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15 Jun 2003

Volume 93, Issue 12, pp. 9429-10148

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Relation between the molecular orientation of a liquid crystal monolayer and the underlying polyimide film exposed to linearly polarized ultraviolet light

Kiyoaki Usami, Kenji Sakamoto, and Sukekatsu Ushioda

J. Appl. Phys. 93, 9523 (2003); http://dx.doi.org/10.1063/1.1572548 (6 pages) | Cited 4 times

Online Publication Date: 30 May 2003

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We have determined the relation between the in-plane anisotropy of the molecular orientation of a liquid crystal (LC) monolayer and the underlying polyimide film exposed to linearly polarized ultraviolet light (LPUVL). To evaluate the anisotropy of the LC monolayer and the polyimide film, the sample orientation dependence of the polarized infrared absorption spectrum was measured. The in-plane anisotropy of the LC monolayer was found to be proportional to that of the polyimide film, the proportionality factor being about 75%. This result strongly suggests that the alignment of the LC molecules in contact with the LPUVL-exposed polyimide film is induced by an interaction between the polyimide and LC molecules. © 2003 American Institute of Physics.
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61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures

Laser-induced decompression shock development in fused silica

Junlan Wang, Richard L. Weaver, and Nancy R. Sottos

J. Appl. Phys. 93, 9529 (2003); http://dx.doi.org/10.1063/1.1574175 (8 pages) | Cited 9 times

Online Publication Date: 30 May 2003

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Laser-induced weak shock formation in fused silica is studied using standard wave mechanics and applied to thin-film laser spallation experiments. Due to the negative nonlinear elasticity of fused silica, a laser-induced Gaussian stress pulse evolves into a shock after traveling a certain distance in a fused silica substrate. Experimental observations confirm theoretical predictions of shock development. A decompression shock forms and greatly enhances interfacial failure of a thin film deposited on the substrate. The effects of laser fluence and substrate thickness (attenuation) on shock development are also investigated. © 2003 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
79.20.Ds Laser-beam impact phenomena
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators

Spectroscopic ellipsometry of thin film and bulk anatase (TiO2)

G. E. Jellison, L. A. Boatner, J. D. Budai, B.-S. Jeong, and D. P. Norton

J. Appl. Phys. 93, 9537 (2003); http://dx.doi.org/10.1063/1.1573737 (5 pages) | Cited 45 times

Online Publication Date: 30 May 2003

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Spectroscopic ellipsometry (SE) measurements were made on thin-film and single-crystal TiO2 anatase using a two-modulator generalized ellipsometer. The TiO2 films were epitaxially stabilized on a LaAlO3 substrate in the anatase crystal structure using reactive sputter deposition. The films were highly crystalline, possessing a “stepped surface” morphology indicative of atomic layer-by-layer growth. The SE results for the anatase film indicate that the material is essentially oriented with the c axis perpendicular to the substrate, but there is some anisotropy near the interface and the surface. Corrugations of the film surface, as observed using atomic force microscopy, are consistent with a surface structure needed to create cross polarization. Accurate values of the optical functions of crystalline anatase were obtained above and below the band edge using SE. Above the band edge, both the ordinary and extraordinary complex dielectric functions exhibited two critical points. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
78.66.Nk Insulators
77.55.-g Dielectric thin films
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
07.60.Fs Polarimeters and ellipsometers
61.66.Fn Inorganic compounds
68.35.B- Structure of clean surfaces (and surface reconstruction)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ch Permittivity (dielectric function)
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Micro-Raman study of electronic properties of inversion domains in GaN-based lateral polarity heterostructures

