外加横向电场作用下石墨烯纳米带电子结构的密度泛函紧束缚计算

采用基于密度泛函理论的紧束缚方法计算研究了外加横向电场对边缘未加氢/加氢钝化的扶手椅型石墨烯纳米带的电子结构及电子布居数的影响.计算结果表明,石墨烯纳米带的能隙变化受其宽带影响.当施加沿其宽度方向的横向外加电场时,纳米带的能带结构及态密度都会产生较大的变化.对于具有半导体性的边缘未加氢纳米带,随着所施加电场强度的增加,会发生半导体-金属的转变.同时,电场也会对能级分布产生显著影响.外加电场导致纳米带内原子上电子布居数分布失去对称性,电场强度越大,其布居数不对称性越明显.边缘加氢钝化可以显著改变纳米带内原子上的布居数分布.     

氢、氟原子边缘修饰β-GeSe纳米带的第一性原理研究

采用第一性原理计算方法研究了二维β相GeSe的电子结构,通过对二维单层β-GeSe剪切得到一维β-GeSe扶手椅型纳米带.研究不同带宽(N=1-5)β-GeSe扶手椅型纳米带的几何结构和电子性质,发现不同带宽纳米带能带带隙不同,带隙总体上随着带宽减小,而纳米带直接带隙半导体性质不受带宽影响.通过使用H、F原子对GeSe扶手椅型纳米带边缘修饰,H原子修饰纳米带导致能带类型从直接带隙向间接带隙的转变.在费米能级附近处F原子各轨道对价带和导带贡献比H原子各轨道贡献多,在边缘修饰中纳米带对F原子更加敏感.未修饰和使用H原子修饰纳米带在可见光范围内没有吸收峰,用F原子修饰纳米带在可见光范围内出现吸收峰.研究表明可以通过边缘修饰调控纳米带光学特性.     

边修饰GeS2纳米带的电子特性及调控效应

GeS₂单层已成功制备,为了进一步扩展其应用范围以及发现新的物理特性,我们构建扶手椅型GeS₂纳米带(AGeS₂NR)模型,并采用不同浓度的H或O原子进行边缘修饰,且对其结构稳定性、电子特性、载流子迁移率以及物理场调控效应进行深入研究.研究表明边修饰纳米带具有良好的能量与热稳定性.裸边纳米带是无磁半导体,而边修饰能改变AGeS₂NR的带隙,使其成为宽带隙或窄带隙半导体,或金属,这与边缘态消除或部分消除或产生杂化能带有关,所以边缘修饰调控扩展了纳米带在电子器件及光学器件领域的应用范围.此外,计算发现载流子迁移率对边缘修饰十分敏感,可以调节纳米带载流子迁移率(电子、空穴)的差异达到1个数量级,同时产生载流子极化达到1个数量级.研究还表明半导体性纳米带在较大的应变范围内具有保持电子相不变的鲁棒性,对于保持相关器件电子输运的稳定性是有益的.绝大部分半导体性纳米带在较高的外电场作用下,都具有保持半导体特性不变的稳定性,但带隙随电场增大而明显变小.总之,本研究为理解GeS₂纳米带特性并研发...     

