Interfacial-energy-controlled deposition technique of microstructures using blade-coating.

A novel blade-coating technique for the fluidic self-assembly of microstructures on large-scale substrates is presented. In our blade-coating technique, water and microstructures dispersion, which includes chemically modified microstructures and water-insoluble solvent, are continuously blade-coated on a substrate on which surface hydrophilic areas are surrounded by a hydrophobic self-assembled monolayer. In the process studied, first, water is selectively placed on the hydrophilic areas; second, the water-insoluble solvent covers the water to create a solvent/water interface; third, fluidic self-assembly of microstructures onto the water takes place by a capillary force between the water and the microstructures; and finally, the microstructures are deposited onto the hydrophilic areas after the evaporation of the water and the solvent. SiO(2) plates sized 10 x 50 x 0.3 microm(3) were used to verify the feasibility of our technique. About 40,000 SiO(2) plates were selectively deposited on the hydrophilic areas on a substrate with an area of 20 cm(2) with a deposition probability of 0.52 by utilizing dispersion consisting of plates chemically modified with 1-chloroethyltrichlorosilane and a mixture of 1,4-dichlorobutane and n-hexane. The deposition probabilities of the plates primarily depended on the type of solvent for plate dispersions and increased with an increase in the value of free energy change of the plate/solvent/water system by the movement of the plate from the solvent to the solvent/water interface during the blade-coating process. These results indicate that the deposition probabilities are governed directly by the capillary force acting on the plates. Our deposition technique for microstructures using blade-coating is potentially applicable to the deposition of micrometer-size electronic devices on large-scale substrates.