Unsubstituted and Fluorinated Copper Phthalocyanine Overlayers on Si(111)-(√7 × √3)-In Surface: Adsorption Geometry, Charge Polarization, and Effects on Superconductivity

Abstract

Surface superconductors such as Si(111)-(√7 × √3)-In (referred to as (√7 × √3)-In, hereafter) can be sensitively doped by surface dopants to tune their transition temperature (Tc) even via a weak interaction induced by molecular overlayers. Here, we examined the effect of Cu-phthalocyanine (CuPc) and Cu-hexadecafluorophthalocyanine (F16CuPc) overlayers on the electronic structure on (√7 × √3)-In. While both molecules formed well-ordered monolayers, molecular adsorption geometries were found to be different; CuPc formed an ordered monolayer of face-on molecules, while F16CuPc tended to adsorb in a slightly tilted geometry. The normal-state electronic structures of (√7 × √3)-In covered with these molecules were found to be similar. Photoelectron spectroscopy have suggested that the charge transfer to the molecules was negligible and that the interaction between the molecules and (√7 × √3)-In were weak. Nevertheless, CuPc enhanced the superconducting transition temperature (Tc) of (√7 × √3)-In by approximate...