Raman spectroscopy of free-standing Ge nanocrystals

ORAL

Abstract

Ge nanocrystals, with an average diameter of 5 nm, are grown in a silica matrix. Free-standing nanocrystals are obtained by selectively etching the oxide. Embedded nanocrystals experience considerable compressive stress relative to the bulk. The Raman line position of free-standing nanocrystals is redshifted by $\sim $6 cm$^{-1}$ relative to that of embedded nanocrystals, indicating relief of the compressive stress. Mixed surface/bulk vibrational modes between 125 and 250 cm$^{-1}$ and surface modes below 125 cm$^{-1}$ are observed by Raman spectroscopy on free-standing nanocrystals. These modes are not observed for the case of embedded nanocrystals. Exposed nanocrystals are stable under ambient atmospheric conditions after the formation of a thin, self-limiting native oxide layer. The effect of oxide layer thickness on the vibrational spectra of free-standing nanocrystals will be discussed. This work is supported in part by U.S. NSF Grant Nos. DMR-0109844 {\&} EEC-0085569 and in part by U.S. DOE under Contract No. DE-AC03-76F00098.

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Authors

  • I.D. Sharp

  • Q. Xu

  • C.Y. Liao

  • D.O. Yi

  • D.C. Chrzan

    • University of California, Berkeley and Lawrence Berkeley National Laboratory
    • University of California, Berkeley and Lawrence Berkeley National Laboratories

  • E.E. Haller

    • UC Berkeley and LBNL, Berkeley, CA 94720

  • J.W. Beeman

  • J.W. Ager III

    • LBNL, Berkeley, CA 94720