Nanoscale spectromicroscopic characterizing technique is indispensable for realization of future high-speed graphene transistors. Highly spatially resolved soft X-ray photoelectron microscopy measurements have been performed using our “3D nano-ESCA” (three-dimensional nanoscale electron spectroscopy for chemical analysis) equipment in order to investigate the local electronic states at interfaces in a graphene device structure. We have succeeded in detecting a charge transfer region at the graphene/metal-electrode interface, which extends over ∼500 nm with the energy difference of 60 meV. Moreover, a nondestructive depth profiling reveals the chemical properties of the graphene/SiO2-substrate interface.

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The change of Fe 3d states accompanied with the Li intercalation/deintercalation process has been successfully revealed by resonant photoemission spectroscopy. The main peak shift and expansion of Fe 3d bands through the Li deintercalation reflect the strong hybridization between Fe 3d states and O 2p states as the Fe–O bond lengths decrease. From the antiresonance spectra, O 2p partial density of states also changes, suggesting the interaction between Fe and O atoms still remains in LiFePO4. Furthermore, density functional theory calculations results strongly support these experimental results. The framework structure of LiFePO4 is more suitable than that of LiCoO2 for the good rechargeable battery, because the change of the electronic structure in LiFePO4 valence band is rather small because of the strong covalent P–O bond.

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