Complex zigzag flexoelectric walls in the Schlieren textures of MBBA: possibility for determination of two basic Schlieren textures with singular or non‐singular surface points

The flexo‐dielectric behaviour of a homeotropic MBBA nematic layer has been experimentally studied. Asymmetric strong‐weak anchoring of the homeotropic nematic layer was achieved by treating the glass plates – one of them with lecithin ensuring the strong anchoring and the other with usual soap ensuring the weak anchoring. The application of a dc voltage with a sufficient amplitude led to the appearance of a complex texture consisting of gradient flexo‐dielectric deformations including Schlieren texture with many singular points and zigzag flexoelectric walls. The application of additional orienting a.c. voltage brought clarification of the Schlieren texture resembling that of the smectic‐C liquid crystal. Inversely, the application of an ac voltage across the homeotropic nematic layer led to formation of a nice Schlieren texture. The additional application of a d.c. voltage created complex zigzag gradient flexoelectric walls which connected the singular points in the Schlieren texture. In this way, one can determine for the first time how many points in the initial Schlieren texture are singular and how many points are non‐singular. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

紫外辐照对MoS2/酚醛环氧树脂黏结固体润滑涂层摩擦学性能的影响

制备了MoS2/酚醛环氧树脂黏结固体润滑涂层,并采用紫外辐照装置进行辐照,考察了紫外辐照对涂层的表面形貌、化学组成以及摩擦学性能的影响.SEM观察发现辐照后涂层表面出现低分子碎片堆积,XPS分析发现辐照后涂层表面O的相对含量显著增加,而C含量明显降低,这说明紫外辐照导致了涂层表面的氧化降解,而氧化作用使得涂层表面的黏结剂发生部分降解.对固体润滑剂MoS2的分析表明,辐照导致MoS2发生部分氧化.辐照后涂层摩擦系数增大,耐磨性降低.     

锯齿型石墨烯纳米窄带中量子霍尔体系的电场调控

应用含自洽格点在位库仑作用的Kane-Mele模型,研究锯齿型石墨烯纳米窄带平面内横向电场对边界带能带结构和量子自旋霍尔(QSH)体系的影响.研究结果显示,当电场强度较弱时,外加电场的方向可以调控自旋向下的两个边界带一起朝不同方向移动,导致波矢q=0.5处自旋向下的两个纯边界态的能量简并劈裂方向可由电场调控;当电场强度进一步增强到超过0.69 V/nm,自旋向下的两个边界带出现较大带隙,能带反转,而自旋向上的电子结构无能隙,系统呈现半金属性,同时QSH体系不再是B类.特别当电场强度为1.17 V/nm时,在自旋向下能带的能隙中,q=0.5处存在自旋向上的纯边界态,意味着在8格点边界处可以产生自旋向上的纯边界电流.当电场强度持续增加时,QSH系统从B类到C类经历3个阶段的变化.当电场强度超过1.42 V/nm后,自旋向上的两个边界带也出现能带反转,分别成为导带和价带,系统成为C类的普通量子霍尔体系.     

金掺杂锯齿型石墨烯纳米带的电磁学特性研究

本文采用基于密度泛函理论的第一性原理计算了金原子填充锯齿型石墨烯纳米带 (ZGNRs)中双空位结构的电磁学特性. 计算结果表明: 边缘位置是金原子的最稳定掺杂位置, 杂质原子的引入导致掺杂边缘的磁性被抑制, 不过掺杂率足够大时, 掺杂边缘的磁性反而恢复了. 金掺杂纳米带的能带结构对掺杂率敏感: 随着掺杂率的增大, 掺杂纳米带分别表现半导体特性、半金属特性以及金属特性. 本文的计算表明金原子掺杂可以调制ZGNR的磁性以及能带特性, 为后续实验起指导作用, 有利于推动石墨烯材料在自旋电子学方面的应用.     

