First-principles investigation on B/N co-doping of metallic carbon nanotubes

Using the first-principles study, we calculate the electronic band structure of metallic carbon nanotubes (MCNTs) with B/N co-doping. We show the formation energies which suggest that the B/N co-doping configuration is the energetically stable structure. We find that the electronic structure properties depend on the doping concentration of MCNTs, as well as the doping position. Energy gap opens rapidly when the symmetry breaking of MCNTs happens. These unconventional doping effects could be used to design novel nanoelectronic devices.     

Boron/nitrogen pairs Co-doping in metallic carbon nanotubes: a first-principle study

By using the first-principles calculations, the electronic structure and quantum transport properties of metallic carbon nanotubes with B/N pairs co-doping have been investigated. It is shown that the total energies of metallic carbon nanotubes are sensitive to the doping sites of the B/N pairs. The energy gaps of the doped metallic carbon nanotubes decrease with decreasing the concentration of the B/N pair not only along the tube axis but also around the tube. Moreover, the I--V characteristics and transmissions of the doped tubes are studied. Our results reveal that the conducting ability of the doped tube decreases with increasing the concentrations of the B/N pairs due to symmetry breaking of the system. This fact opens a new way to modulate band structures of metallic carbon nanotubes by doping B/N pair with suitable concentration and the novel characteristics are potentially useful in future applications.     

Electronic properties of graphene nanoribbon doped by boron/nitrogen pair: a first-principles study

By using the first-principles calculations, the electronic properties of graphene nanoribbon (GNR) doped by boron/nitrogen (B/N) bonded pair are investigated. It is found that B/N bonded pair tends to be doped at the edges of GNR and B/N pair doping in GNR is easier to carry out than single B doping and unbonded B/N co-doping in GNR. The electronic structure of GNR doped by B/N pair is very sensitive to doping site besides the ribbon width and chirality. Moreover, B/N pair doping can selectively adjust the energy gap of armchair GNR and can induce the semimetal-semiconductor transmission for zigzag GNR. This fact may lead to a possible method for energy band engineering of GNRs and benefit the design of graphene electronic device.     

扶手椅型单壁碳纳米管中的B/N对共掺杂

利用第一性原理电子结构计算方法,研究了扶手椅型单壁碳纳米管（SWCNT）的B/N对掺杂效应.研究发现,对于扶手椅型SWCNT两个不同的掺杂位点,B/N对更容易发生在与管轴线成30°角的P₁位点上.B/N对的掺杂使得金属性SWCNT能隙打开,且能隙随着B/N对轴向掺杂浓度的升高而逐渐增大.同时,还发现两B/N对掺杂后SWCNT的电子结构敏感地依赖于B/N对在圆周上的相对位置,能隙随着B/N对相对距离的增大而增大.这归结于B/N对的掺入影响了原有的电荷分布,这种影响是局域的 关键词： 单壁碳纳米管 B/N对掺杂 电子结构 第一性原理     

B,N协同掺杂金刚石电子结构和光学性质的第一性原理研究

基于金刚石的稳定结构, 在实验研究的基础上, 本文采用基于周期性密度泛函理论计算了B/N单掺杂、共掺杂金刚石的晶体结构, 并就掺杂方式和掺杂后形成能进行了对比研究, 得到了B/N双掺杂的最稳定结构. 在此基础上, 进一步计算了N单掺杂及B/N共掺杂最稳定结构的吸收光谱、电子结构和态密度. 通过与实验结果对比可以看出, 较N单掺杂, B/N共掺杂的吸收光谱发生明显红移, 与实验符合较好. 计算结果表明: N原子单掺杂优先于B原子; 由于原子间的协同作用, B/N近邻共掺杂体系的形成能最低, 为掺杂的最可能结构.     

