Monitor the Growth and Oxidation of Cu-nanoparticles in PEG after Sputtering
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.55
Monitor the Growth and Oxidation of Cunanoparticles in PEG after Sputtering Yuen-ting Rachel Chau, Lianlian Deng, Mai Thanh Nguyen, and Tetsu Yonezawa Division of Materials Science and Engineering, Faculty of Engineering, Hokkaido University, Kita 13 Nishi 8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan
ABSTRACT
Metallic Copper nanoparticles (Cu NPs) were obtained via sputtering of Cu target onto liquid polymer, i.e., poly(ethylene glycol), PEG, under vacuum condition. The Cu NPs growth significantly right after the sputtering deposition from 3.1 nm to 4.1 nm in 4 hours as monitored by TEM. There was negligible growth of NPs for longer time and completely PEG acts as the coating material of Cu NPs so no agglomeration was observed for 1 week. The challenge of characterization of Cu NPs was also discussed.
INTRODUCTION Metal nanoparticles (NPs) have raised attention because of their distinct properties to make them have tremendous applications such as catalysts, electronics, heat transfer fluids and antimicrobial applications [1-4]. Copper (Cu) is a potential metal for applications mentioned above but oxidation is always the major challenge of making Cu NPs into practical applications. Even though there are some chemical reduction methods to suppress and control the oxidation rate of Cu NPs, such as surface coating [5], it would give NPs different properties compared with pure Cu NPs. Sputtering is introduced to generate NPs with high purity. Recent researches addressed liquid substrate into sputtering deposition, allowing direct preparation of liquid dispersion of NPs [6-13]. Poly(ethylene glycol), PEG, with molecular weight 600 is a liquid with low vapor pressure which is suitable to be used as the liquid substrate in sputtering [14]. It has been reported that NPs could have good dispersion in PEG by the steric effect and restrict the NPs from agglomerations [6,15]. Cu NPs were obtained by sputtering onto various liquids and their oxidation and conversion is dependent on the liquids use. König et al. reported that sputtered Cu NPs in ionic liquid have size of 6.3 nm but they have not discussed the oxidation of Cu
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NPs [16]. In our previous study, we found that metallic Cu NPs were obtained in pentaerythritol ethoxylate (PEEL) and they were completely oxidized after 7 days. We also observed that when sputtering Cu onto PEEL with sputtering current of 10 mA, the dispersion did not show a clear localized surface plasmon resonance (LSPR) of metallic Cu in UV-vis spectrum [17]. The phenomenon can be caused by the particle size and/or the oxidation of Cu. On the other hand, adding mercaptoundecanoic acid (MUA) to PEG as the liquid for sputtering resulted in stable, blue-emission Cu nanoclusters [18]. Thus, furthe
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