Preparation and Electrochromic Properties of MnO2/PPy Composite Films with Coral-like Structures.

MnO2/polypyrrole (PPy) composite films were deposited on fluorine-doped tin oxide (FTO) conductive glasses by a two-step wet-chemical method, including electrochemical deposition and chemical bath deposition (CBD). The porous MnO2 films were first grown on FTO glasses by an electrodeposition method. Second, polypyrrole nanoparticles were polymerized by the oxidation-reduction reaction between MnO2 and pyrrole, using the presynthesized MnO2 as the skeleton. Then, MnO2/PPy composite films with coral-like structures were obtained. The electrochemical and electrochromic (EC) properties of the prepared films were investigated. The results show that, compared to the single MnO2 or PPy film, the MnO2/PPy composite film has a larger optical modulation (67.3% at a wavelength of 900 nm), faster response times (4 s for coloration and 3 s for bleaching), and a higher coloration efficiency (218.16 cm2·C-1). The high coloration efficiency attests to the exceptional performance of the composite film in converting electrical signals into vivid color changes. The electrochemical stability test results show that the composite film maintains a stable EC performance after 200 coloration/bleaching cycles. The coral-like structures of the composite film are responsible for the better EC properties.

Phonon Transmission Across the Si-Ge Interface.

Interfaces play an important role in nanostructured structures, which have been widely employed to improve the efficiency of thermoelectric materials. Knowledge of how each specific phonon is scattered at an interface are desired to develop novel nanostructured materials with desired thermal properties. Phonon transmission across the interface consisting of silicon (Si) and germanium (Ge) is investigated by using lattice dynamics. It is found that there exists a critical phonon frequency for the thermal transport across the Si-Ge interface. When the phonon frequency is higher than 198 cm(-1), the phonon transmission coefficient is considerably low, which mean that phonons with higher frequencies contribute little to the thermal transport across the Si-Ge interface. While the phonon frequency goes lower than 198 cm(-1), the phonon transmission coefficient becomes much higher, inferring that phonons with lower frequencies contribute dominantly to the thermal conductance at the Si-Ge interface. This is helpful for understanding the underlying mechanisms of phonon transmission across a Si-Ge interface.