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The influence of thin helium films on the phonon spectrum of optically excited silicon
Author(s) -
Türk F.,
Ullrich G.,
Kinder H.
Publication year - 1995
Publication title -
annalen der physik
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.009
H-Index - 68
eISSN - 1521-3889
pISSN - 0003-3804
DOI - 10.1002/andp.19955070302
Subject(s) - phonon , materials science , silicon , spectrometer , surface phonon , excited state , helium , monolayer , atomic physics , molecular physics , condensed matter physics , optics , optoelectronics , physics , nanotechnology
We have studied the phonon spectra resulting from laser pulse excitation of a silicon surface. We used a phonon spectrometer based on pressure tuned boron levels in silicon (Si: B‐spectrometer). A new design allowed us to use the spectrometer in vacuum for the first time. We observed phonon frequencies up to 1 THz. The pulse shapes indicated both, quasidiffusion and a long exciton lifetime. On adding helium films to the surface we have found dramatic changes of the spectrum. Full thermalisation was reached already at a thickness of 1.5 monolayers. This indicates a strong anharmonic interaction in the very first monolayers at these high frequencies and, in addition, a strong confinement of the phonons to the surface by quasidiffusion.