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Phase transitions in low dimensional materials can be a direct consequence of electronic instability against lattice distortions which leads to periodic charge density modulation, making a low symmetric phase the most stable one. We investigate the interplay between electronic properties and surface morphology in thin Bi film adsorbed on Cu(001) both by angle resolved photoemission and first principle approach. Calculations are performed within the density functional theory and using the embedding method [1]. In this framework the effect of a really semi-infinite substrate is taken into account, allowing the evaluation both of the continuous of bulk states and discrete surface features.
The Bi/Cu(001) system presents a long-range ordered c(2x2) phase around half monolayer. For a small increasing of the coverage, both the c(9√2 x √2) R45° and p(10x10) phases can be described in terms of slightly distorted c(2x2) phase, as a consequence of the high surface strain related to the high packing of the Bi adatoms of the surface. Such a distortion of the surface structure may lead to the formation of dislocations, with one and two-dimensional character for the c(9√2 x √2) R45° and p(10x10) phase, respectively [2].
The consequent periodical modulations of the adatom-adatom as well as adatom substrate distance can be supported by a charge density wave [3]. A detailed analysis of the surface electronic dispersion, both from experiments and theory, evidences the appearance of adsorbate-induced surface states crossing the Fermi level. The Fermi surface of the c(2x2) phase fulfills the nesting condition, that can generate the charge density wave responsible for the surface reconstruction.
[1] J.E. Inglesfield, J. Phys. C: Solid State Phys. 14 (1981) 3795.
[2] H.L. Meyerheim, M. De Santis, W Moritz, I.K. Robinson, Surf. Sci. 418 (1998) 295.
[3] T. Nakagawa, Y. Saito, O. Ohgami, H. Okuyama, M. Nishijima, T. Aruga, Phys. Rev. B 72 (2005) 165405.
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