Conversion of Bi₄Se₃ to Bi₂Se₃ via post-annealing under Se flux

Bi₄Se₃ and Bi₂Se₃ are materials with topologically protected surface states that are currently the subject of extensive research as potential next-generation quantum technologies. In this study, DC magnetron sputtering was used to grow Bi₄Se₃ thin films. Conversion of Bi₄Se₃ to Bi₂Se₃ was explored via post-annealing under Se flux at moderate temperatures. The Se flux was generated by RF magnetron sputtering of a Se target onto Bi₄Se₃ films. Bi₄Se₃ was grown under two morphological distinct regimes, an atomically flat surface and faceted surface to contrast the Se incorporation through flat surfaces or grain boundaries. Energy dispersive x-ray spectroscopy was used to analyze film composition, while X-ray diffraction was used to verify crystal structure and orientation. Scanning electron microscopy additionally verified morphological changes post annealing. Determining Se percolation into the film under different temperatures and geometries allows an expansion of thin film sputtering capabilities by further control of film composition under various conditions. This work can lead to techniques in tailoring the fermi-level in chalcogenides.