Monolayers of semiconducting transition metal dichalcogenides (TMDCs) are known for their unique excitonic photoluminescence (PL), which can be tuned by interfacing them with other materials. However, integrating TMDCs into van der Waals heterostructures often results in a significant quenching of the PL because of an increased rate of nonradiative recombination processes. We demonstrate a wide-range tuning of the PL intensity of monolayer MoS2 interfaced with another layered semiconductor, CrSBr. We discover that a thin CrSBr up to ≈20 nm in thickness enhances the PL of MoS2, while a thicker material causes PL quenching, which is associated with changes in the excitonic makeup driven by the charge redistribution in the CrSBr/MoS2 heterostructure. Transport measurements, Kelvin probe force microscopy, and first-principles calculations indicate that this charge redistribution most likely causes n- to p-type doping transition of MoS2 upon contact with CrSBr, facilitated by the type II band alignment and the tendency of CrSBr to act as an electron sink. Furthermore, we fabricate an efficient AC-regime photodetector with a responsivity of 105 A/W from a MoS2/CrSBr heterostructure.

• Klíčová slova
• CrSBr, MoS2, enhancement, heterostructures, optoelectronics, photoluminescence, quenching,
• Publikační typ
• časopisecké články MeSH

The discovery of two-dimensional van der Waals magnets has greatly expanded our ability to create and control nanoscale quantum phases. A unique capability emerges when a two-dimensional magnet is also a semiconductor that features tightly bound excitons with large oscillator strengths that fundamentally determine the optical response and are tunable with magnetic fields. Here we report a previously unidentified type of optical excitation-a magnetic surface exciton-enabled by the antiferromagnetic spin correlations that confine excitons to the surface of CrSBr. Magnetic surface excitons exhibit stronger Coulomb attraction, leading to a higher binding energy than excitons confined in bulk layers, and profoundly alter the optical response of few-layer crystals. Distinct magnetic confinement of surface and bulk excitons is established by layer- and temperature-dependent exciton reflection spectroscopy and corroborated by ab initio many-body perturbation theory calculations. By quenching interlayer excitonic interactions, the antiferromagnetic order of CrSBr strictly confines the bound electron-hole pairs within the same layer, regardless of the total number of layers. Our work unveils unique confined excitons in a layered antiferromagnet, highlighting magnetic interactions as a vital approach for nanoscale quantum confinement, from few layers to the bulk limit.

• Publikační typ
• časopisecké články MeSH

Magnetism in two-dimensional materials reveals phenomena distinct from bulk magnetic crystals, with sensitivity to charge doping and electric fields in monolayer and bilayer van der Waals magnet CrI3. Within the class of layered magnets, semiconducting CrSBr stands out by featuring stability under ambient conditions, correlating excitons with magnetic order and thus providing strong magnon-exciton coupling, and exhibiting peculiar magneto-optics of exciton-polaritons. Here, we demonstrate that both exciton and magnetic transitions in bilayer and trilayer CrSBr are sensitive to voltage-controlled field-effect charging, exhibiting bound exciton-charge complexes and doping-induced metamagnetic transitions. Moreover, we demonstrate how these unique properties enable optical probes of local magnetic order, visualizing magnetic domains of competing phases across metamagnetic transitions induced by magnetic field or electrostatic doping. Our work identifies few-layer CrSBr as a rich platform for exploring collaborative effects of charge, optical excitations, and magnetism.

• Publikační typ
• časopisecké články MeSH

van der Waals heterostructures of two-dimensional materials have unveiled frontiers in condensed matter physics, unlocking unexplored possibilities in electronic and photonic device applications. However, the investigation of wide-gap, high-κ layered dielectrics for devices based on van der Waals structures has been relatively limited. In this work, we demonstrate an easily reproducible synthesis method for the rare-earth oxyhalide LaOBr, and we exfoliate it as a 2D layered material with a measured static dielectric constant of 9 and a wide bandgap of 5.3 eV. Furthermore, our research demonstrates that LaOBr can be used as a high-κ dielectric in van der Waals field-effect transistors with high performance and low interface defect concentrations. Additionally, it proves to be an attractive choice for electrical gating in excitonic devices based on 2D materials. Our work demonstrates the versatile realization and functionality of 2D systems with wide-gap and high-κ van der Waals dielectric environments.

• Klíčová slova
• crystal synthesis, dielectric, excitons, field-effect transistors, heterostructures, high-k, two-dimensional materials,
• Publikační typ
• časopisecké články MeSH

Atomically thin materials, like semiconducting transition metal dichalcogenides (S-TMDs), are highly sensitive to the environment. This opens up an opportunity to externally control their properties by changing their surroundings. Photoluminescence and reflectance contrast techniques are employed to investigate the effect of metallic substrates on optical properties of MoSe2 monolayer (ML). The optical spectra of MoSe2 MLs deposited on Pt, Au, Mo and Zr have distinctive metal-related lineshapes. In particular, a substantial variation in the intensity ratio and the energy separation between a negative trion and a neutral exciton is observed. It is shown that using metals as substrates affects the doping of S-TMD MLs. The explanation of the effect involves the Schottky barrier formation at the interface between the MoSe2 ML and the metallic substrates. The alignment of energy levels at the metal/semiconductor junction allows for the transfer of charge carriers between them. We argue that a proper selection of metallic substrates can be a way to inject appropriate types of carriers into the respective bands of S-TMDs.

• Publikační typ
• časopisecké články MeSH