Etching Studies of Mo in Aqueous Solutions

Molybdenum (Mo) has been a choice of substrate metal for chalcopyrite or kesterite solar cells because of its low thermal expansion coefficient, high melting point, good thermal and electrical conductivity, and high wear resistance. Mo surface, however, is almost always covered with molybdenum oxides, unless kinetic limitations prevail. Previously, we reported the mild electrochemical conditions of forming molybdenum blue as well as molybdenum oxides colored in yellow and red in aqueous solutions. Figure 1 shows the representative changes in resonance frequency and current observed when the potential was applied to the molybdenum/quartz in aqueous solutions. The starting potential was –0.7 V, where the resonance frequency was set to be at the base line. As the potential was scanned up to –0.1 V, apparently the anodic current flew and simultaneously the resonance frequency increased. Near –0.1 V, the sharp increase in current as well as resonance frequency was observed, suggesting the significant dissolution of molybdenum into the solution as molybdenum ions. In this work we wish to report the results of electrochemical quartz crystal microbalance studies of etching of molybdenum in aqueous solutions. The present results may be important in relation to cleaning or polishing of molybdenum, which has been traditionally performed in strong acidic solutions such as mixtures of phosphoric acid and sulfuric acid. Details will be presented at the meeting. Acknowledgements Acknowledgements are made for SACHEM’s supply of some samples used in this work. Helpful discussions with Drs. Craig Allen and Paul Vermeulen are greatfully acknowledged. References. 1. Sang-Min Lee, Young-Ho Kim, Mi-Kyung Oh, Suk-In Hong, Hang-Ju Ko, and Chi-Woo Lee, J. Korean Electrochem. Soc. 13, 89-95 (2010). 2. Sang-Min Lee and Chi-Woo Lee, Bull. Korean Chem. Soc. 33, 1443 (2012) 3. Viswanathan S. Saji and Chi-Woo Lee, Electrochem. Acta, 137, 647-653 (2014). 4. Viswanathan S. Saji, Chan-Yong Jung and Chi-Woo Lee, J. Electrochem. Soc. 162, D465-D479, (2015). Figure 1