Preparation of single-crystalline Nb–Al2O3–Nb structures by molecular-beam deposition

Abstract Single-crystalline γ -Al 2 O 3 layers, several nanometres thick, were prepared by molecular-beam epitaxy on Nb(111) substrates. Alumina was deposited by using a graphite Knudsen cell heated by electron bombardment. The layered structure was investigated by reflection high-energy electron diffraction. Auger spectroscopic analysis showed good stoichiometry of the films. The consecutive molecular-beam deposition of niobium on epitaxial γ -Al 2 O 3 /Nb layers permitted us to obtain a fully single-crystalline Nb(111)||Al 2 O 3 (210)||Nb(111) system that is very promising for the fabrication of very high-quality Josephson tunnel junctions.