Browsing by Author "Su, Tonghui"
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Item DFT methods applications in nanoscale materials modeling(2021-04-30) Su, Tonghui; Yakobson, Boris I.With the development of simulation methods and explorations in the first-principle calculation, the density functional theory methods have more applications that could predict the properties and explain the results from the nanoscale scope for the experiments. Here, in this thesis, we utilized the DFT methods for the simulation of the material to explore their performance in molecular, 1D, and 2D systems. All these examples showed the precise of single-molecule configurations and also the periodic system properties. In the first molecular system, we combined the geometric configurations with the energy conversion, which converts the photoexcitation energy to mechanical energy output in the type of geometric transform. The DFT methods help to find the pathway in this process and got the numeric efficiency for the system. And we could also summarize a principle to connect the spring constant of a molecule with the mechanical efficiency. In the second example, which is about 1D Se nanowire, we utilized the SWCNT to provide the environment for Se nanowire synthesis and explore the mechanical stability after the encapsulation effects. Also, more stable configurations in SWCNT provides more important properties like charge carrier mobility for nanoscale devices application. With electronic properties and band structure calculation, we discovered Rashba effects in 3H configuration and used strain to control the parameter of Rashba splitting in the band structure, which set the basis and another option for 1D light element spintronics devices. In the third example, monolayer MoS2 with Cu atom doping, we use first-principle calculation collaborating with experiment to provide the microscopic structure exploration, like the doping type and substitutional sites for fixed stoichiometry and also the phase diagram with different potential energy for a different source. With these calculations, we could have a thorough picture of Cu doped MoS2 from both macroscopic and microscopic structures and properties. Our work here shows the important use for DFT calculation for many kinds of systems and properties exploration, which could help with more and more materials synthesis and potential applications.Item Substitution of copper atoms into defect-rich molybdenum sulfides and their electrocatalytic activity(Royal Society of Chemistry, 2021) Wang, Zixing; Kannan, Harikishan; Su, Tonghui; Swaminathan, Jayashree; Shirodkar, Sharmila N.; Hernandez, Francisco C. Robles; Benavides, Hector Calderon; Vajtai, Robert; Yakobson, Boris I.; Meiyazhagan, Ashokkumar; Ajayan, Pulickel M.Studies on intercalation or substitution of atoms into layered two-dimensional (2D) materials are rapidly expanding and gaining significant consideration due to their importance in electronics, catalysts, batteries, sensors, etc. In this manuscript, we report a straightforward method to create sulphur (S) deficient molybdenum (Mo) sulfide (MoS2−x) structures and substitute them with zerovalent copper (Cu) atoms using a colloidal synthesis method. The synthesized materials were studied using several techniques to understand the proportion and position of copper atoms and the effect of copper functionalization. Specifically, the impact of change in the ratio of Cu : S and the hydrogen evolution reaction (HER) activity of the derived materials were evaluated. This technique paves the way for the synthesis of various functionalized 2D materials with a significant impact on their physical and chemical behavior making them potential candidates for catalysis and several other applications such as energy storage and the development of numerous functional devices.