A method of forming a thin film on a substrate/workpiece by sputtering, comprising steps of: (a) providing an apparatus comprising a vacuum chamber including at least one sputtering source and a gas supply means for injecting a gas containing at least one reactive component into said chamber, the gas supply means comprising a plurality of differently-sized outlet orifices adapted for providing substantially the same flow rate of gas from each orifice; (b) providing a substrate/workpiece having at least one surface for formation of a thin film thereon; (c) generating a sputtered particle flux from the at least one sputtering source; (d) injecting the gas containing the at least one reactive component into the chamber via the gas supply means, such that the same gas flow rate is provided at each orifice; and (e) forming a reactively sputtered thin film on the at least one surface of the substrate/workpiece, the reactively sputtered thin film having a substantially uniform content of the at least one reactive component.