A process for the preparation of organic material comprising an organic substrate and at least one dielectric layer consisting of one or more oxides of a metal selected from groups 3 to 15 of the periodic table, which comprises the steps of: (a) suspending the organic material in an aqueous solution of fluorine scavenger; (b) adding an aqueous solution of one or more fluorine containing metal complexes which are the precursors of the desired metal oxide coating; and (c) subjecting said suspension to microwave radiation to deposit the metal oxide onto said organic material, wherein steps (b) and (c) can optionally be repeated using different fluorine containing metal complexes to produce one or more metal oxide layers. The substrate can be optionally dissolved with solvent to yield free metal oxide or mixed metal oxides that have a plane-parallel structure.