Etching Technique Research Articles

Synthesis and characterizations of zinc oxide nanorods by cost effective aqueous hydrothermal technique for solid state lighting applications

Zinc oxide (ZnO) is recognized as the most promising and often utilized semiconducting material due to its exceptional physical, chemical, optical, and relatively low-cost production features, as well as its ecologically beneficial nature. ZnO is a prominent candidate owing to its wide band gap (3.37 eV at room temperature) as well as its high exciton binding energy (60 meV) for the next generation of ultraviolet and blue optoelectronic devices. This would be achieved through the development of hybrid heterostructured LED devices with low manufacturing costs by blending gallium nitride (GaN) with zinc oxide (ZnO), which serves as the most efficient opto-electronic device. Due to its high electron mobility, high transparency in the visible wavelength spectrum, and low work function, ZnO is also a highly investigated transparent conducting oxide thin film for several applications. Besides, their incredible optical capabilities, ZnO-based optical devices, such as light-emitting diodes (LEDs) and laser diodes (LDs), have drawn a great deal of interest. This reported research work demonstrates the growth of high-density, high-aspect-ratio ZnO nanorod (NR) arrays on p-type gallium nitride substrates employing low-cost facial aqueous hydrothermal syntheses with optimised growing conditions. Additionally, a top-down chemical etching technique is adapted for fabricating zinc oxide nanotubes. High-quality ZnO nanorods with high intensity that were a few microns long were found across the GaN substrate with FESEM analysis. The chemical composition of the grown nanorods is confirmed with EDAX analysis. The wurtzite crystalline structure and c-axis orientation of the grown ZnO NR-arrays were identified in X-ray diffraction studies. A Schimadzu UV–Vis–NIR spectrophotometer was used to record the optical curve, and the energy gap was determined to be 3.24 eV by plotting the Tauc curve. The good optical quality of the harvested nanorods is ensured by the narrow near-band-edge (NBE) emission at 384 nm and defect emission peaks detected through photoluminescence analyses. Grown specimens are also subjected to Raman spectrum analyses, and the obtained results are presented.

Quantization Conductance of InSb Quantum-Well Two-Dimensional Electron Gas Using Novel Spilt Gate Structures

Electron transport behaviour in InSb semiconductor significantly changes when the conduction is restricted to two-dimensions. Semiconductor materials are an effective tools to characterize the electron transport in this aspect because the energy separation between transverse modes in a low-dimensional semiconductor device are always inversely proportional to the effective mass, in the same way as for sub-bands in a parabolic potential. Therefore, in this article, a range of novel device geometries were designed, fabricated and characterized to investigate ballistic transport of electrons in low-dimensional InSb structures using surface gated devices to restrict the degrees of freedom (dimensionality) of the active conducting channel. In this framework, designs of gates (i.e., line, loop and solid discussed later) have been used over a range of gate dimensions. Consistent measurement of quantised conductance would be promising for both low power electronics and low temperature transport physics where split gates are typically used for charge sensing. This article presents an experimental results of quantization conductance obtained for the range geometries of novel gates, and some model consideration of the implications of the material choice. Furthermore, the etching techniques (wet and dry) exhibited a significant decrease of ohmic contact resistance from around 35kΩ to only roughly 250Ω at room temperature. Interestingly a possible 0.7 anomaly conduction was observed with a loop gate structure. This work showed perfectly that the two-dimensional electron gases can be formed in narrow gap InSb QWs which makes this configuration device promising candidate for topological quantum computing and next generation integrated circuit applications. Keywords: Quantization conductance, InSb QW, 2DEG, spilt gate structure, ballistic transport.