M. Park, J. J. Cuomo, B. J. Rodriguez, W.-C. Yang, R. J. Nemanich, and O. Ambacher

J. Appl. Phys. 93, 9542 (2003); http://dx.doi.org/10.1063/1.1570507 (6 pages) | Cited 14 times

Online Publication Date: 30 May 2003

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The electronic properties of inversion domains in a GaN-based lateral polarity heterostructure were investigated using micro-Raman spectroscopy. The piezoelectric polarization of each domain was calculated from strain determined via Raman scattering. The free carrier concentration and electron mobility were deduced from the longitudinal optical phonon–plasmon coupled mode. The electron concentration in the N-face domain was slightly higher than that in the Ga-face domain. It appears that during growth, a larger number of donor impurities may have been incorporated into the N-face domain than into the Ga-face domain. © 2003 American Institute of Physics.
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78.30.Fs III-V and II-VI semiconductors
73.20.At Surface states, band structure, electron density of states
81.05.Ea III-V semiconductors
78.66.Fd III-V semiconductors
73.61.Ey III-V semiconductors
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
77.65.-j Piezoelectricity and electromechanical effects
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.22.Ej Polarization and depolarization
73.50.Dn Low-field transport and mobility; piezoresistance
63.20.kk Phonon interactions with other quasiparticles
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons

Imaging subwavelength holes using an apertureless near-field scanning optical microscope

F. Formanek, Y. De Wilde, and L. Aigouy

J. Appl. Phys. 93, 9548 (2003); http://dx.doi.org/10.1063/1.1574178 (5 pages) | Cited 10 times

Online Publication Date: 30 May 2003

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We present investigations of the light scattered by subwavelength holes in a chromium film using an apertureless near-field scanning optical microscope, which operates either in the visible (λ=655 nm) or in the infrared (λ=10.6 μm). The near-field optical images exhibit patterns around the holes that seem to coincide with the component of the stray electrical field parallel to the tip axis. A tip–sample dipole coupling model provides a satisfactory description of the experimental data recorded in the infrared with light polarized normally to the sample surface. © 2003 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.37.Uv Near-field scanning microscopy and spectroscopy
78.66.Bz Metals and metallic alloys
07.79.Fc Near-field scanning optical microscopes

Physical and optical properties of sol-gel nano-silver doped silica film on glass substrate as a function of heat-treatment temperature

Wenyan Li, Sudipta Seal, Edward Megan, Jeff Ramsdell, Kirk Scammon, Gerald Lelong, Laurent Lachal, and Kathleen A. Richardson

J. Appl. Phys. 93, 9553 (2003); http://dx.doi.org/10.1063/1.1571215 (9 pages) | Cited 61 times

Online Publication Date: 30 May 2003

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Nano-silver doped silica films were deposited on glass slides using a sol-gel process and heat-treated at different temperatures. The films were characterized by ultraviolet-visible spectroscopy, x-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), Rutherford backscattering spectrometry (RBS), and transmission electron microscopy for their optical, chemical, and structural properties. The absorption peak of silver colloids (wavelength from 400 to 460 nm) was present and a blueshift and intensity reduction of the absorption peak was observed during heat-treatment. Particle size reduction and surface morphology changes in the films were observed by AFM as a function of varying heat treatment temperatures. Silver nanoparticles were formed through spontaneous reduction of silver ions. The oxidation of silver occurs during heat-treatment, causing a reduction of absorption intensity. An interdiffusion between the Ag in the film and Na in the substrate glass was observed by XPS and RBS. Sodium in the coating likely increased the stability of silver oxide at high temperature treated samples. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.40.Gh Other heat and thermomechanical treatments
78.66.Sq Composite materials
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.40.Ha Other nonmetallic inorganics
79.60.Jv Interfaces; heterostructures; nanostructures
68.37.Ps Atomic force microscopy (AFM)
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
68.37.Lp Transmission electron microscopy (TEM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Fx Diffusion; interface formation
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Wigner function modeling of quantum well semiconductor lasers using classical electromagnetic field coupling

Philip Weetman and Marek S. Wartak

J. Appl. Phys. 93, 9562 (2003); http://dx.doi.org/10.1063/1.1574180 (14 pages) | Cited 3 times

Online Publication Date: 30 May 2003

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A model of the quantum well laser is formulated using Wigner functions whose evolution is governed by the quantum Boltzmann equations. This model incorporates the heterostructure potential and electromagnetic interactions using a classical field approximation, scattering processes by simple Boltzmann scattering, and spontaneous emission by quantum Langevin theory. The quantum Boltzmann equations are derived from Heisenberg’s equation of motion and then simplified for practical purposes. Calculations are performed for a simplified test system in the steady state in order to illustrate some numerical techniques as well as results that can be obtained. Results shown are for the electron and hole densities and the self-consistent heterostructure potential with and without electromagnetic coupling, the output power versus energy, and the electron and hole currents versus position for two applied bias potentials. © 2003 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.)

