Oxidative Dissolution Research Articles

Impact of calcium ions on the oxidative dissolution of UO2-based surrogats for spent nuclear fuel

Impact of calcium ions on the oxidative dissolution of UO2-based surrogats for spent nuclear fuel

The Negative Role of Proton Insertion on the Lifetime of Vanadium-Based Aqueous Zinc Batteries.

Vanadium oxides are attracted cathodes for aqueous zinc batteries owing to their high capacity. However, the limited cyclability of vanadium-based oxide cathodes, especially at low current densities, impedes their practical application. Here, it is revealed that proton insertion is responsible for the limited lifetime of vanadium oxides. Proton insertion promotes the dissolution of vanadium oxides, deteriorating electrochemical performance. Propylene carbonate (PC) is introduced into Zn(CF3SO3)2 electrolyte to regulate the coordination environment of water, forming PC-coordinated Zn2+ solvation structure and [H2O-CF3SO3 --PC] complex. The optimized coordination environment of water weakens the adsorption energy between water molecules and vanadium oxides, inhibiting proton insertion. As a result, vanadium-based oxides cathode without proton insertion can maintain the stability of crystal structure and avoid the dissolution of V. Taking CaV8O20·nH2O as cathode, Zn||CaV8O20·nH2O battery without proton insertion performs enhanced cycling performance. This work not only reveals the negative effect of proton insertion on the lifetime of vanadium-based oxides cathode but also provides an effective strategy to modulate proton insertion.

Ab Initio Molecular Dynamics Insights into Stress Corrosion Cracking and Dissolution of Metal Oxides

Oxide phases such as α-Fe2O3 (hematite) and α-Al2O3 (corundum) are highly insoluble in water; however, subcritical crack growth has been observed in humidity nonetheless. Chemically induced bond breaking at the crack tip appears unlikely due to sterically hindered molecular transport. The molecular mechanics of a crack in corundum with a reactive force field reveal minimal lattice trapping, leading to bond breaking before sufficient space opens for water transport. To address this, we model a pre-built blunt crack with space for H2O molecule adsorption at the tip and show that it reduces fracture toughness by lowering the critical J-integral. Then, we explore stress-enhanced dissolution to understand the mechanism of crack tip blunting in the oxide/water system. Density functional theory combined with metadynamics was employed to describe atomic dissolution from flat hematite and corundum surfaces in pure water. Strain accelerates dissolution, stabilizing intermediate states with broken bonds before full atom detachment, while the free energy profile of unstrained surfaces is almost monotonic. The atomistic calculations provided input for a kinetic model, predicting the shape evolution of a blunt crack tip, which displays three distinct regimes: (i) dissolution primarily away from the tip, (ii) enhanced blunting near but not at the apex, and (iii) sharpening near the apex. The transition between regimes occurs at a low strain, highlighting the critical role of water in the subcritical crack growth of oxide scales, with dissolution as the fundamental microscopic mechanism behind this process.

Environmentally Friendly and Simple Recycling of Titanium Alloy Scrap via Deoxygenation with Hybrid Hydrogen Plasma Arc.

The potential of hydrogen plasma arc technology for the efficient deoxygenation and recycling of titanium alloy scrap is explored. The results of thermodynamic analysis reveal that hydrogen plasma is suitable for oxygen removal. The intermediate stages of the deoxygenation process are sequentially analyzed, showing that the hydrogen plasma arc primarily facilitated the reduction and dissolution of oxides as well as eliminated interstitial oxygen. The experimental results demonstrate that the deoxygenation dynamics are governed by the interaction between the hydrogen partial pressure and the surface area of the hydrogen plasma arc irradiation range. Furthermore, the results of the detailed characterization of the recycled titanium alloys indicate that hydrogen plasma arc technology not only reduces the oxygen content to levels compliant with industrial standards for Ti-6Al-4V but also substantially enhances the tensile strength and ductility of Ti-6Al-4V compared with those of conventional cast titanium alloys. The results of microstructural analysis show that hydrogen tends to concentrate in the β phase, whereas oxygen is predominantly found in the α phase. These findings highlight the effectiveness of hydrogen plasma arc technology, which offers environmental benefits and improves the performance of the resulting material, indicating its promise as a solution for titanium recycling.

