Self-Assembled Monolayers of Cyclic Aliphatic Thiols and Their Reaction toward Electron Irradiation

We investigated an old dogma, namely, that aromatic self-assembled
monolayers (SAMs) are cross-linked and stabilized by irradiation with
electrons, whereas aliphatic SAMs on the same substrate are degraded
under the same conditions. To this end, we prepared SAMs of novel
cycloaliphatic molecules (4-cyclohexylcyclohexanethiols, CCHT) on
Au(111) surfaces and studied their response to electron irradiation.
The CCHT monolayers demonstrated a comparably low extent of molecular
defragmentation and damage of the headgroup–substrate interface.
This was explained by the dominance of irradiation-induced cross-linking
over defragmentation and desorption events, which was additionally
supported by the negative resist performance of the CCHT films in
the framework of electron beam lithography. This behavior is distinctly
different from SAMs of linear aliphatic molecules, which become severely
damaged at comparably low irradiation doses and exhibit the positive
resist performance. It is, however, similar to the behavior of aromatic
monolayers, which underlines the role of the cyclic structure in the
balance of cross-linking and defragmentation in monomolecular films.