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27 Mar 2006

Volume 88, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 88, 133105 (2006); http://dx.doi.org/10.1063/1.2189203 (3 pages)

Premila Mohan, Junichi Motohisa, and Takashi Fukui
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Viscoelastic properties of polymer surfaces investigated by nanoscale dynamic mechanical analysis

A. Chakravartula and K. Komvopoulos

Appl. Phys. Lett. 88, 131901 (2006); http://dx.doi.org/10.1063/1.2189156 (3 pages) | Cited 26 times

Online Publication Date: 27 March 2006

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The viscoelastic properties of polymer surfaces were investigated by nanoscale dynamic mechanical analysis (nano-DMA) involving contact force modulation in the frequency range of 10–200 Hz. Nano-DMA experiments were performed with a Berkovich diamond tip of nominal radius of curvature equal to ∼ 100 nm under a mean contact force of 8–10 μN and alternating force equal to 2% of the mean force. Variations in the loss tangent, storage modulus, and loss modulus of low- and high-density polyethylene and ultrahigh molecular weight polyethylene with the force frequency demonstrated significantly different viscoelastic behaviors for shallow depths (<40 nm) than for relatively large depths (i.e., 75–100 nm). The effects of alternating force frequency and indentation depth on the viscoelastic properties of the different polyethylene materials are interpreted in terms of the microstructure characteristics and the molecular chain mobility at the polymer surfaces. The results show that nano-DMA is an effective technique for nanoscale studies of the viscoelastic behavior of polymer surfaces.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
68.35.Gy Mechanical properties; surface strains
61.41.+e Polymers, elastomers, and plastics
77.22.Gm Dielectric loss and relaxation
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

A 200 nm thick glass-forming metallic film for fatigue-property enhancements

C. L. Chiang, J. P. Chu, F. X. Liu, P. K. Liaw, and R. A. Buchanan

Appl. Phys. Lett. 88, 131902 (2006); http://dx.doi.org/10.1063/1.2189917 (3 pages) | Cited 22 times

Online Publication Date: 27 March 2006

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In this letter, we report the fatigue-property enhancement by a thin layer of glass-forming film. The fatigue life of a 316L stainless steel is considerably improved by at least 30 times, depending on the maximum applied stress when it is coated with a 200 nm thick Zr47Cu31Al13Ni9 film. The application of the sputtered film yields an increase of the fatigue limit by 30%. The smooth surface, good adhesion, and compressive residual stress are found to play beneficial roles in achieving superior fatigue properties, revealing the glass-forming film as a potential material to enhance fatigue properties.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
81.65.-b Surface treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)

Size reduction of nanoparticle ink patterns by fluid-assisted dewetting

Cedric P. R. Dockendorf, Tae-Youl Choi, Dimos Poulikakos, and Andreas Stemmer

Appl. Phys. Lett. 88, 131903 (2006); http://dx.doi.org/10.1063/1.2187410 (3 pages) | Cited 8 times

Online Publication Date: 28 March 2006

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A novel method is proposed to considerably reduce the size of partially wetting patterns of nanopaticle solutions (nanoinks) on a substrate. A nanoink prepared by suspending gold nanoparticles in toluene was deposited on a glass substrate by writing a thin line with the width of 70 μm. A water droplet of about 100 μl covering the pattern was employed to shrink the pattern by transport of the toluene from the nanoink to the water region triggered by controlled heat addition from the substrate, which increased the solubility of toluene into water (these two liquids are practically immiscible at room temperature). During the dewetting phase, the three-phase-contact line is pulled by the uncompensated Young’s force. The dewetting dynamics is explained by the action of thermocapillarity enhanced by the convection microflow generated in the water layer.
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68.08.Bc Wetting
82.70.Kj Emulsions and suspensions
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
64.75.-g Phase equilibria
47.55.P- Buoyancy-driven flows; convection