Corrosion of Low-Alloy Steel in Ethanolamine Steam Generator Chemistry-The Effect of Temperature and Flow Rate.

The corrosion of low-alloy steel in ethanolamine solution, simulating steam generator chemistry, is studied by in situ chronopotentiometry and electrochemical impedance spectroscopy combined with ex situ analysis of the obtained oxide films and model calculations. Hydrodynamic calculations of the proposed setup to study flow-assisted corrosion demonstrate that turbulent conditions are achieved. Quantum chemical calculations indicate the adsorption orientation of ethanolamine on the oxide surface. Interpretation of impedance spectra with a kinetic approach based on the mixed-conduction model enabled estimating the rate constants of oxidation at the alloy-oxide interface, as well as charge transfer and ionic transport resistances of the corrosion process. In turbulent conditions, the dissolution of Fe oxide and ejection of Fe cations are enhanced, leading to Cr enrichment in the oxide and alteration of its electronic and electrochemical properties that influence the corrosion rate.

Atomic-scale understanding of oxide growth and dissolution kinetics of Ni-Cr alloys

Aqueous corrosion of metals is governed by formation and dissolution of a passivating, multi-component surface oxide. Unfortunately, a detailed atomistic description is challenging due to the compositional complexity and the need to consider multiple kinetic factors simultaneously. To this end, we combine experiments with a first-principles-derived, multiscale computational framework that transcends thermodynamic descriptions to explicitly simulate the kinetic evolution of surface oxides of Ni-Cr alloys as a function of composition, temperature, pH, and applied voltage. In the absence of pitting, we identify three distinct voltage regimes, which are kinetically dominated by oxide growth, dissolution, and competitive dissolution and reprecipitation. Evolving compositional gradients and oxide thickness are revealed, including a transition between a metastable Ni-Cr mixed oxide and a thick, porous Ni-dominated oxide. Beyond elucidating the underlying physics, we highlight the need for competing kinetics in models to properly predict the transition from passivation to corrosion. Our results provide a key step towards co-design of alloy composition alongside environmental conditions for sustainable use across a variety of critical energy and infrastructure applications.

Improving Bioactivity of Anodic Titanium Oxide (ATO) Layers with Chlorine Ion Addition in Electrolytes

Improving Bioactivity of Anodic Titanium Oxide (ATO) Layers with Chlorine Ion Addition in Electrolytes

The role of hydrogen peroxide in the acid dissolution of indium tin oxide (ITO) in the context of selective indium recovery from secondary sources

The role of hydrogen peroxide in the acid dissolution of indium tin oxide (ITO) in the context of selective indium recovery from secondary sources

Effects of Thermal Pretreatment on the Oxidative Dissolution of Chalcopyrite: Electrochemical Study with Synthetic Minerals

Effects of Thermal Pretreatment on the Oxidative Dissolution of Chalcopyrite: Electrochemical Study with Synthetic Minerals

Oxidative Dissolution of Sulfide Minerals in Porous Media Under Evaporative Conditions: Multiphase Experiments and Process‐Based Modeling

AbstractThe dissolution of sulfide minerals in subsurface porous media has important environmental implications. We investigate the oxidative dissolution of pyrite under evaporative conditions and advance a mechanistic understanding of the interactions between multiple physical processes and mineral/surface reactions. We performed a set of experiments in which initially water saturated and anoxic soil columns, containing a top layer of pyrite, are exposed to the atmosphere under no evaporation (single‐phase) and natural evaporative (two‐phase) conditions. The oxidative dissolution of pyrite was monitored by non‐invasive high‐resolution measurements of oxygen and pH. Additionally, we developed and applied a multiphase and multicomponent reactive transport model to quantitatively describe the experimental outcomes and elucidate the interplay between the physico‐chemical mechanisms controlling the extent of pyrite dissolution. The results confirm that the extent of pyrite dissolution under single‐phase conditions was constrained by the slow diffusive transport of oxygen in the liquid phase. In contrast, during evaporation, the evolution of fluid phases and interphase mass transfer processes imposed distinct physical constraints on the dynamics of pyrite oxidation. Initially, the invasion of the gaseous phase led to a fast delivery of high oxygen concentrations in the reactive zone and thus markedly increased pyrite oxidation and acidity/sulfate production. However, such enhanced release of reaction products was progressively limited over time as drying conditions prevailed in the reactive zone and inhibited pyrite oxidation. The transient phase displacement was also found to control the distribution of aqueous species and formation of secondary minerals by creating spatio‐temporally variable redox conditions.

