Single Step Integration of ZnO Nano- and Microneedles in Si Trenches by Novel Flame Transport Approach: Whispering Gallery Modes and Photocatalytic Properties Tim Reimer, † Ingo Paulowicz, ‡ Robert Rö der, § Sö ren Kaps, ‡ Oleg Lupan, ‡,∥ Steffen Chemnitz, †,⊥ Wolfgang Benecke, ⊥ Carsten Ronning, § Rainer Adelung, ‡ and Yogendra K. Mishra* ,‡ † Technology for Silicon Based Micro- and Nanosystems, Institute for Electrical Engineering University of Kiel, Kaiserstr. 2, D-24143 Kiel, Germany ‡ Institute for Materials Science, Functional Nanomaterials, University of Kiel, Kaiserstr. 2, D-24143 Kiel, Germany § Institute of Solid State Physics, Friedrich-Schiller-University Jena, Max-Wien-Platz 1, 07743 Jena, Germany ∥ Department of Microelectronics and Biomedical Engineering, Technical University of Moldova, 168 Stefan cel Mare Boulevard, MD-2004, Chisinau, Moldova ⊥ Fraunhofer Institute for Silicon Technologies (ISIT), Fraunhoferstr. 1, 25524 Itzehoe, Germany * S Supporting Information ABSTRACT: Direct growth of quasi-one-dimensional nano- and microstructures in desired places of complex shaped substrates using simple growth methods is highly demanded aspect for various applications. In this work, we have demonstrated direct integration of ZnO nano- and microneedles into Si trenches by a novel flame transport synthesis approach in a single fabrication step. Growth of partially and fully covered or filled trenches in Si substrate with ZnO nano- and microneedles has been investigated and is discussed here. Detailed microstructural studies revealed the evolution of the ZnO nano- and microneedles as well as their firm adhesion to the wall in the Si trenches. Micro-photoluminescence measurements at different locations along the length of needles confirmed the good crystalline quality and also the presence of whispering gallery mode resonances on the top of needles due to their hexagonal shape. Faceted ZnO nano- and microstructures are also very important candidates with regard to photocatalytic activity. First, photocatalytic measurements from the grown ZnO nano- and microneedles have shown strong degradation of methylene blue, which demonstrate that these structures can be of significant interest for photocatalysis and self- cleaning chromatography columns. KEYWORDS: ZnO, nano- and microneedles, flame transport synthesis, Si trenches, whispering gallery modes, photocatalysis 1. INTRODUCTION Quasi-one-dimensional (Q1D) metal oxide nano- and micro- structures are currently under intensive investigation because of their extraordinary potentials for building real technological devices. Nanoscopic materials have been particularly interesting in the sense of excellent properties, but their integration into functional devices for real applications is still a challenging task. However, larger Q1D structures having intermediate dimen- sions in nano−micro scale are appropriate substitutes because they still exhibit desired nanoscale properties for advanced applications and they can be easily integrated to fabricate devices. ZnO nano- and microstructures are one of the most investigated materials because of their versatile synthesis approaches for various applications ranging from nano- electronic devices to biomedical engineering and environmental protection. 1−5 Due to its wide and direct bandgap ∼3.37 eV, large exciton binding energy ∼60 meV, hexagonal crystal structure with Zn and O terminated stacking along c-axis, 6 Q1D ZnO nanostructures have shown their potential for Received: February 21, 2014 Accepted: April 28, 2014 Published: April 28, 2014 Research Article www.acsami.org © 2014 American Chemical Society 7806 dx.doi.org/10.1021/am5010877 | ACS Appl. Mater. Interfaces 2014, 6, 7806−7815