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15 Mar 2003

Volume 93, Issue 6, pp. 3137-3682

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Spectra and energy levels of Er3+(4f11) in Gd3Ga5O12

John B. Gruber, Dhiraj K. Sardar, Bahram Zandi, J. Andrew Hutchinson, and C. Ward Trussell

J. Appl. Phys. 93, 3137 (2003); http://dx.doi.org/10.1063/1.1544647 (4 pages) | Cited 7 times

Online Publication Date: 5 March 2003

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A detailed crystal-field splitting analysis is presented for the energy levels of Er3+(4f11) incorporated into Gd3Ga5O12 single crystals. Spectra are reported between 1600 and 350 nm and were observed at temperatures between 8 K and room temperature. It is most likely that Er3+ ions substitute for Gd3+ ions in cationic sites of D2 symmetry in the cubic garnet host. A parameterized model Hamiltonian including atomic and crystal-field terms is diagonalized over the entire electronic configuration of Er3+(4f11). The diagonalization of the total energy matrix accounts for the intrinsic J–J mixing between states described in terms of the basis set of SLJMJ wave functions. The resolved absorption spectra, representing some 120 transitions from the ground state, 4I15/2, to excited multiplet manifolds, 2s+1LJ, are compared with calculated Stark levels. A final standard deviation of 5.3 cm−1 is obtained between 60 calculated and experimental Stark levels. © 2003 American Institute of Physics.
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71.55.Ht Other nonmetals
71.70.Ch Crystal and ligand fields
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.30.Hv Other nonmetallic inorganics

Emission characteristics of vapor transport equilibrated Er:LiNbO3 crystals

De-Long Zhang and E. Y. B. Pun

J. Appl. Phys. 93, 3141 (2003); http://dx.doi.org/10.1063/1.1543241 (11 pages) | Cited 22 times

Online Publication Date: 5 March 2003

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At room temperature, polarized visible and near infrared emission characteristics of 488 nm pumped vapor transport equilibration (VTE) treated Er:LiNbO3 crystals were investigated in comparison with the corresponding as-grown ones. The observed characteristics of the VTE crystal, whether it precipitates or not, include the retained polarization dependence, slight shift (less than 5 Å) of peak position, narrowing of some individual emission peaks, the appearance of additional emission peak near 1536.5 nm and the about 10% lengthening of 1.5 μm lifetime. In addition, in the case of lower Er doping level, the spectral shape are well reserved for the VTE crystals and no obvious changes in both visible and IR emission intensity. On the other hand, for those highly doped crystals, the VTE treatment not only results in a definite change of relative intensity between some emission peaks in IR region, but also causes the drop of both visible and IR emission intensity. Combining with the related absorption characteristic allow to conclude that the drop of the emission intensity results from the scattering of the nanocrystalline grains inside these crystals formed by VTE treatment. © 2003 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials

Temperature and injection current dependence of electroluminescence intensity in green and blue InGaN single-quantum-well light-emitting diodes

A. Hori, D. Yasunaga, A. Satake, and K. Fujiwara

J. Appl. Phys. 93, 3152 (2003); http://dx.doi.org/10.1063/1.1554475 (6 pages) | Cited 31 times

Online Publication Date: 5 March 2003

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Temperature and injection current dependence of electroluminescence (EL) spectral intensity of the superbright green and blue InGaN single-quantum-well (SQW) light-emitting diodes has been studied over a wide temperature range (T=15−300 K) and as a function of injection current level (0.1–10 mA). It is found that, when temperature is slightly decreased to 140 K, the EL intensity efficiently increases in both cases, as usually seen due to the improved quantum efficiency. However, with further decrease of temperature down to 15 K, unusual reduction of the EL intensity is commonly observed for both of the two diodes. At low temperatures the integrated EL intensity shows a clear trend of saturation with current, accompanying decreases of the EL differential quantum efficiency. We attribute the EL reduction due to trapping of injected carriers by nonradiative recombination centers. Its dependence on temperature and current shows a striking difference between the green and blue SQW diodes. That is, we find that the blue InGaN SQW diode with a smaller In concentration shows more drastic reduction of the EL intensity at lower temperatures and at higher currents than the green one. This unusual evolution of the EL intensity with temperature and current is due to less efficient carrier capturing by SQW. The carrier capture in the green and blue diodes also shows a keen difference owing to the different In content in the InGaN well. These results are analyzed within a context of rate equation model, assuming a finite number of radiative recombination centers. Importance of the efficient carrier capture processes by localized tail states within SQW at 180–300 K is thus pointed out for explaining the observed enhancement of radiative recombination of injected carriers in the presence of high-density misfit dislocations. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices

