扶手椅型缺陷硫化钼纳米带电子性质的第一性原理计算

基于密度泛函理论的第一性原理计算,研究了含空位缺陷的扶手椅型二硫化钼纳米带的电子性质.发现缺陷会导致纳米带结构稳定性降低,单空位钼缺陷和三空位缺陷使得纳米带从半导体变成金属性,而单空位硫缺陷和两种双空位缺陷仅减小纳米带的带隙;电子态密度和能带的本征态表明缺陷纳米带费米能级附近的杂质态主要是缺陷态的贡献.研究了四类半导体性质的纳米带带隙与宽度的关系,对于完整的纳米带,带隙随宽度以3为周期振荡变化;而引入空位缺陷后,纳米带的带隙振荡不再具有周期且振荡幅度变小.同时发现,当缺陷的浓度变小后,缺陷仅使纳米带的带隙减小,不会使其变为金属性.这些结果有望打开其在新型纳电子器件中的应用潜能.     

Consistency-dependent optical properties of lubricating grease studied by terahertz spectroscopy

The optical properties of four kinds of lubricating greases (urea, lithium, extreme pressure lithium, molybdenum disulfide lithium greases) with different NLGL (National Lubricant Grease Institute of America) numbers were investigated using terahertz time-domain spectroscopy. Greases with different NLGL grades have unique spectral features in the terahertz range. Comparison of the experimental data with predictions based on Lorentz--Lorenz theory exhibited that the refractive indices of each kind of lubricating grease were dependent on the their consistency. In addition, molybdenum disulfide (MoS₂) as a libricant additive shows strong absorption from 0.2 to 1.4 THz, leading to higher absorption of MoS₂-lithium grease than that of lithium grease.     

水热法合成纳米花状二硫化钼及其微观结构表征

本文以钼酸钠、硫代乙酰胺为前驱体, 硅钨酸为添加剂, 成功用水热法合成高纯度纳米花状二硫化钼. 产物特性用X射线衍射(XRD)、能量色散谱(EDS)、扫描电子显微镜(SEM)进行表征. XRD和EDS图显示实验产物为二硫化钼, 且其结晶度和层状堆垛良好. SEM图谱则表明二硫化钼为纳米花状结构, 颗粒直径300 nm左右, 由几十上百片花瓣组成, 每片花瓣厚度十个纳米左右. 通过以硅钨酸为变量的梯度实验, 研究发现, 硅钨酸对于纳米花状MoS₂的形成具有重要作用, 不添加硅钨酸, 无法形成纳米花状MoS₂, 此外, 硅钨酸的剂量会影响合成MoS₂的大小和形貌. 本文还对纳米花状二硫化钼的形成机理做了初步的讨论.     

单层和双层二硫化钼化学气相沉积生长的动力学蒙特卡罗模拟研究

Controllable synthesis of MoS₂ with desired number of layers via chemical vapor deposition (CVD) remains challenging. Hence, it is highly desirable to develop a theoretical model that can be used to predict the single- and multilayer growth of MoS₂ quantitatively, and provide guidelines for experimental fabrication. Herein we have established a kinetic Monte Carlo (kMC) model to predict the CVD growth of mono- and bilayer MoS₂. First, we proposed that the growth rates of layer 1 and layer 2 were governed by the distribution of the adatom concentration, and the growth kinetics of compact triangular MoS₂ followed the kink nucleation-propagation mechanism. The adatom concentration was formulated in terms of adatom flux, effective lifetime of adatoms, growth temperature, binding energies, edge energies, and nucleation criterion. The kink nucleation and propagation were determined by energy barriers of the adatom attachments to the zigzag and armchair edges. We then employed an analytic thermodynamic criterion to extract these parameters. Using the calibrated model, we found that the growth rate of layer 2 strongly depended on the size of layer 1 and decreased monotonically with increasing size of layer 1, and might even become prohibited at the maximum size of layer 1. Furthermore, we analyzed the size and morphology evolutions of bilayer MoS₂ at different growth temperatures and adatom fluxes. Throughout the growth processes of bilayer MoS₂, the morphologies of layers 1 and 2 maintained triangular shapes with compact edges, consistent with the kink nucleation-propagation growth mechanism. Our simulations revealed that the growth of bilayer MoS₂ was promoted by increasing the growth temperature or decreasing the adatom flux, which corroborated the experimental observations. The increase in growth temperature led to reduced adatom concentration at the edge of layer 2 in accordance with the adatom concentration far from the edge of layer 2, resulting in a consistent difference in the adatom concentration to promote the growth of bilayer MoS₂. Similarly, the decrease in adatom flux lowered the difference between the adatom concentrations far from the edge and at the edge of layer 1, decelerating the growth of layer 1. The decelerated growth of layer 1 reduced the difference between the adatom concentrations far from the edge and at the edge of layer 2 to zero, permitting the growth of bilayer MoS₂. To guide the experimental synthesis, we constructed a phase diagram to delineate the permitted or prohibited growth of bilayer MoS₂ at different growth temperatures and adatom fluxes. Hence, this work not only unveils the conditions for the growth of mono- and bi-layer MoS₂, but also provides guidelines for controllable synthesis of MoS₂ with the desired number of layers.     

