Showing papers on "Isotropic etching published in 2020"

Exfoliation and Defect Control of Two-Dimensional Few-Layer MXene Ti3C2Tx for Electromagnetic Interference Shielding Coatings.

Abstract: Defect-controlled exfoliation of few-layer transition-metal carbide (f-Ti3C2Tx) MXene was demonstrated by optimizing chemical etching conditions, and electromagnetic interference (EMI) shielding coatings were explored. The structural features such as layer morphology, lateral size, layer thickness, defect density, and mechanical stability of the exfoliated f-Ti3C2Tx were strongly dependent on exfoliation conditions. By selecting appropriate exfoliation conditions, moderate etching time leads to the formation of quality f-Ti3C2Tx with lesser defects, whereas longer etching time can break the layer structure and increase defect density, structural misalignment, and oxidative products of f-Ti3C2Tx. The resultant fabricated free-standing flexible f-Ti3C2Tx films exhibited electrical conductivity and electromagnetic interference (EMI) shielding effectiveness (SE) in the X-band of about 3669 ± 33 S/m and 31.97 dB, respectively, at a thickness of 6 μm. The large discrepancy in EMI SE performance between quality (31.97 dB) and defected (3.164 dB) f-Ti3C2Tx sheets is attributed to interconnections between f-Ti3C2Tx nanolaminates interrupted by defects and oxidative products, influencing EMI attenuation ability. Furthermore, the demonstrated solution-processable high-quality f-Ti3C2Tx inks are compatible and, when applied for EM barrier coating on various substrates, including paper, cellulose fabric, and PTFE membranes, exhibited significant EMI shielding performance. Moreover, controlling defects in f-Ti3C2Tx and assembly of heterogeneous disordered carbon-loaded TiO2-Ti3C2Tx ternary hybrid nanostructures from f-Ti3C2Tx by tuning etching conditions could play an enormous role in energy and environmental applications.

Metal assisted chemical etching of silicon in the gas phase: a nanofabrication platform for X-ray optics

Abstract: High aspect ratio nanostructuring requires high precision pattern transfer with highly directional etching. In this work, we demonstrate the fabrication of structures with ultra-high aspect ratios (up to 10 000 : 1) in the nanoscale regime (down to 10 nm) by platinum assisted chemical etching of silicon in the gas phase. The etching gas is created by a vapour of water diluted hydrofluoric acid and a continuous air flow, which works both as an oxidizer and as a gas carrier for reactive species. The high reactivity of platinum as a catalyst and the formation of platinum silicide to improve the stability of the catalyst pattern allow a controlled etching. The method has been successfully applied to produce straight nanowires with section size in the range of 10–100 nm and length of hundreds of micrometres, and X-ray optical elements with feature sizes down to 10 nm and etching depth in the range of tens of micrometres. This work opens the possibility of a low cost etching method for stiction-sensitive nanostructures and a large range of applications where silicon high aspect ratio nanostructures and high precision of pattern transfer are required.

Continuous and pulsed selective laser melting of Ti6Al4V lattice structures: Effect of post-processing on microstructural anisotropy and fatigue behaviour

Abstract: Additive manufacturing technologies in general and laser powder bed fusion (L-PBF) in particular have been on the rise in different applications, including biomedical implants. The effects of the various l -PBF process parameters on the microstructure and properties of Ti6Al4V lattice structures have been studied before. However, the relationship between the different modes of laser scanning and the resulting microstructure, internal imperfections, and surface morphology is still underexplored. In this study, the aforementioned parameters and their effect on the compressive mechanical properties and fatigue behaviour of lattice titanium have been studied for both continuous and pulsed laser scanning modes. Moreover, the influence of various combinations of post-processing treatments, such as hot isostatic pressing (HIP), sandblasting, and chemical etching, on the quasi-static mechanical properties and fatigue endurance of the resulting materials were investigated. It was found that continuous laser strategy results in fewer imperfections and higher fatigue resistance, while pulsed laser showed a more homogenous microstructure; likely leading to a more isotropic behaviour. Furthermore, the continuous mode showed larger prior β grains preferentially oriented in the building direction, while pulsed specimens exhibited finer equiaxed grains with no preferred orientations. The highest level of fatigue life was obtained by using an optimized combination of HIP, sandblasting, and chemical etching.

Large-Scale Synthesis of Highly Uniform Silicon Nanowire Arrays Using Metal-Assisted Chemical Etching.

