Advanced Materials Research Vols. 60-61

Abstract: Electrolytic products are hard to be removed from the machining gap in micro ECM (electrochemical machining) process, which may lower the machining speed or even stop the machining process. Intermittent withdrawal of electrode is an effective way to cleanse electrolytic products, renew electrolyte in the gap, and promote the continuance of machining process. The influence of electrolytic products’ removal rate upon machining speed is analyzed in the case of intermittent withdrawal of electrode. Results show that the machining speed does not increase monotonously with the decrease of inter-electrode distance. Considering machining efficiency and accuracy, machining gap should be the corresponding gap value when the machining speed reaches its maximum.

Abstract: The stable and homogeneneous aqueous suspension of carbon nanotubes was prepared in this study. The stability of the nanofluids was improved greatly due to the use of a new dispersant, humic acid. The thermal conductivity of the aqueous suspension was measured with the 3ω method. The experimental results showed that the thermal conductivity of the suspensions increases with the temperature and also is nearly proportional to the loading of the nanoparticles. The thermal conductivity enhancement of single-walled carbon nanotubes (SWNTs) suspensions is better than that of the multi-walled carbon nanotubes (MWNTs) suspensions. Especially for a volume fraction of 0.3846% SWNTs, the thermal conductivity is enhanced by 40.5%. Furthermore, the results at 30°C match well with Jang and Choi’s model.

Abstract: Nowadays research on nano-electronic device based on carbon nanotube (CNT) raises much interest among researchers, but in the fabrication process, crucial problems exist in making and improving the electrical contact between CNT and microelectrode. Here pulse gas alignment method, combined with nanomanipulation technology based on atomic force microscope (AFM) if necessary, is proposed for the first time to assemble and make electrical contact between CNT and microelectrode. After the assembly, a processing technique of applying sweeping voltages is performed for producing electrical current induced local Joule heat, which will decompose and remove the sodium dodecyl sulfate (SDS) molecules adsorbed on the CNT and at the interface region, or even have some annealing effect, to reduce the contact resistance between CNT and microelectrode and thus to improve the electrical contact. Experiments of assembly and improvement of electrical contact between multi-wall carbon nanotube and microelectrode are performed to verify the effectiveness of the proposed methods

Abstract: Mechanical scratching and chemical self-assembling can be combined to fabricate nano- or micro-scale functional structures on the oxide-coated silicon. The chemo-active species, such as NO2C6H4 groups, can be produce from aryldiazonium salt due to the breaking of chemical bond of silicon substrate when the diamond tool scratches the silicon sample in the presence of 4-benzoic nitryl diazonium tetrafluoroborate (NO2C6H4N2BF4). They may then induce grafting of an organic monolayer on the substrate via Si-C connection. The surface morphologies before and after chemomechanical reaction are characterized with Atomic Force Microscopy (AFM). We propose that chemomechanical reaction, which occurred during scratching the silicon surface, produce NO2C6H4 groups from aryldiazonium salt. The NO2C6H4 groups further bond with surface Si atoms via Si-C covalent bonds as confirmed from Infrared Spectroscopy (IR) results. To better understand the framework of the self-assembly monolayers (SAMs) on Si (100) surface, the first principles calculation at density functional theory levels has been employed to investigate the binding energy, bonds length and bonds angle. The reduced energy of system illuminates that the SAMs can be fabricated easily between aryldiazonium salt and Si (100) surface. The stability of system can be improved and SAMs can firmly stay on Si (100) surface.

Abstract: A model for the bending and twisting deformation of the giant magnetostrictive cantilever is established in the framework of the principle of minimal free energy and four-parameter bending regime. The angular and magnitude dependence of the torsion and flexion response on the external field was discussed for cantilever beam. The torsion behavior of the cantilever is very sensitive to the external field and shows a hysteresis. Furthermore, the torsion hysteresis of the cantilever calculated by our model qualitatively agrees with recent experimental result, which suggests that our model is effective in describing the cantilever system with magnetic anisotropy.

Abstract: . Carbon nanofibers have been attracted many attentions for their potential applications in nanocomposites and electromagnetic wave-absorbing materials due to their remarkable mechanical, electrical and other properties. Ethanol as carbon source possesses low toxicity, easier storage and transportation. In this paper, we report ethanol catalytic chemical vapor deposition (ECCVD) for synthesizing carbon nanofibers. We utilized ferrocene as catalyst precursor and use ethanol as carbon source to synthesize carbon nanofibers by ethanol chemical vapor deposition. The deposits were characterized by employed scanning electron microscopy, transmission electron microscope and Raman spectroscopy.

Abstract: The spring-mass-capacitor structure in micro-electro-mechanical systems (MEMS) is a typical macromodel, its response and stability under step voltage is presented in this paper. Energy method is used to analyze the dynamic behavior of mass block where its velocity is zero and accelerometer is zero, respectively. The condition of stability under step voltage is the initial stiffness ratio must less than 0.25, and finally the relation of energy loss and oscillating behavior of block is analyzed. The conclusion is useful to analyze the response of structure and helpful to design a MEMS system composing of spring-mass-capacitor structure.

Abstract: Parylene C, an emerging material in microelectromechanical systems (MEMS), is now widely applied to neural prosthesis devices, such as artificial retinal implants, due to its well-known biocompatibility and ability to be easily patterned by oxygen plasma etching. This work presents a flexible parylene-based microelectrode array（MEA）using MEMS techniques aiming for the chronic subretinal stimulation. The MEA was successfully manufactured and inserted into the subretinal space of a rabbit eye by a novel surgical operation. Optical Coherence Tomography(OCT) showed that a chronic implantation of parylene-based electrode arrays in the rabbit retina over a three month follow-up period demonstrated that the present chip system has a good biocompatibility with the subretinal organs without obvious damages.

Abstract: In this article, we select corresponding Tersoff potential energy to build potential energy model and investigate the thermal conductivities of single-crystal carbon thin-film. The equilibrium molecular dynamics (EMD) method is used to calculate the nanometer thin film thermal conductivity of diamond crystal at crystal direction (001), and the non-equilibrium molecular dynamics (NEMD) is used to calculate the nanometer thin film thermal conductivity of diamond crystal at crystal direction (111). The results of calculations demonstrate that the nanometer thin film thermal conductivity of diamond crystal is remarkably lower than the corresponding bulk experimental data and increase with increasing the film thickness, and the nanometer thin film thermal conductivity of diamond crystal relates to film thickness linearly in the simulative range. The nanometer thin film thermal conductivity also demonstrates certain regularity with the change of temperature. This work shows that molecular dynamics, applied under the correct conditions, is a viable tool for calculating the thermal conductivity of nanometer thin films.

Abstract: In nanometric cutting process, the actual material removal can take place at atomic level, which makes the observation of machining phenomena and the measurement of cutting parameters difficult or impossible in experiments. However, it is crucial to investigate the cutting process in nanoscale. In this work, molecular dynamics (MD) is used to study effects of cutting parameters on nanometric cutting process with the aid of EAM potential. The result of the simulation shows that higher cutting speed leads to a rough machined surface with a relative large deformation in workpiece. It is found that a smaller cutting depth results in less plastic deformation and fewer dislocations in workpiece, and also results in a smoother machined surface. Rake angle has big effect on the chip formation, potential energy and the machined surface.