Local Etching Research Articles

Local Droplet Etching with Indium Droplets on InP(100) by Metal-Organic Vapor Phase Epitaxy.

The local droplet etching (LDE) by using indium droplets on bare InP(100) surfaces is demonstrated in a metal-organic vapor phase epitaxy (MOVPE) environment for the first time. The role of an arsenic flow applied to self-assembled metallic indium droplets is systematically studied. Increasing the arsenic supply leads to the formation of ring-like nanostructures and nanoholes. The results are analyzed with reference to LDE in a molecular beam epitaxy environment, where such a technique is well established, particularly for arsenide-based III-V semiconductors, and where only one group-V material is involved. Here, As-P exchange reactions at droplet sites are identified as the drivers for the formation of nanoholes. Such nanoholes can serve as nucleation sites for subsequent fabrication of highly symmetric QDs by nanohole-infilling or as a means for in situ surface nanopatterning. LDE on InP by MOVPE can thus be considered as a promising approach for the cost-effective fabrication of novel quantum emitters at the telecom C-band.

Local Strain-Dependent Etching Patterns of Chemical Vapor Deposited Molybdenum Disulfide.

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.

Preparation of Supercapacitor Carbon Electrode Materials by Low-Temperature Carbonization of High-Nitrogen-Doped Raw Materials from Food Waste.

To address the problem of the low nitrogen (N) content of carbon materials prepared through the direct carbonization of food waste, soybean meal and egg whites with high N contents were selected to carry out carbonization experiments on food waste. At 220 °C, the effects of hydrothermal carbonization and microwave carbonization on the properties of supercapacitor electrode materials were investigated. The results show that food waste doped with soybean meal and egg whites could achieve good N doping. At a current density of 1 A·g-1, the specific capacitance of the doped carbon prepared by hydrothermal doping is as high as 220.00 F·g-1, which is much greater than that of the raw material prepared through the hydrothermal carbonization of food waste alone, indicating that the hydrothermal carbonization reactions of soybean meal, egg white, and food waste promote the electrochemical properties of the prepared carbon materials well. However, when a variety of raw materials are mixed for pyrolysis carbonization, different raw materials cannot be fully mixed in the pyrolysis process, and under the etching action of potassium hydroxide, severe local etching and local nonetching occur, resulting in a severe increase in the pore size distribution and deterioration of the electrochemical performance of the prepared carbon materials. At a current density of 1 A·g-1, the specific capacitance of these prepared carbon materials is 157.70 F·g-1, whereas it is only 62.00 F·g-1 at a high current density of 20 A·g-1. Therefore, this study suggests that the hydrothermal carbonization process is superior to the microwave pyrolysis carbonization process for preparing supercapacitor electrode materials with multiple samples doped with each other.

Engineering Three-Dimensional Interconnected Pores with Plentiful Edge Sites via a Confined Space for Enhanced Oxygen Reduction.

N-Doped carbon sheets based on edge engineering provide more opportunities for improving oxygen reduction reaction (ORR) active sites. However, with regard to the correlation between porous structural configurations and performances, it remains underexplored. Herein, a silica-assisted localized etching method was employed to create two-dimensional mesoporous carbon materials with customizable pore structures, abundant edge sites, and nitrogen functionalities. The mesoporous carbon exhibited superior electrocatalytic performance for the ORR compared to that of a 20 wt % Pt/C catalyst, achieving a half-wave potential of 0.88 V versus RHE, situating them in the leading level of the reported carbon electrocatalysts. Experimental data suggest that the edge graphitic nitrogen sites played a crucial role in the ORR process. The three-dimensional interconnected pores provided a high density of active sites for the ORR and facilitated the efficient transport of electrons. These unique properties make the carbon sheets a promising candidate for highly efficient air cathodes in rechargeable Zn-air batteries.

Theoretical analysis of nanoscale local etching of a rough quartz surface under direct illumination.

A 3D model of photochemical polishing of rough quartz surfaces under direct illumination has been developed. One of the features of the model is its ability to predict the results of a photochemical polishing process without the need for time-consuming calculations. The proposed model analyzes the characteristics of the surface evolution during polishing based on the initial roughness parameters and the polarization of the incident radiation. When a rough surface is irradiated with linearly polarized light, a textured surface in the form of furrows is produced. Non-polarized radiation is recommended to obtain a flatter surface.

