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1 Jul 2005

Volume 98, Issue 1, Articles (01xxxx)

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Plasmonics: Localization and guiding of electromagnetic energy in metal/dielectric structures

Stefan A. Maier and Harry A. Atwater

J. Appl. Phys. 98, 011101 (2005); http://dx.doi.org/10.1063/1.1951057 (10 pages) | Cited 232 times

Online Publication Date: 11 July 2005

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We review the basic physics of surface-plasmon excitations occurring at metal/dielectric interfaces with special emphasis on the possibility of using such excitations for the localization of electromagnetic energy in one, two, and three dimensions, in a context of applications in sensing and waveguiding for functional photonic devices. Localized plasmon resonances occurring in metallic nanoparticles are discussed both for single particles and particle ensembles, focusing on the generation of confined light fields enabling enhancement of Raman-scattering and nonlinear processes. We then survey the basic properties of interface plasmons propagating along flat boundaries of thin metallic films, with applications for waveguiding along patterned films, stripes, and nanowires. Interactions between plasmonic structures and optically active media are also discussed.
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81.07.Bc Nanocrystalline materials
42.70.-a Optical materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
78.30.Er Solid metals and alloys
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
01.30.Rr Surveys and tutorial papers; resource letters
84.40.-x Radiowave and microwave (including millimeter wave) technology
42.79.Gn Optical waveguides and couplers
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Compact high-Q filters based on one-dimensional photonic crystals containing single-negative materials

Haitao Jiang, Hong Chen, Hongqiang Li, Yewen Zhang, and Shiyao Zhu

J. Appl. Phys. 98, 013101 (2005); http://dx.doi.org/10.1063/1.1949273 (5 pages) | Cited 17 times

Online Publication Date: 11 July 2005

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A mechanism to design compact high-Q filters is proposed in this paper, based on the properties of a defect mode in a one-dimensional (1D) photonic crystal composed of alternating layers of negative-permeability material and negative-permittivity material. The eigenfrequency equation for the defect mode is derived by means of the transfer-matrix method, and then, the dependence of the eigenfrequency on the thicknesses of the two host layers and the defect layer is calculated. In contrast to the case for a filter based on a conventional 1D photonic crystal (with positive refractive indices), we find that the quality factor Q of the filter involved in this paper can be boosted noticeably while the volume of the filter decreases.
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42.79.Ci Filters, zone plates, and polarizers
42.70.Qs Photonic bandgap materials
42.15.Eq Optical system design

A robust design against comb electrode spacing variations for in-plane switching mode thin-film transistor liquid-crystal displays

Makoto Yoneya, Masuyuki Ohta, and Katsumi Kondo

J. Appl. Phys. 98, 013102 (2005); http://dx.doi.org/10.1063/1.1949277 (8 pages)

Online Publication Date: 13 July 2005

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A method to reduce the transmittance nonuniformity caused by comb electrode spacing variations of in-plane switching mode thin-film transistor liquid-crystal displays is proposed. The method is based on the compensation of the effect of the comb electrode spacing variations with effective driving voltage variation via feed-through voltage in the thin-film transistor addressing. The conditions for this compensation were analyzed theoretically taking into account gate delay (recharging) effects. It was observed that the common dc driving was superior to the common inversion driving in terms of compensation efficiency. An alternative driving method was proposed to enhance the compensation in common inversion driving.
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42.79.Kr Display devices, liquid-crystal devices

Characterization of buried photonic crystal waveguides and microcavities fabricated by deep ultraviolet lithography

Iwan Märki, Martin Salt, Hans Peter Herzig, Ross Stanley, L. El Melhaoui, P. Lyan, and J. M. Fedeli

J. Appl. Phys. 98, 013103 (2005); http://dx.doi.org/10.1063/1.1948507 (4 pages) | Cited 5 times

Online Publication Date: 13 July 2005

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We present results of the optical characterization of silicon photonic crystal waveguides and microcavities that are completely buried in a silicon dioxide cladding and are fabricated by deep ultraviolet (UV) lithography. The advantages of buried waveguides and deep UV lithography are discussed. Transmission spectra and loss factors for photonic crystal waveguides, as well as quality factors for resonant microcavities, are obtained. The observed characteristics are in good agreement with three-dimensional simulations.
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81.05.Cy Elemental semiconductors
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
42.86.+b Optical workshop techniques
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Etching process of silicon dioxide with nonequilibrium atmospheric pressure plasma

