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1 Oct 2007

Volume 91, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 143101 (2007); http://dx.doi.org/10.1063/1.2789812 (3 pages)

Hyun S. Kim, Hua Qin, and Robert H. Blick
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Unexpected formation of ε iron nitride by gas nitriding of nanocrystalline α-Fe films

M. Wohlschlögel, U. Welzel, and E. J. Mittemeijer

Appl. Phys. Lett. 91, 141901 (2007); http://dx.doi.org/10.1063/1.2793176 (3 pages) | Cited 7 times

Online Publication Date: 1 October 2007

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Polycrystalline iron thin films exhibiting different crystallite sizes, which were deposited on α-Al2O3 substrates by molecular beam epitaxy, were nitrided in a NH3/H2 gas mixture. After different nitriding treatments the specimens were prepared and analyzed by focused ion beam microscopy and x-ray diffraction. It was found that formation of ε-Fe3N1+x occurs upon nitriding of specimens exhibiting a small crystallite size at values of the thermodynamic nitriding parameters for which pure γ′-Fe4N1−x is predicted to form according to bulk thermodynamics. This unexpected phenomenon is explained as a consequence of the nanocrystalline nature on the thermodynamics of the binary system iron-nitrogen.
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81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
61.46.Hk Nanocrystals

Fullerene nanostructure-induced excellent mechanical properties in hydrogenated amorphous carbon

Qi Wang, Chengbing Wang, Zhou Wang, Junyan Zhang, and Deyan He

Appl. Phys. Lett. 91, 141902 (2007); http://dx.doi.org/10.1063/1.2794017 (3 pages) | Cited 23 times

Online Publication Date: 1 October 2007

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Hydrogenated amorphous carbon films were deposited by dc-pulse plasma chemical vapor deposition. The structure of as-prepared films, characterized by transmission electron microscopy, Raman spectra, and x-ray photoelectron spectra, is considered as nanocomposite thin films with C60 and fullerene crystalline nanoparticles embedded in amorphous sp2 and sp3 carbon matrices. The high hardness and high elastic recovery of as-prepared films are attributed to the unique structure that C60 and fullerene nanocrystalline grains (soft) dispersed in amorphous carbon phase (hard) to form a network structure, which restrains the dislocation migration, assists the stress relaxation, and hence, enhances the mechanical properties of the films.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.25.-g Mechanical properties of nanoscale systems
68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
61.46.-w Structure of nanoscale materials

Complete in-plane polarization anisotropy of the A exciton in unstrained A-plane GaN films

Pranob Misra, O. Brandt, H. T. Grahn, H. Teisseyre, M. Siekacz, C. Skierbiszewski, and B. Łucznik

Appl. Phys. Lett. 91, 141903 (2007); http://dx.doi.org/10.1063/1.2794402 (3 pages) | Cited 12 times

Online Publication Date: 1 October 2007

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Using reflectance spectroscopy, the in-plane polarization behavior of unstrained C- and A-plane GaN films is experimentally investigated. While no in-plane polarization anisotropy is observed for all three band-gap related excitons (A, B, and C) in unstrained C-plane GaN films, the A exciton is completely linearly polarized perpendicular to the c axis in unstrained A-plane GaN films. However, the B and C excitons are only partially polarized. This observation is in excellent agreement with results based on band-structure calculations using the Bir-Pikus Hamiltonian for the wurtzite crystal structure.
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78.66.Fd III-V semiconductors
71.35.-y Excitons and related phenomena
71.20.Nr Semiconductor compounds

Design and formation mechanism of self-organized core/shell structure composite powder in immiscible liquid system

Cui Ping Wang, Xing Jun Liu, Rong Pei Shi, Chen Shen, Yunzhi Wang, Ikuo Ohnuma, Ryosuke Kainuma, and Kiyohito Ishida

Appl. Phys. Lett. 91, 141904 (2007); http://dx.doi.org/10.1063/1.2794415 (3 pages) | Cited 9 times

