点缺陷石墨烯的电导（英文）

作为纳米材料中最有前途的的材料之一,石墨烯由于其超高的电导率、优异的热稳定性和机械强度受到了研究者的广泛关注。本文通过非平衡格林函数法结合密度泛函理论计算了石墨烯点缺陷(包括Stone-Waals,反Stone-Waals,单空位和双空位)及其浓度对石墨烯电输运性质的影响。石墨烯的电导在很大程度上依赖于点缺陷的类型及浓度。低浓度的Stone-Waals和反Stone-Waals缺陷不会显著地降低石墨烯的电输运,而双空位可使电导降低约50%左右。石墨烯中明显的电输运行为变化是由带缺陷石墨烯的能带结构决定的——由于点缺陷破坏了石墨烯蜂窝状晶格的对称性,会在费米能级附近引入局域态,进而导致狄拉克点处有能带劈裂。高缺陷浓度的双空位会在费米能级附近引入更多的平带以及在缺陷处更多的局域态,因此可能对载流子进行一定的散射,降低石墨烯的电导。此外,局部电荷密度表现出增强的局域性,阻碍了载流子的运动。石墨烯电导随着缺陷浓度和能带劈裂的增加呈指数下降。这些理论结果为研究真实单层石墨烯的电输运特性提供了重要的理解,并将有助于实验上控制石墨烯基器件的性能。     

基于电化学方法研究以铜和银为电极的对苯二甲酸单分子结电导

利用基于电化学跳跃接触的扫描隧道显微镜裂结法(ECSTM-BJ), 通过现场形成金属电极, 对以Cu和Ag为电极的对苯二甲酸单分子结电导进行了测量. 研究结果表明: 利用该方法对所有数据直接线性统计即可得到很好结果; 两种电极下都存在两套高和低电导值, 其中以Cu为电极的单分子结电导高低值分别为11.5和4.0 nS, 而以Ag为电极的单分子结电导分别为10.3和3.8 nS, 高值都约为低值的3倍, 且以Cu为电极的单分子结电导要略大于以Ag为电极的电导, 可归结于电极和分子的耦合不同造成的. 与同样条件下测量得到的烷基链羧酸单分子结电导只存在一套值相比,对苯二甲酸表现出两套电导值, 反应了分子内主链对分子结电导的影响.     

ZnO和ZnS本征点缺陷的理论研究

基于第一性原理和热动力学方法,通过模拟计算分析了不同温度和分压下ZnS和ZnO晶体本征点缺陷的性质.振动熵的计算结果表明,在高温条件下,振动熵对缺陷形成能的贡献不能忽略.对比分析2种晶体本征点缺陷随环境条件变化的规律,结果表明,2种晶体的主导缺陷均为空位型.氧空位(V_O)在ZnO中更易形成,富氧和低温条件有利用于ZnO的p型本征掺杂.而锌空位(V_(Zn))在ZnS中形成能最低,因此ZnS比ZnO更容易形成p型掺杂.研究还发现2种晶体的肖特基缺陷都不稳定,而弗伦克尔缺陷比较稳定.除ZnS反弗伦克尔缺陷外,有价态的缺陷对的形成能均比中性缺陷对的形成能低.     

熔盐电导的多维键参数分析

本文用模式识别－人工神经网络结合化学键参数法，总结熔盐电导的半经验规律，在此基础上讨论了熔盐电导的主要影响因素及电导机理。     

二甲基甲酰胺-二氧六环混合溶剂中KBr,KSCN及KClO_4的电导研究

本文报告了KBr、KSC N、KClO_4和KI在二甲基甲酰胺(DMF)和1,4-二氧六环混合溶剂中的电导测定值、溶剂的粘度和溶液的密度,按Pitts,Fuoss1978和Lee-Wheaton电导方程拟合实验数据得出溶液的无限稀释摩尔电导A_o,离子缔合常数K_α和正负离子间的距离参数R。对三个方程的适用性和溶液中离子-离子-溶剂分子间的相互作用作了初步讨论。     

新型微型电导池的研制及其地效应的消除

使用简便的方法制作了电极面积大、无死体积、分辨率高、检测限低的微型电导池;较好地消除了毛细管电泳ＣＥ）在柱 存在的共地效应,排除了在线检测时高压分离回路对电导检测回路的干扰。并对制作的躲开电导池的性能进行了测试。     

