Due to the strong capillary condensation, the adhesion force between a Si3N4 atomic force microscope (AFM) tip and silicon oxide was observed to first increase and then decrease with an increase of humidity. In contrast, due to weak capillary condensation, the adhesion force between the AFM tip and the N-octadecyltrimethoxysilane (OTE,CH3(CH2)17Si(OCH2CH3)3) self-assembled monolayer (SAM) was found to be almost independent of humidity. It was found that the formulation commonly used for acroscopic objects fails to explain our data. Using an accurate formulation and an assumed tip shape, we can explain the observed decrease of adhesion for SiO2 at high humidity as being due to the decreased capillary pressure force when the dimension of the meniscus becomes omparable with the tip size. However, theobserved late onset of adhesion of SiO2 cannot be understood within the framework of the classical continuum theory. We attribute this late onset to the properties of an ultrathin water film at molecular thickness. The new formulation predicts a vanishing water meniscus between the AFM tip and OTE over the entire humidity range and can also fully account for the humidity-independent adhesion results for OTE.

For the friction measurements with AFM/FFM, usually the relative values of friction signal can be obtained. In order to compare the micro-tribological properties of different samples, mica is often used as an reference sample for friction measurement. However, due to the friction force of new cleaved mica surface is unstable, it is urged to systematically investigate the tribological properties of mica to design the experimental rules of the reference sample mica for friction measurements. Experimental results show that the friction of mica varies with the cleaving time, humidity and surface state of tip. The friction measured with different tips on mica varies in the range of

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.

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。

The fretting behavior of superelastic nickel titanium (NiTi) shape memory alloy was studied at various displacement amplitudes on a serve-hydraulic dynamic test machine. The results showed that the superelastic properties of the material played a key role in the observed excellent fretting behavior of NiTi alloy. Due to the low phase transition stress (only 1/4 the value of its plastic ield stress) and the large recoverable phase transition strain (5%) of NiTi, the friction force of NiTi/GCr15 stainless steel pair is smaller than the value of GCr15/GCr15 pair and at the same time the Rabinowicz wear coefficient of NiTi plate is about 1/9 the value of GCr15 plate under the same fretting conditions. For NiTi/GCr15 pair, even NiTi has a much lower hardness than GCr15, the superelastic NiTi alloy exhibits superior fretting wear property than GCr15 steel. It was found that the weak ploughing was the main wear mechanism of NiTi alloy in the partial slip regime. While in the mixed regime and gross slip regime, the wear of NiTi was mainly caused by the abrasive wear of the GCr15 debris in the three-body wear mode.