Exploration of Physisorbed Monolayers for Molecular-Scale Surface Patterning

Citation

Papadantonakis, Kimberly Marshall (2009) Exploration of Physisorbed Monolayers for Molecular-Scale Surface Patterning. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/JZCK-B721. https://resolver.caltech.edu/CaltechETD:etd-07222008-144633

Abstract

Many simple organic molecules, such as straight-chain alkanes and simple aromatics, spontaneously assemble into highly ordered monolayers at solid–liquid interfaces. These monolayers are composed of molecules that lie flat at the interface without forming chemical bonds to the surface of the solid. These monolayer structures are highly ordered and produce patterns with features on the scale of just a single nanometer in length. The exploitation of this physisorption phenomenon may provide a promising route toward an inexpensive nanometer-scale surface patterning technique. However, two fundamental challenges must be overcome before physisorbed monolayers can be useful in surface-patterning applications: (1) absence of control over the particular pattern formed by the molecules; and (2) pattern impermanence.

This document opens with an introductory chapter that contains background on physisorbed monolayers and a brief description of scanning tunneling microscopy, the experimental technique which is commonly used to study monolayers. The second and third chapters present details on the results of experiments with a monolayer templating technique. This templating technique involves replacement of the molecules comprising a monolayer of either normal alkanes or symmetrical thioethers by symmetrical ethers. The ethers are forced to conform to the structure of the existing template monolayer, which differs from the structure of an ether monolayer formed in the absence of the template. The monolayer templating technique offers researchers a limited method for exercising control over the surface patterns formed by particular molecules.

The challenge of pattern impermanence is addressed in the fourth chapter of this document. The molecules comprising physisorbed monolayers are free to exchange with molecules in the solution contacting the surface, thus the orientation of the monolayer structure within a particular surface region can change with time. A technique analogous to traditional lithographic methods that may allow physisorbed monolayers to be used for permanent surface patterning is described. The technique would employ physisorbed monolayers as surface masks while other molecular species chemically bond to regions of the surface left uncovered by the masking monolayer. Descriptions of the progress made toward the development of the patterning technique, and of the substantial challenges encountered during efforts to develop such a patterning method close the chapter.

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