Thermal diffuse scattering as a probe of large-wave-vector phonons in silicon nanostructures

Gokul Gopalakrishnan, Martin V. Holt, Kyle M. McElhinny, Josef W. Spalenka, David A. Czaplewski, Tobias U. Schülli, and Paul G. Evans

Accepted Thursday Apr 4, 2013

Large-wavevector phonons have an important role in determining the thermal and electronic properties of nanoscale materials. The small volumes of such structures, however, have posed significant challenges to experimental studies of the phonon dispersion. We show that synchrotron x-ray thermal diffuse scattering (TDS) can be adapted to probe phonons with wavevectors spanning the entire Brillouin zone of nanoscale silicon membranes. The TDS signal from flat Si nanomembranes with thicknesses from 315 nm to 6 nm, and a sample volume as small as 5 ��m3, has the expected linear dependence on the membrane thickness and also exhibits excess intensity at large wavevectors, consistent with the scattering signature expected from lowlying large-wavevector modes of the membranes.