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27 Jul 1998

Volume 73, Issue 4, pp. 423-552

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Viscosity of eutectic Pd78Cu6Si16 measured by the oscillating drop technique in microgravity

I. Egry, G. Lohöfer, I. Seyhan, S. Schneider, and B. Feuerbacher

Appl. Phys. Lett. 73, 462 (1998); http://dx.doi.org/10.1063/1.121900 (2 pages) | Cited 25 times

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During the STS-83 Spacelab mission, a sample of Pd78Cu6Si16 was processed in the electromagnetic levitation facility TEMPUS. Surface oscillations of the levitated liquid droplet were excited, and frequency and damping of the oscillations were observed. Under microgravity conditions, the damping constant is simply related to the viscosity. This method was successfully applied. The experiments were performed in a temperature range of 400 K, including the eutectic temperature Te = 1033 K. At this temperature, our data agree well with those of S. K. Lee, K. H. Tsang, and H. W. Kui [J. Appl. Phys. 70, 4842 (1991)]. © 1998 American Institute of Physics.
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66.20.-d Viscosity of liquids; diffusive momentum transport

Thickness dependence of dielectric loss in SrTiO3 thin films

Hong-Cheng Li, Weidong Si, Alexander D. West, and X. X. Xi

Appl. Phys. Lett. 73, 464 (1998); http://dx.doi.org/10.1063/1.121901 (3 pages) | Cited 88 times

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We have measured the dielectric loss in SrTiO3 thin films grown on SrRuO3 electrode layers with thickness ranging from 25 nm to 2.5 μm. The loss depends strongly on the thickness but differently above and below T ≈ 80 K: as the thickness increases, the loss decreases at high temperatures but becomes higher at low temperatures. Our result suggests that, in the high temperature regime, the interfacial dead layer effect dominates while, in the low temperature regime, the losses related to the structural phase transition and quantum fluctuations are important. © 1998 American Institute of Physics.
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77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)

On the role of interface imperfections in thermoelectric nondestructive materials characterization

Jiangtao Hu and Peter B. Nagy

Appl. Phys. Lett. 73, 467 (1998); http://dx.doi.org/10.1063/1.121902 (3 pages) | Cited 12 times

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This letter draws attention to a previously unnoticed artifact associated with the most common type of thermoelectric nondestructive materials characterization technique. It is shown that contact heating between the specimen to be tested and the reference electrode gives rise to a considerable offset in the measured thermoelectric voltage. The resulting bias significantly reduces the feasibility of thermoelectric measurements in nondestructive testing applications that require sensitive materials discrimination, for example, to sort metals of similar alloying content, to distinguish similar grades of heat treatment, and to detect slight variations in the thermoelectric power of metals due to hardening, texture, fatigue, etc. It is also suggested that the demonstrated intrinsic sensitivity of the thermoelectric contact technique to imperfect interfaces could be exploited for nondestructive detection of tightly compressed but metallurgically not bonded interfaces in spot welds, diffusion bonds, and other types of solid-state bonds. © 1998 American Institute of Physics.
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81.70.Ex Nondestructive testing: electromagnetic testing, eddy-current testing
68.35.Gy Mechanical properties; surface strains
81.40.Gh Other heat and thermomechanical treatments

Wide viewing angle, homeotropic nematic liquid-crystal display controlled by effective field

S. H. Lee, H. Y. Kim, Y. H. Lee, I. C. Park, B. G. Rho, H. G. Galabova, and D. W. Allender

Appl. Phys. Lett. 73, 470 (1998); http://dx.doi.org/10.1063/1.121903 (3 pages) | Cited 11 times

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The electro-optic properties of a liquid-crystal display associated with a homeotropic to multidomainlike transition for a liquid crystal with a positive dielectric anisotropy have been investigated. The cell plates are prepared in such a way that, in the absence of an electric field, the liquid-crystal alignment is homeotropic. an electric field created by interdigitated electrodes on both substrates causes a director deformation of a multidomain type. The display shows wide viewing angle, excellent color characteristics, and a fast response time. The molecular director configuration, together with the electro-optic characteristics of the device, are discussed in this letter. © 1998 American Institute of Physics.
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42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems

Stress-induced amorphization at moving crack tips in NiTi

P. R. Okamoto, J. K. Heuer, N. Q. Lam, S. Ohnuki, Y. Matsukawa, K. Tozawa, and J. F. Stubbins

Appl. Phys. Lett. 73, 473 (1998); http://dx.doi.org/10.1063/1.121904 (3 pages) | Cited 22 times

