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15 Dec 2003

Volume 94, Issue 12, pp. 7397-7951

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Aging process of electrical contacts in granular matter

S. Dorbolo, M. Ausloos, N. Vandewalle, and M. Houssa

J. Appl. Phys. 94, 7835 (2003); http://dx.doi.org/10.1063/1.1627458 (4 pages) | Cited 3 times

Online Publication Date: 2 December 2003

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The electrical resistance decay of a metallic granular packing has been measured as a function of time. This measurement gives information about the size of the conducting cluster formed by the well connected grains. Several regimes have been encountered. Chronologically, the first one concerns the growth of the conducting cluster and is identified to belong to diffusion processes through a stretched exponential behavior. The relaxation time is found to be simply related to the initial injected power. This regime is followed by a reorganization process due to thermal dilatation. For the long-term behavior of the decay, an aging process occurs and enhances the electrical contacts between grains through microsoldering. © 2003 American Institute of Physics.
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84.32.Dd Connectors, relays, and switches
73.40.Cg Contact resistance, contact potential

Wave simulation in partially frozen porous media with fractal freezing conditions

José M. Carcione, Juan E. Santos, Claudia L. Ravazzoli, and Hans B. Helle

J. Appl. Phys. 94, 7839 (2003); http://dx.doi.org/10.1063/1.1606861 (9 pages) | Cited 10 times

Online Publication Date: 2 December 2003

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A recent article [J. M. Carcione and G. Seriani, J. Comput. Phys. 170, 676 (2001)] proposes a modeling algorithm for wave simulation in a three-phase porous medium composed of sand grains, ice, and water. The differential equations hold for uniform water (ice) content. Here, we obtain the variable-porosity differential equations by using the analogy with the two-phase case and the complementary energy theorem. The displacements of the rock and ice frames and the variation of fluid content are the generalized coordinates, and the stress components and fluid pressure are the generalized forces. We simulate wave propagation in a frozen porous medium with fractal variations of porosity and, therefore, realistic freezing conditions. © 2003 American Institute of Physics.
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62.65.+k Acoustical properties of solids

Focusing of surface-acoustic-wave fields on (100) GaAs surfaces

M. M. de Lima, F. Alsina, W. Seidel, and P. V. Santos

J. Appl. Phys. 94, 7848 (2003); http://dx.doi.org/10.1063/1.1625419 (8 pages) | Cited 16 times

Online Publication Date: 2 December 2003

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Focused surface-acoustic waves (SAWs) provide a way to reach intense acoustic fields for electro- and optoacoustic applications on semiconductors. We have investigated the focusing of SAWs by interdigital transducers (IDTs) deposited on (100)-oriented GaAs substrates. The focusing IDTs have curved fingers designed to account for the acoustic anisotropy of the substrate. Different factors that affect focusing, such as the aperture angle and the configuration of the IDT fingers, were systematically addressed. We show that the focusing performance can be considerably improved by appropriate choice of the IDT metal pads, which, under appropriate conditions, create an acoustic waveguide within the IDT. We demonstrate the generation of narrow (full width at half maximum of approx 15 μm), high-frequency (0.5 GHz), continuous SAW beams with vertical displacement as high as 4 nm collimated over distances that exceed 100 μm. © 2003 American Institute of Physics.
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68.35.Iv Acoustical properties
43.38.Gy Semiconductor transducers

Interfacial slip on a transverse-shear mode acoustic wave device

Jonathan S. Ellis and Gordon L. Hayward

J. Appl. Phys. 94, 7856 (2003); http://dx.doi.org/10.1063/1.1627949 (12 pages) | Cited 13 times

Online Publication Date: 2 December 2003

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This article describes a mathematical relationship between the slip parameter α and the slip length b for a slip boundary condition applied to the transverse-shear model for a quartz-crystal acoustic wave device. The theory presented here reduces empirical determination of slip to a one-parameter fit. It shows that the magnitude and phase of the slip parameter, which describes the relative motion of the surface and liquid in the transverse-shear model, can be linked to the slip length. Furthermore, the magnitude and phase of the slip parameter are shown to depend on one another. An experiment is described to compare the effects of liquid-surface affinity on the resonant properties of a transverse-shear mode wave device by applying different polar and nonpolar liquids to surfaces of different polarity. The theory is validated with slip values determined from the transverse-shear model and compared to slip length values from literature. Agreement with literature values of slip length is within one order of magnitude. © 2004 American Institute of Physics.
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43.60.Qv Signal processing instrumentation, integrated systems, smart transducers, devices and architectures, displays and interfaces for acoustic systems
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Mechanical properties of sputtered silicon nitride thin films

