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Ridge microstructures were prepared by etching through samples consisting of a series of stacked InAs x P 1 − x quantum wells (QWs) with step graded composition grown on InP by molecular beam epitaxy. Different etching techniques were used: wet etching with HCl/H 2 O and reactive ion etching with CH 4 /H 2. These microstructures were characterized by low-temperature micro-photoluminescence. The photoluminescence (PL) emission associated with each QW was clearly identified. The PL was measured in detail across etched ridge stripes of various widths. Variations of the integrated PL intensities across the etched stripes were observed. The PL intensities for all QWs increase gradually from the edge to the center of the ridge microstructures. The PL intensity measured at the ridge center is systematically reduced for ridges which are 10 or 20 μ m wide as compared to ridges which are 30 μ m wide or larger. On the other hand, the spectral peak position of the PL lines remained constant with high accuracy (0.2–0.4 meV) across the microstructures. These observations are discussed in terms of the different possible mechanisms which determine the PL intensity variations, namely, non-radiative recombination at the etched walls and effects of stray electric fields which result from the etching process. Based on this discussion, we compare quantitatively the different etching processes which we have used. Altogether, this study illustrates the contribution that specially designed test structures, coupled with advanced spectroscopic characterization, can provide to the development of semiconductor photonic devices (e.g., lasers or waveguides) involving etching processes. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate an in situ etch technique for β-Ga2O3 inside a metalorganic chemical vapor deposition (MOCVD) reactor using triethylgallium (TEGa) as the etching agent. At sufficiently high substrate temperatures (Tsub), TEGa is introduced into the MOCVD reactor which undergoes pyrolysis, resulting in the deposition of Ga on the β-Ga2O3 surface. These Ga adatoms react with Ga2O3 to form gallium suboxide (Ga2O), which desorbs from the β-Ga2O3 surface resulting in the etching of the epilayer. MOCVD chamber parameters such as TEGa molar flow rate, substrate temperature, and chamber pressure were shown to be key in controlling the etch rate and surface morphology. A wide range of etch rates from ∼0.3 to 8.5 μm/h is demonstrated by varying the etch parameters. In addition, smooth surface morphology on (010) and (001) β-Ga2O3 substrates is also demonstrated. This new etch technique could enable damage free fabrication of 3D structures like fins and trenches, which are key components in many β-Ga2O3 device structures. [ABSTRACT FROM AUTHOR]

Epitaxial growth of wurtzite AlN films on Si {111} results in 19% lattice misfit, which gives rise to a large density of threading dislocations with different recombination rates of electron–hole pairs. Here, we investigate types and distributions of threading dislocations of the MOVPE-grown 200 nm AlN/Si {111} film, whereby the dislocations are visualized using the technique of wet chemical etching. Atomic force microscopy suggests the existence of four different types of etch pits without any topological differences. Cross-sectional transmission electron microscope studies on etched samples are employed to associate the types of dislocations with the shapes of their etch pits. The recombination activity of individual dislocations was quantified by measuring the electron beam induced current and by correlative measurement of topography, secondary electron imaging, and the electron beam absorbed current. The strongest recombination activity was obtained for the m + c-type (mixed), c-type (screw), and a + c-type (mixed) threading dislocations, whereas the a-type (edge) threading dislocations were nearly recombination-inactive. [ABSTRACT FROM AUTHOR]

[Display omitted] It is critical and challenging to develop highly active and low cost bifunctional electrocatalysts for the hydrogen/oxygen evolution reaction (HER/OER) in water electrolysis. Herein, we propose cerium-vanadium-based hollow nanopillar arrays supported on nickel foam (CeV-HNA/NF) as bifunctional HER/OER electrocatalysts, which are prepared by etching the V metal–organic framework with Ce salt and then pyrolyzing. Etching results in multidimensional optimizations of electrocatalysts, covering substantial oxygen vacancies, optimized electronic configurations, and an open-type structure of hollow nanopillar arrays, which contribute to accelerating the charge transfer rate, regulating the adsorption energy of H/O-containing reaction intermediates, and fully exposing the active sites. The reconstruction of the electrocatalyst is also accelerated by Ce doping, which results in highly active hydroxy vanadium oxide interfaces. Therefore, extremely low overpotentials of 170 and 240 mV under a current density of 100 mA cm−2 are achieved for the HER and OER under alkaline conditions, respectively, with long-term stability for 300 h. An electrolysis cell with CeV-HNA/NF as both the cathode and anode delivers a small voltage of 1.53 V to achieve water electrolysis under 10 mA cm−2, accompanied by superior durability for 150 h. This design provides an innovative way to develop advanced bifunctional electrocatalysts for overall water electrolysis. [ABSTRACT FROM AUTHOR]

Electrochemical nanoimprinting (ECNI) is a microstructure fabrication technique that combines metal-assisted chemical etching (MaCE) with nanoimprint lithography. A significant advantage of ECNI over traditional MaCE is the reusability of the stamp and excellent pattern consistency. This work studies the effects of various etchant components on etching results, discussing the associative parameters separately. Experimental results demonstrate that ECNI successfully fabricates bi-layer microstructures with flat surface morphology, where the second layer has a feature size of 40 μ m and a depth of 12.5 μ m. These findings highlight ECNI's potential as a scalable method for producing complex multi-layer structures, positioning it as a promising solution for large-scale microfabrication of semiconductors. [ABSTRACT FROM AUTHOR]

The development of high-performance oxygen evolution reaction (OER) electrocatalysts based on earth-abundant elements is of great significance for the production of hydrogen fuel through water electrolysis. Herein, defect rich NiO nanosheet arrays were synthesized on nickel foam (NF) by rapidly quenching NiO in Al salt solution at 0 °C and followed by partially etching Al in alkaline solution. With the approach, the quenching can simultaneously achieve the required surface metal doping and generation of abundant oxygen vacancies. Moreover, more active sites can be provided for OER due to the leaching of Al during the etching process. As a result, the quenching-etching surface engineering endows the NiO catalyst with the desired advantages, including high conductivity and large specific surface area. The as-obtained optimal electrode (72h Al–NiO/NF) with an etching time of 72 h exhibited much enhanced electrocatalytic activity towards OER in alkaline solution, which needs a low overpotential of 277 mV to achieve 10 mA cm−2 water oxidation current. Furthermore, the catalyst also showed a very low Tafel slope of 51.8 mV dec−1 and excellent durability. The synthesis of defect rich NiO nanosheets through the quenching-etching route confirms the importance of elaborate engineering of material surface for high-performance OER. • Defect rich NiO nanosheet arrays grown on NF were successfully fabricated by a quenching-etching surface engineering route. • The obtained electrode successfully combined the desired merits, including high conductivity and large specific surface area. • The as-obtained 72h Al–NiO/NF shows superior activity, favorable reaction kinetics and robust durability for OER in alkaline media. [ABSTRACT FROM AUTHOR]

