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14 Feb 2013

Volume 113, Issue 6, Articles (06xxxx)

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J. Appl. Phys. 113, 064301 (2013); http://dx.doi.org/10.1063/1.4789897 (11 pages)

Y. G. Marinov, G. B. Hadjichristov, A. G. Petrov, S. Marino, C. Versace, and N. Scaramuzza
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back to top Interdisciplinary and General Physics

Charge emissions from electrosprays in vacuum: Mixtures of formamide with methylammonium formate

David Garoz and Juan Fernández de la Mora

J. Appl. Phys. 113, 064901 (2013); http://dx.doi.org/10.1063/1.4790580 (8 pages)

Online Publication Date: 8 February 2013

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The charge/mass distribution f(q/m) of nanodrops and ions electrosprayed in vacuum from mixtures of formamide (FM) and methylammonium formate (MAF) is studied by time of flight mass spectrometry at MAF/FM volumetric concentrations of 5%, 10%, 25%, and 50%. Positive and negative polarities yield comparable f(q/m) curves, though the negative mode yields ∼30% larger currents. On shifting from the highest to the lowest liquid flow rates at which a cone-jet is stable, the more conductive solutions evolve from mostly drop to primarily ion emission. A purely ionic regime is not reached under any condition, but the drops achieve unusually high q/m. As a result, these sprays have excellent electrical propulsion characteristics, some being able to cover a 25-fold range of average q/m with a polydispersive efficiency typically in the range of 80%. Results of formamide electrolytes with formates and nitrates of several other amines are more briefly reported.
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78.67.Tf Nanodroplets
82.45.Gj Electrolytes
82.80.Rt Time of flight mass spectrometry

Erosion evolution in mono-crystalline silicon surfaces caused by acoustic cavitation bubbles

David Fernandez Rivas, Joris Betjes, Bram Verhaagen, Wilco Bouwhuis, Ton C. Bor, Detlef Lohse, and Han J. G. E. Gardeniers

J. Appl. Phys. 113, 064902 (2013); http://dx.doi.org/10.1063/1.4791582 (13 pages)

Online Publication Date: 12 February 2013

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The early stages (<180 min) of cavitation erosion of silicon surfaces were studied for three different crystallographic orientations. We introduce a quantity defined as the ratio of the relative eroded area to the number of pits, αp, to evaluate the evolution of erosion among the different substrates used. Different erosion evolution was observed for (100), (110), and (111) silicon surfaces when exposed to cavitation bubbles generated by an ultrasound signal of 191 kHz. (100) silicon substrates showed the most erosion damage, with an eroded area 2.5 times higher than the other two crystallographic orientation substrates after 180 min sonication. An apparent incubation period of 50 min was measured. The number of erosion pits increased monotonically for (110) and (111), but for (100) no increase was detected after 120 min. The collapse of a spherical bubble was simulated using an axisymmetry boundary integral method. The calculated velocity of the jet from the collapsing bubble was used to estimate the pressure P that is induced by the jet upon impact on the silicon substrate.
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81.40.Pq Friction, lubrication, and wear
62.20.Qp Friction, tribology, and hardness

Building the isotropic acoustic potential well with strong constraint boundary to improve the stability of ultrasonic transportation

Kun Jia, Jianxin Meng, Keji Yang, Zongwei Fan, and Bing-Feng Ju

J. Appl. Phys. 113, 064903 (2013); http://dx.doi.org/10.1063/1.4790711 (8 pages)

Online Publication Date: 12 February 2013

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A quantitative analysis of the acoustic potential well has been proposed for the purpose of realizing stability improvement of ultrasonic transportation. It was found that the boundary Rp and elastic constant kl(l,θ) of the acoustic potential well, acoustic radiation force offset ratio βfl, and elastic constant offset ratio βkl are the critical parameters that define the trapping ability. They were made clear both their intrinsic significance. The stability of the ultrasonic transportation using three transducers is theoretically studied. Long range ultrasonic transportation of silica beads with better stability is realized by optimizing the acoustic parameters to get the well-defined acoustic potential wells. No slip-off the equilibrium position has been observed, which proved its strong ability of trapping and transportation. Because of its simplicity, flexibility, and non-destructivity, the ultrasonic transportation offered a competitive micro-manipulation technology and will provide a promising tool for life science, chemistry and micro-assembly.
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43.35.Ty Other physical effects of sound

Material selection considerations for coaxial, ferrimagnetic-based nonlinear transmission lines

