Nanofriction properties of molecular deposition films

The nanofriction properties of Au substrate and monolayer molecular deposition film and multilayer molecular deposition films on Au substrate and the molecular deposition films modified with alkyl-terminal molecule have been investigated by using an atomic force microscope. It is concluded that ( i ) the deposition of molecular deposition films on Au substrate and the modification of alkyl-terminal molecule to the molecular deposition films can reduce the frictional force; (ii) the molecular deposition films with the same terminal exhibit similar nanofriction properties, which has nothing to do with the molecular chain-length and the layer number; (iii) the unstable nanofriction properties of molecular deposition films are contributed to the active terminal of the molecular deposition film, which can be eliminated by decorating the active molecular deposition film with alkyl-terminal molecule, moreover, the decoration of alkyl-terminal molecule can lower the frictional force conspicuously; (iv) the relat     

Micro/nanotribological behaviors of ionic liquid nanofilms with different functional cations

Four kinds of molecularly thin films of room temperature ionic liquids (RTILs) with different functional cations were prepared on silicon substrates by dip‐coating method. Thermal stability of the RTILs was evaluated using Mettler thermal gravity analysis (TGA) in a nitrogen atmosphere. Chemical compositions of the RTIL nanofilms were examined by means of multifunctional XPS. Nanoscaled adhesion and friction forces between the films and AFM tip were measured by FFM whereas the morphologies of the films were also investigated. Microscaled friction and wear behaviors between the films and Si₃N₄ ball were further measured by the microtribometer. The micro/nanotribological behaviors of different RTIL films were comparatively investigated and discussed in terms of functional cations of the RTILs molecules. Results in this paper revealed that the functional cations of the RTIL films significantly affected their tribological behaviors both in micro‐ and nanoscales. The corresponding micro/nanotribological mechanism of the tested ultrathin RTIL films under the test conditions was consequently proposed based on the experimental results. Copyright © 2010 John Wiley & Sons, Ltd.     

基底支撑刚度梯度变化对石墨烯层间摩擦力的影响

基于纳米摩擦能耗理论,利用分子动力学方法建立了公度接触下支撑刚度梯度变化的石墨烯层间摩擦力模型,分析了基底质心刚度和支撑刚度梯度变化对基底和薄片各接触区摩擦能耗的贡献.结果表明:软边界区始终贡献驱动力;硬边界区贡献的摩擦力最大,且随着支撑刚度的增大,硬边界区对总摩擦的贡献比也越高.各接触区的摩擦力是薄片和基底之间的褶皱势和接触区产生的法向变形差两部分的共同作用.前者是公度接触下阻碍滑移的界面势垒和刚度梯度方向上不同刚度支撑原子热振动引起的势梯度;后者是接触边界过渡区两侧原子的非对称变形和自由度约束突变引起的非平衡边界势垒相耦合的结果.本文对研究公度接触下刚度梯度支撑的纳米器件的相对运动规律有指导意义.     

Non‐Lipschitzian control algorithms: application to a nanofriction model

Recently we proposed a new feedback control algorithm for quantities describing global features of non‐linear dynamical systems. The performance of the algorithm, which is based on the concepts of non‐Lipschitzian dynamics and global targeting, has been successfully demonstrated for systems confined to one spatial dimension and for a specific targeted global quantity, namely the velocity of the centre of mass. In this paper we extend the scope of the non‐Lipschitzian control scheme to multi‐dimensional systems and different targeted quantities. We illustrate the efficiency of the non‐Lipschitzian feedback w.r.t. the ordinary (Lipschitzian) feedback, as well as the robustness and accuracy of the algorithm in a broad variety of control scenarios on the 2‐d Frenkel‐Kontorova model for nanofriction. Published in 2005 by John Wiley & Sons, Ltd.     

Dynamical phenomena in fast sliding nanotube models

The experimentally known fact that coaxial carbon nanotubes can be forced to slide one inside the other stimulated in the past much detailed modelling of the dynamical sliding process. Molecular dynamics simulations of sliding coaxial nanotubes showed the existence of strong frictional peaks when, at large speed, one tube excites the other with a ‘washboard’ frequency that happens to resonate with some intrinsic vibration frequency. At some of these special speeds we discover a striking example of dynamical symmetry breaking taking place at the nanoscale. Even when both nanotubes are perfectly left–right symmetric and nonchiral, precisely in correspondence with the large peaks of sliding friction occurring at a series of critical sliding velocities, a nonzero angular momentum spontaneously appears. A detailed analysis shows that this internal angular momentum is of phonon origin, in particular arising from preferential excitation of a right polarized (or, with equal probability, of a left polarized) outer-tube ‘pseudorotation’ mode, thus spontaneously breaking their exact twofold right–left degeneracy. We present and discuss a detailed analysis of nonlinear continuum equations governing this phenomenon, showing the close similarity of this phenomenon with the well-known rotational instability of a forced string, which takes place under sufficiently strong periodic forcing of the string. We also point out new elements appearing in the present problem which are ‘nano’, in particular the involvement of Umklapp processes and the role of sliding nanofriction.     