Effect of liner thickness on electromigration lifetime

E. G. Liniger, C. -K. Hu, L. M. Gignac, and A. Simon

J. Appl. Phys. 93, 9576 (2003); http://dx.doi.org/10.1063/1.1575497 (7 pages) | Cited 15 times

Online Publication Date: 30 May 2003

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Electromigration lifetime was measured as a function of liner thickness for Cu/SiO2 interconnect structures. A significant increase in mean lifetime was observed for structures in which the liner thickness at the base of the test via was less than approximately 6 nm, with a current density <5 mA/μm2 in the power line connected to the test via. This is attributed to the continuous flow of Cu across the thin and possibly discontinuous liner at the base of the via. For extremely thin liner coverage, <1.4 nm at the base of the via and 2.5 at the bottom of the test line, the mean lifetime was observed to decrease as a rapid diffusion path was created which partially offset the beneficial effects of continuous flow. Failure distributions appeared to be trimodal and this was confirmed through failure analysis. In the case of thin liner coverage (<6 nm), early fails, which are typically characterized by slitlike voids at the via/line interface, were not observed. © 2003 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Qx Microcircuit quality, noise, performance, and failure analysis
66.30.Qa Electromigration
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Annealing-induced Ge/Si(100) island evolution

Yangting Zhang and Jeff Drucker

J. Appl. Phys. 93, 9583 (2003); http://dx.doi.org/10.1063/1.1575914 (8 pages) | Cited 15 times

Online Publication Date: 30 May 2003

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Ge/Si(100) islands were found to coarsen during in situ annealing at growth temperature. Islands were grown by molecular-beam epitaxy of pure Ge and annealed at substrate temperatures of T=450, 550, 600, and 650 °C, with Ge coverages of 6.5, 8.0, and 9.5 monolayers. Three coarsening mechanisms operate in this temperature range: wetting-layer consumption, conventional Ostwald ripening, and Si interdiffusion. For samples grown and annealed at T=450 °C, consumption of a metastably thick wetting layer causes rapid initial coarsening. Slower coarsening at longer annealing times occurs by conventional Ostwald ripening. Coarsening of samples grown and annealed at T=550 °C occurs via a combination of Si interdiffusion and conventional Ostwald ripening. For samples grown and annealed at T⩾600 °C, Ostwald ripening of SiGe alloy clusters appears to be the dominant coarsening mechanism. © 2003 American Institute of Physics.
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68.55.Nq Composition and phase identification
61.72.Cc Kinetics of defect formation and annealing
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Cy Elemental semiconductors
68.35.Fx Diffusion; interface formation

Growth diagram and morphologies of AlN thin films grown by molecular beam epitaxy