Fast gas spectroscopy using pulsed quantum cascade lasers

T. Beyer, M. Braun, and A. Lambrecht

J. Appl. Phys. 93, 3158 (2003); http://dx.doi.org/10.1063/1.1555271 (3 pages) | Cited 43 times

Online Publication Date: 5 March 2003

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Laser spectroscopy has found many industrial applications, e.g., control of automotive exhaust and process monitoring. The midinfrared region is of special interest because it has stronger absorption lines compared to the near infrared (NIR). However, in the NIR high quality reliable laser sources, detectors, and passive optical components are available. A quantum cascade laser could change this situation if fundamental advantages can be exploited with compact and reliable systems. It will be shown that, using pulsed lasers and available fast detectors, lower residual sensitivity levels than in corresponding NIR systems can be achieved. The stability is sufficient for industrial applications. © 2003 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.62.Fi Laser spectroscopy
42.62.Cf Industrial applications
42.60.By Design of specific laser systems
07.57.Ty Infrared spectrometers, auxiliary equipment, and techniques

X-ray investigations of formation efficiency of buried azobenzene polymer density gratings

Thomas M. Geue, Marina G. Saphiannikova, Oliver Henneberg, Ullrich Pietsch, Paul L. Rochon, and Almeria L. Natansohn

J. Appl. Phys. 93, 3161 (2003); http://dx.doi.org/10.1063/1.1554753 (6 pages) | Cited 7 times

Online Publication Date: 5 March 2003

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We present the results of time-dependent x-ray scattering measurements during the formation of a buried, modulated density structure below polymer film surface created at temperatures above the glass transition temperature TG during the thermal erasure of a holographically written surface relief grating. The surface relief gratings are initially formed on polymer films containing azobenzene side groups by exposure to a polarization holographic pattern made using light at 488 nm. The material responds to the actinic light by forming a sinusoidal surface relief pattern in a one-step process. Theoretical predictions show that the surface relief grating formation is accompanied by a density grating just below the film surface. Upon annealing above polymers glass transition temperature the surface relief grating melts while some of the density modulation in the bulk remains and a nonsinusoidal density grating is rebuilt after long term annealing at a temperature approximately 30 K above the glass transition temperature. The growth of density volume structure is assisted by exposure to red laser light during annealing. The observed homopolymer pDR1M was found to be the most effective material to build the modulated buried density grating. This might be due to the formation of clusters below the former peak positions of the surface relief grating. A quantitative description and preliminary model is given for this behavior. © 2003 American Institute of Physics.
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42.40.Eq Holographic optical elements; holographic gratings
61.41.+e Polymers, elastomers, and plastics
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
78.70.Ck X-ray scattering
68.55.-a Thin film structure and morphology

Unintended filtering in a typical photodiode detection system for optical tweezers

Kirstine Berg-Sørensen, Lene Oddershede, Ernst-Ludwig Florin, and Henrik Flyvbjerg

J. Appl. Phys. 93, 3167 (2003); http://dx.doi.org/10.1063/1.1554755 (10 pages) | Cited 28 times

Online Publication Date: 5 March 2003

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We characterize the frequency-dependent response of a photo detection system based on a Si-PIN photodiode and a laser with wavelength 1064 nm, a system commonly used with optical tweezers. We chopped the laser beam with chopper frequencies from 200 Hz to 14 kHz, and found an exponentially delayed response of the detection system with a characteristic delay time of ∼20 μs. The physical mechanism causing this time delay is silicon’s transparency to 1064 nm light: Photons are absorbed and create charge carriers not only in the diode’s depletion layer, where they are detected within nano-seconds, but predominantly in the n-layer, where they remain undetected till transported out by thermal diffusion. The diode’s response is dominated by this delay which can be characterized as a first-order low-pass filter with a 3dB-frequency of 8–9 kHz, depending on laser intensity. Measurements exploiting frequencies near or above this 3dB-frequency must be corrected for this unintended filter effect. We describe how to do this, and how to diagnose other systems which may or may not have the same problem. Explanations are intended for users of photo detection systems, and present the little semi-conductor physics needed to make sense. © 2003 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
37.10.Vz Mechanical effects of light on atoms, molecules, and ions
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
85.60.Dw Photodiodes; phototransistors; photoresistors
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

