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NiCoS has good conductivity, and the sulfur it contains is known to improve the activity for hydrogen evolution reaction. Thus NiCoS has recently attracted much attention as a catalyst for hydrogen evolution reaction catalyst in neutral-pH water electrolysis. In this study, NiCoS was fabricated using pulse electrodeposition method and the effect of off time on the composition, morphology, and hydrogen evolution reaction activity was investigated. The physical and chemical characteristics of the catalyst were analyzed using field emission scanning electron microscopy, X-ray diffractometry, electrochemical impedance spectroscopy, etc. It was observed that the surface area of NiCoS, the sulfur content, and hydrogen evolution reaction activity of NiCoS increased together as the off time increased at a constant on time. The NiCoS with the highest sulfur content, produced by pulse electrodeposition, showed overpotentials of 262 and 285 mV to deliver current densities of 10, 50 mA/cm2, respectively, in the neutral pH region.

As hydrogen emerges as a next-generation clean energy source, the production of hydrogen is generating much research interest. Water electrolysis, one of the promising methods of hydrogen production, has the advantage of no resource depletion or carbon dioxide emissions. In this study, a Pt@C core–shell catalyst in which an N-containing carbon layer covers individual Pt nanoparticles was applied to the hydrogen evolution reaction (the cathodic reaction of water electrolysis), and the effect of the carbon shell on the activity and stability of the catalyst was investigated. The catalyst was synthesized by simple annealing of Pt-aniline complexes at 600 °C in a N2 atmosphere. The thermal decomposition of aniline during annealing resulted in N-containing carbon shells. The carbon shell had a positive effect on both the activity and stability of the catalyst in the hydrogen evolution reaction. Graphitic N and pyridinic N on the carbon shell, along with Pt, served as active sites for the hydrogen evolution reaction, increasing the catalytic activity. The carbon shell also effectively protected the Pt core from dissolution and agglomeration while allowing the transport of the reactant protons through the shell, improving stability with minimal loss of catalytic activity.

Development of a simple, effective, and practical method for (Z)-selective semihydrogenation of alkynes has been considered necessary for easy-to-access applications at organic laboratory scales. Herein, (Z)-selective semihydrogenation of alkynes was achieved using a copper nanocatalyst which was generated in situ simply by adding ammonia borane to an ethanol solution of copper sulfate. Different types of alkynes including aryl–aryl, aryl–alkyl, and aliphatic alkynes were selectively reduced to (Z)-alkenes affording up to 99% isolated yield. The semihydrogenation of terminal alkynes to alkenes and gram-scale applications were also reported. In addition to eliminating catalyst preparation, the proposed approach is simple and practical and serves as a suitable alternative method to the conventional Lindlar catalyst.

In this study, we developed a simple transition-metal-free borylation reaction of aryl bromides. Bis-boronic acid (BBA), was used, and the borylation reaction was performed using a simple procedure at a mild temperature. Under mild conditions, aryl bromides were converted to arylboronic acids directly without any deprotection steps and purified by conversion to trifluoroborate salts. The functional group tolerance was considerably high. The mechanism study suggested that this borylation reaction proceeds via a radical pathway.

In this study, we developed a metal-free and highly chemoselective method for the reduction of aromatic nitro compounds. This reduction was performed using tetrahydroxydiboron [B

(Z)-1,8-Di(pyren-1-yl)oct-4-ene (1) was prepared as a probe for olefin metathesis. The conversions of substrate by olefin metathesis under various conditions were calculated using the ratiometric fluorescence intensity change of 1. The conversions calculated by 1 and gas chromatography were consistent. These results show that conversions of olefin metathesis can be simply obtained from the fluorescence change of 1 and this method can be applied to the high-throughput screening (HTS) method for various olefin metathesis.

The key to popularizing proton exchange fuel cells is developing highly active, stable, and cost-effective catalysts for oxygen reduction reaction. Pd is considered as an alternative to Pt due to its high tolerance to poisoning and electronic similarity with Pt, which is a robust but expensive catalyst. However, its vulnerability to dissolving in acidic media prevents the use of Pd as an oxygen reduction reaction catalyst. In this study, a facile synthesis method was developed to prepare a carbon-encapsulated Pd catalyst using aniline. The oxidative polymerization of aniline with a Pd precursor formed Pd nanoparticles embedded in a rod-shaped polyaniline matrix. The polyaniline matrix was carbonized using heat treatment, which then acted as a source of N-containing carbon layer that protects Pd nanoparticles from dissolution and improves oxygen reduction reaction activity. The stability and oxygen reduction reaction activity of the synthesized Pd catalyst were strongly dependent on the heat treatment temperature. The Pd catalysts heat-treated at 300 °C and 500 °C exhibited improved activity and stability as compared to commercial Pd/C. We envision that this method is suitable for mass production of active and stable oxygen reduction reaction catalysts in proton exchange fuel cells.