Rb吸附石墨烯纳米带电子性质和光学性质的研究

本文基于密度泛函理论的第一性原理方法了计算了Rb、O和H吸附石墨烯纳米带的差分电荷密度、能带结构、分波态密度和介电函数，调制了石墨烯纳米带的电子性质和光学性质，给出了不同杂质影响材料光学特性的规律.结果表明本征石墨烯纳米带为n型直接带隙半导体且带隙值为0.639 eV；Rb原子吸附石墨烯纳米带之后变为n型简并直接带隙半导体，带隙值为0.494eV；Rb和O吸附石墨烯纳米带变为p型简并直接带隙半导体，带隙值增加为0.996eV；增加H吸附石墨烯纳米带后，半导体类型变为n型直接带隙半导体，且带隙变为0.299eV，带隙值相对减小，更有利于半导体发光器件制备.吸附Rb、O和H原子后，石墨烯纳米带中电荷密度发生转移，导致C、Rb、O和H之间成键作用显著.吸附Rb之后，在费米能级附近由C-2p、Rb-5s贡献；增加O原子吸附之后，O-2p在费米能级附近贡献非常活跃，杂化效应使费米能级分裂出一条能带；再增加H原子吸附之后，Rb-4p贡献发生蓝移，O-2p在费米能级附近贡献非常强，费米能级分裂出两条能带.Rb、O和H的吸附后，明显调制了石墨烯纳米带的光学性质.     

第一性原理研究Be-S共掺杂AlN纳米片的电子结构和光学性质

基于密度泛函理论体系下广义梯度近似(GGA),利用第一性原理方法计算了Be替代Al、S替代N和Be-S共掺杂对氮化铝纳米片的电子结构和光学性质的影响.计算结果表明,掺杂改变了氮化铝纳米片的带隙,但仍显示半导体特性. Be掺杂类型对氮化铝纳米片的晶体结构影响不大,而S掺杂和Be-S共掺杂都使得氮化铝纳米片有不同程度的弯曲.同时Be-S共掺杂中S原子起到激活受主杂质Be原子的作用,使得受主能级向低能方向移动.共掺杂比单掺杂具有更高的受主原子浓度,并减小局域化程度.光学性质也发生较大改变:S原子掺杂氮化铝纳米片的介电函数虚部出现第二介电峰,Be掺杂和Be-S共掺杂使得损失谱的能量区间有所展宽,峰值降低并向高能区移动.     

弯曲BN纳米片的电子性质及其调制

BN纳米片是具有一定宽度、无限长度的一维蜂窝构型单层带状氮化硼材料,弯曲的BN纳米片因为P z轨道旋转,将表现出一定的独特的电子性质.通过第一性原理计算,利用MS(Material Studio)中的DMOL3(local density functional calculations on molecules)软件计算了Zigzag和Armchair型BN纳米片弯曲以后的能带结构.BN纳米带的带隙会随着弯曲角度的变化而改变,以Armchair型BN纳米带的变化较为明显;在弯曲的基础上再加入外电场,却是Zigzag型BN纳米带的带隙变化更显著.当电场加大到一定的值,纳米带就会从半导体变为金属,并且这一临界电场值的大小和纳米带的弯曲程度有关.电场对带隙的调制还和纳米带的尺寸有关系,电场对大尺度的纳米带的调控性更好,从半导体转变为金属所需要的电场值要更小.     

BaZrO3和CaZrO3能带和光学性质的第一性原理研究

采用基于密度泛函理论基础上的CASTEP软件包,计算了BaZrO3和CaZrO3的能带以及光学性质.计算得到BaZrO3直接带隙和间接带隙分别为3.49 eV和3.23eV,CaZrO3直接带隙和间接带隙分别为3.73 eV和3.38 eV.对这两种材料的介电函数、吸收系数、反射系数、折射系数、湮灭系数和能量损失系数等光学系数进行了计算,并基于电子能带对光学性质进行了解释.得出,光学特性的异同是由于其内部微观结构上的异同所引起的.     

