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Single-crystal silicon carbide (4H-SiC) has a range of useful physical, mechanical and electronic properties that make it a promising material for fabrication of next-generation semiconductor devices. In this work, we report a hybrid polishing process combining thermal oxidation pretreatment and soft abrasive polishing to realize the damage-free and atomic-scale smooth finishing of the carbon face of 4H-SiC. By thermal oxidation pretreatment, the hardness of the carbon face has been reduced from 4.6 GPa to 1.7 GPa, which enables highly efficient polishing using CeO 2 slurry. For conventional CeO 2 slurry polishing without pretreatment, scratches still existed after a long polishing duration for 16 h. The probable scratch removal mechanism in CeO 2 slurry polishing has been proposed based on surface morphology changes during polishing. Whereas a scratch-free surface with well-ordered SiC atomic steps was obtained within a short polishing duration of only 3 h when polishing was conducted on a thermally oxidized surface. Our results demonstrate that hybrid polishing combining surface pretreatment and soft abrasive polishing is a promising approach to realize the damage-free and atomic-scale smooth finishing of the carbon face of 4H-SiC. [ABSTRACT FROM AUTHOR]

Abstract: Au–CeO2/SiO2 was prepared via adsorbed-layer reactor technique combined with alcohol-thermal treatment. The catalytic performance in complete oxidation of benzene was investigated. TEM, Raman characterization showed that Au particles grew up obviously during alcohol-thermal process, while CeO2 particles maintained 4nm in diameter. The content of oxygen vacancies and adsorbed oxygen species on catalysts surface increased apparently. Alcohol-thermally treated Au–CeO2/SiO2 and CeO2/SiO2 showed similar change in catalytic performance, and were much superior to calcined CeO2/SiO2. Of alcohol-thermally treated and calcined CeO2/SiO2, initial temperatures of the reaction were 80°C and 150°C, respectively. The benzene conversions reached 85% and 40% at 300°C. [Copyright &y& Elsevier]

• Electrochemical etching-enhanced CMP is proposed for efficient polishing of GaN. • Identical-site observation was conducted to study the etching behaviors of GaN. • A maximum etching rate of 1.462 μm/min has been achieved. • Sa roughness of a dia-lapped GaN surface has been reduced from 69.8 nm to 0.64 nm. An electrochemical etching-enhanced CMP process was proposed to realize the highly efficient and damage-free finishing of GaN. In this process, electrochemical etching was first used to remove the damaged layer induced by grinding or lapping, and CMP was then conducted to flatten the etched surface. The etching rate could reach 1.46 μm/min using NaOH solution as the electrolyte which was highly efficient. It was found that the etching rate and surface roughness can be balanced by adjusting the applied potential. CMP was carried out on an etched GaN sample and the surface roughness was reduced from 69.8 nm to 0.64 nm, and its surface quality was also confirmed to be desirable through photoluminescence. These results demonstrate that the proposed electrochemical etching-enhanced CMP process is highly effective and efficient to obtain a crack-free, damage-free and smooth GaN surface. [ABSTRACT FROM AUTHOR]

Highlights • A comprehensive study of ECP of tungsten under different applied potentials is carried out. • A mirror surface of tungsten with a Sa roughness of 3.73 nm has been obtained by ECP for 10 mins. • ECP of tungsten is divided into 3 stages including etching stage, brightening stage and pitting stage. Abstract Tungsten is a promising material for the mold of glass components owing to its excellent mechanical and chemical properties. Electrochemical polishing (ECP) has been proposed for the damage-free and highly efficient surface finishing of tungsten. In the paper, a comprehensive study of the anodic behaviors of tungsten during ECP under different applied potentials has been carried out. A mirror surface with a Sa roughness of 3.73 nm has been obtained by ECP for 10 mins demonstrating its effectiveness. The changes of surface morphology, roughness and electric current under different potentials have been experimentally investigated and analyzed. On the basis of the changes of surface morphology and current density, ECP of tungsten was divided into 3 stages including the etching stage in which rough etching marks were formed by crystallographic etching, the brightening stage in which ultra-smooth surfaces with clear boundaries were obtained and the pitting stage in which crystallographic pitting occurred. The probable material removal mechanisms of these 3 ECP stages were proposed and experimentally validated. The presented findings are of great value for understanding and process development of ECP of tungsten. [ABSTRACT FROM AUTHOR]