Abstract: The combination of metal-assisted chemical etching (MACE) with colloidal lithography has emerged as a simple and cost-effective approach to nanostructure silicon. It is especially efficient at synthesizing Si micro- and nanowire arrays using a catalytic metal mesh, which sinks into the silicon substrate during the etching process. The approach provides a precise control over the array geometry, without requiring expensive nanopatterning techniques. Although MACE is a high-throughput solution-based approach, achieving large-scale homogeneity can be challenging because of the instability of the metal catalyst when the experimental parameters are not set appropriately. Such instabilities can lead to metal film fracture, significantly damaging the substrate and thus compromising the nanowire array quality. Here, we report on the critical parameters that influence the stability of the metal catalyst layer for achieving large-scale homogeneous MACE: etchant composition, metal film thickness, adhesion layer thickness, nanowire diameter and pitch, metal film coverage, Si/Au/etchant interface length, and crystalline quality of the colloidal template (grain size and defects). Our results investigate the origin of the catalyst film fracture and reveal that MACE experiments should be optimized for each Si wire array geometry by keeping the etch rate below a certain threshold. We show that the Si/Au/etchant interface length also affects the etch rate and should thus be considered when optimizing the MACE experimental parameters. Finally, our results demonstrate that colloidal templates with small grain sizes (i.e., <100 μm2) can yield significant problems during the pattern transfer because of a high density of defects at the grain boundaries that negatively affects the metal film stability. As such, this work provides guidelines for the large-scale synthesis of Si micro- and nanowire arrays via MACE, relevant for both new and experienced researchers working with MACE.

Morphology-Graded Silicon Nanowire Arrays via Chemical Etching: Engineering Optical Properties at the Nanoscale and Macroscale.

Abstract: We report on a quick, simple, and cost-effective solution-phase approach to prepare centimeter-sized morphology-graded vertically aligned Si nanowire arrays. Gradients in the nanowire diameter and ...

Recent Progress of Black Silicon: From Fabrications to Applications.

Abstract: Since black silicon was discovered by coincidence, the special material was explored for many amazing material characteristics in optical, surface topography, and so on. Because of the material property, black silicon is applied in many spheres of a photodetector, photovoltaic cell, photo-electrocatalysis, antibacterial surfaces, and sensors. With the development of fabrication technology, black silicon has expanded in more and more applications and has become a research hotspot. Herein, this review systematically summarizes the fabricating method of black silicon, including nanosecond or femtosecond laser irradiation, metal-assisted chemical etching (MACE), reactive ion etching (RIE), wet chemical etching, electrochemical method, and plasma immersion ion implantation (PIII) methods. In addition, this review focuses on the progress in multiple black silicon applications in the past 10 years. Finally, the prospect of black silicon fabricating and various applications are outlined.

Microfabrication of X-ray Optics by Metal Assisted Chemical Etching: A Review.

Abstract: High-aspect-ratio silicon micro- and nanostructures are technologically relevant in several applications, such as microelectronics, microelectromechanical systems, sensors, thermoelectric materials, battery anodes, solar cells, photonic devices, and X-ray optics. Microfabrication is usually achieved by dry-etch with reactive ions and KOH based wet-etch, metal assisted chemical etching (MacEtch) is emerging as a new etching technique that allows huge aspect ratio for feature size in the nanoscale. To date, a specialized review of MacEtch that considers both the fundamentals and X-ray optics applications is missing in the literature. This review aims to provide a comprehensive summary including: (i) fundamental mechanism; (ii) basics and roles to perform uniform etching in direction perpendicular to the Si substrate; (iii) several examples of X-ray optics fabricated by MacEtch such as line gratings, circular gratings array, Fresnel zone plates, and other X-ray lenses; (iv) materials and methods for a full fabrication of absorbing gratings and the application in X-ray grating based interferometry; and (v) future perspectives of X-ray optics fabrication. The review provides researchers and engineers with an extensive and updated understanding of the principles and applications of MacEtch as a new technology for X-ray optics fabrication.

Elucidating the Effect of Etching Time Key-Parameter toward Optically and Electrically-Active Silicon Nanowires.

