sarah Kurtz

Appl. Phys. Lett. 86, 081104 (2005); http://dx.doi.org/10.1063/1.1868068 (3 pages) | Cited 18 times

Online Publication Date: 15 February 2005

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Photoluminescence of GaAs passivated with GaInP is studied over the temperature range 7–450 K. Different photocarrier recombination mechanisms are identified as the temperature changes. An interface recombination velocity of less than 0.6 cm/s is measured at 300 K. Lift-off processing inhibits but does not preclude laser cooling of GaAs.
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78.66.Fd III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
78.55.Cr III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Dynamic spectral interferometry for measuring the nonlinear amplitude and phase response of a saturable absorber mirror

Gero Stibenz, Günter Steinmeyer, and Wolfgang Richter

Appl. Phys. Lett. 86, 081105 (2005); http://dx.doi.org/10.1063/1.1868861 (3 pages)

Online Publication Date: 15 February 2005

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We report on spectral interferometry for measuring the spectrally resolved nonlinear phase and amplitude response in a pump–probe experiment. Using nJ pulses from a femtosecond oscillator, we demonstrate the method by measuring the nonlinear response of a GaAs/AlGaAs single-quantum-well saturable absorber mirror. The demonstrated sub-mrad phase sensitivity constitutes a two-order-of-magnitude improvement of phase resolution, compared to earlier demonstrations. Dynamic spectral interferometry proves to be a powerful tool for evaluating the phase response on nonlinear optical semiconductor devices for mode locking of lasers, optical switching, and other photonic applications.
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07.60.Ly Interferometers
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.87.-d Optical testing techniques
42.79.Bh Lenses, prisms and mirrors
85.30.-z Semiconductor devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.60.Fc Modulation, tuning, and mode locking

Quantum well intermixing enhancement using Ge-doped sol-gel derived SiO2 encapsulant layer in InGaAs/InP laser structure

H. S. Djie, C. K. F. Ho, T. Mei, and B. S. Ooi

Appl. Phys. Lett. 86, 081106 (2005); http://dx.doi.org/10.1063/1.1868867 (3 pages) | Cited 8 times

Online Publication Date: 15 February 2005

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The intermixing enhancement in InGaAs/InGaAsP quantum well laser structure has been investigated using the Ge-doped sol-gel derived SiO2 encapsulant layer. A band-gap shift of ∼ 64 nm has been observed from 16% Ge-doped SiO2 capped sample at the annealing temperature of 630 °C with effective intermixing suppression using the e-beam-evaporated SiO2 layer. Ge incorporation in the sol-gel cap reduces the mismatch of thermal expansion coefficients efficiently retaining preferential vacancies, and therefore enhancing the interdiffusion rate. The intermixed material retains a good surface morphology and preserves the optical quality as evidenced by the absence of any appreciable photoluminescence linewidth broadening.
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42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters

Creation of second-order nonlinearity and quasi-phase-matched second-harmonic generation in Ge-implanted fused silica planar waveguide

Huai-Yi Chen, Chun-Lin Lin, Yu-Hsien Yang, Shiuh Chao, Huan Niu, and Chih T’sung Shih

Appl. Phys. Lett. 86, 081107 (2005); http://dx.doi.org/10.1063/1.1871343 (3 pages) | Cited 4 times

Online Publication Date: 17 February 2005

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A planar waveguide was formed in fused silica plate by implantation of 5-MeV Ge2+ ions to a dose of 1015 ions/cm2. Thermal poling created larger second-order nonlinearity in the waveguide than in blank fused silica plate. The nonlinearity could be erased by 266 nm ultraviolet exposure. Periodical nonlinearity distribution in the waveguide was implemented by periodical UV exposure. The first-order quasi-phase-matched second-harmonic generation from 1064 nm fundamental mode to 532 nm fundamental mode was achieved in the waveguide. The d33:d31 ratio was found to be 3.2:1, in favor of the built-in electric field model for Ge-implanted silica waveguide.
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42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.80.Jh Ion radiation effects
42.70.Ce Glasses, quartz

Codirectional couplers in GaAs-based planar photonic crystals

David Leuenberger, Rolando Ferrini, L. Andrea Dunbar, Romuald Houdré, Martin Kamp, and Alfred Forchel

Appl. Phys. Lett. 86, 081108 (2005); http://dx.doi.org/10.1063/1.1871346 (3 pages)

