Insight into charge transfer between graphene and palladium nanosheets investigated by Raman spectroscopy

Raman spectroscopy was used to investigate the interaction between graphene and hexagonal palladium nanosheets (Pd NSs). Pd NSs were synthesized by using a conventional CO-confined growth technique, and exhibited a strong surface plasmon resonance (SPR) absorption peak at around 980 nm. Using 514 and 785 nm excitation lasers, a considerable blue-shift of Raman peaks in graphene was found. The blue-shift of the G peak obtained using a 785 nm laser was significantly larger than that obtained using a 514 nm laser, demonstrating that Pd NS absorption induces hole-doping in graphene. Based on both first-principles calculations and variations in work functions, the qualitative analysis reveals that their interaction is driven by electron transport from graphene to Pd NSs. Furthermore, using a 785 nm excitation laser (near to the SPR absorption peak of Pd NSs), hot holes were readily injected into graphene, resulting in increased hole-doping levels.