Ti掺杂NbSe2电子结构的第一性原理研究

采用基于密度泛函理论框架下的第一性原理平面波超软赝势方法, 计算了理想2H-NbSe₂和Ti掺杂2H-NbSe₂晶体的几何结构及电子结构; 对掺杂前后超胞的能带图、态密度及分波态密度图进行了分析. 结果表明, 掺杂后费米能级附近能量区域的电子态密度出现了较高的峰值, 且费米能级位置发生了改变. 理论上可以认为Ti的掺杂会使得NbSe₂的导电性增强, 有利于开发新型的电接触复合材料.     

Na掺杂CaMnO_3晶体材料的结构调控、电子结构与光吸收性质的研究

在平面波和赝势法基础上研究了Ca位Na掺杂的钙钛矿型CaMnO_3晶体材料的晶体结构、电子结构和光吸收性质,分析了Na掺杂CaMnO_3晶体材料的电输运过程。结果表明,Na掺杂Ca位使CaMnO_3的晶胞三轴长度均增大,Na掺杂在CaMnO_3中引入了晶格畸变,且晶格畸变是各向异性的。Na掺杂之后,CaMnO_3晶体材料内的O-Mn-O形成的八面体逐步向两个O顶点方向拉长和扭曲。未掺杂和Na掺杂CaMnO_3带隙宽度分别为0.713eV和0.686eV,均呈现明显的半导体特性。在费米能级附近,s态电子对CaMnO_3的态密度贡献最小,p态电子对费米能级以下的态密度贡献最大,d态电子对费米能级以上的态密度贡献最大。Mnp态电子对费米能下方能级形成贡献较大,而Mnd态电子对费米能上方能级形成贡献最大,Op态电子对费米能下方能级形成贡献较大,而Op态电子对费米能上方能级形成贡献最小。与未掺杂CaMnO_3相比,Na掺杂CaMnO_3晶体材料吸收能量向低能量移动,且存在两个强吸收峰,其在6.15eV附近的吸收最强。     

基于密度泛函理论研究掺杂Pd石墨烯吸附O2及CO

基于第一性原理的密度泛函理论研究了单个O₂和CO气体分子吸附于本征石墨烯和掺杂钯(Pd)的石墨烯的体系, 通过石墨烯掺Pd前后气体分子的吸附能、电荷转移及能带和态密度的计算, 发现掺Pd后气体分子吸附能和电荷转移显著增大, 这是由于Pd的掺杂, 在本征石墨烯能带中引入了杂质能级, 增强了石墨烯和吸附气体分子间的相互作用; 氧化性气体O₂和还原性气体CO吸附对石墨烯体系能带结构和态密度的影响明显不同, 本征石墨烯吸附O₂后, 费米能级附近态密度变大, 掺Pd后在一定程度变小; 吸附还原性的CO后, 石墨烯费米能级附近态密度几乎没有改变, 表明掺杂Pd不会影响石墨烯对CO的气体灵敏度, 但由于CO对石墨烯的吸附能增大, 可以提高石墨烯对还原性气体的气敏响应速度.     

Mn-N共掺p型ZnO的第一性原理计算

基于密度泛函理论的第一性原理平面波超软赝势法对ZnO(Mn,N)体系的晶格结构、形成能、态密度以及电荷密度进行了计算和理论研究.研究结果表明,Mn和N共掺杂ZnO体系具有更低的杂质形成能和更高的化学稳定性,更加适合p型掺杂.Mn和N以1:2的比例掺杂时,体系的形成能降低,体系更稳定;同时,体系中形成双受主能级缺陷,使得杂质固溶度增大,体系中载流子数增多,p型化特征更明显.此外,研究发现相比于N单掺杂ZnO体系,Mn和N原子共掺杂ZnO体系有更多的杂质态密度穿越费米能级,在导带与价带之间形成更宽的受主N 2p的杂质态,同时空穴有效质量变小.与Mn-N共掺杂体系相比,Mn-2N共掺杂体系的受主杂质在费米能级附近的态密度更加弥散,非局域化特征明显.因此,Mn-N共掺杂有望成为p型掺杂的更有效的手段.     

