Stabilized epitaxial films of hexagonal Ni1−xS on MgO(001)

This study used molecular beam epitaxy to prepare epitaxial Ni_1−xS films with NiAs-type structures on MgO(001) substrates. The films were characterized using X-ray diffraction method. Nickel vacancies showed an ordered arrangement of alternating metal-rich and metal-deficient layers along the c-axis. The orientations of epitaxial films were (001) [1,−1,0]Ni_1−xS||(001)[110]MgO and its equivalents because of the coexistence of the trigonal axis of the Ni_1−xS film and the four-fold rotation axis of the MgO substrate. Film compositions were obtained using intensity ratios between 0 0 1 and 0 0 2 reflections and EPMA results. They were dependent on substrate temperature. The relation between lattice parameters and the composition, as determined by the intensity ratio, nearly agrees with that of previously reported bulk Ni_1−xS. The films were stable at room temperature after 1 year, which contrasts with deterioration of bulk Ni_1−xS. This paper presents SEM and RHEED assessments of the film's morphology and structure.