第一性原理研究[111]晶向硅纳米线电子结构,光学性质与压阻特性的应变效应

基于密度泛函理论体系下的广义梯度近似(GGA),利用第一性原理方法计算研究了单轴应变对[111]晶向硅纳米线的电子结构、光学性质以及压阻性质的影响.能带结构和光学性质的结果表明:压应变导致硅纳米线的带隙明显线性减小,且使其由直隙半导体转变为间隙半导体,而施加拉应变后硅纳米线仍为直隙半导体材料,但是带隙略有减小,且价带顶附近的能带线产生了较为复杂的变化.由于能带的应变效应导致其光学性质也相应发生了较大改变:拉应变使硅纳米线的介电峰出现宽化现象,低能区内的光吸收增强,静态折射率和反射率峰值增大,而压应变的效果则相反.结合能带结构与压阻系数计算模型得到的压阻特性结果表明:随着压应变的增加压阻系数单调减小,这主要归因于空穴浓度随压应变显著变化引起的;而拉应变作用时,压阻系数呈现波动趋势,这主要是由于空穴有效传输质量的增加程度和载流子浓度的增加程度不同而相互竞争导致的.上述计算结果表明,设计基于硅纳米线的光电和力电器件时,需考虑其应变效应.     

新型二维拉胀材料SiGeS的理论预测及其光电性质

二维材料由于其在力学、电学以及光学等领域的潜在应用而受到广泛关注.基于第一性原理计算,通过有序地排列SiH3SGeH3的Si-S-Ge骨架,设计了一种全新的二维材料SiGeS.单层SiGeS具有良好的能量、动力学以及热力学稳定性. SiGeS具有非常罕见的负泊松比.此外,单层SiGeS是间接带隙半导体,其带隙值为1.95 eV.在应变的作用下, SiGeS可转变为带隙范围为1.32—1.58 eV的直接带隙半导体,可被应用在光学或半导体领域.同时,本征SiGeS拥有优异光吸收能力,其最高光吸收系数可达约10~5 cm^–1,吸收范围主要在可见光到紫外波段.在应变下,光吸收范围可覆盖到整个红外波段.这些有趣的性质使得SiGeS成为一种多功能材料,有望被用于纳米电子、纳米力学以及纳米光学等领域.     

BaHfO3纳米薄膜电子结构、光学和弹性性质的第一性原理研究

采用基于密度泛函理论的第一性原理方法,在局域密度近似（LDA）下研究了厚度为0.626～2.711nm (100)面BaHfO3薄膜的电子结构、光学和弹性性质．电子结构和光学性质计算结果表明：以BaO为表面层原子的BaHfO3纳米薄膜均为直接带隙半导体材料,带隙随薄膜厚度减小而逐渐减小,表现出明显的量子尺寸效应,此时薄膜的光学吸收边发生红移,吸收带出现窄化现象．以HfO2作为表面层原子的BaHfO3薄膜则属于间接带隙半导体材料,且带隙随薄膜厚度减小而微弱增加．弹性性质计算结果表明：体弹模量、剪切模量和杨氏模量等表征材料硬度的力学参数均随BaHfO3纳米薄膜厚度减小而显著减小,呈现尺寸效应．电荷密度分布分析揭示了薄膜厚度改变了BaHfO3纳米薄膜的价健特性,这是材料硬度改变的内在原因．该研究结果为BaHfO3纳米薄膜材料的设计与应用提供了理论依据．     

Common electronic band gaps and similar optical properties of ZnO nanotubes

Electronic and optical properties of single-walled zinc oxide （ZnO） nanotubes are investigated from the firstprinciples calculations. Electronic structure calculations show that ZnO nanotubes are all direct band gap semiconducting nanotubes and the band gaps are relatively insensitive to the diameter and chirality of tubes. The origin of the common electronic band gaps of ZnO nanotubes is explained in terms of band-folding from the two-dimensional band structure of graphite-like sheet. Moreover, the optical properties such as dielectric function and energy loss function spectra of different ZnO nanotubes are very similar, relatively independent of diameter and chirality of tubes. The calculated dielectric function and loss function spectra show a moderate optical anisotropy with respect to light polarization.     

