From K atom pairs to K atomic chains: A semiconducting 2×3 to metallic 2×1 transition on the β-SiC(100) c(4×2) surface

We study the K∕β-SiC(100) c(4×2) surface by atom-resolved scanning tunneling microscopy and spectroscopy, and synchrotron radiation-based photoemission spectroscopy. At intermediate coverages, the K atoms are grouped by pairs around Si dimers at pedestal sites, in a 2×3 long-range ordering leaving 1∕3 of the pedestal sites unoccupied, while keeping the semiconducting c(4×2) surface unchanged as identified by tunneling through the K overlayer. At saturation, additional K atoms adsorb on remaining pedestal sites and act as atomic “contacts” between two K pairs, leading to K atom chain formation in a 2×1 metallic surface.