Ti原子吸附对锯齿型硅烯纳米带的电、磁和热电性质的影响

发布时间：2018-04-22 00:04

本文选题：锯齿型硅烯纳米带 + 吸附　；参考：《苏州大学》2015年硕士论文

【摘要】：本文运用非平衡格林函数结合密度泛函理论的第一性原理方法研究了吸附Ti原子的锯齿型硅烯纳米带(Zigzag Silicene Nanoribbons,ZSi NRs)的电、磁和热电性质。我们主要考虑了几个典型的Ti原子吸附位置,包括硅烯纳米带内部原子六元环中心位置(H)、纳米带上边界处(E)和纳米带下边界处(E')。利用Atomistix Tool Kits(ATK)软件我们首先将所有结构进行优化,然后以完美纳米带作为电极建立两极输运系统,并在此基础上计算了系统的电导、磁阻以及热电系数等。我们假设电极纳米带处于铁磁(FM)态。这可以通过施加外磁场获得。这时两电极的磁化方向可以为相互平行(parallel,P)或者相互反平行(antiparallel,AP),对应于我们考虑两种电极磁化构型:铁磁极化平行(FM-P)和铁磁极化反平行(FM-AP)。在论文中,我们首先简单综述了硅烯的发现背景、制备方法以及其独特的电子结构和物理性质,之后介绍了ATK软件中使用的密度泛函理论和量子输运的格林函数方法,最后论述了研究生期间完成的如下主要工作:研究了零偏压下吸附Ti原子后的锯齿型硅烯纳米带的结构、磁矩、结合能、自旋输运和热电性质。在FM态下,吸附在E位的Ti原子离中心平面的距离小于吸附在H位的Ti原子离中心平面的距离,并且吸附在E位的Ti原子的磁矩和结合能比吸附在H位的Ti原子的要小。当Ti原子吸附在4-ZSi NRs(宽度为4的ZSi NRs)和5-ZSi NRs(宽度为5的ZSi NRs)的相同位置时,4-ZSi NRs的原子吸附结合能要高于5-ZSi NRs的吸附结合能。此外,当Ti原子吸附在4-ZSi NRs的H位置时,系统在FM-P构型下具有较高的电导和自旋极化率。并且完美的和EE'位吸附的4-ZSi NRs均出现了巨磁阻现象。特别有趣的是当原子吸附在H和HE位置时,系统在高温下均具有较高的自旋热电系数。紧接着我们研究了完美的和吸附Ti原子后的ZSi NRs的非线性自旋输运性质。计算发现,Ti原子吸附在4-ZSi NRs的EHE'位(即线吸附)时,系统在FM-P构型下具有自旋负微分电阻效应。在FM-AP构型下,原子吸附对4-ZSi NRs系统自旋下的电流具有抑制作用,对自旋上的电流具有增强效果。其中,当原子吸附在HE位置时,系统出现了自旋负微分电阻现象。完美的5-ZSi NRs的I-V特性曲线在很大偏压范围内,自旋上和自旋下电流均呈现金属性。而当吸附Ti原子后,系统的电流受到抑制,此时的I-V特性曲线出现了一定程度的自旋极化率。
[Abstract]:In this paper, the electrical, magnetic and thermoelectric properties of zigzag Silicene Nanoribbonsm ZSI NRs) adsorbed on Ti atoms have been studied by using the first principle method of nonequilibrium Green's function and density functional theory. We mainly consider several typical sites of Ti adsorption, including the central position of Si-Si nanobelts at the center of the six-member ring, the boundary of the nanobelts (E) and the lower boundary of the nanobelts. Using the Atomistix Tool Kitsn ATK software, we first optimize all the structures, and then use the perfect nanobelts as the electrode to establish the two-pole transport system, and then calculate the conductance, magnetoresistive and thermoelectric coefficient of the system. We assume that the electrode nanobelts are in ferromagnetic FM) state. This can be achieved by applying an external magnetic field. In this case, the magnetization direction of the two electrodes can be parallel to each other parallel or antiparallel to each other, which corresponds to the consideration of two electrode magnetization configurations: ferromagnetic polarization parallelism (FM-P) and ferromagnetic polarization antiparallel (FM-APN), which correspond to the consideration of two electrode magnetization configurations: ferromagnetic polarization parallelism (FM-P) and ferromagnetic polarization antiparallelism (FM-APN). In this paper, we first briefly review the background, preparation methods, electronic structure and physical properties of silicene, and then introduce the density functional theory and the Green function method of quantum transport, which are used in ATK software. At last, the main work done in graduate school is described as follows: the structure, magnetic moment, binding energy, spin transport and thermoelectric properties of zigzag silicene nanobelts adsorbed on Ti atom at zero bias voltage are studied. In FM state, the distance from the center plane of the Ti atom adsorbed at the E site is smaller than that of the Ti atom adsorbed at the H position, and the magnetic moment and binding energy of the Ti atom adsorbed at the E site are smaller than that of the Ti atom adsorbed at the H position. When Ti atoms are adsorbed at the same sites as 4-ZSi NRs (ZSi NRs with width 4) and 5-ZSi NRs (ZSi NRs with width 5), the adsorption binding energy of 4-ZSi NRs is higher than that of 5-ZSi NRs. In addition, when Ti atom is adsorbed at H position of 4-ZSi NRs, the system has higher conductivity and spin polarizability under FM-P configuration. And the 4-ZSi NRs of perfect and EE'site adsorption all appeared giant magnetoresistive phenomenon. It is particularly interesting that the system has high spin thermoelectric coefficients at high temperatures when the atoms are adsorbed at H and HE sites. Then we study the nonlinear spin transport properties of perfect and adsorbed Ti ZSi NRs. It is found that the system exhibits a spin negative differential resistance effect in the FM-P configuration when the Ti atom is adsorbed at the ehe 'site (linear adsorption) of the 4-ZSi NRs. In the FM-AP configuration, atomic adsorption can inhibit the spin current in the 4-ZSi NRs system and enhance the spin current. When the atom is adsorbed at the HE position, the spin negative differential resistance appears in the system. The I-V characteristic curves of the perfect 5-ZSi NRs show gold properties in a wide range of bias voltage, both the spin up current and the spin down current. When Ti atom is adsorbed, the current of the system is suppressed, and the I-V characteristic curve appears a certain degree of spin polarizability.
【学位授予单位】：苏州大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB383.1

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