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10 Nov 2008

Volume 93, Issue 19, Articles (19xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 93, 192501 (2008); http://dx.doi.org/10.1063/1.3013857 (3 pages)

O. Hellwig, A. Moser, E. Dobisz, Z. Z. Bandic, H. Yang, D. S. Kercher, J. D. Risner-Jamtgaard, D. Yaney, and E. E. Fullerton
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Structural relaxation and nanoindentation response in Zr–Cu–Ti amorphous thin films

H. S. Chou, J. C. Huang, L. W. Chang, and T. G. Nieh

Appl. Phys. Lett. 93, 191901 (2008); http://dx.doi.org/10.1063/1.2999592 (3 pages) | Cited 18 times

Online Publication Date: 10 November 2008

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Ternary Zr–Cu–Ti system, especial with a high Ti content, is normally difficult to be fully vitrified. In this paper, we demonstrate that cosputtering can produce amorphous Zr–Cu–Ti thin films with an excessive Ti content even as high as 19%. Sub-Tg annealing of the film induces the formation of medium-range-ordered clusters and to raise the nanohardness by 35% to 6.6 GPa. The promising mechanical properties of the sub-Tg annealed Zr52Cu29Ti19 films offer great potential for microelectromechanical system applications.
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81.05.Kf Glasses (including metallic glasses)
61.43.Fs Glasses
64.70.pe Metallic glasses
68.55.A- Nucleation and growth
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Mechanisms of nonstoichiometry in Y3Al5O12

A. P. Patel, M. R. Levy, R. W. Grimes, R. M. Gaume, R. S. Feigelson, K. J. McClellan, and C. R. Stanek

Appl. Phys. Lett. 93, 191902 (2008); http://dx.doi.org/10.1063/1.3002303 (3 pages) | Cited 10 times

Online Publication Date: 10 November 2008

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Currently, Y2O3–Al2O3 phase diagrams do not show the technologically significant yttrium aluminum garnet (Y3Al5O12,YAG) phase as deviating from the stoichiometric ratio, i.e., YAG is always expressed as a line compound. In this paper, we not only report the synthesis of nonstoichiometric YAG, but also the use of atomistic simulation to predict the defect structure associated with the deviation. By comparing the experimental variation in the lattice parameter as a function of deviation from stoichiometry with the defect volume changes predicted by atomistic simulation, we predict that nonstoichiometry in YAG proceeds via cation antisite defects.
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61.66.Bi Elemental solids
61.66.Dk Alloys
61.66.Fn Inorganic compounds
61.72.J- Point defects and defect clusters

Single shot Hugoniot of cyclohexane using a spatially resolved laser driven shock wave

C. A. Bolme, S. D. McGrane, D. S. Moore, V. H. Whitley, and D. J. Funk

Appl. Phys. Lett. 93, 191903 (2008); http://dx.doi.org/10.1063/1.3025848 (3 pages) | Cited 4 times

Online Publication Date: 10 November 2008

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To develop a more efficient method of determining pressure dependent material response to shock loading, we used the spatial energy distribution of a shock generating laser beam to create a range of nearly one-dimensional stresses in a single laser shot. Ultrafast dynamic ellipsometry was used to measure the Hugoniot and shocked refractive index of cyclohexane subject to this shock loading.
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64.30.Jk Equations of state of nonmetals
62.50.Ef Shock wave effects in solids and liquids
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Pv Polymers, organic compounds
78.47.J- Ultrafast spectroscopy (<1 psec)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Elasticity of amorphous zirconium tungstate at high pressure

Wei Liu and Baosheng Li

Appl. Phys. Lett. 93, 191904 (2008); http://dx.doi.org/10.1063/1.3023049 (3 pages) | Cited 4 times

Online Publication Date: 11 November 2008

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Compressional (VP) and shear wave (VS) velocities of the amorphous phase of ZrW2O8 have been measured up to 10.4 GPa at room temperature using ultrasonic interferometry in conjunction with synchrotron x radiation. The pressure-density relation is determined using the measured velocities. Both VP and VS, as well as the adiabatic bulk and shear moduli, exhibit monotonic increase with increasing pressure. The pressure derivatives of the bulk and shear moduli are determined to be KS0′ = 7.3(1) and G0′ = 1.8(1), with bulk and shear moduli KS0 = 61.7(5) GPa and G0 = 35.0(2) GPa. Comparing with the α phase, VP, VS, KS0, E, Θac, and σ of the amorphous phase decrease by 14.8%, 10.0%, 17.2%, 2.9%, 1.2%, and 15.5%, along with 28% and 3.2% increase in density and shear modulus, respectively.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
62.50.-p High-pressure effects in solids and liquids

