121st General Meeting of the KCS

Type Oral Presentation
Area Oral Presentation for Young Scholars in Physical Chemistry
Room No. Room 402
Time THU 10:00-:
Code PHYS.O-6
Subject Charge Transfer at Graphene-Environment Interface Driven by O2/H2O Redox Reactions
Authors Kwanghee Park, Sunmin Ryu*
Department of Chemistry, Pohang University of Science and Technology, Korea
Abstract Many low dimensional materials such as carbon nanotubes, graphene, and related 2-dimensional crystals undergo spontaneous charge transfer and are found hole-doped in the ambient conditions. Thermal annealing is known to even amplify the charge transfer in silica-supported graphene and 2-dimensional materials. Despite their importance towards low dimensional science and technology, however, the detailed mechanism of the spontaneous and activated charge transfer has yet to be revealed. In this work, we propose a mechanism based on a redox reaction by O2/H2O couple and verify it for two model systems: i) thermally activated charge transfer of graphene/SiO2 in air and ii) acid-induced charge transfer of graphene/SiO2 in water. Raman spectroscopy and water contact angle measurements were used to quantify charge density in graphene and hydrophilicity of substrates, respectively. For the first system, the degree of the activated charge transfer increased with increasing annealing temperature up to 500 oC but decreased in the range of 700 ~ 1000 oC. When interfacial water was scavenged with diethyl zinc vapor, the activated charge transfer was negligible. Modulation of interfacial hydrophilicity by thermal hydroxylation and dehydroxylation was found to be responsible for the phenomenon. For the second system, we found that graphene in acidic solution is hole-doped in the presence of dissolved oxygen and its kinetics is strongly pH-dependent. The proposed mechanism will be discussed using the Marcus-Gerischer theory to explain the results from the two model systems.
E-mail kwanghee@postech.ac.kr