Mn掺杂BaTiO3多铁性的第一性原理研究

本文基于第一性原理方法,对过渡金属元素Mn掺杂四方相BaTiO3体系进行了系统的研究.通过对掺杂前后的电子结构改变及所引起的磁学性能的分析发现,过渡金属元素Mn的掺入可以使BaTiO3产生较大的铁磁性,这一磁性主要源于Mn离子局域磁矩的贡献,且随着Mn掺杂量的增加,材料体系的磁性增强;同时发现掺杂体系在001方向存在畸变,仍然保持BaTiO3原有的自发极化,即掺杂后体系仍具备铁电性.研究结果表明,进一步优化的Mn掺杂BaTiO3有望成为一种性能优越的新型多铁性材料.     

Y,Zr,Nb掺杂对单层MoS2电子结构的影响

本文基于第一性原理的方法研究了Y、Zr、Nb在Mo位掺杂单层MoS2的能带结构和态密度.研究发现:Y、Zr、Nb三种杂质在Mo位掺杂使杂质原子附近的键长发生畸变,畸变最大的是Y掺杂体系;Y、Zr、Nb的掺杂改变了单层MoS2能能带结构,使掺杂体系向导体转变;对于Y、Zr、Nb共掺杂体系,Y、Zr共掺杂增强了单层MoS2导电性能;Y、Nb共掺杂单层MoS2的费米能级穿过杂质能级,此处的能级处于半满状态,容易成为电子的俘获中心;Zr、Nb共掺杂体系的禁带中出现了多条杂质能级,同时导带能量上移;Y、Zr、Nb共掺杂可以很大程度改变单层MoS2材料的电子结构.     

Na掺杂对TiO2基材料电子结构、电子迁移特性及光吸收性质的影响

在赝势法密度泛函理论的基础上,系统研究了Na掺杂对TiO2基材料电子结构、载流子迁移和光吸收性质的影响.纯的TiO2基晶态材料呈现宽的直接带隙,其带隙宽度达2.438 eV,Na掺杂降低了TiO2基晶态材料的带隙至1.976 eV.纯的TiO2电子主要形成五个能带,而Na掺杂TiO2主要形成七个能带.TiO2材料的载流子迁移率较Na掺杂TiO2材料高,而Na掺杂TiO2材料载流子有效质量较TiO2的高.Na掺杂在TiO2材料价带中引入空穴和新的能级.Na掺杂大大提高了TiO2材料的载流子浓度,Ti中的p态电子,Na中的p态电子和O中的p态电子在导电过程中起着关键作用.Na掺杂TiO2材料的低能量光吸收限降低.     

高压与掺杂对KDP晶体能带结构的影响

构建了高压条件下KDP晶体的原子结构模型和掺杂有Li+、Na+、Rb+、Cs+、Be2、Mg2+、Ca2+、Cr3+、Co2+、Cu2+、Al3+、La3+等12种阳离子的KDP晶体超级原胞结构模型,采用第一性原理计算了高压下的KDP晶体的能带结构和态密度,研究了替位式掺杂的形成能以及不同掺杂离子对电子结构的影响.结果表明:KDP晶体的带隙宽度随着压强的增加呈线性增长趋势;Co2+、Cu2+、La3+等重金属离子具有较低的掺杂形成能而易于形成替位式掺杂;碱金属离子掺杂后其带隙比二价离子和三价离子替位掺杂情形大得多,且随原子序数增大而增大.文章还依据能带理论构建了材料的电导率和热导率与带隙的关联式,分析讨论了高压和掺杂对KDP晶体热导率和激光损伤的影响.     

固态源MBE系统生长高质量的调制掺杂GaAs结构材料和InP/InP外延材料的兼容性研究

通过固态源的分子束外延系统生长了调制掺杂AlGaAs/GaAs结构材料和InP/InP外延材料.在生长含磷材料之后,生长条件(真空状态)变差;我们通过采取合理的工艺方法和生长工艺条件的优化,获得了电子迁移率为1.86×105cm2/Vs(77K)调制掺杂AlGaAs/GaAs结构材料和电子迁移率为2.09×105cm2/Vs(77K)δ-Si掺杂AlGaAs/GaAs结构材料.InP/InP材料的电子迁移率为4.57×104 cm2/Vs(77K),该数值是目前国际报道最高迁移率值和最低的电子浓度的InP外延材料.成功地实现了在一个固态源分子束外延设备交替生长高质量的调制掺杂AlGaAs/GaAs结构材料和含磷材料.     