Online Publication Date: 1 October 2007

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Under the guidance of the calculation of phase diagrams method, the self-organized Cu alloy/stainless steel composite powders with a core/shell microstructure were developed based on the gas atomization process, and the formation evolution of self-organized core/shell structure composite powders was modeled by the phase field method. This paper gives a more detailed explanation for the formation of self-organized core/shell structure composite powders from the viewpoints of thermodynamics and kinetics. Such core/shell structure composite powders have good combination of high strength and corrosion resistance (Fe-rich phase) and high electric and thermal conductivities (Cu-rich phase) with many potential advanced applications in electronic devices.
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81.05.Ni Dispersion-, fiber-, and platelet-reinforced metal-based composites
81.65.Kn Corrosion protection
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Pump-probe optical switching in prism-coupled Au:SiO2 nanocomposite waveguide film

Kyeong-Seok Lee, Taek-Sung Lee, Won-Mok Kim, Sunghun Cho, and Soonil Lee

Appl. Phys. Lett. 91, 141905 (2007); http://dx.doi.org/10.1063/1.2795338 (3 pages) | Cited 10 times

Online Publication Date: 1 October 2007

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The resonance properties due to the surface plasmon excitation of metal nanoparticles make the nanocomposite films promising for various applications such as optical switching devices. In spite of the well-known ultrasensitive operation of optical switches based on a guided wave, the application of nanocomposite film has inherent limitation originating from the excessive optical loss related to the surface plasmon resonance. In this study, we address this problem and present the experimental and theoretical analyses on the pump-probe optical switching in prism-coupled Au(1 vol %):SiO2 nanocomposite waveguide film.
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42.79.Ta Optical computers, logic elements, interconnects, switches; neural networks
42.65.Pc Optical bistability, multistability, and switching, including local field effects
42.65.Wi Nonlinear waveguides
42.79.Gn Optical waveguides and couplers
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
42.79.Bh Lenses, prisms and mirrors

Atomic-scale observation of the grain-boundary structure of Yb-doped and heat-treated silicon nitride ceramics

A. Ziegler, M. K. Cinibulk, C. Kisielowski, and R. O. Ritchie

Appl. Phys. Lett. 91, 141906 (2007); http://dx.doi.org/10.1063/1.2789390 (3 pages) | Cited 2 times

Online Publication Date: 2 October 2007

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The effect of secondary sintering additives and/or a post-sintering heat treatment on the semicrystalline atomic structure of the intergranular phase in silicon nitride ceramics is investigated. Three different Yb-doped Si3N4 ceramic compositions are examined using a scanning transmission electron microscope, whereby the intergranular atomic structure is directly imaged with Ångstrom resolution. The resulting high-resolution images show that the atomic arrangement of the Yb takes very periodic positions along the interface between the intergranular phase and the matrix grains, and that a postsintering 1250 °C heat treatment, as well as a change of the secondary sintering additives (Al2O3 vs SiO2), does not alter the atomic positions of Yb. This result has implications for the understanding of how the mechanical properties of ceramics are influenced by the presence of the nanoscale intergranular phase, and for associated computational modeling of its precise role and atomic structure.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
61.72.Mm Grain and twin boundaries
61.46.-w Structure of nanoscale materials
81.40.Gh Other heat and thermomechanical treatments
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)

Stress-induced magnetization in polycrystalline Ni–Fe–Ga ferromagnetic shape memory alloy

Sergey Kustov, Miquel Corró, and Eduard Cesari

Appl. Phys. Lett. 91, 141907 (2007); http://dx.doi.org/10.1063/1.2789698 (3 pages) | Cited 5 times

