MoSi2表面电子结构

利用ＬＭＴＯ－ＡＳＡ方法研究了Ｃ１１_b晶体结构的ＭｏＳｉ₂三种（００１）表面电子结构，分别给出了三种不同表面总体态密度和表面层原子局域态密度及分波态密度，与体结构相关原子态密度作了对比，并对费密能级上的态密度作了比较讨论。就表面稳定性而言，以Ｍｏ原子为表层原子的表面结构最不稳定，以单层ｓｉ原子为表面的表面结构最稳定，该结论支持了Ｔ．Ｋｏｍｅｄａ等的实验结果^［１５］。 关键词：     

Pr3+在SBN晶体中的发光特性

通过测量Ｐｒ：ＳＢＮ晶体的吸收光谱和荧光光谱来确定Ｐｒ³⁺在ＳＢＮ晶体中的能级位置。由于Ｐｒ³⁺离子占据晶体中的不同格位而引起荧光带呈现双峰结构。测量荧光寿命随温度的变化关系，表明Ｐｒ³⁺在ＳＢＮ晶体中 ³Ｐ₀态的无辐射弛豫主要是 ³Ｐ₀→¹Ｄ₂多声子弛豫过程。 关键词：     

势垒区δ掺杂量子阱Ge0.3Si0.7/Si/Ge0.3Si0.7的子带间跃迁光吸收系数

采用包络函数方法对生长在Ｇｅ_0.3Ｓｉ_0.7（００１）衬底上势垒区δ掺杂量子阱Ge_0.3Si_0.7/Si/Ge_0.3Si_0.7的电子能带结构及子带间光吸收特性进行了自洽的计算．对光吸收系数与量子阱的阱宽、δ掺杂位置及δ掺杂密度间的变化关系进行了讨论．最后对由高浓度的二维电子气的退极化效应所引起的频率位移进行了研究 关键词：     

ZnO-Bi2O3-Sb2O3-BaO系陶瓷的晶界相与抗退降性能

在通常的ＺｎＯ－Ｂｉ₂Ｏ₃－Ｓｂ₂Ｏ₃系电压敏陶瓷中，加入能构成压敏特性的钡添加剂，发现除已知的Ｂｉ₂Ｏ₃和Ｚｎ_2．３３Ｓｂ_０．６７Ｏ₄晶界相以外，还出现新的晶界相，分析表明是固溶有微量其它成分的偏锑酸钡（ＢａＳｂ₂Ｏ₆）晶相。同时还发现，ＢａＳｂ_{2关键词：}     

金刚石晶格上的对角无序与非对角无序非晶量子点

报道金刚石晶格上对角无序与非对角无序非晶量子点的理论研究，用简单的紧束缚哈密顿量描述模型的电子结构，用ｒｅｃｕｒｓｉｏｎ方法求解哈密顿方程，用边界条件对本征值的影响判断局域化，研究发现，带边为扩展态时，带宽的变化趋势与晶态量子点类似；带边为局域态时，尺寸超过某一临界长度后，带宽不变，但带边态密度随尺寸增大而增大。还研究了非晶量子点的介电函数虚部ε₂（?ω）。与扩展态对应的ε₂（?ω），对尺寸变化较敏感。与局域态对应的ε₂（?ω），当尺寸大于 关键词：     

LaxBi2-xTi4O11的合成及相变研究

合成了Ｌａ_xＢｉ_2-xＴｉ₄Ｏ₁₁系列样品，并完成了它们的喇曼光谱和ｘ射线衍射测量；结果表明，该体系在Ｘ＝１．２经历了一次相变，且相变与最低频声子模随Ｘ的变化有关。Ｌａ_0.2Ｂｉ_1.8·Ｔｉ₄Ｏ₁₁的相变温度为２００℃。初步获得Ｌａ₂Ｔｉ₄Ｏ₁₁的结构为正交结构。 关键词：     

