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24 Dec 2012

Volume 101, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 101, 263501 (2012); http://dx.doi.org/10.1063/1.4772532 (4 pages)

Youngki Yoon and Sayeef Salahuddin
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Spatial resolution of synchrotron x-ray microtomography in high energy range: Effect of x-ray energy and sample-to-detector distance

D. Seo, F. Tomizato, H. Toda, K. Uesugi, A. Takeuchi, Y. Suzuki, and M. Kobayashi

Appl. Phys. Lett. 101, 261901 (2012); http://dx.doi.org/10.1063/1.4773239 (5 pages)

Online Publication Date: 26 December 2012

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Spatial resolution of three-dimensional images obtained by synchrotron X-ray microtomography technique is evaluated using cyclic bar patterns machined on a steel wire. Influences of X-ray energy and the sample-to-detector distance on spatial resolution were investigated. High X-ray energies of 33-78 keV are applied due to the high X-ray absorption of transition metals. Best spatial resolution of about 1.2 μm pitch was observed at the sample-to-detector distance range of 20-110 mm and at the energy range of 68-78 keV. Several factors such as X-ray scattering and diffraction phenomena affecting the degradation of spatial resolution are also discussed.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
07.85.Tt X-ray microscopes

Non-perpendicular hypersonic and optical stop-bands in porous silicon multilayers

J. Manzanares-Martinez, D. Moctezuma-Enriquez, Y. J. Rodriguez-Viveros, B. Manzanares-Martinez, and P. Castro-Garay

Appl. Phys. Lett. 101, 261902 (2012); http://dx.doi.org/10.1063/1.4773243 (4 pages)

Online Publication Date: 26 December 2012

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We study by theoretical simulations the non-perpendicular propagation of electromagnetic and elastic waves in porous silicon multilayers. We proceeded in three steps. First, we found the conditions to obtain a simultaneous photonic-phononic mirror at normal incidence. Second, we determined the angular variation of the mirrors computing the projected band structure. In a third step, we found out, on the one hand, that there are no conditions to obtain an omnidirectional mirror for electromagnetic waves. But, on the other hand, we found the conditions were possible to obtain an omnidirectional mirror for elastic waves. Moreover, the elastic mirror is revealed to be a polarization-converter due to the conversion of evanescent modes in the band gap.
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78.66.Db Elemental semiconductors and insulators
81.05.Rm Porous materials; granular materials
61.43.Gt Powders, porous materials
62.30.+d Mechanical and elastic waves; vibrations
68.65.Ac Multilayers

Dielectric function spectra at 40 K and critical-point energies for CuIn0.7Ga0.3Se2

S. G. Choi, R. Chen, C. Persson, T. J. Kim, S. Y. Hwang, Y. D. Kim, and L. M. Mansfield

Appl. Phys. Lett. 101, 261903 (2012); http://dx.doi.org/10.1063/1.4773362 (4 pages) | Cited 1 time

Online Publication Date: 26 December 2012

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We report ellipsometrically determined dielectric function ε spectra for CuIn0.7Ga0.3Se2 thin film at 40 and 300 K. The data exhibit numerous spectral features associated with interband critical points (CPs) in the spectral range from 0.74 to 6.43 eV. The second-energy-derivatives of ε further reveal a total of twelve above-bandgap CP features, whose energies are obtained accurately by a standard lineshape analysis. The ε spectra determined by ellipsometry show a good agreement with the results of full-potential linearized augmented plane wave calculations. Probable electronic origins of the CP features observed are discussed.
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78.66.Li Other semiconductors
82.60.-s Chemical thermodynamics
07.60.Fs Polarimeters and ellipsometers
68.55.-a Thin film structure and morphology
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Direct observation of substitutional Ga after ion implantation in Ge by means of extended x-ray absorption fine structure

S. Decoster, B. Johannessen, C. J. Glover, S. Cottenier, T. Bierschenk, H. Salama, F. Kremer, K. Temst, A. Vantomme, and M. C. Ridgway

Appl. Phys. Lett. 101, 261904 (2012); http://dx.doi.org/10.1063/1.4773185 (4 pages)

Online Publication Date: 27 December 2012

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We present an experimental lattice location study of Ga atoms in Ge after ion implantation at elevated temperature (250°C). Using extended x-ray absorption fine structure (EXAFS) experiments and a dedicated sample preparation method, we have studied the lattice location of Ga atoms in Ge with a concentration ranging from 0.5 at. % down to 0.005 at. %. At Ga concentrations ≤ 0.05 at.%, all Ga dopants are substitutional directly after ion implantation, without the need for post-implantation thermal annealing. At higher Ga concentrations, a reduction in the EXAFS amplitude is observed, indicating that a fraction of the Ga atoms is located in a defective environment. The local strain induced by the Ga atoms in the Ge matrix is independent of the Ga concentration and extends only to the first nearest neighbor Ge shell, where a 1% contraction in bond length has been measured, in agreement with density functional theory calculations.
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61.72.uf Ge and Si
61.50.Lt Crystal binding; cohesive energy
78.70.Dm X-ray absorption spectra

Efficient focalization of antisymmetric Lamb waves in gradient-index phononic crystal plates

Jinfeng Zhao, Rémi Marchal, Bernard Bonello, and Olga Boyko

Appl. Phys. Lett. 101, 261905 (2012); http://dx.doi.org/10.1063/1.4773369 (4 pages)

Online Publication Date: 27 December 2012

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The focalization of elastic waves within a two dimensional gradient-index phononic crystal (GRIN PC) is numerically and experimentally investigated. The structure is formed by a square lattice of air holes in a silicon plate with transverse variation of holes’ diameters. The geometry and efficiency of focalization are computed with a finite element method. A non-contact laser-ultrasonic technique is used both to excite flexural Lamb waves and to monitor in situ the displacements field within the GRIN PC. The efficient subwavelength focusing is achieved and analyzed; furthermore, we describe the oscillatory behavior of focusing and show the relationship between the responses of waves in GRIN PC and the source intensity.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
42.70.Qs Photonic bandgap materials
42.79.Ry Gradient-index (GRIN) devices

Nanoscale study of the current transport through transrotational NiSi/n-Si contacts by conductive atomic force microscopy

Alessandra Alberti and Filippo Giannazzo

Appl. Phys. Lett. 101, 261906 (2012); http://dx.doi.org/10.1063/1.4773488 (4 pages)

Online Publication Date: 28 December 2012

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See Also: Publisher's Note

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The average electrical behaviour of transrotational NiSi layers used as contacts in diode structures on n-type Si was correlated to the local structure and conduction paths inside each domain by using conductive-atomic force microscopy. It was found that, independently of the domain orientation, the central portion of the domain (core ∼ 20 nm) possesses a Schottky barrier lower than in the rest of the structure. This was ascribed to an effect of the structural coupling between the NiSi lattice and the silicon substrate as realised at the interface in virtue of the pseudoepitaxial relationship established since the early stages of the reaction.
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85.30.Kk Junction diodes
73.30.+y Surface double layers, Schottky barriers, and work functions
85.30.Hi Surface barrier, boundary, and point contact devices
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