Effect of ultrasonic treatment on tin recovery from decommissioned displays in sulphuric, hydrochloric, and methanesulphonic acid solutions

The study investigates the physicochemical patterns of tin leaching from the surface of glass substrates from decommissioned displays in hydrochloric, sulphuric, and methanesulphonic acids. The effects of acid concentration (0.1–1.0 N), duration (10–60 min), temperature (298–353 K), and ultrasonic treatment intensity (UST) (120–300 W/cm2) on leaching performance were evaluated. It was demonstrated that ultrasonic treatment positively impacts sulphuric acid leaching of tin, increasing its recovery by 14–16 %. However, during leaching in hydrochloric and methanesulphonic acid solutions, UST led to a reduction in tin recovery to 28 % and 1.7 %, respectively, due to acid decomposition under ultrasound. The partial reaction orders for tin leaching in HCl, H2SO4, and CH3SO3H were determined to be 0.8, 1.4, and 1.1, respectively, and changed to 1.5, 1.1, and 0.3 under ultrasound for the corresponding acids. An increase in temperature from 298 K to 333 K significantly improved tin recovery in sulphuric and hydrochloric acids. However, raising the temperature to 353 K led to a decrease in tin ion concentration after 10–20 min, likely due to tin hydrolysis and precipitation. The calculated apparent activation energies of tin oxide dissolution in HCl solutions were 40.4 kJ/mol without UST and 22.9 kJ/mol with UST. For H2SO4, the apparent activation energy was 4.0 kJ/mol, increasing to 29.0 kJ/mol under ultrasonic treatment. Therefore, the study showed that tin leaching from glass substrates of decommissioned displays proceeds in a kinetic regime when HCl is used and in a diffusion regime in H2SO4 solutions, with ultrasonic treatment facilitating the transition to a mixed regime.

Reductive Dissolution Mechanisms of Manganese Oxide Mediated by Algal Extracellular Organic Matter and the Effects on 17α-Ethinylestradiol Removal.

Reductive dissolution of manganese oxide (MnOx) is a major process that improves the availability of manganese in natural aquatic environments. The extracellular organic matter (EOM) secreted by algae omnipresent in eutrophic waters may affect MnOx dissolution thus the fate of organic micropollutants. This study investigates the mechanisms of MnOx reductive dissolution mediated by EOM and examines the effects of this process on 17α-ethinylestradiol degradation. The influences of EOM concentration (1.0-20.0 mgC/L) and pH (6.0-9.0) in both dark and irradiated conditions were assessed. In the dark, EOM was found to facilitate MnOx reductive dissolution via the ligand-to-metal charge transfer (LMCT). The dissolution was further enhanced under irradiation, with the participation of superoxide ions (O2•-). Higher EOM concentrations increased the contents of available reducing substances and O2•-, accelerating the reductive dissolution. Higher pH slowed the photoreductive dissolution rates, while O2•--mediated reduction became more important. Polyphenols and highly unsaturated carbon and phenolic formulas in EOM were found to drive the reductive dissolution. Soluble reactive Mn(III) formed through reductive dissolution of MnOx effectively removed 17α-ethinylestradiol in solution. Overall, the findings regarding the mechanisms behind reductive dissolution of MnOx have broad implications for Mn geochemical cycles and organic micropollutant fate.

Robust MnO2-WO3 Complementary Electrochromic Device Enabled by Reversible Electrodeposition of MnO2.