Two-way indent depth recovery in a NiTi shape memory alloy

Yijun Zhang, Yang-Tse Cheng, and David S. Grummon

Appl. Phys. Lett. 88, 131904 (2006); http://dx.doi.org/10.1063/1.2189201 (3 pages) | Cited 4 times

Online Publication Date: 28 March 2006

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Controlled reversible changes in surface texture and topography are of interest to many applications, including information storage, optical communication devices, micro-fluidic instruments for drug delivery, and smart tribological surfaces for friction and wear control. Here, we demonstrate a method of inducing two-way reversible changes in an indentation made on the surface of a shape memory NiTi alloy. The two-way indent shape change is accomplished by thermomechanical training of spherical indents in NiTi shape memory alloy. After training, spherical indents exhibit two-way depth recovery: Shallow indent depth at high temperature and deep indent depth at low temperature. The reversible depth change is about 45% of the total indent depth and is stable over many cycles. The reversible depth change can have a wide range of engineering applications.
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81.40.Lm Deformation, plasticity, and creep
68.47.De Metallic surfaces
68.35.Gy Mechanical properties; surface strains
64.70.K- Solid-solid transitions
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Pq Friction, lubrication, and wear

Raman spectroscopy of pressure-induced amorphous boron carbide

X. Q. Yan, W. J. Li, T. Goto, and M. W. Chen

Appl. Phys. Lett. 88, 131905 (2006); http://dx.doi.org/10.1063/1.2189826 (3 pages) | Cited 26 times

Online Publication Date: 28 March 2006

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We report low- and high-temperature Raman spectroscopy of pressure-induced amorphous boron carbide (a-B4C). Coarsening of carbon clusters in a-B4C was characterized during heating, whereas unusual temperature coefficients of a-B4C Raman peak shifts were observed during cooling. These results experimentally evidence that the amorphization of B4C is associated with the destruction of the C–B–C chains and a-B4C is composed of sp2 carbon aromatic rings and boron clusters. This disordered structure with relatively weak carbon sp2 bonds is believed to be responsible for the loss of B4C shear strength at high pressures.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
78.35.+c Brillouin and Rayleigh scattering; other light scattering
61.43.Er Other amorphous solids
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties
62.20.-x Mechanical properties of solids

Free volume kinetics during sub-Tg structural relaxation of a bulk Pd40Ni40P20 metallic glass

Osami Haruyama and Akihisa Inoue

Appl. Phys. Lett. 88, 131906 (2006); http://dx.doi.org/10.1063/1.2189833 (2 pages) | Cited 15 times

Online Publication Date: 28 March 2006

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The structural relaxation of bulk Pd40Ni40P20 metallic glass was examined under glass transition region. Assuming the isoconfigurational structural change, the room temperature density was measured after relaxing the bulk sample at 549 K for any given time. The density relaxation was manifested by the process with a spectrum of relaxation times. The data were well described by a stretched exponential function with an average relaxation time of 1389 s and Kohlrausch exponent of 0.66. The relaxation of reduced free volume was impossible to reproduce by means of bimolecular model for flow defect concentration.
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61.43.Fs Glasses
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

Excellent soft-ferromagnetic bulk glassy alloys with high saturation magnetization

Baolong Shen, Masahiro Akiba, and Akihisa Inoue

Appl. Phys. Lett. 88, 131907 (2006); http://dx.doi.org/10.1063/1.2189910 (3 pages) | Cited 29 times

Online Publication Date: 28 March 2006

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The development of Fe-based bulk glassy alloys (BGAs) with high glass-forming ability has become a very hot research topic, not only because of the soft-magnetic properties, but also of the high fracture strength. Here we report the discovery of excellent soft-ferromagnetic BGAs in FeMoPCBSi system, without the expensive element Ga, which can be cast into glassy alloy rods with diameters range up to 4 mm by copper mold casting. These low cost Fe-based ferromagnetic BGAs exhibit high saturation magnetization of 1.27–1.44 T and superhigh initial permeability of 13 400–25 000 at 1 kHz under a field of 1 A/m.
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75.50.Bb Fe and its alloys
81.05.Bx Metals, semimetals, and alloys
81.20.-n Methods of materials synthesis and materials processing
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Microstructural refinement mechanism by controlling heating process in multiphase materials with particular reference to γ-TiAl

