Junqin Shi

Influence of normal load on the three-body abrasion behaviour of monocrystalline silicon with ellipsoidal particle

Currently, monocrystalline silicon has been widely applied in micro-electro-mechanical systems (MEMSs). It is of importance to reveal the wear behavior of the MEMS and evaluate the planarization of silicon surface in chemical mechanical polishing (CMP). In this study, molecular dynamics simulation was used to investigate the nano three-body abrasion of monocrystalline silicon with a diamond ellipsoidal particle sandwiched between two silicon specimens. The normal load acting on the ellipsoidal particle was varied from 80 nN to 240 nN. Results indicate that the movement pattern of the particle changes from rolling to sliding when the normal load becomes greater than 160 nN. Using the criterion of particle movement pattern by comparing the value of e/h and coefficient of friction, the particle movement pattern can be accurately predicted. The evolution of force in the abrasion process depicts both friction force and normal load fluctuations in sinusoid-like curve for the rolling ellipsoidal particles, whereas the front cutting of particle results in an increase in the friction force, making it greater than the normal force for sliding particles under high velocity. The plastic deformation of monocrystalline silicon is attributed to the phase transformation, which is clearly impacted by the movement pattern of the particle. The rolling of the particle causes substrate deformation with periodical inhomogeneous characteristics, while sliding helps produce a high-quality surface and improves efficiency in the CMP process.

Effect of water film on the plastic deformation of monocrystalline copper

The mechanical behavior of nanoscale materials is strongly influenced by the working conditions. The corresponding research about plastic properties, however, is very limited especially in liquid environments. In this work, the effect of a water film on the plastic deformation of monocrystalline copper (Cu) is performed by a nanoindentation process using molecular dynamics simulations. The results indicate that the water film induces strong fluctuation of the load–indentation depth curves and increase of the load at the same indentation depth. The plastic deformation of monocrystalline Cu is obviously strengthened due to the water film facilitating dislocation propagation sufficiently into the inner Cu substrate. In addition, the mechanism of plasticity response to the nanoindentation process is discussed based on the interaction force. The results reveal that with the water film thickness increasing, the interaction force between the indenter and monocrystalline Cu exhibits obvious delay and its value is significantly smaller compared with that of the nanoindentation without a water film. The water molecules under and around the indenter transmit the force stemming from the indenter to the Cu substrate, which strengthens the dislocation propagation into the inner substrate but blocks the dislocation propagation to the surface, leading to a larger plastic deformation of monocrystalline Cu. In addition, the effect tendency of the water film on the nanoindentation property of the Cu substrate slows down rather than increases continuously once the thickness is large enough. Our findings can help us to understand more thoroughly the plastic deformation mechanism of nanomaterials under liquid or humid conditions.

Regulating the hydrothermal synthesis of ZnO nanorods to optimize the performance of spirally hierarchical structure-based glucose sensors

This paper reports the effects of the synthesizing parameters on the surface morphologies of ZnO nanorod-based spirally hierarchical structures and the performance of related spirally hierarchical structure-based glucose sensors. ZnO nanorods were hydrothermally synthesized on Au cylindrical spirals with 3 sets of the synthesizing parameters, and glucose oxidase (GOx) was immobilized on these ZnO nanorods, thus 3 batches of the spirally hierarchical structure-based glucose enzymatic electrodes were fabricated. Geometric, crystalline and electrochemical characterization indicates that of all 3 batches of the spirally hierarchical structures, those fabricated respectively at 25 mM Zn2+ concentration of the growth solution, for 1.5 h the growth duration, and at 0.5 mM Zn2+ concentration of the seed solution all have Gaussian random rough surfaces. This gives rise to the largest surface area of the related spirally hierarchical structure, the most effective GOx immobilization of the corresponding enzymatic electrode, and the optimal performance of the related glucose sensor. The results benefit not only the batch construction but also the standardization of other hierarchical structure-based glucose sensors.

