The surface structure and charge distribution of ZrSe3 and ZrTe3

The (0 0 1) Van der Waals surfaces of ZrSe3 and ZrTe3 single crystals were studied by scanning tunneling microscopy at room temperature. It is shown that both the semiconducting ZrSe3 and the semimetallic ZrTe3 crystals show a charge instability between various selenium/tellurium chains forming the surface. The semimetallic ZrTe3 crystals were shown by electron probe analysis to contain excess tellurium, which forms zigzag chains with every second linear chain of the average structure. Consequently, an incommensurate modulation was observed in these crystals with approximate surface unit cell parameters am=a/ cos (γ−90°), bm=b and γ=102° with regard to those of the average structure. Calculations carried out within the extended Hückel tight binding approximation show that in case of Te-rich ZrTe3 the contribution to conductivity along the Zr chains may be increased.