Facet and ripple formations on single crystal diamond tools machined by low energy oxygen ion beam

In this paper, we have studied the facet and ripple formation on a hemispherical diamond stylus by low energy (0.3–3.0 keV) oxygen ion beam bombardment at different ion incidence angle. The sputtered stylus was observed by SEM. From SEM image, we measured the ion incidence angle θmax where the etching rate is maximum and compared them with the theoretical values of θmax derived from Witcomb formula. From experimentally and theoretically obtained values of θmax, we measured the facet angles of the processed hemispherical diamond stylus. Our result shows increasing discrepancy between theoretical and experimental values of both θmax and facet angle towards lower ion energy (< 2 keV) due to dominance of chemical sputtering over physical sputtering. From our observation we found a diamond stylus can be sharpened at 3 keV ion energy if the original apex angle is > 70°. We also observed surface morphology of the processed hemispherical diamond stylus machined by 0.3–3 keV oxygen ion beam at different tilted conditions. Our observation confirms the formation of ripple on the processed diamond stylus at higher angles of ion incidence. The ripple orientation at ion incidence 40°–60° processed by 3 keV oxygen ion beam is in well agreement with the predictions of linear BH model. However, ripples were not observed at near normal incidence and grazing incidence in contrast to BH model. In order to avoid ripple formation, the diamond stylus needs to be processed within the region of low ion incidence angles. The smoothing region is broader in the low ion energy range but some etch pits are seen to form in this region due to chemical sputtering of the impurities present in the diamond stylus.

► A diamond stylus with an apex angle of 70° or greater can be sharpened O2/O+ ion without forming any facet.
► Facet formation does not depend on ion dose.
► Ripples were observed at ion incidence angle of 40° to 60°.
► The ripple wave vector changes from parallel to perpendicular at ion incidence angle of 60°.
► The smoothing region lies within the region of low ion incidence angle and it becomes narrower towards higher ion energy.