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As an emerging fringe science, bionics integrates the understanding of nature, imitation of nature, and surpassing nature in one aspect, and it organically combines the synergistic complementarity of function and structure–function integrated materials which is of great scientific interest. By imitating the microstructure of a natural biological surface, the bionic superhydrophobic surface prepared by human beings has the properties of self-cleaning, anti-icing, water collection, anti-corrosion and oil–water separation, and the preparation research methods are increasing. The preparation methods of superhydrophobic surface include vapor deposition, etching modification, sol–gel, template, electrostatic spinning, and electrostatic spraying, which can be applied to fields such as medical care, military industry, ship industry, and textile. The etching modification method can directly modify the substrate, so there is no need to worry about the adhesion between the coating and the substrate. The most obvious advantage of this method is that the obtained superhydrophobic surface is integrated with the substrate and has good stability and corrosion resistance. In this article, the different preparation methods of bionic superhydrophobic materials were summarized, especially the etching modification methods, we discussed the detailed classification, advantages, and disadvantages of these methods, and the future development direction of the field was prospected.

Silicon nanowires (SiNWs) have a strong potential in many fields. The investigation of fabrication methods for SiNWs has attracted much attention in semiconductor applications. This paper proposes a metal-assisted chemical etching (MACE) method as a low-cost and simple method for fabrication of SiNWs. This method is based on the electroless metal deposition (EMD) principle. We have studied the conditions of MACE method for fabrication of SiNWs on (100) p-type silicon wafer. A 0.005 AgNO3 and 4.8 M HF solution is used for metal-assisted depositing of the silver nanodots. The etching process is achieved by etchant solution consisting of 4.8 M HF and different concentrations of H2O2. The effect of etching parameters, such as etching time, H2O2 concentration and the dipping time, are investigated. Taguchi with L9 orthogonal array is used by software package MINITAB 17 for designing the experiments. The results of scanning electron microscopy (SEM) observations shows the formation of the silicon nanowires. The effect of the different conditions on the size of the SiNWs is analyzed using S/N ratio and ANOVA approach. The results show that etching time was the most significant factor in the SiNWs fabrication.

The mechanical durability of a superhydrophobic aluminum alloy surface is an important indicator of its practical use. Herein, we propose a strategy to prepare a superhydrophobic 2024 aluminum alloy surface with highly enhanced mechanical durability by using a two-step chemical etching method, using a NaOH solution as the etchant in step one and a Na2CO3 solution as the etchant in step two. Robust mechanical durability was studied by static contact angle tests before and after an abrasion test, potentiodynamic polarization measurements after an abrasion test and electrochemical impedance spectroscopy tests after an abrasion test. Furthermore, the mechanism for enhanced mechanical durability was investigated through scanning of electron microscopy images, energy-dispersive X-ray spectra, Fourier transform infrared spectra and X-ray photoelectron spectra. The testing results indicate that a hierarchical rough surface consisting of regular micro-scale dents and some nano-scale fibers in the micro-scale dents, obtained with the two-step chemical etching method, contributes to highly enhanced mechanical durability. Meanwhile, the as-prepared superhydrophobic 2024 aluminum alloy surface retained a silvery color instead of the black shown on the superhydrophobic 2024 aluminum alloy surface prepared by a conventional one-step chemical etching method using NaOH solution as the etchant.

Although Si nanowires (NWs) arrays are superior candidates for visible light photocatalysis, reports about the photodegradation activity of various crystal-orientated Si NWs are still insufficient. Here, light-doped hydrogen-terminated Si NWs arrays with different crystal orientations were prepared via a metal-assisted chemical etching method (MACE), which simply modulated the concentration of the oxidizer, H2O2. Their dye photodegradation activities were systematically and comprehensively investigated. When compared with Si NWs arrays with crystal orientations of (110) and (111), Si NWs arrays with (100) crystal orientation exhibit a superior photodegradation activity and stability due to the anisotropy of optical and physical properties. The n-type Si NWs arrays exhibit better photodegradation activity than the p-type Si NWs arrays of the same crystal orientation and similar length. The results provide a further understanding of the synthesis of Si NWs arrays with various orientations, and the relationships between photodegradation activity/stability and crystal orientations.

