Optimized graphene transfer: Influence of polymethylmethacrylate (PMMA) layer concentration and baking time on graphene final performance

The influence of transfer parameters on the final structure, morphology and electrical properties of graphene were investigated in this work. Optical microscopy and atomic force microscopy (AFM) images showed that a double layer of PMMA can enhance or degrade graphene quality depending on its concentration. When properly diluted (15% in anisole, resulting in a PMMA layer of 1.35%) the transfer technique using double layer PMMA produces high quality graphene with fewer PMMA residues, non-cracked surface and sheet resistance around 247 ohm/square. We also investigated the influence of different baking times and temperature, and observed that the increase in baking time can degrade graphene quality thus leaving higher amounts of PMMA residues. Several works regarding graphene transfer are reported in the literature, but PMMA-based transfer processes still present challenges in yielding a clean and high quality graphene. (C) 2014 Elsevier Ltd. All rights reserved.