Pt掺杂CdS光学性质的第一性原理研究

采用基于密度泛函理论的平面波超软赝势方法分析了CdS和Pt掺杂CdS的几何、电子结构和光学性质,计算结果表明Pt掺杂的CdS结构引入了由Pt贡献的导电载流子,增强了CdS的电导率,另外,费米能级下移进入价带.研究表明,Pt掺杂的CdS结构在费米能级附近出现了杂质能级,这是由Pt的5d态电子所形成;在光学性质上,Pt掺杂的CdS在可见光区的吸收系数比理想CdS高,能量损失峰出现红移现象,可见,Pt掺杂的CdS晶体具有更高的光催化活性.     

Nd掺杂Mg2Si电子结构和光学性质的第一性原理研究

采用基于密度泛函理论的第一性原理赝势平面波方法,探究了未掺杂Mg₂Si以及Nd掺杂Mg₂Si的能带结构、态密度和光学性质。计算结果表明: Nd掺杂Mg₂Si后,Mg₂Si禁带宽度从0.290 eV降低到0 eV,导电性能提升;未掺杂的Mg₂Si,当光子能量大于0.9 eV时,才开始慢慢具备吸收能力,掺杂Nd之后的Mg₂Si对能量为0.2 eV的光子就开始吸收,大大改善了Mg₂Si对红外光电子的吸收。掺杂后的光吸收系数和反射率都变小,表明掺杂后的Mg₂Si对光的穿透率增大。计算结果为Mg₂Si材料在光电器件方面的应用提供了理论依据。     

Co元素掺杂CrSi2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Co掺杂CrSi₂的几何结构、电子结构和光学性质进行了计算与分析.结果表明,掺杂后的CrSi₂晶格常数无明显变化,禁带宽度增大.由于Co元素3d电子的影响,在费米能级附近出现了杂质能级.掺杂后的CrSi₂复介电函数虚部在低能方向发生红移,在小于1.20 eV,大于2.41 eV的能量范围内光跃迁强度增强.吸收系数的主峰向高能方向移动,峰值增大,在小于1.38 eV,大于3.30 eV的能量范围改善了CrSi₂对红外光子的吸收.光电导率的主峰向高能方向移动,在小于1.16 eV,大于2.36 eV的能量范围内光电导率增强,说明掺杂Co元素后改善了CrSi₂特别是红外光区的光电性质,计算结果为CrSi₂光电器件的研究制造提供了理论依据.     

Mg掺杂浓度对GaN电子结构和光学性质的影响

基于密度泛函理论的第一性原理,分析了Mg掺杂浓度对GaN晶格参数、能带结构、电子态密度和光学性质的影响.研究表明:Mg掺杂GaN体系,晶格常数增大,禁带宽度增加,而且禁带宽度随着Mg含量的增加而增加,同时N2p和Mg2p态电子轨道的相互杂化,从而在费米能级附近引入受主能级,随着Mg含量的增加,费米能级进入价带的位置加深,同时Mg掺杂浓度越高,价带和导带带宽越窄.掺Mg后在介电函数和光学吸收谱的低能区和高能区均出现了新的介电峰,这些峰的出现和禁带中的杂质能级到导带底的跃迁有关,由于带隙的增加使介电峰向高能量方向发生偏移.     

Sc、Ce掺杂CrSi2的电子结构与光学性质的第一性原理

采用基于密度泛函理论的第一性原理赝势平面波方法对Sc、Ce单掺和共掺后CrSi₂的几何结构、电子结构、复介电函数、吸收系数和光电导率进行了计算。结果表明:Sc、Ce掺杂CrSi₂的晶格常数增大,带隙变小。本征CrSi₂的带隙为0.386 eV,Sc、Ce单掺及共掺CrSi₂的禁带宽度分别减小至0.245 eV、0.232 eV、0.198 eV,费米能级均向低能区移动进入价带。由于Sc的3d态电子和Ce的4f态电子的影响,Sc、Ce掺杂的CrSi₂在导带下方出现了杂质能级。掺杂后的CrSi₂介电函数虚部第一介电峰峰值增加且向低能方向移动,说明Sc、Ce掺杂使得CrSi₂在低能区的光跃迁强度增强,Sc-Ce共掺时更明显。Sc、Ce掺杂的CrSi₂吸收边在低能方向发生红移,在能量大于21.6 eV特别是在位于31.3 eV的较高能量附近,本征CrSi₂几乎不吸收光子,Sc单掺和Sc-Ce共掺CrSi₂吸收光子的能力有所增强,并在E=31.3 eV附近形成了第二吸收峰。说明掺杂Sc、Ce改善了CrSi₂对红外和较高能区光子的吸收。在小于3.91 eV的低能区掺杂后的CrSi₂光电导率增加。在20.01 eV<E<34.21 eV时,本征CrSi₂光电导率为零,但Sc、Ce掺杂后的体系不为零,掺杂拓宽了CrSi₂的光响应范围。研究结果为CrSi₂基光电器件的应用与设计提供了理论依据。     