G. Koblmueller, R. Averbeck, L. Geelhaar, H. Riechert, W. Hösler, and P. Pongratz

J. Appl. Phys. 93, 9591 (2003); http://dx.doi.org/10.1063/1.1575929 (6 pages) | Cited 38 times

Online Publication Date: 30 May 2003

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A growth diagram for molecular beam epitaxy of AlN on sapphire and 6H–SiC was established using reflection high energy electron diffraction, atomic force microscopy, and Rutherford backscattering spectrometry. In varying the Al/N ratio and growth temperature, distinctive surface morphologies emerge, which are assigned to three regimes of growth, one N-rich (Al/N<1) and two Al-rich (Al/N>1) regimes. Under N-rich conditions, AlN films exhibit rough surface morphologies. In contrast, Al-rich conditions produce excellent smooth surface morphologies, but with the constraint of Al droplet formation at very high Al/N ratios and low temperatures. The differentiation between N-rich and Al-rich regimes is given only by the Al/N ratio, while the two Al-rich regimes (intermediate self-regulated and droplet regime) are separated by the boundary line of Al droplet formation. For this boundary an Arrhenius dependence of growth temperature was found, yielding an activation energy of 3.4±0.1 eV. The observed morphology transitions are attributed to varying surface adatom mobilities present under the different Al/N ratios. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Fx Diffusion; interface formation
68.37.Ps Atomic force microscopy (AFM)
82.80.Yc Rutherford backscattering (RBS), and other methods of chemical analysis

Improved brightness and efficiency in Ce codoped ZnS:TbOF electroluminescent thin films

J. P. Kim, M. R. Davidson, and P. H. Holloway

J. Appl. Phys. 93, 9597 (2003); http://dx.doi.org/10.1063/1.1574592 (7 pages) | Cited 4 times

Online Publication Date: 30 May 2003

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ZnS:TbOF alternating current thin film electroluminescent devices codoped with Ce by rf magnetron sputtering were shown to be brighter than Tb singly doped films. This brightness improvement is shown to results predominantly from increased radiative efficiency, with a secondary improvement in excitation efficiency. At 20 V above threshold for electroluminescence, V20, the radiative efficiency of Ce codoped films is improved ≈130%. The nonlinear exponential decay and improved efficiency of electroluminescent emission for Ce codoped films is attributed to energy transfer from Ce+3 to Tb+3 luminescent centers. The improved excitation efficiency is attributed to reduced space charge. © 2003 American Institute of Physics.
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78.60.Fi Electroluminescence
78.66.Hf II-VI semiconductors
71.55.Gs II-VI semiconductors

Surface acoustic wave propagation characteristics of aluminum nitride thin films grown on polycrystalline diamond

G. F. Iriarte

J. Appl. Phys. 93, 9604 (2003); http://dx.doi.org/10.1063/1.1574172 (6 pages) | Cited 19 times

Online Publication Date: 30 May 2003

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Diamond has the highest surface acoustic wave (SAW) velocity among all materials and thus provides substantial advantages for the fabrication of high-frequency SAW devices when combined with a piezoelectric thin film. The properties of layered film structures consisting of a piezoelectric material layer, aluminum nitride (AlN), and a polycrystalline diamond layer grown on a silicon substrate have been examined. Highly textured AlN thin films have been sputter-deposited onto polycrystalline diamond substrates at room temperature. X-ray diffraction analysis of the multilayer structure as well as atomic force microscope images of the AlN surface indicate that the deposited AlN films were c-axis oriented with a full width at half maximum of the rocking curve of the AlN-002-peak of 2.1°. The thickness of the AlN layer was of 4.3 μm, whereas the diamond layer was 50 μm thick and resting on a 3-in Si wafer. Standard one-port SAW resonators with aluminum (Al) metallization have been subsequently fabricated and evaluated. Experimental results indicate that the fundamental as well as higher Rayleigh SAW modes are excited. Thus, the phase velocities of the first, second, third, and fourth mode are found to be 6.850, 10.000, 11.800, and 14.450 m/s respectively. A very good out-of-band rejection of −50 dB was obtained. © 2003 American Institute of Physics.
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77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
43.35.Pt Surface waves in solids and liquids
68.35.Iv Acoustical properties
77.55.-g Dielectric thin films
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
68.65.Ac Multilayers
68.47.Fg Semiconductor surfaces
68.37.Ps Atomic force microscopy (AFM)

Broadband photopyroelectric thermal spectroscopy of a supercooled liquid near the glass transition

