We demonstrate several approaches for the generation of metallic nanowires and nanocontacts, which combine self-organization, standard electron beam lithography, electron beam lithography in ultra-high vacuum (UHV) with epitaxy of silver and lead on Si(111), Si(100) and vicinal surfaces. Low doped Si is used in all cases as insulating substrate at or below room temperature. The UHV technique allows direct writing with the electron beam into ultrathin oxide with partial reduction processes.
Crystalline metal nanowires of few atomic layers thickness and a width of less than 20 nm on Si(111) are generated in UHV. The experiments are performed in a combined SEM-STM system for confocal and simultaneous operation of both microscopes at variable sample temperatures in the range 60-900 K. Employing electron beam-induced selective thermal desorption, clean Si(111) windows are generated within a thin thermal surface oxide layer of 0.3-0.7 nm thickness.
Macroscopic contact pads made of TiSi2 were generated by evaporating stacks of Ti and Si in the correct thickness ratio. They serve as connectors to the outside world, and were shown to withstand the necessary thermal treatment so that atomically clean Si could be obtained in presence of the pads in UHV.
This method was extended in order to combine e-beam structuring with self-organization in order to generate Pb wires on a vicinal Si(557) surface. With only one monolayer of Pb, high temperature annealing close to desorption temperature leads to spontaneous formation of almost atomic-size wires with a separation of only 1.5 nm. We show that a few of these wires can be singled out using our lithography technique in UHV. The smallest set of wires is only 3 wires wide with a characteristic smallest structure size of only 5.7 nm in the oxide. Self-limitation at the step edges lead to very regular structures.
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