Spatially resolved, substrate-induced rectification in C₆₀ bilayers on copper

We demonstrate rectification ratios (RR) of ≳1000 at biases of 1.3 V in bilayers of C₆₀ deposited on copper. Using scanning tunneling spectroscopy and first-principles calculations, we show that the strong coupling between C₆₀ and the Cu(111) surface leads to the metallization of the bottom C₆₀ layer, while the molecular orbitals of the top C₆₀ are essentially unaffected. Due to this substrate-induced symmetry breaking and to a tunneling transport mechanism, the system behaves as a hole-blocking layer, with a spatial dependence of the onset voltage on intra-layer coordination. Together with previous observations of strong electron-blocking character of pentacene/C₆₀ bilayers on Cu(111), this work further demonstrates the potential of strongly hybridized, C₆₀-coated electrodes to harness the electrical functionality of molecular components.