CCl4,CH2Cl2和CHCl3对磷脂酰胆碱紫外电子吸收光谱的影响

测量了ＣＣｌ₄，ＣＨ₂Ｃｌ₂和ＣＨＣｌ₃对生物膜中磷脂酰胆碱作用的紫外电子吸收光谱，实验结果表明，由于ＣＣｌ₄，ＣＨ₂Ｃｌ₂和ＣＨＣｌ₃分子结构的差异，三种溶剂的极性依次递增，磷脂酰胆碱π－π^*电子跃迁的吸收峰红移。磷脂酰胆碱在ＣＣｌ₄中光谱呈单吸收峰，在ＣＨ₂Ｃｌ₂和ＣＨＣｌ₃中光谱特征呈双蜂结构，存在聚集体的激子态跃迁，由此给出了脂质分子聚集状态的光谱依据。 关键词：     

Sm2(Fe,M)17C1.5(M=Ga,Si)化合物的形成和磁性

用电弧炉熔炼方法制备了Ｓｍ₂Ｆｅ_17-xＭ_xＣ_1.5（Ｍ＝Ｇａ，Ｓｉ）化合物，研究了它们的形成、结构与磁性。实验结果表明，用Ｇａ替代Ｆｅ，当２≤ｘ≤６时，可形成Ｔｈ₂Ｚｎ₁₇型单相化合物，而Ｓｉ的替代仅在ｘ＝２时为单相结构。居里温度随Ｇａ含量的增加从ｘ＝２时的６３３Ｋ下降到ｘ＝６时的３５１Ｋ，Ｓｍ₂Ｆｅ₁₅Ｓｉ₂关键词：     

三角对称下3d3离子2E态g因子性质研究

采用完全对角化方法,以尖晶石结构的ZnAl₂Ｏ₄:Cr^3＋,ZnGa₂Ｏ₄:Cr^3＋和MgAl₂Ｏ₄:Cr^3＋系列晶体为例,联系晶格局域结构,对三角对称下3d³离子²E态g因子性质进行了研究.研究中考虑了包括自旋与自旋相互作用、自旋与另一轨 关键词： 2E态g因子')" href="#">²E态g因子 3离子')" href="#">3d³离子 尖晶石结构 磁相互作用     

3d系列 (TM)4 团簇的结构和磁性

基于第一性原理，在密度泛函理论下，用局域自旋密度近似(LSDA)和广义梯度近似(GGA)对(TM)₄团簇的所有几何构型进行优化、能量、频率和磁性计算.确定出3d系列(TM)₄团簇的基态构型，对其磁性、结合能和平均原子间距作了系统的研究，得出在3d系列(TM)₄团簇中，Mn₄的局域磁矩最大，V₄的局域磁矩最小，并且除Cr₄在LSDA和GGA均为反铁磁性耦合及GGA下的V_{关键词： 4}团簇')" href="#">(TM)₄团簇 基态构型 结合能 局域磁矩 平均原子间距     

Thermoelectric energy conversion in layered structures with strained Ge quantum dots grown on Si surfaces

The efficiency of the energy conversion devices depends in many ways on the materials used and various emerging cost-effective nanomaterials have promised huge potentials in highly efficient energy conversion. Here we show that thermoelectric voltage can be enhanced by a factor of 3 using layer-cake growth of Ge quantum dots through thermal oxidation of SiGe layers stacked in SiO₂/Si₃N₄ multilayer structure. The key to achieving this behavior has been to strain the Ge/Si interface by Ge dots migrating to Si substrate. Calculations taking into account the carrier trapping in the dot with a quantum transmission into the neighboring dot show satisfactory agreement with experiments above ≈200 K. The results may be of interest for improving the functionality of thermoelectric devices based on Ge/Si.     

Evolution of Si0.8Ge0.2 quantum dots during Si encapsulation

Surface structure, determined by scanning tunneling microscopy (STM), surface morphology, determined by atomic force microscopy (AFM), and surface composition, determined by X-ray photoelectron spectroscopy (XPS) of 20.0 nm Si_0.8Ge_0.2 quantum dots formed at 800 °C and encapsulated with 0-10 nm of Si at 500 °C and 800 °C are presented. It is observed that the quantum dot surface morphology changes during the Si encapsulation at 800 °C by the smoothing of the quantum dots. The height of the quantum dots decreases faster than can be accounted for from the amount of Si deposited, indicating that there is movement of material out of the quantum dots during the encapsulation process. Encapsulation at 500 °C results in a retention of the quantum dot surface morphology with increased Ge segregation compared to Si encapsulation at 800 °C. We conclude that the changing surface morphology at 800 °C is not the result of Ge segregation but due to intermixing resulting from the tensile strain of Si depositing on SiGe.     

