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4 May 2009

Volume 94, Issue 18, Articles (18xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 94, 181502 (2009); http://dx.doi.org/10.1063/1.3126452 (3 pages)

A. Yogo, K. Sato, M. Nishikino, M. Mori, T. Teshima, H. Numasaki, M. Murakami, Y. Demizu, S. Akagi, S. Nagayama, K. Ogura, A. Sagisaka, S. Orimo, M. Nishiuchi, A. S. Pirozhkov, et al.
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Toward photonic crystal based spatial filters with wide angle ranges of total transmission

A. E. Serebryannikov, A. Y. Petrov, and Ekmel Ozbay

Appl. Phys. Lett. 94, 181101 (2009); http://dx.doi.org/10.1063/1.3127443 (3 pages) | Cited 4 times

Online Publication Date: 5 May 2009

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Spatial filters with steep switching between wide ranges of total transmission and total reflection can be obtained by using two-dimensional dielectric photonic crystals, which are a few wavelengths thick. The guidelines for engineering bandpass and bandstop filters are given. The flatness of isofrequency contours that are localized around a periphery point of the first Brillouin zone is a necessary but insufficient condition for the existence of wide angle ranges of total transmission at intermediate and large angles of incidence. Such ranges that are wider than 20° are demonstrated.
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42.79.Ci Filters, zone plates, and polarizers
42.70.Qs Photonic bandgap materials

Electroluminescent measurement of the internal quantum efficiency of light emitting diodes

Amorette Getty, Elison Matioli, Michael Iza, Claude Weisbuch, and James S. Speck

Appl. Phys. Lett. 94, 181102 (2009); http://dx.doi.org/10.1063/1.3129866 (3 pages) | Cited 10 times

Online Publication Date: 5 May 2009

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An experimental method is demonstrated for the determination of internal quantum efficiency (IQE) in III-nitride-based light-emitting diodes (LEDs). LED devices surrounded with an optically absorbing material have been fabricated to limit collected light to photons emitted directly from the quantum wells across a known fraction of the recombination area. The emission pattern for this device configuration was modeled to estimate the extraction efficiency. IQE can then be calculated from the measured input current and output power. This method was applied to c-plane InxGa1−xN-based LEDs emitting at 445 nm. Initial measurements estimate an IQE of 43%±1% at a current density of 7.9 A/cm2.
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85.60.Jb Light-emitting devices
78.67.De Quantum wells
85.60.Bt Optoelectronic device characterization, design, and modeling

Probability density optical tomography of confined quasiparticles in a semiconductor microcavity

Gaël Nardin, Taofiq K. Paraïso, Roland Cerna, Barbara Pietka, Yoan Léger, Ounsi El Daif, François Morier-Genoud, and Benoît Deveaud-Plédran

Appl. Phys. Lett. 94, 181103 (2009); http://dx.doi.org/10.1063/1.3126022 (3 pages) | Cited 4 times

Online Publication Date: 6 May 2009

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We present the optical tomography of the probability density of quasiparticles, the microcavity polaritons, confined in three dimensions by cylindrical traps. Collecting the photoluminescence emitted by the quasimodes under continuous nonresonant laser excitation, we reconstruct a three-dimensional mapping of the photoluminescence, from which we can extract the spatial distribution of the confined states at any energy. We discuss the impact of the confinement geometry on the wave function patterns and give an intuitive understanding in terms of a light-matter quasiparticle confined in a box.
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42.30.Wb Image reconstruction; tomography
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.55.Sa Microcavity and microdisk lasers
71.35.-y Excitons and related phenomena
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Plasmon-based photosensors comprising a very thin semiconducting region

J. Le Perchec, Y. Desieres, and R. Espiau de Lamaestre

Appl. Phys. Lett. 94, 181104 (2009); http://dx.doi.org/10.1063/1.3132063 (3 pages) | Cited 8 times

Online Publication Date: 7 May 2009

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We theoretically investigate an elementary subwavelength plasmonic sensor comprising a very thin active region. High quantum efficiency (QE), broad spectral band and nearly no sensitivity to the incidence angle and polarization can be achieved. We particularly discuss different examples based on HgCdTe for infrared detection: QEs of 75% are obtained for active layers λ/(8n) thin, corresponding to a tenfold absorption enhancement.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
78.66.Hf II-VI semiconductors
73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Experimental characterization of three-wave mixing in a multimode nonlinear KTiOPO4 waveguide

