Confocal microscopy studies of colloidal assembly on microfabricated physically templated surfaces
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In this research we consider two different approaches for microfabricating physical templates to be used in template directed colloidal self-assembly experiments. Fabrication of templates, usable with confocal microscopy, forms an essential part of observation and analysis of template directed colloidal self-assembly studies. We use existing laboratory based microfabrication methods for patterning thin glass coverslips and polymeric films. These templates when used for directing colloidal self-assembly along with confocal microscopy analysis provide us with relevant information on the effect of confined geometries of the template on particle packing and order. The first method of template fabrication involves ultraviolet photolithography, thin film deposition, and glass micro machining. Various stages of the process were optimized while selecting reactive ion etch (RIE) and nickel etch mask with a suitable etch recipe for microfabrication of patterns on thin multi-component glass coverslips. Pattern dimensions were shown to be nearly commensurate with patterns on the microfiche, which was used as a field mask. In another approach, mechanical machining for fabricating polymeric templates was attempted on poly(methyl methacrylate) films spin coated on thin glass cover slips. The mechanical machining was implemented using computer numerical control (CNC) machines with the pattern dimensions in the range of 50 Mu m-150 Mu m. The glass and polymeric templates were used in template directed colloidal self-assembly experiments us ing polystyrene or silica particles. Confocal microscopy was used to obtain images of particle packing in template geometries. Imaging of the particles confined in the template geometries show increased particle concentration along pattern walls and corners. Inherent pattern irregularities and roughness possibly resulted in limited order in particle. Using a simple fortran program, image stack generated from confocal microscopy is used for obtaining images of particle packing in four different view planes which includes top, side, cross sectional and diagonal view of the image stack. The results from this research show the application of simple microfabrication processes for creating physical templates for template directed colloidal self-assembly. Confocal microscopy imaging combined with fortran image processing program can provide images of particle packing in different view planes. These images of the particles confined in various pattern geometries illustrate greater possibility of packing order in straight and regular pattern geometries or profiles.