Mn2+、N2-共掺杂Zn2GeO4晶体电子结构和光学性质的研究

采用基于密度泛函理论的平面波超软赝势方法对本征Zn2GeO4,Mn2+掺杂Zn2GeO4,Mn2+/N2-共掺杂Zn2GeO4超晶胞进行了几何结构优化,计算了掺杂前后体系的晶格常数、能带结构、态密度和光学性质。结果表明,Mn离子掺入后,Mn离子3d轨道与O离子2p轨道之间有强烈的轨道杂化效应,掺杂系统不稳定,而Mn/N离子共掺后,Mn离子和N离子之间的吸引作用克服了Mn离子之间的排斥作用,能够明显地提高掺杂浓度和体系的稳定性。光学性质计算结果表明,Mn离子与N离子共掺杂能改善Zn2GeO4电子在低能区的光学跃迁特性,增强电子在可见光区的光学跃迁;吸收谱计算结果显示,Mn离子与N离子掺入后体系对低频电磁波吸收增加。     

第一性原理研究铝氮掺杂小半径碳纳米管

基于第一性原理的密度泛函理论,计算并分析了铝氮共掺杂小半径碳纳米管的电子结构.结果表明,铝氮共掺杂的情况下,更容易形成相邻的铝氮对.在掺杂的七种位置中,电子性质都发生了很大的变化,原来的金属性碳纳米管转变为半导体性质.为了更好的理解其电子性质的变化,我们分析其能带结构和态密度.     

Manipulation of inherent characteristics of graphene through N and Mg atom co-doping; a DFT study

First-principles calculations were performed to investigate the structural, electronic, magnetic and optical properties of nitrogen (N) and magnesium (Mg) atom co-doped graphene systems. We observed that, N and Mg atom co-doping in graphene, introduces half-metallic properties in the electronic structure of graphene, introduces ferromagnetism behavior along with new trends in optical properties of graphene. Doping site and concentration of N and Mg atoms in graphene was changed and resulting effects of these changes on aforementioned properties were investigated. Through density of states plots we observed that, Mg atom sp orbitals mainly induced magnetic moments in graphene. It was revealed that, N/Mg atoms substitution in graphene introduces a red shift in absorption spectrum towards visible range and a finite absorption coefficient quantity value in 0 to 3 eV and 7 to 11 eV energy intervals is also produced, that is unavailable for absorption spectrum of intrinsic graphene. Moreover, N/Mg atoms co-doping produces increment in the reflectivity parameter of graphene in low lying energy region, while producing diminishing behavior in the higher energy range. These results offer a possibility to tune electronic, magnetic and optical characteristics of graphene sufficiently for utilization in graphene based spintronic and optoelectronic devices.     

B/N掺杂对双层石墨烯电子特性影响的第一性原理研究

利用平面波超软赝势方法研究了B/N原子单掺杂和共掺杂对双层石墨烯电子特性的影响.对掺杂双层石墨烯进行结构优化,并计算了能带结构、态密度、分波态密度等.分析表明,层间范德瓦尔斯相互作用对双层石墨烯的电子特性有比较明显的影响;B/N原子单掺杂分别对应p型和n型掺杂,会使掺杂片层的能带平移,使得体系能带结构产生较大分裂;双层掺杂的石墨烯能带结构与掺杂原子的相对位置和距离有关,对电子特性有明显的调控作用.其中特别有意义的是,B/N双层共掺杂在不同位置情况下会得到金属性或禁带宽度约为0.3 eV的半导体能带.     

基于密度泛函理论下O和Na掺杂单层h-BN的电子结构性质和光学效应的分析

基于密度泛函理论的第一性原理方法研究了O、Na单掺杂及O和Na共掺杂单层h-BN的形成能、电子结构和光学性质.结果表明:单掺杂体系中,O掺杂N位置、Na掺杂B位置时,掺杂形成能最低;共掺杂体系中,O和Na邻位掺杂,掺杂形成能最低.与单层h-BN相比,引入杂质原子后的体系禁带宽度均减小,其中O掺杂为n型掺杂,Na掺杂为p型掺杂,而O和Na共掺h-BN体系为直接带隙材料,有利于提高载流子的迁移率.在光学性质方面,Na掺杂h-BN体系与O和Na共掺h-BN的静介电常数均增大,在低能区介电虚部和光吸收峰均发生红移,其中Na掺杂体系红移最为显著,极化能力最强.因此Na单掺和O和Na共掺有望增强单层h-BN的光催化能力,可扩展其在催化材料、光电器件等领域的应用.     

