TUNGSTEN OXO-ALKOXIDES-β-DIKETONATES

Tungsten oxo alkoxides  β-diketonate complexes [WO(OR)3L] (R = Me, Et, iPr, 'Bu, CHtBu; L = acac, hfac) were proposed as potential MOCVD precursor by Chisholm et al. [] Metal atom (W) is strongly bonded to the oxygen of the alkoxide ligand, and upon decomposition organic groups are easily removed, with the subsequent formation of volatile, non-reactive, organic byproducts. Addition of β-diketonate group to the complex generally increases thermal stability and reduces moisture susceptibility, what can be advantageous for the use of the complex as MOCVD precursor.

Tungsten oxo tris(methoxide) acetylacetonate WO(OMe)3(acac)

Tungsten oxo tris(neopentoxide) (2,2,6,6-tetramethylhaptane-3,5-dionate) WO(ONep)3(thd)

Tungsten oxo-alkoxides β-diketonates:  tungsten oxo tris(methoxide) acetylacetonate WO(OCH3)3(acac) and tungsten oxo tris(neopentoxide) (2,2,6,6-tetramethylhaptane-3,5-dionate) WO(ONep)3)3(thd) (and for comparison tungsten oxo-alkoxides β-ketoesterates WO(OCH2C(CH3)3)3(tbac), WO(OC(CH3)3)3(tbac), and WO(OCH2C(CH3)3)3(tbpa)) have been applied for the deposition of continuous dense WOx films and nanorods by AACVD. The systematic variation of the ligand chemistry allowed to check influence of the  precursor design on the properties of the obtained films (stoichiometry and crystallinity); precursors and deposition conditions  were varied to control the stoichiometry and phase of deposited WOx and to obtain carbon-free WO3 (a growth temperature window where C-free WOx were obtained were found for WO(OCH2C(CH3)3)3(thd) (as well as WO(OC(CH3)3)3(tbac) and WO(OCH2C(CH3)3)3(tbpa) );  as deposition temperature was increased, the WOx surface morphology changed from amorphous thin film to crystalline nanorods to dendrites. Sub-stoichiometric, amorphous, carbide-contaminated (3–9 at.%) layers were grown between 150-350°C in pure N2 atmosphere; however for higher growth temperature (400–550°C), more oxidized but still sub-stoichiometric crystalline W18O49 monoclinic phase (with increased surface bound C) was obtained. Under oxidizing conditions (1–2% O2 in N2) amorphous WOx was obtained at low temperatures (200 and 300°C) (similar to growth in N2), however at higher growth temperatures (350 and 550°C) a sub-stoichiometric tetragonal phase and at 550°C monoclinic WO3 was detected by GIXRD, demonstrating the increase of WOx crystallinity by increasing growth temperature and addition of O2 to the carrier gas. Annealing in air the N2-grown samples grown at 250 and 350°C at the same temperature, produced C-free material but the morphology remained amorphous.  Growth rate as a function of temperature and activation energies were estimated for growth of amorphous and nanostructured WOx layers; the activation energies variation was consistent with initial dissociation of the alkoxide C-O bonds and change of steric bulk of the β-diketonate ligand.[i]

[i] H. Kim, R.O. Bonsu, D. C. Bock, N.C. Ou, R.Y. Korotkov, L. McElwee-White, T. Anderson, ECS J. Solid State Sci. Techn., 2016, Vol. 5, 11 , Q3095, https://iopscience.iop.org/article/10.1149/2.0171611jss/meta , « Tungsten Oxide Film and Nanorods Grown by Aerosol-Assisted Chemical Vapor Deposition Using κ2-β-Diketonate and β-Ketoesterate Tungsten (VI) Oxo-Alkoxide Precursors »

Tungsten oxo tris(isopropoxide) acetylacetonate WO(OiPr)3(acac)

Tungsten oxo tris(tert-butoxide) acetylacetonate WO(OtBu)3(acac)

Fig. TGA curves of WO(OiPr)3(acac) and WO(OtBu)3(acac) and their comparison with TGA curves of tungsten oxo-alkoxides-ketoesterates

Thermal analysis of the complexes tungsten oxo tris(isopropoxide) acetylacetonate WO(OiPr)3(acac) and tungsten oxo tris(tert-butoxide) acetylacetonate WO(OtBu)3(acac) was reported. [[i]]