静电自组装制备镧掺杂高岭石基纳米TiO2光催化材料研究

采用静电自组装方法制备了镧掺杂高岭石基纳米TiO2光催化材料.采用巯丙基三甲氧基硅烷偶联剂对高岭石进行干法改性,采用30; H2O2/HOAc将偶联剂巯基基团氧化为磺酸基基团.在静电引力的作用下,带负电荷的高岭石与带正电荷的钛聚合阳离子和La3+自发地组装在一起,经一定温度热处理得到镧掺杂高岭石基纳米TiO2光催化材料.采用XRF、XRD、FT-IR、SEM和PL等对材料进行分析,采用甲基橙染料评价材料的光催化性能.研究表明:采用静电自组装方法可有效提高高岭石与纳米TiO2的复合效率;镧掺杂导致TiO2与高岭石之间的结合力增强;适量的镧掺杂导致锐钛矿晶体发生畸变,能带结构改变,电子-空穴对复合几率降低,进而导致其光催化性能增强;镧掺量5 mol;的复合材料对甲基橙溶液表现出更高的光催化脱色效果.     

Ca掺杂ZnO氧化物的电子结构与电性能研究

基于密度泛函理论广义梯度近似第一性原理计算的方法,系统研究了Ca掺杂ZnO氧化物的晶格结构和电子结构,在此基础上分析了其电学性能.结果表明,Ca掺杂ZnO晶胞减小.Ca掺杂氧化物仍为直接带隙半导体材料,带宽达1.5 eV.掺杂体系费米能级附近的能带主要由Cas态、Cap态、Znp态和Op态电子构成,其中p态电子对价带态贡献最大,且Cas态、Znp态和Op态电子之间存在着更强的相互作用.Ca掺杂ZnO氧化物费米能级EF附近载流子浓度增加,运动速度减小,有效质量增加,导电机构为Cas态、Znp态和Op态电子在价带与导带的跃迁,具有更高的电导率,较高的Seebeck系数和综合电性能.     

Mg掺杂对CaMnO3基热电氧化物电子结构及电性能的影响研究

采用超软赝势密度泛函理论计算的方法研究了Mg掺杂Ca位CaMnO3基复合氧化物的能带结构、电子态密度和电荷分布状况,在此基础上分析了Mg掺杂氧化物的电性能.结果表明,Mg掺杂CaMnO3氧化物仍然呈间接带隙型能带结构,带隙宽度由0.756eV减小到0.734eV.CaMnO3氧化物和Mg掺杂CaMnO3氧化物的自旋态密度曲线极值点均位于为-0.8eV附近.Mg掺杂CaMnO3氧化物中Mn原子对体系费米面态密度的贡献有所减小,O原子和Ca原子对体系费米面态密度的贡献有所增大.Mg原子比Ca原子具有更强的释放电子的能力,Mg掺杂对于CaMnO3氧化物属于电子型掺杂.Mg掺杂CaMnO3氧化物导电性能增强,电性能提高.     

N掺杂LaAlO3电子结构的第一性原理研究

采用第一性原理计算N掺杂LaAlO3的稳定性、电子结构和磁学性质.计算结果表明:N掺杂LaAlO3的结构稳定;而且从生成焓数值看,替位掺杂比间隙掺杂结构更稳定.形成能计算结果表明,还原环境比氧化环境更适合N掺杂,并且在还原环境下,NH3作为N源生成替位掺杂的LaAlO3-x Nx的形成能最小,即最容易形成替位掺杂.N替代LaAlO3中的O原子和位于LaAlO3晶胞间隙均产生铁磁性,其磁性均源于掺杂N-2p电子与体系价带顶O-2p电子间的p-p耦合作用.     

B掺杂BaTiO3的电子结构和磁性的第一性原理研究

利用基于第一性原理的自旋极化密度泛函理论计算了B掺杂BaTiO3的稳定性、电子结构和磁学性质.结果表明B掺杂BaTiO3体系稳定,并表现为铁磁性.B替位掺杂BaTiO3体系的磁性机制可归结为部分B2p电子的自旋极化和B2p/O2p与Ti3d电子的p-d耦合作用,B间隙掺杂BaTiO3体系中磁性源于未配对Ti3d电子的自旋极化.     