2.5–3.5 μm optically pumped GaInSb/AlGaInSb multiple quantum well lasers grown on AlInSb metamorphic buffer layers

E. A. Pease, L. R. Dawson, L. G. Vaughn, P. Rotella, and L. F. Lester

J. Appl. Phys. 93, 3177 (2003); http://dx.doi.org/10.1063/1.1544425 (5 pages) | Cited 9 times

Online Publication Date: 5 March 2003

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Room-temperature emission is observed as long as 3.26 μm in optically pumped type-I quantum well lasers on relaxed epitaxial layers grown by molecular-beam epitaxy. A superlattice is used to filter dislocations in the metamorphic buffer to reduce Shockley–Read–Hall losses. The longest wavelength emission of 3.45 μm from these structures is observed at 170 K, and the brightest room-temperature laser emits 0.5 W/facet peak power at 2.81 μm. It has a low threshold power density of 169 W/cm2 and a differential quantum efficiency of 28%. The characteristic temperatures, T0 and T1, are 119 K and 171 K, respectively. Stimulated emission is observed in this sample at a maximum operating temperature of 370 K. © 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.)
81.07.St Quantum wells
78.67.De Quantum wells
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
78.45.+h Stimulated emission
78.55.Cr III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Controlled excitation of electromagnetic band-gap line and point defect modes at microwave frequencies

M. Schuster and N. Klein

J. Appl. Phys. 93, 3182 (2003); http://dx.doi.org/10.1063/1.1554490 (6 pages) | Cited 7 times

Online Publication Date: 5 March 2003

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We report on the controlled excitation of line and point defect modes in a two-dimensional hexagonal electromagnetic band-gap structure made of rods of dielectric material (aluminium oxide). We compared simulation performed with a numerical field simulation software and experimental measurements at microwave frequencies with regard to coupling from external waveguides to line defects and subsequent coupling to resonant modes. We observed that for a line defect in the photonic crystal the impedance matching to a waveguide is strongly dependent on the defect width. We furthermore demonstrated that the coupling to a localized defect resonance can be strongly influenced by the variation of certain single lattice elements, affecting transmission behavior and quality factor of the resonant modes. © 2003 American Institute of Physics.
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84.40.Az Waveguides, transmission lines, striplines
41.20.Jb Electromagnetic wave propagation; radiowave propagation
42.70.Qs Photonic bandgap materials
02.60.-x Numerical approximation and analysis

Photonic band structures for three-dimensionally periodic arrays of coated spheres

Hiroyuki Takeda and Katsumi Yoshino

J. Appl. Phys. 93, 3188 (2003); http://dx.doi.org/10.1063/1.1556189 (6 pages) | Cited 7 times

Online Publication Date: 5 March 2003

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Photonic band structures of three-dimensional periodic structures of opals composed of nanoscale spheres coated with various materials have been studied theoretically. Opals composed of silica spheres coated with different materials can have smaller and larger band gaps at the L and X points, respectively, in the Brillouin zone of the face-centered cubic structure, although the magnitude of the gap at the X point is generally much smaller than that at the L point in conventional opals. Moreover, such a behavior can be explained by applying the same method as the free electron approximation in solid-state physics to photonic crystals. These phenomena may be suitable for practical application of photonic crystals even when the refractive indices of the materials are low. © 2003 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Designing strain-balanced GaN/AlGaN quantum well structures: Application to intersubband devices at 1.3 and 1.55 μm wavelengths

V. D. Jovanović, Z. Ikonić, D. Indjin, P. Harrison, V. Milanović, and R. A. Soref

J. Appl. Phys. 93, 3194 (2003); http://dx.doi.org/10.1063/1.1556177 (4 pages) | Cited 17 times

Online Publication Date: 5 March 2003

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A criterion for strain balancing of wurtzite group-III nitride-based multilayer heterostructures is presented. Single and double strain-balanced GaN/AlGaN quantum well structures are considered with regard to their potential application in optoelectronic devices working at communication wavelengths. The results for realizable, strain-balanced structures are presented in the form of design diagrams that give both the intersubband transition energies and the dipole matrix elements in terms of the structural parameters. The optimal parameters for structures operating at λ∼1.3 and 1.55 μm were extracted and a basic proposal is given for a three level intersubband laser system emitting at 1.55μm and depopulating via resonant longitudinal optical (LO) phonons (ℏωLO≈90 meV). © 2003 American Institute of Physics.
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68.65.Fg Quantum wells
73.21.Fg Quantum wells
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.55.Px Semiconductor lasers; laser diodes
78.67.De Quantum wells
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
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Numerical modeling of capacitively coupled hydrogen plasmas: Effects of frequency and pressure

