STM STUDY OF THE REACTIVITY OF NIOBIUM DISELENIDE IN AIR AND N-2

STM has been used to investigate the variety of processes taking place in the surface of NbSe2 in air and N-2. Induced surface layer by laye r etching and formation and evolution of surface reaction sites both i n air and N-2, are discussed. Residues removed and transported by the tip were found in N-2 but they seemed to get dissolved in air. Rests o f chemicals (and/or surface defects) have been observed to be left in the edges of pre-existing terrace steps in N-2, providing a preferenti al place for the formation of new reaction sites when air was re-intro duced. In places where apparently no defects were present, the tip ind uced etching process was not possible, but focusing in a pre-existing small depression, the etching proceeded fast not only in that layer bu t also in the layers beneath. We propose that the processes taking pla ce at the surface of NbSe2 are due to mechanical and chemical interact ions that unsaturated bonds which are present in surface defects and s tep edges have with the environment and the tip. (C) 1998 Elsevier Sci ence B.V. All rights reserved.