Search

Perovskite stannate SrSnO

We extend our recent 2D trajectory (x–y plane) and diffusion coefficient data of ceria particles near a glass surface obtained at pH 3, 5, and 7 using evanescent wave microscopy and video imaging to 3D trajectories by analyzing the separation distance between the particles and the glass surface in the vertical z‐direction. Mean squared displacement (MSD3D) of ceria particles was calculated to quantify 3D trajectories. Three‐dimensional diffusion coefficients were obtained from the MSD3D curves and were compared with two‐dimensional diffusion coefficients. By analyzing the MSD curves, we found that ceria particles exhibited only confined motion at pH 3 and 5, while both confined and Brownian motion were showed at pH 7. We also evaluated the cleaning ability of DI water adjusted to pH 10 and 12 to remove ceria particles from glass surfaces and related the results to the calculated trajectory, diffusion coefficient, and interaction potential data.

As the minimum feature size of integrated circuit elements has shrunk below 7 nm, chemical mechanical planarization (CMP) technology has grown by leaps and bounds over the past several decades. There has been a growing interest in understanding the fundamental science and technology of CMP, which has continued to lag behind advances in technology. This review paper provides a comprehensive overview of various chemical and mechanical phenomena such as contact mechanics, lubrication models, chemical reaction that occur between slurry components and films being polished, electrochemical reactions, adsorption behavior and mechanism, temperature effects, and the complex interactions occurring at the wafer interface during polishing. It also provides important insights into new strategies and novel concepts for next‐generation CMP slurries. Finally, the challenges and future research directions related to the chemical and mechanical process and slurry chemistry are highlighted.

Using evanescent wave (EW)–based optical detection methods coupled with video microscopy, we investigated in situ trajectories, diffusion, and interaction energies of ∼140 nm ceria particles near a glass surface at pH 3, 5, and 7. Trajectories of a single ceria particle in a 2D (x–y) plane were obtained by linking its time-sequenced positions. Diffusion coefficients of several single ceria particles were calculated from their respective mean-square displacement (MSD) versus time curves, and the results were interpreted based on the interaction potential energy curves obtained from Boltzmann statistics of the EW scattering intensity fluctuations of the particles. The types and characteristics of particle motions were determined by analyzing the MSD curves. Whereas both confined or subdiffusive and Brownian motions of the particles were observed at pH 7, only confined motion was seen at pH 3 and 5, and their corresponding diffusion coefficients are similar to those reported by several authors.

Post-CMP cleaning is a crucial step to eliminate the residual particles, organic residues, foreign materials, metallic impurities, etc., from the wafer surfaces. As post-CMP cleaning technology has grown by leaps and bounds over the past several decades, traditional cleaning solutions (SC-1, SC-2, SPM, and DHF) have been modified to meet the stringent requirements for the level of acceptable defects, and many alternatives have been developed so far. Recent developments of post-CMP cleaning solutions for FEOL, MOL, and BEOL applications are summarized in this chapter. The challenges and future research directions related to post-CMP cleaning solutions and the experimental techniques to evaluate post-CMP cleaning formulations are highlighted.

The performances of CMP show different results according to the process and material variables. In the case of material variable, it includes slurry, pad, conditioner, and wafer. Especially the slurry is complicatedly composed of various components (i.e. abrasive particle, chemical additives, and DIW). As a result, it has a decisive influence on CMP performance such as material removal rate (MRR), uniformity, scratch, and galvanic corrosion. From this point of view, understanding the physico-chemical properties of slurry is important to develop the improved CMP performances. In this chapter, we will give a brief overview on preparation and characterization of CMP slurry, and then mainly discuss on the effect of slurry characterization on CMP performances.

Along with the remarkable growth in the complexity of semiconductor fabrication technology, chemical mechanical planarization (CMP) has evolved and become progressively more sophisticated over the years, enabling the implementation of novel integration schemes. This paper discusses current research and development trends in one specific aspect of the CMP technology, namely, ceria particle usage for advanced technology nodes and provides some perspectives on how to improve CMP performance metrics of the current ceria abrasives and ceria-based CMP slurries and move forward to the next phase.