Hanliang Zhu, K. Maruyama, and J. Matsuda

Appl. Phys. Lett. 88, 131908 (2006); http://dx.doi.org/10.1063/1.2190076 (3 pages) | Cited 2 times

Online Publication Date: 28 March 2006

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The microstructural refinement mechanism by controlling heating rate was investigated in TiAl alloys as an example of multiphase materials. During heating in the α+γ dual phase field of TiAl alloys, the phase transformation of γ to α takes place. The increase in heating rate raises the extent of superheating, leading to increases in driving force and the nucleation rate of the α phase. At higher heating rate, numerous α nuclei form and lengthen, resulting in a fine α2/γ lamellar microstructure after subsequent cooling. The theoretical prediction was demonstrated by the experimental results obtained on a fully lamellar Ti-48Al alloy.
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81.05.Bx Metals, semimetals, and alloys
81.30.-t Phase diagrams and microstructures developed by solidification and solid-solid phase transformations
64.70.K- Solid-solid transitions

Fast synthesis method and phase diagram of hydrogen clathrate hydrate

Konstantin A. Lokshin and Yusheng Zhao

Appl. Phys. Lett. 88, 131909 (2006); http://dx.doi.org/10.1063/1.2190273 (3 pages) | Cited 24 times

Online Publication Date: 29 March 2006

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We report a very fast method for hydrogen clathrate production. The formation of hydrogen clathrate from H2 gas and ice-Ih at 77–273 K occurs at least 100 times faster compared to the reaction with water. This effect is probably the result of a partial penetration of hydrogen into the ice-Ih body, which favors clathrate formation. With the ice method, the ice-Ih/48H2*136H2O system can quickly trap and release up to 3.77 mass % of hydrogen, which gives it an advantage over other chemical-bonding hydrogen storage technologies. New data on the hydrogen-water phase diagram are presented and discussed.
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81.30.Dz Phase diagrams of other materials
84.60.-h Direct energy conversion and storage

X-ray elastic constants for α-Al2O3

D. B. Hovis, A. Reddy, and A. H. Heuer

Appl. Phys. Lett. 88, 131910 (2006); http://dx.doi.org/10.1063/1.2189071 (3 pages) | Cited 6 times

Online Publication Date: 29 March 2006

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It has recently been discovered that there is a long-standing error in the sign of c14 for α-Al2O3—it is +22 rather than −22 GPa. Although c14 is the smallest of the six elastic constants of α-Al2O3 (space group Rmathc), it has a significant effect on the Reuss x-ray elastic constants, particularly for the {02math4} reflection. Measurements using the Advanced Photon Source have confirmed that the sign of c14 must be positive. Use of the wrong sign of c14 can induce errors in excess of 30% in the measured residual stresses of α-Al2O3 scales.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
61.05.cp X-ray diffraction

Strain relief by periodic misfit arrays for low defect density GaSb on GaAs

S. H. Huang, G. Balakrishnan, A. Khoshakhlagh, A. Jallipalli, L. R. Dawson, and D. L. Huffaker

Appl. Phys. Lett. 88, 131911 (2006); http://dx.doi.org/10.1063/1.2172742 (3 pages) | Cited 43 times

Online Publication Date: 30 March 2006

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We demonstrate the growth of a low dislocation density, relaxed GaSb bulk layer on a (001) GaAs substrate. The strain energy generated by the 7.78% lattice mismatch is relieved by a periodic array of 90° misfit dislocations. The misfit array is localized at the GaSb/GaAs interface and has a period of 5.6 nm which is determined by transmission electron microscope images. No threading dislocations are visible. The misfits are identified as 90°, rather than 60°, using Burger’s circuit analysis, and are therefore not associated with generation of threading dislocations. A low dislocation density and planar growth mode is established after only 3 monolayers of GaSb deposition as revealed by reflection high-energy electron diffraction patterns. Calculations corroborate the materials characterization and indicate the strain energy generated by the 7.78% lattice mismatch is almost fully dissipated by the misfit array. The low dislocation density bulk GaSb material on GaAs enabled by this growth mode will lead to new devices, especially in the infrared regime, along with novel integration schemes.
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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.)
68.37.Lp Transmission electron microscopy (TEM)
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.05.Ea III-V semiconductors