M. Vila, D. Cáceres, and C. Prieto

J. Appl. Phys. 94, 7868 (2003); http://dx.doi.org/10.1063/1.1626799 (6 pages) | Cited 33 times

Online Publication Date: 2 December 2003

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Silicon nitride thin films were prepared by reactive sputtering from different sputtering targets and using a range of Ar/N2 sputtering gas mixtures. The hardness and the Young’s modulus of the samples were determined by nanoindentation measurements. Depending on the preparation parameters, the obtained values were in the ranges 8–23 and 100–210 GPa, respectively. Additionally, Fourier-transform infrared spectroscopy, Rutherford backscattering spectroscopy, and x-ray diffraction were used to characterize samples with respect to different types of bonding, atomic concentrations, and structure of the films to explain the variation of mechanical properties. The hardness and Young’s modulus were determined as a function of film composition and structure and conditions giving the hardest film were found. Additionally, a model that assumes a series coupling of the elastic components, corresponding to the Si–O and Si–N bonds present in the sample has been proposed to explain the observed variations of hardness and Young’s modulus. © 2003 American Institute of Physics.
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68.60.Bs Mechanical and acoustical properties
68.55.-a Thin film structure and morphology
62.20.Qp Friction, tribology, and hardness
81.40.Jj Elasticity and anelasticity, stress-strain relations
68.35.Gy Mechanical properties; surface strains
62.20.D- Elasticity
78.30.Hv Other nonmetallic inorganics
78.35.+c Brillouin and Rayleigh scattering; other light scattering
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
78.66.Nk Insulators

Production of gold nanoparticles by laser ablation in liquid alkanes

G. Compagnini, A. A. Scalisi, and O. Puglisi

J. Appl. Phys. 94, 7874 (2003); http://dx.doi.org/10.1063/1.1628830 (4 pages) | Cited 28 times

Online Publication Date: 2 December 2003

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Pulsed laser ablation of Au target in n-alkanes generates Au sols. Experiments have been performed using the second harmonic of a Nd:yttritium–aluminum–garnet at 532 nm wavelength with a 5 ns pulse duration at a repetition rate of 10 Hz and fluences ranging from 1 to 200 J/cm2. Data coming from optical extinction show that the length of the hydrocarbon chain is able to tune the shape of the produced particles and the rate of formation in a controlled way. The data are supported by atomic force microscopy and transmission electron microscope observations. © 2003 American Institute of Physics.
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81.07.Wx Nanopowders
81.16.Mk Laser-assisted deposition
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
81.05.Bx Metals, semimetals, and alloys
42.62.Cf Industrial applications
82.70.Gg Gels and sols

Spectroscopic impedance study of nanocrystalline diamond films

Haitao Ye, Richard B. Jackman, and Peter Hing

J. Appl. Phys. 94, 7878 (2003); http://dx.doi.org/10.1063/1.1622998 (5 pages) | Cited 22 times

Online Publication Date: 2 December 2003

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Nanocrystalline diamond films were synthesized by microwave plasma-enhanced chemical vapor deposition using Ar/H2/CH4 gas mixtures. A Fluke PM6306 RCL meter was used to study the electrical impedance of these diamond films in the frequency range 50 Hz to 1 MHz. The impedance dispersion measurement yields the real and imaginary parts in the form of a Cole-Cole plot in the complex plane. A single semicircular response of the impedance of nanocrystalline diamond films was observed at temperatures below 250 °C, with a second semicircular response appearing at low frequencies at temperatures above this. The semicircular responses were found to fit a double resistor-capacitor parallel circuit model. Physical mechanisms likely to be responsible for these observations are discussed in this paper. © 2003 American Institute of Physics.
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73.63.Bd Nanocrystalline materials
73.61.Cw Elemental semiconductors
81.07.Bc Nanocrystalline materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.U- Carbon/carbon-based materials
68.55.-a Thin film structure and morphology