Michał Karpiński, Czesław Radzewicz, and Konrad Banaszek

Appl. Phys. Lett. 94, 181105 (2009); http://dx.doi.org/10.1063/1.3132086 (3 pages) | Cited 6 times

Online Publication Date: 7 May 2009

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We report experimental determination of the phase-matching function for type-II three-wave mixing in a periodically poled KTiOPO4 waveguide in the 792–815 nm spectral region. The measurement was performed by sum-frequency generation of spectrally tuned fundamental components. Strong dependence of the observed signal on the excited spatial modes in the waveguide has been observed and fully interpreted. These results indicate a route to employ the waveguide for spontaneous parametric down-conversion producing photon pairs in well-defined spatial modes.
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42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation
42.65.Lm Parametric down conversion and production of entangled photons

Terahertz localized plasmonic properties of subwavelength ring and coaxial geometries

Xinchao Lu and Weili Zhang

Appl. Phys. Lett. 94, 181106 (2009); http://dx.doi.org/10.1063/1.3132087 (3 pages) | Cited 8 times

Online Publication Date: 7 May 2009

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We study terahertz properties of periodic arrays of subwavelength metallic ring and coaxial ring-disk structures. Terahertz time-domain spectroscopy and numerical simulations have revealed unique resonance behaviors at terahertz frequencies. A high-frequency antisymmetric resonance in the rings concurs simultaneously with the symmetric mode. In the coaxial structures, the strong and weak resonance interactions are characterized by the plasmon hybridization theory, while the anomalous interaction results in a degenerate resonance which has not yet been observed at visible frequencies. The frequency tunability and strong electric field enhancement in such subwavelength structures are promising in terahertz sensing, spectroscopy, and integrated components.
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78.70.Gq Microwave and radio-frequency interactions
78.68.+m Optical properties of surfaces
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
42.70.-a Optical materials
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Microwave analog to light scattering measurements on a fully characterized complex aggregate

Olivier Merchiers, Jean-Michel Geffrin, Rodolphe Vaillon, Pierre Sabouroux, and Bernard Lacroix

Appl. Phys. Lett. 94, 181107 (2009); http://dx.doi.org/10.1063/1.3129196 (3 pages) | Cited 4 times

Online Publication Date: 7 May 2009

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We present experimental measurements of three-dimensional electromagnetic wave scattering in the microwave frequency range, by a complex aggregate consisting of 74 primary spheres with fully known optical and geometrical properties. We measured the complete amplitude scattering matrix (or Jones matrix), from which the electric fields (amplitude and phase) with arbitrary polarization can be obtained. These results offer the opportunity to test approximate computational methods against experiments.
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07.57.-c Infrared, submillimeter wave, microwave and radiowave instruments and equipment
42.25.Fx Diffraction and scattering
42.25.Ja Polarization

Growth of silver nanoparticles of variable and controlled diameter in silica-based and soda-lime glasses by simultaneous continuous ultraviolet irradiation and heat treatment

F. Goutaland, E. Marin, J. Y. Michalon, and A. Boukenter

Appl. Phys. Lett. 94, 181108 (2009); http://dx.doi.org/10.1063/1.3132584 (3 pages) | Cited 5 times

Online Publication Date: 8 May 2009

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We report on the space-selective precipitation of silver nanoparticles in silica-based and silver-exchanged soda-lime glasses by simultaneous continuous wave ultraviolet exposure and heat treatment. In silica-based glasses, we explain that simultaneous treatments lead to much higher silver nanoparticles concentration than similar treatments performed into two separated steps by minimizing the detrimental influence of oxidation on the nanoparticles’ growth. In the case of silver-exchanged soda-lime glasses, nanoparticles are observed with both small and larger diameters of about 1 and 7 nm, whose concentrations depend both on the laser power density and on the heating temperature.
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81.07.Bc Nanocrystalline materials
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.40.Gh Other heat and thermomechanical treatments
64.75.Jk Phase separation and segregation in nanoscale systems
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.82.Rx Nanocrystalline materials
61.43.Fs Glasses

Twisted-nematic liquid-crystal displays with small grayscale inversion and wide viewing angle

Chi-Huang Lin

Appl. Phys. Lett. 94, 181109 (2009); http://dx.doi.org/10.1063/1.3133864 (3 pages)