Dependence of optical properties of monoclinic MnWO4 on the electric field of incident light

Considering the electric field of incident light along four particular directions [100], [110], [011], and [010], the optical properties of monoclinic MnWO₄ were investigated by the first-principle methods. The calculated electronic structures show that the O 2p states and Mn 3d states dominate the top of the valence bands, while the W 5d and Mn 3d states play a key role in the bottom of the conduction bands. The dielectric function and other optical properties, including absorption coefficient, reflectivity spectra, and energy-loss spectra, were calculated and analyzed. The results predicted the maximum static dielectric function when the electric field of incident light was along the [100] direction; meanwhile the absorption edge was calculated to be consistent with the energy band gap and the values and positions of peaks in absorption coefficient are related with the electric field of light. Otherwise, it is found that the appearance of peaks in the energy-loss spectra is also dependent on the electric field and simultaneously corresponds to the edge of absorption spectra and the peaks' position of reflectivity spectra.     

Photonic band gaps structure properties of two-dimensional function photonic crystals

The tunable two-dimensional photonic crystals band gap, absolute photonic band gap and semi-Dirac point are beneficial to designing the novel optical devices. In this paper, tunable photonic band gaps structure was realized by a new type two-dimensional function photonic crystals, which dielectric constants of medium columns are functions of space coordinates. However for the two-dimensional conventional photonic crystals the dielectric constant does not change with space coordinates. As the parameter adjustment, we found that the photonic band gaps structures are dielectric constant function coefficient, medium columns radius, dielectric constant function form period number and pump light intensity dependent, namely, the photonic band gaps position and width can be tuned. we also obtained absolute photonic band gaps and semi-Dirac point in the photonic band gaps structures of two-dimensional function photonic crystals. These results provide an important theoretical foundation for design novel optical devices.     

硼球烯B_(40)在外电场下的基态性质和光谱特性

以6-31G*为基组,采用密度泛函PBE0方法研究了不同外电场(0—0.060 a.u.)对硼球烯B_(40)的基态几何结构、电荷分布、能量、电偶极矩、能隙、红外及拉曼光谱特性的影响;继而采用含时的TD-PBE0方法研究了硼球烯B_(40)在外电场下的电子光谱.研究结果表明:外电场的加入导致分子对称性降低,当电场从0 a.u.变化到0.060 a.u.时,偶极矩逐渐增加,体系总能量和能隙一直减小;外电场的加入将改变红外和拉曼光谱特征,如谐振频率的移动以及红外和拉曼峰的增强或减弱;外电场对硼球烯B_(40)的电子光谱影响较大,当电场从0 a.u.变化到0.060 a.u.时,电子光谱发生红移,同时对振子强度有很大影响,原来振子强度最强的激发态变弱或成为禁阻跃迁,而原来振子强度很弱或禁阻的激发态变得最强.可以通过改变外电场来改变B_(40)的基态性质,以及控制B_(40)的光谱特性.     

Electric field effect on the electronic properties of double-walled carbon-doped boron-nitride nanotubes

Carbon (C) doped zigzag (8, 0)@(16, 0) and armchair (5, 5)@(10, 10) double-walled boron-nitride nanotubes (DWBNNTs), under the influence of external electric fields applied in different directions are studied through first-principles calculations. We have considered the substitution of a B and a N (one species at each wall—inner or outer) by C atoms, generating a type-n inside a type-p semiconductor ((type-n)@(type-p)) and vice-versa. The resulting doped DWBNNT can be thought as a p–n junction. The obtained formation energies and structural properties results indicate that these structures present good stability and are not affected by the electric field application. For the electronic structure, it was observed that external fields can be used to modulate these systems energy gaps. Also, there is a preferred field direction which minimizes the gap values, and the gap increase or decrease is related to the reverse and direct polarization of the p–n junction, respectively.     

