Protective Layers Based on Carbon Paint To Yield High-Quality Large-Area Molecular Junctions with Low Contact Resistance
Senthil Kumar Karuppannan, Esther Hui Lin Neoh, Ayelet Vilan, Christian A. Nijhuis
Abstract
-alkanethiolates supported by Au were characterized with both dc and ac techniques, revealing that carbon paint protective layers provide a solution to three well-known challenges in molecular junctions: series resistance of the leads, poor interface conductance, and low effective contact area related to the roughness of the interfaces. Transport is constant with coherent tunneling down to 10 K, indicating the carbon paint does not add spurious thermally activated components. The junctions have both high reproducibility and good stability against bias stressing. Finally, normalized differential conductance analysis of the tunneling characteristics of the junctions as a function of molecular length reveals that the scaling voltage changes with molecular length, indicating a significant voltage drop on the molecules rather than on the molecule-electrode interface. There is a clear inverse dependence of the scaling voltage on length, which we deduced has a tunneling barrier height of close to 2 eV. The paper establishes the reliability of carbon paint protective layers and provides a procedure for discriminating genuine molecular effects from interfacial contributions.