纳米Ce1-x(Fe0.5La0.5)xO2-δ固溶体的水热合成及光谱分析

采用水热方法合成Ce1-x(Fe0.5 La0.5)xO2-δ固溶体.利用X射线衍射技术(X-ray diffraction technique,XRD)表征样品的相结构,并对固溶体的晶胞参数进行拟合,通过紫外可见漫反射光谱(UV-Vis diffraction spectrum)及拉曼光谱(Raman spectru...     

Li掺杂对MgH2(001)表面H2分子扩散释放影响的第一性原理研究

本文利用基于密度泛函理论的第一性原理分别研究了MgH₂(001)表面H原子扩散形成H₂分子释放出去的可能路径及金属Li原子掺杂对其影响. 研究结果表明: 干净MgH₂(001)表面第一层释放H原子形成H₂分子有两种可能路径, 其释放能垒分别为2.29和2.50 eV; 当将Li原子替代Mg原子时, 两种H原子扩散释放路径的能垒分别降到了0.31和0.22 eV, 由此表明Li原子掺杂使MgH₂(001)表面H原子扩散形成H₂释放更加容易.     

H掺杂α-Fe2O3的第一性原理研究

α-Fe₂O₃是一种重要的磁性半导体材料, 在电子器件中应用广泛, 具有重要的研究意义. 本文基于密度泛函理论, 采用GGA+U方法, 应用第一性原理对间隙H掺杂前后的六方相α-Fe₂O₃的晶格常数、态密度、Bader 电荷分布进行了计算分析. 研究了U值对结果的影响, 发现U=6 eV时, 体相α-Fe₂O₃的晶胞平衡体积、Fe原子磁矩、带隙值与实验值最符合. 在选取合适U值后, 第一性原理计算结果表明, H掺杂后, 间隙H部分被氧化, 其最近邻的Fe 和O部分被还原, H和O有一定程度的成键. 在费米面附近, 出现了新的杂化能级, 杂化能级扩展了价带顶的宽度, 同时导带底下移, 引起带隙减小, 表明H掺杂是一种有效的能带结构调控方法.     

双层h-BN/Graphene结构稳定性及其掺杂特性的第一性原理研究

采用基于密度泛函理论的第一性原理计算方法研究了双层h-BN/Graphene的稳定性及其掺杂特性.研究发现,双层h-BN/Graphene能带结构在K点处有一个小的带隙,在费米能处有类Graphene的线性色散关系.通过施加应变和掺杂来调节带隙,发现掺杂后费米能级附近引入的新能级,主要是N原子的贡献,掺杂后的Na原子和N,C之间存在电荷转移,材料转变为金属性.电荷的转移、载流子密度的增加,在电子元器件中有重要的应用前景.     

RE(POA)3phen配合物的合成、表征及荧光性能

合成了以稀土离子Sm³⁺、Eu³⁺、Tb³⁺、Dy³⁺及Tb³⁺为发光中心,以苯氧乙酸(HPOA)和邻菲罗啉(phen)为配体,掺杂La³⁺、Gd³⁺、 Y³⁺的7种稀土配合物, 对配合物进行了C、H、N元素分析、稀土络合滴定、红外光谱、紫外光谱和发光光谱的研究。结果表明配合物的组成分别为SmL₃L'·1/2H₂O,EuL₃L'·1/2H₂O,TbL₃L'· 1/2H₂O,DyL₃L'·1/2H₂O,掺杂配合物组成分别为Tb_0.5Gd_0.5L₃L'·1/2H₂O,Tb_0.5Y_0.5L₃L'·1/2H₂O,Tb_0.5La_0.5L₃L'·1/2H₂O(L=C₆H₅OCH₂COO^-, L'=phen)。配合物中的稀土离子与苯氧乙酸中羧基的一个氧原子和苯氧基的氧原子配位,与邻菲罗啉中的两个氮原子配位成键;荧光光谱表明,铽三元配合物的发射强度要远大于其它三元配合物的发光强度,掺杂发光惰性稀土离子La³⁺、Gd³⁺、Y³⁺的铽配合物中,Y³⁺掺杂配合物的发光强度有所增强。     

Transition metal encapsulated hydrogenated silicon nanotubes: Silicon-based half-metal

One-dimensional hydrogenated silicon nanotubes (H-SiNTs) with transition metal atom encapsulated were systematically studied by using density functional theory. The band structures and magnetic properties of the H-SiNTs can be tailored by doping transition metal (TM) (TM = Cr, Mn, Fe, Co) atoms within the tube. The hydrogenated silicon nanotubes are semiconductors with wide band gaps. TM doping turns H-SiNTs to be metals or semiconductors with a very small gap, and TM atoms at the center of the tubes keep large magnetic moments. Robust half-metallicity is observed in Mn-doped H-SiNTs and it is free from Peierls distortion. Thus, H-SiNTs with encapsulated magnetic elements may find important applications in spintronic devices.     