Graphitic carbon @ silver nanoparticle @ porous silicon Bragg mirror composite SERS substrate for gallic acid detection

Graphite carbon (G) @ silver (Ag) @ porous silicon Bragg mirror (PSB) composite SERS substrate was successfully synthesized using electrochemical etching (ec) and hydrothermal carbonization (HTC) techniques with silver nitrate as the source of silver and glucose as the source of carbon. The PSB was used as a functional scaffold for the synthesis of graphite-carbon and silver composite nanoparticles (G@AgNPs) on its surface, thereby combining SERS activity and antioxidant properties. To our knowledge, this is the first time that G@AgNPs has been synthesized on the PSB using glucose as a carbon source. The synthesized G@Ag@PSB was utilized as a SERS platform for the detection of gallic acid (GA). Test results demonstrated that the substrate exhibited a remarkable SERS enhancement capability for GA, with the enhancement factor (EF) reaching 2 × 105. The reproducibility of the SERS spectral signal was excellent, with a relative standard deviation (RSD) of 7.5 %. The sensitivity test results showed that the linear range of GA detection based on G@Ag@PSB composite SERS substrate was 2 × 10-3-2 × 10-12M. The relationship between GA concentration and SERS signal intensity exhibited a strong linear correlation, with a linear correlation coefficient (R2) of 0.97634. Moreover, even with an extended storage period, only a marginal decline in the signal intensity of GA on the substrate was observed. The results of this study demonstrate that the prepared G@Ag@PSB composite SERS substrate had good potential application performance as a low-cost SERS detection platform suitable for commercial use. In addition, this advance facilitates the further exploration of more nanomaterials with ultra-high sensitivity in SERS technology.

Patterning optimization for device realization of patterned GaAsSbN nanowire photodetectors

Vertically grown nanowires (NWs) are a research interest in optoelectronics and photovoltaic applications due to their high surface to volume ratio and good light trapping capabilities. This study presents the effects of process and design parameters on self-catalyzed GaAsSbN NWs grown by plasma-assisted molecular beam epitaxy on patterned silicon substrates using electron beam lithography. Vertical alignment of the patterned NWs examined via scanning electron microscopy show the sensitivity of patterned NW growth to the parameters of NW diameter, pitch, dose time, etching techniques and growth plan. Diameters range from 90 nm to 250 nm. Pitch lengths of 200 nm, 400 nm, 600 nm, 800 nm, 1000 nm, and 1200 nm were examined. Dry etching of the oxide layer of the silicon substrate and PMMA coating is performed using reactive ion etching (RIE) for 20 s and 120 s respectively. Comparisons of different HF etch durations performed pre and post PMMA removal are presented. Additionally, the report of an observed surfactant effect in dilute nitride GaAsSbN NWs in comparison to non-nitride GaAsSb is presented. Optimizations to patterning, RIE, and HF etching are presented to obtain higher vertical yield of patterned GaAsSbN NWs, achieving ∼80% of the expected NW µm2. Room temperature and 4 K photoluminescence results show the effect of nitride incorporation for further bandgap tuning, and patterned pitch on the optical characteristics of the NWs which gives insights to the compositional homogeneity for NWs grown at each pitch length.

Plasma-free anisotropic selective-area etching of β-Ga2O3 using forming gas under atmospheric pressure

ABSTRACT We demonstrate a facile and safe anisotropic gas etching technique for β-Ga2O3 under atmospheric pressure using forming gas, a H2/N2 gas mixture containing 3.96 vol% H2. This etching gas, being neither explosive nor toxic, can be safely exhausted into the atmosphere, simplifying the etching system setup. Thermodynamic calculations confirm the viability of gas-phase etching above 676°C without the formation of Ga droplets. Experimental verification was achieved by etching ( 1 ˉ 02) β-Ga2O3 substrates within a temperature range of 700–950°C. Moreover, selective-area etching using this method yielded trenches and fins with vertical and flat sidewalls, defined by (100) facets with the lowest surface energy density, demonstrating significant anisotropic etching capability.

Performance characteristics of ultra-thin flat plate oscillating heat pipes with alternate channels and auxiliary micro-grooved structures

