掺杂β-FeSi2的电子结构及光学性质的第一性原理研究

采用基于密度泛函理论的赝势平面波方法,对掺入Mn,Cr,Co,Ni的β-FeSi2的几何结构、能带结构和光学性质进行了研究.计算结果表明:(1)杂质的掺入改变了晶胞体积及原子位置,掺杂足调制材料电子结构的有效方式;(2)系统总能量的计算表明Mn掺杂时倾向于置换Fel位的Fe原子,而Cr,Co,Ni倾向于取代Fell位的Fe原子;能带结构的计算表明掺Mn,Cr使得β-FeSi2的费米面向价带移动,形成了P型半导体;而掺Co,Ni则使得β-FeSi2的费米面向导带移动,形成了n型半导体;(3)杂质原子的掺入在费米面附近提供了大量的载流子,改变了电子在带间的跃迁,对β-FeSi2的光学性质造成影响.     

掺杂β-FeSi2的电子结构及光学性质的第一性原理研究

采用基于密度泛函理论的赝势平面波方法,对掺入Mn,Cr,Co,Ni的β-FeSi2的几何结构、能带结构和光学性质进行了研究.计算结果表明:(1)杂质的掺入改变了晶胞体积及原子位置,掺杂足调制材料电子结构的有效方式;(2)系统总能量的计算表明Mn掺杂时倾向于置换Fel位的Fe原子,而Cr,Co,Ni倾向于取代Fell位的Fe原子;能带结构的计算表明掺Mn,Cr使得β-FeSi2的费米面向价带移动,形成了P型半导体;而掺Co,Ni则使得β-FeSi2的费米面向导带移动,形成了n型半导体;(3)杂质原子的掺入在费米面附近提供了大量的载流子,改变了电子在带间的跃迁,对β-FeSi2的光学性质造成影响.     

金红石相TiO_2(110)面吸附H_2S分子光学气敏效应的微观机制与特性

光学气敏材料吸附气体分子后导致光学性质发生变化,运用这一原理来检测环境中的气体成分,称为光学气敏效应。采用基于密度泛函理论(DFT)体系下的第一性原理平面波超软赝势方法,研究了光学气敏材料金红石相TiO2(110)表面吸附H2S分子的微观特性,计算了TiO2(110)表面吸附能、电荷密度、态密度和光学性质的变化。结果表明,TiO2最稳定的表面是终止于二配位O原子的(110)面,只有含有氧空位的表面才能稳定吸附H2S,且氧空位比例越高,越有助于H2S吸附于表面;表面吸附H2S以水平吸附方式为主,在氧空位比例达到33%时,吸附能为0.7985eV;吸附的实质是表面氧空位具有氧化性,氧化了H2S分子。在可见光400~760nm范围内,存在氧空位的TiO2(110)表面吸附H2S后都可改善表面的光学性质。氧空位缺陷浓度越高,改善材料对可见光的吸收和反射能力越强,光学气敏响应能力越佳。     

Ni在Si(111)和Si(100)面上吸附的理论研究

采用集团模型和分立变分的 Xα方法研究 Ni原子在Si(111)顶位和三度开位吸附,以及在Si(100)四度位和桥位吸附的可能性,由体系的总能量最低确定稳定吸附位置,并在稳定吸附位讨论了Ni-Si成键特性和态密度.结果表明,只有当Si(111)表面弛豫情况下Ni原子才能沿[111]方向进入表面以下,但Ni原子也能沿[100]方向进入Si表面层.计算所得态密度与实验符合较好.比较所得的态密度和 NiSi_2/Si(111)的界面态密度表明位于表面下的Ni可能是生长NiSi_2的先兆.     

Si(111)面氟吸附的研究

本文先用集团模型和电荷自治的EHT方法研究了Ⅶ族元素F在 Si(111)面的化学吸附,利用能量极小原理确定了化学吸附位置;在此基础上,采用薄片(SLAB)模型和EHT经验紧束缚方法对吸附体系的电子结构作了计算.计算结果表明,F可以吸附在Si(111)面的顶位和三度空位上,但以顶位为更稳状态.顶位吸附时,F与表面的距离为1.53A,吸附能为4.7eV;三度位吸附时,F与表面的距离为-2.2A,吸附能为3.1eV.吸附后,F对总态密度和能带的贡献主要局域在真空能级下-17eV～-19eV之间.此外,顶位吸附使原清洁表面悬键引起的表面态消失.     

