•We achieved a high MRR of 120 nm/h for CMP of GaN by using S2O82−-Fe2+ additives.•We obtain atomic-level smooth surface by S2O82−-Fe2+ additives and advanced AFM technique.•We demonstrate the special change rule of terraces topography from the surface of GaN.In this paper, a significant improvement of chemical-mechanical polishing on gallium nitride with S2O82−-Fe2+ based slurry is presented in detail. The results indicate that the S2O82−-Fe2+ additives possessed obvious effect to enhance the polishing efficiency of GaN, and successfully achieved good surface quality after polishing. The addition of complexing agent obviously improves the stability of catalytic system. Besides, we also studied the special change rule of atomic step-terrace topography from the surface of GaN to describe the material removal mechanism during CMP process. The results show that the removal of materials by CMP follows rigid rules, which may help to improve the material removal mechanism of CMP.

•Removal rate of sapphire by 10 nm silica could approach to that by 100 nm silica.•The removal mechanisms using different sizes silica have been investigated via XPS.•Effects of silica size on the formation and removal of soft layer are studied by AFM.•Reaction model of sapphire with silica of different sizes during polishing is proposed.•Roughness shows a positive correlation with the size of the solid reaction product.Sapphire chemical mechanical polishing (CMP) performances using silica particles with different sizes have been studied. We find that MRR by 10 nm silica slurry could appear rather high, approaching to that by 100 nm silica slurry. The removal mechanisms of sapphire using different sizes silica have been investigated via X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) measurements. XPS results reveals that the surface polished by 10 nm silica could also present aluminum silicate resulting from solid-solid state reaction with silica and sapphire, the same with that by 100 nm silica. The effects of silica nanoparticle size on the formation and removal of soft product layer on the atomic step smooth surface are studied through AFM analysis. 10 nm silica particles could exhibits the smaller residual product on the surface, and the reaction model of sapphire with silica particles of different sizes is proposed. Meanwhile, 10 nm silica particles could realize smoother surface of 0.06 nm and straighter atomic step edge.Fig. AFM images (1 × 1 μm2 area) of the atomic step-terrace morphology on the sapphire surfaces polished by the slurry with the different size silica particles, from the bare atomic step ultra-smooth surface. a. 10 nm silica, b. 100 nm silica.Using silica nanoparticles in chemical mechanical polishing of sapphire, when the reaction product generates, compared with the polished surface by 100 nm silica particles, that by 10 nm silica particles exhibits the smaller and less residual product via atomic force microscopy measurements. Thus, the reaction model of sapphire with silica particles of different sizes during polishing is proposed. It is inferred that the surface roughness could show a positive correlation with the size of the solid state reaction product by silica particles yet.

The behavior of Fe-based dual-doped non-noble metal electrocatalyst (Fe-N/C-TsOH) pyrolyzed at different condition and the repercussion for the oxygen reduction reaction (ORR) has been studied. Cyclic voltammetry (CV) and rotating disk electrode (RDE) with Tafel theory as well as Koutecky-Levich were used to quantitatively obtain the oxygen reduction reaction (ORR) kinetic constants and the reaction mechanisms. The pyrolyzed catalysts showed significantly improved ORR activity as well as different ORR mechanism, indicating that heat-treatment is a necessary step for improving catalyst activity. In addition, the optimal heat-treatment temperature was found to be 600 °C, and the overall ORR electron transfer numbers were found to be about 3.899, suggesting that the ORR catalyzed by Fe-N/C-TsOH-600 is a 4-electron transfer process from O2 to H2O. Furthermore, the catalysts also have been subjected to chemical treatments in 0.5 mol·L−1 H2SO4 to remove impurities and reheating was emplyed to optimize the electrocatalytic activity of the catalyst towards the ORR in alkaline medium. And the activity of the catalyst for the ORR increases obviously after H2SO4 leaching and reheating. This effect account to the removal of impurities and purify the active sites as well as the factor that increase the amount of smaller pores which can provide a large surface area and expose more ORR-relevant active sites. In order to understand the heat-treatmen effect on catalyst, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) are employed to detect surface structure changes. The results revealed a fact that the temperature of thermal treatment has a direct influence on crystal structure and compositions of the catalysts.

