Spectroscopic ellipsometry was used to characterize the complex refractive index of chemical-vapordeposited monolayer transition metal dichalcogenides (TMDs). The extraordinary large value of the refractive index in the visible frequency range is obtained. The absorption response shows a strong correlation between the magnitude of the exciton binding energy and band gap energy. Together with the observed giant spin-orbit splitting, these findings advance the fundamental understanding of their novel electronic structures and the development of monolayer TMDs-based optoelectronic and spintronic devices. V

We have revealed that cubelike and hexarhombic docadehedron-like Cu single crystals showed an enhancement of C2 products (ethylene and ethanol) while octahedron-like Cu nanoscale single crystals promoted C1 products of CO2 reduction. This product selectivity was revealed to be highly associated with the atomic arrangement on the surface. The remarkable high selectivity of ethanol (faraday efficiency of 25% with 14 mA/cm2, J ethanol ≈ 3.5 mA/cm2) for H–Cu was investigated and unraveled by using in situ X-ray absorption spectroscopy and density functional theory calculation. It was shown that the binding energy of adsorbed *O atom on the surface is substantial, which causes bifurcation of the reaction pathway and leads to the formation of ethanol.

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THz absorption and spectroscopic ellipsometry were used to investigate the charge dynamics and electronic structures of chemical-vapor-deposited monolayer MoS2 films. THz conductivity displays a coherent response of itinerant charge carriers at zero frequency. Drude plasma frequency (∼7 THz) decreases with decreasing temperature while carrier relaxation time (∼26 fs) is almost temperature independent. The absorption spectrum of monolayer MoS2 shows a direct 1.95 eV band gap and charge transfer excitations that are ∼0.2 eV higher than those of the bulk counterpart. The ground-state exciton binding energy is found to be about 0.48 eV.

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