Electrically isolated nanostructures fabricated using self-assembled multilayers and a novel negative-tone bi-layer resist stack

We create metal nanoelectrode structures with precise proximal placement by blending traditional top-down and bottom-up lithography. Multiple levels of conventional lithography are used in combination with self-assembled multilayer resists (molecular rulers) to generate metallic electrode structures with nanoscale spacings. These multilayers are deposited on initial lithographic gold electrode structures forming a type of lift-off resist used to fabricate proximally placed secondary metal structures with nanometer-scale resolution. By controlling the thicknesses of these multilayers, selective self-assembly is exploited to generate molecular ruler resists, enabling the creation of tailored nanogaps in the 10-50 nm regime. The ability to fabricate electrically isolated nanoelectrodes would enable reliable measurement of the conducting properties of single molecules, nanoparticles and other low-dimensional materials. This paper outlines a new process using a lift-off resist (LOR)/SU-8 negative-tone bi-layer stack to improve the yield of nanoelectrodes. SU-8 finds application in a variety of fabrication techniques, but is difficult to release from the substrate. The LOR/SU-8 process that we have developed possesses the following additional advantages: easy chemical removal of the resist stack with the LOR acting as a release layer, creation of metal lift-off patterns with near-vertical sidewalls, and the ability to withstand chemical processing.