The development of low-cost catalysts for the oxygen reduction reaction is an important step for the commercialization of proton-exchange membrane fuel cells. Pd is a robust catalytic material for this reaction and is considered as an alternative to Pt due to its similarity with Pt. However, since Pd is oxidized at a lower positive potential than Pt, it is less active and less stable than Pt in an oxygen reduction reaction. We developed a simple synthesis route for N-doped carbon-caged Pd catalysts supported on carbon nanofibers using Pd-polyaniline composites. Oxidative polymerization of aniline spontaneously produced Pd-polyaniline composites with the reduction of Pd ions. The subsequent heat treatment of Pd-polyaniline composites produced N-doped carbon-caged Pd catalysts, in which the polyaniline served as the source of the N-doped carbon cage. The catalytic activity and stability of the synthesized catalyst were dependent on the heat-treatment temperature and the synthesis method. The optimized catalyst heat-treated at 500 °C (Pd@NC/CNF500 (NDA, US)), which was synthesized with non-distilled aniline under ultrasound irradiation, exhibited higher catalytic activity and stability in oxygen reduction reaction than general Pd catalysts reported in literature. Pd@NC/CNF500 (NDA, US) showed high performance even in the unit cell test.

In the thermal decomposition method, organic solvents, ligands, and compounds are usually used under an N2 atmosphere to synthesize pure metal and alloy nanostructures with high specific surface areas. However, the organic materials, which are used during the synthesis of metallic nanostructures, need to be completely eliminated to obtain cleaned surface states for effective catalytic reactions in aqueous atmospheres. Herein, we synthesize PtIr nanostructures using a thermal decomposition method, followed by a heating process of the nanostructures under an air atmosphere to eliminate the organic materials covering the surface of PtIr catalysts. The heated PtIr alloy nanostructure catalysts represent the superior oxygen reduction and evolution performance due to an increased electrochemical active surface area caused by the complete removal of organic materials.

Through silicon via (TSV) is one of the most important technologies in 3-dimensional wafer/chip stacking. However, there are some issues related to defect-free TSV filling and Cu pumping. In this study, a defect-free TSV filling was achieved using iodide ions. The working mechanism of iodide ions in TSV filling was systemically investigated by electrochemical measurements; It was found that the formation of CuI on the electrode surface is a key process for inhibiting Cu ion reduction. This inhibition effect of iodide ions enables defect-free TSV filling. Furthermore, the study of microstructure of the filled Cu revealed that the electrochemical reduction of CuI during the TSV filling forms small Cu grains in TSV. The small Cu grains cause Cu pumping in subsequent processes, which damages semiconductor devices. We achieved a defect-free TSV filling with enlarged Cu grains using a two-step filling method that effectively promotes the direct reduction of Cu ions rather than electrochemical reduction of CuI.

Development of a simple, effective, and practical method for (Z)-selective semihydrogenation of alkynes has been considered necessary for easy-to-access applications at organic laboratory scales. Herein, (Z)-selective semihydrogenation of alkynes was achieved using a copper nanocatalyst which was generated in situ simply by adding ammonia borane to an ethanol solution of copper sulfate. Different types of alkynes including aryl-aryl, aryl-alkyl, and aliphatic alkynes were selectively reduced to (Z)-alkenes affording up to 99% isolated yield. The semihydrogenation of terminal alkynes to alkenes and gram-scale applications were also reported. In addition to eliminating catalyst preparation, the proposed approach is simple and practical and serves as a suitable alternative method to the conventional Lindlar catalyst.

Multi-metallic Pd@FePt core&ndash, shell nanoparticles were synthesized using a direct seed-mediated growth method, consisting of facile and mild procedures, to increase yield. The Fe/Pt ratio in the shell was easily controlled by adjusting the amount of Fe and Pt precursors. Furthermore, compared with commercial Pt/C catalysts, Pd@FePt nanoparticles exhibited excellent activity and stability toward the methanol oxidation reaction (MOR), making them efficient in direct methanol fuel cells (DMFC).

Suzuki–Miyaura (SM) cross-coupling is one of the most effective strategies for carbon–carbon bond formation, but previous methods have several drawbacks, such as the requirement of complicated ligands, toxic organic solvents, and high-content-Pd catalysts. Thus, in this study, a highly efficient SM cross-coupling was developed using metal oxide catalysts: 0.02 mol% Pd, aqueous solvent, no ligand, and room temperature. Metal oxides containing low Pd content (ppm scale) were prepared by a simple co-precipitation method and used as a catalyst for the SM reaction. A fluorescence-based high-throughput screening (HTS) method was developed for the rapid evaluation of catalytic activity and reaction conditions. Among the various metal oxides, Pd/Fe2O3 showed the highest activity for the SM reaction. After further optimization by HTS, various biaryl compounds were obtained under optimal conditions: Pd/Fe2O3 (0.02 mol% Pd) in aqueous ethanol at mild temperature without any ligands.