This study reveals a local strain‐dependent etching behavior that enables the formation of distinguished etching patterns in differently strained chemical vapor deposited (CVD) 2D molybdenum disulfide (MoS2) monolayers. It is demonstrated that when the local tensile strain of CVD 2D MoS2 is as uniformly low as ɛ ≈ 0.33% or less, the oxidative etching pattern possesses conventional triangular etching pits (TEPs), while when the local tensile strain is as uniformly high as ɛ ≈ 0.55% or larger, the oxidative etching pattern consist of uniformly oriented hexagonal etching channels (HECs). More interestingly, when the CVD 2D MoS2 monolayer has heterogenous strain distribution from ɛ ≈ 0.55% (center region) to ɛ ≈ 0.33% (perimeter region), the oxidative etching pattern comprise of non‐uniformly hexagonal‐mixed‐parallel etching channels (HPECs). The further characterization and analysis reveal the formation mechanism of such strain‐dependent etching patterns is built on the local strain‐related fractures propagation under oxidative etching, as well as the anisotropy fractures‐based oxidative etching kinetics. This study may enhance the understanding of the relationship between etching and growth features of 2D TMDs, and paves the way to etching‐nanostructured (or defect) engineering of 2D TMDs and other 2D materials for potential applications in electrocatalysis and optoelectronics. [ABSTRACT FROM AUTHOR]

A new wafer warpage model is proposed for the full process design of trench field‐plate (FP) power metal‐oxide‐semiconductor fileld‐effect transitors (MOSFETs) using large‐sized wafer. Trench FP power MOSFETs feature a deep trench and thick oxide at the wafer surface. Wafer warpage occurs due to the stress imbalance between the front and back sides of the wafer. This warpage leads to significant problems with transport errors in manufacturing equipment. This issue is expected to become even more crucial as lateral pitch narrowing is employed to reduce on‐resistance. In this study, two methods are compared to estimate the warpage of a 200 mm diameter Si‐wafer after trench etching and oxidation process. The mechanical stress generated by the oxidation process in several cell units is calculated using a 3D simulation. In the first approach, wafer warpage is converted from the displacement of the cell units. In the second approach, wafer warpage is estimated based on the surface film stress, which is calculated in the 3D simulation. The second approach shows good agreement with experimental results and is applicable to the 300 mm diameter Si process. This method yields more accurate measurements than the method using displacement. [ABSTRACT FROM AUTHOR]

An understanding of the structural changes induced by the ovalization treatment of diamonds is necessary to produce crystals with controlled sizes and morphologies. In this investigation, the treatment of natural diamonds in a rotary vortex apparatus was used to modify the surface morphology of the particles and obtain the ovalized crystals. The size of the starting diamond crystals was in the 250–350 μm range. In the product of treatment in the rotary vortex apparatus, particles with sizes above 300 μm were ovalized, while those with sizes below 300 μm demonstrated irregular shape. The formation of particles of irregular shape during the treatment was caused by the fracture of the starting diamond crystals along the defect regions. The ovalized crystals were formed by "blunting" the edges and vertices of the starting crystals under the action of friction forces. The ovalized diamond consisted of a crystalline core and a defect shell. The crystals were subjected to oxidative etching to reveal the structural changes of the surface layers caused by the ovalization treatment. During oxidative etching, the ovalized crystals developed a system of etch pits over the entire surface. In contrast, the oxidative etching of the starting (untreated) diamonds showed the facet selectivity. [ABSTRACT FROM AUTHOR]

We report a new image-based inter-analyst study to investigate fission-track grain selection and analysis by 13 participants from an image data set that included grains of variable quality. Results suggest that participants with less experience show a higher rate of selecting unsuitable grains, while participants from the same laboratories generally provide similar results. Less analysis experience may result in the rejection of suitable grains, or inclusion of unsuitable ones. While inappropriate omission and inclusion can both bias results, the latter is more pernicious due to the standard practice of achieving a predecided number of analyses; particularly in difficult samples, there is a danger of "squeezing the rock" by weakening selection criteria. Juxtaposing selected regions of interest (ROIs) on the same grains indicates that zoned grains and grains with inclusions and defects yield varying track density estimates, indicating that ROI placement can be an influential factor. We propose developing image data repositories for global data transparency, a global guidance for fission-track analysis, digital teaching modules, and open science. We also point out the need for new approaches for zeta calibration that include consideration of grain quality, methods of uranium determination, and etching protocols. [ABSTRACT FROM AUTHOR]

The influence of the etching method on the occurrence of defect levels in InAs/InAsSb type-II superlattice (T2SLs) and MCT photodiode is presented. For both analyzed detectors, the etching process was performed by two methods: wet chemical etching and dry etching using an ion beam (RIE—reactive ion etching). The deep-level transient spectroscopy (DLTS) method was used to determine the defect levels occurring in the analyzed structures. The obtained results indicate that the choice of etching method affects the occurrence of additional defect levels in the MCT material, but it has no significance for InAs/InAsSb T2SLs. [ABSTRACT FROM AUTHOR]

Layer number‐dependent band structures and symmetry are vital for the electrical and optical characteristics of 2D transition metal dichalcogenides (TMDCs). Harvesting 2D TMDCs with tunable thickness and properties can be achieved through top‐down etching and bottom‐up growth strategies. In this study, a pioneering technique that utilizes the migration of in situ generated Na‐W‐S‐O droplets to etch out 1D nanotrenches in few‐layer WS2 is reported. 1D WS2 nanotrenches are successfully fabricated on the optically inert bilayer WS2, showing pronounced photoluminescence and second harmonic generation signals. Additionally, the modulation of inkjet‐printed Na2WO4‐Na2SO4 particles to switch between the etching and growth modes by manipulating the sulfur supply is demonstrated. This versatile approach enables the creation of 1D nanochannels on 2D TMDCs. The research presents exciting prospects for the top‐down and bottom‐up fabrication of 1D‐2D mixed‐dimensional TMDC nanostructures, expanding their use for electronic and optoelectronic applications. [ABSTRACT FROM AUTHOR]

