Fabrication of Transparent Superhydrophobic Surface from ZnO Nanorods.

A transparent superhydrophobic surface was fabricated from ZnO nanorods grown on Si and glass substrates in a thermal furnace for industrial applications such as surface coating. Two types of glasses were used for the substrates: slide glass and Corning glass. The ZnO nanorods were then coated with PTFE using existing sputtering technology and then grown on the glasses. The optical transparency and processing temperature of the nanorods on the substrates with and without a ZnO buffer layer were investigated, for comparison. The superhydrophobic surface formed on Corning glass with a 50-nm-thick ZnO buffer layer exhibited a transparency of 80% or higher and a water contact angle of 150° or higher in the visible light region. High optical transmittance of the superhydrophobic surface was achieved by controlling the size and growth direction of the nanorods. X-ray diffraction and scanning electron microscopy images showed that the nanorods on the glass substrates were thicker than those on Si, and the nanorods predominantly grew in the vertical direction on the buffer layer. However, the growth direction did not affect the wettability of the surface. Vertically grown nanorods can still affect optical transmittance because they facilitate the propagation of light. In the case of Corning glass, superhydrophobic surfaces with contact angles of 150° and 152.3° were formed on both samples with buffer layers of 50 nm and 100 nm, respectively. Therefore, a buffer layer thickness in the range of 50-100 nm is suitable for realizing a transparent superhydrophobic surface on a glass substrate.

Optimization of Super-Hydrophobic Property by Two-Step Surface Modification.

The super-hydrophobic surface can be used in anti-pollution, self-cleaning, and anti-corrosive properties. Two-step surface treatment process on Al-coated glass was conducted by surface etching using potassium hydroxide (KOH) and surface coating using lauric acid for super-hydrophobic surface. The KOH-etched Al surface (1st etching) was changed to a hydrophilic property with a water contact angle (WCA) of 68° to 48°. On the other hand, the WCA of the etched Al surface was changed to about 153° with super-hydrophobic property when the lauric acid coating (2nd coating) was applied on the KOH-etched Al surface for 30 minutes. We found that the hydrophobicity of Al surface was related to the roughness by surface modification as well as the Al film thickness by sputtering method.

Super-Hydrophobic Properties of Aluminum Surfaces Synthesized by a Two-Step Chemical Etching Process.

In this study, super-hydrophobic coatings on Al surfaces were prepared by a two-step chemical etching process using potassium hydroxide and lauric acid as the etching solution and coating solution, respectively. The Al surface was roughened by immersion in potassium hydroxide, and an ethanolic solution of lauric acid was then coated onto the rough Al surface to lower the surface energy. The wettability and surface morphologies of the treated Al surfaces were characterized using contact angle measurement and scanning electron microscopy, respectively. Microstructures were formed on the treated Al surfaces, which increased the contact angle of the surface (>150°). The contact angle hysteresis was measured between 2.7° and 3° on average, indicating that the surface energy of the Al substrate was low, and the lauric acid was uniformly coated on the substrate. This super-hydrophobic coating showed excellent self-cleaning and corrosion-resistant behavior. The coated samples floated on the water surface and demonstrated excellent water repellent properties. In addition, the coatings were mechanically stable and had an excellent regeneration ability, as verified experimentally. The lauric acid used to lower the surface energy is considered more environment-friendly and more durable than the widely used polytetrafluoroethylene (PTFE).

Preparation and Characterization of the Sputtered TiAlN Coatings Using a Ti-Al Alloy Metal Target.

Titanium aluminium nitride (TiAlN) ternary coatings were deposited on glass substrates by means of reactive magnetron sputtering technique, using a Ti-Al alloy metal target (Ti0.5Al0.5). The depositions were performed at various N2 and Ar flux ratios of N2/(Ar + N2) ═ 33, 50, 67, 83%. The structure, morphology, chemical composition and mechanical properties were investigated by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), energy dispersive X-ray spectroscopy (EDS), and nano indenter (MTS System), respectively. The orientation of coatings depends on the flux ratios of N2/(Ar + N2) and substrate temperature. The coatings deposited with N2/(Ar + N2) ratios of 33, 50 at.% consists of pyramid-like column grains separated by porous and voids, which can be attributed to cubic-TiN (220) preferred orientation. The coatings deposited with N2/(Ar + N2) greater than 67% exhibits the phase of hexagonal-AlN and cubic-TiN. The surface of coatings becomes more compact and smoother with the N2/(Ar + N2) ratios increase. The coatings deposited with N2/(Ar+N2) ratio of 83% shows the largest hardness of 21.5 GPa, which is attributed to the preferred (200) orientation. However, this hardness increases significantly with increasing substrate temperature. The coatings deposited at more than 100 °C exhibited the (111) and/or (200) orientation. The amounts of grains grown along the (111) and (200) orientations play a significant role on the mechanical performance of TiAlN coatings. Four independent mechanisms, such as TiAlN stoichiometry and lattice parameter, the (111) preferred growth orientation, and the density increases (elimination of void), were found to contribute to the enhancement of TiAlN mechanical performance.

