扶手椅型二硫化钼纳米带的电子结构与边缘修饰

采用基于密度泛函理论的第一性原理计算方法, 研究了扶手椅型二硫化钼纳米带的几何构型与电子结构, 发现其稳定性与电子性质敏感地依赖于边缘修饰. 随着边缘修饰的H原子数增加, 纳米带变得更加稳定, 并在间接带隙半导体、半金属和直接带隙半导体之间转变. 纳米带的能带结构和电子态密度显示, 其费米能级附近的能带主要由边缘态贡献. 当二硫化钼纳米带两边用不同数目的H原子修饰时, 纳米带同时具有由这两种修饰引起的边缘态并且两种边缘态的相互影响很小. 研究了三类纳米带带隙与宽度的关系, 对于每个原胞修饰0个或8个H原子的纳米带, 带隙随宽度以3为周期振荡变化; 而对于每个原胞修饰4个H原子的纳米带, 带隙振荡不再具有周期并且振荡幅度变小.     

Lattice Distortion and H-passivation in Pure Carbon Electrocatalysts for Efficient and Stable Two-electron Oxygen Reduction to H2O2

The exploration of inexpensive and efficient catalysts for oxygen reduction reaction (ORR) is crucial for chemical and energy industries. Carbon materials have been proved promising with different catalysts enabling 2 and 4e⁻ ORR. Nevertheless, their ORR activity and selectivity is still complex and under debate in many cases. Many structures of these active carbon materials are also chemically unstable for practical implementations. Unlike the well-discussed structures, this work presents a strategy to promote efficient and stable 2e⁻ ORR of carbon materials through the synergistic effect of lattice distortion and H-passivation (on the distorted structure). We show how these structures can be formed on carbon cloth, and how the reproducible chemical adsorption can be realized on these structures for efficient and stable H₂O₂ production. The work here gives not only new understandings on the 2e⁻ ORR catalysis, but also the robust catalyst which can be directly used in industry.     

Calculation of the surface energy of bcc-metals with the empirical electron theory

We have used the dangling bond analysis method (DBAM) based on the empirical electron theory (EET) to establish a database of surface energy for low index surfaces of the bcc-metals such as V, Cr, Fe, Nb, Mo, Ta, and W. And a brief introduction of the new surface energy models will be presented in this paper. Under the first-order approximation the calculated results are in agreement with experimental and other theoretical values. And the calculated surface energy shows a strong anisotropy. As we predicted, the surface energy of the close-packed (1 1 0) is the lowest one of all index surfaces. It is also found that the dangling bond electron density and the spatial distribution of covalent bonds have a great influence on surface energy of various index surfaces. The new calculation method for the research of surface energy provides a good basis for models of surface science phenomena, and the model may be extended to the surface energy estimation of more metals, alloys, ceramics, and so on, since abundant information about the valence electronic structure (VES) can be generated from EET.     

Dependence of the product on the P–P ligand in reactions of [RuCl3(NO)(P–P)] complexes (P–P = aromatic diphosphines) with 2-mercaptopyridine

This study presents the syntheses and characterization of 2-mercaptopyridine (pyS⁻) complexes containing ruthenium(II) with the following general formula [Ru(pyS)₂(P–P)], P–P = (c-dppen) = cis-1,2-bis(diphenylphosphino)ethylene) (1); (dppe) = 1,2-bis(diphenylphosphino)ethane (2); (dppp) = 1,3-bis(diphenylphosphino)propane (3) and (dppb) = 1,4-bis(diphenylphosphino)butane (4). The complexes were synthesized from the mer- or fac-[RuCl₃(NO)(P–P)] precursors in the presence of triethylamine in methanol solution with dependence of the product on the P–P ligand. The reaction of pyS⁻ with a ruthenium complex containing a bulky aromatic diphosphine dppb disclosed a major product with a dangling coordinated dppbO-P, the [Ru(pyS)₂(NO)(η¹-dppbO-P)]PF₆(5). In addition, this work also presents and discusses the spectroscopic and electrochemical behavior of 1–5, and report the X-ray structures for 1 and 5.     