Online Publication Date: 2 October 2007

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Results are reported for simultaneous experimental studies of the stress-induced magnetic induction and of anelasticity in a polycrystalline Ni–Fe–Ga ferromagnetic shape memory alloy. The authors found in the martensitic state a linear relationship between mechanically induced induction and stress amplitude, in contrast to a strong nonlinearity of the anelastic strain. This difference between elastic and magnetic responses to applied stress points to inefficient coupling between the motion of elastic twins/domain boundaries and magnetic domain walls. They argue that, in acoustic experiments, magnetic domain walls in Ni–Fe–Ga polycrystals perform only linear displacements within local potential minima, characteristic for the microeddy current magnetomechanical damping.
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75.80.+q Magnetomechanical effects, magnetostriction
61.72.Mm Grain and twin boundaries
75.50.Bb Fe and its alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Ch Domain walls and domain structure
64.70.K- Solid-solid transitions

Vacancy clusters in ultrafine grained Al by severe plastic deformation

X. L. Wu, B. Li, and E. Ma

Appl. Phys. Lett. 91, 141908 (2007); http://dx.doi.org/10.1063/1.2794416 (3 pages) | Cited 6 times

Online Publication Date: 2 October 2007

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Bulk nanostructured metals are often formed via severe plastic deformation (SPD). The dislocations generated during SPD evolve into boundaries to decompose the grains. Vacancies are also produced in large numbers during SPD, but have received much less attention. Using transmission electron microscopy, here we demonstrate a high density of unusually large vacancy Frank loops in SPD-processed Al. They are shown to impede moving dislocations and should be a contributor to strength.
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81.40.Lm Deformation, plasticity, and creep
61.72.J- Point defects and defect clusters
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Mm Grain and twin boundaries
62.20.F- Deformation and plasticity

Optical properties of air-stable semiconducting copolymer based on polythiophene

Yusuke Shimizu, Takashi Kobayashi, Takashi Nagase, and Hiroyoshi Naito

Appl. Phys. Lett. 91, 141909 (2007); http://dx.doi.org/10.1063/1.2794729 (3 pages) | Cited 2 times

Online Publication Date: 2 October 2007

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Optical properties of thiophene based copolymer poly(2,5-bis(3-dodecylthiophen-2-yl)thieno[2,3-b]thiophene) (pBTCT) thin films have been investigated by means of optical absorption, photoluminescene (PL), PL quantum efficiency, time-resolved PL, and electroluminescence measurements. It is found that pBTCT exhibits relatively higher PL quantum efficiency (ϕPL ∼ 16%) in solid state than poly(3-hexylthiophene) (P3HT). Although the PL quantum efficiency is relatively higher, the transition dipole moment of the lowest excited state of pBTCT is not large, as found in P3HT. The electroluminescence from pBTCT light-emitting diodes is observed and its spectrum is essentially the same as the PL spectrum of pBTCT.
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78.47.-p Spectroscopy of solid state dynamics
78.55.Kz Solid organic materials
78.60.Fi Electroluminescence
78.66.Li Other semiconductors

The role of Y/lanthanides on the glass forming ability of amorphous steel

H. J. Wang, G. J. Shiflet, S. J. Poon, K. Matsuda, and S. Ikeno

Appl. Phys. Lett. 91, 141910 (2007); http://dx.doi.org/10.1063/1.2786598 (3 pages) | Cited 11 times

Online Publication Date: 3 October 2007

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The effect of yttrium on improving the amorphous steel glass formability (GFA) is investigated through chemical analysis during the early devitrification stage by employing energy dispersive x-ray spectroscopy and three-dimensional atom probe techniques. Atomic segregation and partitioning are found to occur in association with the formation of the principal competing crystalline M23(CB)6 phase. The partitioning of Y from crystallite particles is confirmed, in agreement with first principles calculations. Additionally, the GFA improvement is also attributed to the strong interatomic bonding between lanthanide and metalloids. The role of Y on improving GFA is verified with growth kinetic measurements.
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64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
61.43.Dq Amorphous semiconductors, metals, and alloys

