In-induced variation in the electronic structure of the In nanoclusters on Si(001)

Hojin Jeong and Sukmin Jeong

Department of Physics, Chonbuk National University, Chonju 561-756

Control of the position and size of nanoclusters is a greatly important issue in nanotechnology for practical applications. A magic cluster is, in this sense, a promising material for such purposes since it shows enhanced stability at selected sizes with periodic arrangement. Knowledge of the atomic and electronic structures of a magic cluster is thus essential for fabrication of nanodevices using the magic cluster. The In-adsorbed Si(001)4×3 surface, forming a magic cluster at the In coverage of ~ 0.5 ML, has provided interesting problems on the atomic and electronic structures. Its atomic structure had been controversial for a decade until Bunk et al. determined a structural model that contains six In and seven Si atoms on the surface forming a pyramid-like structure (Si₇In₆ cluster). Recently, it was found that more In atoms can be put into the Si₇In₆ cluster and form a metastable structure. The scanning-tunneling spectroscopy (STS) experiment shows that the In-doped cluster is metallic (metallization by autodoping) [1] while photoemission spectroscopy (PES) reveals that the In-doped cluster remains semiconducting [2].

In this talk, in order to solve the puzzling behavior of the electronic structures of the In-doped nanoclusters, we perform pseudopotential total-energy calculations on the In/Si(001)4×3 surfaces with change of In doping. We consider the In-doped clusters, including the pristine Si₇In₆ cluster. The calculated electronic structures show that the Si₇In₆ and Si₅In₈ clusters are semiconducting while the Si₆In₇ cluster is metallic. The electronic structure analysis and scanning-tunneling microscopy (STM) simulation suggest that the Si₆In₇ cluster, rather than the Si₅In₈ cluster, is consistent with the STS measurement. And, the semiconducting In-doped cluster, observed in PES, corresponds to the Si₅In₈ cluster. Calculation of formation energies as a function of the In chemical potential implies that both the Si₆In₇ and Si₅In₈ cluster possibly appear, depending on experimental conditions.

[1] V. G. Kotlyar et al., Phys. Rev. Lett. 91, 026104 (2003).

[2] J. R. Ahn et al., Phys. Rev. B, in press (2004).