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12 Mar 2012

Volume 100, Issue 11, Articles (11xxxx)

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Appl. Phys. Lett. 100, 111101 (2012); http://dx.doi.org/10.1063/1.3691957 (3 pages)

Christina Alpmann, Michael Esseling, Patrick Rose, and Cornelia Denz
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High power impulse magnetron sputtering discharges: Instabilities and plasma self-organization

A. P. Ehiasarian, A. Hecimovic, T. de los Arcos, R. New, V. Schulz-von der Gathen, M. Böke, and J. Winter

Appl. Phys. Lett. 100, 114101 (2012); http://dx.doi.org/10.1063/1.3692172 (4 pages) | Cited 9 times

Online Publication Date: 12 March 2012

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We report on instabilities in high power impulse magnetron sputtering plasmas which are likely to be of the generalized drift wave type. They are characterized by well defined regions of high and low plasma emissivity along the racetrack of the magnetron and cause periodic shifts in floating potential. The azimuthal mode number m depends on plasma current, plasma density, and gas pressure. The structures rotate in math×math direction at velocities of ∼10 km s−1 and frequencies up to 200 kHz. Collisions with residual gas atoms slow down the rotating wave, whereas increasing ionization degree of the gas and plasma conductivity speeds it up.
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52.80.Hc Glow; corona
52.35.Py Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)
52.35.Kt Drift waves
52.25.Fi Transport properties
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions
52.25.Jm Ionization of plasmas

Energy exchange between a vortex ring and an ionic polymer metal composite

Sean D. Peterson and Maurizio Porfiri

Appl. Phys. Lett. 100, 114102 (2012); http://dx.doi.org/10.1063/1.3693184 (4 pages) | Cited 9 times

Online Publication Date: 12 March 2012

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In this letter, we study the transient response of a cantilevered ionic polymer metal composite impacted by a self-propagating vortex ring in an otherwise quiescent fluid. Experiments are performed using time-resolved particle image velocimetry to elucidate the flow physics during the vortex ring propagation and subsequent interaction with the cantilever. Images from these experiments are analyzed to extract the vibration of the structure, which is used to estimate the energy transferred from the vortex ring. A small fraction of this energy is further transduced into an electrical signal by the chemoelectromechanical behavior of the ionic polymer metal composite.
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47.80.Jk Flow visualization and imaging
47.32.C- Vortex dynamics

Green luminescence in silica glass: A possible indicator of subsurface fracture

Jessica Fournier, Jerome Neauport, Pierre Grua, Evelyne Fargin, Véronique Jubera, David Talaga, and Stéphane Jouannigot

Appl. Phys. Lett. 100, 114103 (2012); http://dx.doi.org/10.1063/1.3693393 (3 pages) | Cited 1 time

Online Publication Date: 12 March 2012

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We investigate the nature of defects triggering laser damage in fused silica in subsurface fractures in nanosecond near ultraviolet regime. Mechanical, laser induced surface flaws as well as pristine silica surface were characterized by optical microscopy and luminescence confocal microscopy before and after acid etching. In all cases, photoluminescence decreases with etching time assessing the existence of defects close to the surface. Spectral analysis of the evolution of these signals during etching allows new interpretations of the nature of precursors inducing damage. Green luminescence around 2.25 eV is seen as a potential subsurface fracture indicator leading to laser damage.
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78.55.Hx Other solid inorganic materials
81.65.Cf Surface cleaning, etching, patterning
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mm Fracture
78.40.Ha Other nonmetallic inorganics

Optimal configurations of bistable piezo-composites for energy harvesting

D. N. Betts, H. A. Kim, C. R. Bowen, and D. J. Inman

Appl. Phys. Lett. 100, 114104 (2012); http://dx.doi.org/10.1063/1.3693523 (4 pages) | Cited 2 times

