A method, comprising: generating a vapour of a material from a source of said material comprising a plurality of separate solid pieces (10, 16) of said material supported on a surface of a base (14) in a configuration in which said plurality of solid pieces of said target material are arranged at two or more levels to cover the whole of said surface of said base whilst providing a gap between adjacent pieces at the same level; and depositing said material from said vapour onto a substrate.
