Methods for making a nanocrystalline diamond layer are disclosed herein. A method of forming a layer can include activating a deposition gas comprising an alkane and a hydrogen containing gas at a first pressure, delivering the activated deposition gas to the substrate at a second pressure which is less than the first pressure, forming a nanocrystalline diamond layer, treating the layer with an activated hydrogen containing gas to remove one or more polymers from the surface and repeating the cycle to achieve a desired thickness.