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O: Fachverband Oberflächenphysik

O 12: Surface dynamics

O 12.10: Vortrag

Montag, 26. März 2012, 18:15–18:30, H 2013

Heat Transport from Self Organised Ge Nano-Structures to Si(001) Substrate — •Tim Frigge, Anja Hanisch-Blicharski, Simone Wall, Annika Kalus, Martin Kammler, and Michael Horn-von Hoegen — University of Duisburg-Essen and CENIDE, Duisburg, Germany

We used ultrafast time-resolved reflection high energy electron diffraction to investigate the heat transport from nanoscale Ge clusters to a Si(001) substrate. From the transient cooling behaviour upon fs-laser excitation the thermal properties of these nanostructures could be determined without further calibration. On Si(001) Ge grows in a Stranski-Krastanov mode and can be used for self organisation of nanostructures. Island formation occurs at a critical coverage of 3 monolayers with metastable hut-clusters of a width of 25nm and a height of 2.5nm. Further Ge deposition results in the formation of 50 nm wide dome-clusters with a height of 6nm. Both cluster-types exhibit atomically flat side facets, are mono-crystalline, epitaxial, defect-free, and have a uniform size distribution. The interface between the Ge-islands and the Si(001)-substrate is abrupt. At a base temperature of 25K and a transient heating by 100K, caused by the fs laser pump-pulse, different cooling rates for both clusters were determined. Hut-clusters cool in 50ps while dome-clusters cool three times slower in 150ps. A comparison with the theoretically expected thermal boundary conductance of the diffuse mismatch model (DMM) for two-dimensional uniform Ge layers shows that the cooling rate of the nano scale islands is reduced by more than a factor two!