Scanning tunneling microscopy studies of ultrafast laser damage on bulk MoS₂

We present initial results from a novel instrument combining scanning tunneling microscopy (STM) with ultrafast laser excitation to investigate laser-induced damage mechanism and carrier dynamics at atomic resolution. Using a 1030nm Yb:KGW laser delivering 77 fs Gaussian pulses, we studied in situ single-shot damage mechanisms in bulk MoS₂ at peak fluences ranging from 0.8 to 1.2 J/cm² under s-polarized illumination at a 68 degrees incident angle. The damage morphology exhibits fluence-dependent characteristics, with a single boundary at lower fluences transitioning to dual boundaries at higher fluences. At lower fluences, laser-induced periodic surface structures (LIPSS) emerge parallel to the polarization with λ/4 periodicity, while higher fluences produce ridge formation. In regions exceeding 1/e of the peak fluence, we observed nano-crack patches. Furthermore, we investigated defects evolution under ultrafast laser irradiation, providing insights of ultrafast laser damage mechanism at atomic scale. Complementary surface photovoltage (SPV) measurements elucidate carrier dynamics in bulk MoS₂, offering crucial insights for next-generation optoelectronic applications.