Regensburg 2007 – scientific programme

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O: Fachverband Oberflächenphysik

O 5: Nanostructures at Surfaces I (Wires, Tubes)

O 5.6: Talk

Monday, March 26, 2007, 12:30–12:45, H36

In-situ preparation of contacts for metal nanostructures — •Svend Vagt, Tammo Block, Jan Rönspies, and Herbert Pfnür — Institut für Festkörperphysik, Leibniz Universität Hannover

For direct transport measurements on single ultrasmall structures leads are needed. We present different techniques for this purpose.

In a first attempt contact pads are prepared ex-situ via e-beam lithography and titanium evaporation, followed by annealing to about 1000K. This results in TiSi pads, that exhibit a good electrical conductance. However, to clean the Si areas between the pads, a flash temperature of 1400K is necessary, at which deep trenches are formed at the edges of the pad due to stress induced diffusion of Si into the TiSi pad. We present mulitilayer stacks of Ti and Si, that can be used to improve the situation.

Here we describe another method that completly avoids such step bunches by flashing the silicon prior to the evaporation of Ti. This whole process has to take place completely in UHV. A few microns thin tungsten wire acts as a simple "shadow mask" and is removed after metal deposition. This leads to ultrathin, but still well conducting TiSi pads, that are stable up to 1000K. The penumbra of the wire also forms a ramp-like shape at the border of the pad and avoids the formation of deeper trenches. Between such contact pads metallic nanostructures are prepared by electron-beam stimulated thermal desorption of oxygen (EBSTD) from a ultrathin SiO₂ layer on the remaining Si(111) area. Subsequent metal deposition and annealing leads to metallic structures in electric contact with the pads.