Preparation and STM study of clean Nb(111) surfaces

Niobium with its highest transition temperature among all elemental superconductors has become a favorable substrate for realizing well-defined low-dimensional magnet-superconductor hybrid systems exhibiting novel types of exotic electronic states such as Majorana zero-energy modes. While a preparation procedure for obtaining atomically clean Nb(110) substrates has previously been reported, a suitable preparation method for clean Nb(111) surfaces is still lacking. Here, we report a recipe for cleaning Nb(111) surfaces based on an atomic hydrogen treatment followed by short flashes to elevated temperatures. The atomic surface structure of clean non-reconstructed Nb(111) is investigated by high-resolution scanning tunneling microscopy (STM), as well as a surface reconstruction with a reduced atom density compared to the (111) plane of a bcc crystal resulting from a surface premelting at high annealing temperatures.