E. H. Bentefour, C. Glorieux, M. Chirtoc, and J. Thoen

J. Appl. Phys. 93, 9610 (2003); http://dx.doi.org/10.1063/1.1576300 (5 pages) | Cited 6 times

Online Publication Date: 30 May 2003

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Using different photopyroelectric configurations, we have experimentally studied the frequency dependence of the thermal properties of the glass former glycerol near its glass transition. With our method, an unambiguous and separate determination of the frequency dependence of the specific heat capacity and the thermal conductivity is possible. Within experimental uncertainty, in the frequency range from 0.1 Hz to 1100 Hz, unlike the specific heat capacity, the thermal conductivity of glycerol does not show any frequency dependence through the glass transition region. We have also extended the thermal spectroscopy frequency range to 100 kHz, which is one decade higher than other methods. © 2003 American Institute of Physics.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
77.70.+a Pyroelectric and electrocaloric effects
66.25.+g Thermal conduction in nonmetallic liquids
65.20.-w Thermal properties of liquids
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Band-tail characteristics in polysilicon

J. H. Sun, W. Z. Shen, and F. Y. Meng

J. Appl. Phys. 93, 9615 (2003); http://dx.doi.org/10.1063/1.1576303 (5 pages) | Cited 2 times

Online Publication Date: 30 May 2003

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The temperature- and growth-dependent Urbach band-tail characteristics in polysilicon wafers have been investigated both experimentally and theoretically for the improvement of solar cells. The band-tail parameter in polysilicon has been obtained by temperature-dependent transmission spectra, with the aid of a detailed calculation of the transmission profile. The band-tail parameter is in the range of 30–90 meV in polysilicon. A band-tail model based on the calculation of density of occupied states and the carrier–phonon interaction has been employed to analyze the temperature-dependent band-tail characteristics. It is found that the yielded structural information can be well explained by Raman measurements. We have correlated various aspects of the observed structural properties, such as the band-tail parameter, trap concentration, grain–surface charge density, and correlation length, with the conversion efficiency of the polysilicon solar cells. © 2003 American Institute of Physics.
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71.20.Mq Elemental semiconductors
84.60.Jt Photoelectric conversion
78.40.Fy Semiconductors
78.30.Am Elemental semiconductors and insulators
63.20.K- Phonon interactions

Kinetics of highly spin-polarized electron photoemission from an InGaAlAs strained layer by energy and spin-resolved measurements

Yu. Mamaev, H.-J. Drouhin, G. Lampel, A. Subashiev, Yu. Yashin, and A. Rochansky

J. Appl. Phys. 93, 9620 (2003); http://dx.doi.org/10.1063/1.1575919 (5 pages) | Cited 1 time

Online Publication Date: 30 May 2003

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High-resolution energy distribution curves and spin polarization versus energy distribution curves from an AlInGaAs layer, capped by a heavily doped thin GaAs quantum well layer has been measured. Polarization P of up to 83% in conjunction with quantum yield Y=0.5% at T=130 K has been obtained. These results are compared to polarization and quantum yield spectra at high excitation power. The narrow-band quantum well is shown to provide large effective negative electron affinity values with no harm to electron polarization. The studies in linear and nonlinear excitation regimes bring insight into the kinetics of photoemission and favor the photoemission model with elastic electron tunneling through the surface barrier. © 2003 American Institute of Physics.
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79.60.Jv Interfaces; heterostructures; nanostructures
68.47.Fg Semiconductor surfaces
73.21.Cd Superlattices
73.40.Gk Tunneling
73.21.Fg Quantum wells