Reversible electrodeposition and dissolution of manganese oxide (MnO2) represent an emerging electrochromic system. However, challenges such as "dead MnO2" formation, limited optical modulation across a narrow wavelength range, and difficulties in scaling up have significantly hindered the development of MnO2 reversible electrodeposition-based electrochromic windows. In this work, we introduced Fe2+/Fe3+ mediator ions into the electrolyte to suppress the Jahn-Teller effect, thereby preventing the formation of "dead MnO2" and achieving stable and reversible MnO2 deposition/dissolution. Furthermore, by employing WO3 as the counter electrode, we developed a complementary electrochromic device based on ion insertion and metal oxide deposition. This complementary system exhibits color neutrality in the colored state and high optical contrast across the entire visible spectrum, with an average optical modulation of 67.3%, excellent cycling stability (85.0% retention after 3000 cycles), and capability to switch uniformly over areas as large as 100 cm2.

Investigation of the Origin of Elevated Amounts of Iron and Manganese in a Dam Reservoir

On the outskirts of the Pinios dam reservoir (Ilia Regional Unit, Greece), a water treatment plant serves the water supply needs of the surrounding municipalities, in which high concentrations of Fe and Mn, before treatment, have been observed. The main purpose of this research was to investigate the mechanism of increased iron (Fe) and manganese (Mn) levels in the reservoir of the Pinios dam, which impacts its water treatment plant operation. A wide range of hydrochemical and sedimentological analyses were conducted over a hydrological year, focusing on the spatial and temporal distribution of Fe and Mn in both water and sediment samples across the established research monitoring stations. Sediment samples from the reservoir’s bottom revealed predominantly fine-grained material, rich in total organic carbon, with elevated Mn and Fe oxide levels. Significant seasonal variations in Fe and Mn levels were also discovered, with higher Mn levels observed in the anoxic bottom waters of the reservoir during the dry season, attributed to the reduced conditions favoring Mn oxide dissolution over Fe. Conversely, during the wet season, a homogenization of metal concentrations throughout the water column was observed due to increased oxygenation and freshwater inflow. These outcomes were confirmed by the hydrochemical analysis, indicating that the redox conditions, pH, and temperature, as well as the presence of organic matter, significantly influence the mobility and bioavailability of these metals in the reservoir. The findings of this study clarify that the high concentration of Fe and Mn can be linked to the mineral composition of the upstream Neogene and flysch formations in the study area. As these formations are affected by geological weathering, they tend to enrich the streams, through soil erosion and runoff processes, with metals like Fe and Mn, which are eventually transported into the dam reservoir. This study highlights the critical influence of lithological, sedimentological, and hydrological factors on the redox conditions and seasonal stratification that govern the behavior of Fe and Mn concentrations and mobility in dam reservoirs. These findings are critical for informing water resource management practices and dam infrastructure operators and developing effective environmental conservation strategies in similar cases.

Aqueous oxidation of coal-associated pyrite and standard pyrite mineral towards understanding the depyritization kinetics and acid formations

In coal mining areas, the ambient atmospheric and aqueous oxidation of pyrite minerals (FeS2) associated with coal as well as the other accompanying strata is significant in understanding the extent of acid mine drainage (AMD), the cause of severe environmental pollution. Therefore, in this paper, the oxidation kinetics of the coal-associated pyrite (CAPy) present in a coal sample (TpHM1) has been studied via aqueous leaching depyritization experiments at variety of temperatures and time intervals without the incorporation of any oxidizer. The outcomes obtained are juxtaposed with the standard pyrite mineral (SPM) oxidation at the same experimental conditions. Also, the coal and SPM slurry residues and filtrates obtained after aqueous leaching at 25 °C and 90 °C for 0 h and 24 h, respectively, were extensively analyzed through high-resolution transmission electron microscopy (HR-TEM), Powder X-ray diffraction (P-XRD), and X-ray-photoelectron spectroscopy (XPS) for evaluation of the mineralogical composition and proportions of iron and sulfur components during progression of the oxidation reaction. Both the reactions obey pseudo first-order kinetics during pyrite (FeS2) oxidation but a significant difference in the experimentally found activation energies (Ea) and rate constants (k) values of oxidation kinetics of both CAPy and SPM may be attributed to the varied geochemical compositions of the coal associated pyrite (CAPy). The rate constant for CAPy is much greater than that of SPM implying a higher Ea around 10.838 kJ/mol for SPM as compared to 1.941 kJ/mol for CAPy. The CAPy in coal (TpHM1) is more susceptible to atmospheric oxidation than that of SPM, leading to the formation of acid mine drainage with lower pH. In this paper, the pH values on the basis of stoichiometric pyrite oxidation reaction were calculated and compared with the pH values obtained after aqueous leaching of CAPy to interpret the extent of acid formation and pyrite dissolution. Hence, with the assistance of the current study, further studies on the effects of mineral impurities, whereabouts of pyrite minerals in coal seams, the significance of compositional differences in the CAPy, the effect of metal oxides, and the role of alkalinity producing neutralizing agents of coal in the oxidative dissolution process of pyrite can be investigated.

