TUNGSTEN SILICIDE FORMATION ON AN STM TIP DURING ATOM MANIPULATION

We have used a scanning tunneling microscope (STM) combined with an at om probe (AP) to identify chemical species of atoms captured on an STM tip during atom manipulation. First we briefly show the performance o f STM combined with AP (AP-STM). Then the surface of clean Si(001):2x1 was modified by the STM with a bias of +5 V and 2 nA at the sample. T he AP mass spectrum showed that Si as well as W atoms were detected. F urther, the detected ratio of W to Si is 1:2 at first and then 5:3, wh ich indicates that two types of stable tungsten silicide, WSi2 and W5S i3, respectively, are formed on an STM tip. Direct evidence of silicid e formation during atom manipulation was clearly shown by AP-STM.