Partially fluorinated oxo-alkoxide tungsten complexes bearing β-diketonate or ketoesterate ligands have been synthesized and their thermal and physical properties have been evaluated for Aerosol Assisted Chemical Vapor Deposition (AACVD) of WO x. Volatility and thermal stability of the complexes have been shown to depend on the bidentate ligand and the degree of fluorination of the alkoxides. Growth of tungsten oxide from the precursor WO(OC(CH 3) 2 CF 3) 3 (tbac) (tbac = tert-butyl acetoacetate) has been demonstrated. Deposits grown at temperatures from 150 to 300 °C are amorphous thin films of substoichiometric WO x. Deposition at temperatures from 350 to 500 °C produced either polycrystalline films or crystalline nanorods of W 18 O 49 .

Reactions of [WO(OR)4]x (x = 1, 2) complexes with bidentate ligands (LH = acacH, tbacH, dpmH, tbpaH) afforded complexes : [WO(OCH3)3(acac) (); WO(OCH2CH3)3(acac) (); WO(OCH(CH3)2)3(acac) (); WO(OCH3)3(tbac) (); WO(OCH2CH3)3(tbac) (); WO(OCH(CH3)2)3(tbac) (); WO(OCH2CH3)3(dpm) (); WO(OCH(CH3)2)3(dpm) (); WO(OCH2C(CH3)3)3(acac) (); WO(OCH2C(CH3)3)3(tbac) (); WO(OCH2C(CH3)3)3(dpm) (); WO(OCH2C(CH3)3)3(tbpa) (); WO(OC(CH3)3)3(tbac) ()]. 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 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 on ITO or bare glass resulted in growth of continuous, dense and amorphous thin films of substoichiometric WOx between 250-350 °C and nanorods of W18O49 above 350 °C.

No abstract

Deposition of continuous, dense WOx films and nanorods was accomplished by aerosol-assisted chemical vapor deposition (AACVD) using the recently synthesized precursors WO(OCH3)3(acac) (1), WO(OCH2C(CH3)3)3(tbac) (2), WO(OCH2C(CH3)3)3(dpm) (3), WO(OC(CH3)3)3(tbac) (4), and WO(OCH2C(CH3)3)3(tbpa) (5). This works seeks to define the deposition conditions and precursors that yield C-free tungsten oxide and the potential to control the stoichiometry and phase of deposited WOx. In addition, the systematic variation of the ligand chemistry provides insight into precursor design. Variation of the precursor and growth temperature during deposition revealed a window where C-free WOx was deposited using 3, 4, and 5. The surface morphology of the WOx varied from amorphous thin film to crystalline nanorods to dendrites as temperature was increased. Films grown between 150 and 350°C in pure N2 atmosphere are sub-stoichiometric, amorphous and contaminated with carbide species (3–9 at.%). As the deposition temperature increased (400–550°C), the tungsten became more oxidized, the sub-stoichiometric crystalline W18O49 monoclinic phase formed, and increased surface bound C was detected. Material was also deposited under oxidizing conditions (1–2% O2 in N2) as well as annealing in air at the deposition temperature. The material grown in N2/O2 carrier gas at low temperatures (200 and 300°C) is amorphous WOx, similar to that grown in N2. At higher temperature (350 and 550°C), however, GIXRD results reveal WOx corresponding to a sub-stoichiometric tetragonal phase transitioning to the monoclinic WO3 phase for samples grown at 550°C. This demonstrates that crystalline structure of WOx is affected by the growth temperature and introducing O2 in the carrier gas. Air annealing samples grown in pure N2 also produced structural and compositional changes, but not identical to those grown in a N2/O2 carrier gas. Notably, annealing samples grown at 250 and 350°C at the same temperature, produced C-free material with unchanged amorphous morphology. The measured stoichiometry and crystallinity showed a dependence on the precursor structure. The growth rate of deposited material was measured as a function of temperature and activation energies were estimated for growth of amorphous and nanostructured material. The systematic variation in activation energies is consistent with initial dissociation of the alkoxide C-O bonds and modifications of the steric bulk of the β-diketonate ligand.

Tungsten­(VI) oxo complexes of the type WO­(OR)3L [R = C­(CH3)2CF3, C­(CF3)2CH3, CH­(CF3)2, L = hexafluoroacetylacetonate (hfac), ethyl trifluoroacetoacetonate (etfac), acetylacetonate (acac)] bearing partially fluorinated alkoxide and/or chelating ligands were synthesized. Thermal decomposition behavior and mass spectrometry (MS) fragmentation patterns of selected examples were studied. The thermolysis products of WO­(OC­(CF3)2CH3)3(hfac) were characterized by nuclear magnetic resonance and gas chromatography–MS. Studies of the sublimation behavior of the complexes demonstrated that their volatility depends on the degree of fluorination. Comparative studies of the deposition of tungsten oxide by chemical vapor deposition (CVD) and aerosol-assisted CVD were carried out using WO­(OC­(CF3)2CH3)3(hfac) as a single-source precursor. WO x materials were successfully deposited by both deposition methods, but the deposits differed in morphology, structure, and crystallinity.

First row transition metal complexes (Ni, Co, Cu, Zn) with N,N-disubstituted-N'-acylthiourea ligands have been synthesized and characterized. Bis(N,N-diisopropyl-N'-cinnamoylthiourea)nickel was found to have the lowest onset temperature for thermal decomposition. Thin film deposition of Ni, Co, and Zn sulfides by aerosol assisted chemical vapor deposition from their respective N,N-diisopropyl-N'-cinnamoylthiourea complexes at 350 °C has been demonstrated.