Movement patterns of ellipsoidal particles with different axial ratios in three-body abrasion of monocrystalline copper: a large scale molecular dynamics study

In three-body abrasion, the abrasive particle shape has a major impact on the movement patterns. These consist of sliding or rolling relative to the abraded surfaces. It has been recognized that the movement patterns of the particles dominate the wear mechanism of the materials in three-body abrasion. In this paper, the movement patterns of monocrystalline diamond ellipsoidal particles, which are sandwiched between monocrystalline copper workpieces, were investigated by large-scale molecular dynamics (MD). During the simulations, the axial ratio of the ellipsoidal particle varied from 0.90 (an approximate sphere) to 0.50 (a flattened ellipsoid). It has been found that there is a transition of the movement patterns between rolling and sliding. The particle slides when the axial ratio is smaller than 0.83, and it rolls when the axial ratio is larger than 0.83. Normal load and friction force curves were also obtained relative to the wear time. It has been shown that the average friction coefficient of rolling particles is lower than that of sliding particles. If the ratio of two-moment arms, such as the driving and resistant force moment arms of the particle, is defined as e/h, the curves for the friction coefficient and value e/h can determine the movement patterns of particles at the nanoscale, the same as at the macroscale. When the friction coefficient is higher than e/h, rolling of the particle occurs, whereas the particle slides if the friction coefficient is smaller than e/h. By comparing with macroscale three-body abrasion, a particle at the nanoscale has a strong tendency to roll because of its significant elastic recovery. When the particle rolls, the defect depth, groove depth and dislocation length are all increased relative to particle sliding, resulting in more severe subsurface defects of the monocrystalline copper.

Nanoindentation and deformation behaviors of silicon covered with amorphous SiO2: a molecular dynamic study

A fundamental understanding of the mechanical properties and deformation behaviors of surface modified silicon during chemical mechanical polishing (CMP) processes is difficult to obtain at the nanometer scale. In this research, MD simulations of monocrystalline silicon covered with an amorphous SiO2 film with different thickness are implemented by nanoindentation, and it is found that both the indentation modulus and hardness increase with the growing indentation depth owning to the strongly silicon substrate effect. At the same indentation depth, the indentation modulus decreases shapely with the increase of film thickness because of less substrate influence, while the hardness agrees well with the trend of modulus at shallow depth but mismatches at larger indentation depth. The observed SiO2 film deformation consists of densification and thinning along indentation direction and extension in the deformed area due to the rotation and deformation of massive SiO4 tetrahedra. The SiO2 film plays an important role in the onset and development of silicon phase transformation. The thinner the SiO2 film is, the earlier the silicon phase transformation takes place. So the numbers of phase transformation atoms increase with the decrease of SiO2 film thickness at the same indentation depth. It is suggested that the thicker film should be better during CMP process for higher material removal rate and less defects within silicon substrate.

Surface Removal of Copper Thin Film under the Ultrathin Water Environment for Nanoscale Process

The surface planarity and asperity removal behaviors of atomic scale under the ultrathin 11 water environment was studied for the nanoscale process by molecular dynamics simulation. The 12 monolayer atomic removal was achieved under the noncontact and monoatomic layer contact 13 conditions with different water film thickness, and the newly formed surface is relatively smooth 14 and no deformed layer and plastic defects exist. The nanoscale processing is governed by the 15 interatomic adhering action during which the water film transmits the loading forces to Cu surface 16 and thereby result in the migration and removal of surface atoms. With scratching depth ≥ 0.5 nm, 17 the abrasive particle squeezed out the water film from scratching region and scratched Cu surface 18 directly, leading to the surface quality deterioration mainly governed by the plowing action. This 19 study brings the goals of “0 nm planarity, 0 residual defects and 0 polishing pressure” closer to us 20 in the nanoscale process for the development of ultra-precision manufacture technology. 21