Electrochromic tungsten oxide films: Review of progress 1993–1998

Transition-metal oxide nanocrystals are interesting candidates for localized surface plasmon resonance hosts because they exhibit fascinating properties arising from the unique character of their outer-d valence electrons. WO3−δ nanoparticles are known to have intense visible and near-IR absorption, but the origin of the optical absorption has remained unclear. Here we demonstrate that metallic phases of WO3−δ nanoparticles exhibit a strong and tunable localized surface plasmon resonance, which opens up the possibility of rationally designing plasmonic tungsten oxide nanoparticles for light harvesting, bioimaging, and sensing.

Tunable localized surface plasmon resonances in tungsten oxide nanocrystals.

Transport properties and reactivity of tungsten trioxide

Role of air exposure in the improvement of injection efficiency of transition metal oxide/organic contact

Localized surface plasmon resonances (LSPR) of nanostructures can be tuned by controlling their morphology, local dielectric environment, and free carrier concentration. We report the colloidal synthesis of an ∼3 tungsten-oxygen (W-O) layer thick (∼1 nm), two-dimensional (2D) WO3-x nanoplatelets (NPLs) (x ≈ 0.55-1.03), which display tunable near-infrared LSPR properties and additionally high free electron density (Ne) that arises predominantly from the large shape factor of 2D NPLs. Importantly, the W to O composition ratios inferred from their LSPR measurements show much higher percentage of oxygen vacancies than those determined by X-ray diffraction analysis, suggesting that the aspect ratio of ultrathin WO3-x NPLs is the key to producing an unprecedentedly large Ne, although synthesis temperature is also an independent factor. We find that NPL formation is kinetically controlled, whereas thermodynamic parameter manipulation leads to Ne values as high as 4.13 × 1022 cm-3, which is close to that of plasmonic noble metals, and thus our oxide-based nanostructures can be considered as quasi-metallic. The unique structural properties of 2D nanomaterials along with the high Ne of WO3-x NPLs provide an attractive alternative to plasmonic noble metal nanostructures for various plasmon-driven energy conversions and design of photochromic nanodevices.

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Ultrathin Plasmonic Tungsten Oxide Quantum Wells with Controllable Free Carrier Densities.

Measurements of electrical conductivity, thermoelectric power, and crystallographic structure of tungsten trioxide are presented. It is found that the predominant charge carriers are electrons related to nonstoichiometry in the oxygen sublattice (WO 3-y ). At y = 0.1 the investigated material undergoes a semiconductor metal transition of Mott type.

J. Molenda

Papers

Electrical Properties of Nonstoichiometric WO3−y at Temperatures 77 to 300 K