Two flat plate oscillating heat pipes (FPOHPs) characterized by the same thickness of 1 mm and alternating channel widths were fabricated using the wet etching technique. HFE-7100 was used as a working fluid at volumetric filling ratios ranging from 30%–60%. The startup and heat transfer characteristics of FPOHPs with and without embedded parallel microgrooves on the bottom wall of wider channels were experimentally compared and evaluated. The dual-diameter FPOHPs could operate at both horizontal and vertical orientations. The introduction of microgrooves reduced the duration of the startup time, lowered the startup temperature, and avoided the temperature overshoot. Furthermore, the microgrooves significantly reduced the temperature of the evaporator. At the combined condition of 30% filling ratio and 24 W power input, the effective thermal conductivities (ETCs) of the FPOHP with microgrooves were 1241 and 1226 W/(m·°C), respectively, at horizontal and vertical orientations, approximately 25.6% and 18.8% higher than those without microgrooves, or approximately 3.1 times higher than pure copper. At the horizontal orientation, the heat transfer enhancement was more pronounced for the micro-grooved FPOHP compared to that without micro-grooves. The micro-grooved structures facilitated the unidirectional fluid circulation and reduced the gravity dependence, showing the application prospects at both terrestrial and microgravity conditions.

Mitigation of Volumetric Expansion in Silicon Anodes via Engineered Porosity: Electrochemical Performances and Stress Distribution Implication

To overcome the significant volume expansion issue encountered by traditional silicon anodes in lithium‐ion batteries, this study employs chemical etching techniques to treat aluminum–silicon alloys of various ratios, successfully preparing three types of porous silicon electrode materials with different pore structures. Through a series of electrochemical tests, this article investigates the role of porous silicon structures in improving electrode performance. The results demonstrate that the porous silicon anodes exhibit superior cycle stability and rate capability compared to traditional solid silicon anodes. This confirms the effectiveness of the porous structure in mitigating the significant volume expansion during the charge and discharge process of silicon materials and in preventing premature electrode failure, thereby significantly enhancing the electrode's cycle life. Remarkably, the porous silicon with a high porosity rate shows exceptionally outstanding performance. Additionally, using computer simulations, this study also models the impact of changes in pore size within the porous silicon material at different states of charge and discharge on the stress distribution at the particle center and surface. These experimental and simulation results jointly provide strong empirical evidence for applying porous silicon materials as high‐performance anode materials for lithium‐ion batteries and offer essential guidance for future stress analysis and electrode design of porous silicon electrode materials.

Heated-H3PO4 etching of (001) β-Ga2O3

β-Ga2O3 is a promising ultra-wide bandgap semiconductor with melt-grown substrates that are scalable, particularly in the (001) orientation. In this study, we report on the heated-phosphoric acid etching of (001) β-Ga2O3. A wagon wheel pattern with spokes aligned to a range of specific crystallographic directions was fabricated on (001) β-Ga2O3. At 160 °C, the (001) etch rate was 1.47 μm/h, which is comparable to etch rates obtained via dry etch techniques. The etched (001) surface had a morphology that was smoother than an inductively coupled plasma etched surface. All spokes possessed relatively smooth sidewalls. Spokes oriented along the [100] direction exhibited minimal SiO2 mask undercut rates at lower etch temperatures and symmetric trapezoidal profiles with near vertical (010)-like sidewalls, which are ideal for device structures with a trench geometry. Spokes oriented along the [010] direction exhibited significant SiO2 mask undercut rates and asymmetric trapezoidal profiles with different sidewall angles. These spokes also possessed reduced sidewall angles, which is favorable for field management at device corners and edges. The etch process was used to realize a dense array of [100]-oriented trenches with a height of 1.5 μm, a base width of 2.0 μm, and a mask width of 0.8 μm. The work highlights the potential for ion damage-free, standalone heated-H3PO4 etching as a viable alternative to the dry etching of (001) β-Ga2O3 for high-performance device applications.

Enhancing the catalytic performance of H-ZSM-5 in bio n-butanol dehydration by zeolite crystal engineering

