Local pH control by electrolysis for ZnO epitaxial deposition on a Pt cathode

• Published in: Electrochimica acta Vol. 62; pp. 348 - 353
• Main Authors: Yagi, Shunsuke, Kondo, Yusuke, Satake, Yuichi, Ashida, Atsushi, Fujimura, Norifumi
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 15.02.2012; Elsevier
• Subjects: Cathodes; Chemistry; Deposition; Diffusion; Electrochemistry; Electrodes: preparations and properties; Electrolysis; Epitaxial growth; Epitaxy; Exact sciences and technology; General and physical chemistry; Local pH distribution; Microorganisms; Other electrodes; Potential-pH diagram; Semiconductors; Zinc oxide; Zinc oxide; Potential-pH diagram; Local pH distribution; Epitaxial growth; Diffusion; Zinc Nitrates; Scanning electron microscopy; Crystal orientation; Cathode; Transition metal; Zinc Oxides; Semiconductor epitaxial layers; Electrode material; X ray diffraction; Surface structure; Transport process; Electrolysis; Platinum; p type semiconductor; Morphology; Potential pH diagram; pH; Modified material
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2011.12.059

The epitaxial deposition of an oxide semiconductor ZnO thin film was demonstrated on a Pt(1 1 1)/sapphire(0 0 0 1) cathode by local pH control in the vicinity of the cathode. The local pH near the cathode was increased by the selective reduction of NO 3 − ions, resulting in the deposition of a ZnO thin film only on the cathode surface by hydrolysis. The pH distribution near the cathode during electrolysis was calculated using a 1-dimensional discrete model, which is simple but concise and beneficial to expeditiously estimate an appropriate deposition condition in combination with the obtained potential-pH diagram of a Zn–H 2O system. An investigation undertaken using a quartz crystal microbalance revealed that ZnO started to deposit immediately after the application of electrical current at 100 μA cm −2, and that it grew linearly to ca . 350 nm over 5000 s, suggesting that the film thickness can be easily controlled by electrolysis time.