In situ determination of surface composition, polarity, crystallographic relationship, and periodicity of GaN films by mass spectroscopy of recoiled Ions and direct recoiled spectroscopy

L. A. Carreño, C. Boney, and A. Bensaoula

J. Appl. Phys. 94, 7883 (2003); http://dx.doi.org/10.1063/1.1627456 (5 pages) | Cited 3 times

Online Publication Date: 2 December 2003

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Applicability of time-of-flight (TOF) mass spectroscopy of recoiled ions (MSRI) and direct recoiled spectroscopy (DRS) as in situ techniques for both optimization and characterization of thin film materials is presented in this article. TOF DRS/MSRI were used to monitor the growth process of GaN and (Ga,Mn)N by chemical-beam epitaxy. We show that all important growth parameters can be optimized real time and that under our experimental conditions, all epilayers are metal polar, as confirmed ex situ by wet etching. The surface periodicities of c-sapphire and the final GaN and (Ga,Mn)N epilayers were determined and found to be parallel to each other, but with a 30° in-plane relative rotation between them—as reported by several researchers. Finally, analysis of the Ga and Mn azimuthal surface signals supports that for all concentrations (0.5% to 2.5%) in our studies, the Mn atoms are substitutional into the GaN crystal structure. © 2003 American Institute of Physics.
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68.35.Dv Composition, segregation; defects and impurities
68.55.-a Thin film structure and morphology
68.55.Nq Composition and phase identification
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Photovariation of grating-assisted coupling of terahertz waves into a silicon waveguide

F. Aquistapace, L. Duvillaret, F. Garet, J.-F. Roux, and J.-L. Coutaz

J. Appl. Phys. 94, 7888 (2003); http://dx.doi.org/10.1063/1.1629387 (4 pages) | Cited 3 times

Online Publication Date: 2 December 2003

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Using terahertz (THz) time-domain spectroscopy, we study the coupling of THz waves into a silicon waveguide by means of a grating coupler. We vary the efficiency of the coupling coefficient for selected frequencies up to 20% in amplitude (40% in intensity) by generating photocarriers in the silicon material through illumination of the waveguide with white light. The experimental data are well fitted using the differential method to model the grating diffraction. © 2003 American Institute of Physics.
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84.40.Az Waveguides, transmission lines, striplines
42.79.Gn Optical waveguides and couplers
42.79.Dj Gratings
72.40.+w Photoconduction and photovoltaic effects
72.80.Cw Elemental semiconductors
68.47.Fg Semiconductor surfaces
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques

SiGe relaxation on silicon-on-insulator substrates: An experimental and modeling study

E. M. Rehder, C. K. Inoki, T. S. Kuan, and T. F. Kuech

J. Appl. Phys. 94, 7892 (2003); http://dx.doi.org/10.1063/1.1628406 (12 pages) | Cited 8 times

Online Publication Date: 2 December 2003

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The strain relaxation behavior of Si0.82Ge0.18 films on silicon-on-insulator (SOI) substrates was investigated for films grown beyond the critical thickness and strain-relaxed during growth and metastable films, grown beyond the critical thickness, which relaxed during subsequent thermal annealing. The thickness of the top silicon layer of the SOI substrate was varied over a range from 40 nm to 10 μm. In all cases, the SiGe film relaxation occurred via the nucleation and propagation of dislocations with the same onset of film relaxation and same relaxation rate for both SOI and bulk Si substrates. The SOI substrate does not serve as a compliant substrate but does alter the dislocation structure and motion. The buried amorphous oxide layer in the SOI substrate leads to the relaxation of the dislocation strain field through the removal of the dislocation line tension. This removal of the dislocation line tension drives dislocation motion and leads to the development of strain in the thin Si layer of the SOI substrate. Models of this dislocation behavior for SiGe growth on the SOI substrate are presented and calculation of the equilibrium strain of the thin Si substrate layer closely fits the measured strain of several SOI substrates. The article addresses the implications of the modified dislocation structure and kinetics for film relaxation on SOI substrates. © 2003 American Institute of Physics.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
81.40.Jj Elasticity and anelasticity, stress-strain relations
61.72.Hh Indirect evidence of dislocations and other defects (resistivity, slip, creep, strains, internal friction, EPR, NMR, etc.)
66.30.Lw Diffusion of other defects
61.72.Cc Kinetics of defect formation and annealing

