Micro-four-point probes in a UHV scanning electron microscope for in-situ surface-conductivity measurements

For in-situ measurements of surface conductivity in ultrahigh vacuum (UHV), we have installed micro-four-point probes (probe spacings down to 4 mum) i n a UHV scanning electron microscope (SEM) combined with scanning reflectio n-high-energy electron diffraction (RHEED). With the aid of piezoactuators for precise positioning of the probes, local conductivity of selected surfa ce domains of well-defined superstructures could be measured during SEM and RHEED observations. It was found that the surface sensitivity of the condu ctivity measurements was enhanced by reducing the probe spacing, enabling t he unambiguous detection of surface-state conductivity and the influence of surface defects on the electrical conduction.