Methanol crossover is one of the largest problems in direct methanol fuel cells (DMFCs). Methanol passing from the anode to the cathode through the membrane is oxidized at the cathode, degrading the DMFC performance, and the intermediates of the methanol oxidation reaction (MOR) cause cathode catalyst poisoning. Therefore, it is essential to develop a cathode catalyst capable of inhibiting MOR while promoting the oxygen reduction reaction (ORR), which is a typical cathode reaction in DMFCs. In this study, a carbon-encapsulated Pt cathode catalyst was synthesized for this purpose. The catalyst was simply synthesized by heat treatment of Pt-aniline complex-coated carbon nanofibers. The carbon shell of the catalyst was effective in inhibiting methanol from accessing the Pt core, and this effect became more prominent as the graphitization degree of the carbon shell increased. Meanwhile, the carbon shell allowed O

Herein, an easily accessible and efficient green method for the reduction of nitroarene compounds was developed using metal oxide catalysts. Heterogeneous metal oxides with or without Pd were prepared by a simple and scalable co-precipitation method and used for the reduction of nitroarenes. A fluorescence-based high-throughput screening (HTS) method was also developed for the rapid analysis of the reaction conditions. The catalytic activity of the metal oxides and reaction conditions were rapidly screened by the fluorescence-based HTS method, and Pd/CuO showed the highest catalytic activity under mild reaction conditions. After identifying the optimal reaction conditions, various nitroarenes were reduced to the corresponding aniline derivatives by Pd/CuO (0.005 mol% of Pd) under these conditions. Furthermore, the Pd/CuO catalyst was used for the one-pot Suzuki&ndash, Miyaura cross-coupling/reduction reaction. A gram-scale reaction (20 mmol) was successfully performed using the present method, and Pd/CuO showed high reusability without a loss of catalytic activity for five cycles.

The carbon encapsulation of nanosized Pt cathode catalysts for ultra-low Pt loading proton exchange membrane fuel cells is an effective approach to enhance their stability and catalytic activity for the oxygen reduction reaction (ORR). However, the synthesis procedures for such a catalyst are delicate and cumbersome. Therefore, it is difficult to use such procedures for mass production. Here, we have developed a facile strategy for synthesizing carbon-encapsulated Pt nanoparticles supported on carbon nanofibers (CNFs) using a Pt–aniline complex. This strategy begins with applying a wet Pt–aniline complex coating to CNFs. Heat-treating the coated CNFs produced 3–4 nm-sized Pt nanoparticles that were uniformly coated with a layer of carbon on the CNF surface (Pt@CS/CNF). Compared to other carbon-coated Pt catalysts, the stability and catalytic activity of Pt@CS/CNF for the ORR are high owing to the robustness of the carbon shells that secure the Pt nanoparticles. In a unit cell test, the performance of Pt@CS/CNF heat-treated at 900 °C was almost maintained for 30 000 accelerated stability test cycles, showing a negligible voltage loss at an operating current density of 0.8 A cm−2.

Owing to the growth of the size of convolutional neural networks (CNNs), quantization and loop tiling (also called loop breaking) are mandatory to implement CNN on an embedded system. However, channel loop tiling of quantized CNNs induces unexpected errors. We explain why channel loop tiling of quantized CNNs induces the unexpected errors, and how the errors affect the accuracy of state-of-the-art CNNs. We also propose a method to recover accuracy under channel tiling by compressing and decompressing the most-significant bits of partial sums. Using the proposed method, we can recover accuracy by 12.3% with only 1% circuit area overhead and an additional 2% of power consumption.

Porous Sn and Sn-based binary catalysts are facilely fabricated by an electrodeposition method. Varying conditions for Sn electrodeposition enables a control of Sn roughness, which exhibits a significant effect on catalytic performance for electrochemical CO2 reduction. At a specific applied potential, the porous Sn catalyst with relative roughness factor of 56.5 demonstrates a HCOOH Faradaic efficiency of 40.7% with a H2/CO ratio of 2.2. Further improvement of the HCOOH Faradaic efficiency to 59.2% is achieved by using a porous Sn0.29In0.71 catalyst. This catalyst also achieves a H2/CO ratio of 2.2, which can be used as syngas to produce value-added hydrocarbons.

