Self-Assembly and Molecular Ordering

Conversely, one could consider a random SAM formation of different molecule types, and hence logic types, followed by testing of the chip properties once the SAM formation is complete. If this random approach were used, it would mean that none of the chips would have a known function a priori however, the technique could be efficacious since some logic applications could be programmed into the chip post-fabrication. This will be discussed later in the context of the NanoCell approach. 

Therefore, self-assembly, or the process of permitting the molecules to attach in place, is quite attractive for molecular ordering which can also be done in three-dimensional arrays. However, in three dimensions, heat dissipation and addressing issues become extreme challenges. Despite the problems associated with using self-assembly, it promises to be far superior to tedious singlemolecule manipulations. 

Note that we used thioacetate (sometimes referred to as thiolacetate) end groups since these could be selectively deprotected in solution, to afford the free thiol, using NH4OH or acid during the deposition process. Alkali metal salts can be avoided since they tend to disrupt electronics measurements. Use of the free thiols, rather than the thioacetates, proved to be somewhat problematic since they were prone to very rapid oxidative disulfide formation. But if a quality inert atmosphere box is used, use of the free thiol can be effective a N2-flush bag is not adequate to prevent the aromatic disulfide formation. Furthermore, the disulfides formed can self-assemble on gold, but the assembly is approximately KXX) times slower than with the thiols. When using the a,(i)-dithiols, oxidative polymerization ensues which rapidly results in insoluble material. Hence, in situ removal of the acetates has proven to be quite effective although not essential if strict exclusion of air is maintained. 

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