Charge states of vacancies in germanium investigated by simultaneous observation of germanium self-diffusion and arsenic diffusion

Miki Naganawa, Yasuo Shimizu, Masashi Uematsu, Kohei M. Itoh, Kentarou Sawano, Yasuhiro Shiraki, and Eugene E. Haller

Appl. Phys. Lett. 93, 191905 (2008); http://dx.doi.org/10.1063/1.3025892 (3 pages) | Cited 22 times

Online Publication Date: 11 November 2008

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Diffusion of germanium (Ge) and arsenic (As) has been investigated simultaneously using As-implanted Ge isotope superlattices. No transient enhanced diffusion of As that could have arisen by the implantation damage is observed. A quadratic dependence of the Ge self-diffusion on the carrier concentration due to the Fermi level effect is observed. A precise reproduction of the Ge and As diffusion profiles by a numerical simulator lets us conclude that doubly negatively charged vacancies are the dominant point defects responsible for more than 95% of the self-diffusion in intrinsic Ge and this fraction increases even further in n-type Ge.
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61.72.jd Vacancies
66.30.H- Self-diffusion and ionic conduction in nonmetals
61.72.U- Doping and impurity implantation
61.72.J- Point defects and defect clusters

High quality AlN grown on SiC by metal organic chemical vapor deposition

Z. Chen, S. Newman, D. Brown, R. Chung, S. Keller, U. K. Mishra, S. P. Denbaars, and S. Nakamura

Appl. Phys. Lett. 93, 191906 (2008); http://dx.doi.org/10.1063/1.2988323 (3 pages) | Cited 14 times

Online Publication Date: 12 November 2008

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Growth conditions for AlN in two dimensional (2D) and three dimensional (3D) growth modes were explored on SiC using metal organic chemical vapor deposition. High quality AlN layers were obtained by alternating between 3D and 2D growth modes, referred to as modulation growth (MG). Long parallel atomic terraces without step terminations were observed in atomic force microscopy (AFM) scans of MG AlN, indicating a reduced dislocation density. X-ray diffraction rocking curves yielded full widths at half maximum (FWHM) of 86 and 363 arc sec for the (002) and (102) reflections, respectively, giving further evidence of low dislocation density in the film. 3D-2D MG also releases some of the tensile strain in the AlN film, enabling the growth of thick, crack-free AlN on SiC substrates.
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68.55.ag Semiconductors
68.37.Ps Atomic force microscopy (AFM)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.60.Bs Mechanical and acoustical properties
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

A comprehensive diagram to grow InAlN alloys by plasma-assisted molecular beam epitaxy

S. Fernández-Garrido, Ž. Gačević, and E. Calleja

Appl. Phys. Lett. 93, 191907 (2008); http://dx.doi.org/10.1063/1.3026541 (3 pages) | Cited 14 times

Online Publication Date: 12 November 2008

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Indium incorporation and surface morphology of InAlN layers grown on (0001) GaN by plasma-assisted molecular beam epitaxy were investigated as a function of the impinging In flux and the substrate temperature in the 450–610 °C range. In incorporation was found to decrease with substrate temperature due to thermal decomposition of the growing layer, while for a given temperature it increased with the impinging In flux until stoichiometry was reached at the growth front. The InN losses during growth followed an Arrhenius behavior characterized by an activation energy of 2.0 eV. A growth diagram highly instrumental to identify optimum growth conditions was established.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.66.Bi Elemental solids
61.66.Dk Alloys
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Improvement of magnetic properties of an Fe-6.5 wt. % Si alloy by directional recrystallization

Z. W. Zhang, G. Chen, H. Bei, F. Ye, G. L. Chen, and C. T. Liu

Appl. Phys. Lett. 93, 191908 (2008); http://dx.doi.org/10.1063/1.3026742 (3 pages) | Cited 8 times

