The Effect of Vapor Transport Annealing on FeSe Films Deposited on 2D Material

Abstract

Owing to its simple crystal structure, tetragonal FeSe has been considered as a perfect candidate for investigating the interplays among the superconductivity, magnetism and structural phase transition. Previous works had revealed that superconductivity could only be seen in samples with Se deficiency for the otherwise ferromagnetic tetragonal FeSe. In this study, we investigated the effect of vapor transport annealing on the crystalline quality of FeSe films deposited on flexible muscovite (mica) substrates by pulsed laser deposition. The annealing processes were conducted by sealing FeSe powder in tandem with the as-deposited FeSe films in a quartz tube. The FeSe powder was placed at a distance of about 18.5 cm from the FeSe films and the entire sealed quartz tube (about 1.2 cm in diameter) assembly was put into a Lindberg three-zone furnace and maintained a temperature gradient between the two ends of the quartz tube. The results showed that FeSe films successfully grown on flexible mica substrates and the annealing did improve the morphology and crystallinity of the films, however, the films appeared to have more inhomogeneous phases. We suspect that this might be due to uncompleted FeSe phase nucleation in non-optimum condition. The interface between the muscovite substrate and the FeSe films also could be the caused of the formation of other impurity phases, such as FeSe2 and Fe3Se4. Consequently, the obtained films exhibited only paramagnetic behaviors, and there was no sign of zero-resistance down to 2 K.