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15 Apr 2012

Volume 111, Issue 8, Articles (08xxxx)

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J. Appl. Phys. 111, 084701 (2012); http://dx.doi.org/10.1063/1.3698319 (11 pages)

Xerxes Lopez-Yglesias, Jason M. Gamba, and Richard C. Flagan
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back to top Interdisciplinary and General Physics

The effect of continuous pore stratification on the acoustic absorption in open cell foams

Sararat Mahasaranon, Kirill V. Horoshenkov, Amir Khan, and Hadj Benkreira

J. Appl. Phys. 111, 084901 (2012); http://dx.doi.org/10.1063/1.3701710 (10 pages) | Cited 2 times

Online Publication Date: 16 April 2012

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This work reports new data on the acoustical properties of open cell foam with pore stratification. The pore size distribution as a function of the sample depth is determined in the laboratory using methods of optical image analysis. It is shown that the pore size distribution in this class of materials changes gradually with the depth. It is also shown that the observed pore size distribution gradient is responsible for the air flow resistivity stratification, which is measured acoustically and non-acoustically. The acoustical absorption coefficient of the developed porous sample is measured using a standard laboratory method. A suitable theoretical model for the acoustical properties of porous media with pore size distribution is adopted. The measured data for open porosity, tortuosity, and standard deviation data are used together with this model to predict the observed acoustic absorption behavior of the developed material sample. The transfer matrix approach is used in the modeling process to account for the pore size stratification. This work suggests that it is possible to design and manufacture porous media with continuous pore size stratification, which can provide an improvement to conventional porous media with uniform pore size distribution in terms of the attained acoustic absorption coefficient.
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43.40.-r Structural acoustics and vibration
43.25.Dc Nonlinear acoustics of solids

Effect of pretreatment of Si interlayer by energetic C+ ions on the improved nanotribological properties of magnetic head overcoat

Ehsan Rismani, S. K. Sinha, H. Yang, and C. S. Bhatia

J. Appl. Phys. 111, 084902 (2012); http://dx.doi.org/10.1063/1.3699058 (10 pages) | Cited 1 time

Online Publication Date: 18 April 2012

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A thin layer of silicon has been used to improve the adhesion between amorphous carbon coatings and different substrates. However, the mechanism responsible for this improved adhesion to ceramic substrates, especially the Al2O3-TiC (AlTiC) substrate of magnetic recording heads, has not been well studied. In this work, this mechanism was investigated by conducting simulation and experimental tests. A tetrahedral amorphous carbon (ta-C) overcoat was deposited on Si-coated ceramic substrates by using filtered cathodic vacuum arc (FCVA) at ion energy of 100 eV. The chemical structure of the ta-C overcoats and interlayers as well as the nanotribological properties of the ta-C coated AlTiC substrate were studied by means of XPS analysis, nanoscratch and ball-on-flat tests. The formation of a Si-C network between the Si interlayer and ta-C overcoat as well as the formation of Al–O–Si and Si–O–C bonds between the interlayer and the substrate were found to be the two main phenomena which strongly bond the ta-C film to its ceramic substrate. Prior to deposition of the ta-C overcoat, surface of the Si interlayer was bombarded (pretreated) by C+ ions with ion energy of 350 eV. Effect of this pretreatment on the structure and tribological properties of the coated surfaces was also studied. The results revealed that pretreatment of the Si interlayer by energetic C+ ions is an effective way to form a mixed interface and enhance the formation of a larger number of strong chemical bonds between the substrate and the overcoat which improves the adhesion of the overcoat to the substrate. In addition, this method increased the sp3 content of the ta-C film which further improves the wear resistance and durability of the coating.
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81.65.-b Surface treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)
62.20.Qp Friction, tribology, and hardness
68.35.Np Adhesion
68.60.Bs Mechanical and acoustical properties
81.40.Pq Friction, lubrication, and wear