Mg在Si(100)-2?1表面的化学吸附

用紧束缚下的Muffin-tin轨道线性组合方法研究了0.5个单层Mg原子在Si(100)-(2×1)表面的化学吸附。计算了Mg 原子在不同位置时吸附体系的能量。结果表明,Mg原子在吸附面上方的cave位吸附最稳定,同时在吸附面上方还存在一个亚稳位置shallow位,这与实验结果一致。同时对电子转移情况和层投影态密度进行了研究。     

N2在Fe2Ge高对称晶面的吸附特性研究

采用基于密度泛函理论的第一性原理方法计算了N2在Fe2Ge多个晶面上的吸附特性,对模型的真空层厚度及截断能进行了收敛性测试,测试结果表明当真空层厚度和截断能分别设置为1 nm和900 eV时,体系结构具有较好的收敛效果.计算了Fe2Ge的(001)、(010)、(100)、(110)、(111)、(210)六个不同晶面...     

用“胶体-原子薄片”模型计算W(100)-Cs吸附系统的逸出功

碱或碱土金属的原子吸附于过渡金属表面时,会使后者的逸出功急剧下降。作者提出了“胶体-原子薄片”模型来研究这一现象。过渡金属基底用薄膜线性级加平面波(LAPW)法精确处理,而简单金属覆层则用胶体(jellium)模拟。此模型可在充分考虑构成基底的过渡金属特点的情况下,研究单原子层覆盖度以下的吸附系统的电子性质。 文中给出了计算所得W(100)面吸附Cs后的φ-θ曲线。所得逸出功极小值φ_(min)=1.44—1.48eV与实验结果(φ_(min)=1.35—1.55eV)吻合较好,文中还讨论了E_v参量的选择等问题。     

Ca_3La_2 W_2O_(12):Mn和Ca_3La_2Te_2O_(12):Mn的发光

西德 Tubingen 大学有机化学研究所的H.D.Autenrieth 和 S.Kemmler—Sack 对新型基质材料 Ca_3La_2W_2O_(12)的发光进行了一系列研究。用过渡族金属原子和主族元素M=Cr,Mn,Fe,Ni,Sn,Pb,Bi(Ca_3     

硫钝化GaP(001)表面的结构及电学性质研究

基于第一性原理的密度泛函理论,分析了覆盖度为1 ML(monolayer)的硫吸附在磷截止和镓截止的GAP(001)(1×2)表面的结构和电学属性.能量计算表明,最稳定的吸附模型均是SHB ST4,镓和磷二聚物都被断开,周期单元由(1×2)变成(1×1),硫原子吸附在桥位置,Ga-S键比P-S键更稳定.电学性质分析可知,硫吸附在镓截止GaP表面后能隙中的表面态大幅度减少,而吸附在磷截止的表面时表面态并没有减少且在0.74 eV处多了一个新峰,硫吸附在镓截止表面后的态密度分布与实验结果吻合很好.因此,1 ML的硫吸附在GAP(001)面时表面上最主要形成Ga-S键.     

Influence of Ni and Cr impurities on the electronic properties of Cu(In,Ga)Se2 thin film solar cells

Deposition of Cu(In,Ga)Se₂ (CIGS) thin film solar cells on metallic substrate is an attractive approach for development of low cost solar modules. However, in such devices, special care has to be taken to avoid diffusion of impurities, such as Fe, Ni, and Cr, from the substrate into the active layers. In this work, the influence of Ni and Cr impurities on the electronic properties of CIGS thin film solar cells is investigated in detail. Impurities were introduced into the CIGS layer by diffusion during the CIGS deposition process from a Ni or Cr precursor layer below the Mo electrical back contact. A high temperature and a low temperature CIGS deposition process were applied in order to correlate the changes in the photovoltaic parameters with the amount of impurities diffused into the absorber layer. Solar cells with Ni and Cr impurities show a reduction in the device performance, whereas the effect was most pronounced in Ni containing devices. The presence of deep defect levels in the absorber layer was identified with admittance spectroscopy and can be related to Ni and Cr impurities, which diffused into the CIGS layer according to secondary ion mass spectroscopy depth profiles and inductively coupled plasma mass spectrometry. Copyright © 2014 John Wiley & Sons, Ltd.     

