A combination of a double-tip scanning tunneling microscope with a scanning electron microscope in ultrahigh vacuum environment is presented. The compact beetle-type design made it possible to integrate two independently driven scanning tunneling microscopes in a small space. Moreover, an additional level for coarse movement allows the decoupling of the translation and approach of the tunneling tip. The position of the two tips can be controlled from the millimeter scale down to 50 nm with the help of an add-on electron microscope. The instrument is capable of atomic resolution imaging with each tip.

We demonstrate the ability of a double-tip scanning tunneling microscope ͑STM͒ combined with a scanning electron microscope ͑SEM͒ to perform charge transport measurements on the nanoscale. The STM tips serve as electric probes that can be precisely positioned relative to the surface nanostructures using the SEM control and the height reference provided by the tunneling contact. The tips work in contact, noncontact, and tunneling modes. We present vertical transport measurements on nanosized GaAs/AlAs resonant tunneling diodes and lateral transport measurements on the conductive surface of 7 ϫ 7 reconstructed Si͑111͒. The high stability of the double-tip STM allows nondestructive electrical contacts to surfaces via the tunneling gaps. We performed two-point electrical measurements via tunneling contacts on the Si͑111͒͑7 ϫ 7͒ surface and evaluated them using a model for the charge transport on this surface.

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Nonalloyed ohmic contacts with lateral dimensions in the sub‐100 nm range have been processed and characterized. The contacts are suitable for the fabrication of GaAs/AlGaAs nanocolumns designed in a ‘top down’ approach. They are realized on n‐type GaAs using a thin low‐temperature grown GaAs cap layer and Ti/Au metallization. For the lateral patterning of the nanoscaled ohmic contacts, electron‐beam lithography based on Hydrogen Silsesquioxan (HSQ) negative resist is used, followed by sputtering and plasma etching of the metals. The I –V characteristics show ohmic contact behavior and demonstrate the scaling of the proposed contacts down to 50 nm lateral dimension. The specific contact resistance is situated in the range of 1–2 × 10–5 Ω cm2. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)