Domain fracture and recovery process of metal phthalocyanine monolayers via NO2 and H2O

Abstract

CuPc ultrathin films (5 monolayers) are employed to detect NO2 in chemFETs [organic thin film transistors (OTFTs)]; while the NO2 causes OTFT degradation, H2O restores OTFT performance. To develop an atomic understanding of this H2O induced performance recovery, NO2/CuPc/Au(111) was exposed to H2O, then observed using ultrahigh vacuum scanning tunneling microscopy. After dosing NO2 (10 ppm for 5 min) onto CuPc monolayers under ambient conditions, domain fracture is induced in CuPc monolayers, and CuPc aggregates are formed near new grain boundaries, consistent with dissociative O adsorption between CuPc molecules and Au(111). Conversely, after exposing H2O onto a fractured CuPc monolayer for 30 min, fractured domains merge, then large area domains are generated. As the duration of H2O exposure increases to 4 h, second layer growth of CuPc molecules is observed on the CuPc monolayers consistent with H2O breakdown of CuPc aggregates which have formed at the domain boundaries. The results are consistent with H2O driving the removal of atomic O between CuPc molecules and Au(111) consistent with previous sensing results.