Showing papers on "Isotropic etching published in 2019"

High-Temperature Behavior and Surface Chemistry of Carbide MXenes Studied by Thermal Analysis

Abstract: Two-dimensional (2D) transition-metal carbides and nitrides (MXenes) have attracted significant attention due to their electronic, electrochemical, chemical, and optical properties. However, understanding of their thermal stability is still lacking. To date, MXenes are synthesized via top-down wet chemical etching, which intrinsically results in surface terminations. Here, we provide detailed insight into the surface terminations of three carbide MXenes (Ti3C2Tx, Mo2CTx, and Nb2CTx) by performing thermal gravimetric analysis with mass spectrometry analysis (TA–MS) up to 1500 °C under a He atmosphere. This specific technique enables probing surface terminations including hydroxyl (−OH), oxy (═O), and fluoride (−F) and intercalated species, such as salts and structural water. The MXene hydrophilicity depends on the type of etching (hydrofluoric acid concentration and/or mixed acid composition) and subsequent delamination conditions. We show that the amount of structural water in Ti3C2Tx increases with decre...

Three-dimensional femtosecond laser nanolithography of crystals

Abstract: So far, nanostructuring of hard optical crystals has been exclusively limited to their surface, as stress-induced crack formation and propagation render high-precision volume processes ineffective1,2. Here, we show that the rate of nanopore chemical etching in the popular laser crystals yttrium aluminium garnet and sapphire can be enhanced by more than five orders of magnitude (from <0.6 nm h−1 to ~100 µm h−1) by the use of direct laser writing, before etching. The process makes it possible to produce arbitrary three-dimensional nanostructures with 100 nm feature sizes inside centimetre-scale laser crystals without brittle fracture. To showcase the potential of the technique we fabricate subwavelength diffraction gratings and nanostructured optical waveguides in yttrium aluminium garnet and millimetre-long nanopores in sapphire. The approach offers a pathway for transferring concepts from nanophotonics to the fields of solid-state lasers and crystal optics. Direct laser writing is shown to dramatically enhance the chemical etch rate of laser crystals yttrium aluminium garnet and sapphire, allowing nanostructuring.

Investigation of electrochemical post-processing procedure for Ti-6Al-4V lattice structure manufactured by direct metal laser sintering (DMLS)

Abstract: Additive manufacturing has become very popular nowadays to create complex geometries that cannot be achieved by any other manufacturing processes. The purpose of this study is to investigate and characterize the electrochemical polishing and chemical etching methods as a post-process treatment to improve the surface finish of lattice structures made from Ti-6Al-4V manufactured by direct metal laser sintering (DMLS). A lattice sample is designed with external and internal struts to compare the influence of the post-processing on different features. The post-processing parameters are studied via the Taguchi method. This work will provide critical information on the surface and geometrical characterization as well as the post-process treatment of a Ti-6Al-4V lattice. The metrological data will be analyzed to determine how the post-process treatment affects the surface finish, considering the final roughness and geometrical integrity of lattice samples. It is found that the material removal rate was more important at the edges, specifically on the external features. It was also confirmed that the average roughness is linked to the material removal for both processes. The more material is removed from the parts, the better the surface finish. It is also found that the etching process helps the electrochemical polishing go deeper inside the geometry.

High Aspect Ratio β-Ga2O3 Fin Arrays with Low-Interface Charge Density by Inverse Metal-Assisted Chemical Etching.

Abstract: β-Ga2O3, with a bandgap of ∼4.6–4.9 eV and readily available bulk substrates, has attracted tremendous interest in the wide bandgap semiconductor community. Producing high aspect ratio β-Ga2O3 3D n...

Vertical GaN Nanowires and Nanoscale Light-Emitting-Diode Arrays for Lighting and Sensing Applications

Abstract: For various lighting and monolithic sensor systems application, vertically aligned three-dimensional (3D) gallium nitride (GaN)- and indium gallium nitride (InGaN)/GaN-based LED nanowire arrays with sub-200 nm feature sizes (down to 35 nm) were fabricated using a nanosphere lift-off lithography (NSLL) technique combined with hybrid top-down etching (i.e., inductively coupled plasma dry reactive ion etching (ICP-DRIE) and wet chemical etching). Owing to the lithographic opening and well-controlled surface functionalization prior to the polystyrene nanosphere (PN) deposition, vertical GaN nanowire arrays with an area density of 9.74 × 108 cm–2 and an aspect ratio of >10 could be realized in a specified large area of 1.5 × 1.5 mm2. Optoelectrical characteristics of the nanoLEDs were further investigated in cathodoluminescence (CL) measurements, in which multiquantum well (MQW) shows a clear CL-emission at a wavelength of 465 nm. Thus, using NSLL to manufacture low-cost but highly ordered 3D GaN-based nanowir...