Transparent and Conducting Oxide Films: SiO2-Doped ZnO.

(SiO2)x(ZnO)100-x films with x = 2, 3, 4, and 5 wt.% were deposited on slide glass substrates at room temperature by the conventional Rf magnetron sputtering method. Their resistivities were investigated as a function of SiO2 content. The lowest resistivity of 4.5×10-3 Ω.· cm was obtained for the (SiO2)x(ZnO)100-x film with x = 2 wt.%. This film showed an excellent average transmittance of 85% in the visible range with a wide band gap over 3.4 eV and a high refractive index of 2.1. In addition, the electrical conductivity of the films was improved by annealing at a temperature films decrease range from 100 °C to 400 °C in vacuum. The resistivities of (SiO2)x(ZnO)100-x with increasing annealing temperature. In particular, SZO film with x = 2 wt.% shows a minimum resistivity of ~10-3 Ω.cm after the heat treatment for 30 min at 300 °C in vacuum. Thus, we suggest that (SiO2)x(ZnO)100-x films being sufficiently transparent and having a high conductivity, are suitable for application as transparent and conductive oxide films.

Switchable Super-Hydrophilic/Hydrophobic Indium Tin Oxide (ITO) Film Surfaces on Reactive Ion Etching (RIE) Textured Si Wafer.

We have developed a surface texturing process for pyramidal surface features along with an indium tin oxide (ITO) coating process to fabricate super-hydrophilic conductive surfaces. The contact angle of a water droplet was less than 5 degrees, which means that an extremely high wettability is achievable on super-hydrophilic surfaces. We have also fabricated a super-hydrophobic conductive surface using an additional coating of polytetrafluoroethylene (PTFE) on the ITO layer coated on the textured Si surface; the ITO and PTFE films were deposited by using a conventional sputtering method. We found that a super-hydrophilic conductive surface is produced by ITO coated on the pyramidal Si surface (ITO/Si), with contact angles of approximately 0 degrees and a resistivity of 3 x 10(-4) Ω x cm. These values are highly dependent on the substrate temperature during the sputtering process. We also found that the super-hydrophobic conductive surface produced by the additional coating of PTFE on the pyramidal Si surface with an ITO layer (PTFE/ITO/Si) has a contact angle of almost 160 degrees and a resistivity of 3 x 10(-4) Ω x cm, with a reflectance lower than 9%. Therefore, these processes can be used to fabricate multifunctional features of ITO films for switchable super-hydrophilic and super-hydrophobic surfaces.

Effects of Ga- and Al-codoped ZnO buffer layer on the performance of inverted polymer solar cells.

A Ga, Al-doped zinc oxide (GAZO) buffer layer was applied to inverted polymer solar cells (PSCs) based on P3HT [poly(3-hexylthiophene)]:PCBM [[6,6]-phenyl C61-butyric acid methyl ester] blend films. The work function of the GAZO layer on indium-tin oxide (ITO) was measured to be 4.45 eV. The insertion of the GAZO layer between the ITO electrode and the P3HT:PCBM blend film in the inverted PSC led to an improved short-circuit current (Jsc), open-circuit voltage (Voc) and fill factor (FF) compared to those of the reference cell without GAZO layer. The Jsc enhancement in the inverted PSC with the GAZO layer was attributed to both the effective electron extraction and the increased crystallinity of P3HT, and the work function difference between Ag and GAZO layer induced the increase in Voc. The improved FF value was due to the lowered series resistance and elevated shunt resistance. Thus, the power conversion efficiency of the device with the GAZO layer was improved by more than 200% relative to the reference cell.