Formation of 2D-Structured InSe Ceramics from Amorphous Phase Deposited on a Kapton Foil

The formation kinetics of the 2D-layered InSe crystalline phase in thin amorphous InSe films was studied by means of differential scanning calorimetry, Raman spectroscopy, X-ray diffraction analysis, and X-ray absorption spectroscopy. All measurements were performed on as-deposited films (thicknesses ranging between 200 and 1500 nm), with Kapton foil used as a substrate. In the films with thickness ≥ 1000 nm, the formation was found to proceed via two steps: the exothermic re-organization of the amorphous phase (activation energy of 420 kJ·mol^-1), followed by the exothermic formation of the crystalline phase (activation energy of 227 kJ·mol^-1). For InSe films with thickness ≤ 500 nm, the two processes merged, but their reaction mechanism was still found to consist of two sequential phase transformations, with the reorganization in the amorphous phase being the necessary preliminary step. Both kinetic processes were found to be slowed down by the presence of mechanical defects and by the surface/interface imperfections. The possibility of two-step preparation of ideally layered flexible 2D InSe ceramics is suggested based on the separated high-temperature amorphous phase reorganization, followed by a low-temperature crystal growth step (during which excellent 2D InSe layering could be achieved).