Effect of bottom electrode on rectification performance in pyrene-terminated n-alkanethiolate

Rectification performance of pyrene-terminated alkanethiolate in large-area tunneling junction was explored on the effect of bottom-electrode identity (Ag, Au, Pt, Pd) as non-molecular factors. Rectification ratio (log|r –|) of pyrene-terminated junction significantly decreased in order of Ag (log|r –|= 2.2 ± 0.3) ≈ Pt (log|r –|= 2.2 ± 0.5) > Pd (log|r –|= 2.0 ± 0.5) > Au (log|r –|= 1.3 ± 0.6). Three hypotheses were considered for the origin of the bottom-electrode effect: (i) surface topography of bottom electrode, (ii) electronic structure, and (iii) supramolecular packing structure. Structural analyses on a molecular scale using atomic force microscopy, ultraviolet photoelectron spectroscopy, and near-edge X-ray fine structure spectroscopy revealed that the effect of bottom electrode on the supramolecular structure dominates the trend of rectification performance ruling out the other possibilities. These experimental results demonstrate that rectification performance in pyrene-based molecular diode is sensitive to the change in electrode's identity. Our work offers important insight about structure-rectification relationship in organic molecular diode