Self assembled monolayers are surfaces consisting of a single layer of molecules on a substrate. Rather than having to use a technique such as chemical vapor deposition or molecular beam epitaxy to add molecules to a surface (often with poor control over the thickness of the molecular layer), self assembled monolayers can be prepared simply by adding a solution of the desired molecule onto the substrate surface and washing off the excess.
A common example is an alkane thiol on gold. Sulfur has particular affinity for gold and an alkane with a thiol head group will stick to the gold surface with the alkane tail pointing away from the substrate.
