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9 Jan 2012

Volume 100, Issue 2, Articles (02xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 023701 (2012); http://dx.doi.org/10.1063/1.3673335 (3 pages)

Biswarup Pathak, Henrik Löfås, Jariyanee Prasongkit, Anton Grigoriev, Rajeev Ahuja, and Ralph H. Scheicher
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X-ray diagnostics of runaway electrons generated during nanosecond discharge in gas at elevated pressures

S. Yatom, D. Levko, J. Z. Gleizer, V. Vekselman, and Ya. E. Krasik

Appl. Phys. Lett. 100, 024101 (2012); http://dx.doi.org/10.1063/1.3675462 (3 pages)

Online Publication Date: 9 January 2012

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The properties of high-energy runaway electrons generated during a nanosecond discharge in an air filled diode at pressures up to 3 × 105 Pa were studied using x-ray absorption spectroscopy. The results of studies of the discharge at different pressures and with different lengths of cathode-anode gap allow an insight into the factors that influence the energy distribution of runaway electrons. Energy distribution functions for runaway electrons produced in particle-in-cell simulation were used to create the x-ray attenuation curves via a computer-assisted technique simulating the generation of x-ray by energetic electrons. The simulated attenuation curves were compared to experimental results.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.80.-s Electric discharges
52.25.Fi Transport properties
52.75.Fk Magnetohydrodynamic generators and thermionic convertors; plasma diodes
52.70.La X-ray and γ-ray measurements

Coupling effects in inductive discharges with radio frequency substrate biasing

J. Schulze, E. Schüngel, and U. Czarnetzki

Appl. Phys. Lett. 100, 024102 (2012); http://dx.doi.org/10.1063/1.3675879 (3 pages) | Cited 5 times

Online Publication Date: 10 January 2012

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Low pressure inductively coupled plasmas (ICP) operated in neon at 27.12 MHz with capacitive substrate biasing (CCP) at 13.56 MHz are investigated by phase resolved optical emission spectroscopy, voltage, and current measurements. Three coupling mechanisms are found potentially limiting the separate control of ion energy and flux: (i) Sheath heating due to the substrate biasing affects the electron dynamics even at high ratios of ICP to CCP power. At fixed CCP power, (ii) the substrate sheath voltage and (iii) the amplitude as well as frequency of plasma series resonance oscillations of the RF current are affected by the ICP power.
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52.80.Pi High-frequency and RF discharges
52.25.Fi Transport properties
52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.35.Fp Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.40.Kh Plasma sheaths
52.70.Kz Optical (ultraviolet, visible, infrared) measurements

Performance of a piezoelectric energy harvester driven by air flow

C. A. Kitio Kwuimy, G. Litak, M. Borowiec, and C. Nataraj

Appl. Phys. Lett. 100, 024103 (2012); http://dx.doi.org/10.1063/1.3676272 (3 pages) | Cited 1 time

Online Publication Date: 11 January 2012

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A turbulent wind source for possible energy harvesting is considered. To increase the amplitude of vibration, we apply a magnetopiezoelastic oscillator having a double well Duffing potential. The output voltage response of the system for different level of wind excitations is analyzed. The energy harvesting appeared to be the most efficient for the conditions close to the stochastic resonance region where the potential barrier was overcame.
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84.60.-h Direct energy conversion and storage

Directed jetting from collapsing cavities exposed to focused ultrasound

B. Gerold, P. Glynne-Jones, C. McDougall, D. McGloin, S. Cochran, A. Melzer, and P. Prentice

Appl. Phys. Lett. 100, 024104 (2012); http://dx.doi.org/10.1063/1.3676414 (3 pages) | Cited 3 times

Online Publication Date: 11 January 2012

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We demonstrate directed jetting from pulsed laser-induced cavities subjected to a burst of focused ultrasound. Alignment of the ultrasound focus and the pressure amplitudes in the vicinity of the cavity dictate the direction and length of the resulting jet, respectively. We interpret our observations in terms of radiation forces exerted on the cavity, due to the pressure gradient introduced to the ultrasound focus by its presence. We support our hypothesis with a linear analysis of the force distribution across the cavity surface, at the moment of maximum inflation, which shows reasonable predictive agreement with the observed jet characteristics.
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43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.35.Ei Acoustic cavitation in liquids
43.35.Pt Surface waves in solids and liquids
47.15.Uv Laminar jets

Acoustic dipole radiation based conductivity image reconstruction for magnetoacoustic tomography with magnetic induction

Xiaodong Sun, Feng Zhang, Qingyu Ma, Juan Tu, and Dong Zhang

Appl. Phys. Lett. 100, 024105 (2012); http://dx.doi.org/10.1063/1.3676446 (4 pages) | Cited 2 times

Online Publication Date: 11 January 2012

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Based on the acoustic dipole radiation theory, a tomograhic conductivity image reconstruction algorithm is developed for the magnetoacoustic tomography with magnetic induction (MAT-MI) in a cylindrical measurement configuration. It has been experimentally proved for a tissue-like phantom that not only the configuration but also the inner conductivity distribution can be reconstructed without any borderline stripe. Furthermore, the spatial resolution also can be improved without the limitation of acoustic vibration. The favorable results have provided solid verification for the feasibility of conductivity image reconstruction and suggested the potential applications of MAT-MI in the area of medical electrical impedance imaging.
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87.63.dh Ultrasonographic imaging
43.80.Qf Medical diagnosis with acoustics
87.63.Pn Electrical impedance tomography (EIT)
87.57.nf Reconstruction

Evolution of nanoscale roughness in Cu/SiO2 and Cu/Ta interfaces

Andrew P. Warren, Tik Sun, Bo Yao, Katayun Barmak, Michael F. Toney, and Kevin R. Coffey

Appl. Phys. Lett. 100, 024106 (2012); http://dx.doi.org/10.1063/1.3675611 (4 pages) | Cited 2 times

Online Publication Date: 12 January 2012

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Synchrotron x-ray scattering was used to study the evolution of interface roughness with annealing for a series of Cu thin films. The films were encapsulated in SiO2 or Ta/SiO2 and prepared by sputter deposition. Specular x-ray reflectivity was used to determine the root mean square roughness for both the upper and the lower Cu/SiO2 (or Cu/Ta) interfaces. The lateral roughness was studied by diffuse x-ray reflectivity. Annealing the films at 600 °C resulted in a smoothing of only the upper interface for the Cu/SiO2 samples, while the lower Cu/SiO2 interfaces and both interfaces for the Ta encapsulated films did not evolve significantly. This difference in kinetics is consistent with the lower diffusivity expected of Cu in a Cu/Ta interface (compared to a Cu/SiO2 interface) and the mechanical rigidity of the lower Cu/SiO2 interface. As a function of roughness wavelength, the upper Cu/SiO2 interfaces exhibited a roughness decay with annealing that was only 12.5% of that expected for classical capillarity driven smoothening of a free surface.
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68.35.Ct Interface structure and roughness
68.35.Gy Mechanical properties; surface strains
78.70.Ck X-ray scattering
81.15.Cd Deposition by sputtering
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
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