The creation of vacancies and/or pores into two‐dimensional materials, like graphene and MXenes, has shown to increase their performance for sustainable applications. However, a simple and affordable method with controlled and tailorable vacancy concentration and/or pores size remains challenging. Herein, a simple and reproducible method is presented for controlled synthesis of Mo1.74CTz MXene with randomly distributed vacancies and pores, obtained from selective etching of both Ga and Cr in the Cr‐alloyed MAX‐phase like precursor Mo1.74Cr0.26Ga2C. Structural and compositional analysis of the 3D alloy show ≈13% Cr on the metal site, homogeneously distributed between different particles and within the atomic structure. After etching, it translates to Mo1.74CTz MXene, exhibiting defect‐rich sheets. Notably, the incorporation of Cr facilitates a shorter etching time with an improved yield compared to Mo2CTz. The Mo1.74CTz MXene displays excellent electrochemical properties, almost doubling the capacitance values (1152 F cm−3 and 297 F g−1 at 2 mV s−1 scan rate), compared to its pristine counterpart Mo2CTz. The presented method and obtained results suggest defect engineering of MXenes through precursor alloying as a pathway that can be generalized to other phases, to further improve their properties for various applications. [ABSTRACT FROM AUTHOR]

The present work investigates the etching of coated polytetrafluoroethylene (PTFE) films using an atmospheric pressure dielectric barrier discharge operating in nitrogen in a filamentary regime. For different treatment durations, the optical emission spectra were recorded over time. Most of the emissions are attributed to the N2 second positive system. The presence of CN is also observed, and its emissions rise with the exposure time of PTFE. This rise is attributed to the density of CN produced. The X‐ray photoelectron spectroscopy surface characterization suggests two etching regimes. This is linked with a change in slope in the intensity evolution of the optical emissions of the CN. At longer times, a fluorinated deposit on the electrode is observed, confirming a different nature of the etched material. [ABSTRACT FROM AUTHOR]

Oxide/Nitride/Oxide/Nitride (ONON; SiO2/SiNx/SiO2/SiNx) stacked structure is widely used in the 3D vertical structure of semiconductor cells. Previously, to form a 3D cells, photoresist (PR) was patterned and repeatedly trimmed on the top of ONON after the etching of one ON layer. Due to the time-consuming process of etching layer-by-layer of ON layer, two-step etch processing using C4F8-based or C4F6-based gases composed of maskless ONON stack feature etching and followed one ON layer-by layer etching by PR trimming in the ONON stack feature are employed these days. However, the two-step etching method resulted in poor etch profiles of maskless ONON stack feature in addition to high global warming potential of C4F8 and C4F6. In this study, we investigated the etching of maskless ONON stack feature using C4H2F6-based gas having a low global warming potential and the effects of C4H2F6-based gas on the etch characteristics of maskless ONON stack feature such as etch rate, etch profile, change in critical dimensional (CD), and etch selectivity between SiO2 and SiNx have been investigated. C4H2F6-based gas showed the highest etch rates compared to C4F6 and C4F8-based gases in addition to the etch selectivity of ~ 1:1 between SiO2 and SiNx due to hydrogen included in the gas structure. In addition, the change in horizontal CD was lower in the order of C4H2F6, C4F6, and C4F8-based gases due to the more effective sidewall passivation in the order of C4F8, C4F6, and C4H2F6-based gases. The thicker carbon-based polymer layer on the sidewall also played an important role in maintaining the shape of the top edge shape of maskless ONON stack feature when etching a line feature in an environment without a mask. [ABSTRACT FROM AUTHOR]

The paper demonstrates the possibility of forming specific nanostructures of the "parquet" type of nanowires on the InP surface. The resulting nanostructure is characterised by an ordered transverse and longitudinal relative shift of separate nanowires. A dislocation model is proposed that explains the mechanism of such structure formation. The numerical estimates of the geometric parameters of the nanostructure obtained during theoretical modelling are quite adequate for the experimental results. [ABSTRACT FROM AUTHOR]

Diamond is renowned as the ultimate semiconductor thanks to its exceptional physical properties, including unmatched hardness, exceptional wear resistance, superior mechanical and tribological characteristics, and high fracture strength. Diamond solution-gate field-effect transistors (D-SGFETs) leverage these advantages, along with their outstanding high-power and high-frequency performance, excellent thermal conductivity, wide bandgap, high carrier mobility, and rapid saturation speed. These features make D-SGFETs highly promising for fast and precise biomedical detection applications. This paper provides a comprehensive review of the fabrication techniques for diamond SGFETs, encompassing diamond film synthesis, surface conduction layer formation, source/drain fabrication, and FET packaging. Furthermore, the study delves into the surface functionalization of diamond SGFETs and their diverse applications in biomedical detection. Finally, the paper discusses the future outlook of diamond SGFETs in advancing biomedical detection technologies. [ABSTRACT FROM AUTHOR]

Various alloys demand customized etchants due to their diverse chemical compositions, particularly in the realm of aluminum alloys. Consequently, in this study, a technique is proposed for metallographic visualization of small grain structures within Al–Mg–Zn–(Cu) crossover alloys. In this method, a thermal pretreatment combined with an etching process is relied on. In the study, it is primarily sought to comprehend how grain‐boundary precipitation affects etchability, addressing the complexities of characterizing these alloys. The demonstrated approach facilitates the swift assessment of grain sizes <10 μm using light optical microscopy. Exploring the etchability of Al–Mg–Zn–(Cu) crossover alloys across a standard heat‐treatment pathway identifies the optimal treatment and suitable etchant for grain visualization. Through process refinement, a reduction in processing time is achieved by employing a single‐step preheat treatment lasting 20 min at 180 °C post solution annealing. Transmission electron microscope analysis reveals continuous occupancy of the grain boundary with T‐phase as the key factor influencing the alloy's etchability. Grain size assessment involves line intercept counting and equivalent circle diameter measurement for precise characterization. [ABSTRACT FROM AUTHOR]

The integration of nanowires onto electrode surfaces marks a significant advancement over traditional electrode materials, conferring upon nanowire-modified electrodes a vast array of applications within electrochemical and electrophysical domains. The nanowires used for electrode modification can be catalogized into two distinct types: anchored nanowires and free-standing nanowires. A critical advantage of anchored nanowires lies in their enhanced electrical connectivity with the substrate, which reduces electrode resistance and facilitates charge transport. Furthermore, the anchorage of nanowires onto electrodes provides additional mechanical support, bolstering the structural stability of the nanowire assembly. Here, we review the development of anchored nanowires designed for applications in energy storage, electrocatalysis, and electric field treatment (EFT) over the past decade. We focus on the synthesis and modification strategies employed for anchored nanowires, culminating in the evaluation of these fabrication and enhancement techniques. Through this analysis, we aim to furnish comprehensive insights into the preparation of anchored nanowires, guiding the selection of appropriate fabrication processes and subsequent functional modifications. [ABSTRACT FROM AUTHOR]

