Investigation of availability of metal chalcogenides in infrared detectors and lithium-ion batteries

In recent years, metal chalcogenides (MX; M=Metal and X=Chalcogens) have taken a solid place in the technology due to their band gaps in the visible region. In particular, while many MX composites have indirect band gap in their three dimension forms, it can turn to direct band gap for their low dimensional forms. This feature takes them one step forward in making optical or electronic devices. Experimental demonstration of the high lithium storage capacity of two-dimensional MoS2 and the theoretical and experimental acquisition of MoS2 nanoparticles have generated the motivation for this thesis topic. Therefore, in this thesis, the electronic and optical properties of metal di- and tri-chalcogenides have been investigated with the help of density function theory (DFT) based on first-principles calculations. In addition to these structures, physical and chemical properties of two dimensional structures such as BN, AlN, silicene, arsenene are discussed. Adsorption energies of lithium atom on the MX2 (M=Mo, W ; X=O, S, Se, Te) monolayer were calculated and high adsorption energies ranging from 1.42 eV to 3.10 eV were obtained. The minimum energy values required for diffusing on the layer are in the range of 0.158 eV to 0.282 eV and diffusion coefficient values are higher than nanocrystalline 2H-MoSe2 or in different carboneous materials on the order of 102-105. The number of lithium atoms was gradually increased over the structures to obtain the adsorption energy curves for per atom. We also investigated the availability of MoS2(x−1) Se2x (x=0.33, 0.67, 0.83) metal chalcogen alloys in lithium-ion batteries. We find that the Li adatom is attached to MoS2 and MoSe2 monolayers via a molybdenum atom, while Li moves through the Mo-S bond for MoS2(x−1) Se2x alloys. NEB calculation results show that their energy barriers make them suitable for using in lithium-ion batteries. In this thesis, the existence of new RuS2 and RuSe2 metal dichalcogenides stabilized by Peierls distortion, which is not stable in the structure of hexagonal or tetragonal metal di-chalcogenides known in the literature, is theoretically presented. The mechanical, dynamical and thermal stability tests of the new structures were performed and it was shown that the structures could be at room temperature and above. The single layer RuS2 and RuSe2 were found to be semiconducting materials with a band gap in the visible region with HSE06 calculations, but the band gaps of the two- and three-layer structures decrease to the infrared region. The electronic and optical properties of TiX3 (X=S, Se, Te) metal tri-chalcogenides and their alloys have been investigated. Alloys formed by a mixture of sulfur and selenium atoms have band gaps in the near infrared region, whereas when incorporated into TiS3 or TiSe3 tellurium atoms are found to have all metal or semi-metal properties. The results have provided important information on how lithium is bound to metal dichalcogenides and their alloys in atomic dimensions, and these results will contribute theoretically to the development of lithium-ion batteries and to the efficiency of lithium batteries. In addition, it has been demonstrated that the theoretically recommended new metal dichalcogenides can be used in optoelectronic materials and infrared detectors due to their band gaps.