Structure and chemical composition of LiB3O5 surfaces

The electronic and structural properties of LiB₃O₅ (LBO) surfaces have been studied by X‐ray photoemission spectroscopy (XPS) and reflectance high‐energy electron diffraction (RHEED). The as‐grown (110) crystal face and mechanically polished (001) surfaces have been investigated comparatively. Electronic structure of LBO has been determined on as‐grown (110) crystal face previously cleaned by chemical etching with RHEED control. The correlation of valence band structure and measured binding energies with earlier reported results has been discussed. Core‐level spectroscopy reveals strong enriching of mechanically polished LBO surface with carbon, when nanodiamond powder is used as an abrasive. So high carbon level as C:B = 0.7 has been observed at the surface while the ratio Li:B:O remains according to LBO chemical composition. The association of LBO Kikuchi‐lines with strong background has been shown by RHEED analysis of the surface. Thus, the polished LBO surface constitutes a high structure quality LBO with the inclusions of some amorphous carbon compound. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis,spectral characteristics,and the crystal and molecular structures of 2,3-dimethyl-1-phenyl-4-(<Emphasis Type="Italic">N</Emphasis>-phthalimido)pyrazolone-5

2,3-Dimethyl-1-phenyl-4-(N-phthalimido)pyrazolone-5 (I) is synthesized and isolated in the form of single crystals. The crystal structure of compound I is determined using X-ray diffraction. The phthalimide and pyrazolone rings in the molecule are not coplanar: the angle between their median planes is 56.4°. The bond lengths in the rings level off, which indicates the delocalization of the electron density. The spectral characteristics (IR and electronic spectra) of molecule I are determined.     

Mg2Sn机械性质及热电输运性能的第一性原理计算

窄带隙半导体材料Mg₂Sn具有丰度大、密度低、无毒及环境友好等特点,是中低温热电材料的优秀候选者。本文基于密度泛函理论,结合不同形式的电子交换关联能系统分析了Mg₂Sn晶体的弹性系数、声子振动谱和电子能带结构,并基于非平衡玻尔兹曼输运理论计算了Mg₂Sn的热电性能。结果表明,GGA-PBE作为电子交换关联能可以很好地拟合立方相Mg₂Sn的力学性能(声子振动谱无虚频率),其体弹性模量为42.1 GPa且各向同性。同时,当工作温度高于300 K,Mg₂Sn的德拜温度开始趋于平缓且不高于315 K,表明Mg₂Sn在该温度区域内具有低声子热导率。使用B3LYP作为电子交换关联能可以估算Mg₂Sn费米能级附近的电子结构,发现价带顶附近存在三重简并态。同时计算结果表明,Mg₂Sn p型掺杂下的热电优值(ZT值)优于n型掺杂,可达1.05。本研究结果为进一步优化Mg₂Sn热电性能的研究提供借鉴。     

The localization of electrons in amorphous semiconductors: A twenty-first century perspective

This review covers those consequences of the localization of electronic states that appear to be universal features embracing all amorphous semiconducting materials where the electron–lattice interaction can be neglected, such as hydrogenated amorphous silicon. Several experimental measurements of these features are described. The role of strong electron–lattice interactions in some amorphous semiconducting systems, such as many chalcogenide glasses, is also discussed. In these systems, the electron–lattice interaction is so strong that it more than offsets the coulomb repulsion needed to put two electrons in the same energy state. Some experimental consequences of these so-called negative-U_eff systems are described. In addition, some universal features of metastable excitations for systems with both weak and strong electron–lattice interactions are discussed in the light of some recent experimental results.     

First-principle molecular dynamics study of the structural and electronic properties of liquid and amorphous Ni-Al alloys

Atomic and electronic structures of liquid and rapidly quenched Ni-Al (NiAl₃, NiAl, and Ni₃Al) alloys were studied by ab initio molecular dynamics simulation. Pair correlation function, structure factor, bond pair, electron population, and density of states were calculated. It is found that amorphous Ni-Al alloys can be prepared by rapid quenching of liquid alloys, with the former bearing similar structures to the latter, although amorphous alloys have a more ordered structure. Bond pair analysis indicates that both the liquid and amorphous Ni-Al alloys consist mainly of 1441, 1431, 1421, and 1422 pairs of tetrahedral local order. The positions of the first peaks of the Al-Ni pair correlation functions are lower than the sum of the metallic radii of Ni and Al, suggesting the occurrence of chemical bonding between Ni and Al in Ni-Al alloys. Electronic structure analysis further revealed that the interaction between the d-electrons of Ni and the p-electrons of Al is responsible for the bonding. The main peak positions of the total DOS of amorphous Ni-Al alloys become more and more positive when the content of Ni in the alloys increases.     