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In situ fracture studies have been carried out on thin films of the NiTi intermetallic compound under plane stress, tensile loading conditions in the high-voltage electron microscope. Local stress-induced amorphization of regions directly in front of moving crack tips has been observed. The upper cutoff temperature, TC–Amax, for the stress-induced crystalline-to-amorphous transformation was found to be 600 K, identical to that for heavy ion-induced amorphization of NiTi and for ion-beam mixing-induced amorphization of Ni and Ti multilayer specimens. 600 K is also both the lower cutoff temperature, TA–Cmin, for radiation-induced crystallization of initially-unrelaxed amorphous NiTi and the lowest isothermal annealing temperature, TXmin, at which stress-induced amorphous NiTi crystallizes. Since TXmin should be TK, the ideal glass transition temperature, the discovery that TC–Amax = TA–Cmin = TXmin = TK implies that disorder-driven crystalline-to-amorphous transformations result in the formation of the ideal glass, i.e., the glassy state that has the same entropy as that of the defect-free crystal. As the glassy state with the lowest free energy, its formation can be understood as the most energetically-favored, kinetically-constrained response of crystalline alloys driven far from equilibrium. © 1998 American Institute of Physics.
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62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
64.70.K- Solid-solid transitions
65.20.-w Thermal properties of liquids
65.40.gd Entropy
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition

Phase transition of C60 crystal in high temperature regime

Feng Yan and Ye-Ning Wang

Appl. Phys. Lett. 73, 476 (1998); http://dx.doi.org/10.1063/1.121905 (2 pages) | Cited 2 times

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The internal friction of the polycrystalline C60 films was measured in the temperature range of 320–620 K. Around 426 K, a λ-shaped internal friction peak was detected. The peak was interpreted in terms of another phase transition above the order-disorder phase transition temperature. © 1998 American Institute of Physics.
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64.70.K- Solid-solid transitions
61.48.-c Structure of fullerenes and related hollow and planar molecular structures
68.60.Wm Other nonelectronic physical properties
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations

Luminescence characteristics of impurities-activated ZnS nanocrystals prepared in microemulsion with hydrothermal treatment

S. J. Xu, S. J. Chua, B. Liu, L. M. Gan, C. H. Chew, and G. Q. Xu

Appl. Phys. Lett. 73, 478 (1998); http://dx.doi.org/10.1063/1.121906 (3 pages) | Cited 83 times

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Cu-, Eu-, or Mn-doped ZnS nanocrystalline phosphors were prepared at room temperature using a chemical synthesis method. Transmission electron microscopy observation shows that the size of the ZnS clusters is in the 3–18 nm range. New luminescence characteristics such as strong and stable visible-light emissions with different colors were observed from the doped ZnS nanocrystals at room temperature. These results strongly suggest that impurities, especially transition metals and rare-earth metals-activated ZnS nanoclusters form a new class of luminescent materials. © 1998 American Institute of Physics.
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78.55.Et II-VI semiconductors
61.46.-w Structure of nanoscale materials
81.07.-b Nanoscale materials and structures: fabrication and characterization

Transmission electron microscopy of defects in GaN films formed by epitaxial lateral overgrowth

Akira Sakai, Haruo Sunakawa, and Akira Usui

Appl. Phys. Lett. 73, 481 (1998); http://dx.doi.org/10.1063/1.121907 (3 pages) | Cited 79 times

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We have investigated by transmission electron microscopy (TEM) defect morphology and structure in GaN films formed using an epitaxial lateral overgrowth (ELO) technique on SiO2-mask/window-stripe-patterned GaN layers in hydride vapor-phase epitaxy. In this experiment, the regions overgrown on the SiO2 masks were thoroughly examined. Cross-sectional TEM clearly revealed characteristic defects along the [0001] direction in the overgrown region, which consisted of arrays of dislocations running along the mask stripe direction. These defects caused crystallographic tilting in that region near the mask with respect to the other region grown from the window area. We also observed, at the coalesced site on the mask, vertical repropagation of dislocations that had propagated laterally during ELO. The origin of the observed defects and their influence on the residual dislocation distribution near the film surface are discussed. © 1998 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.05.Ea III-V semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
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