α-Cu_2Se精细结构的球差校正扫描透射电镜表征

目前学界对Cu_2Se低温α相的结构仍未认识清楚,而解决这一问题对理解Cu_2Se在相变过程中热电性能提升等特性具有重要意义。本文首次报道了由球差校正扫描透射电镜(STEM)拍摄到的沿■带轴的原子级分辨率高角环形暗场(HAADF)像,揭示了由Se原子以多种形式有序起伏产生的复杂结构。结合电子衍射图谱,分析了包含不同层数、通过相互组合构成α-Cu_2Se晶体的多种结构变体。使用QSTEM软件对构建的结构变体进行高分辨图像模拟,得到了与实验对应的HAADF像。该工作为更全面地理解α-Cu_2Se的结构提供了新的重要信息。     

有机镧系金属络合物的研究(L)——Cp_2′SmI和Cp′SmI_2·2THF的合成和晶体结构测定

本文首次合成了含分子内氧杂原子配位的双-(2-甲氧乙基环戊二烯基)碘化钐CP_2′SmI(Ⅰ)(Cp′=CH_3OCH_2CH_2C_5H_4)及四氢呋喃溶剂化的2-甲氧乙基环戊二烯基二碘化钐Cp′SmI_2·2THF(Ⅱ)。络合物(Ⅰ)和(Ⅱ)经元素分析及质谱等鉴定。并得到了它们的单晶。结构研究表明,晶体(Ⅰ)属于P2_12_12_1空间群,晶胞参数:a=11.074(4)(?),b=12.929(9)(?),c=12.269(4)(?),(Ⅰ)中每个钐原子和两个环戊二烯基,二个醚基取代基上的氧原子和一个碘原子配位,形成单体结构,Sm(Ⅲ)的配位数为9。晶胞中含有4个单体分子,晶体(Ⅱ)属于P2_1/c空间群,晶胞参数:a=16.304(6)(?),b=8.335(2)(?),c=16.527(5)(?),β=111.8(1)°。晶体(Ⅱ)中每个钐通过一个环戊二烯基,一个醚基取代基上的氧原子,二个四氢呋喃的氧原子和二个碘原子配位形成单体结构,Sm(Ⅲ)的配位数为8。晶胞含4个单体分子。     

NbS_(2-x)Se_x的制备、表征及其摩擦学性能

本文采用固相反应合成了NbS2-xSex纳米材料。并分别采用XRD、SEM、TEM、HRTEM进行了结构、形貌和成分的分析表征。系统研究了合成温度、保温时间及不同掺杂量对产物晶型和形貌演化的影响及规律性。结果表明Se的掺杂使NbS2-x Sex的形貌由纳米带(板)转变为纳米片,衍射峰明显宽化,峰强变弱,晶粒细化。且掺杂量、保温温度及时间对产物的形貌影响较大;在750℃下保温2 h得到的掺杂5at%Se的NbS1.9Se0.1形貌良好。将NbS2-xSex作为液体石蜡油的添加剂的UMT-2摩擦学实验结果表明掺杂后的NbS2-xSex具有优异的摩擦性能,其中掺杂5at%的Se在750℃下保温2 h的NbS1.9Se0.1摩擦性能最佳,同时对其摩擦机理进行了解释。     

稀土夹杂物诱导钢中ε-Cu析出的错配度计算

为改善铜原子在奥氏体晶界处的偏析,探究稀土夹杂物对钢中残余铜元素析出的影响,采用二维错配度理论,对稀土夹杂物成为钢中ε-Cu异质形核核心的有效性进行了计算。结果表明,ε-Cu的(111)面与Ce_2O_3的(0001)面和La_2O_3的(0001)面二维错配度分别为6.7%和7.9%,与Ce_2O_2S(0001)面上的二维错配度为8.8%,即Ce_2O_3,La_2O_3和Ce_2O_2S均可以作为ε-Cu的中等有效形核核心;而CeS的(100)面与ε-Cu(100),(110)和(111)面的二维错配度分别为50.3%,27.2%和31.1%,说明CeS不能作为ε-Cu的异质形核核心。     

N掺杂TiO_2纳米管阵列的制备及可见光光催化性能研究

分别以氨水、乙二胺、丁胺为氮源,利用阳极氧化法和湿化学法合成氮掺杂的二氧化钛(TiO2)纳米管阵列.通过扫描电镜(SEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)等表征方法对氮掺杂TiO2纳米管形貌,晶型和氮元素掺杂方式进行分析,并通过可见光光催化降解六氯苯(HCB)废水,研究氮元素掺杂方式与可见光光催化活性的关系.结果表明有序排列的TiO2纳米管阵列垂直生长在钛基底表面,管长500nm左右,管径100nm左右.氮元素掺杂阻碍了TiO2晶粒的增长,抑制了锐钛矿向金红石相的转变.无机氮比有机氮更加利于氮元素进入TiO2晶格,取代态氮比间隙态氮表现出更高的可见光光催化活性.     

