Precise mechanical polishing of brittle materials with free diamond abrasives dispersed in micro–nano-bubble water

•Water containing micro-nano-bubbles (MNB water) shows the dispersion effect for micro-sized abrasive particles.•A remarkably increased removal rate with no surface degradation was observed for chemically strong Ga-face of GaN substrate using MNB water-based slurry.•A significantly reduced subsurface damage for chemically weak N-face of GaN substrate was also shown.•A possible mechanism for the unique polishing properties with MNB water-based slurry has been discussed. We have studied the effects of using water containing micro–nano-bubbles (MNB water) as the solution in which the diamond abrasives with a mean diameter of 0.5μm are dispersed for the polishing slurry used in the precise mechanical polishing (PMP) of brittle material of GaN. While the formation of small number of clusters of abrasives was seen in the MNB water, the abrasives were basically well dispersed, which were almost comparable to that in pure water with a dispersion agent such as ethylene glycol. Since flocculation was observed for dispersion in pure-water without the addition of the dispersion agent, it was found that MNBs have dispersion effect for micro-sized abrasive particles. Regarding the polishing properties of GaN substrate with the MNB water based polishing slurry, we observed a remarkable increase in the removal rate with no additional surface or subsurface degradation. Additionally, we observed a significantly reduced subsurface damage (SSD) for chemically weak N-face of GaN substrate. It was suggested that these observed effects were most probably a result of the cluster formation in the MNB water and the chemical effect in relation to high energy generation through bubble collapse, respectively.