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8 May 2000

Volume 76, Issue 19, pp. 2647-2800

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Surface electronic density of states of tetrahedral amorphous carbon investigated by scanning tunneling spectroscopy and ab initio calculations

K. Jarmo Koivusaari, Tapio T. Rantala, J. Levoska, and S. Leppävuori

Appl. Phys. Lett. 76, 2794 (2000); http://dx.doi.org/10.1063/1.126478 (3 pages) | Cited 6 times

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The surface electronic density of states of tetrahedral amorphous carbon has been measured by scanning tunneling microscopy and calculated by density functional theory. An analysis of these results and their comparison is presented here for a series of structures with different microscopic mass densities. The experimental structures were obtained by pulsed laser deposition with varying conditions resulting in diamond-like carbon thin films. The calculated carbon structures were generated by simulating a melting–cooling cycle with molecular dynamics using the density functional energetics within the local density approximation. The experimental and calculated densities of states show good agreement. Graphitic-like surface reconstruction is both observed at the sp3-rich tetrahedral amorphous carbon (ta-C) sample and found in the calculated ta-C slab structure. © 2000 American Institute of Physics.
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73.20.At Surface states, band structure, electron density of states
71.23.Cq Amorphous semiconductors, metallic glasses, glasses
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Rh Phase transitions and critical phenomena

Precise velocity measurement of surface acoustic waves on a bearing ball

Kazushi Yamanaka, Hideo Cho, and Yusuke Tsukahara

Appl. Phys. Lett. 76, 2797 (2000); http://dx.doi.org/10.1063/1.126481 (3 pages) | Cited 23 times

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Using the photoacoustic effect of interference fringes scanned at the phase velocity of surface acoustic waves (SAW), we excited tone bursts of SAW with a center frequency of around 30 MHz on a 8 mm ϕ steel bearing ball. A surprisingly large number (around 20 turns) of round-trip propagations was observed. The time interval between the SAW at the first and the twelfth turn was as large as 93 μs, however it could be determined with a 2 ns resolution since an exact overlapping of the two wave forms was possible. Thus, we achieved a very high resolution of 0.002% in the velocity measurement, and a velocity change of 2 m/s due to the deposition of a 50-nm-thick Ag film was easily detected. Because of its noncontact nature, this method would be useful for nondestructive evaluation of bearing balls. © 2000 American Institute of Physics.
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68.35.Gy Mechanical properties; surface strains
62.65.+k Acoustical properties of solids
78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
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