Wet chemical etching of silicon has been a topic of significant interest due to its importance in microelectromechanical systems (MEMS), nanotechnology, and semiconductor device fabrication. Many kinds of MEMS components (e.g., cavity, diaphragm, cantilever, etc.) are fabricated through wet anisotropic etching-based silicon bulk micromachining of {100} and {110} oriented silicon wafers. Wet anisotropic etching of silicon is primarily carried out using alkaline solutions such as potassium hydroxide (KOH), tetramethylammonium hydroxide (TMAH), etc. The etching rate of Si{111} crystal planes is significantly slower compared to other planes like Si{100} and Si{110} as a result of its atomic structure and surface properties. Therefore, the Si{111} crystal plane is of particular interest owing to its unique properties and potential applications. In this work, we report the wet anisotropic etching characteristics of Si{111} in KOH with addition of isopropyl alcohol (IPA). Surface morphology of the etched Si{111} surfaces was examined using confocal laser scanning microscopy (CLSM). In all experimental scenarios, the Si{111} crystal surface gives rise to triangular etch pits, the size and depth of these etch pits are contingent upon the etching time. Following your advice, we revised the abstract phrase "become more sharper" in the summary and quantified the angle data of the triangle. The entire statement has been specifically modified to Furthermore, when the additive IPA is incorporated into the etchant, the corners of these triangular etch pits on the surface transitions from rounded to sharp (with each angles of approximately 60°), indicating that the overall shape of these triangular etch recesses approaches that of an equilateral triangle. In addition, the theory of crystal cleavage is introduced to explain the formation mechanism of surface triangular flat-bottom etch pits during the etching process of Si{111} crystal planes. At the same time, the relevant experiments on Si{111} samples with a SiO₂ mask layer on the surface have been completed, and the results verify the correctness of the analysis of the relevant mechanism. The relevant results and mechanism presented in this article are of large significance for engineering applications in both academic and industrial laboratories.

In this study, magnesium aluminate spinel (MgAl₂O₄) was synthesized by a self-propagating high-temperature synthesis method using Mg–Al alloy with a Mg/Al mass ratio of 50:50 as raw material. Synthesized MgAl₂O₄ was characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, UV–vis diffused reflectance spectroscopy, photoluminescence, and thermogravimetric differential scanning calorimetry techniques. The results show that synthesized products are of high purity and excellent crystallinity. However, the particle size is not uniform and there is obvious agglomeration. The crystallite size of spinel phase is calculated to be 37.78 nm. In the UV band, the synthesized MgAl₂O₄ has a certain absorption capacity, and the extrapolated band gap is 4.02 eV. The synthesis mechanism was studied, and continued rupture and growth of the oxidation layer is thought to be responsible for grain refinement.