A simple approach to increase the reliability of nano-gap electrode fabrication techniques is presented. The method is based on maskless sputter etching of An electrodes using a focused ion beam (FIB) and in-situ monitoring of the etching steps by measuring a current fed to the An electrodes. The in-situ monitoring is crucial to form nano-gaps much narrower than a FIB spot size. By using this approach, gaps of similar to 3-6 nm are fabricated with the high yield of similar to 90%, and most of the fabricated nano-gap electrodes showed high resistances of 10 G Omega- 1 T Omega. The controllability of the fabrication steps is significantly improved by using triple-layered films consisting of top Ti, Au, and bottom adhesion Ti layers. The applicability of the fabricated nano-gap electrodes to electron transport studies of nano-sized objects is demonstrated by electrical measurement of An colloidal nano-particles. (c) 2005 Elsevier B.V. All rights reserved.