Regulation of ionic current through a surround-gated nanopore via field effect control.

Ability to control ionic current flowing through a nanopore has been demonstrated using the electric field effect on an electrical gate surrounding the nanopore. The gate electrode was introduced onto a single nanopore by depositing an Au layer on a silicon nitride diaphragm prior to pore milling using a focused ion beam technique. A hafnium oxide layer was subsequently deposited onto the nanopore structure as an insulating layer to protect the gate electrode. The device operation was investigated in KCl electrolyte and the ionic current regulating ability was examined under the influence of the gate voltage and the nanopore size. It was found that the device shows significant ionic current response with respect to the applied gate voltage. The resulting electric field dependent behavior of the fabricated nanopore suggests that the ionic current is influenced by positive surface charge inside the nanopore. The gate influence was more pronounced in the smaller nanopore and with higher source-drain voltage. The gate and pore size dependence behavior allows the potential to regulate ionic current as a nanoscale valve in nanochannel applications.

Fabrication of High Aspect Ratio Micro-Structures with Superhydrophobic and Oleophobic Properties by Using Large-Area Roll-to-Plate Nanoimprint Lithography.

Bio-inspired surfaces with superamphiphobic properties are well known as effective candidates for antifouling technology. However, the limitation of large-area mastering, patterning and pattern collapsing upon physical contact are the bottleneck for practical utilization in marine and medical applications. In this study, a roll-to-plate nanoimprint lithography (R2P NIL) process using Morphotonics' automated Portis NIL600 tool was used to replicate high aspect ratio (5.0) micro-structures via reusable intermediate flexible stamps that were fabricated from silicon master molds. Two types of Morphotonics' in-house UV-curable resins were used to replicate a micro-pillar (PIL) and circular rings with eight stripe supporters (C-RESS) micro-structure onto polycarbonate (PC) and polyethylene terephthalate (PET) foil substrates. The pattern quality and surface wettability was compared to a conventional polydimethylsiloxane (PDMS) soft lithography process. It was found that the heights of the R2P NIL replicated PIL and C-RESS patterns deviated less than 6% and 5% from the pattern design, respectively. Moreover, the surface wettability of the imprinted PIL and C-RESS patterns was found to be superhydro- and oleophobic and hydro- and oleophobic, respectively, with good robustness for the C-RESS micro-structure. Therefore, the R2P NIL process is expected to be a promising method to fabricate robust C-RESS micro-structures for large-scale anti-biofouling application.

Increasing active surface area to fabricate ultra-hydrophobic surface by using "Black silicon" with bosch etching process.

Needle-shaped pillars so-called "Black silicon" (B-Si) were fabricated by etching cleaned silicon wafer with fluorine-based deep reactive ion etching plasma. The B-Si pillar with the pillar size (a) and spacing (b) of 250 nm, and height (h) of 6.47 microm, coated with SiOxFy film had water contact angle (WCA) and ethylene glycol contact angle (ECA) of 159.8 degrees and 135.5 degrees, respectively. After coating the pillar with trichloro(1H,1H, 2H,2H-perfluorooctyl)silane (TPFS), the WCA and ECA increased to 166.2 degrees and 161.8 degrees, respectively. At the optimum etching condition, the B-Si pillar with the size a = 376 nm, b = 576 nm, h = 6.47microm, and the aspect ratio of 14.80 showed the WCA and ECA of 4.25 degrees and 14.77 degrees, respectively. After coating with the TPFS, liquid droplets ran across the sample's surface rapidly and the WCA and ECA could not be measured. Moreover, when the pillar height was increased twice, the WCA and ECA of the B-Si with and without the TPFS coating were greater than 170 degrees, indicating excellent water-and-oil repellency and can be applied for Micro-Electro-Mechanical Systems (MEMS).

An effect of silicon micro-nano-patterning arrays on superhydrophobic surface.

Superhydrophobic surface can be fabricated by creating a rough surface at very fine scale and modify it with low-surface energy material. To obtain the optimum superhydrophobicity, the surface roughness must be maximized. To avoid the limitation of scaling down the pattern size by using an expensive lithography tools, the surface roughness factor (r) was increased by means of changing an asperity shape so as to increase its overall surface area. In this paper, the patterns of the asperities under studied were wave stripes, line stripes, cylindrical pillars, square pillars, pentagonal pillars, hexagonal pillars, and octagonal pillars. All pillar shapes were arranged in square arrays, hexagonal arrays, and continuous stripes. The asperities sizes and the pitches were varied from 1 to 5 microm with 10 microm of asperity height. Then the patterned surfaces were coated with polydimethylsiloxane mixed with 10 wt% dicumylperoxide. It was found that the stripe asperities can generate only hydrophobic surface with water contact angle (WCA) of 135 degrees to 145 degrees. The pillars with square and hexagonal arrays had the WCA of 149 degrees to 158 degrees. The pentagonal pillars with square and hexagonal arrays achieved the highest WCA with an average WCA of 156 degrees. It was evident that the pillar shape had significant effect on the superhydrophobicity.