Paper GR+AS+NS+SS-ThM11
Exfoliation, Sorting, and Applications of Few Layer Graphene Sheets

Thursday, October 31, 2013, 11:20 am, Room 104 B

Graphene is one of the strongest, lightest and most conductive materials known so far. The common approach to prepare single layer graphene sheets is the reduction of graphene oxide which is made with well-known Hummer method. Due to the high level of the defects, the conductivity and the mechanical strength are significantly decreased comparing to the pristine graphene sheets. CVD growth is a very promising method to prepare large scale and high quality of graphene. It is still a challenge to transfer the sheet to insulate substrates. The liquid exfoliation of graphite without chemical modification is still desired for the electronics-grade graphene sheets. We are developing a simple and efficient exfoliating method to produce high quality and large scale graphene material.

The starting material is expandable graphite. This material is a product of flake graphite reacting with intercalation reagents in order to migrate between the graphene layers in a graphite crystal and remain as stable species. The materials were heat treated and then dispersed in N-Methyl-2-pyrrolidone (NMP). After the sonication and centrifuge process, the graphene sheets have been characterized by SEM, TEM, AFM, XPS, and Raman.

The material was treated at 450 ºC for 30 min in nitrogen atmosphere and was changed to be very fluffy. The XPS shows that the carbon has a narrow peak and it indicates the fraction of bonding to oxygen is negligible. The result shows that most graphite is pristine and not oxidized by the intercalation process. The exfoliated graphene sheets have been observed with AFM and TEM. The result shows that the majority of the sheets are several layer thick and submicrometer to several micrometers long. The Raman measurement was also carried out on these few layer sheets and the result shows the D band is negligible and it indicates that these graphene sheets have little defects. Besides the electronics applications of these few layer graphene sheets, they also have potential applications in conductive composite. The result of the composite of graphene sheets and polystyrene will also be discussed.