Body having a smooth diamond layer, device and method therefor

Method for CVD coating, comprising a coating procedure under a carbon-containing gas atmosphere, wherein a diamond layer is deposited directly on a substrate made out of cemented carbide or silicon, wherein during said coating procedure, process parameters are varied such that said parameters are changed multiple times between a first and a second operating state,

• wherein in said first operating state there is a higher carbon over-saturation of said carbon-containing atmosphere close to said substrate, and in said second operating state there is a lower over-saturation of said carbon-containing atmosphere close to said substrate,
• wherein the change between the two operating states is effected such that during the time in which the layer grows by 1 μm, at least 200 alternations are carried out between the operating states for depositing a nanocrystalline diamond layer on said substrate, wherein the surface of said layer has a surface roughness Rz which is less than the surface roughness Rz of said substrate surface.