Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have demonstrated a very strong application potential. In order to realize it, the synthesis of stoichiometric 2D TMDCs on a large scale is crucial. Here, we consider a typical TMDC representative, MoS 2 , and present an approach for the fabrication of well-ordered crystalline films via the crystallization of a thin amorphous layer by annealing at 800 °C, which was investigated in terms of long-range and short-range orders. Strong preferential crystal growth of layered MoS 2 along the ⟨002⟩ crystallographic plane from the as-deposited 3D amorphous phase is discussed together with the mechanism of the crystallization process disclosed by molecular dynamic simulations using the Vienna Ab initio Simulation Package. We believe that the obtained results may be generalized for other 2D materials. The proposed approach demonstrates a simple and efficient way to fabricate thin 2D TMDCs for applications in nanoand optoelectronic devices.

The paper reports on ≈1.5 μm Stokes photoluminescence (PL) emission and upconversion photoluminescence (UCPL) emission in the visible and near-infrared spectral region in Er3+-doped Ge25Ga8As2S65 chalcogenide glasses at pumping wavelengths of 980 and 1550 nm. The ≈1.5 μm PL emission spectra are broadened with increasing concentration of Er ions which is discussed in terms of radiation trapping and UCPL dynamics affecting the Er3+: 4I13/2 level lifetime. The UCPL emission was observed at ≈530, ≈550, ≈660, ≈810 and ≈990 nm and its overall intensity as well as red-to-green UCPL emission intensity ratio increases with increasing Er concentration. To explore the UCPL dynamics we measured double logarithmic dependency of green (≈550 nm) and red (≈660 nm) UCPL emission versus pump power at pumping wavelength of 975 nm. Moreover, we measured quadrature frequency resolved spectroscopy (QFRS) on green UCPL emission (≈550 nm) using 975 nm pumping wavelength and various excitation powers. The QFRS spectra on green UCPL were analyzed in term of QFRS transfer function for three-level model from which we deduced energy transfer upconversion rate w11 (s−1) originating from Er3+: 4I11/2, 4I11/2→4F7/2, 4I15/2 transitions.

A newly developed unique combination of direct microscopic and calorimetric measurements was used to study the crystal growth in amorphous selenium (a-Se) thin films (500 nm) deposited on Kapton tape and aluminum foil. The crystal growth rates (u r) microscopically determined in the 65–110 °C temperature range were similar to those for bulk selenium glass. The crystal growth kinetics was described in terms of the screw dislocation model with implemented temperature dependences of the growth activation energy E G and Ediger’s decoupling parameter ξ. Extensive analysis of the literature data on the crystal growth rates in thin selenium films revealed the dominant effect of the number and distribution of the dangling bonds of the [Se] n chains adjacent to the film/substrate interface. The seemingly scattered u r – T literature data were found to be consistent when the influences of impurities, substrate quality, illumination, and deposition conditions were accounted for. The macroscopic manifestation of the crystal growth in selenium thin films was observed by means of differential scanning calorimetry (DSC)the corresponding activation energies were similar to the E G values determined by optical microscopy; the Avrami equation with the implemented u r – T dependence was able to accurately describe the macroscopic DSC data. Additional DSC measurements for the selenium thin film scraped off the white glass substrate have shown that the above-T g annealing of such a material suppresses the crystallization, which can be interpreted as the evidence of the dominant growth from the mechanically activated crystallization centers.

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