Online Publication Date: 8 May 2009

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This work proposes a twisted-nematic liquid-crystal display (TN-LCD) with a small grayscale inversion and wide viewing angle. The electro-optical properties of a tilted TN cell are studied to develop the proposed TN-LCD. Calculations reveal that when the applied voltage exceeds a critical voltage, the effective optical property of the tilted TN cell is optically uniaxial with the effective optical axis parallel to the bisector of the twist angle. This bisector effect is used to improve the grayscale inversion of TN-LCDs. A viewing angle of over the entire 80° viewing cone of the proposed TN-LCD is also demonstrated theoretically and experimentally.
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42.70.Df Liquid crystals
42.79.Kr Display devices, liquid-crystal devices
61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
85.60.Pg Display systems
78.20.Jq Electro-optical effects
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Evolution of the electrically exploding wire observed with a Mach–Zehnder interferometer

Zhiguo Mao, Xiaobing Zou, Xinxin Wang, and Weihua Jiang

Appl. Phys. Lett. 94, 181501 (2009); http://dx.doi.org/10.1063/1.3132058 (3 pages) | Cited 6 times

Online Publication Date: 6 May 2009

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The evolution of an exploding titanium wire embedded in 10 kPa air was studied with Mach–Zehnder interferometry. The exploding wire is characterized by a central dense core as well as the surrounding plasma and a rapidly expanding gas shell. Based on the fringe shifts, the electron density of the plasma and the increased density in the gas shell were calculated to be about 1.94×1018/cm3 and 4.78×10−4 g/cm3, respectively. The expanding speed of the gas shell is about 2.28 km/s. A thermal expansion lag of the dense vapor core and two-phase vaporization of the wire were observed. Due to the wire exploding in “under heat” mode, the first phase of the vaporization is by the Joule heating and the second one by the plasma heating.
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07.60.Ly Interferometers

Application of laser-accelerated protons to the demonstration of DNA double-strand breaks in human cancer cells

A. Yogo, K. Sato, M. Nishikino, M. Mori, T. Teshima, H. Numasaki, M. Murakami, Y. Demizu, S. Akagi, S. Nagayama, K. Ogura, A. Sagisaka, S. Orimo, M. Nishiuchi, A. S. Pirozhkov, et al.

Appl. Phys. Lett. 94, 181502 (2009); http://dx.doi.org/10.1063/1.3126452 (3 pages) | Cited 27 times

Online Publication Date: 7 May 2009

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We report the demonstrated irradiation effect of laser-accelerated protons on human cancer cells. In vitro (living) A549 cells are irradiated with quasimonoenergetic proton bunches of 0.8–2.4 MeV with a single bunch duration of 15 ns. Irradiation with the proton dose of 20 Gy results in a distinct formation of γ-H2AX foci as an indicator of DNA double-strand breaks generated in the cancer cells. This is a pioneering result that points to future investigations of the radiobiological effects of laser-driven ion beams. Unique high-current and short-bunch features make laser-driven proton bunches an excitation source for time-resolved determination of radical yields.
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87.55.D- Treatment planning
87.53.Bn Dosimetry/exposure assessment
87.19.xj Cancer
87.14.gk DNA
42.62.Be Biological and medical applications
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Lower limit to phonon thermal conductivity of disordered, layered solids

Patrick E. Hopkins and Edward S. Piekos

Appl. Phys. Lett. 94, 181901 (2009); http://dx.doi.org/10.1063/1.3127224 (3 pages) | Cited 6 times

Online Publication Date: 4 May 2009

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The minimum limit to the thermal conductivity of disordered, layered solids is studied by accounting for minimum scattering times and velocities from oscillations of atoms bound by different interatomic forces. The model developed in this work allows for quantification of changes in the lower limit to thermal conductivity in heavily disordered solids due to force differences arising from planar interfaces. This model sets a lower limit to recent data of thermal conductivity of WSe2 layered films, the data from which were below the lower limits predicted by previous models.
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63.20.-e Phonons in crystal lattices
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves

Transient absorption and higher-order nonlinearities in silver nanoplatelets

J. Jayabalan, Asha Singh, Rama Chari, Salahuddin Khan, Himanshu Srivastava, and S. M. Oak

Appl. Phys. Lett. 94, 181902 (2009); http://dx.doi.org/10.1063/1.3125244 (3 pages) | Cited 6 times

Online Publication Date: 4 May 2009

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We show that the imaginary parts of higher-order optical nonlinearities and their decay times can be determined by a time-intensity domain analysis of the conventional transient absorption data. Using this method we have measured the values and decay times of third, fifth and seventh-order nonlinear susceptibilities of silver nanoplatelets in water. The origin of these higher-order nonlinearities is explained using a two-temperature model.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.65.An Optical susceptibility, hyperpolarizability
78.47.-p Spectroscopy of solid state dynamics