Al-doped ZnO: Electronic, electrical and structural properties

Changes in structural, electrical and electronic properties of zinc oxide (ZnO) due to Al doping are studied using a quantum-chemical approach based on the Hartree-Fock theory. A periodic supercell of 128 atoms has been exploited throughout the study. The atomic parameters for Zn atom were obtained by reproducing the main properties of ZnO crystal as well as the first three ionization potentials of Zn atom. The perturbation imposed by Al atom incorporation leads to the atomic relaxation, which is computed and discussed in detail. A novel effect of electron density redistribution between different atomic orbitals within the same atom has been found. This phenomenon influences atomic rearrangement near Al impurity. The Al doping generates a free electron in the conduction band, which can be considered as a large radius electron polaron increasing the n-type electrical conductivity in the crystal in agreement with the known experimental data. The obtained small increase in the band-gap width due to the impurity incorporation resolves existing experimental debates on this point.     

金掺杂锯齿型石墨烯纳米带的电磁学特性研究

本文采用基于密度泛函理论的第一性原理计算了金原子填充锯齿型石墨烯纳米带 (ZGNRs)中双空位结构的电磁学特性. 计算结果表明: 边缘位置是金原子的最稳定掺杂位置, 杂质原子的引入导致掺杂边缘的磁性被抑制, 不过掺杂率足够大时, 掺杂边缘的磁性反而恢复了. 金掺杂纳米带的能带结构对掺杂率敏感: 随着掺杂率的增大, 掺杂纳米带分别表现半导体特性、半金属特性以及金属特性. 本文的计算表明金原子掺杂可以调制ZGNR的磁性以及能带特性, 为后续实验起指导作用, 有利于推动石墨烯材料在自旋电子学方面的应用.     

稀土元素(La,Y)掺杂GaN的第一性原理计算

采用基于密度泛函理论的第一性原理赝势平面波方法,对稀土元素La,Y单掺杂和La和Y共掺杂GaN的晶格常数、电子结构及光学性质进行了计算与分析.计算结果表明:掺杂改变了GaN的能带结构,未掺杂和Y掺杂形成导带底和价带顶位于G点的直接带隙半导体,而La掺杂和La和Y共掺杂形成导带底位于G点,价带顶位于Q点的间接带隙半导体.可以通过掺杂元素来调制GaN的禁带宽度和带隙类型,掺杂均提高GaN在低能区的静态介电常数、反射率、折射率,使光子的跃迁强度增大,说明稀土元素La,Y掺杂可有效调制GaN的光电性质.     

铂掺杂扶手椅型石墨烯纳米带的电学特性研究

本文采用基于密度泛函理论(DFT)的第一性原理计算了铂原子填充扶手椅型石墨烯纳米带(AGNR)中双空位结构的电学性能.计算结果表明: 通过控制铂原子的掺杂位置, 可以实现纳米带循环经历小带隙半导体—金属—大带隙半导体的相变过程; 纳米带边缘位置是铂原子掺杂的最稳定位置, 边缘掺杂纳米带的带隙值随宽度的变化与本征AGNR一样可用三簇曲线表示, 但在较大宽度时简并成两条曲线, 一定程度上抑制了带隙值的振荡; 并且铂原子边缘掺杂导致宽度系数N_a = 3p和3p + 1(p是一个整数)的几个较窄纳米带的带隙中出现杂质能级, 有效地降低了其过大的带隙值. 此外, 铂掺杂AGNR的能带结构对掺杂浓度不是很敏感, 从而降低了对实验精度的挑战. 本文的计算有利于推动石墨烯纳米带在纳米电子学方面的应用.     

