Dioxo–Fluoroalkoxide Tungsten(VI) Complexes for Growth of WO_x Thin Films by Aerosol-Assisted Chemical Vapor Deposition

Abstract

The soluble bis(fluoroalkoxide) dioxo tungsten(VI) complexes WO2(OR)2(DME) [1, R = C(CF3)2CH3; 2, R = C(CF3)3] have been synthesized by alkoxide-chloride metathesis and evaluated as precursors for aerosol-assisted chemical vapor deposition (AACVD) of WOx. The (1)H NMR and (19)F NMR spectra of 1 and 2 are consistent with an equilibrium between the dimethoxyethane (DME) complexes 1 and 2 and the solvato complexes WO2(OR)2(CD3CN)2 [1b, R = C(CF3)2CH3; 2b, R = C(CF3)3] in acetonitrile-d3 solution. Studies of the fragmentation of 1 and 2 by mass spectrometry and thermolysis resulted in observation of DME and the corresponding alcohols, with hexafluoroisobutylene also generated from 1. DFT calculations on possible decomposition mechanisms for 1 located pathways for hydrogen abstraction by a terminal oxo to form hexafluoroisobutylene, followed by dimerization of the resulting terminal hydroxide complex and dissociation of the alcohol. AACVD using 1 occurred between 100 and 550 °C and produced both substoichiometric amorphous WOx and a polycrystalline W18O49 monoclinic phase, which exhibits 1-D preferred growth in the [010] direction. The work function (4.9-5.6 eV), mean optical transmittance (39.1-91.1%), conductivity (0.4-2.3 S/cm), and surface roughness (3.4-7.9 nm) of the WOx films are suitable for charge injection layers in organic electronics.

Synthesis of tungsten oxo fluoroalkoxide complexes WO(OR)3L as precursors for growth of WOx nanomaterials by aerosol-assisted chemical vapor deposition

“…Oxygen-bound ligands such as oxo, alkoxide, β-diketonate and β-ketoesterate moieties have found use in single source precursors for the deposition of metal oxides because the preexisting metal oxygen bonding can facilitate conversion of the precursor to the oxide material during deposition [25,[34][35][36]. We have previously demonstrated that oxo alkoxide complexes of the type WO(OR) 4 (R = C(CH 3 ) 2 CF 3 and C(CF 3 ) 2 CH 3 ) and the dioxo derivative WO 2 (OR) 2 L (R = C(CF 3 ) 2 CH 3 , L = DME) are low temperature precursors to WO x films and nanorods, consistent with incorporation of the terminal oxo moieties into the deposits [23,41,42].…”

“…Fluorination of ligands has been shown to increase the volatility of complexes as a result of decreased intermolecular interactions due to the repulsion produced by the fluorine atoms [39,40]. Following this strategy, fluorinated tungsten oxo-alkoxide complexes have been used as WO x AACVD precursors [23,37,41,42]. We now report the synthesis of a series of fluorinated oxo alkoxide complexes WO(OR 3 )L [R = C(CH 3 ) 2 (CF 3 ), C(CH 3 )(CF 3 ) 2 ] that bear the chelating βdiketonate/ketoesterate ligands acetyl acetonate (acac), dipivaloylmethanate (dpm), ethyl acetoacetate (etac) and tert-butyl pivaloyl acetate (tbac) and demonstrate the use of WO(OC(CH 3 ) 2 (CF 3 ))tbac as a precursor for AACVD of WO x films and nanorods.…”

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

“…This suggests a facile pathway for conversion of an alkoxide ligand to a second oxo moiety, a process we have previously noted in the mass spectra of the related oxo alkoxide complexes WO[OC(CH 3 ) 2 CF 3 ] 4 and WO[OC(CF 3 ) 2 CH 3 ] 4 . 33,49 Thermolysis of 10…”

Volatile Hexavalent Oxo-amidinate Complexes: Molybdenum and Tungsten Precursors for Atomic Layer Deposition

“…In particular, we envisioned volatile metal–organic complexes bearing intact metal-dioxo functionalities on Mo­(VI) and W­(VI) centers, as sources for the growth of such centers. While vapor-phase deposition of molybdenum and tungsten oxide films has been realized through ALD and chemical vapor deposition (CVD), − including examples using volatile oxo-bearing tungsten precursors, , precise control of deposited surface structures has not yet been reported. Previously, Gordon and co-workers − reported that amidinato- and acetamidinato- ligand platforms are viable for volatile metal–organic ALD precursors.…”