Monolayer GO sheets with a height of ~1 nm can be discovered easily, which can be ascribed to the high hydrophilicity and dispersibility of GO. Significantly different from GO, VG-S shows a largely crumpled fiber-like particle with a height of more than 200 nm. VG-M exhibits sheet features close to GO sheets, however, presenting more homogeneously distributed wrinkles. Additional AFM images are shown in Figure .