Materials are either removed from or added to a device, usually in a selective manner with using thin and/or thick film manufacturing processes that transfer the lithographic patterns into integrated circuits (ICs) or three-dimensional micromachines. This study deals with material removal by chemically assisted mechanical micromachining. Two methods are used chemical mechanical machining method are introduced in this paper. One, mechanically assisted chemical etching, is applied to fabricate a micro beam such as cantilever, and another is chemically assisted mechanical micromachining to fabricate microstructure such as micropattern, microchannel. The results are discussed.

MXenes are a large family of two-dimensional materials that have attracted attention across many fields due to their desirable optoelectronic, biological, mechanical and chemical properties. There currently exist many synthesis procedures that lead to differences in flake size, defects and surface chemistry, which in turn affect their properties. Herein, we describe the steps to synthesize Ti 3 C 2 T x —the most important and widely used MXene, from a Ti 3 AlC 2 MAX phase precursor. The procedure contains three main sections: synthesis of Ti 3 AlC 2 MAX, wet chemical etching of the MAX in hydrofluoric acid/HCl solution to yield multilayer Ti 3 C 2 T x and its delamination into single-layer flakes. Three delamination options are described; these use LiCl, tertiary amines (tetramethyl ammonium hydroxide/ tetrabutyl ammonium hydroxide) and dimethylsulfoxide respectively. These procedures can be adapted for the synthesis of MXenes beyond Ti 3 C 2 T x . The MAX phase synthesis takes about 1 week, with the etching and delamination each requiring 2 d. This protocol requires users to have experience working with hydrofluoric acid, and it is recommended that users have experience with wet chemistry and centrifugation; characterization techniques such as X-ray diffraction and particle size analysis are also essential for the success of the protocol. While alternative synthesis methods, such as minimally intensive layer delamination, are desirable for certain MXenes (such as Ti 2 CT x ) or specific applications, this protocol aims to standardize the more commonly used hydrofluoric acid/HCl etching method, which produces Ti 3 C 2 T x with minimal concentration of defects and the highest conductivity and serves as a guideline for those working with MXenes for the first time. Key points MXenes are two-dimensional materials, the best known of which is Ti 3 C 2 T x . Many diverse and unique properties have been described for MXenes, but it is difficult to compare the data because their physical characteristics depend on their synthesis. This protocol provides a detailed guideline for the synthesis of a Ti 3 AlC 2 MAX phase precursor, wet chemical etching of MAX to yield multilayer Ti 3 C 2 T x and its delamination into single-layer flakes. MXenes are two-dimensional materials with diverse optoelectronic, biological, mechanical and chemical properties. This protocol describes how to prepare single-layer flakes of Ti 3 C 2 T x , the most important and widely used MXene, from a Ti 3 AlC 2 MAX phase precursor.

As high-precision flexible printed circuit boards (FPCBs) are required in electronic products, it is necessary to study wet chemical etching to obtain precise FPCBs with a 16-μm line pitch. First, a π-shaped FPCB model with 16-μm line pitch is established using the finite element method. The evolution of the Cu etching profile and the concentration and velocity distribution of the CuCl2 solution are then analyzed. To analyze the influence of conveyor speed and nozzle spray pressure on the Cu etching profile, wet chemical etching was tested along a horizontally conveyed line with CuCl2 as the acid etchant. The resulting profiles were analyzed by scanning electron microscopy. The experimental results agreed well with the simulation results, and the Cu etching profile obviously depended on both the conveyor speed and nozzle spray pressure. In addition, increasing the conveyor speed under constant nozzle spray pressure (0.16 MPa or 0.17 MPa) decreased the etching depth and increased the etching factor. In particular, when the conveyor speed was set to 3.8 m/min and the nozzle spray pressure raised to 0.18 MPa, the fabricated FPCB had a line pitch of 16 μm, an etching depth of 7.55 μm, and an etching factor of 6.45. This method can aid the selection of parameters for the wet chemical etching process, enabling the future manufacture of high-precision FPCBs and complex FPCB circuits.

