Graphene, a honeycomb structure composed of carbon atoms has drawn attention as a next-generation semiconductor material due to its unique property. Its conduction electrons move at an extremely high speed, said to be approximately 1/300 of the speed of light. In this study, graphene was formed on the surface of gold, one of the common wiring materials, and the chemical bonding that influences the efficiency of charge and spin injection from gold into graphene was investigated using angle-resolved photoemission spectroscopy.
 Fig. 1a shows that on a flat surface of gold with a close-packed structure, the 6s electrons of gold show a three-dimensional electronic structure without chemical bonding with the π-electrons of graphene. In contrast, Fig. 1b shows that chemical bonding between the 6s electrons of gold and the π-electrons of graphene was observed on the gold surfaces with one-dimensional atomic-scale corrugations, which perhaps form on gold foils. Furthermore, because the 6s electrons of gold are highly delocalized in the graphene-gold interface with one-dimensional nature, the characteristic properties of π-electrons of graphene remain intact even after the formation of the chemical bond.
 This study demonstrates that the precise control of the atomic arrangement of gold in the interface with graphene enables the formation of chemical bonds while preserving the intrinsic properties of graphene. These findings provide essential knowledge for controlling the atomic arrangement of wiring metals for efficient current and spin injection into graphene in the development of graphene-based semiconductor devices.

This work was conducted in collaboration with Nagoya University and Osaka University, and was supported by JSPS KAKENHI Grant Number JP19K15400 and the Konica Minolta Science and Technology Foundation.