Koji Yamakawa, Masaru Hori, Toshio Goto, Shoji Den, Toshirou Katagiri, and Hiroyuki Kano

J. Appl. Phys. 98, 013301 (2005); http://dx.doi.org/10.1063/1.1944219 (6 pages) | Cited 9 times

Online Publication Date: 5 July 2005

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An ultrahigh etch rate (14 μm/min) of SiO2 and a high selectivity of SiO2/Si over 200 were achieved using a microwave-excited nonequilibrium atmospheric pressure plasma source employing He, NF3, and H2O gases, which have been developed for application to microelectromechanical systems and other bionanotechnology fields. In order to clarify the etching mechanism, two diagnostic methods have been performed: (1) imaging of plasma emission with an intensified charge-coupled device camera, and (2) absorption measurements using Fourier transform infrared spectroscopy. The etching characteristics are discussed in relation to the spatial distributions of the species involved. The etch rate depended considerably on the distance between the plasma and the substrate. Some radicals generated from the feed gases reached the substrate directly, while other radicals recombined into different species, which reached the substrate. An abundance of HF molecules were produced through a reaction between radicals generated by the atmospheric pressure discharge of NF3 and H2O. From these measurements, it has been found that the HF molecules generated played a role in producing the high etch rate of SiO2 and high etch selectivity of SiO2/Si.
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52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
52.50.Dg Plasma sources
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
78.30.Hv Other nonmetallic inorganics

Numerical description of discharge characteristics of the plasma needle

W. J. M. Brok, M. D. Bowden, J. van Dijk, J. J. A. M. van der Mullen, and G. M. W. Kroesen

J. Appl. Phys. 98, 013302 (2005); http://dx.doi.org/10.1063/1.1944218 (8 pages) | Cited 34 times

Online Publication Date: 7 July 2005

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The plasma needle is a small atmospheric, nonthermal, radio-frequency discharge, generated at the tip of a needle, which can be used for localized disinfection of biological tissues. Although several experiments have characterized various qualities of the plasma needle, discharge characteristics and electrical properties are still not well known. In order to provide initial estimates on electrical properties and quantities such as particle densities, we employed a two-dimensional, time-dependent fluid model to describe the plasma needle. In this model the balance equation is solved in the drift-diffusion approach for various species and the electron energy, as well as Poisson’s equation. We found that the plasma production occurs in the sheath region and results in a steady flux of reactive species outwards. Even at small (<0.1%) admixtures of N2 to the He background, N2+ is the dominant ion. The electron density is typically 1011 cm−3 and the dissipated power is in the order of 10 mW. These results are consistent with the experimental data available and can give direction to the practical development of the plasma needle.
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52.80.Pi High-frequency and RF discharges
52.75.-d Plasma devices
52.40.Kh Plasma sheaths
52.25.Fi Transport properties
52.50.-b Plasma production and heating
02.60.Lj Ordinary and partial differential equations; boundary value problems

Formation of plasma and ion flux on a target, irradiated by an intense electron beam

