Zhen Fan

Numerical Approach to Torsion Deformation of Armchair Single Walled Carbon Nanotubes

In this paper, a new atomic-scale finite element method (AFEM) based on the nonlinear spring model is used to investigate the torsional properties of armchair single walled carbon nanotubes (SWNTs). A simple iteration algorithm is applied to get the solution of the equilibrium function. The torsion deformations of 12 armchair SWNTs with different diameters and lengths are simulated. The development of buckling deformation is observed and discussed. Critical torsion angle of each nanotube is obtained. It is found the shear moduli of the SWNTs range from 391 GPa to 592 GPa, and it is closely related with the diameter of nanotube. However, the nanotube length has little effect on the shear modulus. In addition, it is observed the buckling morphology varies as the parameter of nanotube changes.

Experimental Study of Flow Characteristics of Distilled Water under Pressure Driven in Microchannel

The micro-flow systems have been extensively introduced into the micro-devices in Microelectromechanical System(MEMS), and the flowing characteristics determines the performance of the micro-devices to a great extent. Here, the experiments of characteristics of distilled water flow in a series of round quartz microchannels with the diameters of 13mum, 20mum and the lengths ranging from 40 mm to 100 mm under pressure-driving force were investigated, and the relationship between the flow rates and pressure was investigated as well. The results indicate that the difference occurred in the measurement between experiment and theory for the diameter of 20 mum, the relationship between the flow rates and pressure was linear, but the experimental flow rate less than predicted, and the flow characteristics of the microchannels is basically in agreement with the macroscopic liquid flowing laws, and the same case is for the microchannels of the 15 mum in diameter with their lengths less than 70 mm. However, the flow rate is almost 2.19-3.93 times bigger than the calculated values macroscopically when the length exceeds 80 mm, which is ascribed to the occurrence of boundary slip on channel walls

Experimental Study of Tribological Properties of Silicon-Based MEMS/NEMS Surface with Atomic Force Microscope

A comparative study of the micro-tribological properties of silicon-based component and octadecyltrichlorosilane (OTS) molecular lubricant film which was prepared on Si(100) substrate, and their adhesive and tribological properties were mainly investigated by AFM/LFM. Meanwhile, the effect of relative humidity and scanning velocity was taken into consideration. The results show that the adhesive force of OTS film is much smaller the one of Si (100) substrate which leads to a relatively low friction coefficient, thereby the OTS film presents better lubricant performance; Besides, the Si(100) substrate is much more affected by the variation of humidity than OTS film; The velocity effect on the frictional performance is more significant for Si(100) component due to the Si(OH)4 lubricant film caused by the tribo-chemical reaction. A thermally activated capillary condensation model while taking the surface roughness effect into consideration is also adopted to explain the humidity and velocity effects on the adhesive and tribological properties theoretically. In addition, the durability tests indicate that the OTS lubricant film exhibits not only better wearability but also stability comparatively

Synthesis and Investigation of Micro-Tribological Behavior of WS2 Nanotube

MS2(M=Mo, W, S=S, Se) are often used as solid lubricants in high/low temperature, high load, vacuum, in which oil lubrication is failed. Although WS2 is much more expensive than MoS2, it has better high temperature properties than MoS2. Thermal decomposition method is used to produce fullerence-like WS2 nanotube on Al2O3 template using (NH4)2WS4. The fabricated WS2 nanotube’s diameter is about 100nm and its length is longer than 2µm.The morphology, microstructure and tribological behavior of WS2 nanotube are investigated by means of SEM, TEM, XRD and AFM. The friction force between Si3N4 probe of AFM with WS2 nanotube is lower than that with MoS2 powder. Similar results are also found in pin-disc tester by GCr15 pin and lubricants coating disc. The results of HETEM show that WS2 nanotube has rolling debris between the two antagonist surfaces, and MoS2 powder only has flattened debris. It may be the fullerence structure brings the chemical stability and leads to low friction.

Microstructure and Wear-Resistant SiC Film by RF Magnetron Sputtering

A wear-resistant SiC (silicon carbon) film on titanium substrate was prepared by magnetron sputtering technology. The film exhibits low nano-hardness of 12.1 GPa and low Youngs modulus of 166.2 GPa together with superior friction/wear properties. As sliding against Si3N4 (silicon nitride) ball (2 mm in radius) at room temperature under Kokubo simulation body fluid condition, the film exhibited the friction coefficient of about 0.215 and the special wear rate in the order of magnitude of 10−5 mm3/ Nm even at the load of 500g without film cracking and interface delaminating. The high film-cracking and interface-delaminating resistance is due to the low hardness of the film and the good film/substrate modulus match caused by the low elastic modulus of the film.

