Twisted two-dimensional transition metal dichalcogenide (TMD) moirésuperlattices provide an additional degree of freedom to engineer electronic and optical properties. Nevertheless, controllable synthesis of marginally twisted homo TMD moireś uperlattices is still a challenge. Here, physical vapor deposition grown spiral WS 2 nanosheets are demonstrated to be a marginally twisted moirésuperlattice using scanning tunneling microscopy and spectroscopy. Periodic moirésuperlattices are found on the third layer (3L) and 4L of the spiral WS 2 nanosheet owing to the marginally twisted alignment between two neighboring layers, resulting in a highly localized flat band near the valence band maximum. Their bandgap depends on atomic stacking configurations, which gives a good interpretation for split moiréexcitons using photoluminescence at 77 K. This work can benefit the development of twisted homo TMD moirésuperlattices and could promote the profound research of twisted TMDs in the prospective field, such as strongly correlated physics and twistronics.
Substitutional lanthanide doping of 2D transition metal dichalcogenides (TMDs) is expected to be a promising strategy to engineer optical, electronic, and optoelectronic properties of TMDs. Understanding the interactions between lanthanide dopants and 2D TMDs host is one of the key problems to be resolved for their profound research studies. Herein, the interactions between Ce dopants and monolayer WS2 in a physical vapor deposition grown Ce‐doped WS2 monolayer are studied by combining scanning tunneling microscopy with optical characterizations with high spatial and temporal resolution. It is found that the highly anisotropic crystal field can effectively split the energy levels of the Ce dopants’ f orbital. The electrons in the split energy levels can bind the holes in the valence band maximum of the Ce‐doped WS2, forming optical bright excitons. These excitons collide with the free A excitons when increasing the pump fluences, reducing the A exciton's lifetime. This study may be beneficial for the design and fabrication of optical, electronic, and optoelectronic devices based on lanthanide‐doped TMDs.
1T-TaS2 has attracted much attention recently due to its abundant charge density wave phases. In this work, high-quality two-dimensional 1T-TaS2 crystals were successfully synthesized by a chemical vapor deposition method with controllable layer numbers, confirmed by the structural characterization. Based on the as-grown samples, their thickness-dependency nearly commensurate charge density wave/commensurate charge density wave phase transitions was revealed by the combination of the temperature-dependent resistance measurements and Raman spectra. The phase transition temperature increased with increasing thickness, but no apparent phase transition was found on the 2~3 nm thick crystals from temperature-dependent Raman spectra. The transition hysteresis loops due to temperature-dependent resistance changes of 1T-TaS2 can be used for memory devices and oscillators, making 1T-TaS2 a promising material for various electronic applications.
ZnGeP 2 (ZGP) crystals have attracted tremendous attention for their applications as frequency conversion devices. Nevertheless, the existence of native point defects, including at the surface and in the bulk, lowers their laser-induced damage threshold by increasing their absorption and forming starting points of the damage, limiting their applications. Here, native point defects in a ZGP crystal are fully studied by the combination of high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and optical measurements. The atomic structures of the native point defects of the Zn vacancy, P vacancy, and Ge-Zn antisite were directly obtained through an HAADF-STEM, and proved by photoluminescence (PL) spectra at 77 K. The carrier dynamics of these defects are further studied by ultrafast pump-probe spectroscopy, and the decay lifetimes of 180.49, 346.73, and 322.82 ps are attributed to the donor V p + → valence band maximum (VBM) recombination, donor Ge Zn + → VBM recombination, and donor-acceptor pair recombination of V p + → V Zn − , respectively, which further confirms the assignment of the electron transitions. The diagrams for the energy bands and excited electron dynamics are established based on these ultrahigh spatial and temporal results. Our work is helpful for understanding the interaction mechanism between a ZGP crystal and ultrafast laser, doing good to the ZGP crystal growth and device fabrication.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.