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24 May 2004

Volume 84, Issue 21, pp. 4141-4340

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 4316 (2004); http://dx.doi.org/10.1063/1.1756684 (3 pages)

Seok Pil Jang and Stephen U. S. Choi
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Role of intericosahedral chains on the hardness of sputtered boron carbide films

L. G. Jacobsohn, R. D. Averitt, C. J. Wetteland, R. K. Schulze, M. Nastasi, L. L. Daemen, Z. Jenei, and P. Asoka-Kumar

Appl. Phys. Lett. 84, 4173 (2004); http://dx.doi.org/10.1063/1.1755841 (3 pages) | Cited 8 times

Online Publication Date: 6 May 2004

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The relationship between the structure and mechanical properties of sputter-deposited boron carbide films was investigated. Changes in the structure induced by annealing were characterized in terms of chemical composition, chemical bonding, and concentrations of defects and trapped impurities. The creation of intericosahedral chains for higher annealing temperatures was revealed by infrared and Raman measurements, and the intensity of the infrared band at 1500 cm−1 was found to be related to the hardness. The presence of residual trapped Ar atoms and of open-volume defects is insensitive to relatively high annealing temperatures and does not influence the recovery of the hardness. Our results suggest postdeposition annealing as a pathway to enhance the mechanical properties of boron carbide films. © 2004 American Institute of Physics.
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68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Cd Deposition by sputtering
78.30.Jw Organic compounds, polymers

Spatial distribution of the red luminescence in pristine, γ rays and ultraviolet-irradiated multimode optical fibers

S. Girard, J.-P. Meunier, Y. Ouerdane, A. Boukenter, B. Vincent, and A. Boudrioua

Appl. Phys. Lett. 84, 4215 (2004); http://dx.doi.org/10.1063/1.1755832 (3 pages) | Cited 13 times

Online Publication Date: 7 May 2004

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In this letter, a confocal microscopy setup was used to evaluate, with a resolution of 2 μm, the nonuniform spatial distributions of the red photoluminescence (640–750 nm) in pristine, γ rays (∼1 MeV, 1.2 kGy, and 0.33 Gy/s) and ultraviolet (244 nm and 127 J/cm2) irradiated multimode optical fibers. In pristine samples, the Raman scattering is predominant and the emitting centers are only present at low concentration in the fiber cladding. However, these centers are generated by both irradiations in the whole fiber cross sections, in particular near the core–cladding interface. The spectral deconvolution of the luminescence spectra showed that the Non-Bridging Oxygen Hole Centers are mainly responsible for this red luminescence. For both irradiation types, these centers seem to be predominantly created from precursor sites: strained Si–O–Si bonds which could be induced during the fiber drawing process. © 2004 American Institute of Physics.
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42.81.Cn Fiber testing and measurement of fiber parameters
42.88.+h Environmental and radiation effects on optical elements, devices, and systems
78.55.Hx Other solid inorganic materials

Relationship between the Li ionic conduction and the local structures in LiyLa(1−y)/3NbO3

Masanobu Nakayama, Hiromasa Ikuta, Yoshiharu Uchimoto, and Masataka Wakihara

Appl. Phys. Lett. 84, 4227 (2004); http://dx.doi.org/10.1063/1.1755844 (3 pages) | Cited 4 times

Online Publication Date: 7 May 2004

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In order to demonstrate the importance of local structural study for the lithium ionic conductor, we investigate the local structure of the Li+ conductor with perovskite structure, LiyLa(1−y)/3NbO3 (0 ⩽ y ⩽ 0.25) using the extended x-ray absorption fine structure (EXAFS) technique. The results of EXAFS measurement imply that changes of the local structure are more crucial for the property on ionic conductivity than that of the lattice parameter obtained by x-ray diffraction technique. © 2004 American Institute of Physics.
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66.30.H- Self-diffusion and ionic conduction in nonmetals
61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
82.47.Aa Lithium-ion batteries

Electronic structure of Zn1−xCoxO using photoemission and x-ray absorption spectroscopy