Chemical mechanical planarization (CMP) process has been widely used to planarize a variety of materials including dielectrics, metal, and semiconductors in Si-based semiconductor devices. It is one of the most critical steps to achieve the nanolevel wafer and die scale planarity. However, various contaminants are observed on the wafer surfaces after the CMP process, and they become the most critical yield detractor over many generations of rapidly diminishing feature sizes because they have the most direct impacts on device performance and reliability. This book chapter provides (1) CMP consumables-induced contaminants such as residual particles, surface residues, organic residues, pad debris and metallic impurities, pad contamination, watermark, etc., (2) brush-induced cross-contamination during post CMP cleaning, (3) post-CMP cleaning for removing these contaminants. Fundamental understanding of the formation of various types of CMP contaminants and their characteristics will significantly benefit the development of next-generation CMP slurries and post-CMP cleaning solutions.

Topography of tungsten should be assured at a minimum through chemical mechanical planarization (CMP) in the metal gate structures (e.g., buried gates, replacement metal gates) and via contact in the middle of line (MOL) process for sub−7 nm semiconductor applications. However, excessive tungsten dissolution during the CMP process that results from high oxidizer concentrations and acidic atmospheres results in poor tungsten topography. In this study, we report a novel strategy to improve the tungsten topography by suppressing tungsten dissolution via coordination complex formations between picolinic acid and tungsten oxide. With 1.5 wt% picolinic acid for the inhibitor, the dissolution rate of tungsten was dramatically attenuated, and improved topography with a Ra value of 7.8 nm were demonstrated while validating CMP removal rate.

This paper presents a method to measure the threshold voltage degradation ΔVth along the channel direction due to electrical stress in MOSFETs. This method uses ΔVths measured after electrical stress at different drain bias Vds, and calculated the depletion length Ldep into the channel for each condition under which ΔVth is measured. By substituting ΔVth and Ldep into the proposed equation, the amount of degradation generated in each region of the MOSFET channel can be calculated. The ΔVth profiles of OFF-state stress and negative bias temperature instability in pMOSFET and hot carrier injection in nMOSFET were extracted using the proposed method. The degradation profiles correspond well with each stress characteristic.

We report a polylactic acid (PLA)-polyethylene glycol (PEG) mixture as a thermoplastic binder to prepare shape-machinable ceramic green bodies. During the mixing process, the high viscosity of the PLA binder impedes effective mixing with ceramic powders. To address this issue, PEG was introduced as a plasticizer into ceramic/PLA composites to diminish the overall viscosity of the feedstock, which resulted in effective mixing with ceramic powders. After sintering green bodies composed of PLA-PEG binders and ceramic compounds, the mechanical properties (flexural strength and porosity) of the sintered specimens were investigated and compared with those of sintered specimens made from wax-based green bodies. The sintered specimens made from ceramic/PLA-PEG composites showed comparable mechanical properties and porosities with the sintered specimens made from ceramic/wax composites. In addition, the shape-machinable characteristic of the green bodies made from ceramic/PLA-PEG composites was demonstrated by deforming the entire structure of the green bodies via simple heat treatment.

Temperature is one of the parameters that needs to be continuously monitored and controlled during handling, storage, and transportation to achieve repeatable and consistent CMP performances. Here, we investigated the effect of three different storage temperatures (15, 25, and 45oC) on several slurry health parameters (particle size, zeta potential, pH, total dissolved solids, conductivity, and dissolved oxygen (DO) concentration) of a ceria-based slurry and also on removal rates of SiO2 films during polishing. The changes in all the parameters of slurries stored at 15oC and 45oC for three weeks, except for DO concentration, were reversible and returned to their values at 25oC when the slurries were brought back to 25oC. DO concentration increased by ~14 % and decreased by ~18 % in the slurries stored for three weeks at 15oC and 45oC, respectively, compared to that of ceria slurry stored at 25oC. They did not return to the original values even after keeping them at 25oC for 6 hours. The increase in storage temperature causes an increase in the adsorption of dissolved oxygen onto the ceria surface, which can transform Ce3+ species into less reactive Ce4+-superoxo or a Ce3+-peroxo species, resulting in lower SiO2 removal rates.