原子力显微镜在纳米摩擦学中应用的进展

近年来，原子力显微镜在纳米摩擦学研究中获得了越来越广泛的应用，已经成为进行纳米摩擦学研究的重要工具之一，有力地促进了纳米摩擦学的发展．因此，对应用原子力显微镜研究纳米摩擦、纳米磨损、纳米润滑、纳米摩擦化学反应和微型机电系统的纳米表面工程等方面所取得的主要进展作了系统的综合归纳与阐述，并且提出了原子力显微镜在纳米摩擦学应用中亟待解决的几个主要问题．     

石墨烯摩擦学及石墨烯基复合润滑材料的研究进展

本综述详细介绍了二维碳纳米材料-石墨烯的纳米摩擦学性能,以及作为纳米润滑薄膜、润滑添加剂和润滑填料的研究进展.总结了石墨烯的各种纳米摩擦机理,阐述了通过自组装、多层构筑、表面化学改性等技术改善石墨烯与基底的结合性、润滑剂中的分散性,与基体材料的界面结合强度以及石墨烯提高材料减摩抗磨性能的机制,并指出石墨烯作为高性能润滑材料仍需解决的问题及未来的研究趋势.     

等离子体沉积碳氟聚合物薄膜的纳米摩擦性能研究

利用原子力显微镜研究了感应等离子体刻蚀加工过程中单晶硅表面形成的不同厚度的碳氟聚合物薄膜的纳米摩擦特性，并针对几种不同的摩擦模式探讨了原子力显微镜探针在不同厚度的碳氟聚合物薄膜表面的摩擦行为．结果表明，同硅基体相比，聚合物薄膜的摩擦力信号明显较弱，薄膜的纳米摩擦特性同其厚度密切相关；碳氟聚合物薄膜在同Si3N4针尖接触过程中可向针尖表面转移，从而对针尖起修饰作用，以减轻微观摩擦磨损．     

石墨烯层间纳米摩擦性质的第一性原理研究

基于密度泛函理论的第一性原理计算方法研究了纳米尺度下石墨烯层间摩擦现象, 探讨了对称和非对称两种情况下双层石墨烯层间沿不同方向的摩擦性质. 研究发现对于对称的双层石墨烯, 层间摩擦沿不同方向同性; 摩擦因数依赖于正压力, 随正压力增大, 摩擦因数的变化曲线分为三个阶段, 在较小以及较大压力下, 摩擦因数遵循Amonton法则不随压力变化而变化; 而在中间3-6 nN阶段, 摩擦因数随压力增加线性增加. 整个研究压力范围内摩擦因数在0.05-0.25之间. 对于非对称性双层石墨烯层间摩擦, 不同压力下摩擦因数在0.006上下波动, 摩擦因数较两层对称性石墨烯大大降低. 上述研究结果与实验一致.     

Nanomechanical and nanotribological characterization of multilayer self-lubricating Ti/MoS2/Si/MoS2 nanocoating on aluminium-silicon substrate

Ti/MoS₂/Si/MoS₂ multilayer coating was fabricated by a pulse laser deposition method from a titanium, molybdenum disulphide, and silicon targets, and the coating was deposited in layers on aluminium-silicon substrates, at room temperature. The structural analysis and surface morphology of multilayer Ti/MoS₂/Si/MoS₂ coating were analysed using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy integrated with energy dispersive X-ray spectroscopy. Nanomechanical tests were performed on Ti/MoS₂/Si/MoS₂ coating at small loads of 2000 to 6000 μN to study the effect of load on hardness and Young's modulus. Nanoscratch and nanowear tests were conducted on Ti/MoS₂/Si/MoS₂ coating at a low load of 1000 to 5000 μN and 100 to 500 μN, respectively, to study deformation and failure behaviours of coating/substrate system and also their nanotribological properties. The results show that hardness and Young's modulus of Ti/MoS₂/Si/MoS₂ coating decrease with increase in load. A low friction coefficient of 0.09 to 0.16 was observed, which proves that the Ti/MoS₂/Si/MoS₂ coating possesses self-lubricating property. The wear rate of Ti/MoS₂/Si/MoS₂ coating increases 3.3 × 10⁻¹⁰ to 7.8 × 10⁻¹⁰ mm³/Nm with increase in load. Ti/MoS₂/Si/MoS₂ multilayer coating shows a smooth wear track with no cracks and debris on the surface, which attributed plastic flow of softer coating material around the wear track.