Local droplet etching of a vicinal InGaAs(111)A metamorphic layer

We demonstrated nanopit formation by Ga-assisted local droplet etching technique in InGaAs metamorphic layers grown on vicinal GaAs(111)A substrates. We studied nanopit formation depending on the substrate temperature, Ga flux and Ga amount. The etched pits show a highly symmetrical pyramidal shape with an equilateral triangular base and the edges of the triangle are along <11¯0> directions. The observed behavior, in terms of nanopit density, depth and, aspect ratio is well described by a model taking into account the dynamics of the droplet etching process.

Influence of Etchants on Etched Surfaces of High-Strength and High-Conductivity Cu Alloy of Different Processing States.

With the continuous integration of semiconductor devices, the requirements of the size accuracy and surface quality of etched lead frames are stricter. The etchant is a key factor in the etching process and etched surface quality, while the effects of the difference in etchants on the etched surface morphology of Cu alloy have not been directly studied. In this study, aqua regia, acidic FeCl3 and two CuCl2 solutions were used as etchants, and different CuCrSn specimens were etched and characterized. The results show that the etching rate in aqua regia is high, and the grain orientation, grain boundary (GB) and dislocations have significant influences on the local etching rate. The preferential etching of some atomic planes forms steps between the grains with different orientations, and preferential etching around the GB and dislocation group forms grooves, resulting in high surface roughness. For the surfaces etched by the FeCl3 and CuCl2 etchants, the steps and grooves are blurred; thus, they are less rough. The CuCrSn alloy surface etched by the aqua regia is clean, with little Cr-rich particles, while high-density Cr-rich particles remain on the surfaces etched by the FeCl3 and CuCl2 etchants. For the same kind of etchant, the ion concentration can affect the etching mechanism, rate and the etched surface morphology.

Investigation on femtosecond laser combined with dynamic wet etching machining of SiC/SiC

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.

The role of oxygen in mechanochemical wear of graphene

As a protective coating with wide applications due to its outstanding stiffness and chemical inert, graphene often undergoes significantly local stress and chemical etching in practical use conditions, but the degeneration mechanism of graphene under the mechanical and chemical coupling remains largely open. In this work, the experimental measurement demonstrates that the edges of graphene are vulnerable to mechanochemical wear mainly due to the attack from oxygen atoms. Atomic simulations of density functional theory calculations reveal that the C–C networks of graphene are broken through the stress-driven chemical reactions of interfacial bonds formation between graphene edges and the reactive counterface, leading to oxidation unzipping of graphene under low shear stress. The studies suggest the anti-wear performance of graphene edges can be tuned by suppressing interfacial bonds forming.

Thermoelectric Sensor with CuI Supported on Rough Glass.

Thermoelectric generators convert heat into a potential difference with arrays of p- and n-type materials, a process that allows thermal energy harvesting and temperature detection. Thermoelectric sensors have attracted interest in relation to the creation of temperature and combustible gas sensors due to their simple operation principle and self-powering ability. CuI is an efficient p-type thermoelectric material that can be readily produced from a Cu layer by an iodination method. However, the vapor iodination of Cu has the disadvantage of weak adhesion on a bare glass substrate due to stress caused by crystal growth, limiting microfabrication applications of this process. This work presents a rough soda-lime glass substrate with nanoscale cavities to support the growth of a CuI layer, showing good adhesion and enhanced thermoelectric sensitivity. A rough glass sample with nanocavities is developed by reactive ion etching of a photoresist-coated glass sample in which aggregates of carbon residuals and the accumulation of NaF catalyze variable etching rates to produce local isotropic etching and roughening. A thermoelectric sensor consists of 41 CuI/In-CoSb3 thermoelectric leg pairs with gold electrodes for electrical interconnection. A thermoelectric leg has a width of 25 μm, a length of 3 mm, and a thickness of 1 μm. The thermoelectric response results in an open-circuit voltage of 13.7 mV/K on rough glass and 0.9 mV/K on bare glass under ambient conditions. Rough glass provides good mechanical interlocking and introduces important variations of the crystallinity and composition in the supported thermoelectric layers, leading to enhanced thermopower.

High-precision finishing method for narrow-groove channel-cut crystal x-ray monochromator using plasma chemical vaporization machining with wire electrode.

