Manipulation of electronic and magnetic properties of M2_2C (M=Hf, Nb, Sc, Ta, Ti, V, Zr) monolayer by applying mechanical strains

Tuning the electronic and magnetic properties of a material through strain engineering is an effective strategy to enhance the performance of electronic and spintronic devices. Recently synthesized two-dimensional transition metal carbides M$_2$C (M=Hf, Nb, Sc, Ta, Ti, V, Zr), known as MXenes, has aroused increasingly attentions in nanoelectronic technology due to their unusual properties. In this paper, first-principles calculations based on density functional theory are carried out to investigate the electronic and magnetic properties of M$_2$C subjected to biaxial symmetric mechanical strains. At the strain-free state, all these MXenes exhibit no spontaneous magnetism except for Ti$_2$C and Zr$_2$C which show a magnetic moment of 1.92 and 1.25 $\mu_B$/unit, respectively. As the tensile strain increases, the magnetic moments of MXenes are greatly enhanced and a transition from nonmagnetism to ferromagnetism is observed for those nonmagnetic MXenes at zero strains. The most distinct transition is found in Hf$_2$C, in which the magnetic moment is elevated to 1.5 $\mu_B$/unit at a strain of 15%. We further show that the magnetic properties of Hf$_2$C are attributed to the band shift mainly composed of Hf(5$d$) states. This strain-tunable magnetism can be utilized to design future spintronics based on MXenes

Monte-Carlo-Simulation-Based, Product-Quality-Focused Analysis Of Nanocoating Curing And Post Curing Process

ABSTRACT MONTE CARLO SIMULATION BASED PRODUCT QUALITY ANALYSIS OF POLYMER COATING CURING AND POST CURING By Jianming Zhao May 2017 Advisor：Dr. Yinlun Huang Major: Chemical Engineering Degree: Master of Science To achieve better property of polymer coatings, different categories of nanoparticles are applied before coating’s curing process. However, one of the adverse effects is the change of final property, which leads the difficulty of product quality control. Using mathematical modeling method can actually improve the cost and time to get a prediction of product quality. Still now, different series of models are developed for various purposes. For example, Monte-Carlo simulation suits short-term usage prediction; kinetics simulation suits long-term usage prediction; potential energy simulation suits to model microcosmic particle’s energy change. To solve the difficulty of quality control, Monte-Carlo simulation is used to provide relatively accurate data under given conditions. A series of models are redesigned, based on those developed by Xiao et al. (2009, 2010). From the simulation data, a visualized conversion and final Young’s modulus change can be clearly seen. In this thesis, a linear plot of the general curing process is gained. Monte Carlo simulation methodology is a new method to describe the conversion change. The post-curing process is also simulated, with the contrast of the real data from Yari (2014), the post-curing process and principle can be explained. The effect of the nanoparticle can also be gained in this work. Additionally, with the work of this thesis, people can control the product quality more easily

Electric-field induced dipole blockade with Rydberg atoms

High resolution laser Stark excitation of np (60 < n < 85) Rydberg states of ultra-cold cesium atoms shows an efficient blockade of the excitation attributed to long-range dipole-dipole interaction. The dipole blockade effect is observed as a quenching of the Rydberg excitation depending on the value of the dipole moment induced by the external electric field. Effects of eventual ions which could match the dipole blockade effect are discussed in detail but are ruled out for our experimental conditions. Analytic and Monte-Carlo simulations of the excitation of an ensemble of interacting Rydberg atoms agree with the experiments indicates a major role of the nearest neighboring Rydberg atom.Comment: 4 page

Gas adsorption on MoS2 monolayer from first-principles calculations

First-principles calculations within density functional theory (DFT) have been carried out to investigate the adsorption of various gas molecules including CO, CO2, NH3, NO and NO2 on MoS2 monolayer in order to fully exploit the gas sensing capabilities of MoS2. By including van der Waals (vdW) interactions between gas molecules and MoS2, we find that only NO and NO2 can bind strongly to MoS2 sheet with large adsorption energies, which is in line with experimental observations. The charge transfer and the variation of electronic structures are discussed in view of the density of states and molecular orbitals of the gas molecules. Our results thus provide a theoretical basis for the potential applications of MoS2 monolayer in gas sensing and give an explanation for recent experimental findings.Comment: 15 pages, 5 figure