Advanced Technology and Manufacturing Institute (ATAMI)

Oxo-hydroxo Group 5 metal clusters are an untapped resource to study and advance aqueous solution processing of metal oxide thin films. The tetramethylammonium (TMA) hexatantalate salt (TMA6[H2Ta6O19]) yields dense Ta2O5 films (~95% of the bulk ß-Ta2O5 density) with atomically smooth surfaces (<4 Å root mean square surface roughness). This same precursor produces single-digit-nanometer thick films at low solution concentrations. The diprotonated cluster TMA6[H2Ta6O19] cluster produces films much different from those of the triprotonated analog TMA5[H3Nb6O19]. One additional proton in [H3Nb6O19]5- yields rougher Nb2O5 films with nanoparticles at the surface. A temperature-programmed desorption study of TMA6[H2Ta6O19] elucidates the reaction pathway of precursor to solid oxide. Lastly, the acid-base, ion-exchange chemistry of the basic [H2Ta6O19]6- precursor enables a path to produce amorphous tantalum oxide films at temperatures as low as 200 °C.