SnO2 nanoparticles in silica: Nanosized tools for femtosecond-laser machining of refractive index patterns

A. Paleari, E. Franchina, N. Chiodini, A. Lauria, E. Bricchi, and P. G. Kazansky

Appl. Phys. Lett. 88, 131912 (2006); http://dx.doi.org/10.1063/1.2192579 (3 pages) | Cited 6 times

Online Publication Date: 31 March 2006

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We show that SnO2 nanoclusters in silica interact with ultrashort infrared laser pulses focused inside the material generating a hydrostatic compression and photoelastic response of the surrounding glass. This effect, together with the laser-induced nanocluster amorphization, gives rise to positive or negative refractive-index changes, up to 10−2, depending on the beam-power density. This result points out a wide tuning of the refractive index patterns obtainable in silica-based optical technology.
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78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
42.86.+b Optical workshop techniques
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Rx Nanocrystalline materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.16.-c Methods of micro- and nanofabrication and processing

Effects of Ag/indium tin oxide contact to a SiC doping layer on performance of Si nanocrystal light-emitting diodes

Chul Huh, Nae-Man Park, Jae-Heon Shin, Kyung-Hyun Kim, Tae-Youb Kim, Kwan Sik Cho, and Gun Yong Sung

Appl. Phys. Lett. 88, 131913 (2006); http://dx.doi.org/10.1063/1.2191409 (3 pages) | Cited 10 times

Online Publication Date: 31 March 2006

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We report on the effects of a very thin Ag (2.5 nm) interlayer between the indium tin oxide (ITO) current spreading layer and a SiC doping layer on silicon nanocrystals (nc-Si) embedded in silicon nitride film on the electrical and optical performance of the light-emitting diodes (LEDs). The forward voltage at a current of 20 mA of the nc-Si LED with a Ag interlayer was decreased by 2.5 V compared to that of the nc-Si LED without one due to the decrease in the contact resistance. In addition, the light output power of the nc-Si LED with a Ag interlayer was also enhanced by 40%. This result strongly indicates that the Ag/ITO contact scheme can serve as a highly promising contact scheme to a SiC film for the realization of the nc-Si LEDs with a high efficiency.
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85.60.Jb Light-emitting devices

Atomic structure of (111) SrTiO3/Pt interfaces

Steffen Schmidt, Dmitri O. Klenov, Sean P. Keane, Jiwei Lu, Thomas E. Mates, and Susanne Stemmer

Appl. Phys. Lett. 88, 131914 (2006); http://dx.doi.org/10.1063/1.2191410 (3 pages) | Cited 4 times

Online Publication Date: 31 March 2006

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Atomic resolution high-angle annular dark field (HAADF) imaging in scanning transmission electron microscopy was used to investigate the interface atomic structure of epitaxial, (111) oriented SrTiO3 films on epitaxial Pt electrodes grown on (0001) sapphire. The cube-on-cube orientation relationship of SrTiO3 on Pt was promoted by the use of a Ti adhesion layer underneath the Pt electrode. While a Ti-rich Pt surface was observed before SrTiO3 growth, HAADF images showed an atomically abrupt SrTiO3/Pt interface with no interfacial layers. The SrTiO3 films contained two twin variants that were related by a 180° rotation about the ⟨111⟩ surface normal. HAADF images showed two different interface atomic arrangements for the two twins. The role of Ti in promoting (111) epitaxy and the implications for the dielectric properties are discussed.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
68.37.Lp Transmission electron microscopy (TEM)
68.55.-a Thin film structure and morphology
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