Ion scattering and X-ray photoelectron spectroscopy of copper overlayers vacuum deposited onto mercaptohexadecanoic acid self-assembled monolayers |
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Authors: | Linda S Dake David E King Alvin W Czanderna |
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Institution: | 1. University of Arkansas, Mechanical Engineering, 863 W. Dickson St., Fayetteville, AR 72701, United States of America;2. Materials Electrochemistry Division, CSIR-Central Electrochemical Research Institute (CECRI), Karaikudi 630003, Tamil Nadu, India;1. Department of Physics, Mepco Schlenk Engineering College, Sivakasi 626 005, Tamil Nadu, India;2. Department of Chemistry, Mepco Schlenk Engineering College, Sivakasi– 626 005, Tamil Nadu, India |
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Abstract: | Metal overlayers deposited in vacuum onto self-assembled monolayer (SAM) systems serve as models for more complex metalized polymers. Metals (M) deposited onto SAMs with different organic functional end groups exhibit a wide range of behavior, ranging from strong chemical interactions with the end group to complete penetration of the metal through the SAM. In this work, we have characterized the interactions of Cu with the ---COOH of mercaptohexadecanoic acid (MHA, HOOC(CH2)15SH) SAMs self assembled on gold films by using X-ray photoelectron spectroscopy (XPS) to examine the chemical interactions, and a combination of XPS and ion scattering spectroscopy (ISS) to deduce the growth mode and penetration rate of the deposited Cu. We found that submonolayer amounts of Cu react with HOOC, whereas the rest of the Cu remains metallic and penetrates beneath the SAM surface to the SAM Au interface. Considerable amounts of Cu (5 nm or more) will penetrate beneath the SAM layer, which is ca. 2.5 nm thick, despite the submonolayer presence of Cu at the SAM surface. The penetration rate depends strongly on the Cu deposition rate. Depositing copper onto MHA at 220 K or less, or using faster Cu deposition rates, results in slower or even completely suppressed penetration of the Cu through the SAM layer, whereas exposure to X-rays greatly enhances the penetration rate of large amounts of Cu through the SAM layer. The reacted copper is, based on the XPS 2p and LMM peaks, in the +2 oxidation state, but cannot be identified with a simple, stoichiometric oxide such as Cu2O, CuO, or Cu (OH)2. |
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Keywords: | Self-assembled monolayers Metal organic interfaces Cu interactions with COOH Penetration of Cu through self-assembled monolayers XPS and ISS of Cu HOOC interfaces Surface chemistry |
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