(530g) Theoretical and Experimental Study of Modulation of the Fermi Level of CuPc/HOPG Via NO Adsorption

Metal
phthalocyanines (MPc) have been widely used for chemical vapor sensing due to
their novel gas adsorption properties. In this work, we present both
theoretical and experimental study of copper phthalocyanine (CuPc) interactions
with a nonreactive substrate, HOPG, showing ground-state electronic modulation
of the substrate near the Fermi level. In order to study the NO interactions
onto CuPc molecules, we performed both van der Waals corrected spin-polarized
periodic density functional theory (DFT) calculations and site specific
scanning tunneling spectroscopy (STS) experiments. Both calculations and
experimental results suggest that NO interacts weakly (physisorption) with
CuPc/HOPG surface. The low coverage of NO adsorbates on HOPG in STM images is consistent
with the small perturbation of neighboring density of states of CuPc. DFT
calculations show that as NO adsorbs on metal center of CuPc, negative charge
carriers are injected from CuPc molecules to NO oxidant. During this charge transfer
process, excess electrons can be transfer to CuPc from the underneath layer of
the substrate, HOPG, and HOPG substrates may be doped to p-type. The binding of
NO to CuPc/HOPG also leads to the excess opening of the band gap by 0.18 eV as
compare to the experimental value of 0.25 eV. The results of this work have
shown that CuPc/HOPG could be a potential sensor device for oxidative analytes.