Investigation of Metal Free Naphthalocyanine Vapor Deposited on Au(111)

Naphthalocyanines (Ncs) are promising candidates for future components in electronic devices and applications. To maximize the efficiency of Nc devices, it is critical to understand their structural and electronic properties and how these are impacted by deposition methods. The formation of a metal free naphthalocyanine (H(2)Nc) self-assembled monolayer on a Au(111) crystal was investigated by scanning tunneling microscopy under ultra-high-vacuum conditions at room temperature. A rigorous purification and processing procedure was developed to produce high purity, low defect, and well-ordered monolayers. High-resolution STM images reveal epitaxial growth of H(2)Nc on Au(111) with the observed structure having a molecular spacing of 1.6 +/- 0.05 nm, with molecules orientated slightly off (roughly 2.5 degrees) the low density packing direction of Au(111). A commensurate structure having 4 molecules per unit cell and unit cell parameters of A = 3.25 +/- 0.05 nm, B = 3.17 +/- 0.05 nm, and alpha = 87.5 +/- 2 degrees is proposed. Orbital-mediated tunneling spectroscopy was used to examine the electronic properties of individual molecules within the thin film. The first ionization potential and electron affinity of H(2)Nc adsorbed on Au(111) were measured to be -0.68 +/- 0.03 and 1.12 +/- 0.02 eV, relative to the Fermi energy.