Second‐Harmonic Spectroscopy for Defects Engineering Monitoring in Transition Metal Dichalcogenides

Abstract Defects engineering in transition metal dichalcogenides is a topic of intense research recently, since crystal properties can be controlled and tailored during and after fabrication. In this context, defects characterization is key to understand the material structure and enable specific applications. In this work, second‐harmonic generation (SHG) spectroscopy is used to map concentric triangular defective regions in as‐grown monolayer tungsten disulfide, demonstrating that SHG can be used for defects observation and characterization in layered noncentrosymmetric nanomaterials. In monolayer tungsten disulfide, in regions where sulfur atoms are replaced by vacancies, it is observed that the SHG signal experiences an enhancement of two orders of magnitude due to the presence of mid‐gap states. Moreover, SHG is anticorrelated with photoluminescence emission from the material, showing that both techniques can provide complementary information about the crystalline structure. In comparison with other optical characterization techniques, SHG provides fast response, does not depend on real energy transitions, and can be used for defects mapping in several other materials regardless the optical bandgap energy.