Tribological Properties of the DLC/SEBS/A187/Si Elastomeric Nanocomposite Multilayer Film

A DLC/SEBS/A187/Si multilayer was prepared by self-assembled monolayer (SAM) method and pulse filtered catholic vacuum arc source (FCVA) technology. Microstructure and frictional properties of the film were investigated by using X-ray photoelectron spectroscopy (XPS), AFM, SEM and UMT-2MT tribometer. Results showed that the peaks appearing at 287.8eV for XPS demonstrated the successfully graft of SEBS on the couple agent(A187); The surface of the top DLC film was compactly and uniformly distributed; Friction coefficient of the prepared film was not sensitive to velocity under low load and the coefficient ranged from 0.1 to 0.15, but at high load, the tribological property of the film deteriorated with the increasing of sliding velocity, when the normal load was 2N and the sliding speed was 30 r/min, only the top DLC film was scratched out, but when the sliding velocity increased to 240 r/min, the whole prepared film was scratched out.

Frequency shift of Single-Walled Carbon Nanotube under axial load

An atomic finite element model based on virtual spring model for armchair and zigzag single walled carbon nanotubes is employed to reveal the relation between axial load and frequency shift. Tersoff-Brenner potential is introduced to define the interactions between the atoms as well as the mechanical properties of the springs in the model. The fundamental frequency shifts of transverse and radial vibration modes of strained single walled carbon nanotubes are obtained by applying finite element theory and techniques. It is found that the fundamental frequencies of the two modes are typically as high as hundreds of GHz, and they decrease linearly with the increase of the stretching load, whereas grow linearly with the increase of the compression load. The frequency sensitivities of nanotubes with different diameters, chiralities and lengths are also studied. With the increase of length and diameter, both the frequency sensitivities for transverse and radial vibration modes decrease. However, exception is found in nanotubes with small diameter, and it is attributed to the small-diameter effect and the affect of boundary condition.

Micro Structures and Mechanical Characters of Hydrogenated Nanocrystalline Silicon Thin Films with Different Doped Proportions

Hydrogenated nanocrystalline silicon (nc-Si:H) films were deposited on glass substrates using Radio frequency plasma-enhanced chemical vapor deposition(RF-PECVD)from a B2H6/SiH4/H2 gas mixtures. In this paper, we mainly changed the Borane-Silane flow rate ratio (β), while other parameters were kept constant. Raman spectrum and X-ray diffraction were employed to investigate the micro-structure of the films, and the indentations were used to measure the mechanical characters (the Young’s modulus (E) and hardness (H)). The Raman spectrum showed that, withβincreasing the crystalline fraction decreased, which indicated that more boron doped might not be propitious to the formation of crystalline of the thin films. XRD spectrum revealed that the films have a remarkably preferential orientation. The analysis of the Young’s modulus and hardness by TriboIndenter nano system suggested that the increase inβhad concernful effects in the decrease of E and H values, so we can control the mechanical characters of the thin films by means of changing the doped concentrations. In view of these results, it may be concluded that the use of lowβconditions might lead to growth of nc-Si:H films with high crystallinity, and as well high Young’s modulus and hardness.

Effect of the Prepared Proceeding on Mechanical and Tribological Properties of DLC Films

In order to analyze the effect of proceeding on the mechanical and tribological properties of DLC films. Three DLC films samples on single silicon wafers were prepared by CVD method. The changed bias voltages were 300V, 350V, 450V separately. The structure and topography of prepared films were studied by Raman spectroscopy and atomic force microscopy (AFM), respectively. The hardness and elastic modulus together with friction coefficient of DLC films were measured by Tribolab system. According to the Raman spectra, the G and D peak shift to left with the increasing of bias voltage. Nano indent showed that the hardness (H) of the DLC films decreases from 19.63GPa to 18.12GPa with the increasing of bias voltages, and the value of elastic modulus (E) is also behaving the same trend as H from 157.95GPa to 146.95GPa. Friction coefficients of the three samples were measured by nano-scratch method under the constant normal load of 1000uN and the slide velocity of 3 um/sec, the corresponding friction coefficient is 0.0804 for DLC300, 0.0508for DLC350 and 0.0594 for DLC450 separately, which indicates that high hardness materials may not necessarily the perfect frictional material, but compound properties of hardness and elastic modulus

AFM/FFM study of micro/nano-tribological properties of Diamond-Like Carbon film

Micro-tribological properties of different Diamond Like Carbon (DLC) thin films were studied with the AFM/FFM. The surface topographies of the prepared specimens were observed by AFM, and the adhesive forces were also measured. The results indicate that the friction coefficient of the tested DLC film depends on the combined effect of the adhesion and the sample roughness. The friction force increases over velocity when the scanning velocity is not high, due to the effect of stick-slip behaviour, but their relationship is reversed with the increase of the velocity which is caused by the phase transformation of the DLC films.