STM lithography in an organic self-assembled monolayer

We describe the suitability of ultra-high vacuum scanning tunneling microsc opy (UHV-STM) based nanolithography by using highly ordered monomolecular o rganic films, called self-assembled monolayers (SAMs), as ultrathin resists . Organothiol-type SAMs such as hexadecanethiol (SH-(CH2)(15)-CH3) and N-bi phenylthiol (SH-(C6H6)(2)-NO2) monolayers have been prepared by immersion o n gold films and Au(111) single crystals. Organosilane-type SAMs such as oc tadecyltrichlorosilane (SiCl3-(CH2)(17)-CH3) monolayers have been prepared on hydroxylated Si(100) surfaces as well as hydroxylated chromium film surf aces Dense line patterns have been written by UHV-STM in constant current m ode for various tunneling parameters (gap voltage, tunneling current, scan speed, and orientation) and transferred into the underlying substrate by we t etch techniques The etched structures have been analyzed by means of scan ning electron microscopy (SEM) and atomic force microscopy (AFM). Best reso lution has been achieved without etch transfer for a 20 nm x 20 nm square w ritten in hexadecanethiol/Au(111) with an edge definition of about 5 nm. Et ch transfer of the STM nanopatterns in Au films resulted in 55 nm dense lin t: patterns (15 nm deep) mainly broadened by the isotropic etch characteris tic. while 35 nm wide and 30 nm deep dense line patterns written in octadec yl trichlorosilane/Si(100) and anisotropically etched into Si(100) could be achieved.