Dynamical analysis of relaxation luminescence in ZnS:Er3+ thin film devices

Yu-Jiang Wang, Chen-Xu Wu, Mou-Zhi Chen, and Mei-Chun Huang

J. Appl. Phys. 93, 9625 (2003); http://dx.doi.org/10.1063/1.1574597 (5 pages) | Cited 2 times

Online Publication Date: 30 May 2003

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The relaxation luminescence of ZnS:Er3+ thin film devices fabricated by thermal evaporation with two boats is studied. The dynamical processes of the luminescence of Er3+ in ZnS are described in terms of a resonant energy transfer model, assuming that the probability of collision excitation of injected electrons with luminescence centers is expressed as a Gaussian function. It is found that the frequency distribution depends on the Lorentzian function by considering the emission from excited states as a damped oscillator. Taking into consideration the energy storing effect of traps, an expression is obtained to describe a profile that contains multiple relaxation luminescence peaks using the convolution theorem. Fitting of experimental results shows that the relaxation characteristics of the electroluminescence are related to the carriers captured by bulk traps as well as by interface states. The numerical calculation carried out agrees well with the dynamical characteristics of relaxation luminescence obtained by experiments. © 2003 American Institute of Physics.
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78.66.Hf II-VI semiconductors
78.60.Fi Electroluminescence
73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.15.Qe Excited states: methodology
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Field-induced microdomain liquid-crystal display modes

Hiroshi Ohno, Hiroyuki Okada, and Hiroyoshi Onnagawa

J. Appl. Phys. 93, 9630 (2003); http://dx.doi.org/10.1063/1.1576305 (4 pages)

Online Publication Date: 30 May 2003

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The electro-optical characteristics of field-induced microdomain liquid-crystal display modes are investigated. One side of the substrate has radial electrodes and the other side has concentric electrodes. Large numbers of multidomain structures are induced in one pixel. The electric field gradually decreases from the center to the outer multidomains due to the radial electrodes. The contrast ratio of the homeotropic alignment cell is 210:1. Symmetric viewing angle characteristics without gray scale inversion are also obtained. © 2003 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
78.20.Jq Electro-optical effects
42.70.Df Liquid crystals

Observation of population transfer to dark exciton states by using spin-diffracted four-wave mixing

O. Ikeuchi, S. Adachi, H. Sasakura, and S. Muto

J. Appl. Phys. 93, 9634 (2003); http://dx.doi.org/10.1063/1.1575920 (5 pages) | Cited 6 times

Online Publication Date: 30 May 2003

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We observed the exciton spin dynamical processes in GaAs quantum wells at low temperatures by three-pulse spin-diffracted four-wave mixing measurements. After investigating the merits and demerits of this method as compared with the pump–probe method, we discuss the excitation power dependence of exciton spin relaxation and the population transfer to the dark states. © 2003 American Institute of Physics.
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73.21.Fg Quantum wells
71.35.Gg Exciton-mediated interactions
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
78.67.De Quantum wells

High pressure behavior of titanium–silicon carbide (Ti3SiC2)

J. L. Jordan, T. Sekine, T. Kobayashi, X. Li, N. N. Thadhani, T. El-Raghy, and M. W. Barsoum

J. Appl. Phys. 93, 9639 (2003); http://dx.doi.org/10.1063/1.1573345 (5 pages) | Cited 11 times

Online Publication Date: 30 May 2003

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The dynamic high-pressure behavior and phase stability of titanium–silicon carbide (Ti3SiC2), a unique ceramic having metal-like properties, was investigated in this study. Time-resolved measurements of the Hugoniot equation of state, employing a plate impact geometry, were conducted on the Ti3SiC2 samples in the pressure range of 50–120 GPa using a two stage light gas gun. At pressures around 90–120 GPa, Ti3SiC2 was found to transform to a more compressed state. Shock-recovery experiments were also performed on Ti3SiC2 powders at impact velocities of 1.5–2 km/s using a single capsule geometry, with and without the addition of copper powder to vary the shock-loading pressure (calculated to be 22–58 GPa) and temperature (calculated to be up to 3250 °C) in the sample. No evidence of shock-induced decomposition was observed in these recovery experiments performed on the Ti3SiC2 powders. © 2003 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
81.40.Vw Pressure treatment
64.30.-t Equations of state of specific substances
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Model for high-strain-rate deformation of uranium–niobium alloys