Brush scrubbing is commonly employed for cleaning contaminated polished wafers, especially after chemical mechanical polishing. Here we report the results from real-time video imaging of the brush cleaning of ∼90 nm ceria particles from thin oxide films on transparent glass substrates using evanescent wave microscopy to identify the interactions among the particles, brush, film and cleaning liquid. Two cleaning liquids, DI water (pH ∼ 6) and 0.1 M NH4OH solution at pH ∼ 11, were used. It was found that purely hydrodynamic forces are unable to remove the ceria particles from the oxide film surface and direct contact between brush asperities and film is crucial for particle detachment to occur. However, such a direct contact also causes significant particle loading of the brush as well as redeposition of some of the already dislodged particles. Preventing such redeposition is crucial for efficient surface cleaning. The dislodged particles that are transferred into the fluid flow on the film continued to move without redepositing. Since the 0.1 M NH4OH solution at high alkaline pH created an environment for charge repulsion among the ceria particles, PVA brush and oxide film, particle removal from the film is more rapid and somewhat more efficient compared to DI water.

The chemical and seasonal characteristics of fine particulates in Seoul, Korea, were investigated based on 24-h integrated PM2.5 measurements made over four 1-month periods in each season between October 2012 and September 2013. The four-season average concentration of PM2.5 was 37 μg m−3, and the major chemical components were secondary inorganic aerosol (SIA) species of sulfate, nitrate, and ammonium (49%), followed by organic matter (34%). The mass concentration and most of the chemical components of PM2.5 showed clear seasonal variation, with a winter-high and summer-low pattern. The winter-to-summer sulfate ratio and the winter organic carbon (OC)-to-elemental carbon (EC) ratio were unusually high compared with those in previous studies. Strong correlations of both the sulfate level and the sulfur oxidation ratio with relative humidity, and between water-soluble OC (WSOC) and SIA in winter, suggest the importance of aqueous phase chemistry for secondary aerosols. A strong correlation between non-sea salt sulfate and Na+ levels, a high Cl−/Na+ ratio, and an unusual positive correlation between the nitrogen oxidation ratio and temperature during the winter indicate the influence of transported secondary emission sources from upwind urban areas and from China across the Yellow Sea. Despite the absence of local forest fires and the regulation of wood burning, a high levoglucosan concentration and its correlations with OC and WSOC indicate that Seoul was affected by biomass burning sources in the winter. The unusually high water-insoluble OC (WIOC)-to-EC ratio in winter implies additional transported combustion sources of WIOC. The strong correlation between WIOC and levoglucosan suggests the likely influence of transported biomass burning sources on the high WIOC/EC ratio during the winter.

GPa-grade steels which possess the ultimate tensile strength over 1000 MPa and higher elongation have been thoroughly researched to replace conventional high-strength steels in automobile industry to enhance fuel efficiency without sacrificing crashworthiness. However, high strength of GPa-grade steel does not only induce punching pin buckling due to high contact pressure, but also abrasive wear on the mold surface due to the unstable contact that results from the large amount of springback, which tend to impede widespread usage of GPa-grade steels. In this research, design criteria for an optimal aspect ratio of the punching pin preventing buckling failure has been proposed by linking with experimental and numerical analyses, which is validated with the analytic solutions. Furthermore, in order to prevent stripping failure, it is highly recommended that one of the main factors, a blank holder force (BHF), over 1.5 MPa has to be maintained during the withdrawal process to minimize the effect of springback in stamped panels applying GPa-grade steel, which is able to extend the tool life of the side punching pin about 100,000 cycles.

