Substrate selective patterning on lithography defined gold on silica: Effect of end-group functionality on intermolecular layer formation

An increasing number of applications in nanobiotechnology and other areas call for defined regions of different chemical functionality to achieve site-specific attachment while minimizing any unwanted surface interactions. In order to generate spatially defined chemical patterns on planar surfaces, standard nanofabrication methods are typically employed. However, when incorporating biological and chemical molecules into complex nanofabricated structures the micro/nanofabrication methods needed are often incompatible with the standard approaches used to achieve chemical patterning. An alternative strategy is to use substrate selective patterning (SSP) where two different organic molecules each have a specific affinity to a particular substrate material via a surface anchoring group. Here we use imaging ellipsometry, an ideally suited technique for measuring monolayer films on patterned substrates, and infrared spectroscopy to investigate SSP of alkanethiols with hydrophilic/hydrophobic moieties in combination with a methoxypolyethylenoxypropyltrichlorosilane reagent (mPEGTCS) on patterned gold on native silicon oxide substrates. One central aspect of SSP that was investigated was the cross-reactivity between the various substrate specific molecules, which can cause multilayer formation. Results showed that when the mPEGTCS reagent was used subsequently after formation of hydrophilic self-assembled alkanethiol monolayers (SAMs), there was an additional layer build-up of silane. No multilayer formation was observed for a hydrophobic alkanethiol SAM. SSP can be a practical method to effectively create localized functional chemistry on spatially defined nanofabricated devices.