A simple one-step method is reported to synthesize low-temperature solution-processed transition metal oxides (TMOs) of molybdenum oxide and vanadium oxide with oxygen vacancies for a good hole-transport layer (HTL). The oxygen vacancy plays an essential role for TMOs when they are employed as HTLs: TMO films with excess oxygen are highly undesirable for their application in organic electronics.

Low-temperature solution-processed hydrogen molybdenum and vanadium bronzes for an efficient hole-transport layer in organic electronics.

Tungsten oxide (WO3) thin films have been produced by KrF excimer laser (λ = 248 nm) ablation of bulk ceramic WO3 targets. The crystal structure, surface morphology, chemical composition, and structural stability of the WO3 thin films have been studied in detail. Characterization of freshly grown WO3 thin films has been performed using X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), Raman spectroscopy (RS), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) measurements. The results indicate that the freshly grown WO3 thin films are nearly stoichiometric and well crystallized as monoclinic WO3. The surface morphology of the resulting WO3 thin film has grains of ∼60 nm in size with a root-mean-square (rms) surface roughness of 10 nm. The phase transformations in the WO3 thin films were investigated by annealing in the TEM column at 30−500 °C. The phase transitions in the WO3 thin films occur in sequence as the temperatur...

Structural Stability and Phase Transitions in WO3 Thin Films

The TiO2−N−x%WO3 composite photocatalysts were prepared by introducing WO3 into nitrogen-doped TiO2. The composite catalysts present much higher photocatalytic activity than TiO2 and nitrogen-doped TiO2 under both ultraviolet and visible light irradiation. Diffuse reflectance UV−vis spectra, XPS analysis, and IR spectra show that the coordinated nitrogen species (or N−metal−O linkages) may contribute to the visible light photocatalytic activity. WO3 coupling increases the active nitrogen species and thus enhances the visible light activity of the composite photocatalysts. The superior activity of TiO2−N−x%WO3 composite photocatalysts upon UV light irradiation can be rationalized in terms of efficient charge separation and high adsorption affinity of WO3.

Great enhancement of photocatalytic activity of nitrogen-doped titania by coupling with tungsten oxide.

A plasmonic hybrid having Pd nanoparticles on plasmonic MoO(3-x) is developed by a facile solution process, and its plasmonic resonance displays reversible tunability upon oxidation/reduction. Under visible-light irradiation, the Pd/MoO(3-x) hybrid exhibits plasmon-enhanced catalysis toward H2 evolution from ammonia borane hydrolysis and the Suzuki-Miyaura coupling reaction relative to dark conditions.

A Plasmonic Molybdenum Oxide Hybrid with Reversible Tunability for Visible-Light-Enhanced Catalytic Reactions.

The electronic properties of MoO3 and reduced molybdenum oxide phases are studied by density functional theory (DFT) alongside characterization of mixed phase MoOx films. Molybdenum oxide is utilized in compositions ranging from MoO3 to MoO2 with several intermediary phases. With increasing degree of reduction, the lattice collapses and the layered MoO3 structure is lost. This affects the electronic and optical properties, which range from the wide band gap semiconductor MoO3 to metallic MoO2. DFT is used to determine the stability of the most relevant molybdenum oxide phases, in comparison to oxygen vacancies in the layered MoO3 lattice. The non-layered phases are more stable than the layered MoO3 structure for all oxygen stoichiometries of MoOx studied where 2 ≤ x < 3. Reduction and lattice collapse leads to strong changes in the electronic density of states, especially the filling of the Mo 4d states. The DFT predictions are compared to experimental studies of molybdenum oxide films within the same range of oxygen stoichiometries. We find that whilst MoO2 is easily distinguished from MoO3, intermediate phases and phase mixtures have similar electronic structures. The effect of the different band structures is seen in the electrical conductivity and optical transmittance of the films. Insight into the oxide phase stability ranges and mixtures is not only important for understanding molybdenum oxide films for optoelectronic applications, but is also relevant to other transition metal oxides, such as WO3, which exist in analogous forms.

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Electronic properties of reduced molybdenum oxides

Molybdenum oxide thin films find diverse applications as catalysts, gas sensors, and electrochromic devices. Such films are produced mainly by reactive sputtering and thermal evaporation but other ...

Molybdenum oxide thin films obtained by the hot-filament metal oxide deposition technique

O presente artigo descreve um novo metodo para a sintese de filmes finos de oxidos metalicos. Um filamento de metal, que pode ser aquecido por uma fonte de corrente alternada e instalado numa câmara de vacuo. Por meio de um fluxometro de massa, oxigenio pode ser admitido no interior da câmara. Da reacao entre o oxigenio e o metal do filamento aquecido, especies de oxidos volateis MexOy, onde Me e o metal, sao formadas, se condensando num substrato colocado proximo ao filamento, formando o filme. Foi observado que os filmes finos de WxOy e MoxOy podem ser depositados de forma satisfatoria por este novo metodo. Embora varias outras tecnicas de analise tenham sido usadas para caracterizar os oxidos, esta nota enfatiza os resultados obtidos por espectroscopia de fotoeletrons de raio-X (XPS).

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Hot-filament metal oxide deposition (HFMOD): a novel method for depositing thin films of metallic oxides

Thin films of tungsten oxide deposited by hot filament metal oxide deposition (HFMOD) were thermally annealed up to 800 °C and investigated by means of XRD, Raman spectroscopy, and infrared reflection−absorption spectroscopy (IRRAS). As clearly shown by the XRD and Raman spectroscopy data, the deposited films were amorphous and crystallized by thermal annealing. The monoclinic WO3 phase was formed in all annealed samples. The IRRAS spectra were obtained using the IR beam with p-polarization and an off-normal incidence angle. In this condition, absorptions due to the longitudinal optical (LO) modes (Berreman effect) can be observed in the spectra. Absorptions due to LO modes are not detected by the standard infrared absorption spectroscopy, in which an unpolarized IR beam is used at normal incidence, and thus are not frequently reported in the literature. To analyze the experimental IRRAS spectra, the LO and TO functions were calculated from the transmission spectra of the as-deposited sample, using the Kr...

B. Claudio Trasferetti

Papers

Molybdenum oxide thin films obtained by the hot-filament metal oxide deposition technique

Hot-filament metal oxide deposition (HFMOD): a novel method for depositing thin films of metallic oxides

Berreman Effect in Amorphous and Crystalline WO3 Thin Films

Characterization of Si:O:C:H films fabricated using electron emission enhanced chemical vapour deposition

Nanocomposites of amorphous hydrogenated carbon and siloxane networks produced by PECVD