Nanosphere lithography employs single- or multilayer self-assembled nanospheres as a template for bottom-up nanoscale patterning. The ability to produce self-assembled nanospheres with minimal packing defects over large areas is critical to advancing applications of nanosphere lithography. Spin coating is a simple-to-execute, high-throughput method of nanosphere self-assembly. The wide range of possible process parameters for nanosphere spin coating, howeverand the sensitivity of nanosphere self-assembly to these parameterscan lead to highly variable outcomes in nanosphere configuration by this method. Finding the optimum process parameters for nanosphere spin coating remains challenging. This work adopts a design-of-experiments approach to investigate the effects of seven factorsnanosphere wt%, methanol/water ratio, solution volume, wetting time, spin time, maximum revolutions per minute, and ramp rateon two response variablespercentage hexagonal close packing and macroscale coverage of nanospheres. Single-response and multiple-response linear regression models identify main and two-way interaction effects of statistical significance to the outcomes of both response variables and enable prediction of optimized settings. The results indicate a tradeoff between the high ramp rates required for large macroscale coverage and the need to minimize high shear forces and evaporation rates to ensure that nanospheres properly self-assemble into hexagonally packed arrays.
A promising redox-mediated bromate-ion (BrO 3 − ) based system was investigated through research combined with mathematical modeling, analytical study, and full-cell test to understand the characteristic effect of electrochemical reaction coupled with chemical reaction, called catalytic regenerative reaction (EC'), on the cell behaviors. From the full-cell based discharge test, a unique unsteady behavior induced by the catalytic regenerative reaction was found for the first time, and to understand the underlying physics and nature of the system, theoretical study was conducted through mathematical modeling and analytical method. Three reaction mechanisms (E, EC, and EC') were compared in their characteristic reaction behaviors to understand the nature of each reaction mechanism, and the results were analyzed with respect to reaction time and species concentration at the electrode surface. Furthermore, the effect of actual condition of bromate system (i.e. non-unity stoichiometry and limited amount of bromate) was analyzed at unsteady condition for the first time to understand its characteristic behavior in the actual battery condition. It was found that cell voltage and operation time were increased substantially by the catalytic regenerative reaction, and inclusion of non-unity stoichiometric coefficients induced a significant change in the concentration profiles for reactant and product species, leading to operation time about 4.2 times longer than the unity stoichiometric EC' reaction. As a final step, the effect of catalytic reaction was analyzed in analytical method to define the parameters to control the catalytic reaction, and especially, the relative effect of electrochemical reaction and coupled chemical reaction rates on the autocatalytic reaction was compared through a zone diagram where conditions for pure diffusion controlled and pure kinetic controlled cases were defined.
Size-based separation of particles in microfluidic devices can be achieved using arrays of micro- or nanoscale posts using a technique known as deterministic lateral displacement (DLD). To date, DLD arrays have been limited to parallelogram or rotated-square arrangements of posts, with various post shapes having been explored in these two principal arrangements. This work examines a new DLD geometry based on patterning obtainable through self-assembly of single-layer nanospheres, which we call hexagonally arranged triangle (HAT) geometry. Finite element simulations are used to characterize the DLD separation properties of the HAT geometry. The relationship between the array angle, the gap spacing, and the critical diameter for separation is derived for the HAT geometry and expressed in a similar mathematical form as conventional parallelogram and rotated-square DLD arrays. At array angles <7°, HAT structures demonstrate smaller particle sorting capability (smaller critical diameter-to-gap spacing ratio) compared to published experimental results for parallelogram-type DLD arrays with circular posts. Experimental validation of DLD separation confirms the separation ability of the HAT array geometry. It is envisioned that this work will provide the first step toward future implementation of nanoscale DLD arrays fabricated by low-cost, bottom-up self-assembly approaches.
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