2024/11/08 by Pavel V. Kolesnichenko, Lukas Wittenbecher, Qianhui Zhang +5 · 1 voice
Materials Science · Biochemistry, Genetics and Molecular Biology · #2D Materials and Applications #MXene and MAX Phase Materials #Advanced biosensing and bioanalysis techniques
paper · pdf · doi:10.1021/acs.nanolett.4c03807
openalex publication_date 2024/11/08 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/30
High Resolution Image Download MS PowerPoint Slide Two-dimensional semiconducting transition metal dichalcogenides are promising materials for optoelectronic applications due to their strongly bound excitons. While bright excitons have been thoroughly scrutinized, dark excitons have been much less investigated, as they are not directly observable with far-field spectroscopy. However, with their nonzero momenta, dark excitons are significant for applications requiring long-range transport or coupling to external fields. We access such dark excitons in WS 2 monolayer using transient photoemission electron microscopy with subdiffraction limited spatial resolution (75 nm) and exceptionally high temporal resolution (13 fs). Image time series of the monolayer are recorded at several different fluences. We directly observe the ultrafast formation of dark K-Λ excitons occurring within 14–50 fs and follow their subsequent picosecond decay. We distinguish exciton dynamics between the monolayer’s interior and edges and conclude that the picosecond-scale evolution of dark excitations is defect-mediated while intervalley scattering is not affected by the defects.