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Silicon dioxide is the most important gate oxide dielectric material, and its surface planarization is an important factor in the continuous shrinking of the size of integrated circuits. Developing a novel chemical mechanical polishing auxiliary technique to achieve efficient polishing of oxide wafers is a significant challenge. In this study, a novel in-situ micro-nano bubbles auxiliary method, which used a nano-hydrophobic film to prepare a gas supersaturated slurry that can generate instant in-situ micro-nano bubbles during polishing, was developed for oxide wafers. Compared with conventional slurries, this auxiliary method increased the material removal rate by about 30% and ensured the low surface roughness of the wafer of 0.14 nm. The existence of micro-nano bubbles and the multi-size distribution and zeta potential of the micro-nano bubbles were measured by optical microscope and dynamic light-scattering methods. Then, to investigate the auxiliary mechanism of this in-situ micro-nano bubbles, different analytical methods, such as oxide thickness measurement system, scanning electron microscopy, Fourier transform infrared spectroscopy, and atomic force microscopy, were used to characterize the sample. The results indicated that during the polishing process, the micro-nano bubbles generated in situ have a good cleaning effect. In addition, the free radicals generated after in-situ micro-nano bubbles burst simultaneously modified the surfaces of the wafer and the pad. The improvement of the adsorption between the wafer and abrasives promoted the chemical reaction between them. After conditioning, the rougher and cleaner pad had a higher mechanical effect. Most importantly, this in-situ micro-nano bubbles auxiliary method has the potential to be applicable to all slurries.

Chemical mechanical polishing (CMP), a wafer surface planarization method, is critical in the semiconductor industry because uniform and scratch-free processing is required for a highly integrated circuit on the wafer surface. Thus, the prediction of aggregated particle size during CMP helps achieve stable and precise processing during experimental circumstances. Herein, silica nanoparticle aggregation simulation during CMP process-based Quadrature Method of Moments (QMOM) was first described using ANSYS Fluent as a computational fluid dynamics (CFD) tool. Experiments were also implemented in a 10,000 class cleanroom using a CMP polisher actually used in the semiconductor industry. Moreover, a comparison of experimental particle size measured through zeta-potential and particle size analyzer and simulated Sauter mean diameter (D32) showed that the experimental data agreed well with the simulation results.

This study aims to achieve higher-efficiency zirconia ceramic polishing demands, using a novel rod-shaped SiO2@C abrasive that was synthesized by a simple three-step method. The scanning electron microscopy and transmission electron microscopy results showed that composite abrasives were rod-shaped. As confirmed by Fourier transform infrared spectrometer and Raman spectra, the composite particle had a core-shell structure with a core of silica and a shell of carbon. According to the N2 adsorption-desorption results, this composite abrasive had a mesoporous structure. The material removal rate of 242.5 nm/h and the zirconia ceramic surface roughness of 1.86 nm are 70.4% higher and 27.9% lower, respectively, than those achieved with conventional silica abrasives. The improved polishing performance may be attributed to its line contact mode, the reduction of Young's modulus and the improvement of tribochemical reaction. This study highlights the interaction between the surface microstructure of abrasives and the surface planarization of ceramics.

With the demand for manufacturing large (e.g., 450 mm) wafers, problems arise due to temperature increases associated with the chemical mechanical polishing (CMP) process. Various methods have been employed to stabilize the in-situ polishing temperature. The use of a high-temperature slurry can improve the removal rate, but a degradation in surface morphology occurs during the copper CMP procedure. To explain this mechanism, the effects of temperature on the slurry, CMP pad, and copper wafer were separately investigated. A temperature of approximately 40 °C was demonstrated to be a suitable choice when considering polishing efficiency and quality, thereby facilitating the rapid production of semiconductors. Particle aggregation was also observed with a rise in temperature. The work presented here may allow for a reduction in defects during low-hardness material polishing.

