1ST PRINCIPLES STUDY OF THE EFFECT OF TIP SHAPE ON SCANNING-TUNNELING-MICROSCOPY IMAGES

Effects of the shape of probe tip on observed scanning tunneling micro scopy images have been investigated by first-principles calculations b y taking the Si(111) square-root 3 x square-root 3-Ag surface as an ex ample of sample. By using three tungsten clusters with different shape s and by tilting their symmetry axes, various shapes of the tip were r epresented. Even for those tips which produce images distinctly differ ent from experimental ones when their symmetry axes are normal to the surface, the images change so as to agree with experiments as the axes are tilted gradually. The results indicate that only one atom at the tip apex usually makes an essential contribution to the tunneling curr ent and can explain why an experimental tip prepared quite arbitrarily usually produces good images.