The present work has been focused on the effects of surface-active element sulfur on welding properties during 10 kW high power laser welding of 304 stainless steel thick plate. Molten pool behavior, morphology feature of sulfide inclusions, metallographic structures, XRD patterns, microhardness, potentiodynamic polarization curves and pitted surface have been investigated and discussed. The results indicated that the added sulfur powder improved the weld depth by increasing molten metal fluidity, elongating molten pool and promoting heat transmission. The observed sulfide inclusions had small particle size of 0.65 μm in average and were distributed sparsely in weld joint. The WWS (weld joint with sulfur powder) had higher δ-ferrite content and finer grain size than the WWOS (weld joint without sulfur powder) and BM (base metal) due to the effects of sulfide inclusions on crystallizing process. The preferred orientations of γ-austenite along the (200) and (220) directions were promoted both in WWS and WWOS. Fine grain size and high δ-ferrite content led to high microhardness. The WWS had the highest microhardness among all the specimens. The WWOS and BM had a similar corrosion resistance. By comprehensive comparison, the WWS had a relative lower corrosion resistance than others, since sulfide inclusions in WWS not only had some benefits but also had some bad effects on corrosion property. [ABSTRACT FROM AUTHOR]

[Display omitted] • PAMM is a nonsubtractive surface smoothing process with atomic level roughness achieved. • Energy density transmitted by ICP has a decisive influence on smoothing effect of PAMM. • S a of a ground silica surface can be reduced to 0.17 nm by 8 min of PAMM. Optical manufacturing plays an important role in various fields, such as optical lenses, telescopes, and laser optics. Generally, traditional optical manufacturing techniques are all subtractive processes based on the micro-shearing effect between the tool and surface protrusions. This paper reports a plasma-induced atom migration manufacturing (PAMM) process, which is a nonsubtractive finishing approach by which angstrom level surface roughness of fused silica has been successfully achieved. Inductively coupled plasma (ICP), which is characterized by high temperature and high radical density, is used as the tool of PAMM. After obtaining instantaneous plasma energy input on the fused silica surface, the peak site atoms migrate to the valley sites, thereby reducing the roughness. According to the energy minimization principle, this migration process continues until an ultra-smooth surface with reduced surface energy is formed. Atomic-scale molecular dynamics simulations were performed to clarify the microscopic mechanisms of PAMM, and experiments were conducted to verify its smoothing capability. The roughness of a ground silica surface was drastically reduced from S a 391 nm to S a 0.16 nm. This study demonstrates the feasibility of the PAMM as an alternative approach for atomic-level surface manufacturing. [ABSTRACT FROM AUTHOR]

[Display omitted] • A simple SERS strategy assisted by Ag 2 O for rapid detection of trace amount of uranium oxides was proposed and described. • SERS signals of uranium oxides can be remarkably improved through conversion to uranyl ions. • The efficient photoinduced CT process from Ag 2 O to uranyl ions creates the strong enhancement. The rapid and efficient identification of uranium oxides is of great significance in the field of nuclear security. A feasible SERS strategy assisted by Ag 2 O for rapid detection of trace amount of uranium oxides (∼1.8 μg/mL for UO 2 and ∼ 3.6 μg/mL for U 3 O 8) was proposed and described. The effects of laser power on the Raman and SERS of uranium oxides were investigated. And the SERS mechanism was discussed by constructing several types of SERS substrates. Uranyl ions produced from hydrolysis and oxidation of uranium oxides are the key components for their SERS, where efficient photoinduced charge transfer process from Ag 2 O to uranyl ions occurs, resulting in a more intense Raman mode. The easily obtained but clearly distinguished SERS signals allow us to selectively and quickly detect the uranium oxides from mixtures, which may be practically applied to nuclear antiterrorism. [ABSTRACT FROM AUTHOR]