Ce3+ ions in ceria nanoparticles (NPs) play a role as reactive sites in the adsorption of silicate anions. However, the limited concentration of Ce3+ ions in ceria NPs remains a major challenge in this regard. Herein, we report a simple strategy to synthesize Ce3+-enriched core–shell ceria NPs for enhanced adsorption of silicate anions. To increase the overall Ce3+ concentration, a shell layer is composed of Ce3+-rich ultrasmall ceria NPs approximately 5 nm in size. The Ce3+ concentration of such core–shell ceria NPs is increased by 12.7–17.1% relative to that of the pristine ceria NPs, resulting in increased adsorption of silicate anions. The Freundlich model fits the observed adsorption isotherm well and the constants of adsorption capacity (KF) and adsorption intensity (1/ n) indicate higher adsorption affinity of the core–shell ceria NPs for silicate anions. We attribute these improvements to the increased Ce3+ concentration contributed by the ultrasmall ceria coating. This strategy can be used for enhancing the reactivity of ceria materials.

We demonstrated that the movement of the single ceria particles located at the glass interface could be imaged in situ using evanescent wave (EW) microscopy. (1,2) Here, the flat glass surface of the lens became our model for the SiO2 film surface of interest. 3D trajectories, diffusion coefficients, and interactions of ceria particles with a glass surface at pH 3, 5, and 7 were investigated using EW microscopy. We also defined the types and characteristics of particle motions by analyzing the mean-square displacement (MSD) versus time curves. (1) The removal of single ceria particles from the glass films in the cleaning solution was monitored in situ using EW microscopy coupled with a brush set-up. In situ measurement data collected during cleaning are likely to provide more important insights into the underlying mechanisms of various complex reactions that occur at the particles/brush–wafer interface. (3) This talk will also introduce lateral force microscopy (LFM) mode in the atomic force microscopy (AFM) to obtain the removal force of single ceria particles from the SiO2 film. LFM is a powerful tool to monitor the torsion bending (or twisting) of the cantilever with contact mode, which is corresponding to the removal force. Types of particle removal mechanism depending on the characterization of single particles (size, shape, and surface) will be discussed. Our results will provide a better understanding of how the abrasive particles, the additives, and the film surfaces interact together during cleaning. (1) Seo, J., Gowda, A., Khajornrungruang, P., Hamada, S., Song, T., & Babu, S. (2020). Trajectories, diffusion, and interactions of single ceria particles on a glass surface observed by evanescent wave microscopy. Journal of Materials Research, 35(3), 321-331. (2) Seo, J., Gowda, A., Khajornrungruang, P., Hamada, S., & Babu, S. (2020). 3D trajectories and diffusion of single ceria particles near a glass surface and their removal. Journal of Materials Research, 1-10. (3) Seo, J. (2020). A review on chemical and mechanical phenomena at the wafer interface during chemical mechanical planarization. Journal of Materials Research, 1-23.

