Nano-thick surface-modified layer governs bending deformation of micrographite

This study aimed to investigate the impact of surface-modified layer (SML) on the bending deformation of van der Waals (vdW)-stacked materials. Bending tests were conducted on micrographite (highly oriented pyrolytic graphite, HOPG) cantilevers with controlled SML thickness using various ion beam irradiation conditions. Irradiation of the HOPG surface with ion beams at accelerating voltages of 30, 5 and 0.1 kV resulted in the formation of SMLs with thicknesses of approximately 10, 5 and less than 3 nm, respectively. Microcantilever-beam specimens with SML thicknesses of less than 3 nm and approximately 5 nm exhibited shear deformation with localized interlayer slip. In contrast, specimens with a thickness of approximately 10 nm showed no interlayer slip, with bending deformation dominating. This transition was attributed to the increase in SML thickness. The nominal shear modulus increased by a factor of approximately 1.58 and 2.23 for specimens with SML thicknesses of approximately 5 and 10 nm, respectively, compared with those with thicknesses of less than 3 nm. The resistance to subsequent nonlinear deformation also increased with thicker SML. These results indicate that the presence of SMLs of only a few nanometers to 10 nm suppressed interlayer slip and significantly enhanced the deformation resistance of micro-HOPGs.