T. Novikova, B. Kalache, P. Bulkin, K. Hassouni, W. Morscheidt, and P. Roca i Cabarrocas

J. Appl. Phys. 93, 3198 (2003); http://dx.doi.org/10.1063/1.1555678 (9 pages) | Cited 21 times

Online Publication Date: 5 March 2003

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In the field of plasma deposition of amorphous and microcrystalline silicon, the increase of the excitation frequency has often been considered as a way to enhance the deposition rate. Moreover, the increase of pressure has also been shown to enhance the deposition rate and improve the film properties. We attempt to clarify the effects of frequency in the 13.56–40.68 MHz range and to compare them to those of the pressure in the range of 0.5–1.5 Torr. For that purpose we use a numerical modeling of capacitively coupled hydrogen plasma, particularly relevant for the deposition of microcrystalline silicon. We use a one-dimensional time-dependent fluid model for the description of neutrals, positive and negative ions, and electrons, which involves a chemistry model taking into account 32 reactions in the gas phase and on the surface of the electrodes. The results of the model for the symmetrical system show that both pressure and frequency have pronounced influence on the parameters of the discharge: sheath thickness, ratio between power transferred to ions and electrons, and concentration and flux of atomic hydrogen at the electrode surface. We found that increasing the excitation frequency, while keeping constant the power dissipated in the plasma, leads to a more moderate increase of electron density as compared with the case of constant rf-voltage amplitude. The analysis of this phenomenon reveals that, with increase of frequency, the power coupling to the electrons becomes more efficient due to the decrease of the phase shift between voltage and current for both constant power and constant voltage conditions. There is, in addition, a significant drop of the sheath voltage with frequency when the power dissipated in the plasma is kept constant. This leads to the reduction in the drift loss rate for charged species. The increase of pressure mainly reduces the diffusive component of the loss rate for both charged and neutral species and, as a result, electron density enhancement is less pronounced. The increase of pressure leads to a more uniform spatial dissipation of the power coupled to the plasma, whereas the increase in frequency results in a higher amount of power dissipated on the plasma-sheath boundaries due to the decrease of the sheath width. © 2003 American Institute of Physics.
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52.77.Dq Plasma-based ion implantation and deposition
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
52.65.-y Plasma simulation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
52.40.Kh Plasma sheaths
52.25.Fi Transport properties
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Melt-threshold method to determine the thermal conductivity of thin films in phase-change optical recording stacks

Erwin R. Meinders and Chubing Peng

J. Appl. Phys. 93, 3207 (2003); http://dx.doi.org/10.1063/1.1544651 (7 pages) | Cited 9 times

Online Publication Date: 5 March 2003

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We report on the dynamic melt-threshold method for the in situ determination of the effective thermal conductivity of thin layers in phase-change optical recording stacks. The method is based on the systematic variation of some of the thermal parameters of the thin films in the recording stack such that the temperature of the phase-change layer, calculated with a multilayer numerical model, equaled the measured melt temperature of the phase-change material. The laser power that causes the onset of melting, the melt-threshold power, was determined from the detectable reflection difference between the crystalline and molten state of the phase-change film and served as input for the model calculations. Melt-threshold experiments were performed for different recording velocities, stack structures, layer thicknesses and optical spot sizes. The melt-threshold method provided a consistent set of thermal parameters that accurately predicts the temperature distribution in a recording stack during erasing and recording of data. Hence, the method is very suitable to calibrate a multilayer thermal model that is used for the optimization of, for example, write strategies or thermal stack designs. The accuracy of the determined effective thermal conductivity of the dielectric layers is estimated to be within 10%–20%, that of the phase-change layer is determined with less accuracy. The melt-threshold method is easily extended to recording stacks with metal heat sink layers. © 2003 American Institute of Physics.
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42.79.Vb Optical storage systems, optical disks
07.20.-n Thermal instruments and apparatus