High‐Density Sb2Te3 Nanopillars Arrays by Templated, Bottom‐Up MOCVD Growth

Abstract: Sb2 Te3 exhibits several technologically relevant properties, such as high thermoelectric efficiency, topological insulator character, and phase change memory behavior. Improved performances are observed and novel effects are predicted for this and other chalcogenide alloys when synthetized in the form of high-aspect-ratio nanostructures. The ability to grow chalcogenide nanowires and nanopillars (NPs) with high crystal quality in a controlled fashion, in terms of their size and position, can boost the realization of novel thermoelectric, spintronic, and memory devices. Here, it is shown that highly dense arrays of ultrascaled Sb2 Te3 NPs can be grown by metal organic chemical vapor deposition (MOCVD) on patterned substrates. In particular, crystalline Sb2 Te3 NPs with a diameter of 20 nm and a height of 200 nm are obtained in Au-functionalized, anodized aluminum oxide (AAO) templates with a pore density of ≈5 × 1010 cm-2 . Also, MOCVD growth of Sb2 Te3 can be followed either by mechanical polishing and chemical etching to produce Sb2 Te3 NPs arrays with planar surfaces or by chemical dissolution of the AAO templates to obtain freestanding Sb2 Te3 NPs forests. The illustrated growth method can be further scaled to smaller pore sizes and employed for other MOCVD-grown chalcogenide alloys and patterned substrates.

Superhydrophobicity on aluminum through reactive-etching and TEOS/GPTMS/nano-Al2O3 silane-based nanocomposite coating

Abstract: The aim of this work was achieving of superhydrophobicity on aluminum based on nano/micro hierarchical surface structure through chemical etching and subsequent coating. Hence, the micro-scale roughness was obtained by an ultrafast chemical reactive-etching of Al by CuCl2, and nano-scale roughness was obtained by nanoparticles decorating via a silane-based nanocomposite coating, which acts not only as a supporting matrix for nanoparticles but also acts as a protective layer. By functionalization using a fluoroalkylsilane (FAS) solution, the superhydrophobic nano/micro hierarchical surface structure was achieved with the water contact angle (WCA) and water contact angle hysteresis (WCAH) of 164° and 2.5°, respectively. The silane-based layer has been prepared by sol-gel method using a hybrid of Tetraethylorthosilicate (TEOS), and 3Glycidyloxypropyltrimethoxysilane (GPTMS) and the nanocomposite layer has prepared by addition of Al2O3 nanoparticles. The effect of functionalization of Al2O3 nanoparticles to prepare the highly dispersed nanoparticles within the silane layer has been investigated in details. The surface morphology was characterized by atomic force microscopy (AFM) as well as scanning electron microscopy (SEM), and the chemical bonding state was explored by Fourier transform infrared spectroscopy (FTIR). The robustness of hydrophobicity of the samples was analyzed by sandpaper abrasion test as well as corrosion mitigation evaluation using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The appropriate equivalent circuit model was asserted to analyze the EIS data, quantitatively. The results revealed that the incorporation of functionalized Al2O3 nanoparticles within the silane layer was able to create stable nano/micro hierarchical surface structure leading to the superhydrophobicity along with higher corrosion mitigation performance in comparison to the pure silane layer.

Fabrication of highly homogeneous and controllable nanogratings on silicon via chemical etching-assisted femtosecond laser modification

Abstract: Abstract Femtosecond laser direct writing is widely exploited in surface periodic structures processing. However, this technique still faces challenges in obtaining high surface homogeneity and flexible morphology controllability. In this study, a flexible and efficient approach has been proposed to fabricate highly homogeneous and controllable nanogratings on silicon via chemical etching-assisted femtosecond laser modification. By precisely manipulating the laser-material interaction process, alternating amorphous-crystalline nanofringes are generated when employing femtosecond laser scanning over a Si sample, with almost no material removal. Following auxiliary chemical etching, highly homogeneous nanograting structures are obtained, and the morphology of the nanogratings can be flexibly managed through precisely controlling the duration of the etching process. Complex cross-scale patterns with remarkable structural colors that are visible under indoor light illumination are readily achieved on the sample surfaces exploiting our method. In addition, compared with traditional methods for laser-induced periodic surface structures, the fabrication efficiency is considerably improved. Our processing procedure offers potential applications in the fields of optics, nanoelectronics, and mechatronics.

