  The ability to create micro/nano patterns of organic self-assembled
monolayers on semiconductor surfaces is crucial for fundamental studies and
applications in a number of emerging fields in nanoscience. Here, we
demonstrate the patterning of thiol molecular SAMs on oxide-free GaAs surface
by dip-pen nanolithography and micro-contact printing, facilitated by a process
of surface etching and passivation of the GaAs. A quantitative analysis on the
molecular diffusion on GaAs was conducted by examining the writing of nanoscale
dot and line patterns by DPN, which agrees well with surface diffusion models.
The functionality of the patterned thiol molecules was demonstrated by directed
self-assembly of gold nanoparticles onto a template of 4-Aminothiophenol SAM on
GaAs. The highly selective assembly of the Au NPs was evidenced with atomic
force microscopy and scanning electron microscopy. The ability to precisely
control the assembly of Au NPs on oxide-free semiconductor surfaces using
molecular templates may lead to an efficient bottom-up method for the
fabrication of nano-plasmonic structures.
