Combined effects of hydrogen annealing on morphological, electrical and structural properties of graphene/r-sapphire

We proposed a comprehensive study on the combined effects of hydrogen thermal annealing process on the morphological, structural and electrical properties of graphene transferred on r-plane sapphire (1-102). We found that although thermal annealing can remove the polymeric residues, unintentional p-type doping of polymeric residues and structural breakages arise simultaneously with the in-plane tensile strain. Also, the forming mechanism of cracks and p-type doping effect were investigated through Raman spectroscopy, atomic force microscopy, non-contact Hall and high resolution X-ray photo-electron spectroscopy. It revealed thermal annealing process has a combined influence on the performance of the hydrogen annealed samples with a critical point, which was similar to 250 degrees C in this work. When the annealing temperature was over the critical point, significant p-type doping effects were included in a dominant position because of graphene with in-plane strain. The results can be important for the fabrication or chemical processing of graphene-based materials and devices. (C) 2014 Elsevier Ltd. All rights reserved.