Vladimir Engelko and Georg Mueller

J. Appl. Phys. 98, 013303 (2005); http://dx.doi.org/10.1063/1.1944217 (7 pages) | Cited 1 time

Online Publication Date: 12 July 2005

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Theoretical consideration shows that under the influence of an intense electron beam, first, an ion flux and then plasma are formed on the surface of a target. The target plasma is created when the density of the ion flux achieves a certain limiting value. The time necessary for the plasma formation depends on the beam current density and the efficiency of gas desorption and ionization. This time is few microseconds under typical vacuum conditions of about 5.0×10−5 mbar, electron-beam current density in the range of 10 A/cm2, and kinetic energy of electrons in the range of 100 keV. When the density of the ion flux reaches a limiting value the beam potential decreases to a level, which is half of the initial one. A transient layer is formed between the plasma boundary and the electron beam. For conditions mentioned above its length are few centimeters. The target plasma expands into the beam drift region, with a velocity increasing in time. The expansion of the target plasma is the main reason for neutralization of the electron-beam space charge.
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52.50.-b Plasma production and heating
52.40.Mj Particle beam interactions in plasmas
52.40.Hf Plasma-material interactions; boundary layer effects
52.30.-q Plasma dynamics and flow
61.80.Fe Electron and positron radiation effects
68.43.Mn Adsorption kinetics
51.50.+v Electrical properties (ionization, breakdown, electron and ion mobility, etc.)

The role of higher silanes in silane-discharge particle growth

Gregory Bano, Peter Horvath, Karoly Rozsa, and Alan Gallagher

J. Appl. Phys. 98, 013304 (2005); http://dx.doi.org/10.1063/1.1947895 (7 pages) | Cited 6 times

Online Publication Date: 12 July 2005

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A small concentration of stable higher silanes (HS) build up in an (initially) pure-silane discharge. Here it is shown that these HS cause a major increase in particle growth rates but have no effect on film growth rates. This explains the observed increase of growth rate during the first seconds of a transient discharge, as the HS build up toward a steady-state concentration of several percent. A rapid increase in particle versus film growth rate also occurs at larger values of discharge power and pressure, and the HS also appear to cause this. Possible reasons for this extreme sensitivity of particles, but not of films, to the HS are evaluated.
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52.77.-j Plasma applications

Plasma nonuniformities induced by dissimilar electrode metals

E. V. Barnat and G. A. Hebner

J. Appl. Phys. 98, 013305 (2005); http://dx.doi.org/10.1063/1.1941481 (7 pages) | Cited 8 times

Online Publication Date: 15 July 2005

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Nonuniformities in both sheath electric field and plasma excitation were observed around dissimilar metals placed on a rf electrode. Spatial maps of the rf sheath electric field obtained by laser-induced fluorescence-dip (LIF-dip) spectroscopy show that the sheath structure was a function of the electrode metal. In addition to the electric-field measurements, LIF, optical emission, and Langmuir probe measurements show nonuniform excitation around the dissimilar metals. The degree and spatial extent of the discharge nonuniformities were dependent on discharge conditions and the history of the metal surfaces.
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52.40.Kh Plasma sheaths
52.40.Hf Plasma-material interactions; boundary layer effects
52.70.Ds Electric and magnetic measurements
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.Pi High-frequency and RF discharges

Spectroscopic characterization of laser-induced tin plasma

S. S. Harilal, Beau O’Shay, Mark. S. Tillack, and Manoj V. Mathew

J. Appl. Phys. 98, 013306 (2005); http://dx.doi.org/10.1063/1.1977200 (7 pages) | Cited 43 times

Online Publication Date: 15 July 2005

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Optical emission spectroscopic studies have been carried out on a tin plasma generated using 1064-nm, 8-ns pulses from a Nd:yttrium aluminum garnet laser. Temperature and density were estimated from the analysis of spectral data. The temperature measurements have been performed by Boltzmann diagram method using singly ionized Sn lines, while density measurements were made using the Stark broadening method. An initial temperature of 3.2 eV and density of 7.7×1017 cm−3 were measured. Temporal and spatial behaviors of electron temperature and density in the laser-generated tin plasma have been analyzed. Time evolutions of density and temperature are found to decay adiabatically at early times. The spatial variation of density shows approximately 1/z dependence. The time-integrated temperature exhibits an appreciable rise at distances greater than 7 mm. This may be caused by the deviation from local thermodynamic equilibrium at larger distances from the target surface.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.25.Kn Thermodynamics of plasmas
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Strain-induced enhancement of near-infrared absorption in Ge epitaxial layers grown on Si substrate

Yasuhiko Ishikawa, Kazumi Wada, Jifeng Liu, Douglas D. Cannon, Hsin-Chiao Luan, Jurgen Michel, and Lionel C. Kimerling

