Functional Texture Design and Texturing Processes

Various functions can be obtained by applying regular patterns or textures to surfaces. Depending on the function, the required dimensions of the texture, such as the pitch, vary over a wide range: from nanometers for optical function to millimeters for friction. In addition, the high aspect ratio of the cross sectional profile or the hierarchical structure of a micro- or nano-structure is required to control the wettability, for example. This paper reviews various texturing processes as well as the functionalities thus attained and their application

Combination of silicon microstructures and porous cellulose nanofiber structures to improve liquid-infused-type self-cleaning function

Various fine structures and/or low surface energy material coatings have been designed to develop self-cleaning surfaces. These structures work by trapping air in their vacant spaces. Surfaces based on liquid-infused-type design exhibit better performance than those based on the traditional design; however, their life is limited because the special liquid covering the surface drops off easily. Cellulose nanofibers (CNFs) have amphiphilic characteristics in addition to their small size; thus, an aggregated structure consisting of CNFs will have an improved liquid holding performance. This study discusses the deposition of CNF on silicon microstructured surfaces and the etching of the CNF structure to extend its self-cleaning life. The effects of microstructure design, CNF concentration, and etching conditions on the morphology and porosity of the CNF structures are comprehensively studied. Long-term performance tests were carried out to measure the sliding angle (SA) of diethylene glycol after repeated water dash operations. It was confirmed that the combined structure of highly porous CNF and silicon microstructures exhibits a durable self-cleaning function

An Analysis of Surface Properties of Hetero-Epitaxially Grown SiC Surface on Si Substrate

The molecular beam epitaxy process can produce single crystal and smooth surface at atomic level as well as synthesizing the desired material by supplying the multiple materials on substrates. This paper deals with an application of the hetero-epitaxial process of silicon carbide (SiC) on silicon (Si) substrate, and aims to make clear the attainable surface roughness and its properties. It was found that the steep pits were formed during the carbonization process before the epitaxy and that they strongly affected the final roughness. The attainable roughness was 0.4nm rms. Finally, the applicability to toroidal mirror optics was discussed

Fabrication of high aspect ratio silicon micro-/nano-pore arrays and surface modification aiming at long lifetime liquid-infused-type self-cleaning function

This paper discusses a fabrication process of high aspect ratio (AR) silicon micro-/nano-pore structures and modification of their surfaces to improve the function of liquid-infused-type self-cleaning surfaces. The structure and its hydrophobic surface play an important role to hold a special liquid (a lubricant) on the surface tight to produce an intermediate lubricant layer and any liquid drops, including low surface tension liquids such as oil, can slide easily on it. The nanopore structure with an AR as high as 30 was fabricated by etching in a solution of hydrofluoric acid and hydrogen peroxide. This process based on a catalyst reaction of an array of Au islands that was deposited on a silicon substrate through a particle mask. This original hydrophilic surface was changed to hydrophobic one by depositing self-assembled monolayer of octadecyltrichlorosilane to modify the energy balance at the interface of the solid structure, the lubricant, another liquid, and air. Then the lubricant could be well retained. The functional lifetime was evaluated by measuring the liquid residue on the surface after number of liquid dash. It was confirmed that longer lifetime was obtained with higher AR nanopore structure

Patterned Self-Assembly of Fine Particles and Its Application to Polishing Tool

This study aims to discuss an application of self-assembled particles to a polishing tool. Self-assembly of fine particles is obtained by drying colloidal suspension on a substrate. Using a dispenser and a motored stage, an assembly can be obtained along specific profile like spiral. The assemblies are transferred to another substrate on which ultraviolet curing resin is spin-coated and cured while pressing the substrate each other. Silica particles of 1 µm diameter were assembled over 10mm square and applied to polishing to evaluate the performance. It was found that the glass plate was polished with smooth finish. However, the particles dropped off under severe conditions

Fabrication of High Aspect Ratio Silicon Nanostructure with Sphere Lithography and Metal-Assisted Chemical Etching and its Wettability