Superhydrophobic surfaces (SHS) are attracting attention in many fields owing to their excellent advantages such as anti-freezing, corrosion prevention, and self-cleaning. However, to modify the surface structure, environmental pollution caused by complex processes and chemical treatment must be considered. In this study, the surface of polytetrafluoroethylene (PTFE) was plasma-treated using oxygen and argon plasma to change the surface structure without a complicated process. The PTFE surface was treated in two ways: plasma etching (PE) and reactive ion etching (RIE). The contact angle of the conventional PTFE surface was 113.8 ± 1.4°, but the contact angle of the manufactured surface was 152.3 ± 1.7° and 172.5 ± 1.2°. The chemical composition and physical structure of the samples produced were compared. The treated specimens had the same chemical composition as the specimen before treatment and exhibited differences in their surface structures. Therefore, it was determined that the change in the water repellency was due to the surface structure. After PE treatment, the specimen surface had a mountain range-like structure, and the RIE specimen had a more detailed structure than the PE specimen. The contact rate of water droplets decreased due to the difference in the structure of the specimen before and after treatment, and the increase in the surface contact angle was manifested. In order to confirm that the plasma treatment reduces surface energy, the shape of the liquid collision was observed using a high-speed camera, and the contact time was calculated to confirm water repellency. The contact time of the PE and RIE specimen was 24 milli-second (ms) and 18 ms, respectively. The high contact angle and low sliding angle of the RIE specimen made it easy to restore surface cleanliness in a self-cleaning experiment using graphite.

Solid-state milling has emerged as an alternative, sustainable approach for preparing virtually all classes of compounds and materials. In situ reaction monitoring is essential to understanding the kinetics and mechanisms of these reactions, but it has proved difficult to use standard analytical techniques to analyze the contents of the closed, rapidly moving reaction chamber (jar). Monitoring by Raman spectroscopy is an attractive choice, because it allows uninterrupted data collection from the outside of a translucent milling jar. It complements the already established in situ monitoring based on powder X-ray diffraction, which has limited accessibility to the wider research community, because it requires a synchrotron X-ray source. The Raman spectroscopy monitoring setup used in this protocol consists of an affordable, small portable spectrometer, a laser source and a Raman probe. Translucent reaction jars, most commonly made from a plastic material, enable interaction of the laser beam with the solid sample residing inside the closed reaction jar and collection of Raman-scattered photons while the ball mill is in operation. Acquired Raman spectra are analyzed using commercial or open-source software for data analysis (e.g., MATLAB, Octave, Python, R). Plotting the Raman spectra versus time enables qualitative analysis of reaction paths. This is demonstrated for an example reaction: the formation in the solid state of a cocrystal between nicotinamide and salicylic acid. A more rigorous data analysis can be achieved using multivariate analysis. This protocol describes how to set up and use Raman spectroscopy for monitoring the course of solid-state reactions in vibratory ball mills, which will help increase our understanding of the mechanisms and kinetics of mechanochemical reactions.

Wet anisotropic etching is extensively employed in silicon bulk micromachining to fabricate microstructures for various applications in the field of microelectromechanical systems (MEMS). In addition, it is most widely used for surface texturing to minimize the reflectance of light to improve the efficiency of crystalline silicon solar cells. In wet bulk micromachining, the etch rate is a major factor that affects the throughput. Slower etch rate increases the fabrication time and therefore is of great concern in MEMS industry where wet anisotropic etching is employed to perform the silicon bulk micromachining, especially to fabricate deep cavities and freestanding microstructures by removal of underneath material through undercutting process. Several methods have been proposed to increase the etch rate of silicon in wet anisotropic etchants either by physical means (e.g. agitation, microwave irradiation) or chemically by incorporation of additives. The ultrasonic agitation during etching and microwave irradiation on the etchants increase the etch rate. However, ultrasonic method may rupture the fragile structures and microwave irradiation causes irradiation damage to the structures. Another method is to increase the etching temperature towards the boiling point of the etchant. The etching characteristics of pure potassium hydroxide solution (KOH) is studied near the boiling point of KOH, while surfactant added tetramethylammonium hydroxide (TMAH) is investigated at higher temperature to increase the etch rate. Both these studies have shown a potential way of increasing the etch rate by elevating the temperature of the etchants to its boiling point, which is a function of concentration of etch solution. The effect of various kinds of additives on the etch rate of silicon is investigated in TMAH and KOH. In this paper, the additives which improve the etch rate have been discussed. Recently the effect of hydroxylamine (NH2OH) on the etching characteristics of TMAH and KOH is investigated in detail. The concentration of NH2OH in TMAH/KOH is varied to optimize the etchant composition to obtain improved etching characteristics especially the etch rate and undercutting which are important parameters for increasing throughput. In this article, different methods explored to improve the etch rate of silicon have been discussed so that the researchers/scientists/engineers can get the details of these methods in a single reference.