Online Publication Date: 12 November 2008

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We report that magnetic properties of an Fe-6.5 wt. % Si alloy can be improved through texture control by using directional recrystallization. Columnar grain structures with column sizes of ∼ 0.38×1.2 mm2 were developed during directional recrystallization. It was found that there are low energy boundaries between columns and main textures of the specimen were {110}〈111〉 and {111}〈110〉. As a result, the coercivity of a directionally recrystallized specimen is reduced by a factor of 5 when measured along 60° away from the growth direction, as compared to a specimen consisting of ∼ 77 μm equiaxed grains.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
61.72.Mm Grain and twin boundaries

Mirror-embedded microchannel for three-dimensional measurement of particle position

Sungyoung Choi and Je-Kyun Park

Appl. Phys. Lett. 93, 191909 (2008); http://dx.doi.org/10.1063/1.3027058 (3 pages) | Cited 4 times

Online Publication Date: 12 November 2008

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To enable easy implementation of three-dimensional (3D) characterization of flowing objects, we have developed a mirror-embedded microchannel to obtain 3D positional information from two different orthogonal-axis images. A silicon mirror reflects the side view of the channel and enables simultaneous imaging of the top and side views of the channel with a single lens. The measurement principle was verified by observing fluorescent streams simultaneously in both horizontal and vertical directions of a microchannel and measuring 3D positions of 6 and 10-μm sized beads without any optical modification of a microscope and additional optical equipment.
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47.80.Jk Flow visualization and imaging
47.85.Np Fluidics
47.60.Dx Flows in ducts and channels

Directional adhesion of gecko-inspired angled microfiber arrays

Jongho Lee, Ronald S. Fearing, and Kyriakos Komvopoulos

Appl. Phys. Lett. 93, 191910 (2008); http://dx.doi.org/10.1063/1.3006334 (3 pages) | Cited 33 times

Online Publication Date: 13 November 2008

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Arrays of angled microfibers with a gecko-inspired structure were fabricated from a stiff thermoplastic polymer (polypropylene) with elastic properties similar to those of β-keratin of natural setae. Friction experiments demonstrated that this fibrillar polymer surface exhibits directional adhesion. Sliding of clean glass surfaces against and along the microfiber direction without applying an external normal force produced an apparent shear stress of 0.1 and 4.5 N/cm2, respectively. This directional adhesion is interpreted in the context of a nonlinear elastic bending model of an angled beam. Shearing and normal contact experiments yielded further evidence of the anisotropic adhesion of the fibrillar polymer and revealed the occurrence of a pull-off (adhesive) force at the instant of surface detachment, unlike vertically aligned microfiber arrays of the same material that exhibited a zero pull-off force. The results of this study provide impetus for the design of gecko-inspired adhesives with angled structures that demonstrate directional adhesion against different material surfaces.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
68.35.Np Adhesion
62.20.Qp Friction, tribology, and hardness
81.40.Pq Friction, lubrication, and wear

Optical activity in extrinsically chiral metamaterial

E. Plum, V. A. Fedotov, and N. I. Zheludev

Appl. Phys. Lett. 93, 191911 (2008); http://dx.doi.org/10.1063/1.3021082 (3 pages) | Cited 34 times

Online Publication Date: 13 November 2008

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We demonstrate optical activity in an intrinsically non-chiral anisotropic planar metamaterial. The phenomenon is due to extrinsic chirality resulting from the mutual orientation of the metamaterial structure and the incident electromagnetic wave. The polarization effect, which has a resonant nature, features a spectral band where linear birefringence is practically absent and can be easily tuned by tilting the plane of the metamaterial relative to the incident beam.
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78.20.Ek Optical activity
78.20.Fm Birefringence

Carbides in stainless steels: Results from ab initio investigations

K. O. E. Henriksson, N. Sandberg, and J. Wallenius

Appl. Phys. Lett. 93, 191912 (2008); http://dx.doi.org/10.1063/1.3026175 (3 pages) | Cited 14 times

Online Publication Date: 13 November 2008

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The useful properties of steels are due to a complicated microstructure containing iron and chromium carbides. Only some basic physical properties of these carbides are known with high precision, although the carbides may have a vital impact on the performance and longevity of the steel. To improve on this situation, we have performed extensive density-functional theory calculations of several carbides. The quantitative results are in perfect agreement with the relative empirical stability of the carbides. Also, in contradiction with experimental data, we find that Cr23C6 responsible for the hardness of stainless steels is not the most stable chromium-dominated carbide.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.35.Gy Mechanical properties; surface strains
62.20.Qp Friction, tribology, and hardness

