Adsorption Of Ti Atoms On Zigzag Silicene Nanoribbons:Influence On Electric, Magnetic, And Thermoelectric Properties

We study the adsorption effects of Ti atoms on electric, magnetic and thermoelectric properties of zigzag silicene nanoribbons(ZSi NRs) using the nonequilibrium Green’s function(NEGF) method combined with the density functional theory(DFT).We mainly consider some typical Ti atom adsorption position, include the hex-center of the nanoribbons site(H), the upper edge of the nanoribbons site(E), the lower edge of the nanoribbons site(E’). All geometric optimization is used by the Atomistix Tool Kits(ATK) package, then we establish transport system to study the adsorption effects of Ti atoms on conductance, magnetoresistance and Seebeck coefficients of ZSi NRs. We assume the electrode of nanoribbons in ferromagnetic(FM) status by giving the external magnetic field. In a two probe system, the magnetizations of the two electrodes can be aligned in a parallel(P) or antiparallel(AP) configuration according to the directions that the two electrodes spin polarized. Then the magnetic configurations can be split into FM-P, FM-AP in two probe system.This paper introduces the discovery, the experimental preparation and its unique electronic structure and physical properties of silicene, then introduces the density function theory(DFT), nonequilibrium Green’s Function(NEGF) in Atomistix Toolkits(ATK), after the introduction, I present the work completed during the period of graduate study:At equilibrium, we study the electronic structures of pristine andadsorption of Ti atoms and their magnetic moment, conductance spectra, current voltage curves, spin polarizations, magnetoresistance and Seebeck coefficients. In the ferromagnetic(FM) state, an adatom on edge is much closer to the mid plane of ZSi NRs and has a smaller magnetic moment than that inside the nanoribbon and also has a lower Eb. In addition, 4-ZSi NRs has a higher Eb than 5-ZSi NRs for the same adsorption site. When a Ti adatom is added on site H of the 4-ZSi NRs in the FM-P configuration,the system has a high linear conductance and spin polarization introduced by the adatom. When one adatom is on sites E and another is symmetrically adsorbed on site E’, the system becomes laterally symmetric again and the system has a giant magnetoresistance as a pristine 4-ZSi NRs. Interestingly, the Seebeck coefficients effect can be further enhanced by Ti adatoms on site H or HE in the high temperature in the 4-ZSi NRs in the FM-P configuration.At the nonequilibrium, we study the nonlinear spin transport properties of pristine and adsorption of Ti atoms. In the 4-ZSi NRs, when Ti adatoms is adsorbed on site EHE’(wire adsorption)in the FM-P configuration, we observe a spin negative differential resistance phenomenon. The addition of the adatoms in the 4-ZSi NRs will reduce the spin-down current and increases the spin-up current in the FM-AP configuration. In sample HE in the FM-AP configuration a spin negative differential resistance phenomenon is also observed. In 5-ZSi NRs, for pristine, it is in a large range of bias for both spins and in both magnetization configurations and when adsorption of adatoms, it will reduce the current and might induce spin polarization slightly.