Online Publication Date: 17 February 2005

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Several designs for codirectional couplers in planar photonic crystals etched into GaAs-based heterostructures were investigated both theoretically and experimentally. Two different numerical techniques, i.e., plane wave expansion and finite difference time domain, were used to calculate the coupling lengths. Both methods are shown to be in good agreement with the experimental results. The measured coupling lengths are in the order of 350 periods, leading to a physical length of the order of 80 μm, much smaller than what is achieved in classical integrated optics couplers.
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42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.82.Bq Design and performance testing of integrated-optical systems
42.70.Qs Photonic bandgap materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Direct observation of a photon spin-induced constant acceleration in macroscopic systems

G. Delannoy, O. Emile, and A. Le Floch

Appl. Phys. Lett. 86, 081109 (2005); http://dx.doi.org/10.1063/1.1869539 (3 pages)

Online Publication Date: 17 February 2005

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The use of a spider silk allows the direct observation of the dynamics induced by the transfer of angular momentum of laser light in a Beth-type experiment. In the optical domain, a uniform angular acceleration of a macroscopic object is demonstrated in agreement with the expected equation of motion. The intrinsic angular momentum exerts a stable torque thats modulus can be continuously adjusted from 0 to 10−12 N m by changing the optical power. Moreover, a macroscopic no-node mirror is proposed to improve the optical angular momentum transfer in micro-manipulation in the context of optical tweezers.
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37.10.Vz Mechanical effects of light on atoms, molecules, and ions
06.30.Gv Velocity, acceleration, and rotation
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
42.79.Bh Lenses, prisms and mirrors

Engineering of directional emission from photonic-crystal waveguides

Steven K. Morrison and Yuri S. Kivshar

Appl. Phys. Lett. 86, 081110 (2005); http://dx.doi.org/10.1063/1.1870133 (3 pages) | Cited 50 times

Online Publication Date: 18 February 2005

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We analyze, by the finite-difference time-domain numerical method, different ways to enhance the directional emission from photonic-crystal waveguides through the recently predicted beaming effect. We demonstrate that the substantial enhancement of the light emission can be achieved by adjusting the input wavelength, using a positive surface corrugation, increasing the refractive index of the surface layer, and inducing a near-surface mode.
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42.79.Gn Optical waveguides and couplers
42.70.Qs Photonic bandgap materials

In situ resistance measurement of the p-type contact in InP–InGaAsP coolerless ridge waveguide lasers

S. B. Kuntze, E. H. Sargent, J. K. White, K. Hinzer, St. J. Dixon-Warren, and D. Ban

Appl. Phys. Lett. 86, 081111 (2005); http://dx.doi.org/10.1063/1.1869541 (3 pages) | Cited 2 times

Online Publication Date: 18 February 2005

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Scanning voltage microscopy (SVM) is employed to measure the voltage division—and resulting contact resistance and power loss—at the p‐In0.53Ga0.47As–p‐InP heterojunction in a working InP–InGaAsP laser diode. This heterojunction is observed to dissipate ∼ 35% of the total power applied to the laser over the operating bias range. This in situ experimental study of the parasitic voltage division (and resulting power loss and series contact resistance) highlights the need for a good p-type contact strategy. SVM technique provides a direct, fast and in situ measurement of specific contact resistance, an important device parameter.
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42.55.Px Semiconductor lasers; laser diodes
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Charge losses in expanding plasma created by an XeCl laser

Antonella Lorusso, Josef Krása, Karel Rohlena, Vincenzo Nassisi, Fabio Belloni, and Domenico Doria

Appl. Phys. Lett. 86, 081501 (2005); http://dx.doi.org/10.1063/1.1866215 (2 pages) | Cited 13 times

Online Publication Date: 16 February 2005

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The emission of multiply charged Cuq+ ions from a plasma produced by 308 nm excimer laser is analyzed with respect to the distance from the irradiated target. The critical zone, outside which the charge states of ions of the expanding plasma are frozen, was determined to be approximately 20 cm from the target. This value was estimated using a charge-freezing criterion expressed by a distance dependence of the total charge carried by the ions Q∝L−2, which describes the dilution of plasma by its expansion into a vacuum without collisional recombination processes.
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52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.-b Plasma properties
52.70.Nc Particle measurements
52.25.Tx Emission, absorption, and scattering of particles

Charge-state and energy enhancement of laser-produced ions due to nonlinear processes in preformed plasma

L. Láska, K. Jungwirth, J. Krása, M. Pfeifer, K. Rohlena, J. Ullschmied, J. Badziak, P. Parys, J. Wolowski, S. Gammino, L. Torrisi, and F. P. Boody

Appl. Phys. Lett. 86, 081502 (2005); http://dx.doi.org/10.1063/1.1869546 (3 pages) | Cited 18 times