The performance of chemical mechanical polishing (CMP) was determined by the morphological characteristics of the abrasive particle. In this study, the shape of the aggregate of fumed silica was confirmed by a method of characterizing the morphology of the particles using transmission electron microscopy (TEM). Each aggregate was classified into four types—linear, branched, ellipsoidal, and spheroidal—and the shape distribution of a fumed-silica slurry was investigated with different specific surface areas. The CMP performance of fumed silica slurries at 90 m2/g with numerous linear-shaped aggregates and 400 m2/g with the highest portion of spheroidal aggregates were compared to that of colloidal silica slurry. A model for the effects of bumpy abrasives on CMP explained the reason for this result by using penetration depth and MRR with various numbers of contact bumps. Furthermore, a mixture of spherical and non-spherical abrasives in a ratio of 4:1 exhibited an improved CMP performance.

We focused on the electromagnetic interference shielding effectiveness of multi-layer thin films, which were composed of Cu and NiFe, fabricated by direct current magnetron sputtering. Crystal structures and microstructures of the multi-layer thin films were confirmed through X-ray diffraction and field emission transmittance electron microscopy. In addition, the magnetic properties of the multi-layer thin films and pure NiFe thin films were measured by using a vibration sample magnetometer and vector network analyzer. To improve the electromagnetic interference shielding effectiveness at high frequencies, we selected Cu and NiFe because of their excellent conductive properties and high permeability. The shielding effectiveness of different types of thin films (Cu, NiFe, NiFe/Cu) with 4 μm thickness was measured from 0.7 GHz to 10 GHz, and the shielding effectiveness of the multi-layer thin films was found to be more efficient than that of Cu and NiFe thin films over the entire high frequency range. In the case of the 4 μm NiFe/Cu multi-layer thin films, an improvement in the shielding effectiveness is attributed to multiple reflections at the NiFe/Cu interfaces of the multi-layer thin films.

A pellicle is an important part of mask protection in extreme ultraviolet (EUV) lithography, and nanometer-thickness graphite film (NGF) is an ideal material for pellicle fabrication. In our previous work, we synthesized large-scale NGF on polycrystalline Ni foil by a “two-stage” chemical vapor deposition process with an EUV transmittance of 79 ± 2%. The nonuniformity of EUV transmittance is mainly caused by the thicker NGF formed on the Ni grain boundaries (GBs). Here, we present a simple and cost-effective method to weaken the effects of the Ni GBs by sputtering thin Ni films onto Ni foils. The Ni film provides smaller grains with high GB density so that the non-uniformity of NGFs caused by Ni GBs was averaged out by the large EUV beam size. We investigated the grain growth of Ni films with different thicknesses, and 1-μm Ni film/Ni foil had the minimum average grain size of ∼6 μm. The NGF synthesized on it showed a higher EUV transmittance with better uniformity of 86.3 ± 0.9%. Fullerenic C C and sp3 C C bonding were detected by the X-ray photoelectron spectroscopy, and the NGF on the Ni GBs showed a higher defect density.

In this study, we successfully demonstrate the fabrication of a MoS2-graphene heterostructure (MGH) on a 4 inch wafer at 300 °C by depositing a thin Mo film seed layer on graphene followed by sulfurization using H2S plasma. By utilizing Raman spectroscopy and high-resolution transmission electron microscopy, we have confirmed that 5–6 MoS2 layers with a large density of sulfur vacancies are grown uniformly on the entire substrate. The chemical composition of MoS2 on graphene was evaluated by X-ray photoelectron spectroscopy, which confirmed the atomic ratio of Mo to S to be 1:1.78, which is much lower than the stoichiometric value of 2 from standard MoS2. To exploit the properties of the nanocrystalline and defective MGH film obtained in our process, we have utilized it as a catalyst for hydrodesulfurization and as an electrocatalyst for the hydrogen evolution reaction. Compared to MoS2 grown on an amorphous SiO2 substrate, the MGH has smaller onset potential and Tafel slope, indicating its enhanced catalytic performance. Our practical growth approach can be applied to other two-dimensional crystals, which are potentially used in a wide range of applications such as electronic devices and catalysis.