It has been very difficult to remove smaller ceria particles from oxide surfaces after polishing. As the particle size decreases from 90 to 10 nm, cleaning efficiency of SC1 solution decreases from ~94 % to ~19 %, presumably because smaller ceria particles with a higher surface concentration of Ce3+ are more strongly coupled with silicon dioxide surfaces via strong Ce-O-Si bonding. (1) As was reported earlier, where the cleaning of oxide surfaces of ceria particles from slurries containing no additives, we reported that equimolar solutions containing H2O2 and NH4OH (4.2 mol l−1 each of H2O2 and NH4OH), aided by ultrasonic cleaning, and at high pH could almost completely remove even 10 nm sized ceria particles from silicon dioxide film surfaces. (1) However, a cleaning solution containing H2O2 and NH4OH at equal molar (4.2 mol l−1) was not effective in cleaning oxide and nitride surfaces contaminated with ceria particles in the presence of additives such as proline and citric acid. (2) Recently, we reported a cleaning solution comprising 1 wt% ascorbic acid, 1 wt% ammonium carbonate and 50 ppm Triton X-100 at pH 12, aided by ultransonic energy, to clean ~30 nm ceria particles from both oxide and nitride films with ~ 99% cleaning efficiencies. The binding between the additive-covered ceria particle particles and the oxide/nitride surfaces could be broken by the nucleophilic attack of hydroxyl ions. Ascorbic acid and ammonium carbonate prevent ceria particle redeposition by adsorbing on the surface of the removed particles and blocking the active Ce3+ species. Triton X-100 reduces adhesion between the particle and the film surfaces during cleaning. (1) Seo, J., Gowda, A., & Babu, S. V. (2018). Almost complete removal of ceria particles down to 10 nm size from silicon dioxide surfaces. ECS Journal of Solid State Science and Technology, 7(5), P243. (2) Gowda, A., Seo, J., Ranaweera, C. K., & Babu, S. V. (2020). Cleaning Solutions for Removal of∼ 30 nm Ceria Particles from Proline and Citric Acid Containing Slurries Deposited on Silicon Dioxide and Silicon Nitride Surfaces. ECS Journal of Solid State Science and Technology, 9(4), 044013.

In this study, we have investigated the role of the Ce oxidation state (Ce3+/Ce4+) on the CeO2 surfaces for silicate adsorption. In aqueous medium, the Ce3+ sites lead to the formation of −OH groups at the CeO2 surface through H2O dissociation. Silicate ions can adsorb onto the CeO2 surface through interaction with the −OH groups (−Ce−OH− + −Si−O− ↔ −Ce−O−Si− + OH−). As the Ce3+ concentration increased from 19.3 to 27.6%, the surface density of −OH group increased from 0.34 to 0.72 OH/nm2. To evaluate the adsorption behaviors of silicate ions onto CeO2 NPs, we carried out an adsorption isothermal analysis, and the adsorption isotherm data followed the Freundlich model. The Freundlich constant for the relative adsorption capacity (KF) and adsorption intensity (1/n) indicated that CeO2 NPs with high Ce3+ concentration show higher adsorption affinity with silicate ions. As a result, we have demonstrated that the Ce oxidation state (Ce3+/Ce4+) on the CeO2 surface can have a significant influence on the silicate adsorption.

The concentration of fine particulates in Seoul, Korea has been lowered over the past 10 years, as a result of the city's efforts in implementing environmental control measures. Yet, the particulate concentration level in Seoul remains high as compared to other urban areas globally. In order to further improve fine particulate air quality in the Korea region and design a more effective control strategy, enhanced understanding of the sources and contribution of fine particulates along with their chemical compositions is necessary. In turn, relative contributions from local and transported sources on Seoul need to be established, as this city is particularly influenced by sources from upwind geographic areas. In this study, PM 2.5 monitoring was conducted in Seoul from October 2012 to September 2013. PM 2.5 mass concentrations, ions, metals, organic carbon (OC), elemental carbon (EC), water soluble OC (WSOC), humic-like substances of carbon (HULIS-C), and 85 organic compounds were chemically analyzed. The multivariate receptor model SMP was applied to the PM 2.5 data, which then identified nine sources and estimated their source compositions as well as source contributions. Prior studies have identified and quantified the transported and local sources. However, no prior studies have distinguished contributions of an individual source between transported contribution and locally produced contribution. We differentiated transported secondary and biomass burning sources from the locally produced secondary and biomass burning sources, which was supported with potential source contribution function (PSCF) analysis. Of the total secondary source contribution, 32% was attributed to transported secondary sources, and 68% was attributed to locally formed secondary sources. Meanwhile, the contribution from the transported biomass burning source was revealed as 59% of the total biomass burning contribution, which was 1.5 times higher than that of the local biomass burning source. Four-season average source contributions from the transported and the local sources were 28% and 72%, respectively.

