SURFACE ELECTRONIC TRANSPORT

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(1) We have constructed an ultrahigh-vacuum scanning electron microscope-molecular beam epitaxy apparatus, in which a micro-four point probe (with 8μm-probe spacing) system, which has been developed in Denmark Technical University, has been installed. With this system, we measured electrical conductance of aimed surface areas with aid of the microscope.(2) We have found that the electrical conductance of a Si(111)-√3×√3-Ag surface is higher than that of a Si(111)-7×7 clean surface by two orders of magnitude. This is because the measurements become surface-sensitive due to the small probe spacing so that the intrinsic properties of the respective surfaces are directly detected.(3) By shifting the micro-four point probe along the sample surface, we have found that the surface conductance is quite different between on terraces and across step bands. This directly means that the surface carriers are scattered by surface atomic steps, causing the reduction in conductance.(4) We have done computer simulations using two-dimensional resistors networks to obtain the surface conductance maps of a sample from the measured conductance maps.(5) A nano-four point probe (0.5μm probe spacing), which has been newly devised in Denmark Technical University, has been installed in the above-mentioned microscope, and used for surface conductivity measurements.