Silane Self-Assembled Monolayers: Nanometer Domains by Sequential Adsorption


Nitin Kumar Institute of Soldier Nanotechnology, Massachusetts Institute of Technology

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In recent years, the applications and demand for solid surfaces with nanometer to micrometer patterns have increased because of extensive developments in the fields of nanoscience and nanotechnology. Solid surfaces with nanometer- and micrometer-scale patterns have many potential applications in many fields of nanoscience and nanotechnology, such as phase separation of polymer mixtures, localized crystal growth, the arraying and immobilization of proteins, cells, nanoparticles, etc. Methods for patterning micrometer features on surfaces are well developed and include microlithography of self-assembled units, microcontact printing, photopatterning of self-assembled monolayers (SAMs). On the other hand, methods for developing nanometer-scale features, such as nanowriting, phase-separated Langmuir–Blodgett (LB) films, and block copolymers are time consuming and cumbersome.

Self-assembled monolayers consist of amphiphiles, which spontaneously adsorb onto a solid surface from solution to form a densely packed two-dimensional ordered monolayers. Self-assembled monolayers have been extensively used for modification of surface chemistry of solid surfaces. Recently, Fan et al. have demonstrated that nanometer-scale domains of different chemical functionality can be obtained by co-adsorption and phase separation of different silane molecules. Sequential adsorption of self-assembling monolayers had been suggested as an alternate and simpler route for making such surfaces. The island growth mechanism in silane monolayer can be exploited to prepare surface with nanodomains. In this article, we demonstrate the use of sequential adsorption of silanes to prepare domains of various sizes by controlling their self-assembly on solid surfaces. We describe a procedure to prepare domains of one chemical functionality, with size from nanometer to micrometer surrounded by another chemical functionality, using sequential adsorption of silane self-assembled monolayers. Partial monolayers of octadecyltrichlorosilane (OTS) consisting of condensed islands with controlled size are prepared by varying the deposition conditions. The area surrounding the OTS islands is filled by sequential adsorption of 11-bromo undecyltrichlorosilane (BrUTS) or decyltrichlorosilane (DTS) to obtain nanometer- to micrometer-scale domains of OTS in a monolayer of DTS or BrUTS. First, we describe in detail the methodology to form partial OTS monolayers composed of domains of a desired size. Then, we discuss the procedure and optimum conditions for successful backfilling. These monolayers were analyzed by atomic force microscope (AFM) to obtain the topographical and friction images.