•Effects of atomic step width on the removal of sapphire and SiC wafers are studied.•The reason of effects of step width on the removal and the model are discussed.•CMP removal model of hexagonal wafer to obtain atomically smooth surface is proposed.•The variations of atomic step morphology towards defects are analyzed.•The formation mechanism of the defects is discussed.Towards sapphire and SiC wafer, clear and regular atomic step morphology could be observed all-over the surface via AFM. However, the variations of atomic step widths and step directions are different on the whole of different wafer surfaces: that on sapphire wafer are uniform, while that on SiC wafer are distinct. The effects of atomic step width on removal rate are studied. Removal model of super-hard wafer to realize atomically ultra-smooth surface is proposed. The variations of atomic step morphology toward different defects on sapphire and SiC wafers surface are analyzed, and the formation mechanism is discussed.

•The complete transfer is achieved by optimizing the catalyst inks’ composition and a hot peeling technique.•The thickness of catalyst layers (before transfer) is consistent.•The effects of drying methods, transfer pressure, test temperatures are explored and discussed.•The MEAs show better performance.Decal transfer is an effective method for fabricating membrane electrode assemblies (MEAs), due to its low interfacial resistance and applicability for mass production. Here we introduce a modified decal method which makes it possible and convenient to achieve complete decal transferring. The composition of catalyst inks, drying process and transfer pressure are optimized in detail. During catalyst ink preparation, the viscosity is adjusted by altering the composition of the solvents to obtain catalyst layers (before transfer) with continuous thickness. In addition, MEAs whose catalyst layers (before transfer) were dried in four different ways are tested for application in a proton exchange membrane fuel cell. The transfer pressure is also optimized on the basis of the two previous conditions and the MEAs fabricated by this modified method show simplicity to achieve complete transfer in decal method, good repeatability and improvement in cell performance.

This work demonstrates the feasibility of nitrogen/sulfur co-doped non-noble metal materials (Fe–N/C–TsOH) as platinum-free catalysts for the oxygen reduction reaction (ORR) in alkaline media. Electrochemical techniques such as cyclic voltammetry (CV), rotating disk electrodes (RDEs) and rotating ring-disk electrodes (RRDEs) are employed with the Koutecky–Levich theory to investigate the ORR kinetic constants and the reaction mechanism. It is found that the catalysts doped with TsOH (p-toluenesulfonic acid) show significantly improved ORR activity relative to a TsOH-free catalyst. The overall electron transfer numbers for the catalyzed ORR are determined to be 3.899 and 3.098, respectively, for the catalysts with and without TsOH-doping. Catalysts heat treated at 600 °C exhibit relatively higher activity. In addition, the catalyst doped with TsOH (Fe–N/C–TsOH-600) not only exhibits exceptional stability in 0.1 mol L−1 KOH solution but also has higher methanol tolerance compared to commercial Pt/C catalyst in 0.1 mol L−1 KOH. To some extent, increasing the Fe–N/C–TsOH-600 loading on the electrode favors a faster reduction of H2O2 to intermediate to H2O. X-ray photoelectron spectroscopy analysis indicates that pyrrolic N groups are the most active sites, and that sulfur species are structurally bound to carbon in the forms of C–S(n)–C and oxidized –SO(n)– bonds, an additional beneficial factor for the ORR.