P掺杂6H-SiC的第一性原理研究

采用基于密度泛函理论的第一性原理赝势平面波法,计算未掺杂与P替换Si、C以及P间隙掺杂6H-SiC的电子结构与光学性质。结果显示未掺杂的6H-SiC是带隙为2.052 eV的间接带隙半导体,P替换Si、C掺杂以及P间隙掺杂6H-SiC带隙均减小,分别为1.787 eV、1.446 eV和0.075 eV,其中P间隙掺杂带隙减小幅度最大。P替换掺杂6H-SiC使得费米能级向导带移动并插入导带中,呈n型半导体。P间隙掺杂价带中的一条能级跨入费米能级,因此在禁带中出现一条P 3p杂质能级,P间隙掺杂6H-SiC转为p型半导体。替换与间隙掺杂使得6H-SiC的介电函数实部增大,介电函数虚部、吸收光谱、反射光谱与光电导率红移,其中P间隙掺杂效果最佳。通过P掺杂材料的电导率增强,对红外波段的利用率明显提高,为6H-SiC在红外光电性能方面的应用提供有效的理论依据。     

Mg-N阴阳离子共掺杂SnO2的第一性原理研究

基于密度泛函理论,利用第一性原理计算Mg-N阴阳离子双受主共掺杂SnO₂的电子结构、电荷密度分布和缺陷形成能.Mg、N分别取代SnO₂晶体中的Sn和O,掺杂浓度分别为4.17at;、2.08at;,Mg-N键之间的共价性明显高于Sn-O键,富氧条件下,Mg-N共掺杂的缺陷形成能为2.67 eV,有利于进行有效的受主替代掺杂.Mg单受主掺杂SnO₂时,增加了带隙宽度,费米能级进入价带,Mg-N共掺杂SnO₂时,带隙窄化,表现出明显的p型导电类型.     

稀土元素(Ce/Nd/Eu/Gd)与N共掺金红石相TiO2的第一性原理研究

基于密度泛函理论的第一性原理平面波超软赝势计算方法,计算分析了纯金红石相TiO2,Ce、Nd、Eu和Gd四种稀土元素单掺杂金红石相TiO2,以及与N共掺金红石相TiO2的晶体结构、电子结构和光学性质.由掺杂前后的结果分析发现,掺杂后晶胞膨胀,晶格发生畸变;费米能级上移进入导带,导带底部引入杂质能级,提高了掺杂体系的电导率和对可见光的响应;光学性质、介电函数和吸收谱掺杂体系峰值比纯TiO2小,反射谱和能量损耗谱出现红移现象.     

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.     

(La,Y)掺杂AlN的电子结构和光学性质的第一性原理研究

采用基于密度泛函理论的平面波超软赝势方法对纯AlN、(La,Y)单掺杂以及La-Y共掺杂AlN 超胞进行几何结构优化,计算了稀土元素(La,Y)掺杂前后体系的能带结构、态密度和光学性质。结果表明:未掺杂的AlN是直接带隙半导体,带隙值为E_g=4.237 eV,在费米能级附近,态密度主要由Al-3p、N-2s电子轨道贡献电子,光吸收概率大,能量损失较大;掺杂后使得能带结构性质改变,带隙值降低,能带曲线变密集,总态密度整体下移;在光学性质中,稀土元素掺杂后均提高了静态介电常数、光吸收性能,增强了折射率和反射率,减小了电子吸收光子概率及能量损失;其中La-Y共掺体系变化得较为明显。     

