Due to the excellent electrical transport properties and optoelectronic performance, thin indium selenide (InSe) has recently attracted attention in the field of 2D semiconducting materials.

Strain is a powerful tool to modify the optical properties of semiconducting transition metal dichalcogenides like MoS 2 , MoSe 2 , WS 2 and WSe 2 . In this work we provide a thorough description of the technical details to perform uniaxial strain measurements on these two-dimensional semiconductors and we provide a straightforward calibration method to determine the amount of applied strain with high accuracy. We then employ reflectance spectroscopy to analyze the strain tunability of the electronic properties of single-, bi-and tri-layer MoS 2 , MoSe 2 , WS 2 and WSe 2 . Finally, we quantify the flake-to-flake variability by analyzing 15 different single-layer MoS 2 flakes.

We present a mechanochemical procedure, with solvent-free, greenchemistry credentials, to grow all-inorganic CsPbBr 3 perovskite. The crystal structure of this perovskite and its correlations with the physicochemical properties have been studied. Synchrotron X-ray diffraction (SXRD) and neutron powder diffraction (NPD) allowed us to follow the crystallographic behavior from 4 to 773 K. Unreported features like the observed negative thermal expansion of the b unit-cell parameter stem from octahedral distortions in the 4−100 K temperature range. The mechanochemical synthesis was designed to reduce the impact energy during the milling process, leading to a defect-free, well-crystallized sample characterized by a minimum unit-cell volume and octahedral tilting angles in the low-temperature orthorhombic perovskite framework, defined in the Pbnm space group. The UV−vis diffuse reflectance spectrum shows a reduced band gap of 2.22(3) eV, and the photocurrent characterization in a photodetector reveals excellent properties with potential applications of this material in optoelectronic devices.

Van der Waals materials with narrow energy gaps and efficient response over a broadband optical spectral range are key to widen the energy window of nanoscale optoelectronic devices. Here, we characterize FePS3 as an appealing narrow-gap p-type semiconductor with an efficient broadband photo-response, a high refractive index, and a remarkable resilience against air and light exposure. To enable fast prototyping, we provide a straightforward guideline to determine the thickness of few-layered FePS3 nanosheets extracted from the optical transmission characteristics of several flakes. The analysis of the electrical photo-response of FePS3 devices as a function of the excitation energy confirms a narrow gap suitable for near IR detection (1.23 eV) and, more interestingly, reveals a broad spectral responsivity up to the ultraviolet region. The experimental estimate for the gap energy is corroborated by ab-initio calculations. An analysis of photocurrent as a function of gate voltage and incident power reveals a photo-response dominated by photogating effects. Finally, aging studies of FePS3 nanosheets under ambient conditions show a limited reactivity of the outermost layers of flakes in long exposures to air.

The isolation of air-sensitive two-dimensional (2D) materials and the race to achieve a better control of the interfaces in van der Waals heterostructures has pushed the scientific community towards the development of experimental setups that allow to exfoliate and transfer 2D materials under inert atmospheric conditions. These systems are typically based on over pressurized N2 of Ar gloveboxes that require the use of very thick gloves to operate within the chamber or the implementation of several motorized micro-manipulators. Here, we set up a deterministic transfer system for 2D materials within a gloveless anaerobic chamber. Unlike other setups based on over-pressurized gloveboxes, in our system the operator can manipulate the 2D materials within the chamber with bare hands. This experimental setup allows us to exfoliate 2D materials and to deterministically place them at a desired location with accuracy in a controlled O2-free and very low humidity (<2% RH) atmosphere. We illustrate the potential of this system to work with air-sensitive 2D materials by comparing the stability of black phosphorus and perovskite flakes inside and outside the anaerobic chamber. The deterministic transfer methods, that allow for the placement of 2D materials onto a user defined specific location with an unprecedented degree of accuracy and reliability, are at the origin of the large success of two-dimensional (2D) materials research. [1][2][3][4][5][6] This control over the position of the transferred flakes has been exploited to fabricate devices with rather complex architectures as well as to assemble artificial stacks of dissimilar 2D materials to build-up the so-called van der Waals heterostructures. 7-10 In particular, deterministic placement methods have enabled the fabrication of

We show how the excitonic features of biaxial MoS 2 flakes are very sensitive to biaxial strain. We find a lower bound for the gauge factors of the A exciton and B exciton of (−41±2) meV/% and (−45±2) meV/% respectively, which are larger than those found for single-layer MoS 2 . Interestingly, the interlayer exciton feature also shifts upon biaxial strain but with a gauge factor that is systematically larger than that found for the A exciton, (−48±4) meV/%. We attribute this larger gauge factor for the interlayer exciton to the strain tunable van der Waals interaction due to the Poisson effect (the interlayer distance changes upon biaxial strain).

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We present microfabricated thermal actuators to engineer the biaxial strain in two-dimensional (2D) materials. These actuators are based on microheater circuits patterned onto the surface of a polymer with a high thermal expansion coefficient. By running current through the microheater one can vary the temperature of the polymer and induce a controlled biaxial expansion of its surface. This controlled biaxial expansion can be transduced to biaxial strain to 2D materials, placed onto the polymer surface, which in turn induces a shift of the optical spectrum. Our thermal strain actuators can reach a maximum biaxial strain of 0.64 % and they can be modulated at frequencies up to 8 Hz. The compact geometry of these actuators results in a negligible spatial drift of 0.03 µm/ºC, which facilitates their integration in optical spectroscopy measurements. We illustrate the potential of this strain engineering platform to fabricate a strain-actuated optical modulator with single-layer MoS2.