Online Publication Date: 17 February 2005

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At laser intensities above IL ∼ 1×1014 W/cm2(ILλ2 ∼ 1×1014 W μm2/cm2), nonlinear processes in preformed plasma, such as self-focusing, influence ion generation significantly and ions with higher charge states and energies can be produced than without interaction with preformed plasma. The step (spread) in plots of experimental data of ion energy per nucleon versus ILλ2 reported by other researchers most likely reflects high-intensity laser interactions with and without preformed plasma.
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52.35.Mw Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.38.Hb Self-focussing, channeling, and filamentation in plasmas
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
52.25.-b Plasma properties

Photoconductive switching of a high-voltage spark gap

G. J. H. Brussaard and J. Hendriks

Appl. Phys. Lett. 86, 081503 (2005); http://dx.doi.org/10.1063/1.1866227 (3 pages) | Cited 10 times

Online Publication Date: 17 February 2005

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We have demonstrated photoconductive switching of a gas-filled spark gap. A femtosecond Ti:sapphire laser was focused in a 1 mm spark gap biased at 4.5 kV. There is a clear transition between triggered operation, when only part of the path between the electrodes is ionized, and photoconductive switching, when the entire length of the gap is ionized directly by the laser. The measured standard deviation of the time fluctuations between the rising edge of the transmitted electrical pulse and the laser was less than 15 ps.
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52.75.Kq Plasma switches (e.g., spark gaps)
85.60.-q Optoelectronic devices
52.80.Mg Arcs; sparks; lightning; atmospheric electricity
52.38.Dx Laser light absorption in plasmas (collisional, parametric, etc.)
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Elastic modulus of shape-memory NiTi from in situ neutron diffraction during macroscopic loading, instrumented indentation, and extensometry

S. Rajagopalan, A. L. Little, M. A. M. Bourke, and R. Vaidyanathan

Appl. Phys. Lett. 86, 081901 (2005); http://dx.doi.org/10.1063/1.1863437 (3 pages) | Cited 31 times

Online Publication Date: 14 February 2005

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The elastic modulus of B19’ shape-memory NiTi was determined using three techniques; from the response of lattice planes measured using in situ neutron diffraction during loading, instrumented indentation using a spherical indenter and macroscopic extensometry. The macroscopic measurements resulted in a modulus of 68 GPa, significantly less than the 101 GPa from indentation and the lattice plane average of 109 GPa from neutron diffraction. Evidence from the neutron measurements suggests that the disparity derives from the onset of small amounts of twinning at stresses less that 40 MPa, which might otherwise be considered elastic from a macroscopic view point.
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81.05.Bx Metals, semimetals, and alloys
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
61.72.Mm Grain and twin boundaries

Influence of elastic strains on the mask ratio in glassy polymer nanoimprint

Graham L. W. Cross, Barry S. O’Connell, and John B. Pethica

Appl. Phys. Lett. 86, 081902 (2005); http://dx.doi.org/10.1063/1.1868074 (3 pages) | Cited 11 times

Online Publication Date: 14 February 2005

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During glassy polymer nanoimprint, a supported film is extruded from protruding (punch) to recessed (cavity) regions of a patterned stamp. The completeness of this extrusion determines the mask ratio for lithographic applications. We show that, for a given punch contact size, there is a residual layer of unextruded material with a mean thickness that is independent of initial film thickness, stamping time, or applied maximum load. Depth sensing indentation enables us to monitor deformation during the imprinting as well as after, and so understand the deformation process involved. It is found that both the geometry and mean thickness of the residual layer are influenced by the overall elastic properties of the stamping system.
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81.16.Nd Micro- and nanolithography
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.41.+e Polymers, elastomers, and plastics
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Type I-type II transition in InGaAs–GaNAs heterostructures

C. Schlichenmaier, H. Grüning, A. Thränhardt, P. J. Klar, B. Kunert, K. Volz, W. Stolz, W. Heimbrodt, T. Meier, S. W. Koch, J. Hader, and J. V. Moloney

Appl. Phys. Lett. 86, 081903 (2005); http://dx.doi.org/10.1063/1.1870132 (3 pages) | Cited 8 times

Online Publication Date: 15 February 2005

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Optical interband transitions in a series of In0.23Ga0.77As–GaNxAs1−x quantum well samples are investigated. For changing nitrogen content, a type I-type II transition is identified by a detailed analysis of photoluminescence and photoreflectance spectra. Experimental results are compared systematically with spectra calculated by a microscopic theory. A valence band offset parameter of (1.5±0.5) eV is extracted for this heterostructure system.
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78.67.De Quantum wells
78.55.Cr III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.20.Bh Theory, models, and numerical simulation