Decoupling of redox processes from soil saturation in Arctic tundra

Permafrost thaw in warming Arctic landscapes alters hydrology and saturation-driven biogeochemical processes. Models assume that aerobic respiration occurs in drained soils while saturated soils support methanogenesis; however, saturated soils maintain redox gradients that host a range of anaerobic metabolisms. We evaluated how redox potential and redox-active solutes vary with soil moisture in the active layer of permafrost-affected acidic and non-acidic tundra hillslopes. Oxidizing conditions persisted in highly permeable organic horizons of both unsaturated tussock tundra and saturated wet sedge meadows. Redox potential decreased with depth in all soils as increasing soil bulk density restricted groundwater flow and oxygen diffusion. High concentrations of dissolved iron, phosphate, and organic carbon coincided with redox boundaries below the soil surface in acidic tundra, indicating active iron redox cycling and potential release of adsorbed phosphate during iron (oxyhydr)oxide dissolution. In non-acidic tundra, weatherable minerals affected nutrient dynamics more than redox-driven iron cycling, especially in low-lying, saturated areas where thaw reached mineral soils. The role of thaw depth and the ability of saturated soils to maintain oxidizing conditions in organic surface layers highlight the importance of soil physical properties and hydrology in predicting biogeochemical processes and greenhouse gas emissions.

Leaching behavior of arsenic in coal under the action of mine water

Arsenic, a potentially harmful element in coal, has a detrimental effect on the quality of groundwater and the water cycle. There is a significant safety risk to the drinking water and overall health of residents living near mining areas. It is of great significance to explore the leaching pattern of arsenic in coal under the influence of mining and identify the main controlling factors for the prevention and control of groundwater pollution in mining areas. In this paper, we selected long flame coal and non-caking coal from Wulanmulun Mine, along with four types of water samples from the mine area, as the research subjects. Our aim was to investigate the leaching mechanism of arsenic in groundwater under the influence of coal-water interaction in the mine area. To achieve this, we conducted indoor batch coal-water leaching simulation experiments. The results show that: 1) The four leaching solutions, which correspond to four groundwater types at the coal mine production site, exhibit similar trends in the presence of arsenic ions after water-coal interaction. The leaching process can be divided into three distinct zones: a rapid descent zone, a dissolution shock zone, and a dissolution linear stable zone. The initial decline rate of arsenic content in different water samples is proportional to the initial concentration of arsenic in the water samples. 2) The dissolution of arsenic has a strong negative correlation with DO, and the lower the oxygen content in the solution, the higher the arsenic ion content. There is a relatively strong negative correlation with pH value. It has a strong positive correlation with the leaching of Mg, K, V, Cr, and Fe, and a relatively small positive correlation with the leaching of Mn and Cu. The leaching degree of Mg, K, V, Cr and Fe can be used as a sign to explore the leaching or content change of arsenic in actual mining environment. 3) Most arsenic in coal occurs in pyrite in the form of isomorphism or solid solution, and the dissolution of arsenic is related to pyrite content and its oxidative dissolution behavior. The higher the pyrite content, the greater its oxidation degree, and the higher the arsenic content in the solution. 4) Clay minerals, predominantly kaolinite, found in different coal samples demonstrate varying capacities for arsenic adsorption in the leaching solution. The results of this experiment indicate that the adsorption capacity of clay minerals in long flame coal is considerably higher than that observed in non-caking coal, leading to a substantial decrease in the concentration of arsenic ions in the solution. This reduction is associated with a notable decline in the arsenic concentration within the groundwater associated with the coal samples collected on-site. The results suggest that the leaching of arsenic from the coal samples will not lead to arsenic contamination in four distinct categories of groundwater. This finding holds considerable importance for the management and remediation of water pollution in mining contexts.