Stretchable helical gold conductor on silicone rubber microwire

S. Béfahy, S. Yunus, T. Pardoen, P. Bertrand, and M. Troosters

Appl. Phys. Lett. 91, 141911 (2007); http://dx.doi.org/10.1063/1.2793185 (3 pages) | Cited 20 times

Online Publication Date: 3 October 2007

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Compliant and stretchable three-dimensional golden tracks are produced by metallization of silicone wires maintained under twisting and stretching constraints. Upon release, the metallic track deforms to a helix presenting a wavy and cracked surface. Wavelet and crack orientations are function of three parameters: the wire radius, the number of imposed rotations divided by the length of the cylinder, and the stretching in its axis direction. Electrical conductivity at rest and under stretching can be optimized by finding the prestraining conditions that provide the best trade off between the maximum amount of surface buckling and a limited amount of cracks.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.55.-a Thin film structure and morphology
68.35.Gy Mechanical properties; surface strains
81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
73.61.At Metal and metallic alloys

Control of bonding and epitaxy at copper/sapphire interface

Sang Ho Oh, Christina Scheu, Thomas Wagner, and Manfred Rühle

Appl. Phys. Lett. 91, 141912 (2007); http://dx.doi.org/10.1063/1.2794025 (3 pages) | Cited 4 times

Online Publication Date: 3 October 2007

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The nature of bonding evolving at a metal/oxide interface depends strongly on the termination of oxide surface stabilized in the bonding environment. Specific surface treatments in ultrahigh vacuum allow control of the termination of sapphire (α-Al2O3) (0001) surface varying from hydroxyl-terminated to aluminum-terminated to oxygen-terminated surfaces. With this capability, the interfacial bonding forming between epitaxial Cu films and sapphire (0001) substrates can be tailored. Transmission electron microscopy studies reveal that the interatomic interaction at the interface plays a decisive role in determining wetting, orientation relationship, and thermal behavior of Cu thin films.
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68.35.Np Adhesion
68.37.Lp Transmission electron microscopy (TEM)
68.35.Md Surface thermodynamics, surface energies

High-energy shift of the Urbach ultraviolet absorption from attenuated dynamical disorder in fluorine modified sol-gel silica

A. Paleari, F. Meinardi, A. Lauria, R. Lorenzi, N. Chiodini, and S. Brovelli

Appl. Phys. Lett. 91, 141913 (2007); http://dx.doi.org/10.1063/1.2794429 (3 pages) | Cited 6 times

Online Publication Date: 3 October 2007

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Fluorine modified amorphous silica has been synthetized via sol-gel route and studied through analysis of the temperature dependence of the Urbach absorption tail in the vacuum-ultraviolet region. The modified glass has a steep absorption edge above 8 eV, with the absorption coefficient α∝exp[E/EU(T)] showing Urbach energy values EU(T) ranging between 50 and 66 meV. The comparison of EU(T) with pure silica data indicates a structural softening caused by the reduction of dynamical disorder, and suggests that the F-modified sol-gel synthesis is an appropriate route for achieving high energy shifts of the absorption edge.
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78.40.Ha Other nonmetallic inorganics
61.43.Er Other amorphous solids
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Universal method to determine the thermo-optic coefficient of optical waveguide layer materials using a dual slab waveguide

David R. Cassidy and Graham H. Cross

Appl. Phys. Lett. 91, 141914 (2007); http://dx.doi.org/10.1063/1.2795340 (3 pages)

Online Publication Date: 3 October 2007

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A dual slab waveguide device method for determining the thermo-optic coefficient of waveguide layer materials is demonstrated. Temperature change-induced optical path length imbalance between two single slab waveguide modes provides the primary mechanism for detection. The waveguide mode output field phase change differences are encoded in shifts in the far field interference pattern. To illustrate the method, the thermo-optic coefficients of two In1−xGaxAsyP1−y quaternary alloys, 1.3Q and 1.15Q, are measured at a wavelength of 1.55 μm and at a center temperature of 25.2 °C. Their ratio is in excellent agreement with previous work, in accordance with optical dispersion models.
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78.20.N- Thermo-optic effects
78.20.nb Photothermal effects
42.79.Gn Optical waveguides and couplers

