Zhiyong Ling

Carbon nanotube-based charge-controlled speed-regulating nanoclutch

In this paper, a carbon nanotube-based charge-controlled speed-regulating nanoclutch (CNT-CC-SRNC), composed of an inner carbon nanotube (CNT), an outer CNT, and the water confined between the two CNT walls, is proposed by utilizing electrowetting-induced improvement of the friction at the interfaces between water and CNT walls. As the inner CNT is the driving axle, molecular dynamics simulation results demonstrate that CNT-CC-SRNC is in the disengaged state for the uncharged CNTs, whereas water confined in the two charged CNT walls can transmit the torque from the inner tube to the outer tube. Importantly, the proposed CNT-CC-SRNC can perform stepless speed-regulating function through changing the magnitude of the charge assigned on CNT atoms.

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.

Wetting and motion behaviors of water droplet on graphene under thermal-electric coupling field

Wetting dynamics and motion behaviors of a water droplet on graphene are characterized under the electric-thermal coupling field using classical molecular dynamics simulation method. The water droplet on graphene can be driven by the temperature gradient, while the moving direction is dependent on the electric field intensity. Concretely, the water droplet on graphene moves from the low temperature region to the high temperature region for the relatively weak electric field intensity. The motion acceleration increases with the electric field intensity on graphene, whereas the moving direction switches when the electric field intensity increases up to a threshold. The essence is the change from hydrophilic to hydrophobic for the water droplet on graphene at a threshold of the electric field intensity. Moreover, the driven force of the water droplet caused by the overall oscillation of graphene has important influence on the motion behaviors. The results are helpful to control the wettability of graphene and further develop the graphene-based fluidic nanodevices.

Rapid motion of liquid mercury column in carbon nanotubes driven by temperature gradient

The liquid mercury column can be rapidly transported from high temperature region to low temperature region in single walled carbon nanotubes (SWCNTs) driven by the temperature gradient. Interestingly, the total force acting on the mercury column keeps constant during the temperature gradient-driven process. The motion acceleration of the mercury column is linearly dependent on the magnitude of the temperature gradient. The meniscuses of the hydrophobic mercury column confined in SWCNTs do not appreciably affect the motion behaviors of the mercury column in our proposed model. The influences of the column length and the CNT diameter on the motion behaviors of the mercury column are considered to clarify the mechanism of the size effect. The motion acceleration of the mercury column nonlinearly decreases with increasing the column length and the CNT diameter. The overall oscillation of the SWCNTs plays the dominant role in rapid motion of mercury column for short-length mercury columns and small-diameter SWCNTs.

Reassessing molecular sieving by kinked carbon nanotubes

Based on molecular dynamics simulations for the transport of pure nitrogen (N2), oxygen (O2) and their mixture in kinked single-walled carbon nanotubes (SWCNTs), molecular sieving by the kinked model of SWCNTs is presented. The influences of gas pressure, temperature and the component ratio of N2 in the mixture on gas separation are investigated. Considering the tradeoff between the permeability and the purity of O2, the results show that a large gas pressure, 300–500 K of gas temperature and a low component ratio of N2 in the N2–O2 mixture can be advantageous to the efficiency of gas separation. The purity of O2 can be kept higher than 80% when the component ratio of N2 is lower than 3/4, which will be advantageous to the design of multi-level gas separation mechanisms. The findings may provide theoretical references for the design and manufacture of molecular sieving devices in engineering applications.

Micro machining process of high temperature pressure sensor gauge chip based on SIMOX SOI wafer

The successful batch fabrication of a piezoresistive pressure sensor chip is described based on separation by implantation of oxygen (SIMOX) SOI wafer. The micro machining process mainly includes SIMOX, homoepitaxy silicon, and heavy dose of boron ion implantation doping, thermal oxidation, passivation layer of silicon nitride and standard optical lithography, Inductively Coupled Plasma (ICP), multi-layer metallisation and Au sputtering and so on. The sensor packaged with this kind of sensing chip is presented with high accuracy and a good long-term stability in high temperature testing experiments up to 250?C.

Nanoindentation in a wetting environment: the coupling effect of liquid and surface roughness on mechanical calibration

In situ calibration of a samples mechanical properties in different mediums is of vital importance for engineering and biomedical applications. In this paper, we describe the nanomechanical calibration of two copper specimens with different roughness in dry nitrogen and deionized water. The hardness (H), reduced elastic modulus (), and creep properties of the copper specimen were accurately measured by a nanoindenter. Indentations on the two specimens were performed in both mediums by a spherical fluid cell probe (FCP). It is found that there is no apparent difference in both media for a smooth surface, and this demonstrates the validation of the FCP and the apparatus. Meanwhile, for rough surfaces, the maximum depth measured in a liquid at a given load is larger than that in nitrogen, thus the measured mechanical properties decrease, especially for rough surfaces. A molecular dynamics (MD) model is employed for further investigation of the indentation behaviours and the interaction mechanism at the liquid–solid interface. Our simulation results show that the liquid molecules confined in the narrow surface roughness valleys enlarge the maximum indention depth of the probe tip in a wetting environment, and this results in the corresponding change in the measured mechanical properties.

LOADING, CHARGING AND THERMAL EFFECTS ON THE MECHANISM OF WATER–CARBON NANOTUBE TRANSMISSION

In this paper, the transmission mechanism of a charge-controlled water–carbon nanotubes (CNTs) fluidic transmitting nanodevice is investigated by using molecular dynamics simulation with the loading, charging and thermal effects on the starting process being considered. The results show that the external load on the driven CNT can slow down the startup speed of the nanotransmission while the transmitting stability is better than that in non-loading transmitting process. The startup speed of the water–CNTs transmission increases with the increase in the charge magnitude on CNTs since the charges on CNT atoms can increase the water–CNT interfacial coupling strength. The control of the water temperature can also affect the startup speed of the driven CNT attributed to the thermal effect on the slip velocity of confined water. The configuration, dynamic motion behaviors and temperature of the confined water in both the starting and steady transmitting processes are studied to understand the thermo-electromechanical coupling effects on the transmission mechanism of the water–CNTs charge-controlled fluidic transmitting nanodevice.

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

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.