Temperature dependent exciton photoluminescence of bulk ZnO

D. W. Hamby, D. A. Lucca, M. J. Klopfstein, and G. Cantwell

J. Appl. Phys. 93, 3214 (2003); http://dx.doi.org/10.1063/1.1545157 (4 pages) | Cited 98 times

Online Publication Date: 5 March 2003

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Temperature dependent (4.2–300 K) photoluminescence (PL) of bulk (0001)-oriented ZnO in the range of free- and bound-exciton emission is presented. Emission from several bound excitons and the free A exciton were observed from the low temperature (20 K) PL spectrum. The temperature dependence of the free-exciton peak position was fit using the Manoogian-Woolley equation and the coefficients obtained show reasonable agreement both with first-principle theoretical calculations and empirical values of the coefficients for other II–VI semiconductors. The strongest bound-exciton line with a width (full width at half maximum) of about 1 meV exhibited a thermal activation energy of approximately 14 meV, consistent with the exciton-defect binding energy. It was not observed at temperatures above 150 K. Additional analysis of this particular bound-exciton peak suggests it dissociates into a free exciton and a neutral-donor-like defect-pair complex with increasing temperature. © 2003 American Institute of Physics.
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78.55.Et II-VI semiconductors
71.35.Lk Collective effects (Bose effects, phase space filling, and excitonic phase transitions)
71.55.Gs II-VI semiconductors

Pressure dependence of enhanced x-ray line emission from laser-produced plasmas expanding in an ambient gas

Avijit Chowdhury, V. Arora, P. A Naik, and P. D. Gupta

J. Appl. Phys. 93, 3218 (2003); http://dx.doi.org/10.1063/1.1554474 (5 pages) | Cited 3 times

Online Publication Date: 5 March 2003

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An experimental study of parametric dependence of space-resolved x-ray line emission from laser-produced magnesium plasma expanding in a helium background gas has been performed for different pressures up to 125 mbar. A strong enhancement in MgXI He-α resonance (1s2 1S0−1s2p1P1 at 9.17 Å) and intercombination (1s2 1S0−1s2p3P1 at 9.23 Å) line emission is observed in the expansion region extending up to ∼ 6 mm from the target. At the optimum background gas pressure of about 40 mbar, there is an order of magnitude increase in the x-ray line intensity compared to that observed for a gas pressure of few mbar. The results of measurements of the distance of the peak emission region from the target and width of the emission zone for different pressures are presented, and the role of the background gas for the observed behavior is discussed. © 2003 American Institute of Physics.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.70.La X-ray and γ-ray measurements
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)

Effect of water adsorption on microscopic friction force on SrTiO3(001)

Koichiro Iwahori, Shunji Watanabe, Maki Kawai, Kei Kobayashi, Hirofumi Yamada, and Kazumi Matsushige

J. Appl. Phys. 93, 3223 (2003); http://dx.doi.org/10.1063/1.1540223 (5 pages) | Cited 13 times

Online Publication Date: 5 March 2003

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A friction force microscope study in ultrahigh vacuum was conducted on an atomically flat SrTiO3(001) surface, where SrO and TiO2 domains were distinguished by the difference in friction force. It is revealed that the friction on the SrO became stronger with water adsorption relative to the TiO2 layer. The selective change in friction is attributed to the chemical reaction occurring on the SrO layer, which is supported by the results of x-ray photoelectron spectroscopy. © 2003 American Institute of Physics.
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68.35.Af Atomic scale friction
68.47.Gh Oxide surfaces
68.43.Mn Adsorption kinetics
68.37.Ps Atomic force microscopy (AFM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Dv Composition, segregation; defects and impurities
79.60.Dp Adsorbed layers and thin films

Hydrogen-terminated defects in ion-implanted silicon probed by monoenergetic positron beams

Akira Uedono, Toshiki Mori, Kunitomo Morisawa, Kouichi Murakami, Toshiyuki Ohdaira, Ryoichi Suzuki, Tomohisa Mikado, Kunie Ishioka, Masahiro Kitajima, Shunichi Hishita, Hajime Haneda, and Isao Sakaguchi

J. Appl. Phys. 93, 3228 (2003); http://dx.doi.org/10.1063/1.1542923 (6 pages) | Cited 10 times

Online Publication Date: 5 March 2003

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Hydrogen-terminated vacancies in Si+-implanted Si were studied by means of positron annihilation. After the Si+-ion implantation, hydrogen atoms were introduced into the damaged region using a hydrogen plasma [hydrogen-atom treatment (HAT)]. Monoenergetic positron beams were used to measure Doppler broadening spectra of the annihilation radiation and the lifetime spectra of positrons. It was found that the line shape parameter, S, corresponding to the annihilation of positrons trapped by vacancy-type defects, decreased after HAT. This was attributed to the trapping of positrons by H-decorated vacancy-type defects. Isochronal annealing experiments revealed a strong correlation between positron annihilation parameters and Raman intensities of Si–H, suggesting that hydrogen atoms are released from vacancy-type defects after annealing at 600 °C. © 2003 American Institute of Physics.
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61.72.uf Ge and Si
78.70.Bj Positron annihilation
61.72.J- Point defects and defect clusters
61.72.Cc Kinetics of defect formation and annealing
78.30.Am Elemental semiconductors and insulators

