Mechanically exfoliated graphene from Sri Lankan vein graphite for field effect transistor application

In this work, a single layer of graphene was exfoliated from Sri Lankan vein graphite obtained from the Kahatagaha graphite mines, and field effect transistors (FETs) were fabricated to study their electronic properties. Graphite pieces were carefully examined, and a small piece of graphite was separated with possible large graphene sheets. A simple Scotch tape technique was used to transfer graphene from the selected graphite pieces onto a 300 nm SiO₂ coated Si (SiO₂/Si) substrate for FET fabrication. The thickness and the uniformity of the graphene layers were tested using atomic force microscopy (AFM). The thickness of the transferred single layer graphene was confirmed to be 0.4 nm. The AFM images also confirmed the presence of double layer graphene with thickness of 0.9 nm. FETs were fabricated by creating electrical contacts using successive thermal evaporation of chrome and gold on the transferred graphene layers with a channel length of 5 µm. Results showed that the graphene FETs showed an ambipolar current response with a positive Dirac voltage. The calculated average electron and hole mobility in the graphene channel were 252 (±57) and 592 (±125) cm²V^-1s^-1 respectively. The positive Dirac voltage could be attributed to the sulphur content in the graphite obtained from Kahatagaha graphite mines. Our studies suggests that the Sri Lankan graphite can be used as a raw material for graphene exfoliation and device application.