Graphene nanoribbons with different directions and widths can adjust the zero-energy bandgap of graphene, allowing wide<br />use of graphene in nano-semiconductor devices. Mechanical cutting is a simple and efficient method for preparing graphene<br />nanoribbons. Most current studies assume that the substrate surface and graphene involve physical adsorptions; however, many<br />substrate surfaces involve chemisorption with graphene in actual mechanical cutting. The effect of substrate chemisorption on the<br />mechanical cutting behavior of graphene is not fully understood. This paper investigates the influence mechanism of substrate<br />chemisorption on the mechanical cutting properties of graphene. Based on the ReaxFF reaction potential function and the Verlet<br />algorithm, the mechanical cutting behavior of graphene on Ni, Pt, and Cu metal substrates was studied through reactive molecular<br />dynamics. The effect of substrate chemisorption on bond properties was analyzed according to the bond number and bond strength<br />between tip and graphene (C-T-C-G), graphene layers (C-G-C-G), and graphene and substrate (C-G-M) in nanoindentation. Graphene<br />mechanical cutting depth was determined according to the friction and wear mechanism by oblique scratching. The mechanical cutting depth was used to scratch the graphene, intuitively revealing the influence mechanism of substrate chemisorption on the mechanical<br />cutting properties of graphene through the bond changes between the tip, substrate, and graphene. The results show that the<br />chemisorption capacities of Ni, Pt, and Cu substrate to graphene were decreased in turn. A strong chemisorption substrate increased<br />the C-G-M bond strength and C-T-C-G bond strength, weakened the C-G-C-G bond strength, and greatly reduced the breakage strength of<br />graphene. The breakage strengths of graphene on Ni, Pt, and Cu substrates were 110.19 GPa, 121.71 GPa, and 176.53 GPa,<br />respectively, in mechanical cutting. The graphene under the tip center was at the highest stress and most susceptible to breakage. The<br />decrease in C-G-C-G bond strength promoted the chemical reactivity of graphene and increased C-T-C-G bond strength. The downward<br />pressure of the tip induced C-G-M bonding, weakened C-G-C-G bond strength, and induced C-T-C-G bonding. The coupling effect of strong<br />chemisorption of the substrate and downward tip pressure made graphene more easily breakable in mechanical cutting. C-G-M bonding<br />occurred before the tip scratching process on the Ni substrate; strong chemisorption reduced the overall C-G-C-G bond strength of<br />graphene, increased the C-T-C-G bond number, increased the cutting edge angle of the tip, caused graphene folding and piling on the Ni<br />substrate, and caused extensive graphene tearing and damage. C-G-M bonding only occurred in the tip scratching path on the Pt<br />substrate. C-G-C-G bond strength reduction only occurred in the tip scratching path; graphene outside of the tip scratching path<br />maintained high C-G-C-G bond strength. A weakened chemisorption capacity caused only partial carbon chain stripping of graphene on<br />the Pt substrate. No C-G-M bonding occurred during the tip scratching process on the Cu substrate. All graphene maintained high<br />C-G-C-G bond strength; only the C-G-C-G bond strength under the graphene tip was reduced by downward pressure of the tip. Greatly<br />weakened chemisorption caused only partial carbon atom stripping of graphene on the Cu substrate. Graphene on the Pt and Cu<br />substrates was not folded and piled. In summary, strong chemisorption of the substrate improves the mechanical cutting efficiency of<br />graphene, reduces the mechanical cutting depth, reduces the downward tip pressure, increases the tip friction, and improves the<br />mechanical cutting performance. The chemisorption of the substrate changes the bond region, quantity, and strength of C-T-C-G, C-G-C-G,<br />and C-G-M bonds, and changes the mechanical cutting properties of graphene. The influence and internal mechanism of substrate<br />chemisorption on the mechanical cutting properties of graphene were thoroughly investigated using the reaction molecular dynamics<br />method. This research provides a theoretical basis for preparing graphene nanoribbons by mechanical cutting with high efficiency and high precision in different chemisorption substrate conditions