Characterization of deep level traps responsible for isolation of proton implanted GaAs

H. Boudinov, A. V. P. Coelho, H. H. Tan, and C. Jagadish

J. Appl. Phys. 93, 3234 (2003); http://dx.doi.org/10.1063/1.1554761 (5 pages) | Cited 5 times

Online Publication Date: 5 March 2003

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Deep level transient spectroscopy was employed to determine the electrical properties of defects induced in metalorganic chemical-vapor deposition grown n-type and p-type GaAs during proton bombardment. Thermal stability of these defects was investigated and correlation with defects responsible for isolation of GaAs by ion bombardment was discussed. The annealing temperature region (220–250 °C) is similar to proton isolated GaAs below the threshold dose for complete isolation. At least four of the five traps observed in n-type GaAs are not simple interstitial-vacancy pairs. For p-type GaAs we have observed an unknown level with apparent energy of ∼0.64 eV. © 2003 American Institute of Physics.
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71.55.Eq III-V semiconductors
81.05.Ea III-V semiconductors
61.80.Jh Ion radiation effects
61.82.Fk Semiconductors
68.60.Dv Thermal stability; thermal effects
61.72.uj III-V and II-VI semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
85.40.Ry Impurity doping, diffusion and ion implantation technology
61.72.Cc Kinetics of defect formation and annealing

Orientation effects in shocked nickel single crystals via molecular dynamics

Oyeon Kum

J. Appl. Phys. 93, 3239 (2003); http://dx.doi.org/10.1063/1.1554489 (9 pages) | Cited 8 times

Online Publication Date: 5 March 2003

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Shock wave propagation and crystal deformation features were examined in nickel single crystals using nonequilibrium molecular-dynamics simulations for three crystallographic orientations: 〈100〉, 〈110〉, and 〈111〉. Two Morse-type pair potentials and one embedded-atom method (EAM) empirical potential were used to describe bond forces for single crystal nickel atoms. The two Morse-type pair potentials yield more accurate elastic moduli of nickel than does the EAM potential. The dissipation mechanism leading to shear stress relaxation was investigated at the piston/particle speed up=2.5(ϵ/m)1/2, where ϵ is an energy parameter and m is the atomic mass. For shock propagation along the 〈100〉 orientation, the plastic waves overtook almost all elastic precursors for all three potentials. However, for wave propagation along both 〈110〉 and 〈111〉 orientations, elastic precursors followed by steady plastic waves were observed. A clearly discernible leading solitary wave train followed by an extended elastically deformed region was observed in the 〈110〉 orientation. The EAM potential and the pair potentials showed some differences in shock wave propagation. In terms of crystal deformation, the EAM potential showed a greater degree of plasticity than the pair potentials. The two Morse-type pair potentials showed comparable results with respect to wave propagation features and crystal deformation. The details of the atomistic changes associated with shock-induced elastic-plastic deformation are presented for all three potentials. © 2003 American Institute of Physics.
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62.50.-p High-pressure effects in solids and liquids
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations
02.70.Ns Molecular dynamics and particle methods
62.20.D- Elasticity

Optomechanical properties of stretched polymer dispersed liquid crystal films for scattering polarizer applications

Ichiro Amimori, Nikolai V. Priezjev, Robert A. Pelcovits, and Gregory P. Crawford

J. Appl. Phys. 93, 3248 (2003); http://dx.doi.org/10.1063/1.1554757 (5 pages) | Cited 17 times

Online Publication Date: 5 March 2003

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A scattering polarizer is created by subjecting a polymer dispersed liquid crystal film to tensile strain. The optomechanical properties of the film are investigated by simultaneously measuring the stress–strain and polarization dependent optical transmission characteristics. The correlation between transmittances of two orthogonal polarizations and the stress–strain curve reveals that the polymer orientation as well as the droplet shape anisotropy influences the liquid crystal alignment within the droplets. A Monte Carlo simulation based on the P. A. Lebwohl–G. Lasher [Phys. Rev. A 6, 426 (1972)] model is used to explain the subtle influence of polymer orientation on liquid crystal alignment. © 2003 American Institute of Physics.
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61.30.Pq Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems
78.66.Qn Polymers; organic compounds
68.60.Bs Mechanical and acoustical properties
42.70.Df Liquid crystals
42.70.Jk Polymers and organics