Dendritic Ag (a CO2-to-CO reduction catalyst) has been synthesized on carbon paper (CP) using pulse electrodeposition to fabricate a gas diffusion electrode. A combination of sonication and pulse deposition facilitated mass transfer of Ag ions to the CP, enlarging the catalyst active surface area without significantly changing the Ag crystalline structure. The current density of CO2 reduction was proportional to the surface area of dendritic Ag. Further improvements in performance were achieved by adding polyethylene glycol to the CO2 reduction cell catholyte that removed the CO gas bubbles produced at the electrode surface. The fabrication methods presented herein suggest an effective gas diffusion electrode for application in the membrane-electrode-assembly-type single cell for electrochemical CO2 reduction.

In this study, the facile and direct formation of platinum catalyst on a carbon paper (gas diffusion layer) via the sonochemical deposition method is demonstrated. An ultrasound irradiation with a carbon paper substrate in a platinum precursor solution formed interconnected platinum grains on the carbon paper surface. The surface morphology and deposition amount of platinum were strong functions of both ultrasound parameters (power and time) and solution composition. The platinum-deposited carbon paper was then directly used as a gas diffusion electrode in PEMFC without adding the ionomer. This exhibited high stability in the accelerated stress test in a single cell operation. The interconnected grains of platinum on carbon paper had high resistance to dissolution in an oxidizing environment and the absence of carbon support also enhanced resistance to carbon oxidation. Although the overall performance did not exceed that of the commercial Pt/C, this approach may be an option to form a stable platinum catalyst for PEMFCs.

Organic additives play an important role in regulating film growth and properties in Cu electrodeposition. 3‑Mercapto‑1‑propane sulfonate (MPS) and its dimer bis(3‑sulfopropyl) disulfide (SPS) are representative accelerators that promote Cu electrodeposition rate. In this study, the formal reduction potential of SPS to MPS was determined by measuring the equilibrium constants of thiol–disulfide interchange reactions with the reference thiol/disulfide pairs by 1H nuclear magnetic resonance (1H NMR) spectroscopy. The calculated formal reduction potential of SPS to MPS was 0.153 V (vs. standard hydrogen electrode). Based on this calculation, the cell potentials of Cu(I)(thiolate) formation reaction with either SPS or MPS, which is a key reaction in accelerating mechanism, were also estimated by ultraviolet–visible absorption and 1H NMR spectroscopies: they were found to be 0.202 V and 0.214 V for SPS and MPS, respectively. The positive cell potential indicates that the formation of Cu(I)(thiolate) complexes is thermodynamically favorable in the presence of additives.

Herein we report the demonstration of electrochemical deposition of silicon p-n junctions all in molten salt. The results show that a dense robust silicon thin film with embedded junction formation can be produced directly from inexpensive silicates/silicon oxide precursors by a two-step electrodeposition process. The fabricated silicon p-n junction exhibits clear diode rectification behavior and photovoltaic effects, indicating promise for application in low-cost silicon thin film solar cells.

Electrodeposition of Si films from a Si-containing electrolyte is a cost-effective approach for the manufacturing of solar cells. Proposals relying on fluoride-based molten salts have suffered from low product quality due to difficulties in impurity control. Here we demonstrate the successful electrodeposition of high-quality Si films from a CaCl2-based molten salt. Soluble SiIV−O anions generated from solid SiO2 are electrodeposited onto a graphite substrate to form a dense film of crystalline Si. Impurities in the deposited Si film are controlled at low concentrations (both B and P are less than 1 ppm). In the photoelectrochemical measurements, the film shows p-type semiconductor character and large photocurrent. A p–n junction fabricated from the deposited Si film exhibits clear photovoltaic effects. This study represents the first step to the ultimate goal of developing a cost-effective manufacturing process for Si solar cells based on electrodeposition.

With emerging stability issues in fuel cell technology, a non-conventional catalyst not supported on carbon materials has been highlighted because it can avoid negative influences of carbon support materials on the stability, such as carbon corrosion. The nanostructured thin film catalyst is representative of non-conventional catalysts, which shows improved stability, enhanced mass specific activity, and fast mass transfer at high current densities. However, the nanostructured thin film catalyst usually requires multi-step processes for fabrication, making its mass production complex and irreproducible. We introduce a Pt-Cu alloy nanostructured thin film catalyst, which can be simply prepared by electrodeposition. By using hydrogen bubbles as a template, a three-dimensional free-standing foam of Cu was electrodeposited directly on the micro-porous layer/carbon paper and it was then displaced with Pt by simple immersion. The structure characterization revealed that a porous thin Pt-Cu alloy catalyst layer was successfully formed on the micro-porous layer/carbon paper. The synthesized Pt-Cu alloy catalyst exhibited superior durability compared to a conventional Pt/C in single cell test.

