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17 Jan 2011

Volume 98, Issue 3, Articles (03xxxx)

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Appl. Phys. Lett. 98, 031101 (2011); http://dx.doi.org/10.1063/1.3529469 (3 pages)

Sinan Balci, Askin Kocabas, Coskun Kocabas, and Atilla Aydinli
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Atomic packing in Mg61Cu28Gd11 bulk metallic glass

X. D. Wang, H. B. Lou, S. G. Wang, J. Xu, and J. Z. Jiang

Appl. Phys. Lett. 98, 031901 (2011); http://dx.doi.org/10.1063/1.3544049 (3 pages)

Online Publication Date: 19 January 2011

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Atomic configurations of an Mg61Cu28Gd11 bulk metallic glass and its molten state have been investigated. The supercooled liquid and melt have a volume expansion coefficient only two times as large as that below glass transition temperature. Although the dominant polyhedra are 12- and 13-coordinated, the melt has slightly more polyhedra of low coordinated and less of high coordinated than in the as-cast. By Gd addition, half-octahedra with more volume accommodated are likely formed in the polyhedra, causing the local atomic environments of Mg in the melt quite different from the competing crystalline phase, thereby suppressing crystallization upon quenching.
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61.43.Fs Glasses
64.70.pe Metallic glasses
81.40.Gh Other heat and thermomechanical treatments

Nonlinear absorption of InN/InGaN multiple-quantum-well structures at optical telecommunication wavelengths

F. B. Naranjo, P. K. Kandaswamy, S. Valdueza-Felip, V. Calvo, M. González-Herráez, S. Martín-López, P. Corredera, J. A. Méndez, G. R. Mutta, B. Lacroix, P. Ruterana, and E. Monroy

Appl. Phys. Lett. 98, 031902 (2011); http://dx.doi.org/10.1063/1.3535609 (3 pages) | Cited 1 time

Online Publication Date: 19 January 2011

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We report on the nonlinear optical absorption of InN/InxGa1−xN (x = 0.8,0.9) multiple-quantum-well structures characterized at 1.55 μm by the Z-scan method in order to obtain the effective nonlinear absorption coefficient (α2) of the samples at high repetition rate. Saturable absorption is observed for the sample with x = 0.9, with an effective α2 ∼ −9×103 cm/GW for the studied optical regime. For lower In content in the barrier, reverse saturable absorption is observed, which is attributed to two-photon absorption.
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78.66.Fd III-V semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.65.-k Nonlinear optics

Strong in-plane anisotropy of magneto-optical Kerr effect in corrugated cobalt films deposited on highly ordered two-dimensional colloidal crystals

Z. L. Han, J. H. Ai, P. Zhan, J. Du, H. F. Ding, and Z. L. Wang

Appl. Phys. Lett. 98, 031903 (2011); http://dx.doi.org/10.1063/1.3544582 (3 pages)

Online Publication Date: 19 January 2011

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The corrugated cobalt films are investigated by magneto-optical Kerr effect and vibrating sample magnetometer (VSM). The films are fabricated by depositing thin cobalt layers on a large area single-domain two-dimensional (2D) hexagonal close-packing colloidal crystal. Strong in-plane anisotropy of the Kerr rotation hysteresis loop is found in sharp contrast to isotropic hysteresis loops obtained by the VSM. The anisotropy of such magneto-optical Kerr rotation disappears when randomly distributed colloidal spheres were used as the substrate. Our observations show that the magneto-optical effect does not completely correspond with the average magnetization state in such a 2D periodic magnetic network.
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78.20.Ls Magneto-optical effects
78.66.Bz Metals and metallic alloys
75.30.Gw Magnetic anisotropy
78.20.Ek Optical activity
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.70.Ak Magnetic properties of monolayers and thin films

Probing the atomic structure of amorphous Ta2O5 coatings

R. Bassiri, K. B. Borisenko, D. J. H. Cockayne, J. Hough, I. MacLaren, and S. Rowan

Appl. Phys. Lett. 98, 031904 (2011); http://dx.doi.org/10.1063/1.3535982 (3 pages) | Cited 1 time

Online Publication Date: 19 January 2011

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Low optical and mechanical loss Ta2O5 amorphous coatings have a growing number of applications in precision optical measurements systems. Transmission electron microscopy is a promising way to probe the atomic structure of these coatings in an effort to better understand the causes of the observed mechanical and optical losses. Analysis of the experimental reduced density functions using a combination of reverse Monte Carlo refinements and density functional theory molecular dynamics simulations reveals that the structure of amorphous Ta2O5 consists of clusters with increased contribution from a Ta2O2 ring fragment.
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61.43.Er Other amorphous solids
61.43.Bn Structural modeling: serial-addition models, computer simulation

Enhanced optical constants of nanocrystalline yttrium oxide thin films

C. V. Ramana, V. H. Mudavakkat, K. Kamala Bharathi, V. V. Atuchin, L. D. Pokrovsky, and V. N. Kruchinin

Appl. Phys. Lett. 98, 031905 (2011); http://dx.doi.org/10.1063/1.3524202 (3 pages)

Online Publication Date: 19 January 2011

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Yttrium oxide (Y2O3) films with an average crystallite-size (L) ranging from 5 to 40 nm were grown by sputter-deposition onto Si(100) substrates. The optical properties of grown Y2O3 films were evaluated using spectroscopic ellipsometry measurements. The size-effects were significant on the optical constants and their dispersion profiles of Y2O3 films. A significant enhancement in the index of refraction (n) is observed in well-defined Y2O3 nanocrystalline films compared to that of amorphous Y2O3. A direct, linear L-n relationship found for Y2O3 films suggests that tuning optical properties for desired applications can be achieved by controlling the size at the nanoscale dimensions.
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78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.aj Insulators
81.15.Cd Deposition by sputtering