A channel-cut crystal monochromator (CCM) is a popular and powerful device for producing monochromatic x-ray beams with extreme angular stability at a nano-radian level. Narrowing the groove width of CCMs has various benefits; for example, it is made possible to design more compact CCMs with an equivalent working energy range and to reduce the optical delay and the amount of beam shift, enhancing compatibility with various experimental techniques. An obstacle to the use of narrow-groove CCMs is the lack of a high-precision finishing method for the inner-wall reflecting surfaces, which imposes the distortion of x-ray wavefronts and spectral purity. We propose a new, damage-free surface-finishing method for silicon CCMs with a narrow groove of 1mm or less with a localized etching technique using plasma generated with a wire electrode of 50 µm diameter under atmospheric pressure. Repeating plasma-on and plasma-off periods with a pulsed power supply, we reduce the concentration of reaction products through self-diffusion during the plasma-off periods and minimize the redeposition of the products on the processed surface that deteriorates the surface roughness. Under optimized conditions, we processed a CCM with a groove width of 1.2mm, which has uniform reflection profiles and a nearly ideal reflectivity behavior for coherent monochromatic x rays.

Temperature-Enhanced Exciton Emission from GaAs Cone-Shell Quantum Dots.

The temperature-dependent intensities of the exciton (X) and biexciton (XX) peaks from single GaAs cone-shell quantum dots (QDs) are studied with micro photoluminescence (PL) at varied excitation power and QD size. The QDs are fabricated by filling self-assembled nanoholes, which are drilled in an AlGaAs barrier by local droplet etching (LDE) during molecular beam epitaxy (MBE). This method allows the fabrication of strain-free QDs with sizes precisely controlled by the amount of material deposited for hole filling. Starting from the base temperature T = 3.2 K of the cryostat, single-dot PL measurements demonstrate a strong enhancement of the exciton emission up to a factor of five with increasing T. Both the maximum exciton intensity and the temperature Tx,max of the maximum intensity depend on excitation power and dot size. At an elevated excitation power, Tx,max becomes larger than 30 K. This allows an operation using an inexpensive and compact Stirling cryocooler. Above Tx,max, the exciton intensity decreases strongly until it disappears. The experimental data are quantitatively reproduced by a model which considers the competing processes of exciton generation, annihilation, and recombination. Exciton generation in the QDs is achieved by the sum of direct excitation in the dot, plus additional bulk excitons diffusing from the barrier layers into the dot. The thermally driven bulk-exciton diffusion from the barriers causes the temperature enhancement of the exciton emission. Above Tx,max, the intensity decreases due to exciton annihilation processes. In comparison to the exciton, the biexciton intensity shows only very weak enhancement, which is attributed to more efficient annihilation processes.

Improved uniformity and anisotropy of through-mask electrochemical micromachining by localized etching and homogeneous flow

This contribution aims to point out the potential of through-mask electrochemical micromachining (TMEMM) as an environmentally friendly alternative for thin metal layer patterning for applications such as printed circuit boards (PCBs). Two process chamber concepts with shearing and impinging electrolyte flow, based on the concept of localized etching, are introduced. The etching results, obtained with simple mask designs, were investigated regarding homogeneity in etch depth and anisotropy. Compared to a simple setup with unspecific electrolyte flow and full area etching, a significant improvement in microscopic and macroscopic homogeneity (deviations reduced from >100 to <10%) and anisotropy (etch factors increased from ~4 to >7) could be shown. A comparison to an industrial chemical etching process using a simple mask design revealed equal macroscopic homogeneity and higher etch factors in TMEMM. Only the microscopic homogeneity leaves still room for improvement. It is presented for the first time that island formation can be prevented completely over a large area (5 × 20 mm2) with TMEMM. These results demonstrate the advantages and the potential that can be achieved with TMEMM by designing appropriate tools.

TCAD Study on Suppression of Substrate-Induced Degradation in GaN-on-Si Integrated Half-Bridge Circuit by Local Si Lateral Etch

TCAD Study on Suppression of Substrate-Induced Degradation in GaN-on-Si Integrated Half-Bridge Circuit by Local Si Lateral Etch

The influence of fracture surface morphology on nonuniform etching in limestone acid fracturing

