Coulomb energy determination of a single Si dangling bond
T. H. Nguyen, G. Mahieu, M. Berthe, B. Grandidier, C. Delerue,
D. Stiévenard
Institut d’Electronique, de Microélectronique et de
Nanotechnologie, IEMN, (CNRS, UMR 8520) Département ISEN,
41 bd Vauban, 59046 Lille Cedex, France
Ph. Ebert
Institut für Festkörperforschung, Forschungszentrum Jülich GmbH, 52425 Jülich, Germany
Adding or removing electrons from materials costs energy. This supply of energy
increases as the size of the materials shrinks and has been beautifully demonstrated when
current is flowing through artificial atoms, such as small metal particles and semiconductor
quantum dots [1,2,3]. Indeed, in this confined structures, the tunneling conductance displays
resonances, that arise entirely or partly from Coulomb repulsion between the confined
electrons. A Coulomb blockade mechanism also occurs when electrons are transferred
through the bound states of a single atom [4], but coupling a single atom to electrical leads
through tunnel junctions and switching its charge state is still a difficult task [5]. In addition,
depending on the dielectric environment and the chemical bonding of the atom, changing its
electron population may lead to significant relaxation effects. Such effects modify the intraatomic Coulomb repulsion energy, also called the Hubbard U splitting, and a precise
knowledge of the effective U* energy on an atomic scale basis is still missing.
Point defects in semiconductor materials may consist of a single atom, that exhibits
energy levels in the band gap region of the materials. Due to their localized character, these
deep levels can trap up to two electrons on the same state. Therefore, they form an important
system to study U*, because a change of the trapped electron population may significantly
affect the nature and degree of electrical conductivity in electronic devices. Here, with
scanning tunneling microscopy (STM), we investigate U* for a protypical point defect, a
single Si dangling bond (DB) at the surface of a B-doped Si(111)-3x3 R30° surface. The
cancellation of the energy dependence of the probability transmission allows to characterize
the transition between the single particle electronic spectrum and the shell-filling spectrum,
that is obtained when the inelastic current through the dangling bond ground state approaches
saturation. From the different charge states of the Si dangling bond, the effective correlation
of a single Si dangling bond is measured.6
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