Abstract: In this work, vertically aligned silicon nanowires (SiNWs) with relatively high crystallinity have been fabricated through a facile, reliable, and cost-effective metal assisted chemical etching method. After introducing an itemized elucidation of the fabrication process, the effect of varying etching time on morphological, structural, optical, and electrical properties of SiNWs was analysed. The NWs length increased with increasing etching time, whereas the wires filling ratio decreased. The broadband photoluminescence (PL) emission was originated from self-generated silicon nanocrystallites (SiNCs) and their size were derived through an analytical model. FTIR spectroscopy confirms that the PL deterioration for extended time is owing to the restriction of excitation volume and therefore reduction of effective light-emitting crystallites. These SiNWs are very effective in reducing the reflectance to 9–15% in comparison with Si wafer. I–V characteristics revealed that the rectifying behaviour and the diode parameters calculated from conventional thermionic emission and Cheung’s model depend on the geometry of SiNWs. We deduce that judicious control of etching time or otherwise SiNWs’ length is the key to ensure better optical and electrical properties of SiNWs. Our findings demonstrate that shorter SiNWs are much more optically and electrically active which is auspicious for the use in optoelectronic devices and solar cells applications.

Ultrafast Microwave Activating Polarized Electron for Scalable Porous Al toward High-Energy-Density Batteries

Abstract: Chemical etching of metals generally brings about undesirable surface damage accompanied by deteriorated performance. However, new possibilities in view of structured interfaces and functional surfaces can be explored by wisely incorporating corrosion chemistry. Here, an ultrafast route to scalable Al foils with desired porous structures originating from Fe(III)-induced oxidation etching was presented. Coupling with efficient electron polarization involving microwave interaction, straightforward surface engineering is well established on various commercial Al foils within minutes, which can be successfully extended to bulk Al alloys. As a proof-of-concept demonstration, the well-defined porous Al foils featuring regulated surface energy, demonstrate great potential as current collectors in promoting cycling stability, for example, 85.2% reversible capacity sustained after 550 cycles (comparable to commercial Al/C foils), and energy density, that is, approximately 3 times of that by using pristine Al foils for LiFePO4-Li half cells.

Structural effects of silver-nanoprism-decorated Si nanowires on surface-enhanced Raman scattering.

Abstract: Surface enhanced Raman scattering (SERS) is an important analytical tool for the optochemical detection of molecules. The enhancement is commonly achieved by engineering (i) novel types and morphologies of plasmonic nanomaterials, and (ii) patterned or roughened supporting substrates of high surface area for increased light scattering and molecule adsorption. Si substrates can be easily and reproducibly textured for effective SERS applications. In this work, silver nanoprisms (AgNPr) coated silicon nanowire (SiNWs) of different morphologies have been prepared by metal-assisted chemical etching and tested for SERS detection of R6G dye. By varying the etching time from 5 to 30 min, the nanowires' lengths increased from 2.4 to 10.5 µm and resulted in a variable topological morphology of the substrates in terms of bundles and valleys. We found that an optimum of 10 min etching time led to the highest SERS enhancement of R6G on AgNPr/SiNWs at 612 cm-1 Raman shift (30× compared to R6G/Si and 2× compared to R6G/AgNPr/Si), with a detection limit comparable to that of state-of-the-art performances (down to 5×10-10 M of R6G). Such an enhancement is attributed to a middle ground between increased overall surface area of SiNWs, and the available bundle tops trapping the AgNPr and R6G molecules.

Robust and Chemically Stable Superhydrophobic Aluminum-Alloy Surface with Enhanced Corrosion-Resistance Properties

Abstract: We report a simple method for fabricating micro-nanoscale structures consisting of irregular microscale plateaus with a self-assembled network of zinc oxide nanopetals on an aluminum alloy substrate. The method involves a combination of chemical etching with a hydrothermal process, followed by Polydimethylsiloxane coating via a simple vapor deposition method. Following the coating, surface displays superhydrophobicity with water contact angle of 161° and a sliding angle of 4°. The effect of morphological changes on wettability is examined by varying the hydrothermal processing time. The chemical stability of the superhydrophobic surfaces is examined in a wide range of corrosive media. After being immersed in a 3.5 wt% NaCl solution for 1 month, the surface retained its superhydrophobicity. The potentiodynamic polarization test results reveal that the superhydrophobic surface highly improves the corrosion resistance performance of the bare aluminum surface by three orders of magnitude. In addition, surface exhibited good mechanical durability against sandpaper abrasion, and long-term stability in the ambient environment. The proposed fabrication technique operating at relatively low temperature is simple and provides a new approach for production of large-scale three-dimensional superhydrophobic surfaces for various applications.

