采用光干涉法相对光强原理对点接触中心区进行了润滑膜厚度测量，该方法在垂直方向的分辨率可达O.5nm，水平方向可达1μm，讨论了膜厚与压力，速度和润滑油粘度之刘的关系，观察和分析了流体润滑膜的失效现象。实验结果表明如果接触压力足够小或者润滑油粘度足够高，即使在一个很低的速度下也能清晰地观察到流体动压润滑效应。当压力增至某一定值，在膜厚-速度曲线上可观察到一个转辑点，当速度降到此点以下时，润滑膜厚度将很快减小到几个分子层厚，此时，润滑膜不再具有流体润滑特征，即流体润滑膜失效，失效点会出现在不同的速度和压力下。要使接触区在较高的压力下形成流体膜就必须加更高的速度或使用更大粘魔的润滑油。最后建立了失效点的压力、速度和润滑油粘度之间的关系。

使用原子力/摩擦力显微镜，在5%-9%相对湿度范围，研究了二氧化硅和二氧化硅基体上十八烷基三甲氧基硅烷自组装膜（简称OTEsAM/siO2）表面粘着力随湿度的变化规律。实验表明，二氧化硅表面的粘着力随湿度的增大先逐渐增大，然后急剧减小相反，叫OTE SAM/SiO2由于其良好的斥水性，表面的粘着力随湿度的增大基本不变着重从基本界面力，即表面张力、范德瓦耳斯力和基本键合力的形成与变化，分析了二氧化硅表面粘着力随湿度的增大先增后减的原因，探讨了粘着力的产生机理。

使用原子力/摩擦力显微镜在5%-9%的相对湿度范围，研究了二氧化硅和二氧化硅基体上十八烷基三甲氧基硅烷自组装膜（简称OTEsAM/siO2）表面摩擦力和粘着力随湿度的变化规律实验表明叫OTE SAM/SiO2，不仅能明显改善二氧化硅基体表面的摩擦性能，而且在200nN（接触区HPnz压力约为0.8GPa）的载荷条件下表现出良好的抗磨性能由于强的亲水性，二氧化硅表面的摩擦力随湿度的增大先逐渐增大，然后急剧减小相反，OTE SAM/SiO2由于其良好的斥水性，表面的摩擦力在高湿度条件下略有减小，它可望成为微型机械和高速磁记录系统中较为理想的边界润滑剂。

Using friction force microscopy (FFM) under controlled environments, we have systematically investigated the humidity effect on the frictional properties of two important classes of self-assembled monolayers (SAMs), i.e., N-octadecyltrimethoxysilane (OTE,CH3(CH2)17Si(OCH3)3) on SiO2 (OTE/SiO2); and N-alkanethiols on Au (111), together with their respective substrates. Experimental results show that both OTE and alkylthiol SAMs can decrease the friction force between a Si3N4 atomic force microscope (AFM) tip and substrates. The nearly humidity-independent friction of the two kinds of SAMs indicates that these SAMs are ideal lubricants in applications of micro-electro-mechanical systems (MEMS) under different environments. The humidity dependence-as the humidity increases, the friction first increases and then decreases-of the two substrates, SiO2 and Au (111), can be explained by the adsorption of water. The decrease in the friction at high humidity is attributed to the low viscosity in the multilayers of water, while the increase in the friction at low humidity can be explained by the high viscosity between the water monolayer and the surfaces (AFM tip and sample), possibly due to the confinement effects. The effect of modification of the AFM tip with alkanethiol molecules on the humidity dependence of Au (111) friction has also been investigated.

In this paper, we present our experimental results on the process of the in situ chemical modification of the silicon nitride atomic force microscopy/frictional force microscopy tip by n-octadecyltrimethoxysilane (OTE)/mica, OTE/SiO2, and SiO2. The modified tips have different friction and adhesion properties against mica reference samples compared to those before modification. The resultant tip modification depends not only on OTE self-assembled monolayer (SAM) but also on the substrates the OTE SAM is prepared on. In the case of OTE/mica, the friction of the modified tip against mica reference is greatly reduced; in the case of OTE/SiO2, the friction of the modified tip against mica reference is greatly increased. It is surprising that bare SiO2 can also chemically modify the Si3N4 tip to increase the friction against mica reference. In the case of OTE modification, it was found that the tips could be cleaned by repetitive friction scans on mica. However, a tip modified by SiO2 cannot be mechanically cleaned. Moreover, it was found that humidity and load could also affect the tip chemical modification. Ourresults are important for interpreting tribological data since the actual contact chemistry was often overlooked in the atomic force microscopy experiments in the past.