FORMATION OF TUNGSTEN SILICIDE ON AN STM TIP DURING ATOM MANIPULATION

We have investigated compositional changes of a tip before and after a tom manipulation by a scanning tunnelling microscope (STM) combined wi th an atom probe (AP). On clean Si(0 0 1) : (2 x 1), the surface was m odified by the STM with a bias of + 5 V and 2 nA at the sample. The AP mass spectrum clearly showed that Si as well as W atoms were detected . The detected ratio of W to Si is 1 : 2 at first and then 5 : 3, whic h indicates that two types of stable tungsten silicides, WSI2 and W5Si 3, respectively, are formed on the STM tip. Direct evidence of silicid e formation during atom manipulation was clearly shown by STM combined with AP(AP-STM). (C) 1998 Elsevier Science B.V. All rights reserved.