Ⅲ族元素掺杂对SnO2电子结构及电学性能的影响

采用密度泛函理论研究了Ⅲ族元素掺杂对SnO₂电子结构及电学性能的影响.态密度分析结果表明，以替代位存在的Ⅲ族杂质均使SnO₂的费米能级明显向低能态方向移动，使得价带顶不完全填满，因此在SnO₂中均充当受主作用.部分态密度分析结果表明，相对于掺Al的SnO₂，Ⅲ族元素中的Ga及In对费米能级附近态密度贡献较大，其主要贡献来自Ga3d态或In4d态，这预示着在SnO₂中掺Ga或In能实现更好的p型掺杂效果.电离能计算结果进一步表明，在Al，Ga及In三种元素中，替位In有最小的电离能(0.06 eV)，这说明其在SnO₂中能形成最浅的受主能级，因而在同等掺杂情况下，可引入最高浓度的空穴，从而实现最佳的p型掺杂效果. 关键词： 密度泛函理论 2')" href="#">SnO₂ Ⅲ族元素掺杂 电子结构     

第一性原理研究Te-N共掺p型ZnO

采用基于密度泛函理论的第一性原理赝势法对Te-N共掺杂ZnO体系的晶格结构、 杂质态密度和电子结构进行了理论分析.研究表明, N掺杂引起晶格收缩,而Te的掺入引起晶格膨胀, 从而减小晶格应力促进N的掺杂,并且Te由于电负性小于O而带正电, Te在ZnO中作为等电子施主而存在.研究发现, N掺杂体系中在费米能级附件形成窄的深受主能级, 而Te-N共掺体系中, N杂质带变宽,空穴更加离域,同时,空穴有效质量变小,受主能级变浅, 更有利于实现p型特性.因此, Te-N共掺有望成为一种更为有效的p型掺杂手段.     

Fe，Ag掺杂单层MoSe2光电性质的第一性原理计算

本文基于第一性原理分别计算了Fe, Ag掺杂对单层MoSe₂电子结构和光电效应的影响,结果表明:与本征单层MoSe₂相比,Fe, Ag掺杂体系的能带更加密集,且费米能级附近均出现了较多杂质能带;通过对分波态密度进行分析,发现其分别是由Fe-3d、Se-4p轨道和Se-4p、Mo-4d轨道所贡献.在近乎整个可见光范围内,Fe, Ag掺杂有效加强了单层MoSe₂的光响应能力,其中Ag掺杂效果最好;这可以归结于掺杂显著改变了单层MoSe₂费米能级附近的能带结构.即掺杂进一步减小了体系的带隙,更有利于电子跃迁,进而产生较大的光响应.研究结果可为单层MoSe₂在光电器件的实际应用提供一定的理论参考.     

AgSnO2触头材料在Ni-S共掺杂下的第一原理性计算

该研究采用掺杂的方式对SnO₂的导电性能进行改良,基于密度泛函理论的第一性原理,运用CASTEP软件对单掺杂Ni-SnO₂、S-SnO₂和共掺杂Ni-S-SnO₂的晶格参数、能带结构、电子态密度进行了计算,并对其电荷布居进行了分析.结果表明：S单掺杂时,晶胞体积略微增大;Ni单掺杂时,晶胞体积略微减小;而Ni-S共掺杂时,晶胞体积略微增大但增大幅度小于S单掺杂时的晶胞体积.与未掺杂相比,掺杂使得晶胞禁带减小、杂质能级增多、电子跃迁能减小,使其导电性增强,同时,掺杂使得费米能级附近峰值减小,局域性下降,原子间成键更强,材料更稳定.     

掺杂MgCNi3超导电性和磁性的第一性原理研究

从第一性原理出发，计算了MgCNi₃的电子能带结构.MgCNi₃中C 2p与Ni 3d轨道杂化使穿梭费米面上的Ni 3d能带表现出平面性，费米面落在态密度范霍夫奇异(vHs)峰的右坡上.vHs峰上大的电子态密度和铁磁相变点附近的自旋涨落是决定MgCNi₃超导电性的重要因素.研究了三种替代式掺杂对其超导电性和磁性的影响，发现电子掺杂使费米能级下滑到态密度较低的位置，导致体系转变为无超导电性的顺磁相；同构等价电子数的金属间化合物的轨道杂化，引起费米面上态密度的减少，降低了超导电性；而空穴掺杂使费米面向vHs峰值方向移动，虽然费米面上电子态密度增大可能提高超导电性，但增强了的Ni原子磁交换作用产生铁磁序，破坏了超导电性. 关键词： 电子结构 超导电性 磁性 掺杂     