S. C. Wi, J.-S. Kang, J. H. Kim, S.-B. Cho, B. J. Kim, S. Yoon, B. J. Suh, S. W. Han, K. H. Kim, K. J. Kim, B. S. Kim, H. J. Song, H. J. Shin, J. H. Shim, and B. I. Min

Appl. Phys. Lett. 84, 4233 (2004); http://dx.doi.org/10.1063/1.1756197 (3 pages) | Cited 66 times

Online Publication Date: 7 May 2004

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Electronic structures of homogeneous bulk samples of Zn0.9Co0.1O which do not exhibit diluted ferromagnetic semiconducting (DMS) behavior have been investigated using photoemission spectroscopy and x-ray absorption spectroscopy. We have found that the Co ions in Zn1−xCoxO are in the divalent Co2+(d7) states under the tetrahedral symmetry. Our finding indicates that the DMS properties will not be produced when Co ions are properly substituted for Zn sites, implying that the DMS properties observed in Zn1−xCoxO thin films are likely to be extrinsic. © 2004 American Institute of Physics.
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71.20.-b Electron density of states and band structure of crystalline solids
79.60.-i Photoemission and photoelectron spectra
78.70.Dm X-ray absorption spectra

High-energy x-ray scattering in grazing incidence from nanometer-scale oxide wires

Osami Sakata, Masaki Takata, Hiroyoshi Suematsu, Akifumi Matsuda, Shusaku Akiba, Atsushi Sasaki, and Mamoru Yoshimoto

Appl. Phys. Lett. 84, 4239 (2004); http://dx.doi.org/10.1063/1.1756207 (3 pages) | Cited 11 times

Online Publication Date: 7 May 2004

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A method has been developed for analyzing the structure of crystalline nanowires deposited on a crystal surface. It combined in-air grazing-incidence surface scattering with high-energy synchrotron x-ray scattering. The technique has allowed a direct reciprocal-lattice space mapping of the x-ray intensities scattered from ultrathin nanowires. Using this method, the sheet-shape diffraction emanating from ultrathin NiO wires was observed. The average nanowire–nanowire distance of 46 nm and a crystallographic domain size of approximately 7.5 nm across the nanowire were evaluated. © 2004 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
61.46.-w Structure of nanoscale materials
85.35.-p Nanoelectronic devices

Electric field and temperature-induced removal of moisture in nanoporous organosilicate films

N. Biswas, J. A. Lubguban, and S. Gangopadhyay

Appl. Phys. Lett. 84, 4254 (2004); http://dx.doi.org/10.1063/1.1757019 (3 pages) | Cited 1 time

Online Publication Date: 7 May 2004

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The effects of bias-temperature-stress (BTS) or simply temperature-stress (TS) on nanoporous low-k methylsilsesquioxane films are studied. Initially, the as-given and O2 ashed/etched films exhibit physical adsorption of moisture as revealed from the electrical behavior of the samples after 15 days. The temperature stressing at 170 °C volatilized the adsorbed water but is unable to remove chemisorb and hydrophillic Si–OH groups. As a result, the TS films remain susceptible to moisture. BTS at 170 °C also removes adsorbed water. More important, the surfaces under the metal-insulator structure were dehydroxylated by breaking the chemisorb Si–OH group facilitating the formation of siloxane bonds that prevents adsorption of moisture even after 60 days. © 2004 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
81.05.Rm Porous materials; granular materials
68.43.Mn Adsorption kinetics

Electrochromism in switchable nematic emulsions

F. P. Nicoletta, D. Cupelli, G. De Filpo, and G. Chidichimo

Appl. Phys. Lett. 84, 4260 (2004); http://dx.doi.org/10.1063/1.1758294 (3 pages) | Cited 10 times