Metal-assisted chemical etching (MACE) is a site-selective etching process produced by a catalyst reaction at the interface between noble metal and silicon. This paper aims to make clear the applicability of sphere lithography and MACE to the fabrication of high aspect ratio Si nanostructures. The capacity to control the etched profiles and the scale extension are investigated. First, silica particles (e.g. φ1 μm) were self-assembled on a Si substrate. After the reduction of particle size via argon ion bombardment, a gold layer was deposited using the particles as a mask. The substrate was then etched with a mixture of hydrofluoric acid and hydrogen peroxide. It was found that an array of nanopillars with a regular pitch, good separation, and an aspect ratio of about 52 was produced. The effects of MACE conditions on final profiles were clarified. A limitation of this approach is the small (several millimeters) area fabricated due to the dependence on the vacuum technique (ion bombardment, Au deposition), and the size of the area limits its practical applications. Thus, Ag nanoparticles (e.g. φ150 nm) were applied. The relationship between the concentration of the Ag suspension, the Ag assembled layer, and the morphology of MACE structures was made clear. A spray method was applied to extend the deposited area of Ag particles up to φ100 mm. Finally, the effects of the cross-sectional profile on the contact angle of a water droplet were examined. By applying a high aspect ratio nanostructure on the substrate, the water contact angle increased up to 153 degrees while that without the structure is 58 degrees

Self-assembly of Fine Particles Applied to the Production of Antireflective Surfaces

We introduce a new fabrication process for antireflective structured surfaces. A 4-inch silicon wafer was dipped in a suspension of 300-nm-diameter silica particles dispersed in a toluene solution. When the wafer was drawn out of the suspension, a hexagonally packed monolayer structure of particles self-assembled on almost the complete wafer surface. Due to the simple process, this could be applied to micro- and nano-patterning. The self-assembled silica particles worked as a mask for the subsequent reactive ion etching. An array of nanometer-sized pits could be fabricated since the regions that correspond to the small gaps between particles were selectively etched off. As etching progressed, the pits became deeper and combined with neighboring pits due to side-etching to produce an array of cone-like structures. We investigated the effect of etching conditions on antireflection properties, and the optimum shape was a nano-cone with height and spacing of 500 nm and 300 nm, respectively. This nano-structured surface was prepared on a 30 × 10-nm area. The reflectivity of the surface was reduced 97% for wavelengths in the range 400-700 nm

Instability Phenomenon in Dip-Coating Process for Self-Assembly of Fine Particles and Design Countermeasures

The self-assembly of fine particles is a promising process for the production of nano-structures. In this process, aqueous suspension is often used. The spreading of the suspension on the substrate is a complex phenomenon that sometimes causes problems of instability. This paper discusses the instability phenomenon and proposes countermeasures from various aspects. It was found that special attention should be paid to the pattern design of site-selective assembly. Finally, complex structures made of particles of different sizes and materials are shown to demonstrate the improved stability after repeated dip-coating

Single-crystal SiC thin-film produced by epitaxial growth and its application to micro-mechanical devices

This paper deals with the fabrication process of single-crystal silicon carbide (SiC) thin-films and its application to microdevice. SiC thin-film was synthesized using molecular beam epitaxy, where single-crystal SiC layer was grown on single-crystal silicon (Si) substrate. Using lithography and etching process, microscopic cantilevers were fabricated. Typical dimensions of the cantilevers were 10-60 μm in length, 10-30 μm in width, typically 180 nm in thickness. Young\u27s modulus estimated from bending test was almost the same with that of bulk material. Finally, an application is demonstrated where nickel was deposited on the cantilever and biomorphic actuation was carried out. The displacement at the tip was about 2 μm when the temperature change was 40 K. The time constant of the step response was about 0.07 s

Design of Structured Surfaces for Directional Mobility of Droplets

This paper deals with the directional mobility of droplets on structured surfaces. Structured surfaces were micro-patterned with rectangular lines and spaces of varying pitch and height in the sub-millimeter range. The material used was polydimethylsiloxane, which is hydrophobic and wettable by oil. First, we studied the effect of the structural design on the sliding angle of pure water or oil through experiments. For pure water droplets, we found that a wider pitch enhanced the directionality. On the other hand, oil droplets spread along the groove because of their low surface tension and strong capillary force. The directionality of the sliding angle of oil droplets was larger than that of pure water, especially when the groove was narrower and deeper. Second, we poured a large amount of liquid on the structure and evaluated the removal rate on the tilted surface. We found that a parallel structure enhanced the liquid mobility for both pure water and oil