Low energy ion beam smoothening of artificially synthesized single crystal diamond chips with initial surface roughness of 0.08–0.4 nm rms

High quality ultra- smooth single crystal diamond chips are used as molds for nano-imprints, mirrors for X-ray free-electron lasers, and so on. Conventional mechanical process using lap plate of fine diamond powder cannot be applied in thinning down of diamond materials to the order of 10 μm. Therefore we applied ion beam machining for the smoothening of the surface of artificially synthesized single crystal diamond chips (100) with the initial surface roughness of 0.08–0.4 nm rms. We found that by 1.0 keV Ar+ ion beam at a normal angle of ion incidence, the processed surface became ultra-smooth with the surface roughness of 0.10 nm rms and waviness of 0.12 nm rms. However, the speed of processing by Ar+ ion beam was low. In order to increase the speed, 0.5 keV O2+/O+ beam was applied for the smoothening of the diamond surface at normal incidence angle. In this method, we successfully obtained ultra-smooth surface with a surface roughness of 0.10 nm rms at a much higher processing rate. We also observed that in ion beam machining, a rough surface becomes smooth and smooth surface becomes rough and both trends tend to saturate towards a roughness level at a particular dose. To understand this contrasting phenomenon, we conducted power spectral density (PSD) profile analysis of the un-processed and processed surfaces, and studied the roughening and smoothening mechanisms taking place on the diamond chip surface during its ion beam machining.

► Ultra smooth surface of diamond chip was obtained by 1 keV Ar+ and 0.5 keV O+2/O+ ion beam processing.
► The obtained surface roughness (Rrms) is 0.10 nm rms processed by O+2/O+ ion beam.
► The obtained surface waviness (Wrms) is 0.12 nm rms processed by Ar+ ion beam.
► Rough surface of diamond becomes smooth, smooth surface of diamond becomes rough by ion beam processing.