Key Engineering Materials Vols. 562-565

Abstract: Using the First principles calculations, the crystal structure, band gap, total and partial density of states (DOS) of anatase TiO₂ and anatase TiO₂ doped with Yttrium were calculated by a plane-wave pseudopotential (PWPP) method based on density functional theory (DFT). The generalized gradient approximation (GGA) based on exchange-correlation energy optimization was employed to calculate them. From the calculation results, the band gap of anatase TiO₂ and Y³⁺ doped TiO₂ are about 2.15eV and 0.86eV. The calculated results demonstrated that the mixing of Yttrium (Y) dopants induces states with original titanium 3d and oxygen 2p valence band attributes to the band gap narrowing. This can enhance the photocatalytic activity of anatase TiO₂.

Abstract: A new structure of gap adjustable MEMS resonator has been proposed, and an analytical model of the gap adjustable structure has been developed. This model is a 2D vibration system. An opposite type MATA was used to push the fixed finger structure to move, as a result, the gap between the fingers changed. Simulation results show that the displacement of the mechanical oscillator increased when the MATA provided a step force, and the vibration amplitude was modulated when the force was in a cyclical form. In order to improve the stability of the structure, the folded beams were changed into clamped beams. An FEA simulation told us that when the gap changed, the vibration amplitude increased.

Abstract: Aiming to explain phenomena of “stiction” and “snap-back”, a ball-surface adhesion is simulated with molecular dynamics (MD) based on multi-body EAM potential function. Surface atoms “summon up” and migrate, which lead to the phenomenon of “stiction”. The migration velocity of interface atom is not consistent. Some atoms migrate too fast, which lead to the phenomenon of “snap-back”. The “Snap-back” phenomenon appears twice during the adhesion process. A “neck-separation” phenomenon is found. The adhesive force in the separation process obviously lagged the adhesive force in the contact process, which shows there is energy loss during the adhesion process. The curve of adhesion deformation is simulated finally, and compared with relevant results.

Abstract: Bubble-stretching based dispersion method can be used to prevent the agglomeration of nanoparticles during the process of preparing nanocomposites, whereas its effectiveness is restricted by the practically low migration ratio of particles onto the bubble wall. Theoretical models for bubble vibration and particle migration have been presented, followed by numerically study on effects of different parameters on migration ratio of particles on to the bubble wall. The numerical results have shown that bubble initial radius, bubble initial pressure and particle diameters impact the particle migration ratio obviously and it is found that the particle migration ratio can be improved effectively through the optimal control of the vibration parameters of the bubble happed in the dispersion process. Therefore, this article provides a theoretical basis for the efforts on increasing the particles migration ratio and thus the dispersion effectiveness of nanoparticles in polymer melt.

Abstract: In this paper, the thermal boundary resistance and conductive properties of Cu/Al interface are investigated by using first-principles calculations based on density functional theory (DFT) with considering the pressure influence. Based on the atomic model of Cu/Al interface the simulation results show that the lattice parameters for both Cu and Al are sensitive to pressure and density states of Cu/Al interface increase as pressure increases from 0 to 5 GPa. Although Cu and Al have the same atomic structure, the significant differences of the density of phonon states lead to the thermal resistance that exists at the Cu/Al interface. At the Cu/Al interface, Cu and Al atoms can diffuse into each other and form an alloy-like interfacial region. The change of the copper component in the alloy can considerably affect the conductive properties of Cu/Al interface.

Abstract: With the development of the MEMS technology and the more widely-used micro-systems, micro-power devices are developed for portable consumer electronics. ^[ The MEMS supercapacitor is one of the most important parts for micro-powers. In this paper, a micro-supercapacitor was designed and fabricated with three-dimensional microelectrode arrays configuration. It has been tested by scanning electron microscopy, Cyclic Voltammeter, Galvanostatical charge/discharge curve and electrochemical impedance spectroscopy. These posts were 50 μm in diameter and 100 μm tall; with foot print area of 2×2mm². The capacitance is 89.52mF/cm². The biggest feature in this paper is that the two plates of the supercapacitor are both three-dimensional microelectrode arrays which are shown to offer significant advantages.

Abstract: Finite Difference Time Domain method(FDTD) is used to study the resonance properties of E-type nano antenna in this paper. According to the result of numerical simulation,the size and location of ledge part made a great influence on the resonance properties of holistic nano antenna while major rectangle part is invariant.The electronic field distribution, enhancement factor and corresponding resonance frequency of E-type nano antennas with invariant major rectangle part and different ledge parts are calculated through FDTD method,comparing with rectangle nano antenna without ledge part, E-type nano antenna has a great promotiom in electronic field enhancement at about 100 times of the excite electronic field intensity while regular rectangle nano antenna can achieve about 30times only.The resonance frequency is relate to the ledge part ,by changing the size and location of ledge part,resonant frequency can be adjusted between 340Thz and 400Thz,at the meantime, the field enhancement almost unchanged. After a glass substrate is added under the E-type nano antenna with constant size,the electronic field intensification factor improved significantly and the electronic field spread over the area around the ledge part rather than the junction of glass and metal.The horizontal position of ledge part has an effect on holistic resonance properties.When the ledge part located in the middle, the electronic field intensification factor of three ledge parts rised to 240 times at the same time,and distinct double resonance peak appeared.When the ledge part moved to the edge, the electronic field enhancement around the ledge parts on the sides weaken and middle ledge part rised to 350 times,double resonance peak disappeared.

Abstract: In order to effectively capture the environment vibration energy, convert it into electricity and supply energy for the microelectronics devices, multiple micro piezoelectric cantilevers are designed. It is composed of more than one piezoelectric cantilever array, which broaden the resonant frequency band of the piezoelectric vibrator, and it can produce resonance or similar to the resonance in a frequency range. Compared to a single piezoelectric cantilever, multiple piezoelectric cantilevers can effectively broaden the resonant frequency and improve the piezoelectric power generation capacity. The simulation results show that the finite element method can provide important theoretical guidance for the structural design of multiple micro piezoelectric cantilevers.

Abstract: Piezo-induced surface vibrations in solids with nanometer amplitude are detected and analyzed. The vibrations are excited by the piezo element using a PZT component, which attached to the target material and controlled by a signal generator. The detections of such vibrations are carried out using the atomic force probe (AFP). The AFP is a very sensitive instrument utilizing a nano-tip connected to a cantilever to detect vibrations through an interaction of atomic force between the tip and the target surface with sub-nanometer resolution, about 30 times more precise than the piezoelectric sensor for the same signal detection. The glass material has been chosen as the target solid. The enhancement effect of the vibrations in the glass slice around resonance frequency is confirmed, the maximum amplitude appears at 7.4 kHz. The piezo-induced vibration will be employed in our future research for developing piezo-induced and laser-induced surface acoustic wave (SAW) motor.

Abstract: Dielectrophoresis (DEP) is the action of polarizable particles in non-uniform electric field, which depends on the structure of electrode. In this paper, we present a semi-analytical method, on which the electric field distribution by interdigitated electrode-array with battlement structure is considered. According to the congregational conformation of latex micro-beads which subject to the negative dielectrophoresis movement, the potential-trap by interdigitated electrodes is observed experimentally. The result shows that the theoretical simulation result conforms to actual electric field distribution well. It is proved that semi-analytical method exerts power for the research of dielectrophoresis effectively.