Strongly-hybridized C$_{60}$-decorated copper surfaces enable giant current rectification*

Building on previous rectification demonstrations of strong electron-blocking character of pentacene/C$_{60}$ layers on Cu(111) [1], we demonstrate hole-blocking and rectification ratios ($RR$) of over 1000 at biases of 1.3~V in bilayers of C$_{60}$ deposited on copper [2]. Using scanning tunneling spectroscopy and first-principles calculations, we show that the strong coupling between C$_{60}$ and the Cu(111) surface leads to the metallization of the bottom C$_{60}$ layer, while the molecular orbitals of the top C$_{60}$ 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. This work further demonstrates the potential of strongly-hybridized, C$_{60}$-coated surfaces to harness the electrical functionality of molecular components. [1] J. A. Smerdon {\it et al.}, Nano Letters {\bf 16}, 2603 (2016); [2] J. A. Smerdon {\it et al.}, { \it submitted}.