Aluminum diffusion and reaction in thin films of perylene-3,4,9,10-tetracarboxylic dianhydride: Depth profiles and time-dependent diffusion coefficients

Hiroyuki Yoshida and Naoki Sato

Appl. Phys. Lett. 91, 141915 (2007); http://dx.doi.org/10.1063/1.2763980 (3 pages) | Cited 6 times

Online Publication Date: 4 October 2007

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Diffusion and reaction of aluminum metal species (Al) vacuum deposited on perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) thin films were investigated using angle resolved x-ray photoemission spectroscopy. The acquired data were analyzed assuming that the diffusion of Al is described by a one-dimensional diffusion equation with a time-dependent diffusion coefficient. Depth profiles and diffusion coefficients are obtained for reacted and metallic Al separately. The results show that the metallic Al diffuses rapidly during the deposition while the metal diffusion continues at a lower rate even after the deposition at room temperature. On the other hand, the reacted Al does not diffuse further into the PTCDA layers.
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79.60.Dp Adsorbed layers and thin films

Optical detection of anchoring at free and fluid surfaces using a nematic liquid crystal sensor

Maureen K. McCamley, Gregory P. Crawford, Miha Ravnik, Slobodan Žumer, Andrew W. Artenstein, and Steven M. Opal

Appl. Phys. Lett. 91, 141916 (2007); http://dx.doi.org/10.1063/1.2795347 (3 pages) | Cited 8 times

Online Publication Date: 4 October 2007

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Polarizing micrographs of the free and fluid surfaces in contact with nematic liquid crystals were collected and compared with simulated textures to quantitatively understand surface anchoring direction and strength. Wells with square cross section and an open upper surface were filled with a nematic liquid crystal, and free energy calculations were performed to determine the existing structures and their corresponding simulated optical textures. Homeotropic, uniform planar, and degenerate planar anchorings were differentiated based on comparisons with simulations, and surface anchoring strength was estimated.
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61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order
61.30.Eb Experimental determinations of smectic, nematic, cholesteric, and other structures
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Dimensional oscillation in GaAs/AlAs quantum wells by two-dimensional standing surface acoustic waves

Tetsuomi Sogawa, Hideki Gotoh, Yoshiro Hirayama, Paulo V. Santos, and Klaus H. Ploog

Appl. Phys. Lett. 91, 141917 (2007); http://dx.doi.org/10.1063/1.2790804 (3 pages) | Cited 3 times

Online Publication Date: 5 October 2007

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We have used spatially and time-resolved photoluminescence (PL) spectroscopy recorded using a synchronized excitation method in order to investigate the mechanisms for the dynamic PL modulation of GaAs/AlAs quantum wells by two-dimensional (2D) standing surface acoustic waves (SAWs). It is clearly demonstrated that a square array of dynamic quantum dots (DQDs) is formed, which oscillates with a repetition interval equal to half of the SAW period. A 2D flatband condition appears between the DQD formations. The spatial modulation of the PL intensity is attributed to exciton migration into the tensile-strained dots created by the strain-induced band-gap modulation.
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78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
78.67.De Quantum wells
78.47.-p Spectroscopy of solid state dynamics

Direct determination of dislocation sense of closed-core threading screw dislocations using synchrotron white beam x-ray topography in 4H silicon carbide

Yi Chen and Michael Dudley

Appl. Phys. Lett. 91, 141918 (2007); http://dx.doi.org/10.1063/1.2793705 (3 pages) | Cited 3 times