NH4F etching is used as an unbiased chemical etching technique to hierarchize commercially available nano-sized ZSM-5 crystals. A structure-function relationship is reported, describing how the introduction of mesoporosity in a microporous ZSM-5 zeolite significantly increases its catalytic performance in (aqueous) n-butanol dehydration. Three parent samples are etched under two severity modes: mild (5 minutes of etching) and harsh (40 minutes of etching). Intrinsic features of the parent ZSM-5’s, such as their silanol populations, influence the outcome of the etching procedure. For all materials, crystallinity is unaffected, total pore volume increases while micropore volume is almost constant, and active site accessibility increases. For all materials, etching increases the catalytic activity for n-butanol dehydration. Cofeeding water to n-butanol further increases the stability of all catalysts. Microkinetic modeling reveals that the increased activity is related to a decreased stability of dibutyl ether (DBE), the most abundant surface intermediate. A decreased DBE adsorption energy, due to the increased accessibility of the acid sites, facilitates its desorption. NH4F etching, a flexible and easy technique to engineer zeolites' textural properties, does not affect the intrinsic nature and quantity of their active sites, leading to superior catalytic performances. Our results highlight the possibility to further increase the efficiency of zeolite catalysis in biomass conversion processes.

Experimental study on the preparation of superalloy Inconel718 heat exchanger channels by electrochemical etching method

The nuclear energy field requires the construction of heat exchangers that can withstand sufficiently high temperatures. In this paper, the etching technique was utilized to fabricate heat exchange channels on Inconel718 plates, and experiments were carried out in NaCl-ethylene glycol solution, three temperature conditions of 35 °C, 40 °C, and 45 °C, and two concentrations of electrolyte solutions, 0.5 mol/L and 1 mol/L, with the addition of 50 kHz ultrasound for comparison. The experimental results show that the etching rate can be as high as 2.894 mm/h, and the inter-electrode current is as high as 908 mA. The roughness characterization of the etching channel Ra and Rq measured by the aspheric surface measuring instrument can be as low as 2.416 μm and 2.647 μm, respectively. In the images generated by SEM scanning, it is found that uneven distribution of pits and bumps exist in the etching channel, but their diameters are all less than 0.1 μm, which means the etched channel is acceptably smooth.

The Synthesis and Assembly Mechanism of Micro/Nano-Sized Polystyrene Spheres and Their Application in Subwavelength Structures.

The following study involved the utilization of dispersion polymerization to synthesize micron/nano-sized polystyrene (PS) spheres, which were then deposited onto a silicon substrate using the floating assembly method to form a long-range monolayer. Subsequently, dry etching techniques were utilized to create subwavelength structures. The adjustment of the stabilizer polyvinylpyrrolidone (PVP), together with changes in the monomer concentration, yielded PS spheres ranging from 500 nm to 5.6 μm in diameter. These PS spheres were suspended in a mixture of alcohol and deionized water before being arranged using the floating assembly method. The resulting tightly packed particle arrangement is attributed to van der Waals forces, Coulomb electrostatic forces between the PS spheres, and surface tension effects. The interplay of these forces was analyzed to comprehend the resulting structure. Dry etching, utilizing the PS spheres as masks, enabled the exploration of the effects of etching parameters on the resultant structures. Unlike traditional dry etching methods controlling RF power and etching gases, in the present study, we focused on adjusting the oxygen flow rate to achieve cylindrical, conical, and parabolic etched structures.

Collaborative experiment of the work group “Sample Preparation” on the subject “Reduction of hazardous substances in metallographic etching using electrolytic etching techniques”

Abstract This article shows how conventional etching methods can be replaced by electrolytic processes, thereby reducing hazardous substances during etching. The joint experiment carried out on this topic by the “Sample Preparation” working group uses various materials to show how hazardous substances can be reduced, but also the existing limitations.

Influence of Age and Etching Technique on the Microleakage in Class-V Composite Restorations: An In-vitro Study

Aim: The objective of current research was to evaluate the impact of patient’s age on the microleakage in Class-V composite restorations. Study Design: Research article. Methodology: 30 permanent human molars from various age groups (n=10 each) were collected. The teeth were categorized based on age, Group I (less than 30 years), Group II (30-50 years), and Group III (more than 50 years), standardized Class-V tooth preparations were prepared. Subsequently, each group has further two subgroups: selective enamel etching (Sb A) and self-etching (Sb B), using universal adhesive (3M single bond). Following this, restoration of teeth were done using Z350 composite, and microleakage was analysed by dye penetration method via stereomicroscope and corresponding scoring were recorded. Mann- Whitney Test and Kruskal- Wallis Test was done for statistical analysis. Results: The group III subgroup A and B showed highest microleakage (2.40 and 2.80) followed by group II (1.20 and 1.60) and least in group I (0.40 and 0.80) respectively (P<.005). Therefore, more microleakage was seen with self-etch group as compare to selective etch. Conclusion: Influence of age of patient had significant impact on Class-V restorations. Also, more microleakage was observed in self-etch group as compared to that of selective etch technique.

