One or both contacts in all-carbon molecular junctions can be sufficiently transparent to permit optical spectroscopy as a probe of device structure, and photocurrent generation to investigate photon-induced electron transport. Current-voltage (JV) curves for aromatic molecules depends strongly on molecular structure when molecular layers are more than 5 nm thick, ¹ and photocurrents were used to determine structural factors determining JV behavior. ² As shown in the left figure below, the photocurrent spectrum tracks the molecular absorption spectrum determined directly in the completed molecular junction. A molecular bilayer consisting of an electron donor and acceptor layers yields significantly higher photocurrents, which depend on the order of the layer deposition (right image below). ³ The use of photocurrents and Raman spectroscopy for characterization of molecular junction structure and operation will be discussed. ⁴

(1) Morteza Najarian, A.; McCreery, R. L.; Structure Controlled Long-Range Sequential Tunneling in Carbon-Based Molecular Junctions; ACS Nano 2017, 11, 3542.

(2) Morteza Najarian, A.; Bayat, A.; McCreery, R. L.; Orbital Control of Photocurrents in Large Area All-Carbon Molecular Junctions; Journal of the American Chemical Society 2018, 140, 1900.

(3) Smith, S. R.; McCreery, R.; Photocurrent, Photovoltage and Rectification in Large-Area Bilayer Molecular Electronic Junctions submitted 2018.

(4) Supur, M.; Smith, S. R.; McCreery, R. L.; Characterization of Growth Patterns of Nanoscale Organic Films on Carbon Electrodes by Surface Enhanced Raman Spectroscopy; Analytical Chemistry 2017, 89, 6463.