The success of acid fracturing in tight limestone reservoirs relies on the formation of nonuniform etching on the fracture wall. However, almost all acid fracturing models neglect the effect of fracture surface morphology on nonuniform etching. In this study, a three-dimensional acid fracturing mathematical model is developed to quantify and analyze the influence of rough fracture surface morphology on nonuniform etching for the first time by defining a morphology coefficient to describe the degree of local and overall morphological undulations of the fracture surface from a three-dimensional scale. The model uses the moving mesh partial differential equation (MMPDE) method to describe the flow field and spatial variation in the fracture as the fracture surface is continuously dissolved with the acid during acid fracturing, and the MMPDE moving mesh is coupled with the flow field, mass transfer, acid-rock reaction and fracture width variation. Based on the model, the effects of flow pattern, morphology coefficient, initial fracture width and fracture type on the nonuniform etching are studied. The simulation results demonstrate that the rough fracture surface can disturb the flow field and make the acid distribution more turbulent, which is conducive to the formation of nonuniform etching on the fracture surface. This phenomenon of flow rate differentiation can enhance the acid transfer distance. The local etching degree of the fracture surface decreases with the increase of the morphology coefficient of the area, and the strongly etching areas will appear around it. When the morphology coefficient of the local fracture area is larger than 1.2218, the area can appear obvious strongly etching areas and weakly etching areas after acid etching. The larger the initial fracture width is, the smaller the degree of nonuniform etching on the fracture surface. The prediction model constructed based on multiple linear regression was highly accurate (R2 = 0.9268) for the standard deviation of facture width (StdWidth) after acid etching. The critical value of StdWidth is recommended to be 0.6 as the criterion for judging the nonuniform etching ability. When the nonuniformity of the fracture surface is greater than this value, it is considered that the nonuniform etching ability is strong. In addition, the fracture with shear damage can produce relative sliding distance, which makes the fracture morphology on both sides of the fracture surface unevenly distributed and thus disturbs the flow field, which enhances the degree of nonuniform etching on the fracture surface. As the sliding distance increase, the magnitude of this enhancement also increases gradually. This study proposes a new three-dimensional characterization method for rough fracture surface morphology, solves the issue of mismatching flow field due to dynamic change in fracture width during acid fracturing.

Influence of Chemical Cleaning Procedures and Thermal Oxidation Processes on the Uniformity of MOS Gate Oxides on Abrupt Steps on Silicon Surfaces

This work analyzes the influence of some chemical steps used in standard cleaning recipes on the surface micro-roughness of silicon wafers. The effect of varying the ammonium hydroxide concentration in the NH4OH: H2O2:H2O solution was studied and silicon wafer micro-roughness was characterized by atomic force microscopy technique at different scans of 1µmx1µm. Based on the results, it was possible to point the condition to obtain low surface micro-roughness for NH4OH-based solutions with the lowest NH4OH content before the growth of gate oxides. Following, it silicon-oxide thin films were grown onto periodic rectangular shapes, 100 nm in height, obtained by localized plasma etching on silicon wafer surfaces. Silicon oxides (SiO2), about 4.5 nm thick, were grown in ultrapure dry-O2 or pyrogenic (O2 + H2) environments in order to compare the planar uniformity and the grade of coverage at the step edges of rectangular shapes defined onto silicon surfaces. Pyrogenic and conventional oxidation at 850 oC allowed one to obtain gate oxides on 100 nm-stepped silicon surfaces with high dielectric breakdown field (&gt;10 MV/cm), good planar uniformity and conformal coverage at the step edges. The impact of this result is now the feasibility of fabricating good-quality gate oxides for surrounding gate transistors (SGT’s) and texturized MOS solar cells.

Simultaneous sensing of strain and temperature based on the inline-MZI embedded point-shaped taper structure with low crosstalk.

An embedded spherical dot taper structure (EDT) based on the MZI principle is proposed in this paper, which is mainly fabricated by using two special arc discharges in the preparation process. The proposed structure involves two specialized arc discharge techniques. First, an oversaturated discharge fusion process creates a micro-arc spherical area on the fiber end face to form the first link type. Second, an unsaturated discharge-pulling taper fusion joint creates a local micro-extrusion operation on this micro-arc fiber end face to form the second link. The thermal stress from instantaneous discharge causes a reverse spherical expansion zone to form in the end face structure, similar to the micromachining of long-period fiber gratings that use local CO2 laser etching to create modulated zones. The study involves a mathematical and theoretical analysis of how geometric parameters in the spherical modulation zone impact the structure's characteristic spectrum. The research demonstrates the potential for this structure to function as a light-intensity modulated strain sensor device through both theoretical and experimental means. As per the experimental findings, the optimized structure displays a high level of strain sensing sensitivity at 0.03 dB/µε and temperature sensing sensitivity of 73 pm/°C (20°C-75°C) and 169 pm/°C (75°C-120°C). Additionally, it possesses excellent cross-sensitivity at only ∼0.0015 µε/°C. Therefore, this sensor presents a favorable option for strain and temperature synchronization sensing and monitoring components, and exhibits notable application prospects in precision engineering, which encompasses mechanical manufacturing, the power and electrical industry, healthcare domain, and certain specialized areas of small-scale precision engineering.

