2014 Volume 2014 Issue 261 Pages 29-31
This thesis is devoted for exploration on various host–guest interactions between graphene and adsorbed molecules, in particular concentrating on oxygen as guest adsorbed molecule which serves not only as electron acceptor but also as molecular magnet with triplet spin (S=1). Through the systematic experimental investigation, it is revealed that oxygen adsorption quite differently affects the electron transport on graphene depending on temperature; at room temperature the charge-transfer doping effect by weakly chemisorbed oxygen is dominant, whereas magnetic interaction between spins of physisorbed oxygen molecules and graphene manifests itself in the low temperature regime below 10 K, leading to anomalous oscillations of magnetoresistance. Furthermore, it is clarified that the oxygen adsorption accompanied with charge-transfer doping significantly depends on the electron/hole concentration of graphene, resulting in unconventional adsorption kinetics as well as modification of adsorption states that can be arbitrarily tuned by application of the external electric field. A phenomenological adsorption kinetics model is proposed on the basis of the electrochemistry in which charge transfer process between graphene and the adsorbed molecules should go through an activation barrier dependent on the Fermi level. Notably, the observed characteristics of adsorption are successfully explained by this model. The consistency between the theoretical model and experiments is also kept in the realistic case of graphene device, on which charge inhomogeneity exists on graphene due to potential fluctuation induced by the supporting substrate of the device or due to charge transfer between metal electrodes and graphene. This thesis contributes novel and interdisciplinary aspects on the surface chemistry and condensed-matter physics in low dimension, imparting strategies to control the electronic properties of graphene by regulation of molecular adsorption.
