A method of patterning a thin film, comprising: depositing an intermediate, radiation sensitive, layer on a substrate; depositing the thin film on the intermediate layer, before or after deposition of the thin film: exposing the intermediate layer to patterned radiation in order to initiate a chemical reaction therein; and removing patterned radiation-defined parts of the intermediate layer and corresponding thin film, to leave patterned thin film and patterned intermediate layer on the substrate.