Method for reactive sputter coating at least one article

A method for coating at least one workpiece with at least one layer, comprising the steps of:

• providing a target of ohmically conductive material and a workpiece within a vacuum treatment chamber,
• generating within said chamber a glow discharge by electrically supplying said target with a direct current signal and, superimposed thereon, an alternating current signal,
• said alternating current signal being selected so that its frequency spectrum is between 50 Hz and 250 kHz, both inclusively,
• sputtering said target within said glow discharge,
• reacting particles sputtered off said target in a space between said target and said workpiece with a reactive gas,
• depositing the reaction product of said reaction of said particles with said reactive gas on said workpiece,
• operating said sputtering and said deposition only in an unstable transition mode between a metallic and a reactive mode,
• whereby said reacted sputtered particles are deposited on said workpiece to form a layer of lower conductivity than said material of said target.