Use of Electroless Silver as the Substrate in Microcontact Printing of Alkanethiols and Its Application in Microfabrication

We have employed electroless deposition to prepare smooth films (mirrors) of silver that could be used as substrates in microcontact printing (μCP) of alkanethiols. Good-quality SAMs of hexadecanethiolate were formed on thin films of electroless silver by printing with an elastomeric stamp; these SAMs were effective resists in protecting the underlying silver from etching in an aqueous ferricyanide solution. Thin films of silver prepared by electroless deposition show a granular morphology (the grain sizes are ∼30−60 nm) and have a rougher surface than those prepared using e-beam or thermal evaporation. As a result, hexadecanethiol liquid spreads more rapidly on electroless silver than on evaporated silver when μCP is carried out in air. This process of reactive spreading limits the resolution and fidelity of pattern transfer to electroless silver films by μCP, but could also be used as a convenient method for reducing the sizes of features of SAMs generated using μCP. The smallest features that we have fabricated using this method were trenches etched in electroless silver (∼40 nm thick) with lateral dimensions of ∼200 nm. The procedure demonstrated here allows us to form micropatterns and microstructures without the metal evaporation usually used to prepare the substrates for μCP, and thus opens μCP and related techniques of microfabrication to those who do not have access to the equipment required for evaporation or sputtering of silver. It also makes it possible to carry out micropatterning on hidden surfaces that could not be silvered by evaporation (for example, the inside surface of a glass tube or flask).