All‐inorganic cesium lead halide flexible perovskite solar cells (f‐PSCs) exhibit superior thermal stability compared to their organic‐inorganic hybrid counterparts. However, their flexibility and efficiency are still below‐par for practical viability. This study presents an approach involving the introduction of multifunctional molecule ammonium benzenesulfonate (ABS) to selectively etch 0D‐Cs4Pb(IBr)6 from the mixed‐dimensional perovskite film surface, to attain more contact area between the perovskite and hole transport layer for improved hole extraction and transport. It is found that the ABS molecules bind to the perovskite lattice surface via O atoms and NH4+, effectively passivating surface defects and enhancing phase stability. The hydrophobic nature of the benzene ring in ABS further contributes to operational stability, leading to high cell efficiency of 15.00%, accompanied by enhanced operational stability. Even after undergoing 60 000 flexing cycles at a curvature radius of 5 mm, the ABS‐treated f‐PSC still retains over 98.5% of its initial efficiency. This multifunctional strategy for modifying typical mixed‐dimensional perovskite compositions significantly enhances the photovoltaic performance and stability of flexible all‐inorganic f‐PSCs. [ABSTRACT FROM AUTHOR]

A highly efficient ratiometric electrochemiluminescence (ECL) immunoassay was explored by bidirectionally regulating the ECL intensity of two luminophors. The immunoassay was conducted in a split-type mode consisting of an ECL detection procedure and a sandwich immunoreaction. The ECL detection was executed using a dual-disk glassy carbon electrode modified with two potential-resolved luminophors (g-C3N4-Ag and Ru-MOF-Ag nanocomposites), and the sandwich immunoreaction using glucose oxidase (GOx)-modified SiO2 nanospheres as labels was carried out in a 96-well plate. The Ag nanoparticles (NPs) acted as bifunctional units both for triggering the resonance energy transfer (RET) with g-C3N4 and for accelerating the electron transfer rate of the Ru-MOF-Ag ECL reaction. When the H2O2 catalyzed by GOx in the 96-well plate was transferred to the dual-disk glass carbon electrode, the doped Ag NPs in the two luminophors could be etched, thus destroying the RET between C3N4 and the accelerated reaction to Ru-MOF, resulting in an opposite trend in the ECL signal outputted from the dual disks. Using the ratio of the two signals for quantification, the constructed immunosensor for a model target, i.e. myoglobin, exhibited a low detection limit of 4.7 × 10–14 g/mL. The ingenious combination of ECL ratiometry, bifunctional Ag NPs, and a split-type strategy effectively reduces environmental and human errors, offering a more precise and sensitive analysis for complex samples. [ABSTRACT FROM AUTHOR]

This study investigates the optical properties (light reflectance, absorptance, transmittance, and scattering) of black silicon (b‐Si) layers formed using reactive ion etching method. The corresponding spectra are determined across the visible, near‐infrared, and near‐ultraviolet wavelength ranges (250–1400 nm). It is demonstrated that b‐Si layers reduce the reflectance, and increase the absorptance and light scattering due to the disordered distribution of the nanoneedles. Increasing the etching duration strengthens this trend. It is shown that b‐Si layers etched for 10 min can be considered perfect light scatterers upon reflection at wavelengths less than 700 nm. Based on the obtained results, the possible profits of light scattering from the b‐Si interlayer for perovskite/Si tandem solar cells are analyzed. It is substantiated that the b‐Si interlayer can increase the useful absorptance not only within the bottom Si solar subcell but also in the top perovskite solar subcell. The prospects for future research directions and challenges are also provided. [ABSTRACT FROM AUTHOR]

The etching of p‐GaN requires extremely strict control over etching depth and morphology; otherwise, it will result in poor electrical characteristics. This work uses ALD(Atomic layer deposition) in situ N2 plasma and postanneal‐assisted passivation to effectively recover the electrical properties degraded by p‐GaN etching. Compared to unpassivated devices, this approach eliminates surface oxygen bonds, recovering drain current from 10 to 126 mA mm−1, reducing gate leakage by an order of magnitude, achieving an ON/OFF current ratio exceeding 108, a breakdown voltage of 930 V at 1 μA mm−1, and effectively suppressing current collapse. [ABSTRACT FROM AUTHOR]

Direct Ink Writing has been demonstrated to be a promising route to produce ceramic catalysts with complex geometries and enhanced catalytic performances. To increase the catalytic performances, chemical etching can be conducted to get an interconnected and hierarchical porous structure, to increase the surface area and the contact time of the reactants. In this work, DIW alpha (α)-Al 2 O 3 catalysts were chemically etched with hydrofluoric acid (HF). Several combinations of acid concentrations and etching times were studied to find the optimal etching condition. For HF concentration of 5, 20 and 40 wt%, the optimal etching time was 48, 24 and 5 h, respectively, being 40 wt% the concentration that shows the greatest increase of surface porosity (of around 5%). HF etching can produce an interconnected porosity on 3DP α-Al 2 O 3 , but it does not yield improvement in catalytic performances when the content of fluor (F) is higher than 10 at% since it produces parasite reactions. [ABSTRACT FROM AUTHOR]

SiC/SiC (Silicon Carbide fiber reinforced Silicon Carbide) is widely used in aerospace and gas turbine fields due to its excellent resistance to high temperature, corrosion and low density. However, the difficult processing of SiC/SiC is the main factor limiting its further application. To address these issues, this paper proposes a novel method for processing SiC/SiC using femtosecond laser combined with dynamic wet etching. A comparative analysis of the micro-pore morphology and elemental composition obtained through processing in air, water, and NaOH solution is presented. Demonstrates the excellent surface quality achieved with NaOH processing, which effectively reduces defects such as recast layers and microcracks. The results suggest that the operating mechanism involves the combined effects of a wet-oxygen coupling environment, high-temperature decomposition, localized chemical wet etching, and the influence of the liquid layer. [ABSTRACT FROM AUTHOR]

