Unveiling the mechano-chemical synergy of AMP derivatives as multi-functional pH regulators on C-, R-, and M-plane sapphire CMP via experiments and DFT calculations

The development of sapphire slurry follows the principles of compositional simplification, environmental sustainability, and high efficiency with low cost. This study systematically investigated the effects of polyhydroxyamine pH regulators, 2-amino-2-methyl-1-propanol (AMP), 2-amino-2-methyl-1,3-propanediol (AMPD), and tris(hydroxymethyl)aminomethane (TRIS), on the polishing performance of C-, R-, and M-plane sapphire substrates. The results demonstrated that TRIS exhibited the highest efficacy, achieving material removal rates (MRRs) of 5.512 µm/h, 3.422 µm/h, and 4.541 µm/h for C-, R-, and M-plane sapphire, respectively, while reducing surface roughness (Sq) to 0.191 nm, 0.178 nm, and 0.184 nm. Tribological analysis, SEM characterization, zeta potential measurements, particle size distribution tests, and spectroscopic techniques (UV-Vis, XPS, and FTIR) were employed to elucidate the mechanical and chemical mechanisms governing material removal. All three pH regulators can also function as complexing agents, forming complexes with ${\text{Al}\left(\text{OH}\right)}_4^{-}$, with TRIS demonstrating the strongest chelation capability. Density functional theory (DFT) calculations further verified these findings, revealing that TRIS possesses the highest number of reactive sites. The consistency between computational and experimental results established a quantitative structure-performance relationship. This work provides a green and efficient paradigm for the precision machining of hard, brittle materials.