[i] G.V.Kunte, S.A.Shivashankar, A.M.Umarji, Thermochim. Acta, 2008, Vol.474, Iss.1–2, p.12-15, “Thermal analysis and vapour pressure of a new series of tungsten(VI) oxo-alkoxide-β-ketoesterate complex precursors for the chemical vapour deposition of tungsten oxide”, https://www.sciencedirect.com/science/article/abs/pii/S0040603108001470

WO(OiPr)3(acac), WO(OtBu)3(acac) for WOx by MOCVD

      WO(OiPr)3(acac) and WO(OtBu)3(acac) (and for comparison WO(OiPr)3(hfac) and WO(OtBu)3(hfac)) were applied as precursors for the deposition of tungsten oxide WOx electrochromic layers by MOCVD. The obtained WOx thin films were characterized by XRD, SEM, XPS, and cyclic voltammetry.    [[i]].

[i] D.V. Baxter,  M.H. Chisolm, S. Doherty, N. E. Gruhn, Chem. Commun., 1996, 1129-1130, « Chemical vapour deposition of electrochromic tungsten oxide films employing volatile tungsten(VI) oxo alkoxide/β-diketonate complexes »,  https://doi.org/10.1039/CC9960001129, https://pubs.rsc.org/en/content/articlelanding/1996/cc/cc9960001129#!divAbstract

Tungsten oxo tris(isopropoxide) hexafluoracetylacetonate WO(OiPr)3(hfac) Tungsten oxo tris(tert-butoxide) hexafluoracetylacetonate WO(OtBu)3(hfac)

     Volatile tungsten(VI) oxo alkoxide-β-diketonate complexes WO(OiPr)3(hfac) and WO(OtBu)3(hfac)  (and for comparison acetylacetonate analogues WO(OiPr)3(acac) and WO(OtBu)3(acac)) have been tested as precursors for the MOCVD of tungsten oxide WOx electrochromic thin films. The obtained WOx layers were characterized by XRD, XPS, SEM, and cyclic voltammetry. [i].

[i] D.V. Baxter,  M.H. Chisolm, S. Doherty, N. E. Gruhn, Chem. Commun., 1996, 1129-1130, « Chemical vapour deposition of electrochromic tungsten oxide films employing volatile tungsten(VI) oxo alkoxide/β-diketonate complexes »,  https://doi.org/10.1039/CC9960001129, https://pubs.rsc.org/en/content/articlelanding/1996/cc/cc9960001129#!divAbstract

Tungsten oxo tris(2,2,2,2’,2’,2’-hexafluoro-tert-butoxide] hexafluoracetylacetonate WO[OCMe(CF3)2]3(hfac)

Fig. Structural formula of WO[OCMe(CF3)2]3(hfac)

      Tungsten oxo tris(2,2,2,2’,2’,2’-hexafluoro-tert-butoxide] hexafluoracetylacetonate WO[OCMe(CF3)2]3(hfac),   as well as other tungsten oxo complexes bearing fluorinated alkoxide and chelating ligands (β-diketonate or β-ketoesterate) of the type WO(OR)3L [R = CMe2CF3, CMe(CF3)2, CH(CF3)2, L = acac, hfac, ethyl trifluoroacetoacetonate (etfac)], were synthesized and characterized. Thermal decomposition and mass spectrometry (MS) fragmentation patterns were studied for some of the complexes. NMR and gas chromatography–MS were used for the identification of the thermolysis products of WO(OCMe(CF3)2)3(hfac). The volatility of the complexes depended on the degree of fluorination, as was shown by the studies of the sublimation behavior.

      WO(OCMe(CF3)2)3(hfac) was applied as a single-source precursor for the deposition of WOx thin films by 2 deposition methods: CVD and aerosol-assisted CVD. WOx layers were successfully deposited by both methods, but the morphology, structure, and crystallinity of the grown layers was differing between two methods.[i]

[i]    N.C. Ou, D.C. Bock, X. Su, D. Craciun, V. Craciun, L. McElwee-White, ACS Appl. Mater. Interfaces 2019, 11, 31, 28180–28188, https://doi.org/10.1021/acsami.9b08830 , « Growth of WOx from Tungsten(VI) Oxo-Fluoroalkoxide Complexes with Partially Fluorinated β-Diketonate/β-Ketoesterate Ligands: Comparison of Chemical Vapor Deposition to Aerosol-Assisted CVD »

Share this page