Strain engineering of optical properties in transparent VO2/muscovite heterostructures.

Transparent VO2/muscovite heterostructures have attracted considerable attention because of their unique chemical and physical properties and potential practical applications. In this paper, we investigated the influence of uniaxial mechanical strain on the optical properties of VO2/muscovite heterostructures through Raman scattering and optical transmittance measurements. Under applied strain, linear shifts in peak positions of Raman-active phonon modes at approximately 340, 309, and 391 cm-1 were observed. The extracted Grüneisen parameter values were approximately between 0.44 and 0.57. Furthermore, a pronounced strain-induced change in the metal-insulator transition (MIT) temperature was observed, which decreased under compressive strain and increased under tensile strain. The rates of MIT temperature variation reached 4.5 °C per % and 7.1 °C per % at a wavelength of 1200 nm during heating and cooling processes, respectively. These results demonstrate that the modulation of the optical properties of VO2/muscovite heterostructures is controllable and reversible through strain engineering, opening up new opportunities for applications in flexible and tunable photonic devices.

Kinetic and deuterium isotope analyses of ammonia electrochemical synthesis.

The mechanism of electrochemical promotion of ammonia formation was investigated by kinetic and deuterium isotope analyses using a cell with a Pt (anode)|BaCe0.9Y0.1O3 (BCY)|Fe (cathode) configuration on the introduction of a gaseous mixture of H2(D2)-N2 to the cathode at 550 °C. To clarify the mechanism of electrochemical ammonia synthesis, the reaction orders for hydrogen, α, and nitrogen, ß, were investigated. The values of α and ß did not change after applying a negative voltage, which indicates that the reaction mechanism at rest potential is the same as that with cathodic polarization. Furthermore, deuterium isotope analysis was conducted to investigate the mechanism of electrochemical promotion. The isotopic composition of ammonia (i.e., NH3-x D x ) formed in the cathode was determined using Fourier-transform infrared spectroscopy (FTIR). The results show that the ammonia products with cathodic polarization correspond to the species of H2 (or D2) in the cathode, that is, NH3 (or ND3) was mainly formed when H2 (or D2) was introduced to the cathode. Isotopic analysis revealed that the ammonia formation rate via the electrochemical promotion of catalysis (EPOC) is faster than that via the charge-transfer reaction, suggesting that a significant increase in the ammonia formation rate will be caused by the EPOC.