过渡金属原子掺杂对单层MoS_2磁性的影响

本文利用基于密度泛函理论的第一性原理平面波赝势方法分别计算了本征及过渡金属掺杂单层MoS_2的晶格参数、电子结构和磁性性质.计算结果显示,过渡金属掺杂所引起的晶格畸变与杂质原子的共价半径有联系,但并不完全取决于共价半径的大小.分析电子结构可以看到,VIIB、VIII和IB族杂质中除Ag和Re外的掺杂体系都对外显示磁性,磁矩主要集中在掺杂的过渡金属原子上.掺杂体系的禁带区域都出现了数目不等的杂质能级,这些杂质能级主要由杂质的d、S的3p和Mo的4d轨道组成.     

Filling fraction limit for intrinsic voids in crystals: doping in skutterudites

The doping limit or the filling fraction limit (FFL) of various impurities for the intrinsic voids in the lattice of is studied by the density functional method. The FFL is shown to be determined not only by the interaction between the impurity and host atoms but also by the formation of secondary phases between the impurity atoms and one of the host atoms. The predicted FFLs for Ca, Sr, Ba, La, Ce, and Yb in are in excellent agreement with reported experimental data. A correlation between the FFL of an impurity atom and its valence state and electronegativity is discovered.     

Al高掺杂浓度对ZnO禁带和吸收光谱影响的第一性原理研究

采用密度泛函理论框架下的第一性原理平面波超软赝势方法, 建立了未掺杂与不同浓度的Al原子取代Zn原子的两种Zn_1-xAl_xO超胞模型,分别对模型进行了几何结构优化、态密度分布和能带分布的计算. 结果表明: ZnO高掺杂Al的条件下, 掺杂的Al原子浓度越大,间隙带越窄, 蓝移越弱. 计算结果和实验结果相一致.     

3d过渡金属Co掺杂核壳结构硅纳米线的第一性原理研究

基于密度泛函理论的第一性原理计算,研究了横截面为五边形和六边形的核壳结构硅纳米线的过渡金属Co原子替代掺杂.通过比较形成能发现,核心位置掺杂、壳层单链掺杂以及外壳层全替代掺杂的硅纳米线都具有稳定性,其中核心位置掺杂结构的稳定性最高.掺杂体系均呈现金属性,随着掺杂浓度的增加,电导通道数增加.Co原子掺杂的硅纳米线呈现铁磁性,具有磁矩.Bader电荷分析表明,电荷从Si原子转移至过渡金属Co原子.与自由态时过渡金属Co原子的磁矩相比,体系中Co原子的磁矩有所降低,这主要是由Co原子4s轨道向3d/4p轨道的电荷转移以及4s,3d,4p的上自旋电子转移至下自旋导致的.     

高位K2(1Λg) 与基态原子的碰撞转移

在K原子密度约为0.5～5×1016cm-3的样品池中,脉冲激光710 nm线双光子激发K2基态到高位1Λg态,研究了K2(1Λg)+ K(4S)碰撞转移过程.K原子密度由测量KD2线蓝翼对白光的吸收得到.测量不同K密度下1Λg态发射的时间分辨荧光强度,它是一条指数衰减曲线,由此得到1Λg态的有效寿命,从描绘出的有效寿命倒数与K原子密度关系直线的斜率得到1Λg态总的碰撞猝灭截面为(2.1±0.2)×10-14cm2,从截距得到的辐射寿命为(22±2)ns.测量了K的6S →4P3/2和4D→4P3/2在不同K密度下的时间积分荧光强度,得到了K2(1Λg)+K→K2(11∑ +g)+K(6S,4D)碰撞转移截面为(1.5±0.3)×10-15cm2(对转移到6S)和(8.5±3.0)×10-15cm2(对转移到4D).     

氧化锌掺钡的电子结构及其铁电性能研究

运用基于密度泛函理论的第一性原理方法计算了不同原子百分比含量的Ba掺杂Zn0半导体体材料超晶胞的能带结构、电子态密度、极化率和相对介电值.计算结果表明:Ba掺杂的Zn0体系为直接带隙半导体材料,其禁带宽度随着Ba原子掺杂百分比的增加呈现出逐渐增大的趋势.体系铁电性能的计算表明:与纯Zn0相比,Zn0掺入Ba原子后的极化率与相对介电值发生了较为明显的变化,其极化率随着Ba原子掺杂百分比的增加而增大,相对介电值随着Ba原子掺杂百分比的增加而减小.对角化后的极化率分量的数值结果表明:在电场作用下超胞中可能存在微畴结构,并且由于畴间电偶极矩的强相互作用,使得超胞宏观上表现为几乎具有各向同性的极化率特征.     