F. L. Addessio, Q. H. Zuo, T. A. Mason, and L. C. Brinson

J. Appl. Phys. 93, 9644 (2003); http://dx.doi.org/10.1063/1.1576302 (11 pages) | Cited 5 times

Online Publication Date: 30 May 2003

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A thermodynamic approach is used to develop a framework for modeling uranium–niobium alloys under the conditions of high-strain rate. Using this framework, a three-dimensional phenomenological model, which includes nonlinear elasticity (equation of state), phase transformation, crystal reorientation, rate-dependent plasticity, and porosity growth, is presented. An implicit numerical technique is used to solve the evolution equations for the material state. Comparisons are made between the model and data for low-strain rate loading and unloading as well as heating and cooling experiments. Comparisons of the model and data also are made for low- and high-strain-rate uniaxial stress and uniaxial strain experiments. A uranium–6 wt % niobium alloy is used in comparisons of the model and experiment. © 2003 American Institute of Physics.
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81.05.Bx Metals, semimetals, and alloys
81.40.Lm Deformation, plasticity, and creep
64.30.-t Equations of state of specific substances
81.30.Kf Martensitic transformations
65.40.G- Other thermodynamical quantities
81.30.Bx Phase diagrams of metals, alloys, and oxides
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.F- Deformation and plasticity
62.20.D- Elasticity
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions

Optical studies of strained type II GaAs0.7Sb0.3/GaAs multiple quantum wells

T. T. Chen, C. H. Chen, W. Z. Cheng, W. S. Su, M. H. Ya, Y. F. Chen, P. W. Liu, and H. H. Lin

J. Appl. Phys. 93, 9655 (2003); http://dx.doi.org/10.1063/1.1576497 (4 pages) | Cited 8 times

Online Publication Date: 30 May 2003

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We report a detailed investigation on the optical transitions of strained type II GaAs0.7Sb0.3/GaAs (100) multiple quantum wells. For the theoretical calculations, both of the elastic deformational potential of intrinsic compressive biaxial strain, and quantum confinement effects are included. The asymmetric photoluminescence spectra reveal the features of excited state transition and quantum confinement Stark effect at high and low temperatures, respectively. The asymmetry features have also been investigated and confirmed by low-temperature photoluminescence experiments under different excitation power. From polarized photoluminescence excitation and photoconductivity spectra, both of the type I and type II optical transitions can also be clearly identified. © 2003 American Institute of Physics.
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78.67.De Quantum wells
68.65.Fg Quantum wells
73.21.Fg Quantum wells
78.55.Cr III-V semiconductors
73.63.Hs Quantum wells
78.20.Jq Electro-optical effects
73.50.Pz Photoconduction and photovoltaic effects

Spin-dependent recombination electron paramagnetic resonance spectroscopy of defects in irradiated silicon detectors

V. Eremin, D. S. Poloskin, E. Verbitskaya, M. P. Vlasenko, L. S. Vlasenko, R. Laiho, and T. O. Niinikoski

J. Appl. Phys. 93, 9659 (2003); http://dx.doi.org/10.1063/1.1576488 (6 pages) | Cited 2 times

Online Publication Date: 30 May 2003

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Spin-dependent recombination (SDR) electron paramagnetic resonance (EPR) spectroscopy is applied for investigation of paramagnetic recombination centers in irradiated silicon p−n junction detectors (diodes) formed on float-zone (FZ) silicon wafers. The main radiation defects, associated with SRD-EPR spectra arising from excited triplet states, are assigned to complexes of two substitutional carbon atoms and one interstitial silicon atom (CS+SiI+CS) and to oxygen + vacancy (O+V) complexes (A-centers). In spite of the low concentration of oxygen in FZ silicon the A-centers are found to play an important role in the recombination process in the diodes. At temperatures T<100 K the SDR-EPR spectra are well observable by measurements of the microwave conductivity or by detecting a dc forward current IF below a forward-blocking voltage UFBL. At UFBL the IF has a steep jump followed by a decrease of the voltage over the diode and a negative resistance region with oscillations of the current. The SDR-EPR spectrum arising from the (CS+SiI+CS) complexes was found to decrease strongly in the forward biased diodes. This effect can be attributed to coexistence of two different configurations of the carbon related defect in the bulk n-type region of the diodes. © 2003 American Institute of Physics.
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76.30.Mi Color centers and other defects
29.40.Wk Solid-state detectors
61.72.J- Point defects and defect clusters
71.35.-y Excitons and related phenomena