Monocrystalline silicon carbide (SiC) has attracted attention for applications in devices operating in harsh environments due to its excellent physicochemical properties. However, it is difficult to obtain extremely small-feature sizes with undamaged surfaces due to its extremely high hardness. Herein, a novel method to fabricate SiC microgrooves is proposed that combines molding with inductively coupled plasma (ICP) etching process. First, a Ni–P microgroove master mold was fabricated by ultraprecision cutting and replicated on a polydimethylsiloxane (PDMS) surface, which was then used as the microgroove mold for hot embossing. Then, the patterned mask fabricated by hot embossing was transferred to the SiC substrate by ICP etching. To obtain customized microgrooves, an interface-evolution model based on angular dependence theory was established. A numerical method based on a string algorithm approach is developed for interface-evolution simulations. During ICP etching, the characteristic size d of homogeneous materials and the sidewall angle in heterogeneous materials varied with the sidewall angle of the SU-8 mask due to the angular dependence of etch rate. Finally, seven sets of microgrooves were machined on SU-8 to study the interface-evolution process. Variations in the characteristic size Δ d and sidewall angle θ for each unit in homogeneous material, as well as the variations in sidewall angle before and after etching in heterogeneous materials are described. The high accuracy of the proposed interface-evolution model was experimentally validated. [ABSTRACT FROM AUTHOR]

Porous graphene materials possess a larger specific surface area and a more abundant presence of active sites compared to non‐porous graphene materials, resulting in enhanced electrochemical properties. The presence of in‐plane nanopores facilitates the transmission of ions and mass, further expanding the potential applications of graphene materials in electrochemical energy storage and various other fields. In this study, a rapid synthesis of porous graphene was achieved through a microwave‐assisted chemical etching method. With the aid of microwave radiation, the etchant efficiently reduced the oxygen‐containing groups within the graphene structure, consequently generating nanopores with an approximate diameter of 10 nm. By optimizing the microwave treatment parameters, including pretreatment time, etching time, amount of etchant H2O2, and microwave power, the area percentage of nanopores in the graphene material was controlled to enhance its electrochemical properties. Porous graphene materials exhibited excellent specific capacitance and rate capability, making it a promising material for capacitor applications. Moreover, the lower internal resistance of porous graphene, compared to non‐porous graphene, demonstrated the significant role of nanopores in enhancing the electrochemical performance. These findings highlight the potential of porous graphene for use in electrochemical energy storage. [ABSTRACT FROM AUTHOR]

Wet etching of Silicon nitride (Si3N4) by phosphoric acid (H3PO4) is one of the key steps in the semiconductor fabrication process, especially for three‐dimensional integrated circuits (ICs). Unfortunately, few systematic studies of phosphoric acid etching of Silicon nitride are available. Summarizing how various factors affect etching and determining the reaction mechanism behind the etching process will help further optimize the etching process. In this work, how the boiling point of hydrous phosphoric acid solutions depends on phosphoric acid concentration is firstly investigated. Next, the etching of over 100 samples of Silicon nitride by H3PO4 at different concentrations and temperatures is systematically studied. The results show that the etching rate increases nearly linearly in both temperature and H3PO4 concentration, while temperature play more important role as compared to concentration. For each concentration, the reaction rate is maximal at the boiling point of the hydrous H3PO4 solution. Moreover, the etching rate of 85 wt % phosphoric acid is analyzed using the Arrhenius equation, yielding an apparent activation energy Ea=57.28 KJ/mol. Finally, a mechanism of Silicon nitride etching in phosphoric acid is proposed which explains the prior studies well. This work contributes to precisely control semiconductor processing for three‐dimensional ICs. [ABSTRACT FROM AUTHOR]

Two‐dimensional Ti3C2Tx MXene materials, with metal‐like conductivities and versatile terminals, have been considered to be promising surface modification materials for Zn‐metal‐based aqueous batteries (ZABs). However, the oxygen‐rich and hybridized terminations caused by conventional methods limit their advantages in inhibiting zinc dendrite growth and reducing corrosion‐related side reactions. Herein, −O‐depleted, −Cl‐terminated Ti3C2Tx was precisely fabricated by the molten salt electrochemical etching of Ti3AlC2, and controlled in situ terminal replacement from −Cl to unitary −S or −Se was achieved. The as‐prepared −O‐depleted and unitary‐terminal Ti3C2Tx as Zn anode coatings provided excellent hydrophobicity and enriched zinc‐ionophilic sites, facilitating Zn2+ horizontal transport for homogeneous deposition and effectively suppressing water‐induced side reactions. The as‐assembled Ti3C2Sx@Zn symmetric cell achieved a cycle life of up to 4200 h at a current density and areal capacity of 2 mA cm−2 and 1 mAh cm−2, respectively, with an impressive cumulative capacity of up to 7.25 Ah cm−2 at 5 mA cm−2//2 mAh cm−2. These findings provide an effective electrochemical strategy for tailoring −O‐depleted and unitary Ti3C2Tx surface terminals and advancing the understanding of the role of specific Ti3C2Tx surface chemistry in regulating the plating/stripping behaviors of metal ions. [ABSTRACT FROM AUTHOR]

2D transition metal dichalcogenides (TMDs) have attracted intensive interests for its unique electronic, optical, and thermal properties. Doping is necessary to expand the application. However, the stability of doped materials has been overlooked. This study focuses on the stability of monolayer‐doped MoS2 with different vanadium (V) concentrations. It provides a quantitative assessment of the etching results. Findings indicate that the stability of MoS2 under different etching atmospheres follows the series of lightly doped MoS2, pristine MoS2, moderately doped MoS2, and highly doped MoS2. This research indicates that the stability of the material is linked to the bonding energy of cations and anions, as well as the amount of lattice distortion, which competes with one another. Low levels of V doping do not lead to significant lattice distortion, and the binding energy between sulfur (S) and V surpasses that of molybdenum (Mo), which is the primary factor. Excessive doping results in lattice distortion, which leads to a multitude of defects and a reduction in durability. This work is important for guiding the assessment of the reliability, the protection of degradation, and application scenarios of TMDs. [ABSTRACT FROM AUTHOR]

Fused silica with surface structures has potential applications in microfluidic, aerospace and other fields. To fabricate structures with high dimensional accuracy and surface quality is of paramount importance. However, it is indeed a challenge to strike a balance between accuracy and efficiency at the same time. Here, a temporally shaped femtosecond laser Bessel-beam-assisted etching method with dual-control of incubation effect is proposed to achieve this balance. Instead of layer-by-layer ablation continuously with Gaussian pulses, silica is modified discretely by double pulse Bessel beam with one single layer. During the modification process, incubation effect is dual-controlled in single shot process and spatial scanning process to generate even modified region efficiently. Then, the modified region is etched to form designed structures such as microholes, grooves, etc. The proposed method exhibits high efficiency for fabrication of surface structures in fused silica. [ABSTRACT FROM AUTHOR]

