Nano-structure array has recently attracted great attention in the field of not only micro electronics but also bio- and material engineering. Therefore, it is important to develop the simple method to fabricate nano-structure array with a large area on the solid surface. While, in the field of micro and sub-micro size colloidal mono-dispersed spheres application, the growth of a densely packed structure array induced by self assemble properties was reported. Such a particle-self-assembly method is applicable to fabricating nano-structure array.
We study self-aligned and selective deposition of polystyrene colloidal spheres(PCS) on Si substrate by simple wet process. In this work, we use etch-pit pattern array substrates for wet deposition experiment, which is to lifting the substrate slowly after immersing into the PCS(diameter; 120-1000 nm) suspension. PCS selective deposition strongly depends on the wettability of the substrate. On the hydrophilic substrate, every etch-pit is occupied with PCS completely. In contrast, there is hardly PCS on the hydrophobic substrate. This result indicates that the interface condition between solid and liquid is important part in the selective deposition. In order to discuss the selective deposition mechanism, we investigate the wettablility of substrate and amount of selective deposited PCS. The wettability is estimated by contact angle measurement of droplet on substrates. Selective deposition can be explained that PCS, which walks randomly by the Brownian movement, is pushed into etch-pit by the capillary force, induced by the interface between suspension and substrate.
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