High-Quality FeTe1−xSex Monolayer Films on SrTiO3(001) Substrates Grown by Molecular Beam Epitaxy**Supported by the Ministry of Science and Technology of China under Grant Nos 2015CB921000, 2016YFA0401000, 2015CB921301 and 2016YFA0300300, and the National Natural Science Foundation of China under Grant Nos 11274381, 11574371, 11274362, 1190020, 11334012 and 11674371.

Abstract

We report the growth process of FeTe1−xSex () monolayer films on SrTiO3 (STO) substrates through molecular beam epitaxy and discuss the possible ways to improve the film quality. By exploring the parameters of substrate treatment, growth control and post growth annealing, we successfully obtain a series of FeTe1−xSex monolayer films. In the whole growth process, we find the significance of the temperature control through surface roughness monitored by the reflection high-energy electron diffraction and scanning tunneling microscopy. We obtain the best quality of FeSe monolayer films with the STO substrate treated at T = 900–950°C before growth, the FeSe deposited at T = 310°C during growth and annealed at T = 380°C after growth. For FeTe1−xSex (), both the growth temperature and annealing temperature decrease to T = 260°C. According to the angle-resolved photoemission spectroscopy measurements, the superconductivity of the FeTe1−xSex film is robust and insensitive to Se concentration. All the above are instructive for further investigations of the superconductivity in FeTe1−xSex films.