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Excess specific heat in evaporated amorphous silicon

  • Author(s): Queen, DR
  • Liu, X
  • Karel, J
  • Metcalf, TH
  • Hellman, F
  • et al.
Abstract

The specific heat C of e-beam evaporated amorphous silicon (a-Si) thin films prepared at various growth temperatures TSand thicknesses t was measured from 2 to 300 K, along with sound velocity v, shear modulus G, density nSi, and Raman spectra. Increasing TSresults in a more ordered amorphous network with increases in nSi, v, G, and a decrease in bond angle disorder. Below 20 K, an excess C is seen in films with less than full density where it is typical of an amorphous solid, with both a linear term characteristic of two-level systems (TLS) and an additional (non-Debye) T3 contribution. The excess C is found to be independent of the elastic properties but to depend strongly on density. The density dependence suggests that low energy glassy excitations can form in a-Si but only in microvoids or low density regions and are not intrinsic to the amorphous silicon network. A correlation is found between the density of TLS n0and the excess T3 specific heat cexsuggesting that they have a common origin. © 2013 American Physical Society.

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