Two-level systems in evaporated amorphous silicon

D.R. Queen, X. Liu, J. Karel, H. C. Jacks, T. H. Metcalf, F. Hellman

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21 Citations (Scopus)


In e-beam evaporated amorphous silicon (a-Si), the densities of two-level systems (TLS), n0 and P¯, determined from specific heat C and internal friction Q- 1 measurements, respectively, have been shown to vary by over three orders of magnitude. Here we show that n0 and P¯ are proportional to each other with a constant of proportionality that is consistent with the measurement time dependence proposed by Black and Halperin and does not require the introduction of additional anomalous TLS. However, n0 and P¯ depend strongly on the atomic density of the film (nSi) which depends on both film thickness and growth temperature suggesting that the a-Si structure is heterogeneous with nanovoids or other lower density regions forming in a dense amorphous network. A review of literature data shows that this atomic density dependence is not unique to a-Si. These findings suggest that TLS are not intrinsic to an amorphous network but require a heterogeneous structure to form.

Original languageEnglish
Pages (from-to)19-24
Number of pages6
JournalJournal of Non-Crystalline Solids
Publication statusPublished - 15 Oct 2015
Externally publishedYes


  • Amorphous silicon
  • Two-level systems
  • Specific heat
  • Internal friction

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