EFFECT OF ELECTROSTATIC RESISTANCE ON THE SHUTTLE OF MICRORESONATOR

To improve the performance and reliability of microelectromechanical system＇s devices, it is necessary to understand the effect of friction which exists in the majority of microelectromechanical systems （MEMS） with a large ratio of surface area to their volume. The model of electrostatic tangential force of the shuttle in laterally driven comb microresonator is established based on the rule of energy conservation. The effects of microscale, surface roughness, applied voltage, and micro asperities or dents or holes formed in fabrication are investigated, and the electrostatic resistance between two charged moving plates is analyzed. The analytic results are coincident well with those of ANSYS simulation. It is found that the electrostatic resistance becomes high as the increase of the ratio of the shuttle width to the gap between moving plates and the relative surface roughness or the increment of the applied voltage.

Microscale study of frictional properties of graphene in ultra high vacuum

We report on the frictional properties of epitaxial graphene on SiC in ultra high vacuum.Measurements have been performed using a microtribometer in the load regime of 0.5 to 1 mN.We observed that a ruby sphere sliding against graphene results in very low friction coefficients ranging from 0.02 to 0.05.The friction and also the stability of the graphene layer is higher than that under similar conditions in ambient conditions.The friction shows a load dependence.Finally it was found that graphene masks the frictional anisotropy which was observed on the SiC surface.

Structure and microtribological characteristics of laser-arc deposited TiB_2 thin film

TiB2 thin film was deposited by laser-arc deposition method on the surface of single crystalline Silicon. The morphology, composition, structure and microtribological properties of the film were studied by using XPS, XRD and atomic force/friction force microscope (AFM/FFM). The results show that TiB2 (100) preferred growth on the Si(100) substrate, TiB2(001) preferred growth on the Si(111) substrate. The TiB2 thin film was composed of TiB2 and a smali amount of TiO2. The friction coefficient of TiB2 film on substrates Si (100) and Si(111) in microtribological process were 0.087 and 0.073, respectively. TiB2 thin film displayed distinct ability of anti-scratch and wear-resistance.

The nature of the frictional force at the macro-, micro-, and nano-scales

Nowadays it is accepted that the friction force is a combined effect arising from various phenomena:adhesive forces,capillary forces,contact elasticity,topography,surface chemistry,and generation of a third body,etc.Any of them can dominate depending on the experimental force and length scales of the study.Typical forces in macro-tribology are in the Newtons,while are reduced to milli-/micro-Newtons,and nano-Newtons in micro-and nano-tribology,respectively.In this paper,experimental friction results from fullerene like CNx films and single-crystal Si at the three scales will be discussed.The complex and broad variety of processes and phenomena connected with the dry friction coefficient at the macro-,micro-,and nano-scale point of view will be highlighted.

Protective effects of two food hydrocolloids on dental erosion:Nanomechanical properties and microtribological behavior study

In this study,the protective effects of two food hydrocolloids,Xanthan gum and Arabic gum,on dental erosion are investigated from the perspective of the nanomechanical properties and microtribological behavior of acid-eroded enamel.Enamel specimens prepared from extracted human teeth were immersed in citric acid solution(CAS),CAS with 0.03%w/v Xanthan gum and CAS with 0.03%w/v Arabic gum,respectively,for 10 min to obtain three groups of eroded specimens.The nanomechanical properties and microtribological behavior of enamel were examined using nano-indentation/scratch techniques.The results show that compared with Arabic gum,Xanthan gum inhibits enamel surface demineralization and acid permeation more effectively because of a more uniform and denser adsorption on the surface of the enamel.The impairment of the nanomechanical and microtribological properties of the enamel surface by acid erosion is mitigated more significantly by adding trace amounts of Xanthan gum than Arabic gum.In summary,adding trace food hydrocolloids reduces enamel surface demineralization and inhibits acid permeation to mitigate the influence of erosion on the mechanical and tribological properties of enamel.The adsorption state of food hydrocolloids is the determining factor in the permeability of acid agents into the enamel and plays a significant role in preventing dental erosion.