Triboelectric nanogenerators (TENGs) have been widely used in the recent years to harvest and convert mechanical energy to electrical energy. With the improved performance of TENGs, their stability and robustness in harsh environments have attracted increasing attention as a next challenge. We present herein a superhydrophobic interlayer-integrated TENG that exhibits high performance against humidity and environmental contamination. We used particle lithography to prepare a superhydrophobic interlayer with a three-dimensional (3D), hierarchical, porous pattern, resulting in a high static water contact angle of 161°. This 3D, hierarchical superhydrophobic interlayer played a key role in improving the TENG output performance. In addition, the TENG not only retained up to 86% of its initial electrical output at a high relative humidity of 80%, but also recovered much faster than a TENG with a regular flat interface under the same wet conditions. Finally, we found that the TENG was very robust against external contamination, maintaining approximately 88% of the initial output after five cycles of particulate contamination and washing in water, indicating that the TENGs with a superhydrophobic, 3D, hierarchical interlayer could be used for powering Internet-of-things devices that are exposed to harsh environments, such as highly humid ones with dense particulate matters.

This study demonstrates an our newly designed novel in-line real impactor, which is operated at the inlet flow rate of 1.0 L/min and has vertical annular nozzle to separate particles larger than 20.5 µm in the aerodynamic diameter. The Stk50 for an impactor with a rectangular nozzle was selected as the design parameters of the impactor. The influences of both existences of an orifice and distance between orifice and impaction plate are investigated numerically and experimentally. In numerical simulations, Stk50 of an impactor without an orifice is found to be 20.5% and 17.0% larger than that of an impactor with an orifice when the distance between an orifice and the impaction plate is 1.2 mm and 1.8 mm, respectively. For the impactor with an orifice, the Stk50 is predicted to decrease from 0.74 to 0.43 when the distance between orifice and impaction plate was decreased from 1.8 mm to 1.2 mm with an orifice. It is found that the pressure drop of the impactor with an orifice is at most 2.35% larger than that of the impactor without an orifice. Thus, the presence of an orifice can increase the pressure drop slightly but increase collection efficiency significantly. For our newly developed impactor, the collection efficiency of is primarily influenced by the distance between an orifice and the impaction plate. In experiments, the Stk50 was decreased from 0.50 to 0.25 when the distance between orifice and impaction plate was decreased from 1.8 mm to 1.2 mm. The Stk50 obtained from experimental data shows the same tendency as numerical predictions

This study investigated the reasons for inhomogeneity in the axial direction during spark plasma sintering (SPS) of a thermoelectric material. Bismuth antimony telluride, a p-type thermoelectric material, was sintered using high current (>200 A). X-ray diffraction and power factor analyses confirmed that the preferred orientation improved with increasing sintering temperature, and the power factor increased linearly with temperature. The temperature gradient from 700 to 725 K at 723 K sintering process, estimated from this unique correlation between sintering temperature and power factor, was five-fold that of the reported values. This extraordinary temperature gradient was presumably generated by the Peltier effect.

This paper reports an increase in the optical reflectivity of two kinds of copolymers used in contact lenses, with different proportions of silicon and fluorine derivatives, when irradiated with 4.1 MeV alpha particles from an 241Am source. The fiber-optic reflectance technique showed that the lens with a higher proportion of silicon and fluorine content and a lower proportion of methyl-methacrylate is more susceptible to alpha radiation. X-Ray photoelectron spectroscopy and Raman spectroscopy have revealed the formation of silicon oxide and carbide species as a result of chain scission and recombination in the 20 μm thick irradiated regions of lens materials. It is presumed that the high (260 eV/nm) linear energy transfer of alpha particles in polymers creates trapped gas “Bubbles”, and the observed increase in the optical reflectivity with increased irradiation time is explained on the basis of diffuse reflectance caused by the scattering of light from the hard surfaces of these “Bubbles”.