Thickness dependence of photoluminescence for tensely strained silicon layer on insulator

J. Munguía, J-M. Bluet, M. Baira, O. Marty, G. Bremond, J. M. Hartmann, and M. Mermoux

Appl. Phys. Lett. 93, 191913 (2008); http://dx.doi.org/10.1063/1.3023058 (3 pages) | Cited 1 time

Online Publication Date: 14 November 2008

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Strain and crystalline quality of tensely strained silicon on insulator with thickness ranging from 8 to 100 nm have been evaluated by low temperature photoluminescence (PL). The strain conservation in the strained Si layers was checked by Raman spectroscopy. The PL clearly shows the emission related to the strained silicon optical band gap even for strained layers as much as seven times thicker than critical thickness (hc ∼ 15 nm). For very thin layers (9 nm), a 21 meV blueshift is observed in the PL spectra, which corresponds to a 17 meV calculated one coming from quantum confinement in the sSi layer.
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78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators
78.30.Am Elemental semiconductors and insulators

Monte Carlo analysis of stress-directed phase segregation in binary thin film alloys under nonisothermal annealing

Alex M. Nieves, V. Vitek, and T. Sinno

Appl. Phys. Lett. 93, 191914 (2008); http://dx.doi.org/10.1063/1.3027064 (3 pages) | Cited 2 times

Online Publication Date: 14 November 2008

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The use of patterned stress fields to direct phase separation in thin film alloys is investigated computationally with Monte Carlo simulations in which atomic interactions are represented by a Lennard-Jones potential. We show that careful design of annealing schedules based on consideration of the system phase diagram can lead to vastly enhanced patterning kinetics. In particular, by avoiding the low temperature formation of highly stable nuclei within the entire system, the kinetics of patterning are accelerated by rapid monomer diffusion, rather than classical Ostwald ripening in which small precipitates must dissolve to feed larger ones.
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81.30.Bx Phase diagrams of metals, alloys, and oxides
81.40.Gh Other heat and thermomechanical treatments
66.30.Fq Self-diffusion in metals, semimetals, and alloys

Omnidirectional photonic bandgaps in porous silicon based mirrors with a Gaussian profile refractive index

J. O. Estevez, J. Arriaga, A. Méndez Blas, and V. Agarwal

Appl. Phys. Lett. 93, 191915 (2008); http://dx.doi.org/10.1063/1.3028073 (3 pages) | Cited 11 times

Online Publication Date: 14 November 2008

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We have designed and fabricated one dimensional photonic bandgap (PBG) structures from dielectric multilayers of porous silicon, with a periodic repetition of a unit cell consisting of 21 layers (95%) with the refractive index varying according to the envelope of a Gaussian function and another layer (5%) with a fixed refractive index. The structures can be designed to demonstrate the wavelength scalability within the visible as well as near infrared region. Three different structures have been stacked together to enhance the width of the PBG. The omnidirectional nature of the PBG was verified experimentally and theoretically up to 68° and 89° angles of incidence, respectively.
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42.79.Bh Lenses, prisms and mirrors
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.15.Eq Optical system design
42.70.Qs Photonic bandgap materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Evolution in surface morphology of epitaxial graphene layers on SiC induced by controlled structural strain

Nicola Ferralis, Jason Kawasaki, Roya Maboudian, and Carlo Carraro

Appl. Phys. Lett. 93, 191916 (2008); http://dx.doi.org/10.1063/1.3028091 (3 pages) | Cited 8 times

Online Publication Date: 14 November 2008

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The evolution in the surface morphology of epitaxial graphene films and 6H-SiC(0001) substrates is studied by electron channeling contrast imaging. Whereas film thickness is determined by growth temperature only, increasing growth times at constant temperature affects both internal stress and film morphology. Annealing times in excess of 8–10 min lead to an increase in the mean square roughness of SiC step edges to which graphene films are pinned, resulting in compressively stressed films at room temperature. Shorter annealing times produce minimal changes in the morphology of the terrace edges and result in nearly stress-free films upon cooling to room temperature.
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68.35.bp Fullerenes
68.55.ap Fullerenes
68.60.Bs Mechanical and acoustical properties
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Gh Other heat and thermomechanical treatments
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