•Using catalyst nanoparticles was developed for CMP of Si-face SiC to get a higher MRR.•An ultra-smooth defect-free surface with atomic step structure and low Ra was achieved.•Removal characteristics of catalyst assisted CMP and removal mechanism were studied.•The formation of an atomic step-terrace morphology on the SiC surface was discussed.The application of catalyst nanoparticles in the slurry is developed for chemical mechanical planarization (CMP) of on-axis Si-face (0001) SiC wafer, so as to obtain higher material removal rate (MRR) and defect-free ultra-smooth surface. Fe nanoparticles, as well as Pt/C nanoparticles were used as a catalyst into the slurry, and the polishing experiment results indicate that an Fe catalyst is preferable to CMP of SiC. The removal behaviors of catalyst assisted CMP were studied and the removal mechanism was discussed. The detection results of *OH hydroxyl radicals reveal that the slurries with catalysts could produce *OH radicals so as to induce the oxidation of SiC. The relationship between the removal of SiC wafer by different catalysts and polishing time was investigated. The removal characteristics with different downward pressure and platen rotation speed and relative local temperature were presented. Optical microscope, optical interferometry profiler and atomic force microscope (AFM) were applied to observe the processed surface by the proposed method. Total planarization of the atomically flat defect-free surface with atomic step-terrace structure and extremely low Ra about 0.05 nm was achieved for SiC wafer by using an Fe catalyst slurry. The results affirm that the promising method is helpful to the surface preparation of super-hard and inert materials with high efficiency and high flatness.

In this paper, an empirical expression was deduced based on the experimental data for material removal rate of copper chemical mechanical polishing. The parameters of this expression includes the initial chemical corrosion rate(MRR0), the corrosion inhibition efficiency(k) and the mechanical abrading rate(MRRM). The deduced empirical expression revealed that under certain slurry systems, the corrosion inhibition efficiency may always keep unchanged, which may be useful to characterize the inhibition properties of different inhibitors.

Surface modified SiO2 particles in an aqueous environment with γ-aminopropyl triethoxysilane (APTS)/methyl trimethoxysilane (MTMOS) are introduced as abrasive in the slurry. The modified silica particles are characterized by Particle Size/Zeta Potential Analysis, Fourier Transform Infrared Spectroscopy (FTIR), Thermal Gravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). In addition, the enhancement of polishing rate owning to the modified silicon particles in silicon wafer Chemical Mechanical Polishing (CMP) is observed.Highlights► Silane coupling agents with different functional groups and hydrophilicity (γ-aminopropyl triethoxysilane (APTS) and methyl trimethoxysilane (MTMOS)) are chosen to modify silica particles to be used in final polishing of silicon wafers. ► Higher Material Removal Rate (MRR) and more excellent surface with lower Roughness (Ra) and Peak-to-Valley value (PV) are obtained, because silane modified abrasive particles have better suspension stability and more compatible chemical reactivity. ► Different polishing mechanisms of two modified silica abrasive are demonstrated.

•An atomic step-terrace structure was achieved on GaN surface after CMP.•Double step-terrace structure (a-a or a-b type) on GaN surface was confirmed, and the two types can be controlled by adjusting the abrasive concentration.•The material removal mechanism of GaN according to the variation of atomic step-terrace morphology was presented.An atomic step-terrace topography could be achieved on the surface of gallium nitride (GaN) wafer when it was polished by our colloidal silica (SiO2) based slurry. The corresponding roughness was as low as 0.07 nm (scan area 1 × 1 µm2). The atomic step-terrace topography was proved to be determined by the crystal structure of GaN. Due to the variation of atomic step-terrace topography, the effects of chemical components and mechanical factors on the material removal mechanism were investigated. The results showed that the topography would not be destroyed when adopting slurry with reagent only, and the chemical components could only act on the reactant of GaN. However, in case of SiO2 abrasives were added into the slurry, the step edge on the GaN surface would be disrupted after polishing. Moreover, the step-terrace structure could be changed by adjusting the abrasive concentration in the slurry. A double step-terrace structure with two types (a-a or a-b type) was observed, and the total widths of both the two type double step-terrace structure were the same.