Preparation of Single-Crystal “House-of-Cards”-like ZSM-5 and Their Performance in Ethanol-to-Hydrocarbon Conversion

Abstract: The present study reports the unbiased chemical etching of micron-sized ZSM-5 crystals with an NH4F solution, resulting in house-of-cards-like single crystals containing large rectangular cavities ...

Preparation of corrosion-resisting superhydrophobic surface on aluminium substrate

Abstract: A superhydrophobic surface with micro-nano rough structure and corrosion-resisting property was prepared on aluminium substrate by a simple one-step wet chemical etching in HCl solution and in situ...

Etching silver nanoparticles using DNA

Abstract: While DNA has been widely used for directing the growth and assembly of nanomaterials, the reverse reaction, etching nanoparticles using DNA, has yet to be demonstrated. We herein communicate that poly-cytosine (poly-C) DNA can efficiently etch silver nanoparticles (AgNPs) followed by Ostwald ripening at higher DNA concentrations. The etching process was precisely controlled by varying the length, sequence, and concentration of DNA, and the number of consecutive cytosines is particularly important for the efficacy of etching. In addition to spherical AgNPs, etching also occurred for silver nanoplates displaying interesting color changes. Compared to other chemical etching agents such as H2O2 and ferricyanide, DNA is highly biocompatible, allowing biological applications. Poly-C etching enhanced the cytotoxicity of AgNPs against cancer cells, and Gram-positive and Gram-negative bacterial cells. This study will stimulate many related studies in DNA nanotechnology, bioanalytical sensors and nanomedicine.

Hybrid Anodic and Metal-Assisted Chemical Etching Method Enabling Fabrication of Silicon Carbide Nanowires

Abstract: Silicon carbide (SiC) is one of the most important third-generation semiconductor materials. However, the chemical robustness of SiC makes it very difficult to process, and only very limited methods are available to fabricate nanostructures on SiC. In this work, a hybrid anodic and metal-assisted chemical etching (MACE) method is proposed to fabricate SiC nanowires based on wet etching approaches at room temperature and under atmospheric pressure. Through investigations of the etching mechanism and optimal etching conditions, it is found that the metal component plays at least two key roles in the process, i.e., acting as a catalyst to produce hole carriers and introducing band bending in SiC to accumulate sufficient holes for etching. Through the combined anodic and MACE process the required electrical bias is greatly lowered (3.5 V for etching SiC and 7.5 V for creating SiC nanowires) while enhancing the etching efficiency. Furthermore, it is demonstrated that by tuning the etching electrical bias and time, various nanostructures can be obtained and the diameters of the obtained pores and nanowires can range from tens to hundreds of nanometers. This facile method may provide a feasible and economical way to fabricate SiC nanowires and nanostructures for broad applications.

Synthesis of (V 2/3 Sc 1/3 ) 2 AlC i-MAX phase and V 2−x C MXene scrolls

Abstract: We report the synthesis and characterization of a new laminated i-MAX phase, (V2/3Sc1/3)2AlC, with in-plane chemical ordering between the M-elements. We also present evidence for the solid solution (V2-xScx)2AlC, where x ≤ 0.05. Chemical etching of the Al and Sc results in a two-dimensional (2D) MXene counterpart: V2-xC from the latter phase. Furthermore, etching with HF yields single-sheet MXene of flat morphology, while LiF + HCl gives MXene scrolls. We also show a 4× reduction in etching time for (V2-xScx)2AlC compared to V2AlC, suggesting that traces of Sc changes the phase stability, and make the material more susceptible to etching. The results show a path for improved control of MXene synthesis and morphology, which may be applicable also for other MAX/MXene systems.

Thermal atomic layer etching of crystalline GaN using sequential exposures of XeF2 and BCl3

Abstract: Gallium nitride (GaN) is a wide-bandgap semiconductor that is useful for optoelectronics and high speed and high power electronics. Fabrication of GaN devices requires etching for many processing steps. Gas phase thermal atomic-layer-controlled etching is desirable for damage-free isotropic etching. In this letter, the thermal atomic layer etching (ALE) of crystalline GaN was demonstrated using sequential exposures of XeF2 and BCl3. GaN ALE was achieved with an etch rate of 0.55 A/cycle at 195 °C using XeF2 exposures for 20 s at 40 mTorr and BCl3 exposures for 0.5 s at 50 mTorr. At the same reactant exposures, GaN etch rates varied with temperature from 0.18 A/cycle at 170 °C to 0.72 A/cycle at 300 °C. The GaN etch rates increased slowly with increasing XeF2 exposure. In addition, the GaN etch rate was self-limiting with respect to both increasing BCl3 pressures and BCl3 exposure times. This self-limiting behavior for BCl3 is consistent with a ligand-exchange mechanism for GaN ALE. Alternative fluorination reactants were also investigated including HF, SF4, and NF3 plasma. Sequential exposures of NF3 plasma and BCl3 yielded GaN etch rates of 2.5–2.9 A/cycle at 250 °C. In contrast, the HF and SF4 fluorination reactants could not etch crystalline GaN.

