Polyoxoniobates as molecular building blocks in thin films.

Area of Science:

• Materials Science
• Inorganic Chemistry
• Thin Film Deposition

Background:

• Polyoxometalates (POMs) offer versatile precursors for advanced materials.
• Niobium oxides and titanium-niobium oxides possess unique electronic and catalytic properties.
• Controlling the phase and structure of metal oxide films is crucial for device performance.

Purpose of the Study:

• To synthesize niobium oxide and titanium-niobium oxide thin films using novel polyoxometalate precursors.
• To investigate the influence of precursor composition and annealing conditions on film crystallinity and phase.
• To establish a method for multilayered metal oxide film deposition and analyze film roughness.

Main Methods:

• Spin-coating of aqueous tetramethylammonium salt solutions of polyoxometalate clusters ([Nb10O28]6-, [TiNb9O28]7-, [Ti2Nb8O28]8-) onto silicon wafers.
• Annealing of coated substrates at temperatures of 800 °C and 1000 °C.
• Characterization of resulting thin films using techniques to determine crystal phases, composition, and surface roughness.

Main Results:

• The [Nb10O28]6- precursor yielded orthorhombic and monoclinic Nb2O5 phases at 800 °C and 1000 °C, respectively.
• The [TiNb9O28]7- and [Ti2Nb8O28]8- precursors produced monoclinic titanium-niobium oxides (Ti2Nb12O29 and TiNb2O7) in varying ratios.
• A protocol for depositing successive layers of metal oxide films was successfully demonstrated, with factors influencing film roughness explored.

Conclusions:

• Polyoxometalate clusters serve as effective precursors for depositing crystalline niobium and titanium-niobium oxide thin films.
• Annealing temperature and precursor choice are critical parameters for controlling the phase and structure of the deposited films.
• The developed method enables multilayered film fabrication and provides insights into surface morphology control for tailored material properties.