Water desorption from van der Waals gaps of molybdenite crystal

Abstract

Water desorption from van der Waals gaps in MoS 2 single crystal was observed by cleavage experiments and temperature programmed desorption (TPD) experiments. At cleavage hydrogen atoms or molecules as well as water vapor are identified as the major desorbed species. Emission of these gases decreases significantly after preheating of samples at about 700 °C for 24 h. TPD experiments were carried out with two types of specimen, flake (~5mm) and powder (~0.3mm), using different heating rates of 1 and 0.2 °C/s. Thermal desorption spectra of these specimens, with or without preheating, show several desorption peaks. The spectrum from the flake sample, preheated at 180 °C 17 h 0.2 °C/s, shows a peak from the bulk. Value of the activation energy of desorption was obtained using observed shift of the peak temperature in two different heating rates and was of about 1 eV. This activation energy corresponds to the diffusion energy of water molecules in the van der Waals gap.