Band structure for a bend-core liquid crystal fiber

Laura O. Palomares, P. Castro-Garay, and J. Adrian Reyes

Appl. Phys. Lett. 94, 181903 (2009); http://dx.doi.org/10.1063/1.3129165 (3 pages)

Online Publication Date: 4 May 2009

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We study the propagation of optical fields in a cylindrical fiber of a banana bend-core liquid crystal formed by uniformly tilted coaxial cylindrical smectic layers, surrounded by vacuum. By solving numerically Maxwell’s equations, we find the band structure in both uniaxial and biaxial limits. For the biaxial case, we show that the backward propagation is restricted to certain narrow frequency band gaps, whereas for the forward one the fiber behaves similarly to a standard waveguide. We also find that the fiber modes are elliptically polarized slowly leaky modes whose attenuation coefficients are damped oscillating functions of frequency.
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42.70.Df Liquid crystals
42.81.Dp Propagation, scattering, and losses; solitons
42.25.Ja Polarization
73.20.At Surface states, band structure, electron density of states

Local structure anomaly around Ge dopants in Mn3Cu0.7Ge0.3N with negative thermal expansion

J. Matsuno, K. Takenaka, H. Takagi, D. Matsumura, Y. Nishihata, and J. Mizuki

Appl. Phys. Lett. 94, 181904 (2009); http://dx.doi.org/10.1063/1.3129169 (3 pages) | Cited 12 times

Online Publication Date: 5 May 2009

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Local structure analysis of Cu and Ge atoms in the negative thermal expansion material Mn3Cu0.7Ge0.3N was conducted using x-ray absorption fine structure measurements. The temperature dependence of the interatomic distance was found to reflect the macroscopic negative thermal expansion both for Cu–Mn and Ge–Mn shells, although the magnitude of the relative change was much larger for Ge–Mn than Cu–Mn. An enhanced anomaly of the Debye–Waller factor was observed for the Ge–Mn shell in the temperature region of the negative expansion, indicating the presence of static local disorder around Ge impurities. These local structure anomalies strongly suggest that the local and inhomogeneous strain around Ge is essential in broadening the discontinuous volume contraction.
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65.40.De Thermal expansion; thermomechanical effects
78.70.Dm X-ray absorption spectra
61.66.Fn Inorganic compounds
61.72.up Other materials
71.55.Ht Other nonmetals
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions

Effect of O vacancies on the Young’s modulus of the BaCe1−xYxO3−δ perovskite

F. Cordero, F. Trequattrini, F. Deganello, V. La Parola, E. Roncari, and A. Sanson

Appl. Phys. Lett. 94, 181905 (2009); http://dx.doi.org/10.1063/1.3129873 (3 pages) | Cited 2 times

Online Publication Date: 5 May 2009

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The effect of oxygen vacancies on the elastic properties of BaCe0.9Y0.1O3−δ is studied by measuring the complex Young’s modulus between 80 and 850 K varying the content of O vacancies from 0 to nearly 0.05. The Young’s modulus measured at a fixed temperature above 300 K may change by more than 20% but this is due to a shift of the rhombohedral-orthorhombic transition by 250 K and to proton and vacancy hopping. Below 100 K these effects are frozen and the filling of the O vacancies with OH ions increases the Young’s modulus by ∼ 1.3%.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
64.70.K- Solid-solid transitions
61.72.jd Vacancies
62.20.de Elastic moduli

Theoretical investigation of A-element atom diffusion in Ti2AC (A = Sn, Ga, Cd, In, and Pb)

B. Liu, J. Y. Wang, J. Zhang, J. M. Wang, F. Z. Li, and Y. C. Zhou

Appl. Phys. Lett. 94, 181906 (2009); http://dx.doi.org/10.1063/1.3130093 (3 pages) | Cited 7 times

Online Publication Date: 5 May 2009

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The phase stability and mechanical properties of Ti2AC (A = Ga, Cd, Sn, In, and Pb) have close relationship with the behavior of group-A element atoms in these compounds. This letter shows that although the Al, Ga, and In (or Si, Sn, and Pb) are in the same group, the migration energy and vacancy formation energy of group-A atom in Ti2GaC/Ti2InC (or Ti2SnC/Ti2PbC) are noticeable lower than those in Ti2AlC (or Ti3SiC2). The present results are helpful for a better understanding of easy out diffusion and self-extrusion of group-A atoms in these compounds.
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66.30.Dn Theory of diffusion and ionic conduction in solids
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.fk Ductility, malleability
81.40.Lm Deformation, plasticity, and creep
61.72.jd Vacancies
66.30.H- Self-diffusion and ionic conduction in nonmetals

