Advanced Materials Research Vols. 60-61

Abstract: Direct-Write (DW) technology based on Near-Field Electrospinning (NFES) was introduced to fabricate suspended micro/nano-structure on pattern substrate, and the deposition behaviors of DWed structure under different collector motion speed (CMS) were discussed to improve control of DW technology based on NFES. Deposit point of DWed structure on the substrate can be controlled accurately under the observation of microscope, and position error of micro/nano-structure is less than 5µm. When CMS is compatible with the electrospinning speed, straight line micro/nano-structure can be direct-written across micro-trenches with width of 5~40µm or to bridge two micro-pillars with diameter of 10µm. Due to the water evaporation and surface tension force, DWed structures suspended in the air would shrink smaller compared with that deposited on the top surface of pattern. The shrink ratio of micro-structure is higher than nano-structure and the shrink ratio decreases with the solution concentration increases. When the CMS is lower than electrospinning speed, the electrostatic force and elastic force would play a more prominent role on the deposition behavior of DWed structure. The electrical field strength on the top surface of pattern is higher than the space between two patterns, DWed thin film would deposit along the trip pattern and nanofiber would prefer to aggregate on the top surface of pattern under electrostatic force. When solution concentration is lower than 18%, nanofiber aggregate on the pattern would coagulate to form polymer bundle.

Abstract: In MEMS nodal analysis method, more available libraries of nodal models are needed. By analyzing the mathematic model and the equivalent model of the electro-thermal-mechanical beam, this paper shows the steps of building a library of a nodal element for HSPICE. Then the cell library is used to simulate the opposite type micro-array thermal actuator (MATA). At last it shows the DC sweep performance and the transient performance of opposite type MATA. In this paper, to verify the reusability of the beam cell, opposite type MATA is all consisted of the electro-thermal-mechanical beam cell in library.

Abstract: During hot embossing process of polymer MEMS devices, the parameters such as temperature, pressure and time are important for the duplication precision of patterns. In this work, a novel method of hot embossing lithography for replication of multiple nano bar structure mould was conducted. The effects of hot embossing temperature and pressure on fabrication precision were studied. Linewidth of the pattern on the mould is from 71nm to 980nm. The replicas of nano bar structure were fabricated on the PMMA (polymer methyl methacrylate) layer with silicon substrate. The effects of hot embossing and demoulding temperature on replicating quality were also discussed. Experimental results indicate that higher demoulding temperature help to lessen PMMA leftover and improve the duplication quality. The hot embossing and dmoulding temperature of 110°C～120°C and 60°C～70°C were obtained to produce high quality duplication of multiple nano bar structures. Micro-grating replicas were also fabricated and demonstrated in this paper.

Abstract: NFES is a new and simple way to realize precision-positioning of nanofiber. A model on NFES nanofiber movement is built to analyze the effects of the existed nanofibers which have been collected on the substrate, on the nanofiber’s dropping movement. During electrospinning nanofiber is affected by the electric field force, Coulomb repulsive force, air resistance force gravity and so on. The influence of parameters on the deposition behavior of as-spun nanofiber is discussed. The simulation results show that (i) with charge density increasing, the final spacing between mass center of nanofibers A and B (FSAB) increases and the movement distance of center-of-mass of nanofiber B (MDB) decreases first and then increases; (ii) FSAB increases with applied voltage, but decreased in narrow range with concentration of PEO increasing; (iii) FSAB decreased with the initial spacing between mass center of nanofibers A and B (ISAB) increasing, and then it increases after reaching the minimum. So does ISAB to DMB. This simulation model would improve the controlling of nanofiber in NFES.

Abstract: In this paper, we present our recent works on the measurement of field emission performance of silicon tip arrays and investigate the thermal instability of emission current by measuring the emission current as the function of time under three different cooling conditions—natural free radiation，contact conduction and air forced convection respectively. Draw the conclusions that field emission performance of the silicon-based emitters is quite sensitive to the temperature change and resistive heating produced as emission current flowing through the apex of silicon emitters induces the instability of emission current.