Syntheses and structures of N-phenylmaleimidetriazoles and by-products

The syntheses, properties, and structures of N-phenylmaleimidetriazole derivatives are described. Intermediates and by-products are also discussed. 1b. a = 43.997(7) Å, 5.7610(9) Å, 8.245(1) Å, = 99.339(4), C₂/c; 2a. a = 13.646(4) Å, b = 7.744(2) Å, c = 10.612(3) Å, = 91.979(6), P2₁/c. 3a. a = 22.245(1) Å, b = 22.245(1) Å, 10.010(1) Å, P42/n. 3a. a = 11.727(2) Å, b = 14.075(3) Å, c = 16.080(3) Å, = 105.859(3), = 105.331(3), = 98.187(3), P-1. 3b. a = 8.561(3) Å, b = 14.755(5) Å, c = 22.771(7) Å, = 97.006(5), P2₁/c. 3c. a = 10.500(2) Å, b = 12.189(2) Å, c = 13.040(2) Å, = 109.091(3), = 106.089(3), = 101.022(3), P-1. 8a. a = 16.389(8) Å, b = 5.749(3) Å, c = 19.316(3) Å, = 97.467(9), P2₁/n. 8b. a = 5.822(2) Å, b = 10.114(3) Å, c = 16.705(4) Å, = 84.681(5), = 82.840(5), = 75.769(4), P-1. 9b. a = 11.251(1) Å, 13.335(3) Å, 13.376(3) Å, = 102.456(4), P2₁/n. 9c. a = 15.836(3) Å, b = 8.236(2) Å, c = 5.447(3) Å, = 92.551(3), P2₁/c. 10a. a = 13.177(2) Å, b = 14.597(2) Å, c = 5.5505(8) Å, = 110.979(2), Cc. 11a. a = 14.720(2) Å, b = 13.995(2) Å, c = 38.245(6) Å, = 94.430(3), P2₁/n. 12b. a = 15.067(5) Å, b = 20.378(6) Å, c = 8.669(5) Å, = 99.16(4), = 99.32(3), = 105.23(3), P-1. 13b. a = 8.2824(6) Å, b = 10.5245(7) Å, c = 15.518(1) Å, = 92.305(1), = 100.473(1), = 100.124(1), P-1. 15a. a = 15.357(3) Å, b = 7.778(2) Å, c = 22.957(2) Å, Pbca. 16b. a = 18.0384(4) Å, b = 12.474(3) Å, c = 20.078(5) Å, Pbca.     

Sol-gel synthesis and characterization of adsorbent and photoluminescent nanocomposites of starch and silica

Using sol-gel method, mesoporous and photoluminescent silica nanocomposites of soluble starch have been synthesized and characterized. Different ratios of H₂O, TEOS and EtOH were used at fixed template (soluble starch) and catalyst (NH₄OH) concentrations to obtain materials of different performances in terms of heavy metal binding from a solution which has been monitored using Cd(II) as representative divalent heavy metal ion. Optimum material was obtained when H₂O, TEOS and EtOH were used in 14:1:2 ratio. This sample was not only an efficient metal ion adsorbent but also had an intense luminescence in ultra-violet region and potentially may be used in silicon-based UV-emitting devices. Metal binding by the material was further enhanced after calcination (at 800 °C in air) while its luminescence had a multipeak profile in UV-visible region. In a batch adsorption study, calcined hybrid composite (0.25 g/L) could remove 98.5% Cd(II) from 100 mg/L Cd(II) solution in 2 h. The chemical, structural and textural characteristics of the synthesized materials have been investigated using Fourier Transform Infrared Spectroscopy (FTIR), X-rays Diffraction (XRD), Thermal Analysis (TGA/DTA), Photoluminescence (PL), Brunauer-Emmett-Teller Analysis (BET) and Scanning Electron Microscopy (SEM).     

Chemistry and Electrocrystallization of Organic Metals and Superconductors

Abstract

Considerable variation in the conditions of electrochemical crystal growth of TMTSF₂X (i.e., constant current versus constant potential, ambient versus inert atmosphere, etc.) and in the purity of the constituents (donor, electrolyte, solvent) does not significantly affect the unusual low-temperature properties of this class of materials. Our results suggest that the electrocrystallization procedure may be self-purifying by selecting for conducting crystal phases with constituents having specific oxidation potentials and solubility properties. However, doping solutions with structurally and chemically similar constituents (i.e., TMTTF, and IO^? ₄ in CIO^? ₄) leads to their incorporation in the crystal structure where they have a profound effect. Several mole percent of these dopants suppress superconductivity in the PF^? ₆ and CIO^? ₄ salts, and increase and broaden the metal-insulator phase transition.     

