A study of atom zigzag chains on the surface of Tungsten

Nishigaki and Nakamura have observed zigzag chains on the central (011) face of tungsten after field evaporation at T #62; 140 K. In this paper, a study of the formation, disappearance and structure of such chains is described. Tungsten tips of small radii down to 60 Å were used. Chains of 3 to 9 spots, that are clearly visible, are found even at 90 K. Four different structure models of the zigzag chains are discussed, including the multibranch model proposed by the Japanese authors. The interpretation of our experimental results shows fairly clearly that the real zigzag chain structure is a special non-dense structure. It must be formed by a local displacement of the tungsten adatoms in the field. Without the field, a zigzag chain is transformed into a two-dimensional cluster of the nearest neighbour atom by a small increase in temperature. If the field is reintroduced, the cluster can revert to the initial zigzag structure. The zigzag structure is interpreted as being caused by forces of repulsion between the atom dipoles.