Combinatorial graphene pattern arrays with different geometries. (a) (i) TEM image, (ii) size distribution, (iii) zeta potential, (iv) XPS analysis of NGO used in this study. (b) Schematic diagram of NGO micropatterns and (c) the corresponding NGO patterns (squares, lines, grid and numbers) generated on the Au/glass substrates were visualized by helium ion microscopy (HIM). Scale bars are 5 μm for squares and lines, 100 μm for grid and character, and 10 μm for inset image of grid pattern, respectively.