Surface strain effect on electronic modulations of low-dimensional transition metal chalcogenides and transition metal

Abstract

The low-dimensional materials, such as transition metal (TM), transition metal chalcogenide (TMC), and graphene, are important in different fields of science and studies. These semiconducting materials generally possess specific properties different from bulk materials, such as the appropriate thickness of band gap, strong spin-orbit coupling, and semiconducting characteristics. For the transition metal, the high stability, specific d-state, and synergistic effect are the symbolic properties. Benefitting from the specific properties, these materials are commonly used as components of catalysis, energy storage, new types of energy, and different industrial processes. However, some disadvantages limit the development of these materials, including safety issues, environmental friendliness, high cost, and low efficiency. To overcome the obstacles, scientists invented various methods to improve the performance of these materials. Among various methods, strain engineering is a relatively common and high-efficiency strategy to change the properties of materials. Strain engineering induces strain to the targeted materials, and then deforms the geometry of the material, which enables scientists to tune the properties of low-dimensional materials. For the TMC, MoS₂ and MoSe₂ are chosen as the samples, whereas Pt and Pd are chosen as the samples of TM. These samples are common materials to intensively apply in the fields of catalysis, new types of energy supply, and storage. The studies provide valuable data as a reference for understanding the strain and ripple effect and then guide the development of the next stage. The program, Atomsk, is used to modify geometry and simulate the strain as well as the ripple on the samples. The software, BIOVIA Materials Studio (MS), is applied to validate the modification of the model from Atomsk, and then perform the DFT calculations by the program, CASTEP. Through the DFT calculations, the total energies after geometry optimization, single-point energies, work functions (WF), density of states (DOS), band gaps, and the band structures are calculated and analyzed. The calculated data demonstrate the instability of the models under the strain and ripple effect. The strain and ripple effect significantly change the interatomic distance, bond angle, and orbital overlapping of the models. The structural change brings the property modification of each model and then enhances the electronic performance. The ripple effect is more effective than the simple strain effect to tune the properties of TM and TMC. However, the trend of the property change reflects the difficulty in controlling the ripple effect. In contrast, the strain effect can tune the properties of TMC and TM under a relatively stable condition. The calculated results provide valuable information to investigate the strain and ripple effects of the TM and TMC. The data can be applied as a reference for future work, which reduces the time and resource consumption of further studies. These results will assist in deciding the direction of future work and further development of these materials toward varying applications.