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Process-induced strain engineering is an effective method of crafting the strain state in 2D materials. Much like how it has been used in the fabrication of Si-based electronics, stressed thin films are deposited onto van der Waals-bonded 2D systems where relaxation of the stressor layer causes strain transfer into the 2D materials. This type of strain engineering can be used on a device-by-device level and be controlled for strain magnitude, compression or tension, uniaxiality or biaxiality, and directionality relative to crystal structure by varying film stress or geometry. One critical question in translating this technique to 2D materials is how temperature and time stable this strain engineering process is. In this work, we explore these factors through Raman spectroscopic mapping and photoluminescence spectroscopy ranging in temperatures from 293 to 4 K. It is shown that strain engineering with thin film stressors is equally persistent at all temperatures examined and time stable for a period of at least 14 months (the period of observation). These results suggest that process-induced strain engineering may be used to tune any number of interesting low-temperature properties in 2D materials and that any devices engineered in this way will have long-term stability for applications in electronics, optoelectronics, and beyond. [ABSTRACT FROM AUTHOR]

Isolated spins are the focus of intense scientific exploration due to their potential role as qubits for quantum information science. Optical access to single spins, demonstrated in III-V semiconducting quantum dots, has fueled research aimed at realizing quantum networks. More recently, quantum emitters in atomically thin materials such as tungsten diselenide have been demonstrated to host optically addressable single spins by means of electrostatic doping the localized excitons. Electrostatic doping is not the only route to charging localized quantum emitters and another path forward is through band structure engineering using van der Waals heterojunctions. Critical to this second approach is to interface tungsten diselenide with other van der Waals materials with relative band-alignments conducive to the phenomenon of charge transfer. In this work we show that the Type-II band-alignment between tungsten diselenide and chromium triiodide can be exploited to excite localized charged excitons in tungsten diselenide. Leveraging spin-dependent charge transfer in the device, we demonstrate spin selectivity in the preparation of the spin-valley state of localized single holes. Combined with the use of strain-inducing nanopillars to coordinate the spatial location of tungsten diselenide quantum emitters, we uncover the possibility of realizing large-scale deterministic arrays of optically addressable spin-valley holes in a solid state platform.Quantum emitters in atomically thin materials host optically addressable single spins. Here, the authors demonstrate spin selectivity in the preparation of the spin-valley state of site-controlled localized single holes in CrI3/WSe2 heterostructures. [ABSTRACT FROM AUTHOR]

Monolayer WSe2 hosts bright single-photon emitters. Because of its compliance, monolayer WSe2 conforms to patterned substrates without breaking, thus creating the potential for large local strain, which is one activation mechanism of its intrinsic quantum emitters. Here, we report an approach to creating spatially isolated quantum emitters from WSe2 monolayers that display clean spectra with little detrimental background signal. We show that a bilayer of hexagonal boron nitride and WSe2 placed on a nanostructured substrate can be used to create and shape wrinkles that communicate local strain to WSe2, thus creating quantum emitters that are isolated from substrate features. We compare quantum emitters created directly on top of substrate features with quantum emitters formed along wrinkles and find that the spectra of the latter consist of mainly a single peak and a low background fluorescence. We also discuss possible approaches to controlling the emitter position along hexagonal boron nitride wrinkles. [ABSTRACT FROM AUTHOR]

van der Waals ferromagnets have gained significant interest due to their unique ability to provide magnetic response even at the level of a few monolayers. Particularly in combination with 2D semiconductors, such as the transition metal dichalcogenide WSe2, one can create heterostructures that feature unique magneto-optical response in the exciton emission through the magnetic proximity effect. Here we use 0D quantum emitters in WSe2 to probe for the ferromagnetic response in heterostructures with Fe3GT and Fe5GT ferromagnets through an all-optical read-out technique that does not require electrodes. The spectrally narrow spin-doublet of the WSe2 quantum emitters allowed to fully resolve the hysteretic magneto-response in the exciton emission, revealing the characteristic signature of both ferro- and antiferromagnetic proximity coupling that originates from the interplay among Fe3GT or Fe5GT, a thin surface oxide, and the spin doublets of the quantum emitters. Our work highlights the utility of 0D quantum emitters for probing interface magnetic dipoles in vdW heterostructures with high precision. The observed hysteretic magneto response in the exciton emission of quantum emitters adds further new degrees of freedom for spin and g-factor manipulation of quantum states.

Monolayer transition metal dichalcogenides (TMDCs) have recently emerged as a host material for localized optically active quantum emitters that generate single photons. (1-5) Here, we investigate fully localized excitons and trions from such TMDC quantum emitters embedded in a van der Waals heterostructure. We use direct electrostatic doping through the vertical heterostructure device assembly to generate quantum confined trions. Distinct spectral jumps as a function of applied voltage bias, and excitation power-dependent charging, demonstrate the observation of the two different excitonic complexes. We also observe a reduction of the intervalley electron-hole exchange interaction in the confined trion due to the addition of an extra electron, which is manifested by a decrease in its fine structure splitting. We further confirm this decrease of exchange interaction for the case of the charged states by a comparative study of the circular polarization resolved photoluminescence from individual excitonic states. The valley polarization selection rules inherited by the localized trions will provide a pathway toward realizing a localized spin-valley-photon interface.