J. Appl. Phys. 98, 013501 (2005); http://dx.doi.org/10.1063/1.1943507 (9 pages) | Cited 21 times

Online Publication Date: 1 July 2005

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Epitaxially grown Ge layers on Si substrate are shown to reveal an enhanced absorption of near-infrared light, which is effective for the photodiode application in Si-based photonics. Ge layers as thick as 1 μm were grown on Si substrate by ultrahigh-vacuum chemical-vapor deposition with a low-temperature buffer layer technique. X-ray-diffraction measurements showed that the Ge layer possesses a tensile strain as large as 0.2%, which is generated during the cooling from the high growth temperature due to the thermal-expansion mismatch between Ge and Si. Photoreflectance measurements showed that the tensile strain reduces the direct band-gap energy to 0.77 eV (c.f. 0.80 eV for unstrained Ge), as expected from the theory. Reflecting the band-gap narrowing, photodiodes fabricated using the Ge layer revealed an enhanced absorption of near-infrared light with the photon energy below 0.80 eV, i.e., with the wavelength above 1.55 μm. This property is effective to apply the photodiodes to the L band (1.56–1.62 μm) in the optical communications as well as the C band (1.53–1.56 μm). It is shown that the experimental absorption spectrum agrees with the theoretical one taking into account the splitting of light-hole and heavy-hole valence bands accompanied by the band-gap narrowing. Based on the calculation, the performance of the photodiode using the tensile-strained Ge is discussed.
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81.05.Cy Elemental semiconductors
85.60.Dw Photodiodes; phototransistors; photoresistors
68.55.A- Nucleation and growth
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators
78.20.-e Optical properties of bulk materials and thin films
71.20.Mq Elemental semiconductors
65.40.De Thermal expansion; thermomechanical effects

Near-band-edge slow luminescence in nominally undoped bulk ZnO

T. Monteiro, A. J. Neves, M. C. Carmo, M. J. Soares, M. Peres, J. Wang, E. Alves, E. Rita, and U. Wahl

J. Appl. Phys. 98, 013502 (2005); http://dx.doi.org/10.1063/1.1946200 (6 pages) | Cited 19 times

Online Publication Date: 1 July 2005

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We report the observation of slow emission bands overlapped with the near-band-edge steady-state luminescence of nominally undoped ZnO crystals. At low temperatures the time-resolved spectra are dominated by the emission of several high-energy bound exciton lines and the two-electron satellite spectral region. Furthermore, two donor-acceptor pair transitions at 3.22 and 3.238 eV are clearly identified in temperature-dependent time-resolved spectroscopy. These donor-acceptor pairs involve a common shallow donor at 67 meV and deep acceptor levels at 250 and 232 meV.
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78.55.Et II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics
71.55.Gs II-VI semiconductors
71.35.-y Excitons and related phenomena

Wavelength-tunable (1.55‐μm region) InAs quantum dots in InGaAsP/InP (100) grown by metal-organic vapor-phase epitaxy

S. Anantathanasarn, R. Nötzel, P. J. van Veldhoven, T. J. Eijkemans, and J. H. Wolter

J. Appl. Phys. 98, 013503 (2005); http://dx.doi.org/10.1063/1.1938271 (7 pages) | Cited 31 times

Online Publication Date: 1 July 2005

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Growth of wavelength-tunable InAs quantum dots (QDs) embedded in a lattice-matched InGaAsP matrix on InP (100) substrates by metal-organic vapor-phase epitaxy is demonstrated. As/P exchange plays an important role in determining QD size and emission wavelength. The As/P exchange reaction is suppressed by decreasing the QD growth temperature and the V∕III flow ratio, reducing the QD size and emission wavelength. The As/P exchange reaction and QD emission wavelength are then reproducibly controlled by the thickness of an ultrathin [zero to two monolayers (MLs)] GaAs interlayer underneath the QDs. An extended interruption after GaAs interlayer growth is essential to obtain well-defined InAs QDs. Submonolayer GaAs coverages result in a shape transition from QD to quantum dash at low V∕III flow ratio with a slightly shorter emission wavelength. Only the combination of reduced growth temperature and V∕III flow ratio with the insertion of GaAs interlayers above ML thicknesses allows wavelength tuning of QDs at room temperature in the technologically important 1.55‐μm wavelength region for fiber-optical telecommunication systems. A GaAs interlayer thickness just above one ML produces the highest photoluminescence (PL) efficiency. Temperature-dependent PL measurements reveal zero-dimensional carrier confinement and defect-free InAs QDs.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
78.67.Hc Quantum dots
78.66.Fd III-V semiconductors
68.65.Hb Quantum dots (patterned in quantum wells)
78.55.Cr III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase

