Raman studies of irradiation-induced defects in thin flakes of Bi2Se3 and related materials

We report a Raman spectroscopy study of exfoliated Bi2Se3 flakes of various thicknesses after exposure to irradiation by lasers, electron-beam and oxygen plasma. We observe little effect of irradiations on Raman spectra of thicker ($>$50 nm) Bi2Se3 flakes, which exhibit characteristic Raman peaks at $\sim $130 cm-1 and $\sim $170 cm-1 similar to bulk Bi2Se3. However, spectra from irradiated thinner ($<$20 nm) flakes show the appearance of an extra Raman peak ($\sim $250 cm-1) and attenuation and broadening of the peaks at $\sim $130 cm-1 and $\sim $170 cm-1. This additional peak is not seen in flakes exposed to electron-beam irradiation and lower-power lasers. We interpret the new peak in the Raman spectra as due to irradiation-induced disorder. We also performed similar Raman studies on Bi2Te3, Sb2Se3 and Sb2Te3.