Lithium/Silver-Doped Cu_2ZnSnS_4 with Tunable Band Gaps and Phase Structures: a First-Principles Study

Doping is an effective approach for improving the photovoltaic performance of Cu_2 ZnSnS_4(CZTS). The doping by substitution of Cu atoms in CZTS with Li and Ag atoms is investigated using density functional theory. The results show that the band gaps of Li_(2 x)Cu_(2(1-x))ZnSnS_4 and Ag_(2 x)Cu_(2(1-x))ZnSnS4 can be tuned in the ranges of 1.30-3.43 and 1.30-1.63 eV, respectively. The calculation also reveals a phase transition from kesterite to wurtzite-kesterite for Li_(2 x)Cu_(2(1-x))ZnSnS_4 as x is larger than 0.9. The tunable band gaps of Li_(2 x)Cu_(2(1-x))ZnSnS_4 and Ag_(2 x)Cu_(2(1-x)) ZnSnS_4 make them beneficial for achieving band-gap-graded solar cells.     

B与N掺杂对单层石墨纳米带自旋极化输运的影响

通过第一性原理计算研究了具有锯齿状边沿并且具有反铁磁构型的单层石墨纳米带的自旋极化输运.研究发现,在中心散射区同一位置掺入单个B和N原子,尽管对整个体系磁矩的影响完全相同,但对两个自旋分量电流的影响却完全相反.掺B时,自旋向上的电流显著大于自旋向下的电流;而掺N时,自旋向下的电流显著大于自旋向上的电流.这是由于不管掺B还是掺N都将打破自旋简并,使得导带和价带中自旋向上的能级比自旋向下的能级更高.掺B引入空穴,使完全占据的价带变为部分占据,从而自旋向上的能级正好处于费米能级,使得电子透射能力更强、电流更大,而自旋向下的能级则离费米能级较远使电子透射的能力较弱.掺N则引入电子,使得原来全空的导带变为部分占据,从而费米能级穿过导带中自旋向下的能级,使得自旋向下的电子比自旋向上的电子透射能力更强. 关键词： 自旋极化输运 单层石墨纳米带 第一性原理 非平衡格林函数     

Structural and electronic properties of Fe-doped BaTiO3 and SrTiO3

We have performed first principles calculations of Fe-doped BaTiO3 and SrTiO3. Dopant formation energy, structure distortion, band structure and density of states have been computed. The dopant formation energy is found to be 6.8eV and 6.5eV for Fe-doped BaTiO3 and SrTiO3 respectively. The distances between Fe impurity and its nearest O atoms and between Fe atom and Ba or Sr atoms are smaller than those of the corresponding undoped bulk systems. The Fe defect energy band is obtained, which mainly originates from Fe 3d electrons. The band gap is still an indirect one after Fe doping for both BaTiO3 and SrWiO3, but the gap changes from Γ-R point to Γ-X point.     

Electronic properties of anatase TiO2 doped by lanthanides: A DFT+U study

The effects of mono-doping of 4f lanthanides with and without oxygen vacancy defect on the electronic structures of anatase TiO₂ have been studied by first-principles calculations with DFT+U (DFT with Hubbard U correction) to treat the strong correlation of Ti 3d electrons and lanthanides 4f electrons. Our results revealed that dopant Ce is easy to incorporate into the TiO₂ host by substituting Ti due to its lower substitutional energy (∼−2.0 eV), but the band gap of the system almost keeps intact after doping. The Ce 4f states are located at the bottom of conduction band, which mainly originates from Ti 3d states. The magnetic moment of doped Ce disappears due to electron transfer from Ce to the nearest O atoms. For Pr and Gd doping, their substitutional energies are similar and close to zero, indicating that both of them may also incorporate into the TiO₂ host. For Pr doping, some 4f spin-down states are located next to the bottom of the conduction band and narrow the band gap of the doping system. However, for Gd doping, the 4f states are located in deep valence band and there is no intermediate band in the band gap. The magnetic moment of dopant Gd is close to the value of isolated Gd atom (∼7 μB), indicating no overlapping between Gd 4f with other orbitals. For Eu, it is hard to incorporate into the TiO₂ host due to its very higher substitutional energy. The results also indicated that oxygen vacancy defect may enhance the adsorption of the visible light in Ln-doped TiO₂ system.