Key Engineering Materials Vols. 609-610

Abstract: In this work, carbon films were deposited by magnetron sputtering on silicon substrate. The effect of sputtering time on the surface wettability and mechanical properties of carbon films was investigated. Contact angle measurement was used to analyse surface wettability, and the nanomechanical properties were characterized by nanoindentation. In experiments, the sputtering time was 45 min, 60 min, 75 min and 90 min. The measurement results show that the maximum film hardness was achieved for sputtering time 90 min, with a value of 2.34 GPa. Longer sputtering time resulted in preferable mechanical properties. It was analyzed that the size of the crystal grains on the substrate surface and thickness of the films were increased with the increment of sputtering time. The surface roughness decreased with the increase of sputtering time. Moreover, Youngs modulus increased with sputtering time and the maximum value was 16.94 GPa. The contact angle measurement results show that the prepared films take on the hydrophilicity. The minimum contact angle was achieved for sputtering time 45 min with a value of 54o.

Abstract: A three-dimensional molecular dynamics (MD) simulation is conducted to investigate the effect of the abrasive rotating velocity on monocrystalline silicon specimen by mechanical polishing at atomistic scale. By monitoring relative positions of atoms in the monocrystalline silicon specimen, the microstructure of monocrystalline silicon is clearly identified and analyzed. The simulation results show that better machined surface quality is obtained and more phase transformation atoms occur with small abrasive rotating velocity. When the abrasive rotating is high, the surface quality deteriorates and amorphous layer thickens.These results provide us an effective approach to analyze the mechanism of material deformation and the formation of the machined surface after ultra-precision polishing.

Abstract: Porous alumina films are obtained on aluminum piece by electrochemical method. In this work, we ues a kind of method for alumina nanowires by the alumina films. The result is showed with SEM. We study the effects of etching action in the dilute HF solution, and deduce the reason. We study catalyzed formaldehyde by the alumina nanowire supported titanium dioxide, results show that, the catalytic effect is better than activated carbon supported.

Abstract: Highly dispersed TiO₂ nanotubes (TiO₂-NTs) were synthesized via the reaction of anatase TiO₂ powder with NaOH solution. Au nanoparticles of about 5 nm were deposited on the surface of TiO₂-NTs with hydrothermal reduction method. The prepared nanocomposites were well characterized with TEM and XRD. Their photocatalytic properties and reducing ability were investigated by UV-Vis absorption and photocatalytic reduction of Cd²⁺ ions with different amount of TiO₂-NTs and TiO₂-NTs (Au) varying from 0.1g to 0.001g. The results from absorption patterns and AAS showed that the absorption intensity of TiO₂-NTs (Au) was higher compared with that of TiO₂-NTs. Moreover, the concentration of remanent Cd²⁺ (0.48mg/L) using TiO₂-NTs (Au) was lower than that of Cd²⁺ (0.65mg/L) using TiO₂-NTs.

Abstract: In this paper we report Multi-walled carbon nanotubes (MWCNTs) have been joined together by continuous wave fiber laser operating at 1064 nm. The SEM image clearly shows that there are obvious melting - solidified phenomenon between the jointed Multi-walled carbon nanotubes. MWCNTs wall was complete and smooth without destruction phenomenon. The new graphite layers were found in the connection with transmission electron microscopy (TEM). Besides, we observed that the present multi-walled carbon nanotubes showed the trend of melting connecting to destruction as the laser irradiation time increased in the case of a certain power density. In the end, there were recrystallization phenomena during MWCNTs joining with the Raman spectra. The crystallinity and length to diameter ratio decreased following the increasing irradiation time.

Abstract: The enhancement characteristics of carbon nanotubes (CNTs) on CO₂ absorption were investigated experimentally a stirred thermostatic reactor. A comparison of CNTs with micro active carbon was made. From the experimental results, significant enhancement of CO₂ absorption was obtained by both CNTs and micro active carbon, however, different change trends with stirring speed for the two solid particles was observed. With increasing stirring speed, the enhancement factor was decreased in AcC suspensions, whereas in CNT slurries it is increased. The experimental phenomena demonstrated a difference in enhancement mechanism for different size particles. For nanoparticles, besides the grazing effect, the micro-convection caused by Brownian motion should be also taken into account. The micro-convection strengthens the interaction of the concentration field around the particles and thus increases the diffusion rate of the solute. In addition, the agglomeration of the nanoparticle was also an important influencing factor. Due to the agglomeration of the particle, the enhancement factor for CNTs increases initially with increasing stirring speed. A three-dimensional microcosmic mass transfer model was developed to explain the experimental phenomena. Based on the model, the interaction of the flow field around the particles was analyzed.

Abstract: High energy milling (HEM) was used to the preparation of multi-walled carbon nanotubes reinforced copper matrix (MWCNTs/Cu) composite powders in this paper. And the MWCNTs/Cu composite material was prepared by the cold-press sintering method. The influence law of balls/powder weight ratio to the MWCNTs/Cu composite powders was discussed. Particle size distribution and fracture micrograph were analyzed by XRD and SEM. The results show that particle size distribution of CNTs/Cu composite powders reached a minimum, when the balls/powder weight ratio was 10: 1. The particle size distribution (D50) of CNTs/Cu composite powders was 22.33μm. The CNTs distributes homogeneously , which is in favor of the mechanical combination of the CNTs and Cu substrate. The tensile strength of CNTs/Cu composite reached 189 MPa.

Abstract: In order to achieve a better manipulation performance of ZnO nanowire, the ZnO nanowire forces are analysed, and molecular dynamics simulations are conducted. Force model of ZnO nanowire is established to interprete the drifting, bending and fracturing conditions in ZnO nanowire transfer experiment. As ZnO nanowire force is too complex to build a precise mathematical model, molecular dynamics is proposed to simulate the process. Based on the analysis of ZnO nanostructure, the probe-nanowire-substrate model is established. Through changing the operation path of the probe and operation area between the probe and nanowire, simulation results are got. By the Analysis and comparison of simulation results, the optimal operation path and operation area are obtained.

Abstract: Nanogetters, based on carbon nanotubes (CNTs) coated Ti films, do have higher pumping speed and possibly larger sorbed quantity compared with traditional getters, such as St175 of SAES [1]. Although the nanogetter is with the outstanding performance, it is still hard to be integrated into micro electro mechanical systems (MEMS) packaging and devices due to high growth temperature of CNTs (>700°C) [2], poor adhesion with substrate [3, 4], vulnerability to pollute the wafers and difficulty to pattern. Therefore, this paper proposes a promotion of nanogetter based on transferring out vertically aligned CNTs (VA-CNTs) utilizing the glass frit. Compared with the conventional nanogetters, the promotion processes have advantages of (1) compatibility to the MEMS materials with controllable melting temperature and coefficient of thermal expansion (CTE), (2) Enhancement of the adhesion between CNTs and substrate, (3) Avoiding polluting the package wafer during CNTs growth. The results indicate that the promotion processes can be fulfilled by the silicon wafers and have wide applications such as nanogetters, field emission display, etc.

Abstract: This paper introduces an electromagnetic induction heating method which is demonstrated to be able to bond carbon nanotubes and metal electrodes. Dielectrophoresis method is taken to realize the parallel directional assembly between carbon nanotubes and metal electrode, and then localized induction heating is adopted to bond them. This technique offers a convenient and reliable way in the practical applications of carbon nanotube interconnection. The bonding principle and process are introduced, and the experiment results are also discussed. The results show that the bonding interface exhibits good contact and electrical property.