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

Abstract

The formation kinetics of the 2D-layered InSe crystallinephasein thin amorphous InSe films was studied by means of differentialscanning calorimetry, Raman spectroscopy, X-ray diffraction analysis,and X-ray absorption spectroscopy. All measurements were performedon as-deposited films (thicknesses ranging between 200 and 1500 nm),with Kapton foil used as a substrate. In the films with thickness & GE; 1000 nm, the formation was found to proceed via two steps:the exothermic re-organization of the amorphous phase (activationenergy of 420 kJ & BULL;mol(-1)), followed by the exothermicformation of the crystalline phase (activation energy of 227 kJ & BULL;mol(-1)). For InSe films with thickness & LE; 500 nm,the two processes merged, but their reaction mechanism was still foundto consist of two sequential phase transformations, with the reorganizationin the amorphous phase being the necessary preliminary step. Bothkinetic processes were found to be slowed down by the presence ofmechanical defects and by the surface/interface imperfections. Thepossibility of two-step preparation of ideally layered flexible 2DInSe ceramics is suggested based on the separated high-temperatureamorphous phase reorganization, followed by a low-temperature crystalgrowth step (during which excellent 2D InSe layering could be achieved).