Dresden 2011 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 99: Electron and spin dynamics II
O 99.2: Vortrag
Freitag, 18. März 2011, 11:30–11:45, WIL B321
Time-resolved 2PPE Study of Image-Potential States on Helium Adlayers on Cu(111)/Ru(001) — •Nico Armbrust1, Jens Güdde1, Ulrich Höfer1, Sarah Kossler2, and Peter Feulner2 — 1Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universität, D-35032 Marburg — 2Physik-Department E20, TU München, D-85748 Garching
Image-potential states on thin He films on metal surfaces have attracted interest since their first observation on liquid He in the mid-seventies due to the possibility of preparing a dense two-dimensional electron gas. Because of the difficulties in combining UHV and cryogenic technology with two-photon photoemission spectroscopy (2PPE) image-potential states on well-defined He adlayers on single crystal surfaces have not been investigated systematically up to now. Here we present first results of a time-resolved two-photon photoemission study of the image-potential states on He/Cu(111). We used a specially designed lHe cryostat which made it possible to prepare He adlayers up to a thickness of 2 monolayers. These were deposited on a Cu(111) film which has been grown epitaxially on a Ru(001) substrate. The He adlayers lead to a decoupling of the image-potential states from the metal surface resulting in a reduction of the binding energy of up to 310 meV for the n=1 state and only of about 15 meV for the n=2 state. This goes along with a huge increase of the lifetime from 30 fs up to 350 fs for the n=1 state and from 105 fs to 360 fs for the n=2 state.