Short wavelength thermography: Theoretical and experimental estimation of the optimal working wavelength

B. Serio, J. J. Hunsinger, and P. Pfeiffer

J. Appl. Phys. 111, 084903 (2012); http://dx.doi.org/10.1063/1.4704186 (6 pages)

Online Publication Date: 18 April 2012

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Radiometric temperature measurement methods, such as thermography, use mainly radiation in the infrared spectrum. In this wavelength range, applications are limited by the diffraction to macroscopic devices. The empirical optical resolution limit is given by the Rayleigh criterion. Given the interest in the study of thermal microsystems, we propose an optimization criterion taking into account both the thermal sensitivity and the signal to noise ratio of the considered radiometric methods. The optimization analysis results highlight the opportunity to reduce the working wavelength of thermography applications and, thus, improving the spatial resolution limit of the radiometric method used. This theoretical approach for wavelengths optimization of the radiometric methods is experimentally validated by a phase transition temperature measurement of a fused aluminium bath in both visible and near infrared spectral ranges.
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42.79.Pw Imaging detectors and sensors

High spatial resolution, high energy synchrotron x-ray diffraction characterization of residual strains and stresses in laser shock peened Inconel 718SPF alloy

Amrinder S. Gill, Zhong Zhou, Ulrich Lienert, Jonathan Almer, David F. Lahrman, S. R. Mannava, Dong Qian, and Vijay K. Vasudevan

J. Appl. Phys. 111, 084904 (2012); http://dx.doi.org/10.1063/1.3702890 (12 pages)

Online Publication Date: 19 April 2012

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Laser shock peening (LSP) is an advanced surface enhancement technique used to enhance the fatigue strength of metal parts by imparting deep compressive residual stresses. In the present study, LSP was performed on IN718 SPF alloy, a fine grained nickel-based superalloy, with three different power densities and depth resolved residual strain and stress characterization was conducted using high energy synchrotron x-ray diffraction in beam line 1-ID-C at the Advanced Photon Source at the Argonne National laboratory. A fine probe size and conical slits were used to non-destructively obtain data from specific gauge volumes in the samples, allowing for high-resolution strain measurements. The results show that LSP introduces deep compressive residual stresses and the magnitude and depth of these stresses depend on the energy density of the laser. The LSP induced residual stresses were also simulated using three-dimensional nonlinear finite element analysis, with employment of the Johnson-Cook model for describing the nonlinear materials constitutive behavior. Good agreement between the experimental and simulated data was obtained. These various results are presented and discussed.
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81.65.-b Surface treatments
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.me Fatigue
62.20.F- Deformation and plasticity
62.50.Ef Shock wave effects in solids and liquids

An origami tunable metamaterial

Kazuko Fuchi, Alejandro R. Diaz, Edward J. Rothwell, Raoul O. Ouedraogo, and Junyan Tang

J. Appl. Phys. 111, 084905 (2012); http://dx.doi.org/10.1063/1.4704375 (7 pages)

Online Publication Date: 19 April 2012

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The transmission characteristics of a folded surface decorated with a periodic arrangement of split-ring resonators is investigated. The folding pattern has one displacement degree of freedom, allowing motion that can be used to adjust the separation between the rings. When the geometry of the folded surface is varied by mechanical means, the change in spacing between the rings causes a shift in resonance frequency, making the surface mechanically tunable.
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42.70.-a Optical materials
42.79.-e Optical elements, devices, and systems

Tuning magnetic and transport properties through strain engineering in La0.7Sr0.3MnO3/La0.5Sr0.5TiO3 superlattices

Meng Gu, Chengyu Song, Fan Yang, Elke Arenholz, Nigel D. Browning, and Yayoi Takamura