Online Publication Date: 7 May 2004

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Switchable nematic emulsions are composite systems formed by liquid-crystal droplets dispersed in a fluid, homogeneous, monomer matrix, which can be turned from an opaque to an optically transparent state by application of a suitable ac electric field. An electrochromic device provides a reversible and visible change in its transmittance and/or reflectance as the result of either oxidation or reduction electrochemical processes. Both devices have been proven to be useful for a variety of electro-optical applications as switchable windows, electromagnetic shutters, and displays. This letter reports preliminary results on a bifunctional device based on a switchable nematic emulsion, which hosts electrochemical reactions. The presence of a liquid-crystal dispersion ensures the switching from a scattering and opaque state to a transmissive and transparent state, while the oxidation–reduction reactions allow a contemporary and independent change in color. © 2004 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Pseudoelasticity of shape-memory titanium–nickel films subjected to dynamic nanoindentation

X.-G. Ma and K. Komvopoulos

Appl. Phys. Lett. 84, 4274 (2004); http://dx.doi.org/10.1063/1.1737463 (3 pages) | Cited 18 times

Online Publication Date: 7 May 2004

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Surface force microscopy was used to examine the dynamic indentation response of austenitic titanium–nickel (TiNi) films sputtered on oxidized silicon substrates. Results demonstrate the significance of indentation cycles, time at maximum contact load, and loading/unloading rate on the nanoscale pseudoelastic behavior of the TiNi films. The dynamic behavior of the films is interpreted in terms of the mechanisms responsible for the energy dissipated in the absence of irreversible deformation. The significant amount of mechanical work dissipated without permanent deformation illustrates the potential of TiNi films as structural materials for dynamic microdevice applications. © 2004 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
62.20.D- Elasticity
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
64.70.K- Solid-solid transitions
81.30.Kf Martensitic transformations
68.55.-a Thin film structure and morphology
68.35.Gy Mechanical properties; surface strains
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Boron diffusion in amorphous silicon and the role of fluorine

R. Duffy, V. C. Venezia, A. Heringa, B. J. Pawlak, M. J. P. Hopstaken, G. C. J. Maas, Y. Tamminga, T. Dao, F. Roozeboom, and L. Pelaz

Appl. Phys. Lett. 84, 4283 (2004); http://dx.doi.org/10.1063/1.1751225 (3 pages) | Cited 22 times

Online Publication Date: 7 May 2004

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We demonstrate that boron diffuses at high concentrations during low-temperature thermal annealing in amorphous silicon pre-amorphized by germanium ion implantation. For a typical boron ultrashallow junction doping profile, concentrations as high as 2×1020 cm−3 appear to be highly mobile at 500 and 600 °C in the amorphous silicon region before recrystallization. In crystalline silicon at the same temperatures the mobile boron concentration is at least two orders of magnitude lower. We also show that boron diffusivity in the amorphous region is similar with and without fluorine. The role of fluorine is not to enhance boron diffusivity, but to dramatically slow down the recrystallization rate, allowing the boron profile to be mobile up to the concentration of 2×1020 cm−3 for a longer time. © 2004 American Institute of Physics.
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66.30.J- Diffusion of impurities
61.72.uf Ge and Si
61.72.S- Impurities in crystals
61.72.Cc Kinetics of defect formation and annealing
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)

Visible cathodoluminescence from Eu-implanted single- and polycrystal c-BN annealed under high-temperature, high-pressure conditions

Ulrich Vetter, Hans Hofsäss, and Takashi Taniguchi

Appl. Phys. Lett. 84, 4286 (2004); http://dx.doi.org/10.1063/1.1753053 (3 pages) | Cited 17 times

Online Publication Date: 7 May 2004

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Red and red/blue cathodoluminescence in the temperature range 12 to 300 K was obtained from single- and polycrystal cubic boron nitride bulk samples implanted with europium and annealed under high-temperature, high-pressure conditions. All observed radiative intra-4f electron transitions of Eu3+ can be assigned to transitions starting from the 5D0 level of Eu3+. Additionally, radiative 4fN−15d→4fN electron transitions related to Eu2+ were detected in the polycrystal c-BN specimens. The higher-resolution Stark level as well as the time-resolved cathodoluminescence spectroscopy suggest that the Eu ions occupy at least two different sites in the c-BN host. © 2004 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
68.47.Fg Semiconductor surfaces
61.72.uj III-V and II-VI semiconductors
78.47.-p Spectroscopy of solid state dynamics
61.72.Cc Kinetics of defect formation and annealing

