Controlled patterning of self-assembled monolayer films
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This paper is a critical review of three current methods used in patterning self-assembled monolayer films. It begins with an introduction to monolayer films and their potential uses. This is followed by a discussion of self-assembly and the various experimental methods used to form monolayer films. The discussion focuses mainly on silanes as the compounds used to form the films, but it also includes thiols and carboxylic acids. The mechanism for self-assembly is reviewed too. Various characterization techniques are presented next. Wettability, ellipsometry, XPS, UV-vis spectroscopy, IR spectroscopy, Raman spectroscopy, SIMS, STM, and AFM are all presented and their applications to thin film characterization are mentioned. Following the characterization techniques is a section on patterning. The three methods analyzed include patterning procedures by Kleinfeld and co-workers, Wrighton and Whitesides and co-workers, and Calvert and co-workers. It is concluded that the method by Kleinfeld and co-workers requires too many steps and too much time; the method by Wrighton and Whitesides and co-workers does not produce in-plane patterns but rather stepped ones; and the method by Calvert and coworkers requires expensive equipment not readily available to all laboratories. In addition, none of these three patterning methods can create features any smaller than in the micrometer range. Three more recent patterning methods by Wrighton and Whitesides are presented next. They are micromachining, microwriting, and "rubber stamping" and they are capable of producing pattern features in the hundreds of nanometers range. This is an improvement but it is still not the ideal of being able to pattern molecule by molecule. Suggestions for future research follow the analysis of the patterning methods.