Abstract: Near-Field Electrospinning (NFES) is a newly developed method to fabricate continuous and ordered solid nanofibers, with smaller spinneret-to-collector-distance the behavior of viscous jet would play a more prominent effect on the deposition and morphology of nanofiber. In this paper, a 2-dimentional physical model based on electrohydrodynamics and rheology was set up to discuss the morphology of viscous jet for NFES. The profile of the jet along z direction can be predicted by this model, and the impact of process parameters on the jet radius is analyzed. Radius of jet decreases with spinneret-to-substrate-distance decreasing; jet radius decreases with applied voltage and electric field strength increasing; jet electrospun from PEO solution is thinner than that from PVA solution with the same solution concentration; solution concentration has insignificant influence on the radius of jet from solution of the same polymer (PVA or PEO). This numerical simulation would improve the control of electrospinning process in NFES.

Abstract: Using Quartz particles as the repeat-agents, commercial water glass as the raw material, butyl titanate as the source of titanium, the TiO2 Membrane/ Macroporous Silica gel composite microspheres were successfully prepared. The uniformity transparent TiO2 Membrane on the surface of Silica gel microspheres(SM) was inducted by sol-gel method and dipping extracted method. The structure and performance of the microspheres were characterized by Infrared Spectroscopy (IR) and X-ray diffraction (XRD). The results showed that the composite microspheres were irregular porous materials and their average diameter was 2.18 mm. The crystal type of the TiO2 film was anatase and its average size was 15 nm. Illuminated for 7.5h, the degradation ratio of the composite microspheres was up to 85%. The properties of photocatalysis would be increased with the increasing of the amount of the quartz.

Abstract: The individual and/or combinatory impacts of two surfactants (polyoxyethylene nonyl phenyl ether 10 (Tx-100), Arabic gum powder (AG)) on the dispersivity of multi-wall carbon nanotubes (NMWTs) were firstly investigated and evaluated through naked and microstructures observation; hereafter, NMWTs with 1.0% loading were firstly dispersed in aqueous solution with surfactant ultrasonic dispersion process, and cast-mixed into cement matrix to fabricate 2 groups NMWTs reinforced cement composites (NMTRCs), associated with the plain reference. Wheatstone bridge configurations were simultaneously employed to obtain the resistances and the monoaxial stresses, to investigate the pressure-sensitive properties of these nanocomposites. Results with naked observation reveal that either Tx-100 or AG at some concentration has good dispersion effect on NMWTs, the blackness homogeneity and stability of NMWTs suspended solution could retain more than 15 d; yet microstructures results show that NMTRC with AG has more homogeneous dispersion impact and more compatible with cement hydration than that with Tx-100. Results related on the pressure-sensitive properties of NMTRCs demonstrate that, the fractional change in resistivity of NMTRC with AG linearly falls down by increment of applied pressure within elastic range, this good pressure-sensitive traits mainly contribute to the increasing chance of physical contacts, the denser of current chargers between NMWTs, and the shortened trend of the potential barrier widths between NMWTs and matrix by increment of pressure, after efficient dispersion with AG. Yet that of NMTRC with Tx-100 has not good linearity descending trend, but some exaggerate fluctuations, and that of the reference has also no any regular descending trend.

Abstract: Mesoporous WO3•0.33H2O was synthesized by the microwave radiation method using surfactant as the template-directing agent, and the template was removed by Soxhlet extraction. The degree of framework substitution had been monitored by means of powder X-ray diffraction (XRD), nitrogen adsorption, and UV-vis diffuse reflectance (DRUV) spectroscopy techniques. Nitrogen adsorption data and XRD patterns confirmed that, the structure, high surface area, and uniform pore size distribution were maintained in the crystallized samples. The photocatalytic activity for the photo-oxidation of gaseous formaldehyde on the mesoporous WO3•0.33H2O synthesized was improved by NiO loading, the photocatalytic activity was higher than both that of the materials synthesized using calcination in high temperature and commercial Degussa P25 TiO2 under visible light and UV irradiation.