In this paper, tribological effects on the material removal rate (MRR) are investigated using two types of slurry abrasives (i.e., ceria and silica) and three types of pads. From a micro to macro viewpoint, the physico-chemical interaction between the pad-wafer interface and abrasive was studied based on multi-asperity contact. First, the relative contact pressure in high or low proportions among all asperities was calculated using a contact mechanics model. The results indicate that for the commercial slurry used in the semiconductor industry, relatively high contact pressure due to the asperities can be transferred to the ceria abrasives, and only a low contact pressure can be supported by these silica abrasives. Furthermore, it was confirmed that the two different slurry abrasives showed opposite behaviors according to the real contact area of the pad asperities. That is, as the pad texture changed from ‘Desired pad’ to ‘Smoothed pad’, the MRR of the ceria increased by 47%, while the MRR of the silica decreased 59%. Lastly, the Stribeck curve, which is suitable for the CMP process, was re-analyzed to clarify the abrasion mechanism under the pad asperity scale. The results showed that two-body abrasion may be maintained for the ceria CMP, and transition is possible from two-body to three-body abrasion at the silica CMP as the contact area increases. The present paper is expected to clarify the tribological mechanism of the oxide CMP and can provide further insight into optimizing and selecting consumables such as conditioner, pad, and slurry.

Although ceria particles are currently receiving great interest with their unique catalytic and optical properties, the problem of agglomeration is yet to be overcome, which is caused by their high density and surface energy, consequently hampering the practical applications. Herein, a novel method of preparing hierarchical shells of ceria (CeO2) and silica (SiO2) on a polystyrene (PS) core is introduced to control the shape and surface charge of the particle, which give rise to different dispersion conditions. The PS/CeO2/SiO2 hybrid core–shell microspheres provide a wide spectrum of surface charge via adjustment of the thickness of the outermost silica shell from 20 to 40 nm, which sets the isoelectric point (IEP) in the range of 5.1–8.6. Subsequently, the silica shell significantly extends the product’s stability and utilization windows due to the controlled surface charge and affinity between the particle surface and the dispersion medium. The developed multilayered core–shell microspheres and the method of synthesis have great potential for various applications that require sophisticated control of surface properties.

Many recent studies have employed biomimicry to develop practical systems inspired by natural mechanisms. For instance, several attempts have been made to develop an artificial gill system by mimicking plastron mechanisms, which demonstrates the potential for terrestrial animals to breathe under water by extracting dissolved oxygen and discharging carbon dioxide. In this study, we propose a theoretical model for such artificial gill system comprising essential engineering parameters such as the partial pressure of oxygen inside the system, gas permeability, surface area, and the thickness of membranes. We experimentally investigated the effect of each engineering parameter on the oxygen extraction/supply rate and then validated the theoretical model with experimental results. We also applied the same model and engineering guidelines to develop a scaled-up artificial gill system for a stag beetle. The artificial gill system extracts sufficient dissolved oxygen from water, thus demonstrating that stag beetle can survive for more than 60 h in water; however, carbon dioxide accumulates over time. We believe that the established model and supporting experimental results can further advance artificial gill technology, thereby making it possible for humans to breathe under water without using a conventional scuba gear.

Target analyte detection using whole-cell microbial biosensors can benefit from a microchemostat platform owing to the reduced reagent consumption, a finely controllable environment, and multi-parallel processing. However, the use of the previous microchemostat still has limitations for practical applications, e.g., its single-use design, long time requirements for cell and device preparation, low portability, slow and weak response signals, and the lack of ready-to-use in situ devices. In the present study, we developed a novel microchemostat platform that resolves these issues and enhances the performance of microbial biosensors via its abilities to actively control the cell population and to form a uniform culture environment using a nanoscale hydrodynamic film (NHF). The combination of the microchemostat platform and the microbial biosensors yielded fast and strong signals on demand in response to heavy metal ions (e.g., Pb2+). In addition, the platform enables the long-term on-chip storage of microbial biosensors for over 1 month, without deterioration of growth and detection ability. Lastly, we demonstrated that microbial biosensors can consecutively measure multiple samples by a regeneration process in which the microchemostat platform continuously subcultures the microbial biosensors until the complete recovery of their sensing capabilities. Thus, the microchemostat offers whole-cell microbial biosensors that are fast, ready-to-use, reusable, and storable. It also shows good potential for user-friendly, portable on-site environmental monitoring, particularly where expensive analytical tools and/or instruments for heavy metal ion detection are unavailable.