In this study, cold plasma treatments are employed to modify peanuts. This study systematically investigates the effects of various plasma treatment conditions, including power, duration, and gas type, on the microstructure of peanut seed coats and embryos. Observations under a scanning electron microscope (SEM) reveal that as plasma treatment power increases from 100 W to 500 W, the etching level of peanut seed coats significantly intensifies, surface roughness deepens, and concavities become more pronounced. Additionally, micro-pores on the seed coat gradually enlarge and form cracks. Specifically, when the plasma treatment is set at 200 W for 60 s, the oxygen (O2) treatment group shows interconnected cracks on the peanut seed coat surface, with lipid particles exuding and protein particles and polymers decomposing. In contrast, the helium (He) treatment group displays clear cell structures and deep grooves, with no noticeable lipid particles exuding around surface cracks. The argon (Ar) treatment group exhibits a distinct rectangular cell structure with clear boundaries, and although surface cracks form, only a few protein particles escape from the cracks. The embryo surface structure becomes looser after plasma treatment, leading to the disintegration of lipid particles, protein particles, and polymers, affecting the fusion and migration of large and small lipid bodies within the peanut's internal structure. Increasing treatment duration intensifies the etching phenomenon, resulting in more lipid particles exuding, which indicates a positive correlation between lipid particles exuding and treatment duration. This study sheds light on the mechanisms underlying changes in peanut microstructure due to cold plasma treatment, providing scientific evidence for improving peanut quality, enhancing oil extraction efficiency, and optimizing food processing techniques. [ABSTRACT FROM AUTHOR]

Silicon nanowalls atop the (100) – oriented boron doped P-type (1–10 Ω-cm) single crystalline silicon wafers were prepared using a metal assisted chemical etching route for different durations 1, 5, 15, and 30 min. The scanning electron microscopy results revealed that the structure evolved up on etching is in the form of vertical silicon nanowalls with mean wall thickness of 70 nm. It can be observed that as the etching time increases, the height of the SiNWs increases linearly at an etching rate of ~ 301 nm per minute. The transmission electron microscopy results combined with FTIR spectroscopy results indicate that about one nanometer thick Si–O-Si- bonded amorphous layer formed at the surface of the grown silicon nanowalls. A defect sensitive Variable energy positron beam Doppler broadening technique used to study the etched silicon wafers confirms that the defect structures that are evolved in the silicon nanowalls with etching are different from that of planar Silicon. Analysis of the Doppler broadened line-shape profiles shows that the effective positron diffusion length and height of the silicon nanowalls are related logarithmically with a scaling exponent of—1/2, indicating that the implanted positrons that are thermalized in the silicon nanowalls diffuse back to the wall surfaces and are annihilated at the defects linked (Si–O-Si)/Si interface region. The present positron experimental results abound with literature reports suggest that understanding the microstructure of the surface layer in SiNWs is significantly important in determining their performance for producing efficient solar cells. [ABSTRACT FROM AUTHOR]

This study investigates the suppression of galvanic corrosion between copper and gold using cetyltrimethylammonium bromide (CTAB) and betaine as inhibitors. When copper is electrically connected to gold in PCB etching solutions, the substantial difference in their electrochemical potentials leads to the accelerated corrosion of copper, posing severe reliability risks. To mitigate this, we systematically investigated the galvanic corrosion inhibition properties of CTAB and betaine. Through comprehensive electrochemical analyses, it was found that the galvanic corrosion current density of copper, initially at 3.26 mA/cm2, decreased significantly to 0.251 mA/cm2 with 0.9 mM CTAB, indicating an inhibition efficiency of 92.3%. Furthermore, betaine, at a concentration of 0.1 mM, demonstrated an even higher inhibition efficiency, reducing the corrosion current to 0.03 mA/cm2, achieving a 99.1% inhibition rate. These findings provide strong evidence that CTAB and betaine are highly effective in suppressing galvanic corrosion in copper–gold systems, thereby enhancing the long-term performance and reliability of PCBs in electronic applications. [ABSTRACT FROM AUTHOR]

Extrusion-based polymer three-dimensional (3D) printing, specifically fused deposition modeling (FDM), has been garnering increasing interest from industry, as well as from the research and academic communities, due to its low cost, high speed, and process simplicity. However, bed adhesion failure remains an obstacle to diversifying the materials and expanding the industrial applications of the FDM 3D-printing process. Therefore, this study focused on an investigation of the surface treatment methods for aluminum (Al) foil and their applications to 3D printer beds to enhance the bed adhesion of a 3D-printed polymer filament. Two methods of etching with sodium hydroxide and anodization with phosphoric acid were individually used for the surface treatment of the Al foil beds and then compared with an untreated foil. The etching process removed the oxide layer from the Al foil and increased its surface roughness, while the anodizing process enhanced the amount of hydroxide functional groups and contributed to the formation of nano-holes. As a result, the surface-anodized aluminum foil exhibited a higher affinity and bonding strength with the 3D-printed polymers compared with the etched and pristine foils. Through the increase in the success rate in 3D printing with various polymers, it became evident that utilizing surface-treated Al foil as a 3D printer bed presents an economical solution to addressing bed adhesion failure. [ABSTRACT FROM AUTHOR]

There is a high demand for plasma-resistant coatings that prevent the corrosion of the internal ceramic components of plasma etching equipment, thereby reducing particle contamination and process drift. Yttrium oxyfluoride (YOF) coatings were prepared using atmospheric plasma spraying (APS) with commercially available YOF/YF3 powder mixtures; namely YOF 3%, YOF 6%, and YOF 9%. The etching behaviour of YOF and yttrium oxide (Y2O3) coatings was investigated using an inductively coupled plasma consisting of NF3/He. X-ray photoelectron spectroscopy (XPS) showed that the YOF 6% coating had the thickest fluorinated layer. The scanning electron microscope (SEM) examination revealed that the YOF 6% coating showed exceptional resistance to erosion and generated a reduced quantity of contaminated particles in comparison to Y2O3. Consequently, it is more suitable as a protective material for the inner wall of reactors. The YOF coatings exhibit excellent stability and high resistance to erosion, indicating their appropriateness for use in the semiconductor industry. [ABSTRACT FROM AUTHOR]

In situ-generated acid is commonly employed in ultra-deep, high-temperature carbonate reservoirs during acid fracturing to increase the effective acid penetration distance. However, the variation pattern of acid-etched fracture conductivity with in situ-generated acid has not been systematically studied. This paper investigates the evolution of the conductivity of primary and secondary fractures through a series of experiments involving in situ acid displacement and acid-etched fracture conductivity measurement. Based on the experimental results, a calculation model for the conductivity of acid-etched fractures with in situ-generated acid was established. The study indicates that after acid etching, rough particulate points and grooved dissolution patterns form on the surfaces of primary and secondary fractures, respectively. The dissolution volume in primary fractures is greater than that in secondary fractures, with both showing a linear increase over time. Due to the presence of dissolution grooves on the surfaces of secondary fractures, their conductivity is higher than that of primary fractures under the same acid–rock contact time. The conductivity of both primary and secondary fractures increases with the acid–rock contact time. However, beyond approximately 70 min of contact time, the conductivity of primary fractures shows no significant increase. The conductivity of primary and secondary fractures with in situ-generated acid is slightly lower than that with gelled acid under the same contact time, but significantly higher than that with crosslinked acid. This study provides guidance for the design and parameter optimization of acid fracturing in ultra-deep, high-temperature carbonate reservoirs. [ABSTRACT FROM AUTHOR]