Lithium-sulfur (Li-S) batteries have been intensively investigated as a next-generation rechargeable battery due to their high energy density of 2600 W·h kg(-1) and low cost. However, the systemic issues of Li-S batteries, such as the polysulfide shuttling effect and low Coulombic efficiency, hinder the practical use in commercial rechargeable batteries. The introduction of a conductive interlayer between the sulfur cathode and separator is a promising approach that has shown the dramatic improvements in Li-S batteries. The previous interlayer work mainly focused on the physical confinement of polysulfides within the cathode part, without considering the further entrapment of the dissolved polysulfides. Here, we designed an ultrathin poly(acrylic acid) coated single-walled carbon nanotube (PAA-SWNT) film as a synergic functional interlayer to address the issues mentioned above. The designed interlayer not only lowers the charge transfer resistance by the support of the upper current collector but also localizes the dissolved polysulfides within the cathode part by the aid of a physical blocking and chemical bonding. With the synergic combination of PAA and SWNT, the sulfur cathode with a PAA-SWNT interlayer maintained higher capacity retention over 200 cycles and achieved better rate retention than the sulfur cathode with a SWNT interlayer. The proposed approach of combining a functional polymer and conductive support material can provide an optimiztic strategy to overcome the fundamental challenges underlying in Li-S batteries.

Semiconductors are fabricated through unit processes including photolithography, etching, diffusion, ion implantation, deposition, and planarization processes. Chemical mechanical planarization, which is essential in advanced semiconductor manufacturing processes, aims to achieve high planarity across the wafer surface. This paper presents a case study in which the optimal blend of mixture slurry was obtained to improve the two response variables material loss and roughness at the same time. The mixture slurry consists of several pure slurries; when all of the abrasive particles within the slurry are of the same size, the slurry is referred to as a pure slurry. The optimal blend was obtained by applying a multiresponse surface optimization method. In particular, the recently developed posterior approach to dual response surface optimization was employed, which allows the chemical mechanical planarization process engineer to investigate tradeoffs between the two response variables. The two responses were better with the obtained blend than the existing blend. Copyright © 2016 John Wiley & Sons, Ltd.

We first demonstrate a facile and effective strategy to directly deposit a Nafion nanoweb onto a sulfur cathode to address the challenges underlying in Li–S batteries. The Nafion nanoweb not only blocks the diffusion of polysulfides by electrostatic repulsion but also allows fast Li-ion exchange with the sulfur cathode through the selective protection layer. The Nafion nanoweb-sulfur cathode retained an excellent cycle performance over 200 cycles and delivered an improved rate capability, as compared to a sulfur cathode and a Nafion layer-sulfur cathode.

We investigated the effect of friction force between ceria abrasive and SiO2 film on dishing in STI CMP. The control of adsorption amount of poly acrylic acid (PAA) on ceria surface led to the reduction of the friction force during CMP. The reduced friction force by a thick surface layer on ceria resulted in the decrease of the dishing in STI structure during over-polishing process. In the patterned wafer, the dishing decreased from 976 to 594 A/min at 37.5% pattern density (Si3N4/SiO2 = 30/50 μm) as a maximum adsorption amount increased from 0.49 to 0.64 mg/m2.

Urban particle pollution is affected by not only the emissions of pollutants and secondary aerosol formation through atmospheric chemistry on a local scale, but also the regional transport of particles and precursor gases from highly polluted upwind areas. However, this regional impact on urban particle formation is not well understood. Wintertime haze events occur at Seoul, Korea through the combination of regional transport from China and local formation at Seoul. We perform thermodynamic model simulations based on inorganic component measurements of haze particles collected at Seoul and Deokjeok Island (upwind background). Results suggest that in the downwind area (Seoul) the local formation of sulfates increases the mass concentrations of transported particles through the gas–particle partitioning of semivolatile nitric acid (HNO3) and ammonia (NH3). Therefore, this synergetic effect of local sulfate formation on urban haze with regional transport must be considered in implementing effective particle reduction controls for urban sustainability.

