LEEM Investigation of Refractory Metals Grown on Insulating Substrates: Nb (110) on Sapphire $(11\bar{2}0)$

Abstract

We summarize LEEM studies of Nb (110) single crystals grown by MBE on Al 2 O 3[Formula: see text]. At temperatures between 1300 K and 1600 K the structure relaxes to create flat terraces several μm wide, and stable subgrain boundaries, by clearly visible interfacial and surface processes. The Nb surface exhibits two mirror-equivalent variants of a reconstruction, one of which prevails at low temperatures. Upon approaching Tc at ~1480 K, the two variants alternate in extended stripes along [Formula: see text], with stripe widths that decrease smoothly as T approaches Tc. Both at low T and above Tc, variants are trapped at dislocation strain fields.