High-resolution strain mapping in heteroepitaxial thin-film features

C. E. Murray, H.-F. Yan, I. C. Noyan, Z. Cai, and B. Lai

J. Appl. Phys. 98, 013504 (2005); http://dx.doi.org/10.1063/1.1938277 (9 pages) | Cited 26 times

Online Publication Date: 1 July 2005

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Heteroepitaxial thin-film features that are lattice matched to the underlying substrate undergo elastic relaxation at the free edges of the feature. To characterize the degree of elastic relaxation, we employed synchrotron-based x-ray diffraction techniques to map the change in lattice spacing in the thin film at a submicron resolution. Measurements were conducted on 0.24‐μm thick, heteroepitaxially grown SiGe strips of various widths on Si (001). A comparison of the SiGe diffraction peak positions across the features provides a real-space mapping of the extent of elastic relaxation as a function of linewidth. The resultant in-plane normal film stress measurements were compared to calculated values from several elastic mechanical models to assess their validity in predicting stress distributions within the features.
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68.60.Bs Mechanical and acoustical properties
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.55.-a Thin film structure and morphology

Blueshift of optical band gap in ZnO thin films grown by metal-organic chemical-vapor deposition

S. T. Tan, B. J. Chen, X. W. Sun, W. J. Fan, H. S. Kwok, X. H. Zhang, and S. J. Chua

J. Appl. Phys. 98, 013505 (2005); http://dx.doi.org/10.1063/1.1940137 (5 pages) | Cited 133 times

Online Publication Date: 1 July 2005

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The optical band gap of ZnO thin films deposited on fused quartz by metal-organic chemical-vapor deposition was studied. The optical band gap of as-grown ZnO blueshifted from 3.13 to 4.06 eV as the growth temperature decreased from 500 to 200 °C. After annealing, the optical band gap shifted back to the single-crystal value. All the ZnO thin films studied show strong band-edge photoluminescence. X-ray diffraction measurements showed that samples deposited at low temperatures (<450 °C) consisted of amorphous and crystalline phases. The redshift of the optical band gap back to the original position after annealing was strong evidence that the blueshift was due to an amorphous phase. The unshifted photoluminescence spectra indicated that the luminescence was due to the crystalline phase of ZnO, which was in the form of nanocrystals embedded in the amorphous phase.
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81.05.Dz II-VI semiconductors
81.05.Gc Amorphous semiconductors
81.07.Bc Nanocrystalline materials
78.66.Hf II-VI semiconductors
78.66.Jg Amorphous semiconductors; glasses
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Et II-VI semiconductors
78.55.Qr Amorphous materials; glasses and other disordered solids
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Cc Kinetics of defect formation and annealing

Interaction of wide-band-gap single crystals with 248-nm excimer laser irradiation. IX. Photoinduced atomic desorption from cleaved NaCl(100) surfaces