Influence of O and C co-implantation on the lattice site of Er in GaN

B. De Vries, V. Matias, A. Vantomme, U. Wahl, E. M. C. Rita, E. Alves, A. M. L. Lopes, and J. G. Correia

Appl. Phys. Lett. 84, 4304 (2004); http://dx.doi.org/10.1063/1.1756196 (3 pages) | Cited 5 times

Online Publication Date: 7 May 2004

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The lattice location of low-dose implanted Er in GaN, GaN:O, and GaN:C was investigated using the emission channeling technique. The conversion electrons emitted by the probe isotope 167mEr give direct evidence that the majority ( ≈ 90%) of Er atoms are located on substitutional Ga sites for all samples. Annealing up to 900 °C does not change these fractions, although it reduces the Er root-mean-square (rms) displacements. The only visible effect of oxygen or carbon doping is a small increase in the rms displacements with respect to the undoped sample. © 2004 American Institute of Physics.
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61.72.up Other materials

Transition of deformation and fracture behaviors in nanostructured face-centered-cubic metals

Hongqi Li and Fereshteh Ebrahimi

Appl. Phys. Lett. 84, 4307 (2004); http://dx.doi.org/10.1063/1.1756198 (3 pages) | Cited 55 times

Online Publication Date: 7 May 2004

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Tensile stress–strain curves demonstrate that single-phase nanocrystalline face-centered-cubic (fcc) metals are intrinsically ductile and their failure begins with necking. However, the area reductions and the fracture behaviors were found to be dependent on the grain size. When plastic deformation is governed by dislocation activity, the nanocrystalline samples behave similar to the conventional coarse-grained materials. As the grain size is reduced to the regime where grain boundary sliding dominates, the material shows very high strain-hardening rate and the tensile samples fail by microcracking with no noticeable reduction in area. © 2004 American Institute of Physics.
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62.20.F- Deformation and plasticity
62.20.M- Structural failure of materials
61.46.-w Structure of nanoscale materials

Indium versus hydrogen-terminated GaN(0001) surfaces: Surfactant effect of indium in a chemical vapor deposition environment

John E. Northrup and Chris G. Van de Walle

Appl. Phys. Lett. 84, 4322 (2004); http://dx.doi.org/10.1063/1.1757020 (3 pages) | Cited 17 times

Online Publication Date: 7 May 2004

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First-principles pseudopotential density functional calculations of the relative stability of H- and In-terminated GaN(0001) surfaces are reported. These total energy calculations show that surfaces terminated by one or two monolayers of In are more stable under typical metalorganic vapor deposition conditions than the H-terminated surface structures that have been proposed. Indium may act as a surfactant to improve the growth morphology of GaN films grown by metalorganic vapor deposition via a mechanism similar to that operative in molecular beam epitaxy. © 2004 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Nc Total energy and cohesive energy calculations
73.20.At Surface states, band structure, electron density of states
68.47.Fg Semiconductor surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.-a Thin film structure and morphology
82.70.Uv Surfactants, micellar solutions, vesicles, lamellae, amphiphilic systems, (hydrophilic and hydrophobic interactions)

Measurement and noise characterization of optically induced index changes using THz interferometry

J. A. Small and R. A. Cheville

Appl. Phys. Lett. 84, 4328 (2004); http://dx.doi.org/10.1063/1.1758292 (3 pages)

Online Publication Date: 7 May 2004

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A Michelson interferometer designed for broadband single-cycle THz pulses is used to characterize optically induced index changes in semiconductors which result in submicron changes in optical path length. The interferometric measurements are compared both to standard THz time-domain spectroscopy (THz-TDS) and differential THz-TDS based on modulation of the sample. By analyzing noise contributions in THz spectroscopy systems, it is shown that the destructive interference achieved in THz interferometry reduces both some sources of random errors as well as errors due to system drift. © 2004 American Institute of Physics.
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07.60.Ly Interferometers
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
81.05.Cy Elemental semiconductors
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