ATOMICALLY RESOLVED CHARGE-DENSITY WAVES IN 1T-TAS2

A scanning tunneling microscope (STM), operating in air at room temper ature, has been used to study the charge-density waves (CDW's) on the surface of 1T-TaS2 with many different Pt/Ir, W, Ni, and Co tips. Imag es of CDWs with strong atomic modulation, as well as those with weakly superimposed atomic modulation, have been observed with all different kinds of tips. Changes from one kind of CDW image to the other under the same scanning conditions are also observed. The different CDW imag es are consistent with Chen's [Phys. Rev. Lett. 65, 448 (1990)] atomic -orbital STM theory. The changes of the image are believed to be cause d by changes in the electronic structure of the tip.