CMOS-Compatible Catalyst for MacEtch: Titanium Nitride-Assisted Chemical Etching in Vapor phase for High Aspect Ratio Silicon Nanostructures.

Abstract: Metal-assisted chemical etching (MacEtch) is an emerging anisotropic chemical etching technique that has been used to fabricate high aspect ratio semiconductor micro- and nanostructures. Despite it...

Effect of MACE Parameters on Electrical and Optical Properties of ALD Passivated Black Silicon

Abstract: Metal-assisted chemical etching (MACE) enables efficient texturing of diamond-wire sawn multicrystalline silicon wafers. However, the excellent optics are often sacrificed by polishing the surface to achieve better surface passivation with chemical-vapor-deposited (CVD) silicon nitride (SiN x ). In this paper, we show that a polishing step is not required when CVD SiN x is replaced with atomic-layer-deposited (ALD) aluminum oxide (Al2O3). Indeed, while polishing increases reflectance, it has in general only very modest effect on surface recombination velocity of ALD-passivated b-Si. Furthermore, since ALD Al2O3 is compatible with various surface morphologies due to its excellent conformality, the MACE parameters can be more freely adjusted. First, the concentration of silver nitrate (AgNO3) in AgNO3/H2O solution that is used to deposit Ag nanoparticles is shown to affect the final b-Si morphology. Instead of needle-shaped b-Si produced by 5 mmol/L AgNO3 concentration, two orders of magnitude lower AgNO3 concentration produces porous structures, which are more challenging to passivate. Additionally, we demonstrate that a separate Ag nanoparticle removal step in nitric acid (HNO3) is not a prerequisite for high carrier lifetime. Instead, Ag nanoparticles present during polishing in a HF/HNO3/H2O solution affect the final b-Si morphology by accelerating the etching of Si. The results demonstrate that no tradeoffs are necessary between optical and electrical properties of MACE b-Si when using ALD.

Optimization of selective laser-induced etching (SLE) for fabrication of 3D glass microfluidic device with multi-layer micro channels

Abstract: We present the selective laser-induced etching (SLE) process and design guidelines for the fabrication of three-dimensional (3D) microfluidic channels in a glass. The SLE process consisting of laser direct patterning and wet chemical etching uses different etch rates between the laser modified area and the unmodified area. The etch selectivity is an important factor for the processing speed and the fabrication resolution of the 3D structures. In order to obtain the maximum etching selectivity, we investigated the process window of the SLE process: the laser pulse energy, pulse repetition rate, and scan speed. When using potassium hydroxide (KOH) as a wet etchant, the maximum etch rate of the laser-modified glass was obtained to be 166 μm/h, exhibiting the highest selectivity about 333 respect to the pristine glass. Based on the optimized process window, a 3D microfluidic channel branching to three multilayered channels was successfully fabricated in a 4 mm-thick glass. In addition, appropriate design guidelines for preventing cracks in a glass and calibrating the position of the dimension of the hollow channels were studied.

Intermediate Structures of Pt-Ni Nanoparticles during Selective Chemical and Electrochemical Etching.

Abstract: Both chemical and electrochemical etching are effective methods for tailoring the surface composition of Pt-based catalytic bimetallic nanoparticles (NPs). However, the detailed nanoscale etching mechanisms, which are needed for achieving fine control over the etch processes, are still not understood. Here, we study selective chemical and electrochemical Ni etching of Pt-Ni rhombic dodecahedron NPs using in situ liquid-phase transmission electron microscopy. Our real-time observations show that the intermediate NP structures evolve differently in the two cases. Chemical etching of Ni starts from localized pits on the NP surface, in contrast to the uniform dissolution of Ni during the electrochemical etching. Our study reveals how oxidative etching participates in the removal of a non-noble metal and the subsequent formation of noble-metal-rich NPs. The mechanistic insights reported here highlight the role of a native surface oxide layer on the etching behavior, which is important for the design of NPs with specific surface composition for applications in electrocatalysis.