ARTICLE pubs.acs.org/JPCC
Modulating ZnO Nanostructure Arrays on Any Substrates by Nanolevel Structure Control Byeong-Uk Ye,† Hak ki Yu,‡ Myung Hwa Kim,§ Jong-Lam Lee,*,‡ and Jeong Min Baik*,† †
School of Mechanical and Advanced Materials Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, Korea ‡ Department of Materials Science and Engineering, Division of Advanced Materials Science, Pohang University of Science and Technology (POSTECH), Pohang, Gyeongbuk 790-784, Republic of Korea § Department of Chemistry & Nano Science, Ewha Womans University, Seoul, 120-750, Korea
bS Supporting Information ABSTRACT: A uniform high-aspect-ratio nanotextured surface with a very dense forest of vertically aligned nanowires that was produced by surface chemical postfabrication of ZnO was induced by a structural transformation at the nanolevel. X-ray photoelectron spectroscopy verified the formation of the heterogeneous surface structures (GaOx on GaN and AuOx on Au) at the nanolevel as well as the modification of surface stoichiometry by UV/ozone treatment. The structural transformation contributes to generating a surface charge, acting as nucleation sites for nanotip growth. This led to a significant increase in density and improvement in diameter of the nanotips for various substrates, such as ZnO, Au, GaN, and graphene. However, the surface oxygen by O2 plasma treatment reduced the activity as activation sites of the exposed surface, resulting in the decrease of the density of the nanotips. This rational engineering of substrates by a structural transformation at the nanolevel may provide a promising method for producing highly dense onedimensional nanomaterials.
’ INTRODUCTION One-dimensional (1-D) nanostructures of metal oxide semiconductors such as ZnO have recently attracted great attention due to their potential applications in fabricating electronic, optoelectronic, electromechanical, and electrochemical devices, such as solar cells, light-emitting diodes, sensors, ultraviolet lasers, and nanogenerators.17 Among the various methods for the synthesis of 1-D ZnO nanostructures, catalytic and catalyticfree chemical vapor deposition have typically been used. However, single crystallinity of the substrate and high temperature (>400 °C) are strictly required for the growth, limiting the compatibility of these methods with flexible applications. Hydrothermal synthesis may be an attractive alternative because it is easy to perform and can be carried out at low temperature (
