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After the recent finding that CrI 3 , displays ferromagnetic order down to its monolayer, extensive studies have followed to pursue new two-dimensional (2D) magnetic materials. In this article, we report on the growth of single crystal CrCl 3 in the layered monoclinic phase. The system after mechanical exfoliation exhibits stability in ambient air (the degradation occurs on a time scale at least four orders of magnitude longer than is observed for CrI 3 ). By means of mechanical cleavage and atomic force microscopy (AFM) combined with optical identification, we demonstrate the systematic isolation of single and few layer flakes onto 270 nm and 285 nm SiO 2 /Si (100) substrates with lateral size larger than graphene flakes isolated with the same method. The layer number identification has been carried with statistically significant data, quantifying the optical contrast as a function of the number of layers for up to six layers. Layer dependent optical contrast data have been fitted within the Fresnel equation formalism determining the real and imaginary part of the wavelength dependent refractive index of the material. A layer dependent (532 nm) micro-Raman study has been carried out down to two layers with no detectable spectral shifts as a function of the layer number and with respect to the bulk.

Two-dimensional (2D) magnets like chromium trihalides CrX3 (X = I, Br, Cl) represent a frontier for spintronics applications and, in particular, CrCl3 has attracted research interest for its relative stability...

We studied the effects of thermal annealing (in air and in ultra-high vacuum from room temperature up to 300 °C) of mechanically exfoliated mono-layer and few layer MoS2 onto 270 nm SiO2/Si(1 0 0). The experiments were performed with optical microscopy, atomic force microscopy, non resonant Raman spectroscopy, and photoluminescence (PL) spectroscopy on the mono-layer flakes. We demonstrate the presence of a nano-confined water layer at the interface with the silicon substrate. The thickness of this water layer can be increased by immersing the exfoliated samples in water for one hour, or decreased by post exfoliation annealing. Then, we directly demonstrate the sublimation with annealing of the bottom layer at the interface with SiO2. PL experiments performed on the mono-layers in the 250 °C–300 °C annealing range, together with previous x-ray photoemission experiments, demonstrate the direct correlation of the PL integrated spectral intensity with the concentration of sulfur vacancies that are passivated by oxygen after exposure to air. Namely, the vacancy formation is triggered in the 250 °C–300 °C range independently of the annealing environment, and correspondingly in the same temperature range the PL spectral intensity proportionally increases. With respect to pristine exfoliated MoS2 we estimate via PL an increase by a factor three of the vacancy concentration upon annealing to 300 °C. This, considering the typical vacancy concentration values of mechanical exfoliated MoS2, leads to sulfur vacancy concentration values close to 1014 cm−2. Considering such high value, the sublimation of the bottom layer is then explained via oxidation of the sulfur vacancies upon dissociation of water preferentially supplied by the film present at the interface with the SiO2 substrate.

Via experiments performed by varying the doping level of single-layer mechanically exfoliated MoS2 via post exfoliation thermal annealing in the 200÷300 °C temperature range, we study the power dependent room...