Direct observation of grain boundaries in graphene through vapor hydrofluoric acid (VHF) exposure

The shape and density of grain boundary defects in graphene strongly influence its electrical, mechanical, and chemical properties. However, it is difficult and elaborate to gain information about the large-area distribution of grain boundary defects in graphene. An approach is presented that allows fast visualization of the large-area distribution of grain boundary–based line defects in chemical vapor deposition graphene after transferring graphene from the original copper substrate to a silicon dioxide surface. The approach is based on exposing graphene to vapor hydrofluoric acid (VHF), causing partial etching of the silicon dioxide underneath the graphene as VHF diffuses through graphene defects. The defects can then be identified using optical microscopy, scanning electron microscopy, or Raman spectroscopy. The methodology enables simple evaluation of the grain sizes in polycrystalline graphene and can therefore be a valuable procedure for optimizing graphene synthesis processes.QC 20180604European Research Council through the Starting Grants M&M’s (277879)Swedish Research Council (GEMS, 2015-05112)European Research Council through the Starting Grants InteGraDe (307311)China Scholarship CouncilGerman Federal Ministry for Education and Research (NanoGraM, BMBF, 03XP0006C)German Research Foundation (DFG; LE 2440/1-2)German Research Council (DFG) through the Priority Program SPP 1459 Graphen