Large displacement of germanium atoms in crystalline Ge2Sb2Te5

S. Shamoto, N. Yamada, T. Matsunaga, Th. Proffen, J. W. Richardson, J.-H. Chung, and T. Egami

Appl. Phys. Lett. 86, 081904 (2005); http://dx.doi.org/10.1063/1.1861976 (3 pages) | Cited 20 times

Online Publication Date: 15 February 2005

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Local structure of NaCl-type crystalline Ge2Sb2Te5 has been studied by the atomic pair distribution function analysis of pulsed neutron powder diffraction data. We have found the large displacement of germanium atoms in this crystalline phase. Usually, such a large lattice distortion has disadvantages for the electric conductivity. The electronic band structure, however, implies that this significant distortion in addition to the lattice defect at Na site reduces only thermal conductivity, while the highly ordered tellurium atoms at Cl site keep high electric conductivity.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
73.20.At Surface states, band structure, electron density of states
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
68.60.Wm Other nonelectronic physical properties
61.72.J- Point defects and defect clusters
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations

Snapthrough occurring in the postbuckling of thin films

G. Parry, J. Colin, C. Coupeau, F. Foucher, A. Cimetière, and J. Grilhé

Appl. Phys. Lett. 86, 081905 (2005); http://dx.doi.org/10.1063/1.1868878 (3 pages) | Cited 7 times

Online Publication Date: 15 February 2005

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The postbuckling transition from an initially straight-sided wrinkle to a distribution of bubbles has been investigated by means of finite element simulations in the case of a thin film relying on a rigid substrate. The calculations show that a snapthrough occurs when the buckling wavelength exceeds a critical value. Experimental atomic force microscopy observations of this transition have been reported and found to be in good agreement with the calculations.
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81.05.Bx Metals, semimetals, and alloys
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.60.Bs Mechanical and acoustical properties
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.Qq Microscopic defects (voids, inclusions, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.55.-a Thin film structure and morphology
68.37.Ps Atomic force microscopy (AFM)

Room-temperature boron displacement in crystalline silicon induced by proton irradiation

A. M. Piro, L. Romano, S. Mirabella, and M. G. Grimaldi

Appl. Phys. Lett. 86, 081906 (2005); http://dx.doi.org/10.1063/1.1868874 (3 pages) | Cited 9 times

Online Publication Date: 15 February 2005

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The effect induced by proton irradiation on B-doped crystalline Si at room temperature is investigated in detail. The displacement of B atoms out of substitutional lattice sites is shown to be induced at room temperature by proton irradiation at energies ranging between 300 and 1300 keV. This phenomenon was studied by means of channeling and nuclear reaction analysis techniques using the math(p,α)math nuclear reaction at 650 keV proton energy. For all the irradiation energies used, the fraction of displaced B atoms increases exponentially with proton irradiation fluence until saturation occurs. The B displacement rate strongly increases by decreasing the irradiation energy. We show that B off-lattice displacement is not due to a direct interaction of the proton beam with B atoms, but to the Si self-interstitials (ISi) generated in the lattice by the irradiating beam. The displacement results from the formation of a mobile B-ISi pair when a ISi is trapped by a substitutional B. The measured damage rate has been interpreted in terms of the ISi-B substitutional trapping probability and the resulting cross section at room temperature is (1.00±0.05)×10−16 cm2.
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61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.J- Point defects and defect clusters
61.85.+p Channeling phenomena (blocking, energy loss, etc.)

Near-field spectroscopy of phase segregation in white-light-emitting blends based on low-mass molecules

Marco Salerno, Marco Mazzeo, Maria C. Frassanito, Salvatore Patanè, Roberto Cingolani, and Giuseppe Gigli

Appl. Phys. Lett. 86, 081907 (2005); http://dx.doi.org/10.1063/1.1867556 (3 pages) | Cited 4 times

Online Publication Date: 16 February 2005

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We report on the direct observation of phase segregation occurring in thin-film blends of a thiophene monomer and an ammino compound, used in the fabrication of organic white-light-emitting diodes. In the homogeneous and uniform regions of the films, the interaction between the two molecular components gives rise to exciplex states responsible for a broad redshifted photoluminescence emission band, which disappears in the film zones where segregation occurs. This effect has been observed with submicrometer spatial resolution by means of local spectroscopic measurements performed in a scanning near-field optical microscope.
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85.60.Jb Light-emitting devices
68.55.-a Thin film structure and morphology
68.35.Dv Composition, segregation; defects and impurities
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials
68.37.Uv Near-field scanning microscopy and spectroscopy

