Femtosecond Laser‐Induced Periodic Surface Structuring of the Topological Insulator Bismuth Telluride

Surface structuring of topological insulator Bi2Te3 single crystals with femtosecond laser by varying pulses N and energy E is reported. Interesting effects related to laser-induced periodic surface structures formation in this class of materials are evidenced. At low pulse energy, a clear formation of periodic, subwavelength ripples oriented orthogonally to the laser polarization is observed; those are restricted to an annular region surrounding a featureless central disk as the laser energy progressively increases. The structural analysis shows that some degree of crystallinity is preserved in the rippled area, but the central disk is amorphous resembling what is observed for germanium (Ge) and is associated with the hindering of surface structure formation due to a thick melted surface layer. Interestingly, at larger fluence or number of pulses, a transition to suprawavelength grooves occurs within the annular region covered by surface structures. The findings demonstrate a clear incubation behavior, suggesting that the formation of laser-induced periodic surface structures is coherent with the general features of the process already reported for other materials. However, the disappearance of these structures in the central area, possibly resulting from the influence of the depth of the melt layer, indicates a mixed behavior for Bi2Te3.