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

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• 作者：Jun Hong Park ; James E. Royer ; Evgeniy Chagarov ; Tobin Kaufman-Osborn ; Mary Edmonds ; Tyler Kent ; Sangyeob Lee ; William C. Trogler ; Andrew C. Kummel
• 刊名：Journal of the American Chemical Society
• 出版年：2013
• 出版时间：October 2, 2013
• 年：2013
• 卷：135
• 期：39
• 页码：14600-14609
• 全文大小：603K
• 年卷期：v.135,no.39(October 2, 2013)
• ISSN：1520-5126

文摘

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 掳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 掳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).