Multilength-Scale Chemical Patterning of Self-Assembled Monolayers by Spatially Controlled Plasma Exposure: Nanometer to Centimeter Range

Abstract

We present a generic and efficient chemical patterning method based on local plasma-induced conversion of surface functional groups on self-assembled monolayers (SAMs). Here, spatially controlled plasma exposure is realized by elastomeric poly(dimethylsiloxane) (PDMS) contact masks or channel stamps with feature sizes ranging from nanometer, micrometer, to centimeter. This chemical conversion method has been comprehensively characterized by a set of techniques, including contact angle measurements, X-ray photoelectron spectroscopy (XPS), scanning photoelectron microscopy (SPEM), scanning electron microscopy (SEM), and scanning Kelvin probe microscopy (SKPM). In particular, XPS and SPEM can be used to distinguish regions of different surface functionalities and elucidate the mechanism of plasma-induced chemical conversion. In the case of an octadecyltrichlorosilane (OTS) monolayer, we show that exposure to low-power air plasma causes hydroxylation and oxidation of the methyl terminal group on an OTS-covered Si surface and generates polar functional groups such as hydroxyl, aldehylde, and carboxyl groups, which can allow subsequent grafting of dissimilar SAMs and adsorption of colloid nanoparticles onto the patterned areas with an achievable resolution down to the 50 nm range.

A nanoplasmonic biosensor for label-free multiplex detection of cancer biomarkers

“…Briefly, the cleaned glass slides were dipped in 1% (v/v) trichloro (octadecyl)silane (OTS) in n-hexane for 15 min. To remove excess OTS, glass slides were rinsed with ethanol three times before drying at 60°C for another 4 h. To fabricate hydrophilic-hydrophobic patterned glass slides, a pre-designed PDMS stamp was compressed onto OTS-treated glass and exposed to oxygen plasma at 80 W for 9 s to locally convert the terminal groups of the OTS in exposed regions to hydroxyl groups (Lin et al, 2009). The siteselectively modified glass slide was dipped in 5% (v/v) APTES in 99.9% ethanol for 15 min.…”

Secrets revealed — Spatially selective wetting of plasma-patterned periodic mesoporous organosilica

“…Plasma treatment with the aid of a preformed mask was shown to be a fast (on the order of minutes) and clean (liquid-free) method to create patterns of self-assembled monolayers (SAMs) on flat surface at length scales from sub-100 nm to centimeter. 18 We have previously extended this technique to three dimensional (3D) porous siliceous inverse-opal structures by iterating silanization and shadow-masked oxygen plasma to produce spatial patterns of surface chemistry within the pores. 19,20 The slow propagation of plasma oxidation fronts in porous structures enables patterning by masking only the top surfaces of the structures.…”

“…19,20 The slow propagation of plasma oxidation fronts in porous structures enables patterning by masking only the top surfaces of the structures. [18][19][20] In this report, we use oxygen plasma to convert terminal methyl groups into silanol groups in thermally-treated methane PMO. This conversion switches the hydrophobic pore wall to a hydrophilic one, and enables us to create patterns of different wettability in one single material (Figure 1).…”

Confining Liquids on Silicon Surfaces to Lubricate MEMS

“…The OTS was selectively removed using a technique similar to that developed by Lin et al [40]. A PDMS template was prepared consisting of a flat sheet with a 2-mm-diameter circular hole.…”