Two-Dimensional Superconductivity of Ca-Intercalated Graphene on SiC: Vital Role of the Interface between Monolayer Graphene and the Substrate.

Ca-intercalation has enabled superconductivity in graphene on SiC. However, the atomic and electronic structures that are critical for superconductivity are still under discussion. We find an essential role of the interface between monolayer graphene and the SiC substrate for superconductivity. In the Ca-intercalation process, at the interface a carbon layer terminating SiC changes to graphene by Ca-termination of SiC (monolayer graphene becomes a bilayer), inducing more electrons than a free-standing model. Then, Ca is intercalated in between the graphene layers, which shows superconductivity with the updated critical temperature (TC) of up to 5.7 K. In addition, the relation between TC and the normal-state conductivity is unusual, "dome-shaped". These findings are beyond the simple C6CaC6 model in which s-wave BCS superconductivity is theoretically predicted. This work proposes a general picture of the intercalation-induced superconductivity in graphene on SiC and indicates the potential for superconductivity induced by other intercalants.

Oxidative deterioration of platinum nanoparticle and its prevention by palladium.

Pt nanoparticle is a strong reductant and has been used as an antioxidant in cosmetics and medicine. It was reported to have catalase-like activity, which converts hydrogen peroxide to water and oxygen. However, in this study, freshly prepared Pt nanoparticle was almost inert towards decomposing hydrogen peroxide. The catalase-like activity of Pt nanoparticle increased with increasing weeks of storage at room temperature and became more significant when the Pt nanoparticle was exposed to air. No hydroxyl radical formation was confirmed by several methods such as ESR spin-trapping, dimethyl sulphoxide oxidation, salicylic acid hydroxylation and hydroxytoluene oxidation, indicating that the decomposition of hydrogen peroxide proceeds by the two-electron oxidation/reduction reaction. The oxidatively deteriorated Pt nanoparticle catalytically decomposed ascorbic acid, which is one of the most important biological antioxidants. We found that such oxidation was effectively prevented by the addition of Pd nanoparticle. We also discussed the reaction mechanisms and application of Pt nanoparticle.