Systematic study of Bi-Sb Thin Films Grown by Molecular Beam Epitaxy via X-ray and Raman Spectroscopy

The material Bi x Sb 1−x is a promising candidate for spin-orbit torque (SOT) applications due to its potentially high figure of merit for spin-charge interconversion. This is due to the strong spin-orbit coupling and topological features in the electronic band structure in the appropriate composition range. We systematically grow a series of Bi x Sb 1−x thin films using molecular beam epitaxy and verify their composition using X-ray photoelectron spectroscopy and angle-resolved photoemission spectroscopy measurements. We then study their detailed structural characterization via x-ray diffraction, transmission electron microscopy, and reflection high energy electron diffraction. Finally, we use Raman spectroscopy to investigate the phonon modes in these thin films and compare the results with those from bulk-grown Bi x Sb 1−x crystals previously reported in the literature.