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16 Aug 2004

Volume 85, Issue 7, pp. 1095-1302

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 1277 (2004); http://dx.doi.org/10.1063/1.1783021 (3 pages)

Katsuhiko Nishiguchi, Hiroshi Inokawa, Yukinori Ono, Akira Fujiwara, and Yasuo Takahashi
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Strain field fluctuation effects on lattice thermal conductivity of ZrNiSn-based thermoelectric compounds

J. Yang, G. P. Meisner, and L. Chen

Appl. Phys. Lett. 85, 1140 (2004); http://dx.doi.org/10.1063/1.1783022 (3 pages) | Cited 57 times

Online Publication Date: 10 August 2004

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We present a model calculation of the lattice thermal conductivity of ZrNiSn-based half-Heusler thermoelectric compounds for temperatures where phonon scattering is dominated by Umklapp and point defect scattering. The difference in mass between impurity and host atoms dominates point defect scattering for alloying Hf on the Zr sublattice, whereas differences in size and interatomic coupling forces between impurity and host atoms dominate point defect scattering for alloying Pd on the Ni sublattice. Because Pt is heavier and larger than Pd, we predict that Pt will further reduce lattice thermal conductivity when alloyed on the Ni sublattice of these half-Heusler compounds.
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72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
72.15.Jf Thermoelectric and thermomagnetic effects
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
61.72.Yx Interaction between different crystal defects; gettering effect
63.20.kp Phonon-defect interactions

Morphological healing evolution of penny-shaped fatigue microcracks in pure iron at elevated temperatures

H. L. Zhang, P. Z. Huang, J. Sun, and H. Gao

Appl. Phys. Lett. 85, 1143 (2004); http://dx.doi.org/10.1063/1.1780592 (3 pages) | Cited 3 times

Online Publication Date: 10 August 2004

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This letter reports a joint experimental and numerical investigation of high temperature morphological healing of micron-sized intragranular microcracks in pure iron. Irregular penny-shaped microcracks were first created by low-cycle fatigue and then subjected to annealing in vaccum at 1173 K. It is shown theoretically that, depending on its initial aspect ratio, a penny-shaped microcrack may evolve via surface diffusion into an isolated spherical void, or a doughnut-shaped channel pore with or without a central spherical void. Subsequent evolution causes the doughnut-shaped channel pore to break up into a ring of spherical voids via Rayleigh’s instabilities. These results were confirmed with experimental observations of typical configurations of voids that result from the crack healing process. The experimentally observed evolution time is also in good agreement with the predictions of finite element simulations of the evolution process.
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68.35.B- Structure of clean surfaces (and surface reconstruction)
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
81.40.Gh Other heat and thermomechanical treatments
68.35.Fx Diffusion; interface formation
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Crystallization and phase transformations in amorphous NiTi thin films for microelectromechanical systems

Hoo-Jeong Lee and Ainissa G. Ramirez

Appl. Phys. Lett. 85, 1146 (2004); http://dx.doi.org/10.1063/1.1783011 (3 pages) | Cited 35 times

Online Publication Date: 10 August 2004

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Amorphous sputtered nickel–titanium thin films were deposited onto micromachined silicon-nitride membranes and subjected to heating and cooling conditions. Their associated microstructure was monitored directly and simultaneously with in situ transmission electron microscopy. These electron-transparent membranes constrained the NiTi films and rendered it possible for observation of the complete transformation cycle, which includes: the crystallization of the amorphous phase to austenite phase (cubic B2 structure) with heating; and the conversion of austenite (B2) to martensite (monoclinic B19′ structure) with cooling. Electron micrographs show the nucleation and growth of grains occurs at a temperature of 470°C and at a rate that indicates a polymorphic transformation. The onset of martensitic transformation occurs between 25 and 35°C. Calorimetric measurements are consistent with the observed crystallization.
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61.43.Dq Amorphous semiconductors, metals, and alloys
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
81.30.Kf Martensitic transformations
64.70.K- Solid-solid transitions
81.40.Gh Other heat and thermomechanical treatments
81.15.Cd Deposition by sputtering

Neutron holographic study of palladium hydride

László Cser, Gyula Török, Gerhard Krexner, Manfred Prem, and Ivan Sharkov

Appl. Phys. Lett. 85, 1149 (2004); http://dx.doi.org/10.1063/1.1780594 (3 pages) | Cited 7 times

Online Publication Date: 10 August 2004

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A holographic image of the atomic arrangement in a PdH0.78 single crystal was recorded using spherical neutron waves generated by incoherent neutron-proton scattering (“internal source concept”). The resolution is sufficient to show the positions of single atomic nuclei on their respective lattice sites despite the delocalization of protons due to the weak bonding of hydrogen dissolved in palladium metal. Ways to overcome problems in the reconstruction of atomic positions related to the highly unfavorable sample shape are discussed. The technique offers possibilities for the investigation of various materials containing substantial amounts of hydrogen.
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42.40.Ht Hologram recording and readout methods
64.75.-g Phase equilibria