Mg,Al掺杂对LiCoO2体系电子结构影响的第一原理研究

为了研究Mg, Al掺杂对锂二次电池正极材料LiCoO₂体系的电子结构的影响，进而揭示Mg掺杂的LiCoO₂具有高电导率的机理，对Li(Co, Al)O₂和Li(Co, Mg)O₂进行了基于密度泛函理论的第一原理研究. 通过对能带及态密度的分析，发现在Mg掺杂后价带出现电子态空穴，提高了电导，并且通过歧化效应（disproportionation）改变了Co-3d电子在各能级的分布，而Al掺杂则没有这些作用. O关键词： 2')" href="#">LiCoO₂ 电子结构 第一原理 电导     

TiO_2薄膜的硼掺杂对TiO_2/p~+-Si异质结器件电致发光的增强

利用磁控溅射在重掺硼硅(p+-Si)衬底上分别沉积TiO2薄膜和掺硼的TiO2(Ti O2∶B)薄膜,并经过氧气氛下600℃热处理,由此形成相应的TiO2/p+-Si和TiO2∶B/p+-Si异质结。与Ti O2/p+-Si异质结器件相比,TiO2∶B/p+-Si异质结器件的电致发光有明显的增强。分析认为:TiO2∶B薄膜经过热处理后,B原子进入TiO2晶格的间隙位,引入了额外的氧空位,而氧空位是TiO2/p+-Si异质结器件电致发光的发光中心,所以上述由B掺杂引起的氧空位浓度的增加是TiO2∶B/p+-Si异质结器件电致发光增强的原因。     

SnO_2/p~+-Si异质结器件的电致发光:利用TiO_2盖层提高发光强度

通过在重掺硼硅(p+-Si)衬底上溅射SnO2薄膜并在O2气氛下800℃热处理形成SnO2/p+-Si异质结.基于该异质结的器件可在低电压(电流)驱动下电致发光.进一步地,通过在SnO2薄膜上增加TiO2盖层,使器件的电致发光获得显著增强.这是由于TiO2盖层的引入,一方面使SnO2薄膜更加致密,减少了非辐射复合中心;另一方面TiO2较大的折射率和合适的厚度使SnO2薄膜电致发光的出光效率得到提高.     

Impurity-state-like nature of Fermi-liquid states in Bi2Sr2CaCu2O8 observed by photoemission and x-ray absorption

Photoemission and X-ray absorption spectroscopy have been performed on Bi₂Sr₂Ca_1−xY_xCu₂O₈ in which the hole concentration is controlled by the ratio between Ca and Y atoms. It was found that the density of electronic states at the Fermi level gradually increases as the hole concentration with almost no rigid shift of the electronic structure with respect to the Fermi level. This suggests that the electronic states at the Fermi level (Fermi-liquid states) would not be simple one-electron states but be a kind of impurity states produced through the strong hybridization between doped O2p hole orbitals and empty Cu3d orbitals.     

真空紫外区Ar的高次离化光谱的研究

本文报道了波长在2000—194?真空紫外区域内Ar的高次离化光谱工作。观察到相当数量的新谱线,并归属了其中64条,还找到六个新能级,即:ArIV 3s²3p²(³P)3d²F_5/2,7/2, ArIV 3s²3p²(¹D)3d²S_1/2, ArV3s²3p3d关键词：     

First-principles analysis of the structural,electronic, and elastic properties of cubic organic-inorganic perovskite HC(NH_2)_2PbI_3

The structural, electronic, and elastic properties of cubic HC(NH_2)_2PbI_3 perovskite are investigated by density functional theory using the Tkatchenko–Scheffler pairwise dispersion scheme. Our relaxed lattice parameters are in agreement with experimental data. The hydrogen bonding between NH_2 and I ions is found to have a crucial role in FAPbI_3 stability. The first calculated band structure shows that HC(NH_2)_2PbI_3 has a direct bandgap(1.02 eV) at R-point, lower than the bandgap(1.53 eV) of CH_3NH_3PbI_3. The calculated density of states reveals that the strong hybridization of s(Pb)–p(I) orbital in valence band maximum plays an important role in the structural stability. The photo-generated effective electron mass and hole mass at R-point along the R–Γ and R–M directions are estimated to be smaller: m_e~*= 0.06 m0 and m_h~*= 0.08 m0 respectively, which are consistent with the values experimentally observed from long range photocarrier transport. The elastic properties are also investigated for the first time, which shows that HC(NH_2)_2PbI_3 is mechanically stable and ductile and has weaker strength of the average chemical bond. This work sheds light on the understanding of applications of HC(NH_2)_2PbI_3 as the perovskite in a planar-heterojunction solar cell light absorber fabricated on flexible polymer substrates.     