Comparative study of metal or oxide capped indium–tin oxide anodes for organic light-emitting diodes

Chengfeng Qiu, Zhilang Xie, Haiying Chen, Man Wong, and Hoi Sing Kwok

J. Appl. Phys. 93, 3253 (2003); http://dx.doi.org/10.1063/1.1556184 (6 pages) | Cited 32 times

Online Publication Date: 5 March 2003

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Indium–tin oxide capped with a variety of nanometer-thick metal or oxide buffer layers has been investigated as anodes in organic light-emitting diodes based on N,N′-diphenyl-N,N′ bis(3-methyl-phenyl-1,1′-biphenyl-4,4′-diamine/tris-8-hydroxyquinoline aluminum. Although high work-function metal buffer layers led to enhancement in hole-injection efficiency, none of the metals investigated gave rise to improvement in current or power efficiency. On the other hand, diodes with some of the oxide buffer layers exhibited improvement not only in hole injection but also in power efficiency. In particular, when 1 nm thick praseodymium oxide was used as the cap layer, more than double the power efficiency was obtained. © 2003 American Institute of Physics.
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85.60.Jb Light-emitting devices
85.60.Pg Display systems
78.66.Qn Polymers; organic compounds

Optical properties and frequency upconversion fluorescence in a Tm3+ -doped alkali niobium tellurite glass

Gaël Poirier, Fabia C. Cassanjes, Cid B. de Araújo, Vladimir A. Jerez, Sidney J. L. Ribeiro, Younes Messaddeq, and Marcel Poulain

J. Appl. Phys. 93, 3259 (2003); http://dx.doi.org/10.1063/1.1555674 (5 pages) | Cited 21 times

Online Publication Date: 5 March 2003

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Optical spectroscopic properties of Tm3+-doped 60TeO2−10GeO2−10K2O−10Li2O−10Nb2O5 glass are reported. The absorption spectra were obtained and radiative parameters were determined using the Judd–Ofelt theory. Characteristics of excited states were studied in two sets of experiments. Excitation at 360 nm originates a relatively narrow band emission at 450 nm attributed to transition 1D2→3F4 of the Tm3+ ion with photon energy larger than the band-gap energy of the glass matrix. Excitation at 655 nm originates a frequency upconverted emission at 450 nm (1D2→3F4) and emission at 790 nm (3H4→3H6). The radiative lifetimes of levels 1D2 and 3H4 were measured and the differences between their experimental values and the theoretical predictions are understood as due to the contribution of energy transfer among Tm3+ ions. © 2003 American Institute of Physics.
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78.55.Qr Amorphous materials; glasses and other disordered solids
81.05.Kf Glasses (including metallic glasses)
71.55.Jv Disordered structures; amorphous and glassy solids
42.70.Ce Glasses, quartz

Termination mechanism of inversion domains by stacking faults in GaN

C. Iwamoto, X. Q. Shen, H. Okumura, H. Matsuhata, and Y. Ikuhara

J. Appl. Phys. 93, 3264 (2003); http://dx.doi.org/10.1063/1.1544427 (6 pages) | Cited 4 times

Online Publication Date: 5 March 2003

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GaN film was grown by molecular-beam epitaxy (MBE) with intermittent indium exposure during film growth, and the microstructures were investigated by atomic-resolution high-voltage electron microscopy (ARHVEM). Epitaxial wurzite GaN (0001) film grew on a sapphire (0001) substrate. Although many inversion domains (ID’s) were generated at the film/substrate interface, stacking faults on the basal plane of GaN, which was formed at the position of indium exposure, were found to play an important role in terminating the growth of ID’s. ARHVEM observation revealed that stacking faults I2 with two stacking violations were introduced in the ID while stacking faults I1 with one stacking violation were introduced in the matrix. The difference in the number of stacking violations was related to the change in the ID boundary (IDB) structure and to the reduction of the IDB area. The termination mechanism is considered to be important to the realization of the high-quality GaN film by MBE. © 2003 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.Nn Stacking faults and other planar or extended defects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.Mm Grain and twin boundaries
68.55.-a Thin film structure and morphology
68.37.-d Microscopy of surfaces, interfaces, and thin films

Comparison of the agglomeration behavior of Au and Cu films sputter deposited on silicon dioxide

