Formation mechanism of snowflake-shaped gold nanostructures on graphene oxide (GO). (a) Interfacing the –COOH and –OH groups on GO sheets with a freshly prepared solution of gold nuclei, formed during hydroxyl-amine-assisted reduction of gold salt, results in nuclei attachment and seed-mediated formation of snowflake-shaped gold nanostructures (SFGNs) on the GO surface. (b) Right: Field emission scanning electron microscopy (FESEM) of SFGNs templated on GO lying on silica surface. The SFGNs appearing darker (labeled ‘D’) are on the rear surface, while the SFGNs appearing brighter (labeled ‘B’) are on the front surface of the immobilized GO sheet (scale bar = 500 nm). Center: Higher magnification transmission electron microscopy (TEM) image
showing the detailed characteristics and the structural parameters of SFGN exhibiting a dendritic morphology. Scale bar = 100 nm. Left: FESEM image showing wrinkles (labeled W) on GO associated with a darker SFGN. Scale bar = 200 nm. Reproduced with permission from Ref. [50]. Copyright 2009, American Chemical Society.