Triboelectric nanogenerators (TENGs) harvest and convert mechanical energy to electrical energy. TENGs that are transparent and flexible can be applied to various (opto-)electronic devices supporting finger- or pen-based touchscreen inputs. This paper presents a transparent, flexible TENG that harvests mechanical tapping energy (typically discarded) by simple placement on touchscreen devices. The developed TENG consists of flexible and transparent conducting electrodes (FTCE) with high transmittance (> 93%) and low sheet resistance (18.5 Ω/sq), and transparent 3D-hierarchical polydimethylsiloxane (PDMS) with porous pyramid-patterns. In this study, the developed TENG directly powered eight light-emitting diodes (LEDs) by harvesting the mechanical energy produced by tapping with a touch pen while playing a smartphone game. We also used the transparent TENG as a transparent single-electrode-based, self-powered raindrop detection sensor on a window for a smart home. Our results indicate that the proposed TENG can be used not only as an effective mechanical energy harvester for transparent, flexible, and next-generation optoelectronics devices but also as a self-powered sensor for future Internet-of-Things applications.

A new buff cleaning method to remove particles remaining on the Cu surface after chemical mechanical polishing was developed. Because the van der Waals force is the dominant adhesion force when silica particles are attached to a blanket Cu film, an alkaline solution or hot water was previously recommended to increase the lifting force and weaken the van der Waals force, thereby improving the cleaning efficiency by 92.58% and 92.71%, respectively. In this study, the temperature effects on physical and chemical bonding were thoroughly compared for silica and ceria samples. Soft pads are recommended to improve the particle removal efficiency and prevent scratching the Cu surface during the buff process. Almost all of the particles were dislodged and scratching was successfully prevented after optimization. This work elucidates the mechanisms of particle adhesion and removal in Cu buff cleaning from the standpoints of force and energy, thus optimizing Cu buff cleaning and achieving an ideal cleaning efficiency.

The effect of residual ceria slurry on a pad was investigated to improve the cleaning efficiency while maintaining the removal rate of chemical mechanical planarization (CMP). This combined process consists of two sequential steps: polishing with slurry, then polishing with residual slurry and cleaning with deionized water (DIW). Ceria slurry injected in the first step is used for polishing, while the rest of the ceria slurry remains in the groove or escapes out of the pad. When DIW is injected in the second step, the ceria slurry nanoparticles remaining on the pad participate in polishing, and DIW cleans the wafer surface, preventing contamination. The most efficient ceria injection time uses this two-step process, and the cleaning efficiency for this optimized time was confirmed. With optimal process conditions, particle area ratio decreased from 9.035% to 0.839%, indicating increased cleaning efficiency. This study suggests the time needed for the slurry to attain efficient polishing and demonstrates a method for shortening the ceria process time by simultaneously polishing and cleaning during the CMP process.

The pinch-off phenomenon in a flame refers to flame separation after reaching the critical frequency and amplitude under acoustic excitation. The pinch-off flame consists of the main flame attached to the nozzle and the detached pocket flame, and it is reported that more pollutants are discharged as the residence time of the pocket gas (i.e., the hot products) increases. This study focuses on the mechanism of the pinch-off phenomenon. The flame structure and flow field were analyzed by the simultaneous measurement of OH planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV). Due to a lack of previous research on the necessary conditions for a pinch-off flame, this study mapped the conditions for pinch-off in terms of the forcing frequency and velocity perturbation intensity ( u ′ / u ¯ ) under acoustic excitation. The flame height in the pinch-off region was defined in two ways: the main flame height from the nozzle tip to the tip of the attached flame, and the total flame height including the detached pocket. Strouhal number was calculated based on these two definitions of flame height. In addition, the vortex flow and reverse flow under external forces were measured through analyzing the non-reacting and reacting flow fields. Flame deformation due to the entrainment of air in the vortex flow and the reverse flow was confirmed, and it was found to correlate with the pinch-off phenomenon. To analyze this observation quantitatively, time-dependent strain rate analysis was performed, and a high strain was confirmed to be present upon flame extinction. Therefore, these results demonstrate that pinch-off is correlated with the vortex flow and the reverse flow, and caused by a high strain rate acting on the flame surface.

