Regensburg 2013 – scientific programme

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DS: Fachverband Dünne Schichten

DS 24: Thermoelectric Materials

DS 24.3: Talk

Wednesday, March 13, 2013, 15:15–15:30, H32

Nanoscale Heat Transport from Self-Organised Ge Hut and Dome Clusters into Si(001) — •Tim Frigge, Boris Krenzer, Verena Tinnemann, Annika Kalus, Friedrich Klasing, Anja Hanisch-Blicharski, and Michael Horn-von Hoegen — University of Duisburg-Essen and CENIDE, Duisburg, Germany

The nanoscale heat transport from self-organized Ge hut and dome clusters into Si substrates was determined by ultrafast time-resolved electron diffraction in reflection geometry. Within a temperature range between 400°C and 600°C Ge grows epitaxially in form of kinetically self-limited hut and dome clusters. In-situ deposition of 8ML Ge at 550°C under UHV conditions on Si(001) results in huts of 2 nm height and 20 nm width and domes with a height of 6 nm and a diameter of 50 nm. The clusters were excited in a pump-probe setup by 50 fs-laser pulses at a wavelength of 800 nm and probed by ultrashort electron pulses. Electron diffraction patterns were recorded at different delay times between the pump and probe pulses The observed transient drop of spot intensity is explained by the Debye-Waller effect and reflects the temperature increase from 25 K to 125 K. The cooling rate is determined from the exponential recovery of intensity: huts cool within 50 ps while the larger domes cool three times slower in 150 ps. This is in clear contrast to temperature dependent numerical simulations and reflects that size effects can reduce the heat transfer in nanoscale heterosystems by more than a factor of 8.