Influence of atmosphere humidity on tribological properties in scanning probe microscope observation

Abstract

Nanotribological studies are made using a scanning probe microscope (SPM) which can produce lateral force images as well as normal force images. The SPM is placed in an atmosphere control apparatus and the relative humidity around the tip and the sample is controlled from 30% to 70%. Measurements are also performed in a high-purity water bath. The samples investigated are the cleaved surfaces of mica, HOPG and MoS 2 . In order to discuss the nanotribological effects of adsorbed water molecules and the capillary condensation of water, the lateral force images are examined quantitatively as a function of the normal load on the sample surface. Lateral force images with lattice periodicity are obtained in the same manner as atomic scale topography images. The dependence of lateral force magnitude on the normal force is found to be affected by the atmosphere around the tip and the sample.The scanning probe microscope (SPM) devised to detect changes in the interaction force between a tip and a sample, the atomic force microscope (AFM), is capable of controlling the interaction force and is a unique tool for nanometer-scale modification [1-3] and tribology [4,5]. When a tip scans a sample surface in contact mode, there is not only a normal force (i.e. a repulsive or attractive force), but also a lateral (i.e. frictional) force acting on the tip. Mate et al. were the first to exploit the lateral force microscope (LFM) to study the lateral force. They detected stick-slip motion of a tungsten tip on graphite and mica surfaces with the periodicity of the lattice constant [6,7]. This stick-slip behavior also contributes to the contrast of the atomically resolved topography image [8,9]. The topography image and the lateral force image are assumed to be detected separately by the SPM with a quadrant position-sensitive detector, i.e. AFM/LFM [10,11].In ambient air, the presence of physisorbed or chemisorbed molecules could affect the nanotribological properties between the tip and the sample. The effects should be significant for high-resolution operation [3]. It is important to evaluate the extent of the effects, because the imaging mechanism is not well understood [12]. Recently, the influence of adsorbed water molecules and capillary condensation on nanotribological phenomena has been characterized by means of LFM friction experiments on silicon wafers [13]. It was reported that friction and adhesive forces were affected by the relative humidity of ambient air, but the behavior of these forces in atomic-scale imaging was not mentioned.In the present experiment, the AFM/LFM is placed in an atmosphere control apparatus and the relative humidity around the tip and the sample is controlled from 30% to 70%. In order to discuss the nanotribological effects of adsorbed water molecules and the capillary condensation of water on atomic-scale measurements on the cleaved surfaces of mica, HOPG and MoS 2 , the lateral force images corresponding to atomic-scale topography images are examined. Measurements are also performed in a high-pur...

Mechanical characterization of nanofibers – A review

“…• Adhesion force. In a high humidity environment (>70% relative humidity), the effects of adhesion due to the capillary effect of water condensation between tip and sample can become significant [43]. Such adhesion force have to be accounted for as shown in a study by Park et al [41].…”

Recent progress of graphene orientation determination technology based on scanning probe microscopy

“…It's relatively easy to obtain atomic-resolution images using LFM mode. In the early stage, the imaging conditions of the contact mode were stringent [43][44][45]. Until 2010, Lee et al [46] obtained the atomic resolution images of graphite and graphene in the atmospheric environment.…”

“…In the contact mode, the AFM tip always keeps contacting with the samples, and the scanning angle is usually 90° or 270°. This imaging mode is called lateral force microscopy (LFM) [43]. Using this method, both of the atomic resolution images of the sample and the friction information are saved during the imaging process.…”

The influence of carbon content on the microtribological performance of W-S-C films

“…[21][22][23][24] However, limited information can be found on the tribological properties of these films in the milli-and nano-Newton load range. [25][26][27][28][29] On the other hand, extensive literature about nanotribological behaviour is available for carbon-based films. [30][31][32][33][34][35] These reports primarily discuss the influence of load, surface and bulk chemistry, coating thickness, roughness, etc.…”