Ba6Ge25: low-temperature Ge-Ge bond breaking during temperature-induced structure transformation

In order to find the optimal conditions for sample preparation of the binary germanide Ba₆Ge₂₅, the germanium-rich part of the Ba-Ge phase diagram was redetermined by means of metallography, X-ray powder diffraction and differential thermal analysis. The temperature behavior of cubic Ba₆Ge₂₅ was investigated both on polycrystalline samples and single crystals. The temperature dependence of the lattice parameter exhibits two anomalies at about 180 and 230 K, respectively, which are caused by a structure transformation in two steps with hysteresis. Powder (T=10-295 K) and single-crystal (T=95-295 K) X-ray diffraction studies confirm that the symmetry of Ba₆Ge₂₅ (space group P4₁32) remains unchanged within the entire temperature range. A reconstructive behavior of the structural transformation is observed, involving Ge-Ge bond breaking and barium cation displacements. Some Ge4 type atoms (∼28%) are so significantly displaced during cooling that Ge4-Ge6 bonds break and new three-bonded (3b)Ge⁻ species (electron acceptors) are formed. Consequently, the number of charge carriers is reduced, affecting the physical properties. The reversible bond breaking involved in this process is a typical characteristic of a solid-state chemical reaction.     

SiO/SiO_2超晶格结构界面发光的研究

利用热蒸发技术在硅衬底上制备了层厚不同的SiO/SiO2超晶格样品.对其光致发光谱进行研究发现,随着SiO/SiO2超晶格中SiO层厚度的增加,发光峰在400～600 nm之间移动.研究表明,样品的发光中心来自于SiO/SiO2界面处的缺陷发光(界面态发光).即在样品沉积的过程中,在SiO/SiO2的界面处由于晶格的不连续性,会形成大量的Si-O悬挂键,这些悬挂键本身相互结合可以形成一定数量的缺陷,同时由于O原子容易脱离Si原子的束缚而产生扩散,因此,这些悬挂键可以与扩散的O原子结合,随着SiO层厚度的增加,在SiO/SiO2的界面处先后出现WOB(O3<≡Si-O-O·),NOV(O3≡Si-Si≡O3),E'中心(O≡Si·),NBOHC(O3≡Si-O·)等缺陷,这些缺陷在SiO层厚度增大的过程中对发光先后起到主导作用,从而使得发光峰产生红移.     

密度泛函理论方法研究6H-SiC(0001)表面对氧分子和水分子的吸附

本文通过密度泛函方法计算6H-SiC(0001)表面对氧分子和水分子的吸附. 在6H-SiC(0001)表面上吸附的O₂分子自发地解离成O^*,并被吸收在C与Si原子之间的空位上. 吸附的H₂O自发地分解成OH^*和H^*,它们都被吸附在Si原子的顶部,OH^*进一步可逆地转化为O^*和H^*. H^*可以使Si悬键饱和并改变O^*的吸附类型,并进一步稳定6H-SiC(0001)表面并防止其转变为SiO₂.     

Exponential depletion of neutral dangling bonds density (D) by rare-earth doping in amorphous Si films

In this work we study the effect reduction in the density of dangling bond species D⁰ states in rare-earth (RE) doped a-Si films as a function concentration for different RE-specimens. The films a-Si_1−xRE_x, RE=Y³⁺, Gd³⁺, Er³⁺, Lu³⁺) were prepared by co-sputtering and investigated by electron spin resonance (ESR) and Raman scattering experiments. According to our data the RE-doping reduces the ESR signal intensity of the D⁰ states with an exponential dependence on the rare-concentration. Furthermore, the reduction produced by the magnetic rare-earths Gd³⁺ and Er³⁺ is remarkably greater than that caused by Y³⁺ and Lu³⁺, which led us to suggest an exchange-like coupling between the spin of the magnetic REs³⁺ and the spin of silicon neutral dangling bonds.     

Intrinsic photoluminescence properties of amorphous Si3B3N7 ceramic

Amorphous Si₃B₃N₇ ceramic shows intrinsic photoluminescence. Three distinctive emission regions have been observed. Excitation with wavelengths between 254 and 330 nm stimulates intense blue emissions with peak maxima ranging from 447 to 479 nm. Exciting between 315 and 420 nm results in two broad emission peaks; the first in the range between 400 and 440 nm, and the second between 560 and 690 nm. Of these two latter emissions, the one in the violet region dominates in intensity over the other one in the red region, thus a violet color is perceived with the eye via excitation with 330 nm or higher wavelengths. The three distinct intrinsic emissions in the photoluminescence spectrum of amorphous Si₃B₃N₇ ceramic are related to defect centers in three topologically different regions in its structure. Dependence of emission on excitation wavelength is associated with the Red-Edge Effect and can be explained with a reabsorption mechanism at the red excitation edge.