Zn掺杂对量子点Cd_6Se_6及其配合物Cd_6Se_6-(OPMe_3)_6结构和性质影响的密度泛函理论研究

采用密度泛函理论对有机配体三甲基氧膦OPMe_3吸附到掺杂量子点ZnmCdnSe_6(m+n=6)上形成吸附产物的结构和性质进行了研究。金属原子Zn和Cd与配体OPMe3中的O原子形成Zn-O和Cd-O配位键,其吸附能、电荷分布、HOMO、LUMO和电子吸收光谱等性质随着掺杂Zn原子的增多而逐渐变化。研究表明向Cd6Se6中掺杂Zn原子使其电子吸收光谱出现蓝移,随着掺杂原子的增多,蓝移现象就越明显,研究结果有助于纳米材料的设计和合成。     

[M(dap)3]2(Sb2Se5)·xH2O(M=Ni,x=2;M=Zn,x=0)的溶剂热合成及晶体结构

利用溶剂热法合成了2种新的有机杂化锑硒化合物[Ni(dap)3]2(Sb2Se5)].2H2O(1)和[Zn(dap)3]2(Sb2Se5)](2)(dap=1,2-丙二胺),单晶X射线衍射分析结果表明,1属于三方晶系,P3121空间群,晶胞参数为a=10.7574(14),b=10.7574(14),c=31.672(4),γ=120.00°,z=4。2属于单斜晶系,P21空间群,晶胞参数为a=10.772(2),b=16.391(3),c=11.704(2),β=100.912(4)°,z=4。在2种化合物中,Ni2 与Zn2 离子分别与3个dap配体螯合形成畸变八面体几何构型,其中dap配体的N原子是无序的,而二聚[Sb2Se5]2-阴离子是由2个SbSe3三角锥共用1个Se原子连接而成。     

Mn掺杂TiO_2(101)提高锂空电池阴极催化活性的第一性原理研究

本文基于密度泛函理论对TiO_2(101)和Mn_xTi_(1-x)O_2(101)作为锂空电池阴极催化材料进行了研究,发现其表面能够生成两种不同结构的Li_2O_2,进一步地研究了其中最稳定的生成结构并通过计算锂空电池首次充放电过程中的过电势来评价催化性能.结果表明,Mn掺杂进入Ti O_2(101)对充放电的过电势均有降低作用,深入分析发现掺杂Mn对TiO_2促进阴极催化反应的本质因素源于掺杂原子Mn的d态轨道的分布以及其平均能量.掺杂原子的d态轨道在费米能级处的峰态诱导了附近O的p态轨道,二者共同作用在Mn_xTi_(1-x)O_2(101)的总态密度的费米能级处形成多个新峰,改变了催化剂的导电方式.此外,由于掺杂原子Mn的d态轨道的平均能量高于Ti原子,使得O的p态轨道受到更多的激发,促使在Mn掺杂原子附近的氧空位形成能降低,为放电过程阴极催化反应的氧还原提供了更多的活性位点并且有利于氧气的吸附与还原.     

原位产生的SO42-配位的二维无机钴配合物K2[Co3(OH)2(SO4)3(H2O)2]的水热合成及晶体结构

相同的水热反应条件下4-氨基-二(2-吡啶基)-1,2,4-三氮唑(abpt)、KSCN与钴盐(CoCl2·6H2O)反应合成了2种新的钴配合物:零维的单核配合物[CoSCN(abpt)](1α)和二维的无机层状配合物K2[Co3(OH)2(SO4)3(H2O)2](1β),并通过元素分析和红外光谱对其进行了表征.配合物1α的晶体属于单斜晶系,P21/c空间群.配合物1β晶体属于正交晶系,Cmc21空间群.在配合物1α中,abpt和SCN-配体都参与配位与Co(Ⅱ)离子形成了2个不同的单核单元,这些单核单元又通过S原子和N原子之间的氢键作用连成了三维超分子结构;在配合物1β中,abpt配体没有参与配位,而SCN-配体则被氧化成了SO42-离子并与Co(Ⅱ)离子配位形成了二维配位层状结构,相邻层之间进一步通过氢键作用形成了沿c轴方向有孔道的三维超分子网络,这些孔道里面填充着反离子K+.     