Optical and electronic properties of pure and fully hydrogenated SiC and GeC nanosheets: first-principles study

In this work, the electronic and linear optical properties of pure and fully hydrogenated SiC and GeC nanosheets have been studied using the full potential linearized augmented plane wave method within the density functional theory. Our study on SiC and GeC has confirmed their potential applications in electronic devices. The dielectric tensor is derived within the random phase approximation. The dielectric function, reflectivity, energy loss function and refraction index of these nanosheets for parallel (E||X) and perpendicular (E||Z) electric field polarization directions are well described. It is observed that hydrogenated nanosheets have semiconductor behavior with anisotropic optical spectra for both E||X and E||Z polarization direction. Also, hydrogenated nanosheets provide new electronic transitions between their neighboring atoms.     

C-Mg掺杂GaN电子结构和光学性质的第一性原理研究

基于密度泛函理论第一性原理的方法,计算了GaN、C单掺、Mg单掺和C-Mg共掺体系的电子结构和光学性质,计算结果表明:掺杂后,GaN体系的晶格发生畸变,有利于光生空穴-电子对的分离,C-Mg共掺体系结构最稳定,掺杂体系的禁带宽度均减小,其中C-Mg共掺体系的禁带宽度最小,在禁带中引入了杂质能级,说明掺杂可有效降低电子跃迁所需的能量.在光学性质方面,掺杂后,GaN在低能区介电峰和吸收峰均发生红移,且静介电常数增大;其中C-Mg共掺体系的对可见光的吸收最强,极化能力最强,因此C-Mg共掺将有望提高GaN在光催化性能和极化能力.     

有机分子吸附和衬底调控锗烯的电子结构

锗基集成电子学的发展潜力源于其极高的载流子迁移率以及与现有的硅基和锗基半导体工业的兼容性,而锗烯微小带隙能带特点极大程度地阻碍其应用.因此,在不降低载流子迁移率的情况下,打开一个相当大的带隙是其应用于逻辑电路中首先要解决的问题.本文采用范德瓦耳斯力修正的密度泛函理论计算方法,研究了电场作用下有机分子吸附和衬底对锗烯原子结构和电学性质的影响.研究结果表明,有机分子吸附和衬底通过弱相互作用破坏了锗烯亚晶格的对称性,从而在狄拉克点上打开了相当大的带隙.苯/锗烯和六氟苯/锗烯体系均在K点打开了带隙.当使用表面完全氢化的锗烯(锗烷HGeH)衬底时,苯/锗烯/HGeH和六氟苯/锗烯/HGeH体系的带隙可进一步变宽,带隙值分别为0.152和0.105 eV.在外电场作用下,上述锗烯体系可实现大范围的近似线性可调谐带隙.更重要的是,载流子迁移率在很大程度上得以保留.本文提出了一种有效的可调控锗烯带隙的设计方法,为锗烯在场效应管和其他纳米电子学器件中的应用提供了重要的理论指导.     

Electric field effects on electronic characteristics of arsenene nanoribbons

By using the first-principles calculations, we investigate the effects of electric field on electronic structures of armchair and zigzag arsenene nanoribbons (AsNRs) with different widths. The results show that for each case, quantum size effects induce a smaller band gap in larger AsNRs. Moreover, electric field can reduce effectively the band gap of AsNRs. In addition, the electric field can induce only the transition of band structures in the A-AsNRs or Z-AsNRs with narrow size. The band gap decrease more rapidly and the threshold electric field induced metal becomes smaller in the wider AsNRs.     

The electronic and optical properties of Cu doped CdI2

Based on the density functional pseudopotential method, the electronic structures and the optical properties of CdI₂ doped with Cu are investigated in detail. The calculation results indicate that the defect of Cu(Cd) exists steadily with a certain solubility. For the Cu doped CdI₂, the new highly localized impurity bands induced by Cu 3d states lie just across the Fermi energy at the top of the valence band. The doping of Cu induces reduction of band gap of CdI₂; red shifts are revealed in both the imaginary part of dielectric function and the absorption spectra corresponding to the change in band gaps. Moreover, the study of the reflection spectrum and the loss function shows that the doped Cu is responsible for the increased reflection peak intensity and the red shift of the plasma resonant frequency of CdI₂.