β-Si3N4电子结构和光学性质的第一性原理研究

采用基于密度泛函的平面波赝势方法(PWP)和广义梯度近似(GGA)，计算了β相氮化硅(β-Si₃N₄)的电子结构和光学性质，得到的晶格常数、能带结构等均与实验结果较好符合.进一步还研究了β-Si₃N₄的光吸收系数以及禁带宽度随外压力的变化规律，为β-Si₃N₄材料在高压条件下的应用提供了理论参考. 关键词： β相氮化硅 电子结构 能带结构 光学性质     

Green Eu-doped Ba3Si6O12N2 phosphor for white light-emitting diodes: Synthesis, characterization and theoretical simulation

The Eu²⁺-doped Ba₃Si₆O₁₂N₂ green phosphor (Eu_xBa_3−xSi₆O₁₂N₂) was synthesized by a conventional solid state reaction method. It could be efficiently excited by UV-blue light (250-470 nm) and shows a single intense broadband emission (480-580 nm). The phosphor has a concentration quenching effect at x=0.20 and a systematic red-shift in emission wavelength with increasing Eu²⁺ concentration. High quantum efficiency and suitable excitation range make it match well with the emission of near-UV LEDs or blue LEDs. First-principles calculations indicate that Ba₃Si₆O₁₂N₂:Eu²⁺ phosphor exhibits a direct band gap, and low band energy dispersion, leading to a high luminescence intensity. The origin of the experimental absorption peaks is clearly identified based on the analysis of the density of states (DOS) and absorption spectra. The photoluminescence properties are related to the transition between 4f levels of Eu and 5d levels of both Eu and Ba atoms. The 5d energy level of Ba plays an important role in the photoluminescence of Ba₃Si₆O₁₂N₂:Eu²⁺ phosphor. The high quantum efficiency and long-wavelength excitation are mainly attributed to the existence of Ba atoms. Our results give a new explanation of photoluminescence properties and could direct future designation of novel phosphors for white light LED.     

Luminescent silicon nanocrystal dots fabricated by SiCl4/H2 RF plasma-enhanced chemical vapor deposition

Luminescent nanocrystalline Si dots were fabricated directly on thermally grown SiO₂ at 120°C by conventional RF plasma-enhanced chemical vapor deposition using tetrachlorosilane, SiCl₄ and H₂. As-deposited Si dot exhibits photoluminescence (PL) in the visible region, consisting of two broad bands corresponding to photon energies of 1.38 and 1.48 eV. Storage in air enhances PL and shifts the PL peak energy to higher wavelengths for dots of diameter less than 10 nm. Fourier transform attenuated total reflection absorption spectroscopy (FTIR-ATR) study reveals that the spontaneous oxidation proceeds until saturation after 70 h at dot sizes of 3–5 nm. The relationship between PL intensity, blueshift of PL peak energy, and surface termination species during oxidation indicates that these changes are attributed to the increased density of radiative centers at the Si nanocrystal dot/SiO₂ interface and enhancement of the quantum confinement effect.     

掺杂半导体β-FeSi2电子结构及几何结构第一性原理研究

采用基于第一性原理的密度泛函理论全势线性缀加平面波法，使用广义梯度近似处理交换相关势能，首先计算了β-FeSi₂的电子结构及其各元素各亚层电子的能态密度，β-FeSi₂的电子能态密度主要由Fe的d层电子和Si的p层电子的能态密度确定；其次通过计算不同掺杂系统的总能量确定了掺杂原子在β-FeSi₂中的置换位置，在β-FeSi₂中，Co置换Fe_Ⅱ位置的Fe原子，Al置换Si_Ⅰ位置的Si原子，这种择位置换与现有的计算结果完全一致；最后计算了Fe_1-xCo_xSi₂和Fe(Si_1-xAl_x)₂的电子结构，对它们的电子结构特征进行了分析，并探讨了电子结构对其热电性能(塞贝克系数、电传输及热传输性能)的影响. 关键词： 第一性原理 电子结构 热电性能 2')" href="#">FeSi₂     