Online Publication Date: 5 October 2007

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Grazing-incidence synchrotron white beam x-ray topography images of closed-core threading screw dislocations in 4H silicon carbide appear as roughly elliptically shaped white features, with an asymmetric perimeter of dark contrast which is greatly enhanced on one side or other of the g vector. Ray-tracing simulations indicate that the relative position of the enhanced dark contrast feature reveals the sense of the closed-core screw dislocation. Dislocation senses so obtained were validated using back-reflection images recorded with small Bragg angle. Therefore, the sense of the closed-core threading screw dislocations can be unambiguously revealed using either grazing-incidence or “small Bragg angle” back-reflection synchrotron white beam x-ray topography.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
42.15.Dp Wave fronts and ray tracing

Plastic flow under compression and shear in rotational diamond anvil cell: Finite-element study

Valery I. Levitas and Oleg M. Zarechnyy

Appl. Phys. Lett. 91, 141919 (2007); http://dx.doi.org/10.1063/1.2794431 (3 pages) | Cited 6 times

Online Publication Date: 5 October 2007

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Plastic flow and the evolution of distribution of the components of stress tensor in a sample under compression and shear in rotational diamond anvil cell are studied using the finite-element method (FEM). Pressure self-multiplication effect is revealed during rotation of an anvil after compression below critical force. Significant heterogeneity of accumulated plastic strain (especially near contact surface with diamond) is found. The obtained results are important for determination and interpretation of kinetics of strain-induced phase transformations (PTs) and chemical reactions.
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62.20.F- Deformation and plasticity
62.50.-p High-pressure effects in solids and liquids
02.70.Dh Finite-element and Galerkin methods

Morphological and structural evolutions of diluted Ge1−xMnx epitaxial films

J.-P. Ayoub, L. Favre, I. Berbezier, A. Ronda, L. Morresi, and N. Pinto

Appl. Phys. Lett. 91, 141920 (2007); http://dx.doi.org/10.1063/1.2794723 (3 pages) | Cited 9 times

Online Publication Date: 5 October 2007

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We investigate the structural and morphological evolutions of Ge1−xMnx films, grown by molecular beam epitaxy on Ge(100), as a function of Mn nominal concentration (x). We show that in our experimental growth conditions (growth temperature TG ∼ 160 °C), Mn atoms incorporated in the matrix increases with x up to a concentration m ∼ 0.03. Magnetic properties of the samples are mainly related to Ge3Mn5 cluster phase, while transport properties are connected to Ge:Mn matrix.
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68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
75.50.Pp Magnetic semiconductors
75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Formation mechanisms of self-assembled ZnSe nanostructures on Cl-doped ZnSe thin films grown on (100) GaAs substrates

J. W. Shin, J. Y. Lee, J. H. Jung, I. Lee, T. W. Kim, H. S. Lee, and M. D. Kim

Appl. Phys. Lett. 91, 141921 (2007); http://dx.doi.org/10.1063/1.2795081 (3 pages)

Online Publication Date: 5 October 2007

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Bright-field transmission electron microscopy images, high-resolution transmission electron microscopy images, energy dispersive spectroscopy profiles, and high-resolution x-ray diffraction curves showed that a high density of ZnSe nanostructures with a small size was formed on the Cl-doped ZnSe thin films grown on GaAs substrates. The formation of the ZnSe nanostructures was attributed to the strain energy resulting from the existence of the compressive strain generated by the accumulation of Cl impurities on the surface of the ZnSe thin film and from the residual strain existing in the ZnSe thin film with a thin thickness.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.16.Dn Self-assembly
61.46.Hk Nanocrystals
62.25.-g Mechanical properties of nanoscale systems
68.37.Lp Transmission electron microscopy (TEM)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
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Dangling-bond defects and hydrogen passivation in germanium

J. R. Weber, A. Janotti, P. Rinke, and C. G. Van de Walle

Appl. Phys. Lett. 91, 142101 (2007); http://dx.doi.org/10.1063/1.2793184 (3 pages) | Cited 46 times

