Molecular Patterning and Directed Self-Assembly of Gold Nanoparticles on GaAs

The ability to create micro-/nanopatterns of organic self-assembled monolayers (SAMs) on semiconductor surfaces is crucial for fundamental studies and applications in a number of emerging fields in nanoscience. Here, we demonstrate the direct patterning of thiolate SAMs on <i>oxide-free</i> GaAs surface by dip-pen nanolithography (DPN) and microcontact printing (μCP), 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 (Au NPs) onto a template of 4-aminothiophenol (ATP) SAM on GaAs. The highly selective assembly of the Au NPs was made evident with atomic force microscopy (AFM) and scanning electron microscopy (SEM). 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 nanoplasmonic structures.