J. Appl. Phys. 111, 084906 (2012); http://dx.doi.org/10.1063/1.4705397 (6 pages) | Cited 1 time

Online Publication Date: 24 April 2012

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Superlattices composed of non-magnetic La0.5Sr0.5TiO3 and ferromagnetic La0.7Sr0.3MnO3 were grown by pulsed laser deposition on various substrates to impose different epitaxial strain states. Well-defined superlattice structures with sharp interfaces were observed using scanning transmission electron microscopy and confirmed by electron energy loss spectroscopy. Defects such as misfit dislocations, partial dislocations, and low-angle grain boundaries were found to partially or fully relax the epitaxial strain while dramatically increasing the magnetic coercive field. Conversely, a large tensile strain was seen to induce a tetragonal distortion in the film lattice and alter the magnetic and magneto-transport properties of the superlattices.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Lk Linear defects: dislocations, disclinations
61.72.Mm Grain and twin boundaries
81.15.Fg Pulsed laser ablation deposition
79.20.Uv Electron energy loss spectroscopy

Ultrasonic evaluation of interlayer interfacial stiffness of multilayered structures

Yosuke Ishii and Shiro Biwa

J. Appl. Phys. 111, 084907 (2012); http://dx.doi.org/10.1063/1.4704692 (9 pages) | Cited 1 time

Online Publication Date: 24 April 2012

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A procedure for the ultrasonic evaluation of the interlayer interfacial stiffness of multilayered structures is proposed. As a theoretical background to this proposal, the elastic wave propagation in a multilayered structure, in which the layers are bonded with spring-type interfaces, is analyzed theoretically based on the transfer-matrix method. Using the notion of the Bloch phase which characterizes wave transmission in the corresponding infinite periodic structure, some explicit relations are derived for the reflection coefficient of the multilayered structure. Based on the features clarified theoretically, the interlayer interfacial stiffness of the multilayered structure can be evaluated from the locations of local minima and maxima of the amplitude reflection spectrum. By numerical analysis, the proposed procedure is shown to apply even when the viscous property of the layers is not known precisely, and when a transient waveform of a limited length is used. Using the proposed procedure, the stiffness of interlayer resin-rich regions in a carbon-epoxy cross-ply composite laminate is identified from the experimental reflection spectrum. The identified stiffness is shown to lie within the range as expected from the micrographic observation and a simple estimate for a thin resin layer.
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62.65.+k Acoustical properties of solids
62.20.dq Other elastic constants
81.40.Jj Elasticity and anelasticity, stress-strain relations

Exciton dissociation and charge trapping at poly(3-hexylthiophene)/phenyl-C61-butyric acid methyl ester bulk heterojunction interfaces: Photo-induced threshold voltage shifts in organic field-effect transistors and solar cells

Byoungnam Park, Nam-Ho You, and Elsa Reichmanis

J. Appl. Phys. 111, 084908 (2012); http://dx.doi.org/10.1063/1.4705277 (7 pages)

Online Publication Date: 30 April 2012

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Photoinduced charge transfer at an electron donor/acceptor interface is one of the most crucial processes in determining the power conversion efficiency of organic solar cell devices. Here, we address exciton dissociation and charge carrier trapping at poly(3-hexylthiophene) (P3HT)/phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction interfaces electrically using a field effect transistor (FET). With a P3HT/PCBM composite film, we elucidated exciton dissociation and charge carrier recombination assisted by localized electronic states at the P3HT/PCBM interface via photoinduced threshold voltage shift measurements with respect to wavelength using FETs in combination with organic solar cell devices. Interestingly, the combination of light coupled with a significant quantity of PCBM within the film was required to observe ambipolar charge transport in P3HT/PCBM FETs. This phenomenon was addressed by filling of electron traps associated with PCBM under illumination and formation of the conducting pathways for both electrons and holes. A high density of carrier traps at the interface suggested by the FET results was confirmed in light intensity dependent short-circuit current (Jsc) and open-circuit voltage (Voc) measurements using solar cell devices.
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88.40.jr Organic photovoltaics
88.40.hj Efficiency and performance of solar cells
85.30.Tv Field effect devices
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