Two-hierarchical nanostructures, characterized by two distinct configurations along the height direction, exhibit immense potential for applications in various fields due to their significantly enhanced controllable degree compared to single-order structures. However, due to the limitations imposed by planar technology, the realization of two-hierarchical nanostructures encounters huge challenges. In this work, we developed a one-step etching method based on inductively coupled plasma reactive ion etching for two-hierarchical nanostructures. Thanks to the shrinking effect of the Cr mask and the generation of a passivation layer during etching, the target materials experienced two different states from vertical etching to shrink etching. Consequently, the achieved two-hierarchical nanostructure configuration features a cross-section of an upper triangle and a lower rectangle, showing higher controllable degrees compared to the one-order ones. Both the mask pattern and etching parameters play crucial roles, by which two-hierarchical structures with diversiform shapes can be constructed controllably. This method for two-hierarchical nanostructures offers advantages including excellent control over structural properties, high processing efficiency, uniformity across large areas, and universality in materials. This developed strategy not only presents a simple and rapid nanofabrication platform for realizing optoelectronic devices, but also provides innovative ideas for designing the next generation of high-performance devices. [ABSTRACT FROM AUTHOR]

To enhance the performance of micro-hemispherical gyroscopes, achieving low-damage and high-surface-quality trimming is essential. This enables greater stability and reliability for the gyroscopes. Current methods for reducing frequency split often come with drawbacks such as high cost, adverse effects on the Q-factor, or surface damage. In this paper, a chemical etching trimming method is proposed to reduce frequency split in micro-hemispherical resonators. This method allows for trimming with minimal damage, while also being cost-effective and easy to implement. The theoretical basis of this method was analyzed, followed by a simulation to determine the optimal trimming range and location on the resonator. The simulated Q-factor analysis before and after trimming preliminarily validated the method's low-damage characteristics. Ultimately, the frequency split of the resonator was reduced to below 1 Hz. Additionally, test results of the Q-factor and surface quality before and after trimming further confirmed that chemical etching offers effective low-damage trimming capabilities. The proposed method holds significant potential for improving the performance of micro-hemispherical resonator gyroscopes. [ABSTRACT FROM AUTHOR]

Ion-beam etching (IBE) is widely used in the fabrication of high-quality blazed gratings due to its high resolution and directionality, which allows for the control of blazed angles and smooth surface profiles. Throughout the ion-beam etching process, the redeposition of sputtered species onto the wafer occurs, affecting the profile evolution and blazed angle. To investigate this phenomenon in the fabrication of blazed gratings, a self-consistent simulation model utilizing the cellular method has been developed to analyze the etching and redeposition mechanisms in the IBE process. The model yields good agreement with the experimentally observed evolution of the etching profile. By examining the density and velocity distributions of the sputtered species, the coexistence of etching and redeposition is confirmed and explained, highlighting the visually significant role of redeposition. Our model takes into account the "footing effect" that is unavoidable in mask manufacturing, and its impact on the morphology evolution during blazed grating IBE is studied. [ABSTRACT FROM AUTHOR]

The possibilities of optimization of the two-step atomic layer etching process for HfO2 in conventional plasma etching tools were studied. The surface modification step was realized in Ar/CF4/H2 plasma, and the reaction between the modified layer and the surface was activated by Ar ion bombardment from the plasma in the second step. Investigation of the effects of activation step duration, DC bias during activation, and Ar plasma density was carried out. The mechanism of the etching process has been shown to involve fluorination of oxide during the modification step and subsequent removal of fluorine-containing particles at the activation step. An increase in parasitic sputtering rate and lower process saturation with the growth of DC bias during activation was demonstrated. The advantage of the ALE process in lower surface roughness over the conventional etching process was shown. Similar etching characteristics of HfO2 and ZrO2 suggest a similarity in the etching process for the mixed hafnium-zirconium oxide material. [ABSTRACT FROM AUTHOR]

The dry etching of high crystal quality c-plane AlN grown by metal organic chemical vapor deposition was examined as a function of source and chuck power in inductively coupled plasmas of Cl2/Ar or Cl2/Ar/CHF3. Maximum etch rates of ∼1500 Å min−1 were obtained at high powers, with selectivity over SiO2 up to 3. The as-etched surfaces in Cl2/Ar/CHF3 have F-related residues, which can be removed in NH4OH solutions. The Al-polar basal plane was found to etch slowly in either KOH or H3PO4 liquid formulations with extensive formation of hexagonal etch pits related to dislocations. The activation energies for KOH- or H3PO4-based wet etching rates within these pits were 124 and 183 kJ/mol, respectively, which are indicative of reaction-limited etching. [ABSTRACT FROM AUTHOR]

Solid silicon (Si) microneedles have many applications such as skin pretreatment to form micrometer-sized holes in the skin surface in transdermal drug delivery systems. Wet etching based on tetramethylammonium hydroxide (TMAH) is an efficient method to fabricate solid microneedles. However, it is challenging to increase the density of microneedle arrays due to the faster lateral etching than the vertical etching that requires a large initial mask size. In this work, we used wet etching based on TMAH to fabricate solid Si microneedles. One kind of nonionic surfactant, Triton X-100, was introduced into the TMAH solution to suppress the lateral etching. When Triton X-100 was added into TMAH for a given etching condition, the maximum height (attained right before the mask fell off) of microneedles could reach ∼230 μm for 600 μm square-shaped mask size and 700 μm array period, compared to microneedles of maximum 152 μm height for the same mask size and period without surfactant addition. Correspondingly, when the target heights of microneedles were the same as ∼230 μm, denser (down to 700 μm period, 600 μm mask size) microneedle arrays were achieved with the help of Triton X-100, in comparison to arrays down to 900 μm period (800 μm mask size) without surfactant addition. Furthermore, agitation by a magnetic stirring bar is important for the fabrication of dense solid Si microneedle arrays based on TMAH. The microneedle structures were rhombic pyramid in shape with Triton X-100 and agitation. But microneedle structures obtained with Triton X-100 yet without agitation were octagonal pyramid in shape with a much less steep side surface. [ABSTRACT FROM AUTHOR]

