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15 Jul 2003

Volume 94, Issue 2, pp. 811-1291

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Slowness curves and characteristics of surface acoustic waves propagating obliquely in periodic finite-thickness electrode gratings

Vincent Laude and Sylvain Ballandras

J. Appl. Phys. 94, 1235 (2003); http://dx.doi.org/10.1063/1.1582237 (8 pages) | Cited 4 times

Online Publication Date: 26 June 2003

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The computation of the diffraction of surface acoustic waves (SAWs) on piezoelectric materials is complicated by the anisotropy of their propagation, and requires their slowness curves to be known precisely. In addition, in actual devices these slowness curves are strongly affected by the massive electrodes used for SAW generation. We investigate the characteristics of SAWs propagating obliquely in periodic finite-thickness electrode gratings, with the mass-loading effect taken into account. The velocity of the surface waves, as well as the attenuation, piezoelectric coupling and beam steering are obtained as a function of the propagation angle with respect to the grating axis. The slowness curves for SAWs propagating under periodic electrode gratings are compared with the slowness curves for the same SAWs propagating under a thick homogeneous metallic layer. Numerical examples are presented for the SAWs of 42.75°YX quartz and X112.2°Y lithium tantalate, and the leaky SAWs of 36°YX lithium tantalate. © 2003 American Institute of Physics.
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68.35.Iv Acoustical properties
43.35.Pt Surface waves in solids and liquids
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics

Effects of natural and electrochemical oxidation processes on acoustic waves in porous silicon films

H. J. Fan, M. H. Kuok, S. C. Ng, H. S. Lim, N. N. Liu, R. Boukherroub, and D. J. Lockwood

J. Appl. Phys. 94, 1243 (2003); http://dx.doi.org/10.1063/1.1583148 (5 pages) | Cited 3 times

Online Publication Date: 26 June 2003

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Brillouin scattering has been performed to study the effects of natural and electrochemical oxidation on the surface and bulk acoustic mode properties of porous silicon films. The acoustic mode frequencies are observed to decrease with increasing oxidation time and this is attributed to the progressive transformation of silicon–silicon bonds on the inner pore walls into SiO2. The dependence of the surface and bulk acoustic mode frequencies on the natural oxidation time allows the evaluation of these wave frequencies for a porous-SiO2 glass film, and hence the estimation of its bulk modulus. Both Brillouin and Raman data confirm the expectation that oxidation leads to a reduction in silicon nanoparticle size, and provide a correlation between the redsifted acoustic mode frequency and the oxidation period. © 2003 American Institute of Physics.
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81.65.Mq Oxidation
68.35.Iv Acoustical properties
62.65.+k Acoustical properties of solids
78.35.+c Brillouin and Rayleigh scattering; other light scattering
62.20.D- Elasticity
68.60.Bs Mechanical and acoustical properties
78.30.-j Infrared and Raman spectra
78.66.Db Elemental semiconductors and insulators
68.55.-a Thin film structure and morphology

Interface engineering of cBN films deposited on silicon substrates

Hangsheng Yang, Chihiro Iwamoto, and Toyonobu Yoshida

J. Appl. Phys. 94, 1248 (2003); http://dx.doi.org/10.1063/1.1583153 (4 pages) | Cited 20 times

Online Publication Date: 26 June 2003

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We could determine the substrate pretreatment conditions required for the deposition of cubic boron nitride films without an interfacial amorphous layer by investigating nanostructures, chemical composition, and bonding states of the amorphous layer, which inevitably grew prior to the growth of cubic BN in ion-assisted chemical vapor deposition. The amorphous layer was composed of a native Si oxide layer and a complex oxide layer consisting of B, N, Si, and 10–20 at. % oxygen. However, by the substrate pretreatment, 1200 K heating in 20 mTorr H2 atmosphere for 120 min, the crystallinity of the Si substrate surface could be retained throughout the removal of the native oxide layer, and turbostratic BN was revealed to grow directly on the Si substrate. In addition, we could reduce the thickness of the turbostratic BN layer to less than 3 nm, and increase the adhesion strength markedly. The formation of the amorphous layer was found to be caused by two factors: the native oxide layer and the ion bombardment effects. © 2003 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
61.80.Jh Ion radiation effects
68.35.Np Adhesion

Length-scale dependent variation of the first nucleated phase in nickel–silicon multilayers

Jacob M. Jensen, Xavier J. Kyablue, Sochetra Ly, and David C. Johnson

J. Appl. Phys. 94, 1252 (2003); http://dx.doi.org/10.1063/1.1586465 (6 pages) | Cited 3 times

Online Publication Date: 26 June 2003

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We have studied the first phase nucleation behavior of a series of equiatomic Ni–Si multilayers with ultrathin repeating subunits (λ=1.7–5.8 nm) using x-ray reflectivity and x-ray diffraction. The variation in first nucleated phase is understood in terms of the model of Gösele and Tu, who predicted three length-scale dependent reaction routes in thin film diffusion couples: (i) For multilayers with λ>5.0 nm, interfacial nucleation of Ni2Si is observed, consistent with studies of bulk diffusion couples. (ii) For multilayers with 3.8<λ<5.0 nm, interfacial nucleation tends towards phases richer in Si due to a waning supply of Ni within the multilayer. (iii) For multilayers with λ<2.0 nm complete mixing of the Ni–Si multilayers prefigures first phase nucleation of NiSi. In this regime the composition of the first nucleation phase is determined by the amorphous precursor, which in turn is dictated by the relative ratios of Ni and Si in the initial multilayer. A fourth scenario, between (ii) and (iii), in which Ni2Si is the first nucleated phase is also observed. A possible mechanism for this unexpected result is discussed. © 2003 American Institute of Physics.
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68.65.Ac Multilayers
68.35.Ct Interface structure and roughness
68.35.Fx Diffusion; interface formation