Deep ultraviolet emitting AlGaN quantum wells with high internal quantum efficiency

A. Bhattacharyya, T. D. Moustakas, Lin Zhou, David. J. Smith, and W. Hug

Appl. Phys. Lett. 94, 181907 (2009); http://dx.doi.org/10.1063/1.3130755 (3 pages) | Cited 29 times

Online Publication Date: 5 May 2009

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We report the development of Al0.7Ga0.3N/AlN quantum wells with high internal quantum efficiency. All samples had identical well and barrier thickness but the III/V flux ratio was varied during growth by increasing the Ga flux. The luminescence spectra show single peaks which vary from 220 nm (III/V ∼ 1) to 250 nm (III/V⪢1) with internal quantum efficiency varying from 5% to 50%, respectively. To account for these results, a growth model was proposed in which at III/V ∼ 1 the growth proceeds via vapor phase epitaxy, while at III/V⪢1 the growth proceeds via liquid phase epitaxy.
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81.05.Ea III-V semiconductors
78.55.Cr III-V semiconductors
81.07.St Quantum wells
78.67.De Quantum wells
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.65.Fg Quantum wells

A tunable acoustic filter made by periodical structured materials

Jingshi Wang, Xiaodong Xu, Xiaojun Liu, and Gangcan Xu

Appl. Phys. Lett. 94, 181908 (2009); http://dx.doi.org/10.1063/1.3131043 (3 pages) | Cited 1 time

Online Publication Date: 6 May 2009

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Three kinds of the periodical structures are designed as low-pass, high-pass, and band-pass filters for elastic wave. The theoretical simulations have proved that the periodical surface slots can act as a low-pass filter for elastic wave. With increasing depth of the surface periodical structure in the sample, the cutoff frequency of the low-pass filter is decreased. Unlike the surface periodical structure, the periodical subsurface structure can work as a high-pass filter for elastic wave. The cutoff frequency of the high-pass filter is suppressed by the increase of the subsurface structure thickness. When the two periodical structures are combined together, the band-pass filter is obtained, in which the pass band is determined by the cutoff frequencies of the low-pass and high-pass filters.
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43.58.Kr Spectrum and frequency analyzers and filters; acoustical and electrical oscillographs; photoacoustic spectrometers; acoustical delay lines and resonators

Aluminum induced in situ crystallization of amorphous SiC

Li Wang, Sima Dimitrijev, Philip Tanner, and Jin Zou

Appl. Phys. Lett. 94, 181909 (2009); http://dx.doi.org/10.1063/1.3132053 (3 pages) | Cited 1 time

Online Publication Date: 6 May 2009

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Experimental evidence of aluminum induced in situ crystallization of amorphous SiC is presented. The deposition of SiC films on Si substrates was performed using low pressure chemical vapor deposition method at 600 °C with concurrent supply of Al(CH3)3 and H3SiCH3. Transmission electron micrographs confirm the presence of nanocrystals, whereas capacitance-voltage measurements demonstrate that the deposited films are p type doped. A crystallization mechanism is proposed based on the classic theory of nucleation in the growth rate limited regime. The introduction of Al(CH3)3 enhances the surface reaction and increases the supersaturation, which reduces the activation energy for nucleation.
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81.05.Gc Amorphous semiconductors
64.70.kg Semiconductors
68.37.Og High-resolution transmission electron microscopy (HRTEM)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.ag Semiconductors

Special optical geometry for measuring twist elastic module K22 and rotational viscosity γ1 of nematic liquid crystals

A. V. Dubtsov, S. V. Pasechnik, D. V. Shmeliova, V. A. Tsvetkov, and V. G. Chigrinov

Appl. Phys. Lett. 94, 181910 (2009); http://dx.doi.org/10.1063/1.3129864 (3 pages) | Cited 3 times

Online Publication Date: 6 May 2009

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A special nontraditional optical geometry with a pure twist deformation induced by a homogeneous “in-plane” electric field in the layer of nematic liquid crystal (LC) is presented. A quantitative agreement of the theoretical and experimental results of the measured LC birefringence is obtained. A method for measuring the twist elastic module K22 and the rotational viscosity coefficient γ1 of nematic LC is proposed.
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62.10.+s Mechanical properties of liquids
66.20.-d Viscosity of liquids; diffusive momentum transport
78.20.Fm Birefringence
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures

