Biao Kan

Transverse electric field–induced deformation of armchair single-walled carbon nanotube

The deformation of armchair single-walled carbon nanotube under transverse electric field has been investigated using density functional theory. The results show that the circular cross-sections of the nanotubes are deformed to elliptic ones, in which the tube diameter along the field direction is increased, whereas the diameter perpendicular to the field direction is reduced. The electronic structures of the deformed nanotubes were also studied. The ratio of the major diameter to the minor diameter of the elliptic cross-section was used to estimate the degree of the deformation. It is found that this ratio depends on the field strength and the tube diameter. However, the field direction has little role in the deformation.(See supplementary material 1)

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.

Transformation of ZnO polycrystalline sheets into hexagon-like mesocrystalline ZnO rods (tubes) under ultrasonic vibration

The mesoscale assembly process is sensitive to additives that can modify the interactions of the crystal nucleus and the developing crystals with solid surfaces and soluble molecules. However, the presence of additives is not a prerequisite for the mesoscale transformation process. In this study, ZnO sheet networks were synthesized on Al foils by a hydrothermal process. Scanning electron microscopy and transmission electron microscopy images confirmed that under ultrasonic vibration, monolithic polycrystalline ZnO sheets transformed into hexagon-like mesocrystalline tubes or rods. The formation mechanism was discussed.

A nanoscale transmission system with novel-structured carbon nanotubes

We present a prototype of nanoscale transmission system consisted of three novel-structured carbon nanotubes, namely, the “T,” “I,” and “Ω” type nanotubes. Double-walled carbon nanotubes (DWCNTs) serve as joints and linear bearings in this system. Molecular dynamics simulations were carried out to investigate the transmission properties. The obtained results show that this system can work at ultrahigh rotation speeds ∼109 rps with a broad temperature range 10–1000 K. The maximum variations of the output displacement in the stroke and lateral directions caused by the vibration are, respectively, 2.3–2.6 A and 0.27–0.95 A, which are 6.1%–7.0% and 0.7%–2.5% of the stroke length, respectively. Moreover, the displacement precision can be effectively improved by decreasing the input rotation speed or the temperature. The small change of the van der Waals potential energy in the DWCNTs indicates ultra low frictions in the joints, which contributes to the smooth transmission motion of the system. These results ma...

Mathematical modeling of the interference of seal pair in triple-offset butterfly valve

Avoiding interference of seal pair in triple-offset butterfly valve is critical to its performance and service time. In this article, a mathematical model is proposed for the seal interface. A formula is derived to evaluate the interference of seal pair in triple-offset butterfly valve. Five parameters are considered, including the diameter of valve disc, the effective sealing thickness, axial offset, radial offset, and eccentric angle. The influences of axial offset, radial offset, and eccentric angle on the interference area and position are investigated. The results show that the interference area decreases initially and increases finally when either the axial offset or the eccentric angle increases, whereas it decreases monotonously as the radial offset increases.

Switchable Wettability of Silicon Micro-Nano Structures Surface Produced by Femtosecond Laser

Silicon micro-nanostructures were directly produced by femtosecond laser in air. By varying the laser power, we can tune the surface morphology, the wetting property. As-prepared silicon micro-nanostructures show superhydrophilicity, but with removal of native SiOx, superhydrophobicity is observed without surface modification. And a reversible switch between superhydrophilicity and superhydrophobicity can be realized by immersing samples in hydrofluoric acid and hydrogen peroxide, respectively, for many times.

Study on the electrical contact property at the interface of the NiCr/TiW films

In order to study the electrical contact property at metal film interfaces, a NiCr/TiW film of about 40nm/30nm were deposited on the silicon substrate by magnetron sputtering. The mechanical and electrical properties of the film were studied by nano-ECR system. Different loads from 1500µN to 35OOµN with voltage of 5V were applied to the sample. Changing of the electrical property in NiCr/TiW and its interface was tested. The result showed that the average roughness of the sample was 3.8nm in the area of 1O×10µm2. when the conductive diamond tip contacted the surface of NiCr film. there was a sudden increasing of the current; for further indent, the NiCr/TiW film behaved piezoresistive effect distinctly with the increasing of indenting velocity duo to the lattice distortion of the metal film during the indent and which cumbered the movement of free electron. The compound material of Ti-silicide formed during sputter decreased the contact resistivity between the metal and semiconductor. The mechanical and electrical properties at the interface of metal film and semiconductor behaved evidently under the loading velocity of 350µN/s.

A new atomic-scale finite element simulation method for nanomechanics of single-walled carbon nanotubes

In this paper, a new atomic-scale finite element method based on the nonlinear spring model is developed for SWCNTs (single-walled carbon nanotubes). Atoms are chosen as nodes and supposed to be connected with each other in the finite element model by line-springs and torsion springs, whose mechanical parameters are determined by Tersoff-Brenner potential. The process of establishing global stiffness matrix is given in detail. Some of the application examples are shown, and the results are compared with those obtained by other methods. It is found that by using this method, the simulation can be accelerated without losing accuracy.

Mechanical property of nanoscale ZnO/Al 2 O 3 multilayers: An investigation by nano-indentation

Nanoscale ZnO/Al2O3 multilayers were prepared on Silicon substrates by atomic layer deposition (ALD) method at 200°C. To understand the size effect of ZnO nanoscale layers on hardness, the mechanical properties of the ZnO/Al2O3 multilayers were investigated using nano-indentation technique. As the bilayer period decreases from 60 to 2 nm, the micro-structures of ZnO layers changed from polycrystalline to amorphous. In the bilayer period interval of 60 to 6 nm, the variation of hardness versus bilayer period is similar to Hall-Patch relation, with maximum hardness and elastic modulus of ~10.69GPa and ~138.1GPa, respectively. However when the bilayer period is smaller than 6 nm, the nanolaminates became softer than the single ZnO film.

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.