Synthesis and evaluation of κ2-β-diketonate and β-ketoesterate tungsten(vi) oxo-alkoxide complexes as precursors for chemical vapor deposition of WOx thin films

Abstract

Reactions of [WO(OR)₄]_x (x = 1, 2) complexes with bidentate ligands (LH = acacH, tbacH, dpmH, tbpaH) afforded complexes 1–13: [WO(OCH₃)₃(acac) (1); WO(OCH₂CH₃)₃(acac) (2); WO(OCH(CH₃)₂)₃(acac) (3); WO(OCH₃)₃(tbac) (4); WO(OCH₂CH₃)₃(tbac) (5); WO(OCH(CH₃)₂)₃(tbac) (6); WO(OCH₂CH₃)₃(dpm) (7); WO(OCH(CH₃)₂)₃(dpm) (8); WO(OCH₂C(CH₃)₃)₃(acac) (9); WO(OCH₂C(CH₃)₃)₃(tbac) (10); WO(OCH₂C(CH₃)₃)₃(dpm) (11); WO(OCH₂C(CH₃)₃)₃(tbpa) (12); WO(OC(CH₃)₃)₃(tbac) (13)]. The synthesis is facilitated by the lability of the bridging ligands of the [WO(OR)₄]₂ complexes in solution, which provides a pathway for exchange of L with an alkoxide ligand. Thermogravimetric analysis and the conditions for sublimation or distillation of 1–13 demonstrate that they have sufficient vapor pressure and thermal stability for volatilization in a conventional Chemical Vapor Deposition (CVD) reactor. High solubility in hydrocarbon and ether solvents establishes that the complexes are also potential candidates for Aerosol-Assisted Chemical Vapor Deposition (AACVD). AACVD from 10 on ITO or bare glass resulted in growth of continuous, dense and amorphous thin films of substoichiometric WO_x between 250–350 °C and nanorods of W₁₈O₄₉ above 350 °C.