Ce-Doped bundled ultrafine diameter tungsten oxide nanowires with enhanced electrochromic performance.

Cerium (Ce)-doped tungsten oxide nanostructures were synthesised using a simple solvothermal method from cerium chloride salt (CeCl3·7H2O) and tungsten hexachloride (WCl6) precursors. The as-prepared samples were thoroughly characterised using electron microscopies, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The electrochromic performance of different samples was evaluated using a custom-built UV-VIS spectrometer and an electrochemistry technique. The results showed that the as-prepared samples underwent morphological evolution with the increase in the Ce/W molar ratio, from long, thin and bundled nanowires, through shorter and thicker nanowires to mixed nanowire bundles and nanoparticle agglomerates. From electrochemical testing, we found that the Ce-doped tungsten oxides exhibited higher optical contrasts of 44.3%, 49.7% and 39.4% for the 1 : 15, 1 : 10 and 1 : 5 Ce/W ratios respectively, compared with 37.4% for the pure W18O49 nanowires. The Ce/W = 1 : 15 samples presented an improved colouration efficiency of 67.3 cm2 C-1 against 62 cm2 C-1 for pure W18O49. This work demonstrated that the Ce-doped W18O49 nanowires are very promising candidate materials for the design and construction of electrochemical chromic devices with largely improved efficiency, contrast and stability. The results from this work suggested that smart electrochromic devices based on current Ce-doped WOx nanomaterials could be further developed for future energy-related applications.

Intrinsic Plasmon-Phonon Interactions in Highly Doped Graphene: A Near-Field Imaging Study.

As a two-dimensional semimetal, graphene offers clear advantages for plasmonic applications over conventional metals, such as stronger optical field confinement, in situ tunability, and relatively low intrinsic losses. However, the operational frequencies at which plasmons can be excited in graphene are limited by the Fermi energy EF, which in practice can be controlled electrostatically only up to a few tenths of an electronvolt. Higher Fermi energies open the door to novel plasmonic devices with unprecedented capabilities, particularly at mid-infrared and shorter-wave infrared frequencies. In addition, this grants us a better understanding of the interaction physics of intrinsic graphene phonons with graphene plasmons. Here, we present FeCl3-intercalated graphene as a new plasmonic material with high stability under environmental conditions and carrier concentrations corresponding to EF > 1 eV. Near-field imaging of this highly doped form of graphene allows us to characterize plasmons, including their corresponding lifetimes, over a broad frequency range. For bilayer graphene, in contrast to the monolayer system, a phonon-induced dipole moment results in increased plasmon damping around the intrinsic phonon frequency. Strong coupling between intrinsic graphene phonons and plasmons is found, supported by ab initio calculations of the coupling strength, which are in good agreement with the experimental data.