STM, operated under extremely clean and stable conditions became in the last decade a very powerful nanotechnological tool. It is not only used to probe individual atoms and molecules but also to displace, decompose and assemble individual species into new artificial nanostructures1. These are formed in an atom-by-atom process by precisely controlling the quantum-mechanical interactions between the STM tip and the sample. Such experiments require cryogenic temperatures (below 20 K), atomically clean (pressure below 10-11 hPa) and properly ordered surfaces (controlled by LEED and AES) as well as extreme mechanical and electrical stability of the tip-sample tunneling junction. The experiments presented were performed with a home-built Besocke type UHV STM, cooled with liquid helium. Cu (111) and (112) single crystal surfaces, cleaned by repeated cycles of ion sputtering and annealing, were used as substrates, while STM tips were prepared by electronically controlled etching of polycrystalline W wires in 2M NaOH. Single adatoms of Cu were extracted from the substrate surface by a controlled dipping of the tip into the Cu surface under relatively high tunneling bias voltages. Individual adatoms were manipulated in a controlled manner into desired nanostructures. Submonolayer amounts of Co were deposited onto clean Cu substrates from a Knudsen source. Co atoms, deposited at room-temperature, form agglomerates during deposition already, but can be separated at lower temperatures into individual adatoms by means of the tip-sample interaction. The electronic structures of both, Cu and Co were studied by STS with the lock-in technique2. Differential conductance (dI/dV) spectra, proportional to LDOS, are fully reproducible and can be used to differentiate between Cu and Co species.