量子棒/二维MoS_2界面超快光致电荷分离与复合动力学

基于量子棒良好的光吸收和电荷输运性能以及二维材料优异的光催化性质,构筑了新型的量子棒/二维MoS_2杂化光催化材料.深入理解并调控二者界面处的光致电荷分离与复合过程是该类材料推广应用的前提.本文采用飞秒激光泵浦-探测瞬态吸收光谱技术,直接观测到了从Cd Se和Cd S胶体量子棒到层状二硫化钼(MoS_2)超快的界面电荷转移(分别为205 ps和26 ns)和高效的电荷分离(分离效率为98%和69%)过程.研究发现,与Cd S/MoS_2相比,Cd Se/MoS_2界面处更强的电子耦合作用使其电子转移速率比前者高出两个数量级.电子转移后的Cd Se~+/MoS_2-分离态较长的寿命(12 ns)使分离后的电子在MoS_2中实现长距离(约2.2mm)扩散,这为电子顺利到达二维MoS_2边缘的活性位点进行催化反应提供了有效保障.     

Quantification of grain boundary equilibrium segregation by NanoSIMS analysis of bulk samples

A technique for the quantification of equilibrium grain boundary segregation by high resolution secondary ion mass spectroscopy (NanoSIMS) on simple metallographically polished surfaces has been demonstrated for the model system of sulphur segregation to nickel grain boundaries. Samples of nickel containing 5.4 wt ppm of sulphur were annealed at different temperatures to achieve different equilibrium sulphur grain boundary concentrations, ranging from less than 1% to about 50% of a monolayer. Quantification was carried out from sulphur concentration profiles acquired across about 20 grain boundaries in each sample. An internal standard (nickel containing a known concentration of sulphur in solid solution) was used for calibration. It is found that, depending on the annealing temperature, the average grain boundary sulphur concentration ranges from 0.9 to 25.8 ng cm^–2 (or 1.7 10¹³ to 4.8 10¹⁴ atoms cm^–2), i.e. ~0.015 to ~0.43 monolayer. Thermodynamic analysis gives a segregation free energy of ?97.8 kJ mol^–1 and a grain boundary sulphur concentration at saturation of 26.7 ng cm^–2 (or 5.0×10¹⁴ atoms cm^–2), i.e. ~0.44 monolayer, in good agreement with previous measurements on this system. The limit of detection of the technique is shown to be as low as 0.24 ng cm^–2 (or 4.5×10¹² atoms cm^–2), i.e. ~0.004 monolayer, with a counting time of only 10 min. Copyright © 2012 John Wiley & Sons, Ltd.     

First-principles study on doping of tetragonal ZnSe monolayers

Doping is a very important and effective method to be used to modulate the properties of two-dimensional (2D) materials. In this work, the electronic and magnetic properties of ultrathin tetragonal ZnSe monolayer doped by twenty different kinds of atoms neighboring Zn/Se were systemically investigated using first-principles calculations. Substitution at the Zn/Se sites was found to be easy if the monolayer was grown under Zn-/Se-poor conditions. Among non-metal dopants, only F atom is thermodynamically favored to replace Se atom, while a number of metal atoms (i.e. Ca, Sc, Ti, and Mn) are able to substitute Zn atom. It is suggested by theoretical calculations that pristine ZnSe monolayer inclines as an n-type semiconductor by certain doping. Our results open a new avenue for the modulation of the novel tetragonal ZnSe monolayer for a wealth of potential optoelectronic applications.     

负载型非晶态Cu／SiO2催化剂局域结构的研究

采用ＸＰＳ和ＥＸＡＦＳ方法，研究了以ｓｏｌ－ｇｅｌ法制得的超累粉体ＳｉＯ２为载体，用化学还原沉积法制备的负载型非晶态Ｃｕ／ＳｉＯ２催化剂在甲酸甲酯氢解反应前后的表面结构和局域结构。结果表明，非晶态样品中的铜原子以零价铜的形式存在，但配位数却大幅度地低于铜樯档，意味着铜原子在高比表面超细ＳｉＯ２载体上处于高分散的非晶状态，表面悬空键显著增多，表面能增大，导致配位键收缩。     