Performance of a polymer electrolyte membrane fuel cell with a Pd cathode catalyst was systemically investigated in this study. The Pd catalyst was directly formed on a gas diffusion layer by using electrodeposition (Pd/GDL). The electrodeposition formed aggregates of Pd nanoparticles on a gas diffusion layer with the preferred orientation of Pd(111) and Pd(200). In addition, the Pd aggregates mainly formed on the top surface of the gas diffusion layer. The membrane electrode assembly was fabricated with Pd/GDL as the cathode. The performance of the membrane electrode assembly was investigated by varying hot pressing parameters and back pressures, and the operating condition for the polymer electrolyte membrane fuel cell was optimized. Notably, introducing back pressure increased operating current density at 0.6 V by up to 45%. Durability of the membrane electrode assembly was also examined. Negligible deterioration of surface morphology of the Pd catalyst was observed even after accelerated stress testing, except for a slight increase in particle size. The results indicate that deterioration of the Pd cathode catalyst was not a major factor affecting overall single-cell performance degradation.

Determination of methionine (Met) has garnered increasing attention in various fields because methionine is a biomarker for various diseases. However, chemosensors for Met are very limited compared to those for other amino acids, and many Met chemosensors show low selectivity towards Met over cysteine (Cys) and histidine (His). In this study, a di–thioether amide–Pd2+ complex, 1-Pd2+, based on a 7-diethylaminocoumarin scaffold, was prepared as a sensitive and selective fluorescent chemosensor for Met. The limit of detection (LOD) for Met of 1-Pd2+ was determined to be 1.0 μM and the chemosensor exhibited a high selectivity towards Met over various amino acids including Cys and His. 1-Pd2+ worked well in a broad pH range of 4.0–8.0 and was applied to determine the concentration of Met in tap water samples. In addition, ligand 1 was demonstrated to be a selective and sensitive fluorescent chemosensor for Pd2+. The LOD for Pd2+ of 1 was determined to be 1.7 μM and it exhibited a high selectivity for Pd2+ over various other metal ions.

Novel synthesis of a Pt catalyst encapsulated in a N-containing carbon layer for use in a polymer electrolyte membrane fuel cell is described in this study. A Pt-aniline complex, formed by mixing Pt precursor and aniline monomer, was used as the source of Pt, C, and N. Heat treatment of the Pt-aniline complex with carbon black yielded 5 nm Pt nanoparticles encapsulated by a N-containing carbon layer originating from aniline carbonization. The synthesized Pt catalyst exhibited higher mass specific activity to oxygen reduction reaction than that shown by conventional Pt/C catalyst because pyridinic N with graphitic carbon in the carbon layer provided active sites for oxygen reduction reaction in addition to those provided by Pt. In single cell testing, initial performance of the synthesized catalyst was limited because the thick catalyst layer increased resistance related to mass transfer. However, it was observed that the carbon layer successfully prevented Pt nanoparticles from growing via agglomeration and Ostwald ripening under fuel cell operation, thereby improving durability. Furthermore, a mass specific performance of the synthesized catalyst higher than that of a conventional Pt/C catalyst was achieved by modifying the synthesized catalyst's layer thickness.

For the electrochemical reduction of CO2 to CO, a dendrite-type Ag catalyst was fabricated via an electrodeposition method in an ammonia-based Ag deposition solution containing ethylenediamine (EN) as an additive. The influence of electrodeposition parameters on the properties of this catalyst was examined and further correlated with CO production efficiency. The addition of EN changed the intensity ratio of (220) vs. (111) planes in the Ag catalyst, which was shown to be proportional to the CO production activity. Furthermore, EN modified the chemical shift of Ag3d5/2 in the negative direction, increasing the CO production efficiency. Under optimized deposition conditions (–0.45 V vs. Ag/AgCl, 40 mM EN), which were a compromise between intensity ratio and chemical shift, the fabricated Ag catalysts exhibited the highest Faradaic efficiency and mass activity for CO during CO2 electrolysis in 0.5 M KHCO3. The experimental correlation between CO production efficiency and the crystalline/electronic structures of the catalyst suggested guidelines for further improving the Ag catalyst activity.

We aimed to quantitatively assess the effects of short-term statin use on delayed ischemic neurologic deficits (DINDs) and clinical outcomes in patients with aneurysmal subarachnoid hemorrhage (SAH) through a meta-analysis of the available evidence.We searched the electronic databases up to April 8, 2016 to retrieve relevant studies comparing the outcomes between immediate statin-treated in statin-naïve patients and untreated patients following aneurysmal SAH. Meta-analysis was performed using Review Manager 5.3.Eight randomized controlled clinical trials (RCTs) and 5 observational studies involving 2148 patients met the eligibility criteria. In the RCTs, statins were found to significantly reduce the occurrence of DINDs (relative risk (RR), 0.76; 95% confidence interval (CI), 0.61-0.94; P = 0.01), but did not significantly reduce poor functional outcomes (RR, 1.01; 95% CI, 0.87-1.16; P = 0.93) or mortality (RR, 0.80; 95% CI, 0.58-1.11; P = 0.18). In observational studies, statin use was not associated with any reduction in DINDs, poor outcome, or mortality. Meta-analysis of RCTs indicated a significant reduction in DINDs and mortality in patients with high-dose statin use (RR, 0.63; 95% CI, 0.42-0.95; P = 0.03; IThe present meta-analysis suggests that statin use may prevent DINDs in patients with aneurysmal SAH. Based on our findings, the role of statins in improving neurological outcome was limited. However, the risk of DINDs and mortality decreased with higher statin doses in a dose-dependent manner. Hence, further well-designed RCTs with modified protocols in specific patients are required.