[Display omitted] • Atomic scale smoothing of GaN is realized by plasma-based atom-selective etching. • Temperature is a key factor in determining the PASE etching mode of GaN. • Sa roughness can be reduced from 135.8 nm to 0.527 nm by 2 min of PASE. • PASE demonstrates an extremely high MRR of 93.01 μm/min. Plasma-based atom-selective etching (PASE) of GaN is conducted to realize the highly efficient planarization of the GaN surface. Inductively coupled plasma with high temperature and high concentration of radicals is used as the source of PASE. The non-toxic carbon tetrafluoride is chosen over chlorine as the reaction gas, and the volatility of the etching products will be improved at high temperatures in the PASE of GaN. After 2 min of PASE, the GaN surface roughness is reduced from Sa 135.8 nm to Sa 0.527 nm. The material removal rate of PASE of GaN is measured to be 93.01 μm/min, thousands of times higher than that of the conventional chemical mechanical polishing method. The crystal structure of the GaN subsurface is well-ordered without any damage or defects. PASE is thus proven to be a non-destructive etching method. In this study, the effects of radio frequency power and reaction gas flow rate on PASE are also investigated. Surface temperature and concentration of radicals are found to be the critical factors in the PASE of GaN. [ABSTRACT FROM AUTHOR]

Repetitious sizing treatment was used to modify the carbon fiber (CF) surface with carbon nanotubes (CNTs) for improving interfacial properties of CF/epoxy composites. Interlaminar shear and flexural results showed that mechanical properties of composites were significantly depended on the dispersion state and contents of CNTs in interfacial regions. Increases of 13.45% in interlaminar shear strength and 20.31% in flexural strength were achieved in quintuple sized-CF/epoxy composites, whereas excessive CNTs led to decrease of interfacial performance due to defects induced by agglomerated CNTs. Energy dispersive X-ray spectroscopy and force modulation atomic force microscope were used to detect the structure of interfacial phase and results indicated that gradient interfacial structure with various thicknesses was formed due to CNT incorporation. This means that such a simple and efficient method to improve interfacial performance of composites via regulating the fiber–matrix interphase structure was developed and showed great commercial application potential. [ABSTRACT FROM AUTHOR]

The different rules for γ-ray modifications of carbon fiber (CF) surface were found in previous literature, and the contributing factors were not clear. To investigate the effects of fiber instinct structure and radiation medium on surface modification of CFs in γ-ray irradiation, argon atmosphere (Ar) and epoxy chloropropane (ECP) were chosen as the irradiation media for T300, T400, T700, T800 and T1000, respectively. Based on the Raman spectroscopy and specific surface area results, changes of surface graphitization and roughness depended on the fiber instinct structure after irradiation. The graphitization of T300, T400 and T800 with low graphitization and rough surface was increased after irradiation, while that of T700 and T1000 with high graphite degree and smooth surface was decreased. Specific surface areas of low-graphitization CFs (T300, T400 and T800) were changed clearly, while those of high-graphitization CFs (T700 and T1000) remained almost unchanged after irradiation. X-ray photoelectron spectroscopy provided the evidence that the surface chemistry change after irradiation was determined by the type of the irradiation medium. The oxygen ratio of CFs irradiated in Ar was decreased while that of CFs irradiated in ECP was increased with Cl element detected. Surface free energy of all CFs was improved obviously after irradiation, and CFs irradiated in ECP had higher surface free energy compared with CFs irradiated in Ar. [ABSTRACT FROM AUTHOR]

• Molten KOH etching have been first applied to polishing sliced SiC. • Sa roughness is reduced from 246.5 nm to 16.06 nm within 2 min of molten KOH etching. • A damage-free surface can be obtained. • Etching behaviors and mechanisms for dislocation spot is particularly studied. Single-crystal silicon carbide (4H-SiC) is a promising third-generation semiconductor material because of its excellent electrical, mechanical and chemical properties. However, the high hardness of 4H-SiC makes it a typical difficult-to-machine material, which greatly restricts the development of SiC devices. In this work, molten KOH etching was first used to polish SiC. The perfect crystal surface and dislocation spots were studied separately. For the perfect crystal surface, a typical isotropic etching polishing behavior was observed. The speed of the polishing process was closely correlated with the temperature. An ultrafast polishing of sliced SiC was achieved, reducing the roughness from 246.5 nm to 16.06 nm within 2 min at 800 °C, and all subsurface damage was removed, as demonstrated by TEM. For the dislocation spot, a relationship between the etch pits angle and temperature was found, making it possible to remove the influence of the dislocation spot by increasing the etch pits angle to approach 180°. This study shows that molten KOH etching could be a very promising SiC polishing method and deserves further research. We anticipate that this approach will be applicable to ultrafast polishing of SiC at the industrial scale. [ABSTRACT FROM AUTHOR]