First‐Principles Study on Doping of SnSe2 Monolayers

Doping is a vitally important technique that can be used to modulate the properties of two‐dimensional materials. In this work, by using first‐principles density functional calculations, we investigated the electrical properties of SnSe₂ monolayers by p‐type/n‐type and isoelectronic doping. Substitution at Sn/Se sites was found to be easy if the monolayer was grown under Sn‐/Se‐poor conditions. Substitutions at Sn sites with metallic atoms (e.g. Ga, Ge, In, Bi, Sb, Pb) resulted in positive substitution energies, which indicated that they were not effective doping candidates. For substitutions at Se sites with nonmetallic atoms, no promising candidates were found for p‐type doping (e.g., N, P, As). Among these, N and As showed positive substitution energies. Although P had a negative substitution energy under Sn‐rich conditions, it introduced trap states within the band gap. For n‐type doping (e.g., F, Cl, Br), all the calculated substitution energies were negative under both Sn‐ and Se‐rich conditions. Br was proven to be a promising candidate, because the impurity introduced a shallow donor level. Finally, for isoelectronic doping (e.g., O, S, Te), the intrinsic semiconducting features of the SnSe₂ monolayer did not change, and the contribution from the impurity to the states near the band edge increased with the atomic number.     

二维铁电材料ABP2X6内在极高的负泊松比

Recently, ferroelectric materials have attracted considerable research attention. In particular, two dimensional (2D) ferroelectric materials have been considered as most crucial for next-generation circuit designs because of their application as novel electric memory devices. However, a 2D ferroelectric material is very rare. The ferroelectric materials with the form ABP₂X₆ (A = Ag, Cu; B = Bi, In; X = S, Se) are of interest because of their ferroelectric property maintained in their ultrathin structures. Within the ABP₂X₆ monolayer, the P―P bonds form the pillars that hold the top and bottom X planes, while the off-center A―B atoms between the X layers induce a spontaneous ferroelectric polarization. If the two off-center A―B sites are equally aligned, this would lead to the appearance of the paraelectric state. Such intriguing structures must impart novel mechanical properties to the materials. Until now, there has been no report on the mechanical properties of monolayer ABP₂X₆. Based on first-principles calculations, we studied the structural, electronic, mechanical as well as the electromechanical coupling properties of monolayer ABP₂X₆ (A = Ag, Cu; B = Bi, In; X = S, Se). We found that they are all semiconductors with wide bandgaps of 2.73, 2.17, 3.00, and 2.31 eV for CuInP₂Se₆, CuBiP₂Se₆, AgBiP₂S₆, and AgBiP₂Se₆, respectively, which are calculated based on the Heyd-Scuseria-Ernzerhof (HSE) exchange correlation functional model. The conduction band minimum is mainly from p orbitals of X and B atoms, whereas the valence band maximum is due to the hybridization of the p orbital of X atoms and the d orbital of A atoms. Moreover, there are three short and three long A/B―X bonds due to the A―B off-center displacement. Together with the d-p orbital hybridization, the main reason for the distorted ferroelectric structure in ABP₂X₆ monolayers is the Jahn-Teller effect. ABP₂X₆ monolayers are predicted to be a new class of auxetic materials with an out-of-plane negative Poisson's ratio, i.e., the values of the negative Poisson's ratio are in the order AgBiP₂S₆ (−0.805) < AgBiP₂Se₆ (−0.778) < CuBiP₂Se₆ (−0.670) < CuInP₂S₆ (−0.060). This is mainly due to the tensile strain applied in the x/y direction enlarging the angle between P―P bonds and top layer X atoms, thereby enhancing the bucking height of monolayer ABP₂X₆. Moreover, external strain has a significant impact on the A―B off-center displacement, rendering an out-of-plane piezoelectric polarization. The values of e₁₃ for CuInP₂S₆, CuBiP₂Se₆, AgBiP₂S₆, AgBiP₂Se₆ monolayers are calculated to be −3.95 × 10⁻¹², −5.68 × 10⁻¹², −3.94 × 10⁻¹², −2.71 × 10⁻¹² C∙m⁻¹, respectively, which are comparable to the only experimentally confirmed 2D out-of-plane piezoelectric Janus system (piezoelectric coefficient = −3.8 × 10⁻¹² C∙m⁻¹). This unusual auxetic behavior, ferroelectric polarization, and the electromechanical coupling in monolayer ABP₂X₆ could potentially lead to enormous technologically important applications in nanoelectronics, nanomechanics, and piezoelectrics.     

