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    The nature of self-assembled octadecylphosphonic acid (ODPA) layers on copper substrates

    Year: 2021

    Journal: J. Colloid Interface Sci., Volume 581, JAN 1, page 816–825

    Authors: Zhao, Weijie; Gothelid, Mats; Hosseinpour, Saman; Johansson, Malin B.; Li, Gen; Leygraf, Christofer; Johnson, C. Magnus

    Organizations: China Scholarship Council (CSC); Emerging Talents Initiative (ETI), FAU, Germany [2018/2_Tech_06]; BMBF-MSRT [CAlSAB]

    Keywords: Octadecylphosphonic acid; Self-assembled monolayers; Copper leaching; Atomic force microscopy; Infrared reflection/absorption spectroscopy; X-ray photoelectron spectroscopy

    Hypothesis: The self-assembly of amphiphilic molecules onto solid substrates can result both in the formation of monolayers and multilayers. However, on oxidized and non-oxidized copper (Cu), only monolayer formation was reported for phosphonic acids possessing one phosphate head group. Here, the adsorption of octadecylphosphonic acid (ODPA) on Cu substrates through a self-assembly process was investigated with the initial hypothesis of monolayer formation. Experiments: The relative amount of ODPA adsorbed on a Cu substrate was determined by infrared reflection/absorption spectroscopy (IRRAS) and by atomic force microscopy (AFM) investigations before and after ODPA deposition. X-ray photoelectron spectroscopy (XPS) with sputtering was used to characterize the nature of the layers. Findings: The results show that the thickness of the ODPA layer increased with deposition time, and after 1 h a multilayer film with a thickness of some tens of nm was formed. The film was robust and required long-time sonication for removal. The origin of the film robustness was attributed to the release of Cu ions, resulting in the formation of Cu-ODPA complexes with Cu ions in the form of Cu(I). Preadsorbing a monolayer of octadecylthiol (ODT) onto the Cu resulted in no ODPA adsorption, since the release of Cu(I) ions was abolished. (C) 2020 Elsevier Inc. All rights reserved.
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