J.-W. B. Bragg, J. C. Dickens, and A. A. Neuber

J. Appl. Phys. 113, 064904 (2013); http://dx.doi.org/10.1063/1.4792214 (4 pages) | Cited 1 time

Online Publication Date: 12 February 2013

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The growing need for solid-state high power microwave sources has renewed interest in nonlinear transmission lines (NLTLs). This article focuses specifically on ferrimagnetic-based NLTLs in a coaxial geometry. Achieved peak powers exceed 30 MW at 30 kV incident voltage with rf power reaching 4.8 MW peak and pulse lengths ranging from 1–5 ns. The presented NLTL operates in S-band with the capability to tune the center frequency of oscillation over the entire 2–4 GHz band and bandwidths of approximately 30%, placing the NLTL into the ultra-wideband–mesoband category of microwave sources. Several nonlinear materials were tested and the relationship between NLTL performance and material parameters is discussed. In particular, the importance of the material's ferromagnetic resonance linewidth and its relationship to microwave generation is highlighted. For a specific nonlinear material, it is shown that an optimum relation between incident pulse magnitude and static bias magnitude exists. By varying the nonlinear material's bias magnetic field, active delay control was demonstrated.
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75.50.Gg Ferrimagnetics
84.40.-x Radiowave and microwave (including millimeter wave) technology
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
84.40.Az Waveguides, transmission lines, striplines

Nonlinear mixing of ultrasonic coda waves with lower frequency-swept pump waves for a global detection of defects in multiple scattering media

Y. Zhang, V. Tournat, O. Abraham, O. Durand, S. Letourneur, A. Le Duff, and B. Lascoup

J. Appl. Phys. 113, 064905 (2013); http://dx.doi.org/10.1063/1.4791585 (8 pages)

Online Publication Date: 13 February 2013

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An ultrasonic method providing for an efficient global detection of defects in complex media (multiple scattering or reverberating media) is reported herein; this method is based on the nonlinear acoustic mixing of coda waves (stemming from multiple scattering) with lower frequency-swept pump waves. Such a nonlinear mixing step is made possible by the presence of nonlinear scatterers, such as cracks and delamination, yet remains absent when the waves are scattered only by linear scatterers, as is the case in a complex but defect-free medium. A global inspection is achieved thanks to the use of wide-band coda and pump signals, which ensure the excitation of many resonances along with a homogeneous acoustic energy distribution in the medium. We introduce the existing sensitivity tools developed for Coda Wave Interferometry in extracting the pump amplitude-dependent parameters of the coda waves associated with effective nonlinear parameters of the medium. By comparing results at two damage levels, these effective nonlinear parameters are shown to be correlated with crack presence in glass samples. The mechanisms potentially responsible for the observed amplitude dependence on the tested elastic parameters and waveform modification are discussed.
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81.70.Cv Nondestructive testing: ultrasonic testing, photoacoustic testing
43.25.Zx Measurement methods and instrumentation for nonlinear acoustics
43.35.Zc Use of ultrasonics in nondestructive testing, industrial processes, and industrial products
43.58.Ry Distortion: frequency, nonlinear, phase, and transient; measurement of distortion

Ignition criterion for heterogeneous energetic materials based on hotspot size-temperature threshold

A. Barua, S. Kim, Y. Horie, and M. Zhou

J. Appl. Phys. 113, 064906 (2013); http://dx.doi.org/10.1063/1.4792001 (22 pages) | Cited 1 time

Online Publication Date: 13 February 2013

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A criterion for the ignition of granular explosives (GXs) and polymer-bonded explosives (PBXs) under shock and non-shock loading is developed. The formulation is based on integration of a quantification of the distributions of the sizes and locations of hotspots in loading events using a cohesive finite element method (CFEM) developed recently and the characterization by Tarver et al. [C. M. Tarver et al., "Critical conditions for impact- and shock-induced hot spots in solid explosives," J. Phys. Chem. 100, 5794–5799 (1996)] of the critical size-temperature threshold of hotspots required for chemical ignition of solid explosives. The criterion, along with the CFEM capability to quantify the thermal-mechanical behavior of GXs and PBXs, allows the critical impact velocity for ignition, time to ignition, and critical input energy at ignition to be determined as functions of material composition, microstructure, and loading conditions. The applicability of the relation between the critical input energy (E) and impact velocity of James [H. R. James, "An extension to the critical energy criterion used to predict shock initiation thresholds," Propellants, Explos., Pyrotech. 21, 8–13 (1996)] for shock loading is examined, leading to a modified interpretation, which is sensitive to microstructure and loading condition. As an application, numerical studies are undertaken to evaluate the ignition threshold of granular high melting point eXplosive, octahydro-1,3,5,7-tetranitro-1,2,3,5-tetrazocine (HMX) and HMX/Estane PBX under loading with impact velocities up to 350 ms−1 and strain rates up to 105 s−1. Results show that, for the GX, the time to criticality (tc) is strongly influenced by initial porosity, but is insensitive to grain size. Analyses also lead to a quantification of the differences between the responses of the GXs and PBXs in terms of critical impact velocity for ignition, time to ignition, and critical input energy at ignition. Since the framework permits explicit tracking of the influences of microstructure, loading, and mechanical constraints, the calculations also show the effects of stress wave reflection and confinement condition on the ignition behaviors of GXs and PBXs.
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82.40.Fp Shock wave initiated reactions, high-pressure chemistry
62.50.Ef Shock wave effects in solids and liquids

