Surface and Step Conductivities on Si(111) Surfaces

Abstract

Four-point measurements using a multitip scanning tunneling microscope are carried out in order to determine surface and step conductivities on Si(111) surfaces. In a first step, distance-dependent four-point measurements in the linear configuration are used in combination with an analytical three-layer model for charge transport to disentangle the 2D surface conductivity from nonsurface contributions. A termination of the Si(111) surface with either Bi or H results in the two limiting cases of a pure 2D or 3D conductance, respectively. In order to further disentangle the surface conductivity of the step-free surface from the contribution due to atomic steps, a square four-probe configuration is applied as a function of the rotation angle. In total, this combined approach leads to an atomic step conductivity of ${\ensuremath{\sigma}}_{\text{step}}=(29\ifmmode\pm\else\textpm\fi{}9)\text{ }\text{ }{\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}\text{ }{\mathrm{m}}^{\ensuremath{-}1}$ and to a step-free surface conductivity of ${\ensuremath{\sigma}}_{\text{surf}}=(9\ifmmode\pm\else\textpm\fi{}2)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\text{ }\text{ }{\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}/\ensuremath{\square}$ for the $\mathrm{Si}(111)\text{\ensuremath{-}}(7\ifmmode\times\else\texttimes\fi{}7)$ surface.