Sophisticated in situ investigation techniques at solid/liquid interfaces on the nanometer length scale using scanning tunnelling microscopy (STM) beyond the simple imaging of surfaces, as for example tunnelling spectroscopy, localized electrodeposition of nano-particles, or localized electrochemical (catalytic) reaction detection at the STM tip, require in addition to the usual sharpness for high resolution imaging a well-defined geometrical shape and electrochemical behaviour of STM tips. At present, such tips are not available in STM research at solid/liquid interfaces. In this paper, we show how a combined ultra-high-vacuum (UHV) sputtering and field emission microscopy (FEM) technique can be utilized to prepare well-defined nanoelectrode tips. Not only impurities, adsorbates, or surface oxides can be removed by ion-self-sputtering, but the tip geometry is optimized towards an ideal hemispherical shape and the tip apex diameter can be reduced down to a few nanometers, while monitored and controlled in vacuo by the decrease of the corresponding field emission voltage. A detailed investigation is presented for W, Pt, Ni, and Au nanoelectrode tips, which demonstrates the excellent electrochemical as well as imaging properties and the well-defined geometry of such nanoelectrode tips, predestining them for application in any kind of STM based in situ measurement or preparation technique at solid/liquid interfaces. (c) 2007 Elsevier B.V. All rights reserved.