(Invited) All-Solid-State Photoelectric Conversion Cells Employing the Combination of Metal Nanoparticle and p-Type Semiconductors for Plasmon-Induced Charge Separation

Metal nanoparticles, such as gold and silver nanoparticles, can localize light energy to the nanospace near the particle surface by localized surface plasmon resonance (LSPR) under light irradiation at resonant wavelengths. In addition, by controlling parameters, such as shape and size of the metallic nanoparticles, it is possible to control the light absorption properties at any wavelength in the range from visible to near-infrared. Therefore, LSPR of metal nanoparticles is attracting attention as a technology for effective use of sunlight. When metal nanoparticles combined with semiconductors are irradiated with light at resonant wavelengths, charge is transferred from the metal nanoparticles to the semiconductors. This is called plasmon-induced charge separation (PICS) (Fig. 1(a)), and is expected to be applied to photoelectric conversion, photocatalysis, and sensing using light in the visible to near-infrared region.Conventionally, the semiconductors to be combined are mainly n-type such as TiO2. In conventional systems, a positive charge is generated on the metal nanoparticle side, causing oxidative dissolution into the electrolyte, so the only practical options for metal nanoparticles were Au (or Ag with improved stability). In the case of all-solid-state systems that do not use an electrolyte, the counter electrode must be made of a material with a low work function, such as Al or In, which has an ohmic contact at the interface with the n-type semiconductor, resulting in air oxidation and low long-term device stability (Fig. 1(c)) [1].In this study, we fabricated all-solid-state cells using p-type semiconductors as the semiconductor combined with metal nanoparticles (ITO/metal nanoparticles/p-type semiconductor/Au) (Fig. 1(d)). In this system, it was found that Ag and Cu can also be used as metal species because negative charges are generated on the metal nanoparticle side (Fig. 1(b)). In addition, Au, which makes ohmic contact with p-type semiconductors, could be used as the counter electrode, which dramatically improves the long-term stability of the device in air [2].The all-solid-state photovoltaic cells composed of p-type semiconductors and metal nanoparticles realized in this study is expected to be applied as a cost-effective solar cell with a simple structure and high stability, as well as in various other applications, such as sensing and photocatalytic systems.[1] Y. Takahashi, T. Tatsuma, Appl. Phys. Lett., 99, 182110(1 – 3) (2011).[2] Y. Takahashi, Y. Yamadori, T. Murayama, S. Shingo, S. Yamada, in preparation. Figure 1

Precise Inner Spacer Etch-Back By Combining Ozone Gas Bake and Wet Chemical Etching

