We have succeeded in measuring the resistance across a single atomic step through a monatomic-layer metal on a crystal surface, Si(111)(sqrt[3]xsqrt[3])-Ag, using three independent methods, which yielded consistent values of the resistance. Two of the methods were direct measurements with monolithic microscopic four-point probes and four-tip scanning tunneling microscope probes. The third method was the analysis of electron standing waves near step edges, combined with the Landauer formula for 2D conductors. The conductivity across a monatomic step was determined to be about 5 x 10(3) Omega(-1) m(-1). Electron transport across an atomic step is modeled as a tunneling process through an energy-barrier height approximately equal to the work function.

Temperature-dependent electron transport in a metallic surface superstructure, Si(111)sqrt[3] x sqrt[3]-Ag, was studied by a micro-four-point probe method and photoemission spectroscopy. The surface-state conductivity exhibits a sharp transition from metallic conduction to strong localization at approximately 150 K. The metallic regime is due to electron-phonon interaction while the localization seemingly originates from coherency of electron waves. Random potential variations, caused by Friedel oscillations of surface electrons around defects, likely induce strong carrier localization.

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