After the successful synthesis of graphene using chemical vapor deposition in 2009, the large-area/defect-free transfer method still remains a critical issue for implementing high-performance graphene-based electronic devices. Here, for the first time, we demonstrated a specially prepared water-soluble amorphous WO3 intermediate layer to effectively protect the graphene surface from immediately after its synthesis to transfer and final unit processing. Moreover, using the photodetector to which the proposed protection method was applied, the performance improvement was quantitatively verified. Compared with the control device, the surface-protected photodetector recorded a higher photoresponsivity of 1.74 times and faster temporal photoswitching response time of 4 s or more. The graphene surface protection method using the WO3 intermediate layer allows the reversibility in transfer process and performance enhancement of graphene-based electronic devices.

Point-of-care testing for health and environmental monitoring sometimes requires the detection of specific molecules in liquid media to provide a diagnosis in a resource-limited or outdoor environment. Thus, it is significant to develop portable and self-powered sensor systems to enable in-situ detection of analytes in liquids. Triboelectric nanogenerator (TENG) and microfluidic devices are two nascent technologies that can be used for point-of-care testing. Furthermore, the combination of these technologies is proposed as an attractive research strategy to achieve portable sensors by using the electrical signals generated during the mechanical interactions between the test solution and the device. Herein, a portable TENG-based microfluidic self-powered sensor system is demonstrated. The system consists of a triboelectric microfluidic (TEMF) device, which generates a voltage in response to the target analyte solution flowing through the microchannel. The viability and versatility of this device are illustrated for ionic concentration measurements, as well as in-situ monitoring for the catalytic reduction of an industrial pollutant, 4-nitrophenol (4-NP). The results verify that the proposed sensor system has the potential for application in the field of self-powered chemical sensors for environmental monitoring and analytical chemistry.

We fabricated the large-area (3 × 3 cm2) freestanding nanometer thickness graphite film (NGF) using transfer free process. NGF was grown on Cu foil using CVD and Cu foil is used as the frame of NGF freestanding film. Thickness of the NGF was controlled by gas flow and growth time. Transfer-free process was achieved by selective etching of Cu foil and dipping NGF in alcohol of low surface tension. Freestanding NGF reveals excellent EUV transmittance. This method allowed us to simplify the fabrication process for freestanding film without transfer process and demonstrated a possibility for HVM of pellicle for EUV lithography.

The surface roughness of a chemical mechanical polishing (CMP) pad provides microscopic asperities where the actual polishing takes place. Thus, the roughness should be maintained in a proper regimen to obtain stable CMP process quality. A conditioner is a key consumable in the CMP process because it maintains the roughness of the CMP pad surface against surface glazing or flattening during polishing. Because the conditioner mechanically breaks the pad surface to maintain the roughness, previous research has expressed its ability index in terms of the pad wear rate (PWR). In the present study, we investigate the reason for PWR change of CMP pads having vigorously changing moduli with respect to temperature changes during the mass production. The pad property changed steeply in the process temperature range from 60 to 80 °C. The tensile strength is a key property change that leads to sudden PWR drop. We found that the shape and configuration of the diamond tip are the major parameters affecting the ability to maintain surface roughness of the pads. Thus, we suggested a proper conditioner design for tungsten (W) CMP based on the experimental data to sustain the process quality and increase the consumable lifetime. As a result, the peak surface roughness has improved from 29.4 μm to 32.6 µm and the consumable lifetime was also increased.

