Effect Of The Substrate On The Morphology Of The Graphene Prepared By Physical Method

Graphene, only single atom layer thick, is the thinnest materials discovered up to now. It has shown wide range of potential applications due to its exotic physical and chemical properties. Graphene prepared by physical methods show superior integrity of the graphite lattice; however, the yield is quite low. This research summarized and compared several known physical methods. It is found that graphene samples, prepared by micro-mechanical cleavage method, after being ultrasonically dispersed in ultrapure water, can be stripped off to be thinned at high efficiency.This research focuses on the effect of substrates on the morphology of graphene. The optical microscope and atomic force microscope (AFM) were used to characterize graphite and graphene samples. According to the reported findings that graphene of varied thickness gives different intensity of reflected light and contrast on various substrates, the thickness of graphene samples can be estimated at first hand. Then high resolution AFM is used to accurately study the thickness of few-layer graphene samples. Using highly oriented pyrolytic g raphite samples, we prepared graphene samples by the micro-mechanical cleavage method (Scotch Tape method) and transferred to several substrates, such as oxidized silicon single-crystal, alumina single-crystal, glass and mica. It was found that thin graphene samples conformed the surface morphology of substrates; whereas the topography of thicker graphene samples of more than 5 nm thick did not fit the surface morphology of underlying substrates. Protrusions appeared between the graphene layers and substrates and the origin of it was discussed.Graphene flakes were attached to AFM probes to produce modified―graphene probe‖which was used to compare the interaction between graphene and different substrates including graphite, oxidized silicon, alumina, mica and glass. It was found that the interaction between graphene and graphite was less than that between graphene and oxidized silicon, alumina and mica. This finding was used to explain the feasibility of routine micro-mechanical cleavage method. On the contrary, It was found that the interaction between graphene and graphite was higher than that between graphene and glass. We attributed this fact to high surface roughness of glass substrate which reduced greatly the actual contact area between graphene and glass substrate.