본 연구에서는 구리 배선 공정에서 구리 씨앗층 표면에 형성되는 구리 자연산화물을 제거하는 표면 전처리가 후속 구리 전착에 미치는 영향을 살펴보았다. 구리 배선 공정의 화학적 기계적 연마 공정에서 사용하는 citric acid 기반의 용액을 구리 표면 전처리 과정에 적용하여 표면에 존재하는 구리 자연 산화물을 제거하...

The importance of chemical mechanical planarization (CMP) and post-CMP cleaning is highly critical because both directly affect the yields and performance of semiconductor devices. Ceria nanoparticles are widely used as abrasives for SiO2 CMP because strong ceria–SiO2 interaction enhances CMP performance. However, the interaction is a major drawback in post-CMP cleaning processes where residual ceria nanoparticles must be completely removed from the SiO2 surface. The interaction depends on the cerium oxidation state of the ceria nanoparticles surface. In this study, the ceria–SiO2 interaction was investigated systemically using an atomic force microscope and a quartz crystal microbalance. The analysis revealed that the adhesion energy between ceria and SiO2 and the adsorption rate of ceria nanoparticles on a SiO2 surface increased with the surface concentration of Ce3+. This is direct evidence showing that the ceria–SiO2 interaction becomes stronger as the surface Ce3+ concentration of ceria nanoparticles increases, suggesting that the surface Ce3+ concentration should be reduced for effective post-CMP cleaning.

The effect of surface composition change based on complexing agents on cobalt (Co) post-chemical mechanical polishing cleaning (cleaning) is investigated. The change in chemical composition of the Co surface significantly affects Co cleaning performance, as well as dissolution capacity of the complexing agent and pH of cleaning solution. Oxide composition of the Co surface was manipulated using different types of complexing agents. Addition of citric acid and glycine in cleaning solution resulted in predominant formation of Co3O4 and CoOOH on the Co surface, respectively. The citric acid-derived Co3O4 surface embraces abundant –O– terminates, which attracts the complexing agent and silica abrasive relatively weakly, resulting in suppression of recess formation and reduction of surface particle residue after cleaning. On the contrary, the –OH terminated CoOOH surface formed by glycine bound strongly with silica. Therefore, preferential development of Co3O4 on the surface considerably enhances Co cleaning performance, which is achieved by introducing citric acid in the cleaning solution. To sum up, we suggested an unconventional insight to understand the effect of Co surface chemical state on cleaning performance.

The microstructural changes in electrodeposited Cu films during self-annealing is demonstrated in this study. The structural change is strongly influenced by the organic additives in the Cu electrodeposition. The use of either polyethylene glycol (PEG) or bis-(3-sulfopropyl) disulfide (SPS) decreases the Cu(111) grain size of deposited films, as the adsorption of the additives suppresses the surface diffusion of the Cu ions during the electrodeposition. After the electrodeposition, the average grain size of the deposited film was simultaneously increased by 10% in a self-annealing process to reduce the defect energy, which is mainly composed of the surface energy of the grains. Meanwhile, the grain grew 4 times larger than the as-deposited grain size during the self-annealing when both the PEG and SPS were introduced. The drastic grain growth was attributed to the accumulation of a high defect energy in the deposited film. The dynamic interaction between the co-adsorbed PEG and SPS on the Cu surface during the electrodeposition promotes an unoriented dispersion-type deposition, resulting in high-strain energy as well as surface energy. Releasing the strain energy accumulated by the high density of misorientation also leads to the simultaneous growth of Cu(200) grains.

Onion-like Pt-terminated Pt–Cu bimetallic nano-sized electrocatalysts (Pt/Cu/Pt/C) were synthesized by using an electroless deposition method. The synthesized Pt/Cu/Pt/C consisted of a Pt-enriched shell, a sandwiched Pt–Cu alloy layer, and a Pt core. The Pt/Cu/Pt/C showed higher electrocatalytic activity toward oxygen reduction reaction in half-cell test than that of commercial Pt/C due to an electronic structure change in the Pt-enriched shell, resulting from the sandwiched Pt–Cu alloy layer underneath. The stability of the Pt/Cu/Pt/C was examined by using both half-cell and single-cell degradation tests. In both tests, the Pt/Cu/Pt/C exhibited stronger resistance to catalyst degradation than that of the commercial Pt/C. It is notable that cell performance with the Pt/Cu/Pt/C was fully recovered by N2 purging after single-cell degradation testing, indicating there was no permanent damage to the electrocatalyst during the test. It is suggested that thermodynamically-stable structure of the Pt/Cu/Pt/C contributed to the improved stability.

