Search for: All records

The ability to modulate optical and electrical properties of two-dimensional (2D) semiconductors has sparked considerable interest in transition metal dichalcogenides (TMDs). Herein, we introduce a facile strategy for modulating optoelectronic properties of monolayer MoSe₂with external light. Photochromic diarylethene (DAE) molecules formed a 2-nm-thick uniform layer on MoSe₂, switching between its closed- and open-form isomers under UV and visible irradiation, respectively. We have discovered that the closed DAE conformation under UV has its lowest unoccupied molecular orbital energy level lower than the conduction band minimum of MoSe₂, which facilitates photoinduced charge separation at the hybrid interface and quenches photoluminescence (PL) from monolayer flakes. In contrast, open isomers under visible light prevent photoexcited electron transfer from MoSe₂to DAE, thus retaining PL emission properties. Alternating UV and visible light repeatedly show a dynamic modulation of optoelectronic signatures of MoSe₂. Conductive atomic force microscopy and Kelvin probe force microscopy also reveal an increase in conductivity and work function of MoSe₂/DAE with photoswitched closed-form DAE. These results may open new opportunities for designing new phototransistors and other 2D optoelectronic devices.

Chiral single photons are highly sought to enhance encoding capacities or enable propagation-dependent routing in nonreciprocal devices. Unfortunately, most semiconductor quantum emitters (QEs) produce only linear polarized photons unless external magnets are applied. Magnetic proximity coupling utilizing 2D ferromagnets promises to make bulky external fields obsolete. Here we directly grow Fe-doped MoS₂(Fe:MoS₂) via chemical vapor deposition that displays pronounced hard ferromagnetic properties even in monolayer form. This approach with monolayer ferromagnets enables full utilization of the strain from the pillar stressor to form QE in WSe₂deterministically. The Fe:MoS₂/WSe₂heterostructures display strong hysteretic magneto-response and high-purity chiral single photons with a circular polarization degree of 92 ± 1% (74% average) without external magnetic fields. Furthermore, the chiral single photons are robust against uncontrolled twist-angle and external stray-fields. This ability to manipulate quantum states and transform linear polarized photons into high-purity chiral photons on-chip enables nonreciprocal device integration in quantum photonics.

Two-dimensional (2D) heterostructures (HS) formed by transition-metal dichalcogenide (TMDC) monolayers offer a unique platform for the study of intralayer and interlayer excitons as well as moiré-pattern-induced features. Particularly, the dipolar charge-transfer exciton comprising an electron and a hole, which are confined to separate layers of 2D semiconductors and Coulomb-bound across the heterojunction interface, has drawn considerable attention in the research community. On the one hand, it bears significance for optoelectronic devices, e.g. in terms of charge carrier extraction from photovoltaic devices. On the other hand, its spatially indirect nature and correspondingly high longevity among excitons as well as its out-of-plane dipole orientation render it attractive for excitonic Bose–Einstein condensation studies, which address collective coherence effects, and for photonic integration schemes with TMDCs. Here, we demonstrate the interlayer excitons’ out-of-plane dipole orientation through angle-resolved spectroscopy of the HS photoluminescence at cryogenic temperatures, employing a tungsten-based TMDC HS. Within the measurable light cone, the directly-obtained radiation profile of this species clearly resembles that of an in-plane emitter which deviates from that of the intralayer bright excitons as well as the other excitonic HS features recently attributed to artificial superlattices formed by moiré patterns.

Two-dimensional semiconductors, including transition metal dichalcogenides, are of interest in electronics and photonics but remain nonmagnetic in their intrinsic form. Previous efforts to form two-dimensional dilute magnetic semiconductors utilized extrinsic doping techniques or bulk crystal growth, detrimentally affecting uniformity, scalability, or Curie temperature. Here, we demonstrate an in situ substitutional doping of Fe atoms into MoS₂monolayers in the chemical vapor deposition growth. The iron atoms substitute molybdenum sites in MoS₂crystals, as confirmed by transmission electron microscopy and Raman signatures. We uncover an Fe-related spectral transition of Fe:MoS₂monolayers that appears at 2.28 eV above the pristine bandgap and displays pronounced ferromagnetic hysteresis. The microscopic origin is further corroborated by density functional theory calculations of dipole-allowed transitions in Fe:MoS₂. Using spatially integrating magnetization measurements and spatially resolving nitrogen-vacancy center magnetometry, we show that Fe:MoS₂monolayers remain magnetized even at ambient conditions, manifesting ferromagnetism at room temperature.