Properties of rf-sputtered indium–tin-oxynitride thin films

Elias Aperathitis, Marcus Bender, Volker Cimalla, Gernot Ecke, and Mircea Modreanu

J. Appl. Phys. 94, 1258 (2003); http://dx.doi.org/10.1063/1.1582368 (9 pages) | Cited 8 times

Online Publication Date: 26 June 2003

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Indium–tin-oxide (ITO) and indium–tin-oxynitride (ITON) thin films have been fabricated by rf-sputtering in plasma containing Ar or a mixture of Ar and N2, respectively. The structural, electrical and optical properties of ITON films were examined and compared with those of ITO films. The microstructure of ITON films was found to be dependent on the nitrogen concentration in the plasma. Increasing the amount of nitrogen in the plasma increased the resistivity and reduced the carrier concentration and mobility of the films. The electrical properties of the ITON films improved after annealing. The absorption edge of the ITON films deposited in pure N2 plasma was shifted towards higher energies and showed reduced infrared reflectance compared to the respective properties of ITO films. The potential of indium–tin-oxynitride films for use as a transparent conductive material for optoelectronic devices is addressed. © 2003 American Institute of Physics.
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68.55.-a Thin film structure and morphology
81.05.Hd Other semiconductors
73.61.Le Other inorganic semiconductors
78.66.Li Other semiconductors
72.80.Jc Other crystalline inorganic semiconductors
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering
52.77.Dq Plasma-based ion implantation and deposition
81.15.Jj Ion and electron beam-assisted deposition; ion plating
61.72.-y Defects and impurities in crystals; microstructure
73.50.Dn Low-field transport and mobility; piezoresistance
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
61.72.Cc Kinetics of defect formation and annealing
78.30.Hv Other nonmetallic inorganics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Calculation of three-dimensional electromagnetic force field during arc welding

A. Kumar and T. DebRoy

J. Appl. Phys. 94, 1267 (2003); http://dx.doi.org/10.1063/1.1587006 (11 pages) | Cited 40 times

Online Publication Date: 26 June 2003

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Electromagnetic force is an important driving force for convection in the weld pool during arc welding. Accurate calculation of the electromagnetic force field requires complex numerical calculations of three-dimensional current density and magnetic flux fields. Several simplifying assumptions have been suggested to avoid the complex calculations. The resulting analytical expressions for the electromagnetic force field have been widely used without any critical evaluation of their intrinsic merit, since accurate numerical calculations were difficult in the past because of lack of fast computers. A numerical model has been developed to accurately calculate the current density and magnetic flux fields and the resulting electromagnetic force field in three dimensions in the entire weldment. The model can take into account any current distribution on the work piece surface and evaluate the effects of different arc locations and work piece geometry on the electromagnetic force field. Contributions of the electrode current, arc plasma, and current distribution inside the three-dimensional work piece to the magnetic field and the electromagnetic force field are determined. The electromagnetic force field computed from the model is compared with those obtained from the commonly used simplified expressions of electromagnetic force to examine the accuracy of the commonly used simplifying assumptions. The accuracy of the computed electromagnetic force field can be significantly improved by using the proposed numerical model. © 2003 American Institute of Physics.
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81.20.Vj Joining; welding
47.27.T- Turbulent transport processes

Technique for measurement of photoacoustic waves in situ with ultrasound probe beam

Yong Yao, Da Xing, Ken-ichi Ueda, and Qun Chen

J. Appl. Phys. 94, 1278 (2003); http://dx.doi.org/10.1063/1.1588361 (4 pages) | Cited 3 times

Online Publication Date: 26 June 2003

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A method of measuring photoacoustic (PA) waves in situ is proposed and experimentally demonstrated. A focused probe ultrasonic beam passes through a sample and tags the position of the interested PA signal. The probe beam interacts with PA wave. The PA signal modulated probe beam is recorded outside the sample. Reconstruction of the original in situ PA signal is accomplished by demodulating the probe beam. The method, thus, provides a measurement system with a high signal-to-noise ratio and reduced background noise for PA wave form recording. © 2003 American Institute of Physics.
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43.35.Ud Thermoacoustics, high temperature acoustics, photoacoustic effect
62.65.+k Acoustical properties of solids
43.35.Yb Ultrasonic instrumentation and measurement techniques

Note On Darcy’s Law

A. Cemal Eringen

J. Appl. Phys. 94, 1282 (2003); http://dx.doi.org/10.1063/1.1586951 (1 page)

Online Publication Date: 26 June 2003

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Classical Darcy’s Law expresses pressure gradient in a porous media as a linear function of the velocity difference between solid and fluid constituents. As such, this constitutive equation is frame dependent. The present article is an attempt to express this law in terms of frame independent quantities. The resulting expression shows that classical Darcy’s Law may be justified on an approximate basis when the higher order quantities are neglected. © 2003 American Institute of Physics.
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47.56.+r Flows through porous media
47.11.-j Computational methods in fluid dynamics
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