The direct electrochemical reduction of silicon dioxide in molten CaCl2 has been investigated as a promising candidate for alternative production process of solar silicon. Herein, we study a catalyst-mediated doping, which is carried out by introducing dopant precursors like Al2O3, In2O3, and Sb2O3 into the molten CaCl2 during the electrochemical growth of silicon on Ag catalyst. The photoelectrochemical measurement demonstrates controllable p-type or n-type doping, and the photoresponse of doped silicon reaches 1.1±0.4 mA/cm2 under 100 mW/cm2 irradiation. Doping densities, estimated from two-point micro-probe measurements and Mott–Schottky plot analyses range from 1015 to 1016/cm3. Dopant is incorporated through Si–Ag catalyst droplet, which is supported by a high dopant content in Ag catalyst revealed by the elemental mapping of secondary ion mass spectroscopy. The catalyst-mediated doping mechanism is proposed to elucidate the doping level. The liquid droplet is presumed to be under local equilibrium along with significant loss of the dopant from it whereby the doping level becomes a function of the segregation coefficient and the rate constant of the electrochemical reaction.

Nitrous oxide (N2O), of which global warming potential is 310 times of CO2, is a powerful greenhouse gas [1]. The concentration of N2O has increased steadily from various agricultural and industrial activities such as cultivating crops in low-pH soil and manufacturing semiconductor devices [2,3]. Therefore, the importance of studying N2O reduction is emphasized. Thermal decomposition methods focusing on thermal catalyst have been reported, but there are limits such as process temperature and low efficiency [4,5]. Electrochemical reduction of N2O can be an attractive method since it is conducted at low temperatures and has low energy consumption. However, in aqueous solutions, the electrochemical reduction of N2O inevitably accompanies hydrogen evolution reaction (HER), which is the main side reaction. There were many trials to reduce HER through metal and metal oxide catalysts, but they also had limits in terms of efficiency and high cost of noble metal materials [6-9]. Ionic liquids are promising electrolytes in gas reduction field replacing water because they can avoid hydrogen evolution and enhance the solubility of gaseous reactants. Some imidazolium-based ionic liquids were adopted to electrochemical reduction of CO2 because of their favorable properties such as wide electrochemical potential window and high CO2 dissolution capacity [10,11]. Cations of ionic liquids are known to accept oxygen from CO2, and then return to initial state at counter electrode emitting oxygen [12]. According to the same principle, ionic liquids may also be suitable for the electrochemical reduction of N2O. In this study, an ionic liquid/organic solvent mixture was adopted as an electrolyte for the electrochemical reduction of N2O. The ionic liquid and organic solvent used for electrolyte were 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) and propylene carbonate (PC), respectively. The use of [BMIM][BF4] in place of aqueous solutions could improve the solubility of N2O and also avoid the hydrogen evolution reaction, which is the main side reaction in an aqueous solution. Herein we observed the difference of LSV curves in aqueous solution and [BMIM][BF4]. Hydrogen evolution reaction was excluded, but the low current density was obtained in [BMIM][BF4]. The low electrical conductivity and high viscosity of [BMIM][BF4], the main disadvantages in the context of electrochemical reactions, were compensated on introducing PC. We measured the viscosity and electrical conductivity in various [BMIM][BF4]/PC composition, and the composition of the [BMIM][BF4]/PC was optimized considering both the electrical conductivity and N2O stability in the solution. The current and faradaic efficiency could be evaluated during chronoamperometry in aqueous solution and [BMIM][BF4]/PC. For the optimized [BMIM][BF4]/PC, high current efficiency and faradaic efficiency (>90%) were achieved for N2O reduction to N2. Figure captions Figure 1. LSV curves for Cu electrode in (a) 0.3 M K2SO4 aqueous solution and (b) [BMIM][BF4]. The scan rate was 50 mV s-1. Figure 2. (a) Viscosity (black line) and conductivity (blue line) changes for [BMIM][BF4]/PC according to [BMIM][BF4] content (b) Current efficiency–time curves recorded at –1.3 V vs. SCE in 0.3 M K2SO4 aqueous solution (blue line) and at –2.27 V vs. Fc/Fc+ in 75 vol% [BMIM][BF4] (red line). References [1] C. Kroeze, Sci. Total Environ., 143 (1994) 193-209. [2] P.J. Crutzen, Q. J. Royal Meteorol. Soc., 96 (1970) 320-325. [3] R. N Van den Heuvel, S. E Bakker, M. Jetten, M. Hefting, Geobiology, 9 (2011) 294-300. [4] M. Konsolakis, ACS Catal., 5 (2015) 6397-6421. [5] Z. Liu, F. He, L. Ma, S. Peng, Catal. Surv. Asia, 20 (2016) 121-132. [6] S. Baek, K.H. Kim, M.J. Kim, J.J. Kim, Appl. Catal. B, 217 (2017) 313-321. [7] S. Baek, K.H. Kim, I. Choi, O.J. Kwon, J.J. Kim, Chem. Eng. Trans., 335 (2018) 915-920. [8] A. Kudo, A. Mine, J. Electroanal. Chem., 426 (1997) 1-3. [9] K.H. Kim, T. Lim, M.J. Kim, S. Choe, S. Baek, J.J. Kim, Electrochem. Commun., 62 (2016) 13-16. [10] D. Vasilyev, E. Shirzadi, A.V. Rudnev, P. Broekmann, P.J. Dyson, ACS Appl. Energy Mater., 1 (2018) 5124-5128. [11] L. Sun, G.K. Ramesha, P.V. Kamat, J.F. Brennecke, Langmuir, 30 (2014) 6302-6308. [12] L. Gu, Y. Zhang, Unexpected CO2 splitting reactions to form CO with N-heterocyclic carbenes as organocatalysts and aromatic aldehydes as oxygen acceptors, J. Am. Chem. Soc., 132 (2010) 914-915. Figure 1