K. H. Nwe, S. C. Langford, and J. T. Dickinson

J. Appl. Phys. 98, 013506 (2005); http://dx.doi.org/10.1063/1.1927701 (7 pages) | Cited 4 times

Online Publication Date: 5 July 2005

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Neutral atomic sodium and chlorine emissions from cleaved, single-crystal NaCl(100) surfaces due to pulsed, 248-nm excimer laser irradiation have been characterized by time-resolved, quadrupole mass spectroscopy. At laser fluences below the threshold for optical breakdown, the resulting time-of-flight signals are consistent with particles emitted in thermal equilibrium with a laser-heated surface. Activation energy measurements made by varying the substrate temperature are consistent with F-H pair formation under UV excitation. By varying the laser fluence and estimating the effective surface temperature from the time-of-flight signals, additional activation energy measurements were made. The corresponding rate-limiting step is attributed to a thermally assisted, photoelectronic process involving atomic steps. Atomic force microscope images of surfaces irradiated at low fluences show monolayer islands that are created by the aggregation of material desorbed from steps. At somewhat higher fluences, monolayer pits due to F-center aggregation are also observed.
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68.43.Tj Photon stimulated desorption
79.20.Ds Laser-beam impact phenomena
79.20.La Photon- and electron-stimulated desorption
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
61.72.J- Point defects and defect clusters
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators
68.37.Ps Atomic force microscopy (AFM)
68.43.Fg Adsorbate structure (binding sites, geometry)
78.47.-p Spectroscopy of solid state dynamics

Microstructural and electrical properties of La0.7Ca0.3MnO3 thin films grown on SrTiO3 and LaAlO3 substrates using metal-organic deposition

Kais Daoudi, Tetsuo Tsuchiya, Iwao Yamaguchi, Takaaki Manabe, Susumu Mizuta, and Toshiya Kumagai

J. Appl. Phys. 98, 013507 (2005); http://dx.doi.org/10.1063/1.1943514 (6 pages) | Cited 9 times

Online Publication Date: 5 July 2005

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La0.7Ca0.3MnO3 (LCMO) thin films have been prepared on LaAlO3 and SrTiO3 (STO) (001) single-crystal substrates by the metal-organic deposition process. These films were characterized by transmission electron microscopy (TEM) and temperature dependence of the resistance R(T). The microstructure of the LCMO films and LCMO/substrate interfaces were investigated through cross-sectional TEM observations. High-resolution TEM (HRTEM) observations and electron-diffraction patterns demonstrate the (001) epitaxial growth on both the LAO and STO substrates. The local structure of the LCMO film depends on the type of substrate. HRTEM observations along the LCMO/STO interface display a good epitaxy throughout the entire film without any microstructural defects. On the contrary, in the LCMO film and in the region close to the LAO substrate, we note the presence of misfit dislocations and twins. The temperature coefficient of resistance (TCR) was calculated from the temperature dependence of the resistance measurements. The LCMO/LAO system exhibits a TCR value of 27.5%/K compared with the 10%/K measured for the LCMO/STO system.
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73.61.Ng Insulators
68.55.A- Nucleation and growth
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
75.70.Ak Magnetic properties of monolayers and thin films
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Mm Grain and twin boundaries

Pressure and temperature dependence of shear modulus and yield strength for aluminum, copper, and tungsten under shock compression

Jianxiang Peng, Fuqian Jing, Dahong Li, and Lili Wang

J. Appl. Phys. 98, 013508 (2005); http://dx.doi.org/10.1063/1.1943510 (3 pages) | Cited 5 times

Online Publication Date: 5 July 2005

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Experimental data for the shear modulus and yield strength of shocked aluminum, copper, and tungsten were systematically analyzed. Comparisons between these data and calculations using the Steinberg–Cochran–Guinan (SCG) constitutive model [ D. J. Steinberg, S. G. Cochran, and M. W. Guinan, J. Appl. Phys. 51, 1498 (1980) ] indicate that the yield strength has the same dependence on pressure and temperature as the shear modulus for aluminum for shock pressures up to 50 GPa, for copper to 100 GPa, and for tungsten to 200 GPa. Therefore, the assumption of Yp′/Y0 = Gp′/G0,YT′/Y0 = GT′/G0 is basically acceptable for these materials, and the SCG model can be used to describe the shear modulus and yield strength of the shocked material at high pressure and temperature.
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81.05.Bx Metals, semimetals, and alloys
62.50.-p High-pressure effects in solids and liquids
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.F- Deformation and plasticity

Polymer cholesteric liquid-crystal flake reorientation in an alternating-current electric field