Ni2P和MoS2催化剂在喹啉加氢脱氮反应中的协同效应

设计实验证明了Ni₂P和MoS₂催化剂在喹啉加氢脱氮反应中存在协同效应,该协同效应能够用氢溢流遥控模型理论解释。Ni₂P//MoS₂的协同因子随反应温度升高而减小,并且略微大于相同反应条件下NiS_x//MoS₂的协同因子。Ni₂P产生的溢流氢能够提高MoS₂催化剂上加氢活性位的数量,促使Ni₂P//MoS₂催化体系增加1,2,3,4-四氢喹啉和5,6,7,8-四氢喹啉加氢生成十氢喹啉的速率,提高其脱氮活性;因此,Ni₂P对MoS₂催化剂是很好的助剂。     

Solid‐state reaction as a mechanism of 1T ↔ 2H transformation in MoS2 monolayers

Monolayers of molybdenum disulfide MoS₂ are considered to be prospective materials for nanoelectronics and various catalytic processes. Since in certain conditions they undergo 1T ? 2H phase transitions, studying these phase changes is an urgent task. We present a DFT research of these transitions to show that they can proceed as a solid‐state reaction. Two transition states were discovered with energy barriers 1.03 and 1.40 eV. Sulfur atoms in the transition states are shown to be displaced relative to molybdenum atoms so that a tendency of one structural modification to transform into the other modification is seen. This kind of displacements agrees with electron microscopy data reported earlier. The energy parameters indicate that 1T → 2H reactions are exothermic for both transition states and can possibly proceed in a self‐sustained manner when initially activated by some external energy impact. © 2015 Wiley Periodicals, Inc.     

MoS2 Nanoflowers with Expanded Interlayers as High‐Performance Anodes for Sodium‐Ion Batteries

MoS₂ nanoflowers with expanded interlayer spacing of the (002) plane were synthesized and used as high‐performance anode in Na‐ion batteries. By controlling the cut‐off voltage to the range of 0.4–3 V, an intercalation mechanism rather than a conversion reaction is taking place. The MoS₂ nanoflower electrode shows high discharge capacities of 350 mAh g^?1 at 0.05 A g^?1, 300 mAh g^?1 at 1 A g^?1, and 195 mAh g^?1 at 10 A g^?1. An initial capacity increase with cycling is caused by peeling off MoS₂ layers, which produces more active sites for Na⁺ storage. The stripping of MoS₂ layers occurring in charge/discharge cycling contributes to the enhanced kinetics and low energy barrier for the intercalation of Na⁺ ions. The electrochemical reaction is mainly controlled by the capacitive process, which facilitates the high‐rate capability. Therefore, MoS₂ nanoflowers with expanded interlayers hold promise for rechargeable Na‐ion batteries.     

Graphitic Carbon Nitride Nanoribbons: Graphene‐Assisted Formation and Synergic Function for Highly Efficient Hydrogen Evolution

The development of new promising metal‐free catalysts is of great significance for the electrocatalytic hydrogen evolution reaction (HER). Herein, a rationally assembled three‐dimensional (3D) architecture of 1D graphitic carbon nitride (g‐C₃N₄) nanoribbons with 2D graphene sheets has been developed by a one‐step hydrothermal method. Because of the multipathway of charge and mass transport, the hierarchically structured g‐C₃N₄ nanoribbon–graphene hybrids lead to a high electrocatalytic ability for HER with a Tafel slope of 54 mV decade^?1, a low onset overpotential of 80 mV and overpotential of 207 mV to approach a current of 10 mA cm^?2, superior to those non‐metal materials and well‐developed metallic catalysts reported previously. This work presents a great advance for designing and developing highly efficient metal‐free catalyst for hydrogen evolution.     

Inkjet Printing of 2D Layered Materials

Inkjet printing of 2D layered materials, such as graphene and MoS₂, has attracted great interests for emerging electronics. However, incompatible rheology, low concentration, severe aggregation and toxicity of solvents constitute critical challenges which hamper the manufacturing efficiency and product quality. Here, we introduce a simple and general technology concept (distillation‐assisted solvent exchange) to efficiently overcome these challenges. By implementing the concept, we have demonstrated excellent jetting performance, ideal printing patterns and a variety of promising applications for inkjet printing of 2D layered materials.     

铁基粉末冶金材料中稀土元素与MoS2的交互作用研究

通过实验研究了添加到铁基粉末冶金摩擦材料中的稀土在材料中存在的位置和状态以及稀土对MoS2分解所产生的影响.电子探针检测的结果表明, 稀土在铁基粉末冶金磨擦材料中主要集中分布于孔隙处, 且其分布呈聚集的粒状, 常与Pb等重金属共存; 稀土有强烈的促进MoS2分解的作用, 当加入量超过3倍单位量时即可使加入的4%(质量分数)的MoS2完全分解.