The self-assembly and deposition mechanisms of nanoparticles in droplets on a substrate are of significant importance in many inkjet printing-based industrial applications such as microelectronics, display systems, and paint manufacturing. However, a comprehensive investigation into the velocity field of fluid and its accompanying particle transport behavior in injected droplets undergoing immediate evaporation has not been conducted. In this study, we describe the underlying mechanisms of the self-assembly and deposition behavior of nanoparticles in inkjet-printed, evaporating droplets by visualizing the internal fluid flows. We additionally characterize the relationship between the internal fluid flows and nanoparticle patterns by changing not only the wettability and temperature of the substrate, but also the chemical composition of nanoparticle suspensions. We verify that Marangoni flow generated on a hydrophobic PDMS substrate with a contact angle (CA) of >90° helps the formation of dome-shaped nanoparticle structures, while radially outward flow generated on a hydrophilic glass substrate with a CA of

The main aim of doping DNA lattices with lanthanide ions (Ln-DNA complex) is to change the physical functionalities for specific target applications such as electronics and biophotonics. Ln–DNA complexes based on a double-crossover DNA building block were fabricated on glass using a substrate-assisted growth method. We demonstrated the structural stability of Ln–DNA complexes as a function of Ln ion concentration by the atomic force microscopy. The Ln ion doping in DNA lattices was examined using a chemical reduction process, and the electrical characteristics of Ln–DNA complexes were tested using a semiconductor parameter analyzer. The structural phase transition of DNA lattices from the crystalline to amorphous phases occurred at a certain critical concentration of each Ln ion. Ln ions in DNA lattices are known to be intercalated between the base pairs and bound with phosphate backbones. When DNA lattices are properly doped with Ln ions, Ln–DNA complexes revealed the complete deformation with chemical reduction process by ascorbic acid. The current increased up to a critical Ln ion concentration and then decreased with further increasing Ln ions. Ln–DNA complexes will be useful in electronics and photonics because of their unique physical characteristics.

Mini-channel has been more studied recently than micro-channel to optimize the heat emission and pressure drop by regulating the channel size and length. In this work, a multistage mini-channel heat sink using water coolant was designed to obtain a larger cooling rate in a small area with a lower pressure drop. To confirm the performance of the structure, we conducted numerical simulations under laminar and single-phase conditions. The diameter and length of the channel were 2 and 530 mm, respectively. From the simulation, the local convection coefficient, coolant temperature, channel-wall temperature, effectiveness, and pressure drop were analyzed in relation to the mass flux, heat-source temperature, and number of stage stacks. To obtain valid simulation results on the heat transfer, we used well-matched conventional correlation. The result of the pressure drop was compared with the experimental result to confirm the validity of the hydrodynamic model. The simulation result shows that the maximum cooling rate was 40 W/cm 2 at a pressure drop of 1383 Pa in a quintuple-stage model. However, the triple-stage structure had the best effectiveness of 0.83 under the same simulation conditions. The pressure drop of the multistage structure was higher than that of the single-stage structure. However, the increase of the total pressure drop was small as against the increase of the cooling rate.

In this work, large-scale (120 × 120 mm) nanometer-thick graphite films (NGFs) were synthesized on polycrystalline Ni foils using a “two-stage” chemical vapor deposition (CVD) process. An intermediate cooling process was included in the CVD process; this process affected the isothermal graphene growth, which is explained using a growth model. We mainly studied a graphite film with the thickness of ∼40 nm and the good thickness uniformity was characterized by atomic force microscopy (AFM), Raman spectroscopy and extreme ultraviolet (EUV) mapping. The graphite formed on the Ni grain boundary was analyzed by transmission electron microscopy (TEM). The relationships between the thickness, optical and electrical properties of the NGF and growth temperature were also studied.

Laser printers are widely used in modern society, and VOCs and ultrafine particles emitted from printers have been known to cause adverse effects on indoor environment. In this study we conducted experiments in order to evaluate the ultrafine particles emission characteristics of laser printers and to reduce its concentration. Ultrafine particles emission characteristics was assessed for 15 printers by measuring its number concentration inside the printers (before and after the fuser) while printing. In addition, chemical analysis was performed using transmission electron microscope (TEM), Matrix-assisted laser desorption ionization time of flight mass spectroscopy (MALDI-TOF MS) and gel permeation chromatography (GPC). In order to reduce the occurrence of ultrafine particles from laser printers, an experiment was conducted with lowered fusing temperature, which resulted in the sharp decrease of the ultrafine particles generation due to the decrease in particle nucleation rate. Additionally, based on the fact that ultrafine particles contains paramagnetic material, by applying electromagnetic field, ultrafine particles emitted from laser printer was reduced by ~40%.

