Supplementary Information High-Q, Low-Mode-Volume and Multiresonant Plasmonic Nanoslit Cavities Fabricated by Helium Ion Milling Kai Chen 1†* , Gary Razinskas 1 , Henning Vieker 2 , Heiko Gross 1 , Xiaofei Wu 1 , André Beyer 2 , Armin Gölzhäuser 2 , Bert Hecht 1* 1 Nano-Optics & Biophotonics Group, Experimentelle Physik 5, Physikalisches Institute, Röntgen Center for Complex Material Systems (RCCM), Universität Würzburg, Am Hubland, D-97074, Würzburg, Germany 2 Fakultät für Physik, Universität Bielefeld, D-33615, Bielefeld, Germany † Present address: Institute of Photonics Technology, Jinan University, Guangzhou, 510632, China *kaichen@jnu.edu.cn; hecht@physik.uni-wuerzburg.de S1. An SEM image of a 10 nm nanoslit cavity Figure S1. SEM image of a 10×300 nm nanoslit cavity. Electronic Supplementary Material (ESI) for Nanoscale. This journal is © The Royal Society of Chemistry 2018