Monolayers (MLs) of transition‐metal dichalcogenides host efficient single‐photon emitters (SPEs) usually associated to the presence of nanoscale mechanical deformations or strain. Large‐scale spatial control of strain would enhance the scalability of such SPEs and allow for their incorporation into photonic structures. Here, the formation of regular arrays of strained hydrogen‐filled one‐layer‐thick micro‐domes obtained by H‐ion irradiation and lithography‐based approaches is reported. Typically, the H₂ liquefaction for temperatures T<32 K causes the disappearance of the domes preventing their use as potential SPEs. Here, it is shown that the dome deflation can be overcome by hBN heterostructuring, that is by depositing thin hBN flakes on the domes. This leads to the preservation of the dome structure at all temperatures, as found by micro‐Raman and micro‐photoluminescence (µ‐PL) studies. Eventually, spatially controlled hBN‐capped WS₂ domes show the appearance, at 5 K, of intense emission lines originating from localized excitons, which are shown to behave as quantum emitters here. The electronic properties of the emitters are addressed by time‐resolved µ‐PL yielding time decays of 1–10 ns, and by magneto‐µ‐PL measurements. The latter provide an exciton magnetic moment a factor of two larger than the value observed in planar strain‐free MLs.

Mechanical deformations and ensuing strain are routinely exploited to tune the band gap energy and to enhance the functionalities of two-dimensional crystals. In this Letter, we show that strain leads also to a strong modification of the exciton magnetic moment in ${\mathrm{WS}}_2$ monolayers. Zeeman-splitting measurements under magnetic fields up to 28.5 T were performed on single, one-layer-thick ${\mathrm{WS}}_2$ microbubbles. The strain of the bubbles causes a hybridization of $k$-space direct and indirect excitons resulting in a sizable decrease in the modulus of the $g$ factor of the ground-state exciton. These findings indicate that strain may have major effects on the way the valley number of excitons can be used to process binary information in two-dimensional crystals.

Optical properties of thin layers of rhenium diselenide (${\mathrm{ReSe}}_2$ ) with thicknesses ranging from mono- (1 ML) to nona-layer (9 MLs) are demonstrated. The photoluminescence (PL) and Raman scattering were measured at low ($T=5\mathrm{K}$ ) and room ($T=300\mathrm{K}$ ) temperature, respectively. The PL spectra of ${\mathrm{ReSe}}_2$ layers display two well-resolved emission lines, which blueshift by about 120 meV when the layer thickness decreases from 9 MLs to a monolayer. A rich structure of the observed low-energy Raman scattering modes can be explained within a linear chain model. The two phonon modes of intralayer vibrations, observed in Raman scattering spectra at about $120{\mathrm{cm}}^{-1}$ , exhibit very sensitive and opposite evolution as a function of layer thickness. It is shown that their energy difference can serve as a convenient and reliable tool to determine the thickness of ${\mathrm{ReSe}}_2$ flakes in the few-layer limit.

Moiré excitons (MXs) are electron-hole pairs localised by the periodic (moiré) potential forming in two-dimensional heterostructures (HSs). MXs can be exploited, e.g., for creating nanoscale-ordered quantum emitters and achieving or probing strongly correlated electronic phases at relatively high temperatures. Here, we studied the exciton properties of WSe₂/MoSe₂ HSs from T = 6 K to room temperature using time-resolved and continuous-wave micro-photoluminescence also under a magnetic field. The exciton dynamics and emission lineshape evolution with temperature show clear signatures that MXs de-trap from the moiré potential and turn into free interlayer excitons (IXs) for temperatures above 100 K. The MX-to-IX transition is also apparent from the exciton magnetic moment reversing its sign when the moiré potential is not capable of localising excitons at elevated temperatures. Concomitantly, the exciton formation and decay times reduce drastically. Thus, our findings establish the conditions for a truly confined nature of the exciton states in a moiré superlattice with increasing temperature and photo-generated carrier density.

Atomically thin materials, like semiconducting transition metal dichalcogenides, are highly sensitive to the environment. This opens up an opportunity to externally control their properties by changing their surroundings. In this work, high-quality van der Waals heterostructures assembled from hBN-encapsulated monolayer MoS₂ are studied with the aid of photoluminescence, photoluminescence excitation, and reflectance contrast experiments. We demonstrate that carrier concentration in MoS₂ monolayers, arising from charge transfer from impurities in the substrate, can be significantly tuned within one order of magnitude by the modification of the bottom hBN flake thickness. The studied structures, characterized by spectral lines with linewidths approaching the narrow homogeneously broadened limit enabled observations of subtle optical and spin-valley properties of excitonic complexes. Our results allowed us to resolve three optically-active negatively charged excitons in MoS₂ monolayers, which are assigned to the intravalley singlet, intervalley singlet, and intervalley triplet states.

Gallium sulfide is a semiconducting material with a layered structure and a characteristic low interlayer interaction. Because of weak van der Waals forces, GaS crystals are relatively easy to exfoliate to very thin layers. In this work nanometric-GaS layers were obtained by a micro-mechanical exfoliation process and were transferred to Si/SiO ₂ substrate. The thickness of these layers was estimated from AFM measurements. Raman spectra were collected for different layer thicknesses ranging from one layer to bulk crystal. An analytical function fitted to experimental data is proposed to determine layer thickness from Raman measurements. For the first time, the Raman position and the FWHM of the main Raman peaks were measured on very thin GaS layers as a function of temperature in the range from 80 to 470 K. The first order temperature coefficients of the A _1g Raman peaks were determined. Phonon decay due to anharmonic processes at temperatures above 300 K in layers of thickness below 4 nm was observed. Contribution of optical phonon scattering processes to thermal properties of very thin GaS layers is discussed.