用深能级瞬态谱方法研究赝晶Si/Ge0.25Si0.75/Si单量子阱的价带偏移

应变的Ge_xSi_1-x层和未应变的硅层间的能带偏移主要是价带偏移。量子阱中载流子的热发射能与界面的能带偏移有着密切的关系。本文用深能级瞬态谱(DLTS)研究分子束外延生长的p型Si/Ge_0.25Si_0.75/Si单量子阱的价带偏移,阱宽为15nm,考虑到电场的影响和量子阱中第一子能级的位置,对从DLTS得到的热发射能进行适当的修正,可以计算出Si/Ge_0.25Si_0.75/S 关键词：     

Hole states in artificial molecules formed by vertically coupled Ge/Si quantum dots

In the tight binding approximation, the spatial configuration of the ground state and the binding energy of a hole in a “diatomic” artificial molecule formed by vertically coupled Ge/Si(001) quantum dots are studied. The inhomogeneous spatial distribution of elastic strain arising in the medium due to the lattice mismatch between Ge and Si is taken into account. The strain is calculated using the valence-force-field model with a Keating interatomic potential. The formation of the hole states is shown to be determined by the competition of two processes: the appearance of a common hole due to the overlapping of “atomic” wavefunctions and the appearance of asymmetry in the potential energy of a hole in the two quantum dots because of the superposition of the elastic strain fields from the vertically aligned Ge nanoclusters. When the thickness of the Si layer separating the Ge dots (t _Si) is greater than 2.3 nm, the binding energy of a hole in the ground state of the two-dot system proves to be lower than the ionization energy of a single quantum dot because of the partial elastic stress relaxation due to the coupling of the quantum dots and due to the decrease in the depth of the potential well for holes. For the values of the parameter t _Si, an intermediate region is revealed, where the covalent molecular bond fails and the hole is localized in one of the two quantum dots, namely, in the dot characterized by the highest strain values.     

Electronic structure of SixGe1−x semiconductor solid solutions

The electronic structure of Si_xGe_1?x solid solutions is studied by means of a semi-ab initio method without involving the virtual crystal approximation. The calculations are performed on large cubic cells of the diamond lattice which contain a total of 64 Si and Ge atoms homogeneously distributed in different compositional ratios. The basis functions and the potentials used in the calculation give good band structures of elemental Si and Ge respectively. The calculated variation of band gap with x is in agreement with optical experiment: the two linear curves of gap vs concentration have different slopes at high and low x values with a crossing-over at about x=0.28. The band gaps are direct for xε (0, 0.28) and indirect for x ≥ 0.28. The density of states (DOS) of the solid solution can be very well approximated by the weighted average of the bulk Si and Ge DOS. There is a very slight charge transfer of about 0.05 electron per atom from Si to Ge.     

Growth and optical properties of Ge/Si quantum dots formed on patterned SiO2/Si(0 0 1) substrates

Single and stacked layers of Ge/Si quantum dots were grown in SiO₂ windows patterned by electron-beam lithography on oxidized Si (0 0 1) substrates. The growth of a silicon buffer layer prior to Ge deposition is found to be an additional parameter for adjusting the Ge-dot nucleation process. We show that the silicon buffer layer evolves towards [1 1 3]-faceted pyramids, which reduces the area of the topmost (0 0 1) surface available for Ge nucleation. By controlling the top facet area of the Si buffer layers, only one dot per circular window and a high cooperative arrangement of dots on a striped window can be achieved. In stacked layers, the dot homogeneity can be improved through the adjustment of the Ge deposited amount in the upper layers. The optical properties of these structures measured by photoluminescence spectroscopy are also reported. In comparison with self-assembled quantum dots, we observed, both in single and stacked layers, the absence of the wetting-layer component and an energy blue shift, confirming therefore the dot formation by selective growth.