Effect of (10math0) crystal orientation on many-body optical gain of wurtzite InGaN/GaN quantum well

Seoung-Hwan Park

J. Appl. Phys. 93, 9665 (2003); http://dx.doi.org/10.1063/1.1577402 (4 pages) | Cited 4 times

Online Publication Date: 30 May 2003

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The optical properties of (10math0)-oriented wurtzite (WZ) InGaN/GaN quantum well (QW) lasers are investigated using the multiband effective-mass theory and the non-Markovian gain model with many-body effects. These results are also compared with those of (0001)-oriented WZ InGaN/GaN QW with piezoelectric and spontaneous polarizations taken into account. The optical gain of the (10math0)-oriented QW is largely enhanced over that of the (0001)-oriented QW. This can be explained by the fact that the optical matrix elements near the band edge (k=0) of the (10math0)-oriented InGaN/GaN QW significantly increase compared to that of the (0001)-oriented structure, in addition to the reduction of the effective mass. The threshold current density Jth of the (10math0)-oriented QW is expected to be about half that of the (0001)-oriented QW structure. © 2003 American Institute of Physics.
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78.67.De Quantum wells
73.21.Fg Quantum wells
42.55.Px Semiconductor lasers; laser diodes
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
77.22.Ej Polarization and depolarization
77.65.Ly Strain-induced piezoelectric fields
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Optical characterization of polymer dispersed liquid crystals for holographic recording

D. E. Lucchetta, L. Criante, and F. Simoni

J. Appl. Phys. 93, 9669 (2003); http://dx.doi.org/10.1063/1.1576899 (6 pages) | Cited 24 times

Online Publication Date: 30 May 2003

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In this study we present an extended investigation made on holographic polymer dispersed liquid crystals. A spectroscopic study of the photosensitive mixtures during the polymerization and phase separation process was performed, and an optical characterization of the recorded phase gratings was carried out using two alternative methods. The behavior of the diffraction efficiency of the transmission phase gratings versus time, angle of incidence, and wavelength was experimentally determined, and the results were successfully analyzed using the available theories for anisotropic phase gratings. Finally, the electro-optical properties concerning the beam deflection and response times were measured. © 2003 American Institute of Physics.
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42.40.Lx Diffraction efficiency, resolution, and other hologram characteristics
42.40.Eq Holographic optical elements; holographic gratings
42.70.Df Liquid crystals
42.70.Jk Polymers and organics
61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems
82.35.Ej Nonlinear optics with polymers
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
42.40.Ht Hologram recording and readout methods
42.70.Ln Holographic recording materials; optical storage media
64.75.-g Phase equilibria
78.20.Jq Electro-optical effects
42.79.Kr Display devices, liquid-crystal devices

Guiding characteristics of surface acoustic waves visualized using photoluminescence quenching

Y. Takagaki, M. Ramsteiner, and K. H. Ploog

J. Appl. Phys. 93, 9675 (2003); http://dx.doi.org/10.1063/1.1576900 (4 pages) | Cited 2 times

Online Publication Date: 30 May 2003

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We restrict the surface acoustic wave (SAW) propagation on a GaAs surface within a waveguide by means of reduction of the SAW velocity realized by metal gratings. The spatial variation of the SAW amplitude is evaluated by mapping the efficiency of the quenching of photoluminescence by the SAWs. Confinement of the SAWs is accomplished at a frequency of 1.4 GHz when the angle of SAW incidence with respect to the waveguide boundary is kept less than ∼10° for SAW velocity reduction of 4%. Mapping also reveals interference stripes associated with the SAWs bounce at the waveguide boundary. © 2003 American Institute of Physics.
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68.35.Iv Acoustical properties
78.55.Cr III-V semiconductors
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