IntroductionBeyond nanosheet technology in gate-all-around (GAA) transistor, Forksheet and Complementary FET (CFET) are proposed [1-4], and inner spacer formation is one of the most critical processes to electrically segregate nanosheet channel from source and drain. In this process sacrificial SiGe layers in multilayer structure are recessed, then inner spacer material is deposited on fin sidewall and etched back (Fig. 1). Accurate etch amount control and good uniformity from bottom to top of the structure are required for the etch back, and they become more challenging in CFET since number of inner spacer per fin increases as PMOS and NMOS are vertically stacked. As a solution, we developed digital etch by combining ozone bake and wet etching aiming to ALE-like etching by self-limiting oxidation and selective dissolution of oxidized inner spacer material. ExperimentalThree different types of inner spacer material and SiN as reference were used as etching test sample. Blanket film of each material was deposited to 300 mm Si wafer by ALD. The sample was processed with 0.15 % dilute HF to remove native oxide. After baked at 240 °C with 100 g/m3 ozone ambient for 15 to 120 s, the sample was processed with 0.15 % dilute HF for 30 s to etch oxidized inner spacer materials. Etching amount was characterized by ellipsometry measuring pre and post process thickness. This cyclic process of ozone bakes, wet etch and the characterization were repeated 3 times to check controllability of etching amount. Results/DiscussionEtching amount of inner spacer materials with ozone bake and dilute HF shows 0.5-2.5 nm while etching amount with sole dilute HF shows 0.03-0.25 nm (Fig. 2). SiN also shows 0.04 nm etching amount of dilute HF in both with and without ozone bake. These results suggest that ozone bake oxidized inner spacers then dilute HF removed the oxidized inner spacer selective to non-oxidized inner spacer and SiN which is base material of gate spacer and BDIs/MDIs. Fig. 3 shows etching amount is saturated with ozone bake time in 3 inner spacer materials. We assumed that O radical react at surface of inner spacer material and oxide grows in the initial phase, and then the oxidation stops when it reached to a certain thickness because O radical deactivated in the oxide film during diffusion. This self-limiting process is preferable characteristic considering etching uniformity of both within wafer and local bottom to top inner spacer. Fig. 4 shows linear relationship in 3 inner spacer materials between etching amount and the cycle number of digital etch combining ozone bake and wet etching. This ALE-like etching is also preferable for accurate etching amount control. ConclusionInner spacer etch back is one of critical processes for Nanosheet and CFET integration. Digital etching with ozone bake and wet etching shows self-limiting process and ALE-like etching. These features are expected to enable precise inner spacer etch-back for future device fabrication beyond N3.

Gold and Gold Alloys Electropolishing Using HCl-Glycerol-Ethanol Electrolytes

Electropolishing (EP) is an electrochemical process used in the final stage of metal processing to reduce surface roughness and enhance functional, technical, and aesthetical properties. Some of its advantages are the preservation of surface metallurgical properties and the ability of treating complex geometries.EP is based on a homogeneous dissolution of the surface, driven by a competition between oxidation reactions and dissolution. Compounds such as cyanides and thiourea, which was now classified as a classed 3 carcinogen, can form very stable soluble complex with precious metals like gold and its alloys. Consequently, they have been widely used in the formulation of EP electrolytes for these materials, but their toxicity has led to the research of alternative solutions.This work presents a study based on a cyanide and thiourea free electrolyte previously reported in the literature for pure gold electropolishing and composed by hydrochloric acid, glycerol, and ethanol1,2. The aim was to give new insights in the involved mechanisms to evaluate the electrochemical behavior and the influence of different parameters on pure gold, and to extend this process to 18k jewelry gold alloys (yellow, rose, red and gray). In the first part of the study, only two of the electrolyte components (HCl-glycerol) were used to study the influence of chloride concentration on pure gold EP. Electrochemical techniques and surface properties analysis were evaluated.In the second part, the effects of adding ethanol to electrolyte composition and of variating rotation speed were also evaluated on pure gold. The best results were obtained for a HCl 50%vol. - Glycerol 25%vol. - Ethanol 25%vol. electrolyte at a rotation speed of 1000 rpm. This solution was then used to electropolish 18K gold alloys. Mitigated results were obtained for silver-containing alloys (yellow, rose and red), which were not uniformly polished due to the formation of an AgCl film on the surface that partially masks the substrates, whereas better results were obtained with 18K grey gold3.(1) Peck, W. F.; Nakahara, S. Preparation and Electropolishing of Thin Gold Disc Specimens for Transmission-Electron-Microscope Examinations. Metallography 1978, 11 (3), 347–354. https://doi.org/10.1016/0026-0800(78)90047-2.(2) Verlinden, J.; Celis, J. P.; Roos, J. R. Passivation-depassivation behaviour of gold in a hcl-glycerol solution and its application to electropolishing. Thin Films Sci. Technol. 1983, 341–346.(3) Rodriguez J. ; Doche M-L ; Hihn J-Y ; Electropolishing of gold and gold alloys in HCl-glycerol-ethanol electrolytes App. Surf. Sci. Adv. 21(2024) 100604 https://doi.org/10.1016/j.apsadv.2024.100604