低速Xe~(q+)(4≤q≤20)离子与Ni表面碰撞中的光辐射

实验中测量了0.38V_(Bohr)(460 keV)高电荷态Xe~(q+)(4≤q≤20)离子轰击高纯Ni表面发射的400-510 nm光谱.实验结果包括NiⅠ原子谱线,NiⅡ离子谱线,以及入射离子中性化发射的XeⅠ,XeⅡ和XeⅢ谱线.研究了谱线XeⅡ410.419,XeⅢ430.444,XeⅡ434.200,XeⅡ486.254,NiⅠ498.245,NiⅠ501.697,NiⅠ503.502,NiⅠ505.061和NiⅠ508.293 nm的光子产额随着入射离子电荷态的变化.结果表明,入射离子中性化和溅射Ni原子发射谱线的光子产额随着入射离子电荷态的增加而增加,其趋势与入射离子势能一致.     

Correlation effects in photoelectron spectra of high-Tc superconductive oxides: the hole-induced redistribution of Cu3d states in La2CuO4

In the transition state model using the LMTO-Green function method an investigation is performed of the changes in energy distribution of Cu3d and O2p states in the valence band of La₂CuO₄ which are caused by the presence of the photoelectron hole. It is shown that taking the hole into account leads to a sharp decrease in the density of Cu3d states on the Fermi level and to a low-energy shift of the d band edge relative to the Fermi level. The grounds for the suggestion of the purely oxygenic nature of hole carriers in high-T_c superconductors are discussed.     

GeSn (0.524 eV) single-junction thermophotovoltaic cells based on the device transport model

Based on the transport equation of the semiconductor device model for 0.524 eV GeSn alloy and the experimental parameters of the material, the thermal-electricity conversion performance governed by a GeSn diode has been systematically studied in its normal and inverted structures. For the normal p⁺/n (n⁺/p) structure, it is demonstrated here that an optimal base doping N_d(a) = 3 (7)×10¹⁸ cm^-3 is observed, and the superior p⁺/n structure can achieve a higher performance. To reduce material consumption, an economical active layer can comprise a 100 nm-300 nm emitter and a 3 μm-6 μm base to attain comparable performance to that for the optimal configuration. Our results offer many useful guidelines for the fabrication of economical GeSn thermophotovoltaic devices.     

A Modified Approach for Calculating Dressed Quark Propagator at Finite Chemical Potential

Based on the rainbow approximation of Dyson-Schwinger equation and the assumption that the full inverse quark propagator at finite chemical potential is analytic in the neighborhood of μ = 1, it is proved that the dressed quark propagator at finite chemical potential μ can be written as G0^-1 [μ] =iγ·p↑-A（p↑-^2） ＋B（p↑-^2） with p↑-μ= （p↑-p4 ＋iμ）. From the dressed quark propagator at finite chemical potential in Munczek model the bag constant of a baryon and the scalar quark condensate are evaluated. A comparison with previous results is given.     

Dielectrics for passivation of planar InP/InGaAs diodes

We have investigated dielectrics for passivating planar InP or InGaAs photodiodes: thermally evaporated Al₂O₃ and SiO, sputtered Si₃N₄ and SiO₂ and also SiO₂ using chemical vapour deposition. The measured bulk and field-effect properties of all dielectrics excluding sputtered SiO₂ were suitable for this application. In planar InGaAs diodes with Cd diffused or Mg implanted p⁺-region a disordered dielectric/semiconductor surface led to high reverse current densities above 1 mA/cm². In InP diodes with p⁺-diffusion and dielectrics exhibiting positive flatband voltages, e.g. Si₃N₄ and Al₂O₃, reverse current densities of 10 μA/cm² were measured probably caused by a slight inversion of the semiconductor surface. With a SiO or CVD-SiO₂ passivating layer on n-InP lowest leakage current densities (10 nA/cm²) were achieved. Very low dark-current planar photodiodes InP/InGaAsP/InGaAs have been fabricated using SiO passivation (30 nA/cm²).