Surface and Step Conductivities on Si(111) Surfaces

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 σstep=(29±9) Ω−1 m−1 and to a step-free surface conductivity of σsurf=(9±2)×10−6 Ω−1/□ for the Si(111)−(7×7) surface