Large spatially-resolved rectification in a donor-acceptor molecular   heterojunction
  We demonstrate that rectification ratios (RR) of >250 (>1000) at biases of 0.5 V (1.2 V) are achievable at the two-molecule limit for donor-acceptor bilayers of pentacene on fullerene on Cu using scanning tunneling spectroscopy and microscopy. Using first-principles calculations, we show that the system behaves as a molecular Schottky diode with a tunneling transport mechanism from semiconducting pentacene to Cu-hybridized metallic fullerene. Low-bias RRs vary by two orders-of-magnitude at the edge of these molecular heterojunctions due to increased Stark shifts and confinement effects. 
Joseph A. Smerdon, Noel C. Giebink, Nathan P. Guisinger, Pierre   Darancet, Jeffrey R. Guest
cond-mat.mes-hall