STM study of the reactivity of niobium diselenide in air and N₂

STM has been used to investigate the variety of processes taking place in the surface of NbSe₂ in air and N₂. Induced surface layer by layer etching and formation and evolution of surface reaction sites both in air and N₂, are discussed. Residues removed and transported by the tip were found in N₂ but they seemed to get dissolved in air. Rests of chemicals (and/or surface defects) have been observed to be left in the edges of pre-existing terrace steps in N₂, providing a preferential place for the formation of new reaction sites when air was re-introduced. In places where apparently no defects were present, the tip induced etching process was not possible, but focusing in a pre-existing small depression, the etching proceeded fast not only in that layer but also in the layers beneath. We propose that the processes taking place at the surface of NbSe₂ are due to mechanical and chemical interactions that unsaturated bonds which are present in surface defects and step edges have with the environment and the tip.