We report on thin film transistors (TFTs) based on spinel ZnGa2O4 (ZGO) that was recently spotlighted as an ultra-wide bandgap oxide semiconductor. The ZGO layers were grown in a spinel structure by pulsed laser deposition on the cubic spinel MgAl2O4 (MAO) as well as on cubic MgO substrates while changing the Zn/Ga ratio. The compressive strained epitaxial growth of ZGO on MgAl2O4 (100) and the tensile strained epitaxial growth of ZGO on MgO (100) without any misfit or threading dislocations were confirmed by the reciprocal space map and cross-sectional transmission electron microscopy. The electrical transport properties were demonstrated through TFTs based on ZGO as the channel layer, Al2O3 as the gate oxide, and Sn-doped In2O3 as the source, drain, and gate electrodes. When the Zn/Ga ratio is slightly lower than the ideal value of 0.5 on MgO substrates, the ZGO TFT showed the highest mobility of 5.4 cm2/V s. The ION/IOFF ratio and subthreshold swing (S) value are 4.5 × 108 and 0.19 V/dec, respectively.

A previously developed aqueous cleaning solution (4.2 mol l−1 each of H2O2 and NH4OH) was found to be ineffective in cleaning oxide/nitride surfaces after contamination with ceria particles from slurries containing proline or citric acid. However, a cleaning solution consisting of 1 wt% ascorbic acid, 1 wt% ammonium carbonate and 50 ppm triton X-100 at pH 12, aided by ultrasonic cleaning, removed these ceria particles, even those as small as ∼30 nm, from both oxide and nitride surfaces with efficiencies >99% as determined by AFM imaging. Fourier transform infrared (FTIR) spectroscopy results indicated that ceria particles treated with these additives can also bind with oxide/nitride surfaces through Si–O–C and Si–O–H bonds, in addition to any Ce–O–Si, where the C and H atoms are from the additives adsorbed on the ceria particles. All these bonds are broken effectively by the nucleophilic attack of hydroxyl anions in the cleaning solution while triton X-100 in the cleaning solution reduces adhesion between the particles and the film surface and facilitates cleaning via a wetting mechanism. More importantly, ascorbic acid and ammonium carbonate prevent particle redeposition by complexing with the removed particles and blocking the active Ce3+ species on their surface.

East Asian countries (Korea and China) have been experiencing exceedingly high concentrations of particulate matter (PM) that threatens health and potentially alters climate. However, the formation of East Asian PM is poorly understood. Furthermore, during the winter high PM concentrations at Seoul, Korea often occurs via the combination of the transport of Chinese haze through the prevailing Westerlies and the local formation at Seoul, and this complicates the PM formation. A severe multiday haze event occurred at Seoul during February 24–28, 2014, and the synoptic meteorological conditions suggest the combination the transport and the local formation (Seo et al., 2017). PM at Seoul and Deokjeok Island during this haze period was sampled and analyzed. Deokjeok Island provides background for Seoul PM since it is upwind and emission free. We hypothesize that transported PM from China (PM at Deokjeok Island) is hygroscopic (thus contains water due to high RH) and undergoes multiphase photochemical aging at Seoul. To validate our hypothesis, we conducted smog chamber experiments. In a humid smog chamber, photochemistry of NOx initiates hygroscopic growth of particles and aerosol liquid water in turn facilitates aqueous chemistry forming organonitrates and oligomers. This multiphase chemistry provides chemical insights of chemical aging during a haze event in East Asia. NOx effects on photochemical aging of particles are substantial. Even a few ppb of NOx form nitrates in aerosol liquid water, and acidify neutral particles. NOx reduction is not likely to be an effective strategy for nitrate- and acidity-related health.