电导滴定法快速测定钾的含量

１引言测定钾的含量常用火焰光度法和四苯硼钠重量法，火焰光度法适用于微量分析，四苯硼钠重量法的测定周期长。电导滴定法用于测定一些可发生沉淀反应的离子时，具有快速简便的优点。本文采用四苯硼钠溶液滴定，电导滴定法测定高、中含量组分钾的含量，测定周期仅需１０ｍｉｎ，所用试剂量少，不受样品中水不溶物的干扰，适用于钾盐、卤水和复合肥中钾的测定。２实验部分２．１仪器和药品电导率的测定采用ＤＤＳ－１２Ａ型数字式电导率仪和２１６型电导电极。四苯硼钠（Ｎａ［Ｂ（６Ｈ５）４］）为分析纯试剂，配成水溶液后用基准ＫＣＩ标…     

有机酸分析的柱后缓冲电导法与紫外法、直接电导法的比较

柱后缓冲电导法采用柱后调节pH值,电导检测器检测的方法检测有机酸,它避免了经常使用的紫外法选择性差,直接电导法灵敏度低的缺点,是可以实现有机酸准确定量的一种新型分析方法.本文比较了这三种方法的分析结果.     

电导法确定二元体系中离子的浓度

本文从电化学基本原理出发,推导出稀溶液中二元混合组分的电导与各组分当量浓度的关系,并通过测定纯组分的电导－当量浓度标准曲线,来确定二元混合组分的标准曲线在对其中一组分浓度确定的基础上,可很容易计算另一组分的浓度。该法简便、快速,有望成为化学分析和仪器分析的一个很好的补充。     

贵金属原子与点缺陷石墨烯的键增强作用

通过密度泛函理论研究了Ag、Au、Pt原子在完美和点缺陷(包括N掺杂、B掺杂、空位点缺陷)石墨烯上的吸附以及这些体系的界面性质.研究表明Ag、Au不能在完美的石墨烯上吸附,N、B掺杂增强了三种金属与石墨烯之间的相互作用.而空位点缺陷诱发三种金属在石墨烯上具有强化学吸附作用.通过电子结构分析发现,N掺杂增强了Au、Pt与C形成的共价键,而Au、Ag与B形成了化学键.空位点缺陷不仅是金属原子的几何固定点,同时也增加了金属原子和碳原子之间的成键.增强贵金属原子和石墨烯相互作用的顺序是:空位点缺陷>>B掺杂>N掺杂.     

电导研究贵金属Pt在Co3O4还原过程中的作用

通过考察Co3O4在还原过程中电导率的变化, 并结合程序升温还原方法, 对贵金属Pt的作用进行了研究. 另外, 研究了Co3O4在氢气、氧气和合成气气氛中电导率的连续变化过程, 以便进一步了解Co3O4在实际费-托合成反应条件下的氧化-还原历程, 以及贵金属Pt在该过程中的作用.     

参杂缺陷石墨烯的高分子复合材料导热特性分子动力学模拟

Polymers are widely used advanced materials composed of macromolecular chains, which can be found in materials used in our daily life. Polymer materials have been employed in many energy and electronic applications such as energy harvesting devices, energy storage devices, light emitting and sensing devices, and flexible energy and electronic devices. The microscopic morphologies and electrical properties of the polymer materials can be tuned by molecular engineering, which could improve the device performances in terms of both the energy conversion efficiency and stability. Traditional polymers are usually considered to be thermal insulators owing to their amorphous molecular chains. Graphene-based polymeric materials have garnered significant attention due to the excellent thermal conductivity of graphene. Advanced polymeric composites with high thermal conductivity exhibit great potential in many applications. Therefore, research on the thermal transport behaviors in graphene-based nanocomposites becomes critical. Vacancy defects in graphene are commonly observed during its fabrication. In this work, the effects of vacancy defects in graphene on thermal transport properties of the graphene-polyethylene nanocomposite are comprehensively investigated using molecular dynamics (MD) simulation. Based on the non-equilibrium molecular dynamics (NEMD) method, the interfacial thermal conductance and the overall thermal conductance of the nanocomposite are taken into consideration simultaneously. It is found that vacancy defects in graphene facilitate the interfacial thermal conductance between graphene and polyethylene. By removing various proportions of carbon atoms in pristine graphene, the density of vacancy defects varies from 0% to 20% and the interfacial thermal conductance increases from 75.6 MW·m⁻²·K⁻¹ to 85.9 MW·m⁻²·K⁻¹. The distinct enhancement in the interfacial thermal transport is attributed to the enhanced thermal coupling between graphene and polyethylene. A higher number of broken sp² bonds in the defective graphene lead to a decrease in the structure rigidity with more low-frequency (< 15 THz) phonons. The improved overlap of vibrational density states between graphene and polyethylene at a low frequency results in better interfacial thermal conductance. Moreover, the increase in the interfacial thermal conductance induced by vacancy defects have a significant effect on the overall thermal conductance (from 40.8 MW·m⁻²·K⁻¹ to 45.6 MW·m⁻²·K⁻¹). In addition, when filled with the graphene layer, the local density of polyethylene increases on both sides of the graphene. The concentrated layers provide more aligned molecular arrangement, which result in better thermal conductance in polyethylene. Further, the higher local density of the polymer near the interface provides more atoms for interaction with the graphene, which leads to stronger effective interactions. The relative concentration is insensitive to the density of vacancy defects. The reported results on the thermal transport behavior of graphene-polyethylene composites provide reasonable guidance for using graphene as fillers to tune the thermal conduction of polymeric composites.     