Effect of 0.5 wt % Cu addition in Sn–3.5%Ag solder on the dissolution rate of Cu metallization

M. O. Alam, Y. C. Chan, and K. N. Tu

J. Appl. Phys. 94, 7904 (2003); http://dx.doi.org/10.1063/1.1628387 (6 pages) | Cited 31 times

Online Publication Date: 2 December 2003

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The dissolution of thin film under-bump-metallization (UBM) by molten solder has been one of the most serious processing problems in electronic packaging technology. Due to a higher melting temperature and a greater Sn content, a molten lead-free solder such as eutectic SnAg has a faster dissolution rate of thin film UBM than the eutectic SnPb. The work presented in this paper focuses on the role of 0.5 wt % Cu in the base Sn–3.5%Ag solder to reduce the dissolution of the Cu bond pad in ball grid array applications. We found that after 0.5 wt % Cu addition, the rate of dissolution of Cu in the molten Sn–3.5%Ag solder slows down dramatically. Systematic experimental work was carried out to understand the dissolution behavior of Cu by the molten Sn–3.5%Ag and Sn–3.5%Ag–0.5%Cu solders at 230–250 °C, for different time periods ranging from 1 to 10 min. From the curves of consumed Cu thickness, it was concluded that 0.5 wt % Cu addition actually reduces the concentration gradient at the Cu metallization/molten solder interface which reduces the driving force of dissolution. During the dissolution, excess Cu was found to precipitate out due to heterogeneous nucleation and growth of Cu6Sn5 at the solder melt/oxide interface. In turn, more Cu can be dissolved again. This process continues with time and leads to more dissolution of Cu from the bond pad than the amount expected from the solubility limit, but it occurs at a slower rate for the molten Sn–3.5%Ag–0.5%Cu solder. © 2003 American Institute of Physics.
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85.40.Ls Metallization, contacts, interconnects; device isolation
81.20.Vj Joining; welding
64.75.-g Phase equilibria

Improving the coherence of a low-energy electron beam by modulation

F. Pesty and P. Garoche

J. Appl. Phys. 94, 7910 (2003); http://dx.doi.org/10.1063/1.1627954 (4 pages) | Cited 2 times

Online Publication Date: 2 December 2003

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In a standard low-energy electron generator the beam is formed by particles traveling close to the axis of symmetry. However some electron trajectories are unstable and strongly dependent on the initial conditions. Numerical ray tracing shows that ultimate beam coherence is limited by these trajectories that pass far from the symmetry axis. This contribution can be partly eliminated by modulating the initial conditions and selecting the modulated response. This is exemplified with a low-energy electron beam used for electron diffraction, where the beam current modulation produces a modulated diffraction pattern that displays noteworthy improvement (sevenfold) in wave vector resolution. © 2003 American Institute of Physics.
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41.75.Fr Electron and positron beams

Characterization of porous materials with a rigid frame via reflected waves

Z. E. A. Fellah, F. G. Mitri, C. Depollier, S. Berger, W. Lauriks, and J. Y. Chapelon

J. Appl. Phys. 94, 7914 (2003); http://dx.doi.org/10.1063/1.1629386 (9 pages) | Cited 7 times

Online Publication Date: 2 December 2003

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The inverse problem for waves reflected by porous material is solved at oblique incidence, and an inverse scattering calculation of porosity and tortuosity is given for air-saturated plastic foam samples. The interaction of the sound pulse with the fluid-saturated porous material is described by a time-domain equivalent fluid model. The sensitivity of the porosity and tortuosity is studied and it shows their effect on the reflection coefficient at the first interface. This study shows that porosity is much more sensitive than tortuosity to reflection, especially when the incident angle is less than its critical value, at which the reflection coefficient vanishes. Some advantages and perspectives of this method are discussed. © 2003 American Institute of Physics.
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62.65.+k Acoustical properties of solids
43.20.El Reflection, refraction, diffraction of acoustic waves
43.20.Hq Velocity and attenuation of acoustic waves
43.60.Pt Signal processing techniques for acoustic inverse problems
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