Regensburg 2013 – wissenschaftliches Programm

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DS: Fachverband Dünne Schichten

DS 12: Poster Session II: Functionalized semiconductor nanowires (jointly with HL); Resistive switching (jointly with DF, KR, HL); Thermoelectric materials

DS 12.19: Poster

Montag, 11. März 2013, 17:00–20:00, Poster B1

Unexpected temperature dependence of thermal boundary conductance for epitaxial Bi(111) films on Si(001) — •Verena Tinnemann, Tim Frigge, Boris Krenzer, Anja Hanisch-Blicharski, Friedrich Klasing, Annika Kalus, and Michael Horn-von Hoegen — Faculty of Physics and Center for Nanointegration CENIDE, University of Duisburg-Essen, Lotharstr. 1, 47057 Duisburg, Germany

Ultrafast time-resolved reflection high energy electron diffraction was used to study the heat transfer from epitaxial Bi(111) films into the Si(001) substrate. Films with thicknesses in the range from 25 nm to 120 nm were prepared in-situ under UHV conditions. In a pump-probe setup the Bi films were excited by 50 fs-laser pulses with a wavelength of 800 nm. Short electron pulses were created by photoemission, accelerated to 7 keV, and focused by an electrostatic lens. For variable time delays between laser pump and electron probe diffraction patterns were recorded. The transient drop of spot intensity is explained in terms of the Debye-Waller effect and reflects the instant heating and subsequent cooling of the Bi films. The thermal boundary conductance of the interface is then determined from the exponential cooling of the film. We show that the thermal boundary conductance increases by more than 35% if the substrate temperature is increased from 80 K to 300 K. This is not explained by numerical simulations of the heat transport using temperature dependent parameters. For the 120 nm thick Bi-film a bi-exponential intensity is observed and explained by diffusion in the film and across the interface.