T. Z. Kosc, K. L. Marshall, S. D. Jacobs, and J. C. Lambropoulos

J. Appl. Phys. 98, 013509 (2005); http://dx.doi.org/10.1063/1.1944221 (6 pages) | Cited 3 times

Online Publication Date: 5 July 2005

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The motion of highly dielectric polymer cholesteric liquid crystal (PCLC) flakes suspended in a host fluid can be controlled with an ac electric field. The electric field acts to induce a dipole moment on the flake due to interfacial, or Maxwell–Wagner, polarization. Theoretical modeling of PCLC flakes as oblate spheroids shows that the flakes will reorient to align one of the two major axes parallel to the electric field. The theory also supports the observed dependence of the particle reorientation time on the electric-field magnitude, frequency, and particle shape. A PCLC flake’s orientation determines its ability to reflect light of a specific wavelength and circular polarization. The ability to switch the position of PCLC flakes with an electric field has implications for electro-optic devices and display applications.
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61.30.Vx Polymer liquid crystals
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.25.H- Macromolecular and polymers solutions; polymer melts
77.22.Ej Polarization and depolarization

Delayed electroluminescence in small-molecule-based organic light-emitting diodes: Evidence for triplet-triplet annihilation and recombination-center-mediated light-generation mechanism

Zoran D. Popovic and Hany Aziz

J. Appl. Phys. 98, 013510 (2005); http://dx.doi.org/10.1063/1.1937472 (5 pages) | Cited 31 times

Online Publication Date: 5 July 2005

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We measured delayed electroluminescence in small-molecule-based organic light-emitting diodes based on N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine hole-transport molecule and tris(8-hydroxyquinoline) aluminum electron-transport and emitter molecule after the excitation currents are switched off and reverse bias applied to the sample. The experiments indicate that delayed light emission is a result of two distinct processes: emissive excited singlet-state generation by either triplet-triplet annihilation or recombination of trapped positive and negative charges in the device. Under reverse device bias these two mechanisms have distinctly different signatures. We also found that upon device aging, delayed light emission decreases faster (by about a factor of 4–5) than prompt electroluminescence, which is attributed to an increase of the triplet decay rate due to the presence of aging induced spin-½ trapped charges in the device.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
81.07.Nb Molecular nanostructures
85.65.+h Molecular electronic devices

Raman-scattering study of the InGaN alloy over the whole composition range

S. Hernández, R. Cuscó, D. Pastor, L. Artús, K. P. O’Donnell, R. W. Martin, I. M. Watson, Y. Nanishi, and E. Calleja

J. Appl. Phys. 98, 013511 (2005); http://dx.doi.org/10.1063/1.1940139 (5 pages) | Cited 23 times

Online Publication Date: 5 July 2005

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We present Raman-scattering measurements on InxGa1−xN over the entire composition range of the alloy. The frequencies of the A1(LO) and E2 modes are reported and show a good agreement with the one-mode behavior dispersion predicted by the modified random-element isodisplacement model. The A1(LO) mode displays a high intensity relative to the E2 mode due to resonant enhancement. For above band-gap excitation, the A1(LO) peak displays frequency shifts as a function of the excitation energy due to selective excitation of regions with different In contents, and strong multiphonon scattering up to 3LO is observed in outgoing resonance conditions.
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78.30.Fs III-V and II-VI semiconductors
78.66.Fd III-V semiconductors
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
63.20.K- Phonon interactions

Surface morphology and optical properties of thin films of thiophene-based binary blends

Marco Salerno, Robert Ian Renton Blyth, Julie Thompson, Roberto Cingolani, and Giuseppe Gigli

J. Appl. Phys. 98, 013512 (2005); http://dx.doi.org/10.1063/1.1944215 (5 pages)

Online Publication Date: 6 July 2005

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We report on the relationship between optical and morphological properties of thin films of a blend of thiophene-based monomer and a diamine derivative. This system is of interest as it gives rise to white emission, due to the formation of exciplex energy levels in the solid state. The photoluminescence emission has been collected for different relative concentrations of the two blend components, and the film topography has been mapped correspondingly by means of atomic force microscopy. Along with a complex evolution of the film surface morphology, a significant variation of the emission properties has been observed upon change of the blend composition. In particular, the intensity of the broad low-energy exciplex band turns out to be affected by a balance of two factors, namely, the extension of homogeneous blend film areas, and their effective concentration.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
81.05.Hd Other semiconductors
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.37.Ps Atomic force microscopy (AFM)
78.66.Qn Polymers; organic compounds
78.55.Kz Solid organic materials