Cu,O共掺杂AlN晶体电子结构与光学性质研究

采用基于密度泛函理论的平面波超软赝势方法对纯Al N,Cu单掺杂以及Cu与O共掺杂Al N超胞进行了几何结构优化,计算了掺杂前后体系的晶格常数、能带结构、态密度与光学性质.结果表明:掺杂后晶格体积增大,系统能量下降;Cu掺入后Cu 3d电子与N 2p电子间有强烈的轨道杂化效应,Cu与O共掺后Cu和O之间的吸引作用克服了Cu原子之间的排斥作用,能够明显提高掺杂浓度和体系的稳定性.光学性质分析中,介电函数计算结果表明Cu与O共掺杂能改善Al N电子在低能区的光学跃迁特性,增强电子在可见光区的光学跃迁;复折射率计算结果显示Cu与O掺入后由于电磁波穿过不同的介质,导致折射率发生变化,体系对低频电磁波吸收增加.     

Electronic properties of boron and nitrogen doped graphene nanoribbons and its application for graphene electronics

On the basis of density functional theory calculations, we have systematically investigated the electronic properties of armchair-edge graphene nanoribbons (GNRs) doped with boron (B) and nitrogen (N) atoms. B (N) atoms could effectively introduce holes (electrons) to GNRs and the system exhibits p- (n-) type semiconducting behavior after B (N) doping. According to the electronic structure calculations, Z-shape GNR-based field effect transistors (FETs) is constructed by selective doping with B or N atoms. Using first-principles quantum transport calculations, we demonstrate that the B-doped p-type GNR-FETs can exhibit high levels of performance, with high ON/OFF ratios and low subthreshold swing. Furthermore, the performance parameters of GNR-FETs could be controlled by the p-type semiconducting channel length.     

Nd、N掺杂ZnO的电子结构和光学性质的第一性原理研究

基于密度泛函理论的第一性原理,使用GGA+U方法计算出N、Nd分别单掺ZnO及N、Nd共掺ZnO晶体的形成能,能带结构,态密度及光学性质.经过对比发现:N、Nd各掺杂ZnO中,共掺体系比单掺体系更容易形成,其中低浓度掺杂难度更低;共掺体系随着掺杂浓度的升高,其畸变的强度就越强,禁带宽度变窄,电子跃迁到导带上所需的能量更小,光吸收系数较大,并且都产生了红移,光谱响应范围扩展到了整个可见光区域;共掺体系在低能区域的介电谱峰值较高,说明其极化能力较强,光生电场强度较大,会使光激发载流子在晶体内的迁移变快,对电荷的束缚能力增强.因此N、Nd共掺可以有效提升ZnO的光催化性和极化能力.     

Effects of lanthanides doping on the optical properties of graphene/WSe2 heterostructure based on ab-initio calculations

Based on the density functional theory, we discussed the electronic and optical properties of graphene/ WSe₂ (GW) heterostructure after lanthanides doping. Red shift appears and the optical parameter values are improved in the low energy region after the lanthanides are doped. Different doping types are also discussed. In the case of single doping, substitute Yb atom on W site will improve the peak values of the optical parameters greatly. In the case of co-doping, it is found that the effect will be more obvious when the two doped lanthanide atoms are located in the second neighboring positons. These results suggest that lanthanides doping does adjust the electronic structure and improve the optical properties of GW heterostructures, which providing useful guidance for the design of novel optical nanodevices based on two-dimensional materials.     

Effects of partial hydrogenation and vacancy defects on the electronic properties of metallic carbon nanotubes

Using first-principles calculations based on spin-polarized density functional theory, we investigate the electronic properties of metallic carbon nanotubes (MCNTs) with partial hydrogenation or vacancy defects. The calculated results show that the energy band structures of MCNTs strongly depend on the adsorption site or the vacancy-defect site. Interestingly, our results show the nonmagnetic semiconducting behavior of MCNTs in the case of balanced H adsorption or vacancy defects. However, the MCNTs exhibit magnetic metallic behavior in the case of imbalanced H adsorption or vacancy defects, and the energy band structure of MCNTs shows the appearance of a spin-polarized flat band near the Fermi level. This effect presents a possibility for spintronic device and semiconducting molecular wire applications.     

