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With the rapid development of semiconductors, the number of materials needed to be polished sharply increases. The material properties vary significantly, posing challenges to chemical mechanical polishing (CMP). Accordingly, the study aimed to classify the material removal mechanism. Based on the CMP and atomic force microscopy results, the six representative metals can be preliminarily classified into two groups, presumably due to different material removal modes. From the tribology perspective, the first group of Cu, Co, and Ni may mainly rely on the mechanical plowing effect. After adding H2O2, corrosion can be first enhanced and then suppressed, affecting the surface mechanical strength. Consequently, the material removal rate (MRR) and the surface roughness increase and decrease. By comparison, the second group of Ta, Ru, and Ti may primarily depend on the chemical bonding effect. Adding H2O2 can promote oxidation, increasing interfacial chemical bonds. Therefore, the MRR increases, and the surface roughness decreases and levels off. In addition, CMP can be regulated by tuning the synergistic effect of oxidation, complexation, and dissolution for mechanical plowing, while tuning the synergistic effect of oxidation and ionic strength for chemical bonding. The findings provide mechanistic insight into the material removal mechanism in CMP. [ABSTRACT FROM AUTHOR]

Though YB6 and LaB6 share the same crystal structure, atomic valence electron configuration, and phonon modes, they exhibit drastically different phonon-mediated superconductivity. YB6 superconducts below 8.4 K, giving it the second-highest critical temperature of known borides, second only to MgB2. LaB6 does not superconduct until near-absolute zero temperatures (below 0.45 K), however. Though previous studies have quantified the canonical superconductivity descriptors of YB6's greater Fermi-level (Ef ) density of states and higher electron-phonon coupling (EPC), the root of this difference has not been assessed with full detail of the electronic structure. Through chemical bonding, we determine low-lying, unoccupied 4f atomic orbitals in lanthanum to be the key difference between these superconductors. These orbitals, which are not accessible in YB6, hybridize with π B-B bonds and bring this π-system lower in energy than the σ B-B bonds otherwise at Ef. This inversion of bands is crucial: the optical phonon modes we show responsible for superconductivity cause the σ-orbitals of YB6 to change drastically in overlap, but couple weakly to the π-orbitals of LaB6. These phonons in YB6 even access a crossing of electronic states, indicating strong EPC. No such crossing in LaB6 is observed. Finally, a supercell (the M k-point) is shown to undergo Peierls-like effects in YB6, introducing additional EPC from both softened acoustic phonons and the same electron-coupled optical modes as in the unit cell. Overall, we find that LaB6 and YB6 have fundamentally different mechanisms of superconductivity, despite their otherwise near-identity. [ABSTRACT FROM AUTHOR]

In this research, the needle punched and chemical bonded nonwovens were developed by blending banana fiber and recycled polyester (r-PET) in three blend ratios (90% banana/10% r-PET, 70% banana/30% r-PET, 50% banana/50% r-PET). The developed nonwovens were characterized by thermal insulation and biodegradation properties. Results showed that all developed nonwovens have an excellent insulation performance; the thermal resistance value is in the range of 0.299 to 0.248 m2K/W. It was observed that nonwovens made from 90% banana/10% r-PET have better thermal insulation compared to other blend ratios in both techniques. It was also observed that the chemical bonded nonwovens had a 6.69% higher thermal resistance value compared to the needle punched nonwovens. A bi-layer hybrid structure made with chemical bonded nonwoven and needle punched nonwoven provided a thermal resistance value of 0.43 m2K/W. The chemical bonded nonwovens showed lower biodegradation compared to needle punched nonwovens. [ABSTRACT FROM AUTHOR]

We performed quantum chemical calculations on the geometries, electronic structures, bonding properties, and stability strategy of endohedral metallofullerenes TM@C28 (TM = Sc−, Y−, La−, Ti, Zr, Hf, V+, Nb+, Ta+). Our calculations revealed that there are three different lowest-energy structures with C2v, C3v, and Td symmetries for TM@C28. The HOMO–LUMO gap of all these structures ranges from 1.35 eV to 2.31 eV, in which [V@C28]+ has the lowest HOMO–LUMO gap of 1.35 eV. The molecular orbitals are mainly composed of fullerene cage orbitals and slightly encapsulated metal orbitals. The bonding analysis on the metal–cage interactions reveals they are dominated by the Coulomb term ΔEelstat and the orbital interaction term ΔEorb, in which the orbital interaction term ΔEorb contributes more than the Coulomb term ΔEelstat. The addition of one or two CF3 groups to [V@C28]+ could increase the HOMO–LUMO gap and further increase the stability of [V@C28]+. [ABSTRACT FROM AUTHOR]