Degradation of GFRP bars in alkaline environments: An experimental and molecular dynamics study

Glass fibre reinforced polymer (GFRP) bars are widely used as a replacement for reinforced bars due to their high strength-to-weight ratio, whereas they also show a high safety risk for corrosion potential from alkaline ions attack in concrete. In this study, the mechanical property evolution and degradation mechanism of GFRP bars in alkaline environments was studied by using experimental and molecular dynamics simulations. The results show that the decreased strength of the GFRP was mainly associated with the increase in the hydroxide concentration (COH-) in the corrosive solution rather than other ions. The tensile strength of the GFRP bars declined by approximately 10% after 300 days of exposure when the pH of the corrosion solution approached 13. When the pH barely reached 10, the resin-fibre interlaminar shear strength slumped by approximately 29%. The favorable hydrogen bonding network was disrupted by alkaline ions, resulting in a lower interaction energy between water molecules and epoxy resin chain segments. In addition, OH− was distributed around the ester bond and attacked the ester group, and finally, the ester bond was hydrolysed to form carboxylate and alcohol. Free sodium ions combine rapidly with oxygen lone electrons (Na-Ow), thereby accelerating water-resin debonding aging by breaking hydrogen bonds within the polymer network. The hydroxyl radicals further invade the fibres through the microcracks formed inside the resin, causing localized etching of the fibres. The study will provide a theoretical basis for the design of anti-corrosion modification of GFRP bars.

Telecom C-band photon emission from (In,Ga)As quantum dots generated by filling nanoholes in In0.52Al0.48As layers

We present the fabrication of strain-free quantum dots in the In0.53Ga0.47As/In0.52Al0.48As-system lattice matched to InP, as future sources for single and entangled photons for long-haul fiber-based quantum communication in the optical C-band. We achieved these quantum dots by local droplet etching via InAl droplets in an In0.52Al0.48As layer and subsequent filling of the holes with In0.53Ga0.47As. Here, we present detailed investigations of the hole morphologies measured by atomic force microscopy. Statistical analysis of a set of nanoholes reveals a high degree of symmetry for nearly half of them when etched at optimized temperatures. Overgrowth with 50–150 nm In0.52Al0.48As increases their diameter and elongates the holes along the [01̄1]-direction. By systematically scanning the parameter space, we were able to fill the holes with In0.53Ga0.47As, and by capping the filled holes and performing photoluminescence measurements, we observe photoluminescence emission in the O-band up into the C-band depending on the filling height of the nanoholes.

Microstructure enhanced biocompatibility in laser additively manufactured CoCrMo biomedical alloy

The present work investigated biocompatibility of the unique nanostructural surface morphology inherently evolved in laser-based additively manufactured CoCrMo after biocorrosion in simulated body fluid at physiological temperature (37 °C). The extremely rapid thermokinetics intrinsically associated with the laser-based additive manufacturing technique resulted in heterogeneous cellular dendritic solidification morphologies with selective elemental segregation along the cell boundaries within CoCrMo samples. Consequently, a selective and spatially varying electrochemical response resulted in generation of a nanoscale surface morphology (crests and troughs) due to differential localized electrochemical etching. Also, depth of the trough regions was a function of the applied potential difference during potentiodynamic polarization which resulted in samples with varying morphological ratio (depth of trough/width of cell wall). CoCrMo with such nanoscale surface undulations were proposed for enhanced biocompatibility in terms of viability, spreading, and integration of MT3C3 pre-osteoblasts cells elucidated via MTT assay, immunofluorescence, and microscopy techniques. Furthermore, the influence of the morphological ratio, characteristic to the additively deposited CoCrMo after electrochemical etching (biocorrosion) on biocompatibility of MT3C3 pre-osteoblasts cells was qualitatively and quantitatively compared to a mirror-polished flat CoCrMo surface.