Localization of octadecyltrimethoxysilane self-assembled monolayers by a combination of bottom-up and top-down approaches
Abstract-Bottom-up techniques, such as self-assembling of molecules and particles, are efficient emerging technologies to obtain highly-ordered structures and diverse chemical functionalities. On the other hand, the top-down approach allows an accurate placement of patterns but suffers from a low accuracy in the nanometer range. The technique proposed here is a combination of bottom-up and top-down approaches, and is used to define accurately the chemically functionalized area on a substrate. It consists of four steps: cleaning and preparation of silica surface, pattern definition by ebeam or nanoimprint lithography in a resist layer, silane (octadecyltrimethoxysilane (OTMS)) chemical vapor deposition (CVD) and resist lift-off. The height of the deposited layer is determined by AFM, and the surface energy is determined by contact-angle measurements. These measurements allow to optimise and control the deposition process to obtain self-assembled monolayers of 2.4 nm thickness. A wide range of pattern sizes is achievable from 50 nm to a full wafer. The originality of this work lies in the atmospheric pressure chemical vapour deposition process. This process allows a precise control of deposition parameters (temperature, silane pressure) in a high-purity environment. Monolayers of various densities of OTMS molecules and with surfaces of controlled wettability can be obtained.