AlxGa1−xN bulk single crystals

P. Geiser, J. Jun, S. M. Kazakov, P. Wägli, J. Karpinski, B. Batlogg, and L. Klemm

Appl. Phys. Lett. 86, 081908 (2005); http://dx.doi.org/10.1063/1.1867563 (3 pages) | Cited 3 times

Online Publication Date: 16 February 2005

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AlxGa1−xN bulk single crystals have been grown by a solution growth technique in a cubic anvil cell with a solid pressure medium. GaN powder pellets as starting materials serve as a nitrogen source for crystallization in a Ga/Al alloy. The growth process (up to 3 days at T = 1750 °C, p = 30 kbar) yields crystals up to 0.6×0.4×0.2 mm3 in size. X-ray diffraction investigations confirm the growth of the AlxGa1−xN phase. The crystal composition is studied by mass spectrometry, showing aluminum contents as high as x = 27%. The near-band-gap photoluminescence spectra in AlxGa1−xN are blueshifted with respect to GaN and indicate Al concentrations in agreement with results from mass spectrometry and from the measured lattice parameter contraction.
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81.05.Ea III-V semiconductors
81.10.Dn Growth from solutions
64.70.K- Solid-solid transitions
61.66.Fn Inorganic compounds
78.55.Cr III-V semiconductors

Femtosecond spectroscopy of defect modes in silica glasses

C. Guillon, J. Burgin, P. Langot, F. Vallée, and B. Hehlen

Appl. Phys. Lett. 86, 081909 (2005); http://dx.doi.org/10.1063/1.1867566 (3 pages) | Cited 5 times

Online Publication Date: 16 February 2005

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The D1 and D2 defect modes are investigated in the time domain in normal and densified silica using a high sensitivity femtosecond pump-probe technique with 15 fs pulses. Their frequency and width are precisely determined even when they are partly masked by a broad background in spontaneous Raman spectroscopy. These results open up many possibility for investigation of local structures in glasses.
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78.35.+c Brillouin and Rayleigh scattering; other light scattering
63.50.-x Vibrational states in disordered systems
78.47.-p Spectroscopy of solid state dynamics

Low temperature internal friction in nanocrystalline diamond films

Thomas H. Metcalf, Xiao Liu, Brian H. Houston, Jeffrey W. Baldwin, James E. Butler, and Tatyana Feygelson

Appl. Phys. Lett. 86, 081910 (2005); http://dx.doi.org/10.1063/1.1868065 (3 pages) | Cited 12 times

Online Publication Date: 16 February 2005

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Measurements of the temperature dependence of the internal friction and frequency of three nanocrystalline diamond films grown on silicon oscillator substrates indicate that the mechanical properties of the films are dominated by their interface layers. The films, with thicknesses of 0.3, 0.6, and 1.14 μm, were measured between 0.4 K and room temperature and have low temperature (below 10 K) internal frictions between 2×10−6 and 5×10−6, which is an order of magnitude lower than has been reported previously. Additionally, all films display an internal friction peak at approximately 1.7 K. The shear modulus of the films, 545–551 GPa, is comparable to that for single-crystal diamond.
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81.05.Cy Elemental semiconductors
81.07.Bc Nanocrystalline materials
68.35.Gy Mechanical properties; surface strains
68.60.Bs Mechanical and acoustical properties
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
62.25.-g Mechanical properties of nanoscale systems
62.20.D- Elasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.55.-a Thin film structure and morphology

Determination of electron escape depth in ultrathin silicon oxide

H. Nohira, H. Okamoto, K. Azuma, Y. Nakata, E. Ikenaga, K. Kobayashi, Y. Takata, S. Shin, and T. Hattori

Appl. Phys. Lett. 86, 081911 (2005); http://dx.doi.org/10.1063/1.1868066 (3 pages) | Cited 2 times

Online Publication Date: 16 February 2005

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Show Abstract
Using the high-brilliance synchrotron radiation at SPring-8, we determined the electron escape depths in approximately 1‐nm-thick low-temperature oxide layers, which were formed on Si(100) at 300 °C using three kinds of atomic oxygen and that in approximately 1‐nm-thick thermally grown oxide layer formed in 1 Torr dry oxygen at 900 °C by measuring angle-resolved Si 2p photoelectron spectra at the photon energy of 1050 eV. The results indicated that the electron escape depths in the three kinds of low-temperature oxide layers were 18%–24% smaller than that in the thermally grown oxide layer. Furthermore, the electron escape depth in the thermally grown oxide layer, whose thickness was close to that of the structural transition layer, was 7% smaller than that in bulk SiO2.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
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