Employing ionic liquid electrolytes we succeeded to electrodeposit light and transition metals as well as compound semiconductors on metal and semi conductor substrates at room temperature with nanometer or atomic resolution. For this aim in situ scanning tunnelling microscopy (STM) and scanning tunnelling spectroscopy (STS) have been applied. In this article we present new and recent results of 2D phase formation and growth of Ga underpotential deposition (UPD) and of surface alloying of Cd on Au(111), as well as 3D overpotential deposition (OPD) of Ni nanocrystals and ZnSb semiconductor clusters. Particular attention is given to the respective nucleation and growth mechanisms of the selected examples. Aspects of technological applications are briefly discussed. (C) 2008 Elsevier Ltd. All rights reserved.