With the success of image classification problems, deep learning is expanding its application areas. In this paper, we apply deep learning to decode a polar code. As an initial step for memoryless additive Gaussian noise channel, we consider a deep feed-forward neural network and investigate its decoding performances with respect to numerous configurations: the number of hidden layers, the number of nodes for each layer, and activation functions. Generally, the higher complex network yields a better performance. Comparing the performances of regular list decoding, we provide a guideline for the configuration parameters. Although the training of deep learning may require high computational complexity, it should be noted that the field application of trained networks can be accomplished at a low level complexity. Considering the level of performance and complexity, we believe that deep learning is a competitive decoding tool.

Augmented Reality and Mixed Reality technologies make us feel the real world and the virtual world are mixed with each other through visual matching. However, existing mixed reality contents using these technologies have a limitation that interact only with virtual objects and cannot interact with real objects. If a dynamic real object need to be influenced by a virtual object, or vice versa, illusion of Mixed Reality can be broken by the incongruity of the interaction. If these limitations are improved, real objects, which were always static, can operate dynamically and interact with virtual objects, so becomes difficult to distinguish between real objects and virtual objects. In this paper, we propose extended interactions in a mixed reality environment that can give illusion which is difficult to distinguish between real objects and virtual objects. And to confirm this, we implement authoring environment based Hololens.

Although poly(acrylic acid) (PAA) has been used as a passivation agent for high polish rate selectivity between SiO 2 and Si 3 N 4 in STI CMP, it causes severe dishing during the over-polishing step. Here, we fabricated interpolymer complexes of PAA and poly(ethylene glycol) (PEG) as passivation agent for low dishing as well as high selectivity. PAA and PEG form a cross-linked network structure through H-bonding, which is called an “interpolymer complex”. During the over-polishing step, the cross-linked network structure of the PAA-PEG interpolymer complex prevents abrasives from polishing SiO 2 in the trenches, resulting in a significant decrease in dishing. These results provide researchers with a new approach toward passivation agents to provide low dishing in STI CMP.

Bluetooth Low Energy (BLE) evolved from classical Bluetooth technologies for enabling short-range communication in different services and systems. BLE has many advantages over classical Bluetooth technologies, including low-cost deployment and low-power consumption. Recently, a very few number of research studies have been conducted to improve device discovery process of BLE. But, these studies have still some limitations. Prior studies have assumed that advertising PDUs are immediately processed as long as they are received successfully by a scanner. Practically, however, BLE devices may experience lots of collisions due to contention among neighbors, particularly in a crowded environment. With increasing number of BLE devices, delays of both device discovery and connection setup keep exponential growth, which could influence user experience in terms of either time or energy consumption. In this paper, an enhanced mechanism is proposed to enable BLE advertisers and scanners to learn the network contention and adjust their parameters accordingly, so as to achieve fast discovery latency. Through extensive simulations, the proposed mechanism has shown its effectiveness to reduce unexpected long latency in crowded BLE networks.

We have investigated the synergistic effect with mixing of three different-sized SiO2 abrasives (30 nm-SiO2, 70 nm-SiO2 and 200 nm-SiO2) and the corresponding W chemical mechanical planarization (CMP) performances. W removal rate significantly increased when the different-sized SiO2 abrasives were mixed, which is attributed to the increase in the total contact area between the abrasives and the W film. Based on the statistical model, we obtained the optimal mixing ratio (30 nm, 70 nm, 200 nm) = (0.49, 0.23, 0.28) for the highest W removal rate. These results, investigated in this study, show that the removal rate of W film can be improved via simple mixing process.

Among various deep neural network (DNN) components, this paper studies the activation functions especially for deep feed-forward networks with applications to channel decoding problems of polar code. In line with our previous study, this paper considers the ReLU (Rectified Linear Unit) and its variants for activation functions of DNN. We devise a new ReLU variant, called Sloped ReLU, by varying the slope of the ReLU for the positive domain range. This is analogous to tree architectures between the likelihood function in successive decoding of channel codes and the activation function in DNN. Our numerical results show that the polar decoding performance with the Sloped ReLU improves as the slope increases, up to a certain level. We believe that the idea of utilizing this analogy for determining activation functions of DNN can be applied to other decoding problems as well, which remains as a future work.