Ar/NH3 Plasma Etching of Cobalt-Nickel Selenide Microspheres Rich in Selenium Vacancies Wrapped with Nitrogen Doped Carbon Nanotubes as Highly Efficient Air Cathode Catalysts for Zinc-Air Batteries.

This work utilizes defect engineering, heterostructure, pyridine N-doping, and carbon supporting to enhance cobalt-nickel selenide microspheres' performance in the oxygen electrode reaction. Specifically, microspheres mainly composed of CoNiSe2 and Co9Se8 heterojunction rich in selenium vacancies (VSe·) wrapped with nitrogen-doped carbon nanotubes (p-CoNiSe/NCNT@CC) are prepared by Ar/NH3 radio frequency plasma etching technique. The synthesized p-CoNiSe/NCNT@CC shows high oxygen reduction reaction (ORR) performance (half-wave potential (E1/2) = 0.878V and limiting current density (JL) = 21.88mA cm-2). The JL exceeds the 20wt% Pt/C (19.34mA cm-2) and the E1/2 is close to the 20wt% Pt/C (0.881V). It also possesses excellent oxygen evolution reaction (OER) performance (overpotential of 324 mV@10mA cm-2), which even exceeds that of the commercial RuO2 (427 mV@10mA cm-2). The density functional theorycalculation indicates that the enhancement of ORR performance is attributed to the synergistic effect of plasma-induced VSe· and the CoNiSe2-Co9Se8 heterojunction. The p-CoNiSe/NCNT@CC electrode assembled Zinc-air batteries (ZABs) show a peak power density of 138.29mW cm-2, outperforming the 20wt% Pt/C+RuO2 (73.9mW cm-2) and other recently reported catalysts. Furthermore, all-solid-state ZAB delivers a high peak power density of 64.83mW cm-2 and ultra-robust cycling stability even under bending.

Characteristics of clean SiO2 atomic layer etching based on C6F6 physisorption

SiO2 atomic layer etching (ALE) techniques are widely used to improve the etch issues related to nanoscale semiconductor device etching such as self-aligned contact (SAC) etching requiring high etch selectivity of SiO2/Si3N4. For more precise and cleaner SiO2 ALE, cryo-ALE methods using physisorption of fluorocarbon gas at a cryotemperature are also being investigated. In this study, to avoid the use of cryotemperature for clean SiO2 ALE, a high boiling point (HBP) gas such as C6F6, having 80 °C of boiling point (global warming potential: 7), has been used as the physisorption gas without using cryotemperatures. At a substrate temperature lower than −15 °C, due to the adequate physisorption of C6F6 on the SiO2 and Si3N4 surfaces, high SiO2 etch depth per cycle (EPC) and high etch selectivity of SiO2/Si3N4 could be achieved through the higher chemical reaction of the fluorocarbon layer with SiO2 than that of Si3N4. For the etching of Si3N4 line patterned SiO2, an O2 descumming step was added after every 50 cycles of ALE process to prevent fluorocarbon layer deposition on the sidewall of the Si3N4 mask. Finally, anisotropic SiO2 etch profiles with high etch selectivity of SiO2/Si3N4 could be obtained without contamination of chamber sidewalls.

Subsurface damage evolution of β-Ga2O3 (010) substrates during lapping and chemical mechanical polishing