Synthesis and characterization of type-II textured tungsten disulfide thin films by vdWR process with Pb interfacial layer as texture promoter

The growth of type-II textured tungsten disulfide (WS₂) thin films by solid state reaction between the spray deposited WO₃ and gaseous sulfur vapors with Pb interfacial layer has been studied. X-ray diffraction (XRD) technique is used to measure the degree of preferred orientation ‘S’ and texture of WS₂ films. Scanning electron microscopy (SEM) and transmission electron microscopy techniques have been used to examine the microstructure and morphology. The electronic structure and chemical composition were studied using X-ray photoelectron spectroscopy (XPS). The use of Pb interfacial layer for the promotion of type-II texture in WS₂ thin films is successfully demonstrated. The presence of (0 0 3 l), (where l=1, 2, 3, …) family of planes in the XRD pattern indicates the strong type-II texture of WS₂ thin films. The crystallites exhibit rhombohedral (3R) structure. The large value of ‘S’ (1086) prompts the high degree of preferred orientation as well. The stratum of crystallites with their basal plane parallel to the substrate surface is seen in the SEM image. The EDS and XPS analyses confirm the tungsten to sulfur atomic ratio as 1:1.75. We purport that Pb interfacial layer enhances type-II texture of WS₂ thin films greatly.     

尿素晶体线性和非线性光学系数的计算

本文使用从头计算平面波赝势法计算了尿素晶体的电子能带结构、线性和非线性光学系数,折射率和倍频系数的计算结果与实验结果基本符合.计算发现尿素晶体中C、N和O元素的2p轨道电子态发生了明显杂化,而能量较高的2p轨道电子态的杂化是其非线性光学效应的主要来源.     

Study of the electronic structure of the Al-Cu-Fe quasicrystalline system

The photoelectron spectra, photon absorption spectra, and electron energy loss spectra have been measured in reflection geometry for the clean surface of quasicrystalline samples and ω-phase samples of identical chemical composition that belong to the Al-Cu-Fe system. The investigations performed made it possible to reveal some specific features of the electronic structure of quasicrystals; these features can be successfully used in construction of the model of the actual electronic structure of quasicrystalline materials. The resonant photoelectron spectra have been measured in the range of photon energies corresponding to the Fe2p and Cu2p absorption edges. A sharp increase (by a factor of 3–4) in the spectral intensity is found in the valence band near the Fe2p edge. Near the Cu2p edge, the Auger electron emission resonantly increased, while the emission from the valence band almost did not change.     

Extended fine structure analysis using electron beams

Appearance potential spectroscopy has found use primarily as a core level probe of the electronic structure of solid surfaces. The observation of extended fine structure above appearance potential edges, analogous to that observed above X-ray adsorption edges, gives promise that atomic spacings in the surface region may also be determined. Most previous studies of appearance potentials have depended on observing changes in the soft X-ray yield. Poor detection efficiencies and low flourescence yields have limited the usefulness of this approach. Using the secondary electron yield, however, we have recently succeeded in observing fine structure extending more than 400 eV above appearance potential edges. We are currently employing this approach to study the structure of SiO₂ films on Si substrates. Initial attempts at Fourier inversion and problems due to diffraction of the incident electron beam and multiple scattering effects will be discussed.     

MnGa合金体的电子结构与磁性质的研究

基于密度泛函理论方法系统研究了四方结构MnGa合金体的结构、形成、电子结构和磁性质。结果表明,四方MnGa合金晶胞的生成焓为-4.85 eV,高于一些不含d电子的体系。其呈现导体的能带结构,其中d电子主要形成深能级价带,定域性最强。四方MnGa合金存在着明显的自旋极化,靠近费米能级两侧的s电子和靠近费米能级下方的p电子具有较弱的自旋极化。形成浅能级价带和导带的d电子产生高强度的自旋极化,对磁性质贡献较大。Mn的s电子和Mn的p电子自旋极化作用较弱,Mn的d电子形成浅能级价带和导带,自旋极化作用最强。形成深能级价带的Ga的d电子自旋极化作用较弱,不同位置的Ga原子的自旋极化不同。四方MnGa合金体具有净有效磁矩,呈弱的亚铁磁性。