Diffusion of gold and native defects in mercury cadmium telluride

The diffusion of defects is of great importance in nanoscale device fabrication, making it essential to understand theoretically the microscopic mechanisms governing how native and dopant defects diffuse. To gain this insight, we have performed, for the first time, ab initio density functional calculations to determine the diffusion barriers for multiple pathways of Au impurities and native species in mercury cadmium telluride (MCT). We consider interstitial and vacancy-mediated diffusion mechanisms and calculate the corresponding activation energies using ab initio pseudopotential total energy calculations. Depending on the stoichiometry, the activation energies for Hg self-diffusion are calculated to range from 1.35 eV to 1.60 eV (interstitial mechanism) and from 1.60 eV to 1.85 eV (vacancy mechanism). These theoretical values suggest that Hg self-diffusion is predominantly interstitial mediated, and are in good agreement with existing experimental estimates, which suggest possible activation energies ranging from 1.05 eV to 1.75 eV. For Te self-diffusion via the interstitial mechanism, the calculated activation energy ranging from 2.35 eV to 2.60 eV is also in good agreement with the experimental estimates near 2.30 eV. For Au impurities, whether they are incorporated into the interstitial or Hg site, we find the interstitial mediated mechanism to be the dominant one. Our calculated barrier of 0.35 eV for Au interstitials is also in good agreement with the experimental estimate of 0.45 eV.     

Regulating Electronic Structure of Fe–N4 Single Atomic Catalyst via Neighboring Sulfur Doping for High Performance Lithium–Sulfur Batteries

Constructing high performance electrocatalysts for lithium polysulfides (LiPSs) adsorption and fast conversion is the effective way to boost practical energy density and cycle life of rechargeable lithium–sulfur (Li–S) batteries, which have been regarded as the most promising next generation high energy density battery but still suffering from LiPSs shuttle effect and slow sulfur redox kinetics. Herein, a single atomic catalyst of Fe–N₄ moiety doping periphery with S (Fe–NSC) is theoretically and experimentally demonstrated to enhance LiPSs adsorption and facilitated sulfur conversion, due to more charge density accumulated around Fe–NSC configuration relative to bare Fe–N₄ moiety. Thereafter, the graphene oxide supported Fe–NSC catalyst (Fe–NSC@GO) is modified to the commercial separator through a simple slurry casting method. Thus, Li–S cells with Fe–NSC@GO modified separators display high discharge capacity and excellent cyclability, showing 1156 mAh g⁻¹ at 1 C rate and a low capacity decay of only 0.022% per cycle over 1000 cycles. Even with a high sulfur loading of 5.1 mg cm⁻², the cell still delivers excellent cycling stability. This work provides a fresh insight into electrocatalyst structural tuning to improve the electrochemical performance of Li–S batteries.     

缓冲层对铜催化生长碳管形貌和性能的影响

碳纳米管的生长通常使用Fe,Co,Ni作为催化剂,除此以外的一些过渡元素也能催化裂解生长碳管。其中用铜制备的碳管阈值电场低、发射电流密度大、发射均匀性好等等良好的场发射特性。铜与硅、或金属之间具有很强的的扩散特性,而碳管应用于场发射显示器必然使用玻璃、硅片作为衬底,所以需要一层缓冲层阻挡催化剂铜扩散入衬底。本文使用磁控溅射制备铜薄膜作为催化剂,化学气相沉积方法裂解乙炔生长碳管薄膜形成场发射阴极。并试验W,Ni,Cr和Ti作为铜薄膜的缓冲层,结果表明不同的金属阻挡特性不同,生长后碳管的形貌和特性都有差异。结果表明Ti和W能很好地阻挡铜的扩散,从而使铜催化裂解出附着性好、分布均匀、密度适中、场发射特性良好的碳管薄膜。对于Ni和Cr金属,由于生长的碳管与衬底结合差或者场发射能力差而不适合作铜的缓冲层。     

GaAs中4d过渡杂质Mo与Pd的光电行为

4d过渡杂质Mo、Pd在GaAs中分别引入E(0.42eV)、H(0.61eV)和E(0.66eV)、H(0.69eV)等能级。根据过渡杂质Mo和Pd在GaAs中的光电行为,推测这些杂质在GaAs中不起有效复合中心的作用。     

