Optical Properties of Graphene/Al Hetero-film*

When two metal films stack together forming “hetero-film”, it has been generally accepted that the effective transparency is lower than the respective metal film as a result of the absorption accumulation. Here, we report a counterintuitive phenomenon where transparency of a hetero-film is significantly higher compared to the original metal film. Specifically, we found that by layering one-atom-thick graphene on an aluminum (Al) film, the transparency of the Al film is dramatically increased from ~60% to 80% under 550 nm wavelength light. More surprisingly, similar transparency enhancement is captured when Al film was deposited on the graphene film. Systematic characterizations and numerical simulations were conducted to understand this unusual phenomenon observed in the graphene/Al hetero-film, including Raman, XPS, SEM, AFM analyses. Furthermore, Hall measurements revealed that our graphene/Al hetero-film holds great promise to be used as flexible transparent electrodes.