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.     

Electronic structure and optical properties of Al and Mg co-doped GaN

The electronic structure and optical properties of Al and Mg co-doped GaN are calculated from first principles using density function theory with the plane-wave ultrasoft pseudopotential method.The results show that the optimal form of p-type GaN is obtained with an appropriate Al:Mg co-doping ratio rather than with only Mg doping.Al doping weakens the interaction between Ga and N,resulting in the Ga 4s states moving to a high energy region and the system band gap widening.The optical properties of the co-doped system are calculated and compared with those of undoped GaN.The dielectric function of the co-doped system is anisotropic in the low energy region.The static refractive index and reflectivity increase,and absorption coefficient decreases.This provides the theoretical foundation for the design and application of Al–Mg co-doped GaN photoelectric materials.     

B,P掺杂β-Si3N4的电子结构和光学性质研究

运用第一性原理方法, 计算了B, P两种元素单掺杂和共掺杂的β -Si₃N₄材料的电子结构和光学性质. 结果表明: B掺杂体系的稳定性更高, 而P掺杂体系的离子性更强; 单掺和共掺杂均窄化带隙, 且共掺在禁带中引入深能级, 使局域态增强; 单掺杂体系介电函数虚部、吸收谱和能量损失谱各峰均发生红移、幅值减小, 而共掺后介电函数虚部主峰出现蓝移、能量损失峰展宽、高能区电子跃迁大大增强, 且控制共掺杂的B, P比例可获得较低的带电缺陷浓度.     

In–2N高共掺浓度和择优取向对ZnO最小光学带隙和吸收光谱的影响

目前, 虽然In和2N共掺对ZnO最小光学带隙和吸收光谱影响的实验研究均有报道, 但是, In和2N共掺在ZnO中均是随机掺杂, 没有考虑利用ZnO的单极性结构进行择优取向共掺, 第一性原理的出现能够解决该问题. 本文采用密度泛函理论框架下的第一性原理平面波超软赝势(GGA+U)方法, 计算了纯的ZnO单胞、择优位向高共掺In–2N原子的Zn_1-xIn_xO_1-yN_y(x= 0.0625–0.03125, y=0.0625–0.125)八种超胞模型的态密度分布和吸收光谱分布. 计算结果表明, 在相同掺杂方式、不同浓度共掺In-2N的条件下, 掺杂量越增加, 掺杂体系体积越增加、能量越增加, 稳定性越下降、形成能越增加、掺杂越难、掺杂体系最小光学带隙越变窄、吸收光谱红移越显著. 计算结果与实验结果相一致. 在不同掺杂方式、相同浓度共掺In–2N的条件下, In–N沿c轴取向成键共掺与垂直于c轴取向成键共掺体系相比较, 沿c轴取向成键共掺体系最小光学带隙越变窄、吸收光谱红移越显著. 这对设计和制备新型光催化剂功能材料有一定的理论指导作用.     

N-F共掺杂锐钛矿二氧化钛(101)面纳米管的第一性原理研究

共掺杂是提高二氧化钛纳米管可见光催化性能的一种有效方式. 采用基于密度泛函理论的第一性原理方法, 研究了N单掺杂、F单掺杂及N-F共掺杂二氧化钛纳米管的原子结构、电子性质和光学性质. 计算结果表明, 相比N单掺杂和F单掺杂, N-F共掺杂二氧化钛纳米管的形成能更低, 掺杂后的体系热力学稳定性更好. 此外, 相比未掺杂时的带隙, N-F共掺杂后体系的带隙变化最多, 减少了0.557 eV, 而这主要源于价带顶附近的杂质能级的贡献. 此外, 通过分析掺杂后的光催化活性发现, N-F共掺杂时纳米管的还原性和氧化性都有所降低, 但并没有丧失活性, 并且光吸收谱表明, 共掺杂体系的红移现象最为明显. 因此, N-F共掺杂可有效提高二氧化钛纳米管可见光的光催化性能.