Online Publication Date: 13 March 2012

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This paper presents an arrangement of bistable composites combined with piezoelectrics for broadband energy harvesting of ambient vibrations. These non-linear devices have improved power generation over conventional resonant systems and can be designed to occupy smaller volumes than magnetic cantilever systems. This paper presents results based on optimization of bistable composites that enables improved electrical power generation by discovering the optimal configurations for harvesting based on the statics of the device. The optimal device aspect ratio, thickness, stacking sequence, and piezoelectric area are considered. Increased electrical output is found for geometries and piezoelectric configurations, which have not been considered previously.
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84.60.-h Direct energy conversion and storage
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

Synchronizing noncontact rack-and-pinion devices

Mojtaba Nasiri, MirFaez Miri, and Ramin Golestanian

Appl. Phys. Lett. 100, 114105 (2012); http://dx.doi.org/10.1063/1.3694050 (3 pages)

Online Publication Date: 15 March 2012

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The lateral Casimir force is employed to propose a nanoscale mechanical device composed of one rack and N pinions. A coupling between the pinions via torsional springs is shown to coordinate their motion through a synchronization transition. The system can work against loads that are greater than the lateral Casimir force for each device. The existence of a stable synchronized state ensures that the system could operate in full coordination without the need of delicate fine tuning of all the characteristics such as the spring constants, the corrugation amplitudes, and the distances between the rack and the pinions.
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07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Shape oscillations of an electrically charged diamagnetically levitated droplet

R. J. A. Hill and L. Eaves

Appl. Phys. Lett. 100, 114106 (2012); http://dx.doi.org/10.1063/1.3694055 (4 pages) | Cited 1 time

Online Publication Date: 15 March 2012

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We use diamagnetic levitation to investigate the effect of electrical charge on the normal mode vibration frequencies of charged water droplets with radii 4.5-7.5 mm. This technique allows us to levitate almost spherical droplets, enabling us to directly compare the measured frequencies of the first seven modes with theoretical values calculated by Lord Rayleigh, with which we find good agreement.
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47.65.Cb Magnetic fluids and ferrofluids
75.50.Mm Magnetic liquids
47.55.D- Drops and bubbles

Enhancing mechanical energy harvesting with dynamics escaped from potential well

T. Ma and H. Zhang

Appl. Phys. Lett. 100, 114107 (2012); http://dx.doi.org/10.1063/1.3694272 (4 pages)

Online Publication Date: 15 March 2012

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The potential of utilizing the dynamics outside the potential well of a device for harvesting energy from vibrations is investigated. A pendulum-type system subjected to parametrical excitation is used to demonstrate the concept. When the dynamics of the device is outside the potential well and stays in stable orbits of period-one rotations, the harvested energy is proportional to the energy level of the orbit. It is neither dependent on the natural frequency of the device nor on the intensity of the excitation. For low-level vibrations, the effectiveness of the proposed method is limited in relatively low frequencies.
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88.05.-b Energy analysis

Measurement of sodium-argon cluster ion recombination by coherent microwave scattering

Yue Wu, Jordan Sawyer, Zhili Zhang, Mikhail N. Shneider, and Albert A. Viggiano

Appl. Phys. Lett. 100, 114108 (2012); http://dx.doi.org/10.1063/1.3695064 (4 pages)

Online Publication Date: 16 March 2012

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This present work demonstrates a non-intrusive measurement of the rate constant for sodium-argon cluster ions (Na+·Ar) recombining with electrons. The measurements begin with resonance enhanced multi-photon ionization of the Na followed by coherent microwave scattering (radar) to monitor the plasma density. The Na+·Ar adduct was formed in a three-body reaction. The plasma decay due to recombination reactions was monitored as a function of time and modeled to determine the rate constant. At 473 K, the rate constant is 1.8−0.5+0.7×10−6cm3/s in an argon buffer at 100 Torr and initial Na number density of 5.5 × 1010 cm−3.
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34.80.Lx Recombination, attachment, and positronium formation
33.80.Eh Autoionization, photoionization, and photodetachment
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
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