Mechanistic insight in site-selective and anisotropic etching of prussian blue analogues toward designable complex architectures for efficient energy storage

Abstract: Engineering coordination compounds, e.g., prussian blue (PB) and its analogues (PBAs), with designable complex nanostructures via chemical etching holds great opportunities for improving energy storage performances by adjusting topological geometry, selectively exposing active sites, tuning electronic properties and enhancing accessible surface area. Unfortunately, it remains ambiguous particularly on site-selective and anisotropic etching behaviors. Herein, for the first time, we propose that two distinct regions are formed inside NiCo PBA (NCP) cubes due to the competition between classical ion-by-ion crystallization and non-classical crystallization based on aggregation. Such a unique structure ultimately determines not only the etching position but also the anisotropic pathway by selectively exposing unprotected Ni sites. According to this principle, complex PBA architectures, including nanocages, open nanocubes (constructed by six cones sharing the same apex), nanocones, and chamfer nanocubes can be intentionally obtained. After thermal annealing, NCP nanocones are converted to morning glory-like porous architectures composed of NiO/NiCo2O4 heterostructures with a mean particle size of 5 nm, which show improved rate performance and cycling stability.

Fabrication of micro–nano-roughened surface with superhydrophobic character on an aluminium alloy surface by a facile chemical etching process

Abstract: In the present work, we have fabricated a superhydrophobic surface on aluminium alloy 2024 through a simple immersion chemical etching method in hydrochloric acid followed by a functionalization step in stearic acid solution. The impact of etching time on water contact angle was investigated and a contact angle of $$\sim $$ 167 $$^{{\circ }}$$ was reached on the superhydrophobic surface, which was etched for 4 min. Morphology of the surface was evaluated by scanning electron microscopy and the surface chemical analysis was performed by energy-dispersive X-ray spectroscopy and Raman spectroscopy. We show that the fabricated superhydrophobic samples can besides water, also repel other liquids. We also demonstrate the self-cleaning properties of the fabricated samples using graphite particles as contaminants. Ultimately, we assessed the corrosion resistance properties of the fabricated surfaces by the potentiodynamic polarization method. The superhydrophobic surface exhibited increased corrosion potential and polarization resistance along with reduced corrosion current density, all of which are indicative of a significant improvement in corrosion performance of the superhydrophobic surface in comparison with typical aluminium 2024. The cheap and facile superhydrophobic surface fabrication method presented in this study can be applied to large scale samples with no need for electricity or expensive raw materials.

Post-assembly dimension-dependent face-selective etching of fullerene crystals

Abstract: Herein, we report the face-selective chemical etching of fullerene crystals in solvent under ambient conditions of temperature and pressure. First, fullerene C60 nanorods (FNRs), fullerene C60 nanosheets (FNSs) and fullerene C70 cubes (FCs) were prepared using ultrasound assisted liquid–liquid interfacial precipitation (ULLIP). Chemical etching of these crystals was then performed using ethylene diamine (EDA), which results in selective etching at the ends of FNRs forming hollow-structured fullerene nanotubes. For two dimensional FNSs, etching occurs mostly at the upper and lower surfaces of the sheets with partial etching at the edges. For three dimensional FCs, etching occurs on all faces of the cubes leading to the formation of objects with a gyroid-like morphology. In addition to the excellent water dispersibility due to EDA functionalization, chemically etched fullerene nanostructures showed excellent vapor sensing performance selective for acid vapors (formic or acetic acids) over aromatic vapors (benzene or toluene). In contrast to the established yet costly lithography techniques used to make microstructures, this is a simple and scalable solution process, and it presents a low-cost strategy for which we have coined the term ‘beaker lithography’ for the construction of hollow fullerene nanostructures.

A generic approach of polishing metals via isotropic electrochemical etching

Abstract: Isotropic etching polishing (IEP), which is based on the merging of hemispherical holes that are formed by isotropic etching, is proposed in this study as a universal metal finishing approach. Modeling of the surface evolution during IEP is also carried out, and the formation of a metal surface is predicted. The etching anisotropy of titanium is experimentally studied, and the results show that isotropic etching can be realized under optimized conditions. Isotropic etching sites originate from a breakdown of the passivation layer. Both the density and growth rate of the holes are affected by the current, and a large etching current is preferred for the realization of highly efficient polishing. IEP has been shown to be effective and efficient for surface finishing of TA2. The surface Sa roughness is drastically reduced from 64.1 nm to 1.2 nm, and a maximum polishing rate of 15 μm/min is achieved under an etching current of 3 A. IEP has also been successfully applied for surface finishing of other metals, including TC4, stainless steel 304, aluminum alloy 6063 and pure nickel, demonstrating that IEP can be considered a universal approach for finishing metals.