posted 8 Aug 2014, 01:00 by Lisbeth Kirk Mynster
S. Vermehren Petersen, Nano-Science Center, Department of Chemistry, Univeristy of Copenhagen, Denmark.
Chemically converted graphene is highly relevant for transparent conducting film applications such as display and photovoltaic applications. So far, the major obstacle for realizing the potential has been to fully reduce/deoxygenate the graphene oxide (GO), which is challenging due to the pronounced aggregation during deoxygenation of GO in solution. Surface immobilization of monolayered graphene oxide (mGO) in Langmuir-Blodgett (LB) films was investigated to circumvent this problem. Two types of LB films with different density of mGO flakes where prepared, i.e. diluted and coherent, and efficiently deoxygenated in a three-step reduction procedure involving subsequent treatment with hydrazine in dimethylformamide (DMF) to give rGO1, sulfuric acid to give rGO2, and high temperature annealing to give rGO3. XPS measurements confirmed a full conversion into virtually oxygen free chemically converted graphene. Electrical characterization revealed large variations in the conductivity for single sheets in the diluted LB films, with an average conductivity of 100 S/cm. The large variation in single sheets conductance is assigned to over-oxidation of the GO leading to formation of holes, which cannot be recovered in the chemical reduction procedure. The study shows that this chemically converted graphene is limited by structural defects/holes rather than remaining oxygen functionalities.
Søren Vermehren Petersen is currently a postdoctoral researcher at the University of Copenhagen, Denmark. His primary interest is chemical graphene synthesis and application of graphene in molecular devices, as transparent electrodes, in conductive inks and graphenes effect on the human body. He obtained his B.S. in Nanoscience (2008) and a Ph.D. in Nanoscience (2013) from the University of Copenhagen, Denmark. In his current occupation, he is developing graphene based conductive inks.