Thermal annealing and grain boundary effects on ferromagnetism in Y2O3:Co diluted magnetic oxide nanocrystals

Y. L. Soo, T. S. Wu, C. S. Wang, S. L. Chang, H. Y. Lee, P. P. Chu, C. Y. Chen, L. J. Chou, T. S. Chan, C. A. Hsieh, J. F. Lee, J. Kwo, and M. Hong

Appl. Phys. Lett. 98, 031906 (2011); http://dx.doi.org/10.1063/1.3544059 (3 pages) | Cited 3 times

Online Publication Date: 21 January 2011

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Structures and magnetic properties of Y2O3:Co nanocrystals were investigated using high resolution transmission electron microscopy, x-ray diffraction, x-ray absorption fine structures, and superconducting quantum interference device. Cobalt atoms were found to be driven by thermal annealing from interstitial locations inside the Y2O3 nanoparticles toward particle surface, where increased O vacancies surrounding Co atoms led to increased saturation magnetization. Our results strongly support a bound magnetic polaron model for ferromagnetism in diluted magnetic oxides mostly due to magnetic dopants located on the grain boundaries.
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81.40.Gh Other heat and thermomechanical treatments
61.72.Mm Grain and twin boundaries
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
78.70.Dm X-ray absorption spectra
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Extreme low-temperature molecular beam epitaxy of ZnO-based quantum structures

S. Blumstengel, S. Sadofev, H. Kirmse, and F. Henneberger

Appl. Phys. Lett. 98, 031907 (2011); http://dx.doi.org/10.1063/1.3544575 (3 pages)

Online Publication Date: 21 January 2011

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We report on extreme low-temperature growth of ZnO by plasma-assisted molecular beam epitaxy. Epilayers and quantum well (QW) structures with very good structural and optical properties are prepared at substrate temperatures as low as 50 °C. The growth proceeds in a single crystalline layer-by-layer mode. ZnO QWs prepared on a-plane sapphire show bright excitonic luminescence with a very narrow linewidth of only 6 meV at 5 K. High-resolution transmission electron micrographs confirm that low-temperature single crystalline growth is not restricted to a particular surface termination of ZnO but works also for crystal growth along a nonpolar direction.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.21.Fg Quantum wells
78.67.De Quantum wells
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
68.55.ag Semiconductors

Vacancy-mediated diffusion in biaxially strained Si

Damien Caliste, Konstantin Z. Rushchanskii, and Pascal Pochet

Appl. Phys. Lett. 98, 031908 (2011); http://dx.doi.org/10.1063/1.3548547 (3 pages) | Cited 4 times

Online Publication Date: 21 January 2011

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We present an analysis of stress-enhanced vacancy-mediated diffusion in biaxially deformed Si (100) films as measured by the strain derivative (Q′) of the activation energy. The strain dependence of Q′ is demonstrated by means of a reanalysis of previously published experimental data, which both take into account the temperature dependence of and highlight the differences between tensile and compressive stress. Based on ab initio calculations, we predict that Q′ in pure silicon is higher under compressive conditions due to a broken degeneracy of the split-vacancy configuration.
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66.30.Lw Diffusion of other defects
81.05.Cy Elemental semiconductors
61.72.jd Vacancies
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Ductility of bulk metallic glass composites: Microstructural effects

F. Abdeljawad, M. Fontus, and M. Haataja

Appl. Phys. Lett. 98, 031909 (2011); http://dx.doi.org/10.1063/1.3531660 (3 pages)

Online Publication Date: 21 January 2011

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Recent experimental findings suggest that the problem of catastrophic failure by shear band propagation in monolithic bulk metallic glasses (BMGs) can be mitigated by forming two-phase composites consisting of a glassy metal matrix phase and a soft crystalline reinforcement phase. Here, we employ a recently introduced phase-field model in two spatial dimensions, capable of capturing shear banding in BMG systems, to address the effects of microstructure on the mechanical properties of BMG composites. We identify an important geometric length scale associated with the dendritic particles and demonstrate that it controls the overall ductility and ultimate strength of such BMG composites.
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81.40.Lm Deformation, plasticity, and creep
62.20.fk Ductility, malleability
61.43.Fs Glasses
68.70.+w Whiskers and dendrites (growth, structure, and nonelectronic properties)

Uniaxial strain-modulated conductivity in manganite superlattice (LaMnO3/SrMnO3)

Dan Cao, Meng-Qiu Cai, Wang-Yu Hu, Jun Peng, Yue Zheng, and Hai-Tao Huang

Appl. Phys. Lett. 98, 031910 (2011); http://dx.doi.org/10.1063/1.3548675 (3 pages)

Online Publication Date: 21 January 2011

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We have investigated the magnetic ordering and electrical conductivity transitions of (LaMnO3)2/(SrMnO3)2 superlattices grown on SrTiO3 substrate based on density-functional theory. It is found that the uniaxial tensile strain along the z axis of about 1.4% induced a magnetic transition from antiferromagnetic to ferromagnetic ordering. At the interface the orbital order changes from a combination of x2−y2 and 3z2−r2 to x2−y2 as strain becomes more compressive; as a result the electrical transport is transformed from three-dimensions to two-dimensions at the high uniaxial compressive strain. Our results suggest that the out-of-plane electrical conductivity can be modulated and controlled by uniaxial strain.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
73.63.-b Electronic transport in nanoscale materials and structures
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