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PGI Colloquium: 

Prof. Dr. Bene Poelsema,
Physics of Interfaces and Nanomaterials (PIN), University of Twente, Enschede, the Netherlands


PGI Lecture Hall, Building 04.8, 2nd Floor, Room 365

20 Nov 2015 11:00

An in-depth LEEM study of Pt/Ge(001): birth and death of Pt nanowires and a novel near-surface confined alloy stabilized by quantum size effects

PoelsemaCopyright: Prof. Dr. Poelsema

Deposition of Pt on Ge(001), followed by annealing (@1050 K) and a quick cool-down gives rise to the formation of ultrathin Pt nanowires (NWs). These wires are one atom thick and basically run from defect to defect on Ge(001). Their length thus can exceed 1 micron and thus have the longest aspect ratio ever reported for NWs. The resulting surface patches possess interesting properties, including quantum confined electronic states between the Pt-NWs, selective binding of CO on Pt-NWs, Peierls instability of Pt-NWs. In order to suppress loss of Pt from the surface (-near region) the anneal time was kept short, cool-down took place fast and no information on the processes leading to the Pt-NWs became available.

This changed in our recent study using LEEM (Low Energy Electron Microscopy) as an in-situ probe of structure and electronic property. We observed that a surface confined eutectic phase with a composition close to the bulk one (Pt:Ge = 22:78) is formed during annealing. Subsequent cooling leads to spinodal decomposition into pure Ge and presumably Ge3Pt at the hidden interface. During cooling excretion of Pt is thought responsible for the formation of Pt-NWs nanowires hosted by the surface.

The newly found structure does not occur in the bulk binary phase diagram and we attribute the stabilization of the smooth Ge3Pt film, with locally different thicknesses of about 5 and 9 layers, to Quantum Size Effects. This is further corroborated by the estimated value for the Fermi wave length of 1.32 nm in agreement with the reported ionization energy of 40 meV for Pt embedded as acceptors in Ge. We believe that our current findings may well be seminal for a better understanding of the important class of metal – semiconductor systems.


Prof. Dr. Christian Kumpf
Phone: +49 2461 61-1452
Fax: +49 2461 61-3907