For semiconductor single crystal substrates, subsurface damage (SSD) is an important factor for device failure. For β-Ga2O3 with two cleavage planes, the SSD is the key issue that needs to be addressed. In this work, β-Ga2O3 (010) substrates were lapped and polished precisely. The formation and evolution mechanisms of SSD were analyzed by cross-section transmission electron microscopy and wet chemical etching techniques. The linear distribution of scratches was found on the substrates after lapping. After chemical mechanical polishing (CMP), the surface scratches were eliminated. However, the SSD layer may still exist under the surface. Chemical etching was developed to identify the "invisible damage" to the CMP-finished (010) substrate. The SSD including nanocrystalline, tilt boundary, twist boundary, and high-density dislocations in β-Ga2O3 was first reported. Distinctively, there was no slip occurrence in the SSD of the (010) plane different from the (100) and (001) planes. The Schmid factor of multiple slip systems was calculated to analyze the cause of no slip on the subsurface. The formation mechanism of SSD was believed that when the slip system could not be activated, the stress was released through rotation and distortion of the crystal plane. The accumulation of grain boundary dislocations at twist grain boundary junctions provided a driving force for the formation of nanovoids. The relationship of substrate damage evolution and crystal strain with different machining parameters was established by high-resolution X-ray diffraction and Raman spectra. A non-damaging β-Ga2O3 (010) substrate with a surface roughness of less than 0.2 nm was obtained by the optimized CMP process. The research results had guiding significance for damage control of β-Ga2O3 and other brittle crystals in ultra-precision machining.

Nanoimprint Lithography for Next-Generation Carbon Nanotube-Based Devices.

This research reports the development of 3D carbon nanostructures that can provide unique capabilities for manufacturing carbon nanotube (CNT) electronic components, electrochemical probes, biosensors, and tissue scaffolds. The shaped CNT arrays were grown on patterned catalytic substrate by chemical vapor deposition (CVD) method. The new fabrication process for catalyst patterning based on combination of nanoimprint lithography (NIL), magnetron sputtering, and reactive etching techniques was studied. The optimal process parameters for each technique were evaluated. The catalyst was made by deposition of Fe and Co nanoparticles over an alumina support layer on a Si/SiO2 substrate. The metal particles were deposited using direct current (DC) magnetron sputtering technique, with a particle ranging from 6 nm to 12 nm and density from 70 to 1000 particles/micron. The Alumina layer was deposited by radio frequency (RF) and reactive pulsed DC sputtering, and the effect of sputtering parameters on surface roughness was studied. The pattern was developed by thermal NIL using Si master-molds with PMMA and NRX1025 polymers as thermal resists. Catalyst patterns of lines, dots, and holes ranging from 70 nm to 500 nm were produced and characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Vertically aligned CNTs were successfully grown on patterned catalyst and their quality was evaluated by SEM and micro-Raman. The results confirm that the new fabrication process has the ability to control the size and shape of CNT arrays with superior quality.

Lithography-Free Nanofabrication on Various Semiconductors by the Codeposition Etching Technique.

Nano-/microstructures can be formed with the aid of small amounts of impurities during deposition with noble gas plasma irradiation, which is referred to as codeposition etching. This can be a new method for lithography-free semiconductor nanofabrication. Here, the codeposition etching method was employed with argon plasma and molybdenum (Mo) impurities on various semiconductors. Structures can be formed only on substrates that have a lower sputtering yield than the seed impurity. The density, area, and height of structures are related to both the impurity deposition rate and the substrate material. Moreover, two mechanisms of impurity nucleation are proposed according to time dependence results for the formation of the structures.

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.

Stacked Si Nanosheets Gate-All-Around Transistors with Silicon-on-Nothing Structure for Suppressing Parasitic Effects and Improving Circuits’ Performance

We propose a novel silicon-on-nothing (SON) structure with an air sub-fin for suppressing the parasitic channel effects on stacked Si nanosheets (NS) gate-all-around (GAA) transistors and a systematic investigation is carried out by 3D TCAD simulation. The SON structure could be fabricated using a backside selective etching technique. The proposed SON NSFETs with a designed air sub-fin structure demonstrates systematic advantages, including 40% off-state current reduction in the sub-channel, and 51.37% promotion for on-off current ratio (ION/IOFF) and 7.04% reduction in effective capacitance. Moreover, there is approximately 21.62% power reduction under the same frequency, and about 16.30% energy reduction under the same delay in 17-stage ring oscillators (ROs). The SON NSFETs-based 6T-SRAM exhibits decreased read time and write time by 14.66% and 67.53%, respectively, compared with those of the conventional GAA NSFETs-based 6T-SRAM.