Macroporous silicon membranes as electron and x-ray transmissive windows

J. Schilling, A. Scherer, U. Gösele, and M. Kolbe

Appl. Phys. Lett. 85, 1152 (2004); http://dx.doi.org/10.1063/1.1772519 (3 pages) | Cited 2 times

Online Publication Date: 10 August 2004

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Macroporous silicon membranes are fabricated whose pores are terminated with 60 nm thin silicon dioxide shells. The transmission of electrons with energies of 5 kV–25 kV through these membranes was investigated reaching a maximum of 22% for 25 kV. Furthermore, the transmission of electromagnetic radiation ranging from the far-infrared to the x-ray region was determined. The results suggest the application of the membrane as window material for electron optics and energy dispersive x-ray detectors.
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07.85.Fv X- and γ-ray sources, mirrors, gratings, and detectors
07.78.+s Electron, positron, and ion microscopes; electron diffractometers
41.85.-p Beam optics

Interface structures in MgB2 thin films on (0001) SiC

J. S. Wu, N. Jiang, B. Jiang, J. C. H. Spence, A. V. Pogrebnyakov, J. M. Redwing, and X. X. Xi

Appl. Phys. Lett. 85, 1155 (2004); http://dx.doi.org/10.1063/1.1779338 (3 pages) | Cited 4 times

Online Publication Date: 10 August 2004

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The structure of the MgB2∕SiC interface has been studied by high-resolution electron microscopy. Most of the defects at the interface are dislocations with Burgers vector [0001]. In addition, a minority of dislocations with Burgers vector [11math0]∕3 are also generated to relax the mismatch stress between film and substrate. Energy loss spectra obtained from nanometer regions show that the interface is not affected by oxygen.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.78.-w Superconducting films and low-dimensional structures
68.35.Ct Interface structure and roughness
68.37.Ps Atomic force microscopy (AFM)
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)
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.60.Bs Mechanical and acoustical properties
74.25.Ld Mechanical and acoustical properties, elasticity, and ultrasonic attenuation
79.20.Uv Electron energy loss spectroscopy

Control of photoluminescence properties of Si nanocrystals by simultaneously doping n- and p-type impurities

Minoru Fujii, Yasuhiro Yamaguchi, Yuji Takase, Keiichi Ninomiya, and Shinji Hayashi

Appl. Phys. Lett. 85, 1158 (2004); http://dx.doi.org/10.1063/1.1779955 (3 pages) | Cited 49 times

Online Publication Date: 10 August 2004

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The effects of B and P codoping on photoluminescence (PL) properties of Si nanocrystals (nc-Si) are studied systematically. It is shown that the PL intensity of codoped nc-Si is always higher than that of either P- or B-doped nc-Si. The intensity is sometimes even higher than that of pure nc-Si at relatively low P and B concentrations and low annealing temperatures. By doping P and B simultaneously to very high concentrations, the PL peak shifts below the band gap of bulk Si.
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78.55.Ap Elemental semiconductors
61.72.uf Ge and Si
61.46.-w Structure of nanoscale materials
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments

Pattern formation in a polymer thin film induced by an in-plane electric field

David Salac, Wei Lu, Chia-Wei Wang, and Ann Marie Sastry

Appl. Phys. Lett. 85, 1161 (2004); http://dx.doi.org/10.1063/1.1781751 (3 pages) | Cited 15 times

Online Publication Date: 10 August 2004

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This letter reports experimental work involving use of an in-plane electric field to induce morphological patterns in a thin polymer film. The film was first spin coated onto a glass wafer. Then, it was heated to above its glass transition temperature to achieve mobility in the fluid. An in-plane electric field was applied using two parallel electrodes, spaced 10 mm apart, whereupon the initially flat polymer∕air interface lost stability and formed islands. The self-assembled islands exhibited a narrow size distribution and demonstrated spatial ordering. We attribute the pattern formation to a combined mechanism of minimization of combined interface energy and electrostatic energy.
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68.55.-a Thin film structure and morphology
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
68.35.B- Structure of clean surfaces (and surface reconstruction)
61.41.+e Polymers, elastomers, and plastics
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
68.35.Md Surface thermodynamics, surface energies
68.37.Ps Atomic force microscopy (AFM)

White light emission from transparent SiO2 glass prepared from nanometer-sized silica particles

Takashi Uchino and Tomoko Yamada

Appl. Phys. Lett. 85, 1164 (2004); http://dx.doi.org/10.1063/1.1782263 (3 pages) | Cited 23 times

Online Publication Date: 10 August 2004

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We report that nanometer-sized silicon-dioxide particles are sintered to optical transparency at temperatures even below 1000 °C, forming nonporous bulk silica glass. The resultant silica glass exhibits visible emission, which appears white to the naked eye, in the wavelength range from ∼400 to ∼700 nm at room temperature under ultraviolet excitation. The observed emission is quite stable after prolonged exposure to the atmosphere and shows no appreciable light-induced degradation. The present photoluminescence characteristics are found to be basically different from those reported previously for silica nanoparticles and silica-based porous materials.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.55.Hx Other solid inorganic materials
42.70.Ce Glasses, quartz
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