NANOWIRE BONDING WITH THE SCANNING TUNNELING MICROSCOPE

We have developed a reliable lithographic method to pattern thin gold films by locally exposing a thin layer of an electron beam resist with the tip of a scanning tunneling microscope (STM). The exposure of the resist layer is induced by applying a voltage difference of ca. -10V between the STM tip and the gold film on top of which the resist layer has been deposited with the Langmuir-Blodgett technique. Our resist m aterial is omega-tricosenoic acid which acts as a negative resist. Aft er development, the unexposed areas of the gold film can be removed vi a argon ion milling. We have been able to obtain continuous gold lines having a width down to 15 nm, the linewidth being determined by the e xposure dose. When reducing the tunneling voltage <5 V, exposure of th e Langmuir-Blodgett resist layer no longer occurs and one switches to the classical topographic imaging mode. This switching provides us wit h the unique possibility to attach electrical contacts to existing nan ostructures. As a nice example of this nanowire bonding, gold contacts have been attached to individual multiwalled carbon nanotubes. We hav e made detailed measurements of the nanotube resistance as a function of temperature down to 10 mK and in magnetic fields up to 14 T. Al low temperatures a pronounced negative magnetoresistance is observed whic h is consistent with the two-dimensional weak electron localization oc curring in the cylindrical graphite layers forming the nanotubes. The nanotubes also show reproducible fluctuations of the magnetoresistance which can be related to the Aharonov-Bohm effect in the nanotubes. (C ) 1997 Elsevier Science B.V.