Micro and Nanosystems - Volume 6, Issue 3, 2014

Micro- and nanomachining technologies are commonly categorized into top-down and bottom-up approaches. Making nanoscale structures using top-down approach has been facing difficulties due to the limitation of optical lithography and the low throughput of electron beam and ion beam techniques. Soft lithography and hot embossing can transfer nanostructures across a large wafer. However, these techniques are limited to a soft substrate such as polymers only. A recent work by researchers from the Purdue University, Harvard University, Madrid Institute for Advanced Studies, and the University of California, San Diego demonstrated a new embossing technology to create wafer-scale smooth three-dimensional nanoshapes on hard crystalline metal.

We generated silicone oil micro-droplet in deionized water with a microfluidic T-junction devices made on silicon-glass with different cross-sections (depth and width) of the continuous phase and the dispersed phase micro-channels. We experimentally show that the size of the droplet decreases when the width or the velocity of the dispersed phase micro-channel decreases but is almost insensitive to the channel depth. For describing the observed behaviour, we proposed a modified mechanism of droplet formation consisting of three stages, each with start and end precisely identified. Based on this mechanism, we developed an analytical model for obtaining the droplet diameter in dripping regime when there is partial wetting at the channel boundary. This model is in better agreement with the experiments than other analytical models from the literature, suggesting the effect of channel wetting is significant. We also discuss the use of the capillary number in models, and suggests that the velocity would be a better metrics for comparing different T-junction geometry. In the experiment, the generated droplet diameter is varied between 28 μm and 196 μm.

Considering the disadvantages such as that pseudo-rigid-body method has low precision and it is difficult to build the real deformation-compatibility equations only by using flexibility matrix method, a stiffness analysis method of planar compliant mechanism is put forward. The method takes into account of complex deformations of all flexible structure units. By treating every structure units other than the base as flexible, the whole structure stiffness can be obtained based on force equilibrium equations. It considers deformations of all the flexible units in each direction synthetically, which makes the result close to its actual situation to a great extent. At the same time, it will reduce lots of computational work by avoiding deformation-compatibility problem between flexible and rigid units, which must be dealt with separately for the other methods. Stiffness of a microdisplacement amplification module is analyzed by different methods. Analytical data shows that the pseudo-rigid-body model method will introduce comparatively large error, especially for these compliant mechanisms with longer lever. It can be used only in situations of lower precision requirements. Results of the complete flexible unit method are much closer to that of ANSYS. It is proved that the mechanism stiffness K relates to the ratio of power arm and resisting arm and gains minimum when the two arms are equal. And the inflection point of stiffness-resisting arm history occurs just in this situation. These results are of great importance for the parameter design of lever-amplifier mechanism with given stiffness.

Sm-doped MeMoO4 (Me=Ba, Sr, Ca, and Mg) nanophosphors were fabricated with a sol-gel method and studied for their microstructure and photoluminescence. The matrices of the doped MgMoO4 and BaMoO4 powders show very weak blue emission, but the matrices of the doped MgMoO4 . and BaMoO4 powders show relative strong emission. The Sm3+ cation in all matrices shows very strong red emission that is more red compared with usually reported orange-red emission. Significantly, the photoluminescence efficiency of Sm3+ in SrMoO4 was largest.

In this paper, we model mass and heat transport during manufacturing a field-effect transistor by diffusion or ion implantation in a heterostructure. Based on this modeling we formulate recommendations to optimize annealing of dopant and/or radiation defects to obtain distributions of concentrations of dopants with higher sharpness. The increasing sharpness gives us the possibility to increase integration degree of the field-effect heterotransistor. We also introduce an analytical approach to model redistribution of concentration of dopant and radiation defects and relaxation of spatio-temporal distribution of temperature.

A comprehensive study of a two dimensional MHD (magnetohydrodynamics) micro stirrer with different electrode configurations covering a wide parameter space has been conducted by using computational fluid dynamics simulations. The wall of the circular cavity stirrer acts as the counter electrode. Cylindrical rods ranging in number from one to four, placed inside the cavity act as working electrodes. When two fluids are placed initially in the two halves of the cavity separated by an axial plane, the periodic flow reversal causes stretching, folding and breaking of the interface between the two fluids; an increase in the interfacial area; and enhanced mixing. Parametric studies conducted by varying the time period of the potential difference and the magnitude of the magnetic field intensity show that both significantly influence mixing quality. By having more complex geometries by increasing the number of working electrodes and choosing their locations inside the cavity, and by implementing specific switching schemes for the potential difference on the electrode pairs, secondary flows could be generated which introduced complex chaotic advection and enhanced mixing compared to the configuration with a single working electrode. This work adds to the relatively small body of work that relies on numerical simulations to study MHD microfluidic mixing problems. It also establishes numerical simulations as a tool for optimal design of MHD-based lab-on-a-chip applications.

The aim of the present investigation is to develop a stable formulation for Self-Nanoemulsifying Drug Delivery System (SNEDDS) in order to enhance the solubility and release rate of poorly soluble drug (felodipine). Solubility study was performed to select the oil, surfactant and co surfactant in which the drug is had highest solubility. The pseudo-ternary phase diagram was constructed to study the effect of change in a ratio of surfactant/co-surfactant on nanoemulsion formulation and to find emulsification area in phase diagram. The simplex lattice design was used to optimize the formulation and each formulation was evaluated for various physico-chemical formulation parameters like turbidimetric evaluation, droplet size analysis, drug content, effect of dilution and aqueous phase composition, viscosity, pH and self-emulsification. The results indicate that optimized fomulation as per simplex lattice design contained 23.81% oil (Labrafac PG), 57.14% surfactant (Cremophor EL) and 19.05% co-surfactant (PEG-400) having mean droplet size 26.13 nm, emulsification time 13 seconds, and % transmittance 99%. In vitro drug release indicates that more than 80% drug was released in less than 3 min.