Single-Molecule Vibrational Spectroscopy: Cobalt Tetraphenylporphyrin Deposited on a Cu₂N Ultrathin Insulating Layer

The electronic and vibrational properties of cobalt tetraphenylporphyrin (CoTPP) molecules deposited onto a Cu₂N–Cu(100) surface were studied by scanning tunneling microscopy. The Cu₂N spacer layer promoted the decoupling between the localized electronic states of CoTPP and the metallic substrate, enabling the observation of electronic states of nearly free molecules. The experimental results are supported by ab initio calculations, and the correspondence with C–H and C–C bonding vibrations detected by inelastic electron tunneling spectroscopy (IETS) has been shown. For molecules adsorbed at the interface between Cu₂N and Cu, the IETS signal was also observed.