Impact of Se flux on the defect formation in polycrystalline Cu(In,Ga)Se2 thin films grown by three stage evaporation process

M. M. Islam, A. Uedono, T. Sakurai, A. Yamada, S. Ishizuka, K. Matsubara, S. Niki, and K. Akimoto

J. Appl. Phys. 113, 064907 (2013); http://dx.doi.org/10.1063/1.4792049 (7 pages)

Online Publication Date: 13 February 2013

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Cu(InxGa1−x)Se2 (CIGS) films, grown under various Se fluxes, have been investigated by the positron annihilation spectroscopy. The line-shape parameter (S) of the positron annihilation spectra was used to characterize the defects in the CIGS films. When Se flux was decreased, the S parameter at the surface and subsurface region of the films increased. This phenomenon was attributed to the increased concentration of the defect complex formed between Se and Cu vacancies. S parameter at the surface region was significantly higher than that in the bulk region of each film. It was explained with the model of compositional inhomogeneities along the depth of the film. Solar cell performance strongly correlated to the S parameter at the surface region of the CIGS films. Sufficient Se flux was found to be effective to reduce the S parameter, thereby, to suppress the defects in the films.
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68.55.ag Semiconductors
88.40.hj Efficiency and performance of solar cells
78.70.Bj Positron annihilation
81.05.Hd Other semiconductors
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.72.jd Vacancies

Ordered arrays of Si and Ge nanocrystals via dewetting of pre-patterned thin films

I. Berbezier, M. Aouassa, A. Ronda, L. Favre, M. Bollani, R. Sordan, A. Delobbe, and P. Sudraud

J. Appl. Phys. 113, 064908 (2013); http://dx.doi.org/10.1063/1.4790713 (6 pages)

Online Publication Date: 13 February 2013

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We develop self-organisation processes for the fabrication of 2D arrays of Si and Ge quantum dots. The processes make use of the dewetting phenomenon which involves the transformation of a 2D thin film into an array of isolated 3D islands through a morphological instability. We show that self-organization of monodisperse ultra-small nanocrystals (NCs) into large scale patterns with ad hoc features can be created via heterogeneous dewetting. The process involves dewetting of thin films nanopatterned by electron beam lithography (EBL) or liquid metal alloy source focused ion beam (LMAIS-FIB). Heterogeneous dewetting is initiated at the edges of the patterns. It provokes the retraction of the thin film following the kinetics of surface diffusion and ends by the formation of faceted monocrystalline NCs regularly positioned. Their geometrical features and lateral arrangements can be tuned by changing the pitch, size, and shape of the patterns. The process developed in this study is adapted to the fabrication of NCs based floating gate memories.
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81.05.Cy Elemental semiconductors
81.07.Ta Quantum dots
81.16.Dn Self-assembly
81.16.Nd Micro- and nanolithography
81.16.Rf Micro- and nanoscale pattern formation
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

High-power microwave filters and frequency selective surfaces exploiting electromagnetic wave tunneling through ϵ-negative layers

Chien-Hao Liu and Nader Behdad

J. Appl. Phys. 113, 064909 (2013); http://dx.doi.org/10.1063/1.4790584 (9 pages)

Online Publication Date: 14 February 2013

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In this paper, we experimentally investigate the phenomenon of electromagnetic wave tunneling through ϵ-negative (ENG) metamaterial layers surrounded by double-positive layers. Initial experiments are conducted by using a rectangular waveguide, which operates below its cutoff frequency to emulate an ENG layer. This ENG layer is then sandwiched by two dielectric substrates with relatively high dielectric constants and it is shown that the entire setup acts as a classical microwave filter with a second-order bandpass response. The power handling capability of this filter is examined experimentally using a high-power magnetron source with a frequency of 9.382 GHz, a pulse duration of 1 μs, and a peak power of 25 kW. Based on the results of this experiment, two methods for improving the power handling capability of these multi-layer structures are proposed. In particular, it is demonstrated that emulating the ENG layers with thin perforated metallic sheets with sub-wavelength holes significantly enhances their peak power handling capability. A prototype of such a device is designed, fabricated, and experimentally characterized and it is demonstrated that it can handle extremely high peak power levels. The results presented in this work are expected to be useful in designing microwave filters and frequency selective surfaces that can handle extremely high peak power levels.
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84.30.Vn Filters
84.40.Az Waveguides, transmission lines, striplines
84.40.Dc Microwave circuits
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