Microneedles are a promising technology for drug delivery. They are minimally invasive, painless, and easy to use for various applications. In this paper, a process for fabricating hollow microneedles on a silicon substrate using maskless direct writing grayscale lithography and deep reactive ion etching (DRIE) is investigated. During the process, two approaches are employed to smoothen the needle tip and reduce the roughness of the needle bevel. First, a grayscale lithography process is used to create a 3D photoresist structure with discrete height steps. This structure is then transferred into silicon using DRIE. An SF6 isotropic etching process is utilized to create a smooth surface on the upper portion of microneedles by smoothing out the steplike structures. Alternatively, after grayscale lithography, resist thermal reflow is used to smooth out the resist structures. The resist patterns are then transferred into silicon microneedles using the DRIE technique. The morphology of the microneedles can be adjusted by varying the etching selectivity of silicon over the resist. Hollow microneedles with a height of 360 μm are produced, which offers numerous practical applications. [ABSTRACT FROM AUTHOR]

In contrast to the conventional etching that makes nanoparticles rounder and our previous sharpening etching mode that causes serrated edges, here, we developed a new boring etching mode that targets the faces of Au nanoplates to make holes. The critical factors are the pre-incubation step with the ligand 2-mercapto-5-benzimidazolecarboxylic acid (MBIA) and the subsequent removal of excess ligands in the solution. Thus, etching is focused onto the few sites with initial loss of ligands, which cannot be quickly replaced. The choice of ligand MBIA is also of importance, as it carries negative charge and repels each other. Its inability of forming a dense layer probably plays a critical role in the site-selectivity for faces, because ligands at the higher curvature edges and corners are expected to have less repulsion. The etching results from the comproportionation reaction between Au3+ and Au0 in the nanoplates, where Br− coordination to Au and the extra stabilization from cetyltrimethylammonium bromide (CTAB) are essential. We believe that the ability of boring holes is an important tool for future synthetic designs. [ABSTRACT FROM AUTHOR]

The mechanical and corrosion properties of duplex stainless steels (DSS) depend on the distribution of ferrite and austenite as well as the presence of secondary phases. It is therefore necessary to accurately determine both the distribution of the phases and their morphology. The aim of this research is to define a standard method for the determination of the volume fraction of the phases present in a SAF2507 SDSS by analysing images acquired by light microscope. To do this, the material is heat-treated at 850 °C for 5 min, 15 min, 30 min, 1h, 5h to stimulate the formation of the σ-phase. The metallographic etchant capable of maximising phase contrast is then identified. Micrographic analyses are performed using different reagents at different holding times and temperatures, in order to find the best combination. A standard procedure is then defined for the image analysis. The data obtained were are processed to calculate the phase distribution. The results are compared with the quantitative analysis performed using X-ray diffraction as reference.The research evidence that Kalling's reagent is best etchant for fully solubilised materials, as it accurately estimates ferrite and austenite content. On the other hand, Marble's reagent should be preferred for the detection of σ-phase. For comprehensive analysis of all phases, Murakami's reagent is recommended.The approach defined in this paper not only improves the understanding of the microstructure of DSS, but also provides an important tool for industrial quality control and material characterisation.

In this work, we report on the development and application of a simple reflectivity technique for real-time monitoring of the fabrication of porous-silicon multilayers. The technique allows for high-resolution quantification of the effective optical thickness of the layers during the fabrication process, enabling calibration of attack rates and detection of changes in porosity. Our experiments revealed that the porosity of the layers increases during the attack, indicating incomplete passivation of the pores. By studying thin porous-silicon layers in the absence of applied current, we developed a three-layer model to understand passive chemical etching. Furthermore, our study allowed discrimination between the two mechanisms responsible for the reduction of effective optical thickness with time, with changes in porosity being the dominant one. The technique has the potential to enable real-time control of multilayer fabrication, offering flexibility in controlling environmental conditions and silicon wafer conduction properties. Our results contribute to the understanding of multilayer fabrication and reflectivity-based process monitoring. [ABSTRACT FROM AUTHOR]

GaN is an enabling material for light emitting diodes, advanced radio frequency, and power semiconductor devices. However, fabrication of GaN devices often relies on harsh etch processes, which can leave an etch damage layer, limiting final device performance. In this work, an isotropic atomic layer etching (ALE) process involving SF6 plasma and trimethylaluminium [Al(CH3)3] is presented for the controlled etching of GaN, which reduces oxygen and carbon contamination while smoothing the surface. The ALE chemistry was first examined with density functional theory. A comparison between proposed thermal and plasma-driven reactions is made by implementing Natarajan–Elliott analysis, highlighting that the plasma process is a good candidate for GaN ALE. Saturation was experimentally confirmed for both ALE half-cycles at 150 and 300 °C, with etch rates of 0.31 ± 0.01 and 0.40 ± 0.02 nm/cycle, respectively. Analysis of the films post-ALE shows that the RMS roughness of the films decreases from 2.6 ± 0.1 to 1.9 ± 0.1 nm after 25 nm of etching at 300 °C, in agreement with a previously developed curvature-dependent smoothing model. Taken together, this ALE process enables accurate GaN thickness tuning, surface cleaning, and surface smoothing, allowing for further development of GaN devices. [ABSTRACT FROM AUTHOR]

GaN is an enabling material for light emitting diodes, advanced radio frequency, and power semiconductor devices. However, fabrication of GaN devices often relies on harsh etch processes, which can leave an etch damage layer, limiting final device performance. In this work, an isotropic atomic layer etching (ALE) process involving SF6 plasma and trimethylaluminium [Al(CH3)3] is presented for the controlled etching of GaN, which reduces oxygen and carbon contamination while smoothing the surface. The ALE chemistry was first examined with density functional theory. A comparison between proposed thermal and plasma-driven reactions is made by implementing Natarajan–Elliott analysis, highlighting that the plasma process is a good candidate for GaN ALE. Saturation was experimentally confirmed for both ALE half-cycles at 150 and 300 °C, with etch rates of 0.31 ± 0.01 and 0.40 ± 0.02 nm/cycle, respectively. Analysis of the films post-ALE shows that the RMS roughness of the films decreases from 2.6 ± 0.1 to 1.9 ± 0.1 nm after 25 nm of etching at 300 °C, in agreement with a previously developed curvature-dependent smoothing model. Taken together, this ALE process enables accurate GaN thickness tuning, surface cleaning, and surface smoothing, allowing for further development of GaN devices. [ABSTRACT FROM AUTHOR]