Online Publication Date: 1 October 2007

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The application of germanium in complementary metal-oxide semiconductor technology is hampered by high interface-state densities. Using first-principles calculations, we investigate the effects of dangling bonds (DBs) and their interaction with hydrogen. We find that Ge DBs give rise to electronic levels below the valence-band maximum. They therefore occur exclusively in the negative charge state, explaining why they cannot be observed with electron spin resonance. The associated fixed charge is likely responsible for threshold-voltage shifts and poor performance of n-channel transistors. We also find that passivation of DBs by hydrogen will be ineffective because interstitial hydrogen is also stable exclusively in the negative charge state.
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81.05.Cy Elemental semiconductors
71.55.Cn Elemental semiconductors
71.20.Mq Elemental semiconductors
81.65.Rv Passivation
71.15.-m Methods of electronic structure calculations
76.30.-v Electron paramagnetic resonance and relaxation

The characteristic of strain relaxation on SiGe virtual substrate with thermal annealing

Wu-Ping Huang, Henry H. Cheng, Greg Sun, Re-Fa Lou, J. H. Yeh, and Tzer-Min Shen

Appl. Phys. Lett. 91, 142102 (2007); http://dx.doi.org/10.1063/1.2794016 (3 pages) | Cited 6 times

Online Publication Date: 1 October 2007

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We report the effect of thermal annealing on the strain relaxation of SiGe virtual substrate. The results show that the strain of the SiGe layer relaxes anisotropically with thermal annealing through the formation of the misfit dislocations. The strain field fluctuation persists up to the annealing temperature of 1000 °C, suggesting that the in-plane strain fluctuation could be eliminated by thermal annealing process. In particular, from the analysis of spatially resolved ultraviolet Raman mapping, we found that the normal region relaxes with a faster rate than the crosshatch region as attributed to larger initial strain.
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68.35.Gy Mechanical properties; surface strains
61.72.Cc Kinetics of defect formation and annealing
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)

Characterization of metal-ferroelectric (BiFeO3)-insulator (ZrO2)-silicon capacitors for nonvolatile memory applications

Yu-Wei Chiang and Jenn-Ming Wu

Appl. Phys. Lett. 91, 142103 (2007); http://dx.doi.org/10.1063/1.2794335 (3 pages) | Cited 18 times

Online Publication Date: 1 October 2007

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The electric properties of ferroelectric BiFeO3 (BFO) thin films with ZrO2 insulating buffer on Si substrates fabricated by chemical solution deposition were investigated. ZrO2 demonstrates excellent insulating properties on Si substrates. The metal-ferroelectric-insulator-semiconductor (MFIS) structure exhibits clockwise capacitance-voltage hysteresis loops due to the ferroelectric polarization of BFO. The maximum memory windows are 0.66 and 0.78 V, respectively, for BFO deposited on postannealed ZrO2 and on unannealed ZrO2 insulating layers. The small memory window of the BFO/ZrO2 (postannealed) MFIS is caused by significant interface trap states on the BFO/ZrO2 interface; this is supported by C-V measurements under varying frequency.
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84.32.Tt Capacitors
84.30.Sk Pulse and digital circuits
85.40.Sz Deposition technology

Magnetic field tuning of hot electron resonant capture in a semiconductor device

S. Spasov, G. Allison, A. Patanè, A. Ignatov, L. Eaves, D. K. Maude, M. Hopkinson, and R. Airey

Appl. Phys. Lett. 91, 142104 (2007); http://dx.doi.org/10.1063/1.2794407 (3 pages) | Cited 2 times

Online Publication Date: 1 October 2007

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We study hot-electron capture on resonant N-impurities in the dilute nitride Ga(AsN) alloy under high magnetic fields up to 23 T. We show that when the ratio of electric and magnetic fields reaches a critical value, the trajectory of conduction electrons becomes fully localized in real space; this leads to a negative differential conductance and current instabilities tuneable by magnetic field.
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85.30.Kk Junction diodes
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