Credit: © 2007 AIP

Defining nanostructures from the 'bottom-up' using self-assembled monolayers (SAMs) of molecular films allows for the atomic scale control of their dimensions and physical properties. However, the most widely used alkanethiol SAMs decompose at ˜350 K, which limits the practical applications of this approach.

Now, Andrey Turchanin and colleagues1 of the University of Bielefeld, Germany have shown that SAMs made from molecules containing aromatic rings are stable on gold surfaces up to 1,000 K if irradiated with an electron beam. The enhanced stability of the irradiated samples is attributed to crosslinking of the aromatic rings when exposed to a high-intensity electron beam. In the untreated films, each molecule in the monolayer is held to the surface by a gold–sulphur bond and is only weakly attracted to its neighbours, so can be easily removed. In the crosslinked film, however, what is now one giant molecule is linked to the surface by multiple interactions and is, therefore, much more stable.

These results are the basis of a technique called thermal desorption lithography by which surfaces can be patterned with crosslinked SAMs. Periodic 1.2 µm circular patterns were made by selectively exposing areas of aromatic SAMs to an electron beam, followed by thermal annealing. The untreated areas of the monolayer desorbed from the surface leaving behind ˜1-nm-thick regions in which the molecules were crosslinked.