Electrical Conductivity of Alkaline-reduced Graphene Oxide

A green route using a very simple and straightforward ultrasonic process under alkaline conditions, rather than a general chemical reduction process using hydrazine, was utilized to obtain the hydrophilic reduced graphene oxide(RGO) sheets, via removing oxygen functional groups from graphene oxide(GO) and repairing the aromatic structure. It is found that the conductivity of the obtained RGO could be tuned by changing pH value in alkaline solution, and the current-voltage(I-V) curves of both GO and RGO are nonlinear and slightly asymmetric. Under the same applied voltage, the current of RGO is much larger than that of GO, indicating a pronounced increase in the electrical conductivity of RGO, compared to that of GO.     

结合第一性原理和热力学计算对HfO2晶体本征点缺陷的预测

基于第一性原理和热动力学方法模拟计算得到了不同温度和氧分压下HfO₂晶体本征点缺陷的形成能,并讨论了各种点缺陷的形成能随费米能级变化的规律. 结果表明: 当费米能级在价带顶附近时, 随着温度和氧分压的变化, 出现了不同的最稳定点缺陷(O_i⁰、V_O3²⁺和Hf_i⁴⁺). 当费米能级大于3.40 eV时, 主要点缺陷是带-4价的Hf 空位. 该晶体除Hf 空位在价带顶附近出现了奇数价态, 其它的点缺陷都只显现偶数价态, 这表明该晶体的点缺陷具有典型的negative-U特性. 本文还计算得到了该晶体可能存在的最稳定点缺陷在温度、氧分压和费米能级三维空间的分布, 这为分析该晶体在不同条件下可能出现的点缺陷类型提供清晰的图像, 为调控晶体点缺陷的形成提供参考.     

Electron Spin Catalysis with Graphene Belts

Here, we report kinetic studies using electron spin resonance spectroscopy on spin catalysis reactions caused by using graphene belts which were synthesized by a radical coupling method. The results show that σ-type free radical species provide the dominant sites for catalytic activity through the spin-spin interaction, although there are some other influencing factors. The spin catalysis mechanism can be applied both in the oxygen reduction reaction (ORR) and in organic synthesis. The graphene belt spin catalyst shows excellent performance with a high ORR half-wave potential of 0.81 V and long-term stability with almost no loss of activity after 50 000 cycles in alkaline media. It also shows excellent performance in a benzylamine coupling with molecular oxygen to generate the corresponding imine at an average conversion of ≈97.7 % and an average yield of ≈97.9 %. This work opens up a new research direction for understanding aerobic processes in the field of spin catalysis.     

点缺陷引起中子辐照MgO(110)单晶的铁磁性

对MgO(110)单晶进行中子辐照,辐照剂量从1.0 × 10¹⁶到1.0 × 10²⁰ cm^-2。基于黄昆漫散射理论,我们计算了MgO晶体中的立方缺陷和偶极力缺陷引起的X射线漫散射强度分布图。通过X射线漫散射及紫外-可见光(UV-Vis)吸收光谱实验表征了晶体的点缺陷组态,并利用超导量子干涉仪(SQUID)测量了样品的磁性。ω–2θ和摇摆曲线说明MgO单晶经中子辐照后产生了晶格畸变,晶体中存在一定浓度的点缺陷。倒易空间图(RSM)显示中子辐照的MgO单晶存在漫散射现象。与计算得到的漫散射分布图对比分析可知,中子辐照的MgO(110)单晶中产生了弗仑克尔缺陷。UV-Vis吸收光谱表明所有辐照晶体中存在阴离子单空位缺陷。辐照剂量较高(1.0 × 10¹⁹和1.0 × 10²⁰ cm^-2)的样品中存在O空位的聚集。磁性测量显示中子辐照后的MgO(110)单晶在室温下依然是抗磁性,但在低温下具有铁磁性,最大饱和磁化强度达到0.058 emu·g^-1。通过中子辐照的方法,可以使MgO(110)单晶产生点缺陷引起的低温铁磁性。利用F色心交换机制可以解释中子辐照MgO晶体中的O空位缺陷与铁磁性之间的关系。