Atomic Imaging of the Irreversible Sensing Mechanism of NO₂ Adsorption on Copper Phthalocyanine

Abstract

Ambient NO2 adsorption onto copper(II) phthalocyanine (CuPc) monolayers is observed using ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) to elucidate the molecular sensing mechanism in CuPc chemical vapor sensors. For low doses (1 ppm for 5 min) of NO2 at ambient temperatures, isolated chemisorption sites on the CuPc metal centers are observed in STM images. These chemisorbates almost completely desorb from the CuPc monolayer after annealing at 100 °C for 30 min. Conversely, for high NO2 doses (10 ppm for 5 min), the NO2 induces a fracture of the CuPc domains. This domain fracture can only be reversed by annealing above 150 °C, which is consistent with dissociative chemisorption into NO and atomic O accompanied by surface restructuring. This high stability implies that the domain fracture results from tightly bound adsorbates, such as atomic O. Existence of atomic O on or under the CuPc layer, which results in domain fracture, is revealed by XPS analysis and ozone-dosing experiments. The observed CuPc domain fracturing is consistent with a mechanism for the dosimetric sensing of NO2 and other reactive gases by CuPc organic thin film transistors (OTFTs).

Surface chemistry of porphyrins and phthalocyanines

“…(Note that similar observations were made for the exposure of CuPc on Au(1 1 1) to NO 2 . At small dosages, chemisorption of a not identified species occurred at the Cu centers, while large dosages resulted in destruction of the CuPc domains due to dissociative adsorption of NO 2 [764]). Local information about changes in the electronic structure induced by NO coordination was obtained with STS.…”

Achievement of High-Response Organic Field-Effect Transistor NO2 Sensor by Using the Synergistic Effect of ZnO/PMMA Hybrid Dielectric and CuPc/Pentacene Heterojunction

“…However, the interface property of dielectrics also plays a crucial role in the gas sensing characteristics, as the efficient current channel lies in the first few molecular layers of the OSC upon the dielectric layer [17]. Using scanning Kelvin probe microscopy, Andringa et al have determined that the trapped electrons of OFET-based sensors are located at the dielectric interface [18]. Therefore, modifying dielectrics with certain functional materials could significantly improve the sensing properties of OFET-based chemical sensors.…”

Highly efficient dye-sensitized solar cells based on metal-free and copper(II) phthalocyanine bearing 2-phenylphenoxy moiety

“…Among various synthetic dyes, Pcs have been considered to be promising candidates because of their intensive absorption in the far-red/ near-IR region, and excellent chemical, light, and thermal stability [29,30]. It is also well known that central metals play a major role in tuning the properties of MPcs; Since the CuPcs use as dyes is now overshadowed by other applications such as organic field-effect transistor sensors [31], gas sensor [32], organic solar cells [33], and electro-catalysts [34] copper (II) ion was preferred as central metal.…”