Ar气保护固相合成花状二硫化钼工艺研究

以三氧化钼和硫为原料,采用Ar气保护固相合成法,合成花状二硫化钼。采用XRD、SEM、TEM等手段对样品的结构和形貌进行表征。考察了原料比、反应温度、反应时间、升温速率对样品纯度的影响,制备出纯度较高的二硫化钼。结果表明:当MoO₃与S物质的量之比为1∶7.5,反应温度为450 ℃,反应时间为4 h,升温速率为15 ℃/min,可得到纯度为99.4%的花状二硫化钼,该花状结构由厚度为10 nm左右的翘曲片层组成,TEM照片中可见0.62 nm单层二硫化钼结构,具有较大的比表面积,使其在储能、催化等领域有广阔的应用前景。     

基于硫蒸气处理转移的单层二硫化钼的荧光增强

采用化学气相沉积法在SiO2/Si衬底上制备了单层MoS2,再通过300℃硫蒸气处理用聚甲基丙烯酸甲酯(Polymethyl Methacrylate,PMMA)转移下的单层MoS2.使用原子力显微镜、真空荧光检测和拉曼光谱等手段表征了样品的形貌和光致发光性能.结果表明:经过硫蒸气处理转移后的单层MoS2的光致发光强度比由化学气相沉积法制备的未处理的单层MoS2的光致发光强度增强了约5倍.光致发光强度增强是由于在硫蒸气处理过程中,单层MoS2的部分硫空位被硫原子纳米团簇所填补,从而提高了光致发光效率.此外,分别将单层MoS2转移到SiO2/Si衬底、石英、三氧化铝及氟化镁衬底再经过硫处理后,也观察到了类似的荧光增强现象.     

溅射羽辉与基底夹角对掺氧二硫化钼薄膜光学性质的影响

二硫化钼(MoS₂)在环境中的热稳定性和化学稳定性好,迁移率相对较高,已应用于气体传感器、光电探测器和场效应管等器件的研制。采用氧气辅助技术生长的氧掺杂MoS₂(MoS_2-xO_x)不仅可以调控MoS₂单晶尺寸,还能提高MoS₂单晶光致发光强度。本文采用射频反应磁控溅射技术、自然环境中氧化和热退火工艺,改变溅射羽辉与玻璃基底夹角来制备MoS_2-xO_x薄膜并研究其光学性质。采用X射线光电子能谱分析了样品的元素和价态;扫描电子显微镜观测的结果表明,溅射羽辉与基底成45°(θ=45°)时表面形貌为最优;紫外-可见分光光度计的测试结果表明,随着厚度和氧含量的增加,MoS_2-xO_x薄膜的光学带隙减小;采用COMSOL Multiphysics软件模拟了MoS_2-xO_x薄膜光学透过率,理论和实验结果相吻合。本文的研究结果将为MoS_2-xO_x薄膜在光学领域的应用提供科学参考。     

Hydrothermal exfoliated molybdenum disulfidenanosheets as anode material for lithium ion batteries

Ultrathin MoS2nanosheets were prepared in high yield using a facile and effective hydrothermal intercalation and exfoliation route. The products were characterized in detail using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The results show that the high yield of MoS2nanosheets with good quality was successfully achieved and the dimensions of the immense nanosheets reached 1 μm–2 μm. As anode material for Li-ion batteries, the as-prepared MoS2nanosheets electrodes exhibited a good initial capacity of 1190 mAh g-1and excellent cyclic stability at constant current density of 50 mA g-1. After 50 cycles, it still delivered reversibly sustained high capacities of 750 mAh g-1.     

聚四氟乙烯和二硫化钼填充聚酰亚胺复合材料的摩擦磨损性能研究

采用MM-200型摩擦磨损试验机考察了聚四氟乙烯(PTFE)和MoS2填充聚酰亚胺(PI)复合材料在干摩擦下与GCr15轴承钢对摩时的摩擦磨损性能，并利用扫描电子显微镜和X射线能量色散谱仪分析了PI复合材料及其偶件磨损表面形貌和元素面分布．结果表明，PTFE和MoS2均可降低PI的摩擦系数，其中PI 30％MoS2复合材料的减摩性能最佳，其摩擦系数同纯PI的相比降低了约50％．除PI 10％PTFE 20％MoS2外，其它几种复合材料的抗磨性能均明显优于纯PI，其中PI 20％PTFE 10％MoS2复合材料的抗磨性能最佳，其磨损率比纯PI的低1个数量级．PI复合材料的摩擦磨损性能同其在偶件磨损表面形成的转移膜的性质密切相关，当转移膜厚度适当且分布较均匀时，PI复合材料的减摩抗磨性能良好．