Crystal and molecular structures of benz-p-nitroanilide and benz-p-methoxyanilide

The crystal structures of the two carboxylic amides C₁₃H₁₀N₂O₃ (I) and C₁₄H₁₃NO₂ (II) have been determined by direct methods and refined by full-matrix least squares. The predominant structural feature is the hydrogen bonding (N-H?O=C) which influences the conformations of both structures.     

晶体中负离子配位多面体结晶方位、形变与晶体压电、铁电性

本文研究了压电、铁电晶体中负离子配位多面体的结晶方位与形变,提出了压电晶体中同一种负离子配位多面体的结晶方位是一致的.在铁电晶体中,负离子配位多面体发生形变,伴随着晶体发生顺电-铁电相变,并从这一基本过程出发,对铁电体相变的形成机理进行了讨论.     

Biocrystallization in Bacterial and Fungal Cells and Spores

A series of X-ray diffraction experiments were performed for the first time to study stress-induced biocrystallization (structural response to stress) in the bacteria E. coli, the spore-forming bacteria Bacillus cereus, and in cells and spores of the mycelial fungus Umbelopsis ramanniana. High-intensity areas with spacings of 90 and 44 Å are indicative of a periodically ordered arrangement (most likely nanocrystalline) of the bacterial nucleoid. For the starved bacteria Bacillus cereus, a peak at a spacing of 45 Å is also assigned to nanocrystalline complexes of DNA with the Dps protein. The spores of the fungus Umbelopsis ramanniana VKM F-582, as well as the spores of Bacillus cereus, form ordered arrays of DNA molecules with DNA-condensing acid-soluble proteins SASPs. Starved dehydrated mycelial cells of the fungus Umbelopsis ramanniana form ordered structures with spacings from 27 to 55 Å. A series of peaks reflect the formation of a number of ordered protein arrays, apparently with DNA, with continuously varying characteristic interplanar spacings.     

Preparation and characterization of PbSe nanopowder and quasi-ceramics

By means of the reduction of Pb(II) and Se(IV) with hydrazine, oval monodispersed PbSe nanoparticles characterized by sizes ～100 nm and the cubic symmetry were obtained. Their compaction and sintering into quasi-ceramic state were performed. The samples were investigated by means of scanning electron microscopy, X-ray diffraction and FTIR spectroscopy. The results obtained are discussed.     

Structural and spectral studies of N-trans-cinnamylidene-m-toluidine and N-trans-cinnamylidene-m-chloroaniline

N-trans-cinnamylidene-m-toluidine (1) C₁₆H₁₅N, and N-trans-cinnamylidene-m-chloroaniline (2) C₁₅H₁₂NCl form isomorphous crystals which are monoclinic, space group P2_l/c, with unit cell dimensionsa=5.967(2),b=13.793(3),c=15.048(5) Å, =91.97(3)° anda=5.868(2),b=13.788(4),c=15.191(4) Å, =91.87(3)°, respectively. The single-crystal X-ray structure determinations of the title compounds revealtrans structures. Ring (A) C_10–15 and ring (B) C_1–6, are practically planar in both structures with dihedral angels of 61.3(3) and 63.6(2)°, respectively.¹H nmr, u.v. and i.r. spectra are also reported.     

Melting and short-range order in liquids and glasses

A theory is proposed to explain two-dimensional melting based on the gauge-invariant Lagrangian with spontaneous breaking (Higgs mechanism) or the SU(2) gauge field to U(1) symmetry. The first-order phase transition in two-dimensional melting may be strongly related to the asymptotic freedom-like interaction of the SU(2) gauge field in the case when the distance between each excited disk is shorter than a critical length, 2/ boxv;mboxv, near the melting temperature.     

Broken Symmetries and Hydrodynamics of Hexatic B and Snectic F and I Liquid Crystal Phases

The nature of the spontaneously broken symmetries in hexatic B and smectic F and I phases is investigated and the hydrodynamics of the associated degrees of freedom is discussed.