Shallow trench isolation (STI) is a technology that isolates transistors by constructing trenches and filling them with silicon dioxide. The excess silica should be removed by a subsequent step, chemical mechanical planarization (CMP) process, without any damage to active area. To prevent the damage during polishing, the silicon nitride is used for a stopping layer.1 Therefore, in the CMP process in STI, oxide-to-nitride polishing selectivity is needed. Since ceria nanoparticles (NPs) has high removal rate on silicon oxide but low removal rate on silicon nitride, they are generally utilized for CMP in STI.2 Additionally, Ce3+ concentration on the ceria NPs is considerably related to the oxide-to-nitride selectivity. It was reported that as the Ce3+ concentration on ceria NPs increased, its oxide-to-nitride selectivity was improved.3 However, after CMP process, there exists large amount of contaminants on the substrates which is mainly originated from the abrasives and organic additives in CMP slurry. Especially, on the surface of silicon oxide, the residual ceria NPs caused problems in post-CMP cleaning. Since they have chemical interaction with silicon oxide as reported, they are not easily removed from the surface. As the demands for high-end semiconductor devices with enhanced performance soar, the contaminants should be successfully removed.4-6 Therefore, in-depth research on ceria-silica interaction for effective post-CMP cleaning receives large attention. We directly investigated the ceria-silica interaction using atomic force microscope (AFM) and quartz crystal microbalance (QCM). Using AFM, the adhesion energy between silicon oxide and ceria NPs was quantitatively measured with respect to Ce3+ concentration on the ceria NPs as shown in Figure 1. We changed the surface Ce3+ concentration on the ceria NPs using hydrogen peroxide and ultrasonication, which was classified as Ceria1 to Ceria4.7 Moreover, the adsorption behavior of ceria NPs on the surface of silicon oxide was observed by QCM depending on the surface Ce3+ concentration. From the results of adsorption rate, the activation energy for the ceria-silica adsorption was studied depending on the Ce3+ concentration on the ceria NPs, which is exhibited in Figure 2. Figure Captions Figure 1. Adhesion energy between ceria and silica depending on surface Ce3+ concentration. Figure 2. Plot of the natural logarithm of adsorption rate versus the reciprocal of temperature at different surface Ce3+ concentrations of ceria NPs. References M. C. Kang, J. J. Kim and D.-K. Moon, Jpn. J. Appl. Phys., 44, 5949 (2005). R. Srinivasan, P. V. R. Dandu and S. V. Babu, ECS J. Solid State Sci. Technol., 4, P5029 (2015). K. Kim, D. K. Yi and U. Paik, ECS J. Solid State Sci. Technol., 6, P681 (2017). H. S. Philip Wong, Solid-State Electron., 49, 755 (2005). M. Tsujimura, ECS J. Solid State Sci. Technol., 8, P3098 (2019). C. K. Ranaweera, N. K. Baradanahalli, R. Popuri, J. Seo and S. V. Babu, ECS J. Solid State Sci. Technol., 8, P3001 (2018). J. F. Changjian Ma, Jiaxiang Chen, Yaoyao Wen, Paul O Fasan, Hua Zhang, Nuowei Zhang,* Jinbao Zheng, and Bing-Hui Chen, Ind. Eng. Chem. Res., 56, 9090 (2017). Figure 1