This study investigated the flashback phenomenon coupled with self-excited combustion instability in turbulent premixed bluff-body flames using the pressure fluctuation measurement, high-speed OH-PLIF, and PIV techniques. Previous studies investigating flashback in a bluff-body have found that the flame moves back and forth around the trailing edge of the bluff-body; however, the phenomenon in which the flame propagates beyond the bluff-body has not been sufficiently studied. Therefore, this study focused on understanding a strong flashback, which can damage the upper section of a combustor and which is vulnerable to heat due to flame propagation over the front of the bluff-body. The combustion instability frequency resulting from changes in the combustion length occurred within the range of the resonance frequency of the combustor, thereby confirming that thermal-acoustic combustion instability occurred in the combustor. When the strong flashback occurs, an instantaneous adverse pressure gradient is formed within a combustion instability cycle. Consequently, the generated reverse flow pushed the flame attached at the trailing edge of the bluff-body to the upstream from the bluff-body. The flame propagated rapidly along the side of the bluff-body by the influence of the boundary layer flow and the decreased quenching distance. This propagated flame became the ignition source at the front tip of the bluff-body and generated the flame surface that propagated in all directions; thus, it was found to be the primary cause of the increase in the flashback distance. The flame flashback distance also varied depending on the combustor length and the initial flow condition. An attempt was made to concentrate the measured data of flashback distance under various conditions into a single line, and turbulence intensity and combustion instability frequency were the dominant factors that impacted the flashback distance.

This paper presents experiments showing the response of a diffusion jet flame to acoustic forcing. The experimental results from the Burke–Schumann flame, which is a special case of the diffusion flame, are compared with the analytical results. The flame response is described by comparing the flame surface, flame length, and heat release oscillation measurements with those from reference papers that have calculated the analytical solution. The flame shape depends on both the forcing frequency and the mean input velocity. The flame shape is divided into three types depending on the forcing frequency. The local stagnation point of the flame propagation and the cutting phenomenon are shown with a low-frequency forcing of the test condition. The flame consists of an undulation form when a high forcing frequency is used as the test condition. At a specific frequency, no flame oscillation is seen, even with acoustic forcing. The forcing frequency also affects the flame length. The mean input velocity affects the magnitude of flame surface oscillations. The heat release ratio oscillation shows that both a premixed flame and a diffusion flame act like low-pass filters. The Peclet number's dependence on the flame surface and the response of the heat release both fit well with the analytical results, whereas the Strouhal number's dependence on the flame surface varies slightly from the analytical solution. The heat release rate oscillation is closely connected to the flame surface oscillations.

Abrasive-free slurries which control polysilicon removal and surface roughness are highly desirable for polysilicon buffing chemical mechanical planarization (CMP). Here, we show that the addition of poly(ethylene glycol) (PEG) to poly(diallyldimethylammonium chloride) (PDADMAC) solutions inhibits adsorption of PDADMAC on polysilicon films. The effects of PEG additive on polysilicon static etching and removal behavior during CMP were investigated as a function of PEG concentration. Polysilicon static etching and removal amounts were suppressed with an increase in PEG concentration, and surface roughness was improved by 19.2% and 55.3% compared to those obtained with 250 ppm PDADMAC and 1 wt% silica slurry, respectively, within a certain range of PEG concentrations. The adsorption mechanism of PEG on polysilicon films was investigated using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, contact angle measurements, X-ray photoelectron spectroscopy (XPS) and zeta potential measurements. Our results suggest that PEG adsorbs on the surface of polysilicon films and forms a passivation layer that interferes with the approach of PDADMAC. A possible mechanism for improvement in surface roughness was also proposed based on the inhibition effect of PEG during the CMP process.