Jang-Yeon Kwon, Tae-Sik Yoon, Ki-Bum Kim, and Seok-Hong Min

J. Appl. Phys. 93, 3270 (2003); http://dx.doi.org/10.1063/1.1556178 (9 pages) | Cited 37 times

Online Publication Date: 5 March 2003

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The agglomeration behavior of Cu and Au films each with a thickness of 5 and 50 nm, deposited on thermally grown SiO2 by dc magnetron sputtering, was investigated with scanning electron microscopy. The size of Cu islands formed by agglomeration increased with increasing annealing temperature. Also, the agglomeration of Cu films seem to follow the grain boundary grooving process. On the other hand, Au islands have an identical size at different annealing temperatures. Au films were observed to agglomerate via nucleation of voids followed by the fractal growth of voids. The fractal dimension was determined to be 1.7 indicating that the fractal growth of voids can be described with a diffusion limited aggregation model. Finally, the kinetics of agglomeration of the Au films was described with an Avrami-type equation. © 2003 American Institute of Physics.
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68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering
61.72.Cc Kinetics of defect formation and annealing
05.45.Df Fractals

Yield and fracture properties of the wide band-gap semiconductor 4H-SiC

P. Pirouz, M. Zhang, J.-L. Demenet, and H. M. Hobgood

J. Appl. Phys. 93, 3279 (2003); http://dx.doi.org/10.1063/1.1555255 (12 pages) | Cited 21 times

Online Publication Date: 5 March 2003

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The flow stress of the wide band-gap semiconductor, 4H-SiC, has been measured by uniaxial compression tests over the temperature range 500–1400 °C at different strain rates. At low strain rates, 4H-SiC shows a transition in the yield stress at a temperature Tc. In addition, the brittle-to-ductile transition (BDT) temperature TBDT of the same material has been determined on precracked samples at different values of strain rate math by 4-point bend tests. Intriguingly, the transition temperature Tc in yielding is very close to the brittle-to-ductile transition temperature TBDT in the fracture behavior. In previous transmission electron microscopy (TEM) investigations, significant microstructural differences were found between low-temperature (T<Tc) and high-temperature (T>Tc) deformed crystals. There, the results showed that in the samples deformed below the transition temperature Tc, deformation proceeds by the generation and motion of single leading partial dislocations on different (0001) planes. Moreover, all the partials appeared to have the same core, silicon. On the other hand, at temperatures above Tc, the samples deformed by the generation and motion of perfect dislocations dissociated in the form of leading/trailing partial pairs separated by a ribbon of stacking fault. Based on the present mechanical tests and previous TEM results—together with experimental evidence from other semiconductors—a model is presented in which Tc and TBDT are identified and correspond to the temperature at which crystal shear takes place by different dislocation types. Below Tc, single leading partials are responsible for crystal shear, whereas above Tc, perfect dislocations (i.e., leading/trailing pairs) accomplish the slip. Since generation of a leading partial from crack tip sources basically shuts the sources off, the crystal remains brittle below this transition temperature. At Tc=TBDT, trailing partials are nucleated from the same sources to clean up the stacking fault and allow multiplicative generation of dislocation avalanches resulting in transition to the ductile mode. © 2003 American Institute of Physics.
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62.20.M- Structural failure of materials
62.20.F- Deformation and plasticity
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
61.72.Nn Stacking faults and other planar or extended defects

Time-resolved x-ray diffraction measurements and analysis to investigate shocked lithium fluoride crystals

P. A. Rigg and Y. M. Gupta

J. Appl. Phys. 93, 3291 (2003); http://dx.doi.org/10.1063/1.1556197 (8 pages) | Cited 10 times

Online Publication Date: 5 March 2003

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Experimental methods to permit continuous, time-resolved x-ray diffraction measurements in plate impact experiments were developed and used to examine lattice deformation in shock compressed LiF single crystals. Using an x-ray streak camera diffraction data with 2–4 ns resolution were obtained from crystals subjected to both shock and ramp wave loading along the [111] direction. Because of the penetration depth of x rays into the sample, interpretation of the ramp wave loading data required an analytic model to simulate the results. The penetration depth used in the model was determined experimentally from the time-resolved shock wave loading data. Good agreement between the simulations and experimental data was found for both loading conditions, suggesting that the analytic model has broad applicability. © 2003 American Institute of Physics.
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61.05.cp X-ray diffraction
62.50.-p High-pressure effects in solids and liquids
06.60.Jn High-speed techniques (microsecond to femtosecond)
07.68.+m Photography, photographic instruments; xerography
07.85.-m X- and γ-ray instruments
61.66.Fn Inorganic compounds
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