Quantitatively Deciphering Electronic Properties of Defects at Atomically Thin Transition-Metal Dichalcogenides

Defects can locally tailor the electronic properties of 2D materials, including the band gap and electron density, and possess the merit for optical and electronic applications. However, it is still a great challenge to realize rational defect engineering, which requires quantitative study of the effect of defects on electronic properties under ambient conditions. In this work, we employed tip-enhanced photoluminescence (TEPL) spectroscopy to obtain the PL spectra of different defects (wrinkle and edge) in mechanically exfoliated thin-layer transition metal dichalcogenides (TMDCs) with nanometer spatial resolution. We quantitatively obtained the band gap and electron density at defects by analyzing the wavelength and intensity ratio of excitons and trions. We further visualized the strain distribution across a wrinkle and the edge-induced reconstructive regions of the band gap and electron density by TEPL line scans. The doping effect on the Fermi level and optical performance was unveiled through comparative studies of edges on TMDC monolayers of different doping types. These quantitative results are vital to guide defect engineering and design and fabrication of TMDC-based optoelectronics devices.

Automated summary

In this study, we used tip-enhanced photoluminescence spectroscopy to quantitatively investigate the impact of defects on electronic properties in 2D materials. By analyzing the spectral features of excitons and trions, we obtained the band gap and electron density at defect sites with nanometer spatial resolution. Furthermore, using spectral line scans, we visualized the strain distribution in defect regions and the reconstructive regions of the band gap and electron density. By comparing different doping types on the edges, we revealed the doping effect on the Fermi level and optical performance.