Degeneracy of the thermal properties of buried structures

A. Salazar, F. Garrido, A. Oleaga, and R. Celorrio

J. Appl. Phys. 98, 013513 (2005); http://dx.doi.org/10.1063/1.1946914 (7 pages) | Cited 2 times

Online Publication Date: 6 July 2005

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In thermal wave physics the surface temperature of a material depends on the thermal diffusivity and thermal effusivity of the components. Therefore these thermal properties of buried structures are expected to be retrieved from the measurement of the surface temperature using photothermal techniques. Then, from the constitutive equations, thermal conductivity and specific heat of the inclusions can be calculated. In this paper we demonstrate analytically that when the thermal properties of the inclusions are very different from those of the matrix they are degenerate. Three kinds of inclusions have been studied: layers, cylinders, and spheres. If the transport thermal properties of the inclusion are much higher (much lower) than those of the matrix; only its specific heat (thermal effusivity) can be retrieved. On the other hand, for a gas inclusion only its thermal conductivity can be determined. Photothermal measurements performed on three calibrated samples containing buried cylinders confirm the theoretical conclusions.
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44.10.+i Heat conduction

Substrate influence on the growth of Co-doped La0.5Sr0.5TiO3−δ epitaxial thin films

R. Ranchal, M. Bibes, A. Barthélémy, K. Bouzehouane, S. Guyard, E. Jacquet, J.-P Contour, C. Pascanut, P. Berthet, and N. Dragoe

J. Appl. Phys. 98, 013514 (2005); http://dx.doi.org/10.1063/1.1938278 (5 pages) | Cited 8 times

Online Publication Date: 6 July 2005

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We report on the growth of thin films of the diluted magnetic oxide Co-doped La0.5Sr0.5TiO3−δ on SrTiO3 and LaAlO3 substrates. The films are ferromagnetic at room temperature, with no indications of parasite phases from high-resolution x-ray diffraction experiments. The structural mismatch with the substrate is shown to have a strong impact on the growth mechanisms and, consequently, on the surface morphology. In this sense, to grow the films on SrTiO3, for which the mismatch is minimized, appears to be more appropriate for the future integration of Co-doped La0.5Sr0.5TiO3−δ layers into heterostructures for perpendicular transport.
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75.50.Dd Nonmetallic ferromagnetic materials
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
75.70.Ak Magnetic properties of monolayers and thin films
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.72.up Other materials

The dependence of the radiation damage formation on the substrate implant temperature in GaN during Mg ion implantation

S. Whelan, M. J. Kelly, R. Gwilliam, C. Jeynes, and C. Bongiorno

J. Appl. Phys. 98, 013515 (2005); http://dx.doi.org/10.1063/1.1940142 (5 pages) | Cited 4 times

Online Publication Date: 6 July 2005

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In pursuit of p-type doping, we have implanted GaN with Mg ions at 200 and 500 keV with the substrate temperature maintained at −150 (cold) or +300 °C (hot) during ion irradiation. The samples have been annealed at 1000 °C postion implantation. The radiation damage peak position (and its profile), the dopant distribution, and the damage stability during annealing were all shown to be dependent upon the GaN substrate temperature during implantation. The damage peak position in the solid was reduced for cold implantation. The dopant distribution in the solid depends upon the implant temperature and in agreement with the damage measurements, the Mg range is shallower in GaN for cold implants when compared to hot implants. The trends observed suggest that the dynamic defect annealing rate during irradiation is reduced for cold implantation, and the subsequent increase in the damage level (scattering centers) formed during the damage buildup reduces the ion range in the solid. In turn, the reduced ion range subsequently limits the final damage range. The rate of damage removal during thermal annealing in the samples implanted at cold temperature was increased: this is explained by the greater complexity of defects caused during high-temperature implantation, due to the raised level of dynamic defect annealing.
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81.05.Ea III-V semiconductors
61.72.uj III-V and II-VI semiconductors
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.S- Impurities in crystals
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