Electronic Metal-Support Interactions in Atomically Dispersed Fe(III)-VO2 Nanoribbons for High-Performance Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries have attracted wide attention as high-energy-density energy storage devices, but their practical applications are hindered by the severe shuttle effect and sluggish kinetics of lithium polysulfides (LiPSs). To address these challenges, polar mediators are employed to chemisorb and catalyze LiPSs, but most of them suffer from low electronic conductivity and poor catalytic activity. Here, a novel strategy is reported to enhance both properties by dispersing Fe(III) atoms in VO₂ nanoribbons(Fe-VO₂), creating electronic metal-support interactions (EMSI) that modulate the electronic structure and charge transfer of VO₂. Theoretical calculations reveal that EMSI lowers the energy barrier for the decomposition of Li₂S from 1.60 to 1.32 eV and increases the electronic conductivity of VO₂. Fe doping reduces the Li-ions diffusion barrier from 1.42 eV in VO₂ to 0.99 eV in Fe-VO₂. The Fe-VO₂ catalyst shows strong adsorption and fast converstion of LiPSs, resulting in high energy density and long cycling life of Li-S batteries. The cathode with Fe-VO₂ maintains a higher capacity retention of 67% after 500 cycles at 1 C, compared with 52.4% and 53.6% for the carbon black based cathode and VO₂  based cathode, respectively. This work demonstrates the potential of EMSI for designing efficient catalysts for Li–S batteries and provides new insights into the electronic structure engineering of polar mediators.     

GaAs光电阴极Cs,O吸附研究

提出了基于第一性原理的密度泛函理论框架下的广义梯度近似投影缀加波赝势法,在结构优化的基础上采用平板模型计算了GaAs（110）表面单一吸附0.5 ML Cs元素、单一吸附0.5 ML O元素及0.5 ML Cs、0.5 ML O共吸附系统的特定吸附位、吸附系统总能及吸附系统的电子结构。吸附系统总能的计算结果对比及电子结构图表明:当Cs、O元素吸附量在GaAs（110）表面达到=1 ML时,它们并非各自在表面形成局域畴形态的竞争性共化学吸附,而是将在表面形成混合均匀相的协同共化学吸附。采用偶极子校正进一步计算三种吸附系统的功函数分别是4.423 eV、5.749 eV、4.377 eV,从而得出GaAs光电阴极制备过程中提高并保持光电阴极发射性能的方法及机理。     

Shallow acceptor levels in 4H- and 6H-SiC

Shallow impurities are the principal means of affecting the electrical properties of semiconductors in order to induce desired characteristics. They can be used to isolate a region by introducing carriers of opposite charge, or they can be used to enhance the number of carriers of a particular type. Thermal admittance spectroscopy has been used to determine the activation energies of the principal p-type dopants, Al and B, in 4H and 6H-SiC, and temperature dependent Hall effect measurements were used to study the shallow B acceptors in 6H-SiC. The accept or species B and Al occupy inequivalent lattice sites in the Si sublattice, and would be expected to exhibit distinct energy levels for each site in analogy to the well known donor energy levels of N. Activation energies for B in 6H-SiC were found to be E_h=E_v+0.27 eV, E_k1=E_v+0.31 eV, and E_k2=E_v+0.38 eV. Al acceptors in 4H-SiC were found to exhibit two energy levels at E_h=E_v+0.212 eV and E_k=E_v+0.266 eV.     

聚焦光束合金化工艺对合金化层成型及显微组织的影响

采用Cr,Ni单质粉末及B ,Si造渣剂以聚焦光束合金化方法在 4 5 # 钢表面合成了奥氏体型表面层。借助扫描电镜 (SEM) ,能谱仪 (EDS) ,X射线等方法研究了合金化工艺对合金化层的成型、显微组织及物相组成的影响规律。试验结果表明 ,当合金化元素加入量一定时 ,合金化层的成型及其显微组织不仅取决于热输入量 ,还与造渣元素B ,Si的加入量有关。为获得成型良好的合金化层 ,热输入量增加时必须提高造渣元素B ,Si的加入量。采用低热输入合成的合金化层的显微组织由大量的γ(Fe ,Ni)及少量的晶界α(Fe Cr)构成 ,而高热输入合成的合金化层中的γ(Fe ,Ni)晶界为γ(Fe ,Ni) +Cr2 B双相共晶     

Electronic structure of cubic silicon carbide with substitutional 3<Emphasis Type="Italic">d</Emphasis> impurities at Si and C sites

The full-potential linear muffin-tin orbital method is used to calculate the electronic structure and cohesive energies for cubic silicon carbide doped with transition 3d metal impurities (Me=Ti, V, Cr, Mn, Fe, Co, Ni), substituting Si or C at the corresponding sublattice of the atomic matrix. It is established that all 3d impurities mainly occupy silicon sites. For the Ti → Si substitution, dopant impurity levels are located in the conduction band of SiC, whereas doping silicon carbide with other 3d impurities gives rise to additional donor or acceptor levels in the band gap. For 3C-SiC the effect of impurities on the lattice parameter (with the substitutions Me → Si) and on the impurity local magnetic moments (with the substitutions Me → Si, C) is studied.