High aspect ratio solid silicon microneedles with a concave conic shape were fabricated. Hydrofluoric acid-nitric acid-acetic acid (HNA) etching parameters were characterized and optimized to produce microneedles that have long and narrow bodies with smooth surfaces, suitable for transdermal drug delivery applications. The etching parameters were characterized by varying the HNA composition, the optical mask's window size, the etching temperature and bath agitation. An L9 orthogonal Taguchi experiment with three factors, each having three levels, was utilized to determine the optimal fabrication parameters. Isoetch contours for HNA composition with 0% and 10% acetic acid concentrations were presented and a high nitric acid region was identified to produce microneedles with smooth surfaces. It is observed that an increase in window size indiscriminately increases the etch rate in both the vertical and lateral directions, while an increase in etching temperature beyond 35 • C causes the etching to become rapid and uncontrollable. Bath agitation and sample placement could be manipulated to achieve a higher vertical etch rate compared to its lateral counterpart in order to construct high aspect ratio microneedles. The Taguchi experiment performed suggests that a HNA composition of 2:7:1 (HF:HNO 3 :CH 3 COOH), window size of 500 μm and agitation rate of 450 RPM are optimal. Solid silicon microneedles with an average height of 159.4 μm, an average base width of 110.9 μm, an aspect ratio of 1.44, and a tip angle and diameter of 19.2 • and 0.38 μm respectively were successfully fabricated.

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The synthesis of a poriferous and high energy (001) faceted anatase Zn-doped TiO 2 nanowall (ZnTNW), vertically grown on an indium tin oxide substrate, is presented. The ZnTNW was prepared using a modified liquid phase deposition method using zinc nitrate (Zn(NO 3 ) 2 $xH 2 O) as a fluoride scavenger in the presence of hexamethylenetetramine. In a typical procedure, the ZnTNW nanowall with length and thickness of approximately 2 mm and 60 nm, respectively, can be obtained from the reaction during a 5 h growth process. X-ray diffraction analysis shows that the nanowall has an anatase structure with a dominant high energy (001) basal plane. Meanwhile, the X-ray energy dispersive analysis confirms the presence of Zn in the TiO 2 nanowall. High resolution transmission electron microscopy analysis results reveal, surprisingly, that the ZnTNW is single crystalline in nature although it has a highly porous (surface and bulk) structure. Photocatalytic properties of the ZnTNW were examined in the degradation of methylene blue. It was found that the ZnTNW exhibits excellent photocatalytic efficiency with kinetic reaction rate, turnover number and turnover frequency as high as 0.004 min À1 , 760 and 11 min À1 , respectively. The photocatalytic performance of the ZnTW was found to be higher for about 10% and 50% than the pristine TiO 2 nanowalls and (001) faceted poriferous TiO 2 microtablet, which reflected the effective effect of the Zn doping. The ZnTNW may find potentially use in photocatalytic heterogeneous applications.

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The optical properties of heavy metal-free quaternary CuZnInS3 QDs can be optimized by tuning the composition, which is promising for improving the efficiency of QDs-PEC hydrogen generation.