KInSe~2的中温固相合成及结构表征

采用反应性熔盐法,以n(K~2Se~3):n(In):n(Se)=1:1:5的摩尔比,在500℃下反应5d,生成淡黄色柱状晶体KInSe~2。该晶体属于单斜晶系,空间群为C2/c,晶胞参数,a=1.414(2)nm,b=1.1410(2)nm,c=1.5586(3)nm,β=100.60(3)°,Z=16,R=0.0656。KInSe~2晶体具有层状结构,每层由具有二维网状结构的[InSe~2]^-负离子和K^+组成,层与层之间按ABAB方式堆积。     

Se掺杂对单层MoS2电子能带结构和光吸收性质的影响

基于密度泛函理论的第一性原理方法,计算了Se掺杂单层MoS₂能带结构和光吸特性,并分析了对其光解水性质的影响。结果表明：本征单层MoS₂为直接带隙结构,禁带宽度为1.740 eV,导带底电位在H⁺/H₂还原势之上0.430 eV,价带顶电位在O₂/H₂O的氧化势之下0.080 eV,具有可见光催化分解水的能力,但氧化和还原能力不均衡,导致单层MoS₂作为光催化剂分解水的效率不高。通过Se掺杂计算发现,单层MoS₂的禁带宽度变为1.727 eV,相应的光吸收谱变化幅度几乎不变,且体系的形成能较低,表明其热力学稳定性良好。然而,导带底电位调整到H⁺/H₂还原势之上0.253 eV,价带顶电位处于O₂/H₂O的氧化势之下0.244 eV,平衡了氧化与还原能力,单层MoS₂可见光催化分解水的效率得到提高。     

The first, discrete Zn4 tetrahedron with a selenium atom in the center: x-ray structure and solution study of [Zn4(mu4-Se)[Se2P(OPr)2]6

The first discrete, selenium-centered tetranuclear zinc cluster [Zn4(mu4-Se)[Se2P(OPr)2]6] was isolated and characterized. The cluster consists of six edge-bridged dsep ligands with four zinc atoms in a slightly distorted tetrahedron and a mu4-Se atom in the center. In addition, 12 mu2-bridging selenium atoms form a Se12 icosahedron. From variable-temperature 31P NMR studies, it was observed that the cluster [Zn4(Se)[Se2P(OPr)2]6] is partly decomposed to [Zn[Se2P(OPr)2]2] and the monomeric species [Zn[Se2P(OPr)2]2] is further in equilibrium with its dimer [Zn[Se2P(OPr)2]2]2.     

Oriented adsorption of NO2 on WSe2 monolayer

An oriented adsorption behavior of NO₂ is disclosed on the WSe₂ monolayer in this work regardless the monolayer is perfect or defective based on density functional theory study by large-scale sampling. The presence of typical defects, including selenium vacancy, tungsten vacancy, and antisite defect of selenium on tungsten site, does not modify the anisotropic adsorption behavior of NO₂ molecule at all. The adsorbed NO₂ exhibits similar behavior on the four kinds of monolayers with its extending orientation all main lines along the two directions of the Se–W bond and the Se–W–Se trough, in spite of the symmetry is decreased somewhat from trigonal of the perfect monolayer to bilateral of the defective monolayers. Molecular dynamic simulations well reproduce these trends. The anisotropic adsorption behavior can be attributed to the polar properties of both heteroatomic bond of the WSe₂ monolayer and NO₂ molecule itself. Out of plane polarization is believed to play key role in the vertical and then the oriented adsorption behavior formation. The sensitivity is estimated to be very good based on moderate adsorption energy (0.35, 0.42, 0. 95 and 0.78 eV on pure, selenium vacancy, tungsten vacancy, and selenium on tungsten site monolayers) and considerable charge transfer number (0.205, 0.208, 0.164, and 0.160 e, respectively), with different degrees of change by defect. These fantastic findings may provide substantial foundation for wide applications beyond thought.     

1,3‐Bis[2‐(dimethylaminomethyl)phenyl]triselenide

The title compound, C₁₈H₂₄N₂Se₃, consists of discrete molecules; owing to the presence of strong intramolecular N...Se interactions [N...Se = 2.671 (4) and 2.873 (4) Å], the chalcogen Se atoms of the angular Se₃ chain exhibit different coordination geometries, i.e. the terminal Se atoms are tricoordinated and exhibit a T‐shaped environment of the CNSe₂ core [N...Se—Se = 173.73 (9) and 172.29 (9)°], while the central Se atom is dicoordinated to the other two Se atoms, with an Se—Se—Se angle of 108.32 (2)°.