Rippling instability on surfaces of stressed crystalline conductors

Vivek Tomar, M. Rauf Gungor, and Dimitrios Maroudas

Appl. Phys. Lett. 94, 181911 (2009); http://dx.doi.org/10.1063/1.3130742 (3 pages) | Cited 6 times

Online Publication Date: 7 May 2009

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We report a surface morphological stability analysis for stressed, conducting crystalline solids without and with the simultaneous application of an electric field based on self-consistent dynamical simulations according to a fully nonlinear model. The analysis reveals that in addition to a cracklike surface instability, a very-long-wavelength instability may be triggered that leads to the formation of secondary ripples on the surface morphology. We demonstrate that the number of ripples formed scales linearly with the wavelength of the initial perturbation from the planar surface morphology and that a sufficiently strong electric field inhibits both the cracklike and the rippling instability.
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68.35.B- Structure of clean surfaces (and surface reconstruction)

Influence of global magnetic state on chemical interactions in high-pressure high-temperature synthesis of B2 Fe2Si

A. V. Ponomareva, A. V. Ruban, N. Dubrovinskaia, L. Dubrovinsky, and I. A. Abrikosov

Appl. Phys. Lett. 94, 181912 (2009); http://dx.doi.org/10.1063/1.3131784 (3 pages) | Cited 2 times

Online Publication Date: 7 May 2009

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We show that effective chemical interactions in an alloy can be tuned by its global magnetic state, which opens exciting possibilities for materials synthesis. Using first-principles theory we demonstrate that at pressure of 20 GPa and at high temperatures, the effective chemical interactions in paramagnetic Fe–Si system are strongly influenced by the magnetic disorder favoring a formation of cubic Fe2Si phase with B2 structure, which is not present in the alloy phase diagram. Our experiments confirm theoretical predictions, and the B2 Fe2Si alloy is synthesized from Fe–Si mixture using multianvil press.
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75.20.En Metals and alloys
62.50.-p High-pressure effects in solids and liquids
81.05.Bx Metals, semimetals, and alloys
75.30.Cr Saturation moments and magnetic susceptibilities

Strain-induced Stranski–Krastanov three-dimensional growth mode of GaSb quantum dot on GaAs substrate

K. Fu and Y. Fu

Appl. Phys. Lett. 94, 181913 (2009); http://dx.doi.org/10.1063/1.3132054 (3 pages) | Cited 2 times

Online Publication Date: 8 May 2009

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The growth dynamics of self-assembled GaSb quantum dots (QDs) on GaAs substrate was investigated using kinetic Monte Carlo method. The strain induced by the lattice mismatch between the epitaxial material and the substrate was shown to be directly responsible for the three-dimensional QD formation. Different geometries of the initial seeds on the surface which are equally favorable from an energy point of view can result in different GaSb nanostructures (nanostrips and nanoring).
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68.55.ag Semiconductors
81.07.Ta Quantum dots
68.47.Fg Semiconductor surfaces
81.16.Dn Self-assembly
61.43.Bn Structural modeling: serial-addition models, computer simulation

Study of the effect of dielectric porosity on the stress in advanced Cu/low-k interconnects using x-ray diffraction

C. J. Wilson, C. Zhao, L. Zhao, T. H. Metzger, Zs. Tőkei, K. Croes, M. Pantouvaki, G. P. Beyer, A. B. Horsfall, and A. G. O’Neill

Appl. Phys. Lett. 94, 181914 (2009); http://dx.doi.org/10.1063/1.3133345 (3 pages) | Cited 4 times

Online Publication Date: 8 May 2009

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High intensity x-rays at an advanced light facility were used to probe the strained atomic spacing of Cu interconnects embedded in ultralow-k dielectrics of different porosities. The assumption that the strain-free atomic spacing of a thin film can be extrapolated from a relationship based on the material stiffness coefficients used in literature is tested and demonstrated experimentally using a series of blanket wafers. This is used to calculate the stress of 100 nm interconnects. High porosity materials show in-plane relaxation reducing the stress. The air gap architecture is shown to provide little constraint with the lowest Cu stress.
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85.40.Ls Metallization, contacts, interconnects; device isolation
77.55.-g Dielectric thin films
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