The Effect of the Degree of Fluorination on the MOCVD Growth of Cobalt Oxide Thin Films using Co(II) Acetylacetonate Complexes

• Published in: European journal of inorganic chemistry 2021-11, Vol.2021 (41), p.4298-4306
• Main Authors: Stienen, Christian, Rogalla, Detlef, Prymak, Oleg, Bendt, Georg
• Format: Article
• Language: English
• Subjects: Backscattering; Cobalt; Cobalt oxide; Cobalt oxides; Contaminants; Differential scanning calorimetry; Fluorination; Fluorine; Infrared analysis; Infrared spectroscopy; Inorganic chemistry; Ions; Metalorganic chemical vapor deposition; MOCVD; Morphology; Nitrogen; Nuclear reactions; Oxygen evolution reactions; Phase composition; Photoelectrons; Precursor chemistry; Precursors; Scientific imaging; Secondary ion mass spectrometry; Thermal decomposition; Thermogravimetric analysis; Thin films; Water splitting
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.202100662

The structurally related cobalt β‐diketonate complexes Co(acac)2, Co(acac)2 ⋅ TMEDA, Co(tfac)2 ⋅ TMEDA, and Co(hfac)2 ⋅ TMEDA (acac=2,4‐pentanedionate, tfac=1,1,1‐trifluoro‐2,4‐pentane‐dionate, hfac=1,1,1,5,5,5‐hexafluoro‐2,4‐pentane‐dionate, TMEDA=N,N,N′,N′‐tetramethylethylenediamine) were thermochemically (thermogravimetric analysis, differential scanning calorimetry) and spectroscopically (infrared, UV‐VIS and electron resonance spectroscopy) characterised and used as precursor for the MOCVD growth of cobalt monoxide (CoO) thin films. The influence of the degree of fluorination of the cobalt precursors on the morphology (scanning electron microscopy) and phase composition (X‐ray diffraction) of the CoO films is demonstrated. Carbon, nitrogen and fluorine impurities as a result of the thermal decomposition of the 2,4‐pentanedionate and tetraamine ligands in the films were identified by X‐ray photoelectron spectroscopy, time‐of‐flight secondary ion mass spectrometry, Rutherford backscattering spectrometry and nuclear reaction analysis. In addition, the influence of these contaminants on the electrocatalytically activity for the oxygen evolution reaction (OER) in alkaline media of the MOCVD grown CoO films is shown. The four structural related cobalt‐β‐diketonate complexes Co(acac)2, Co(acac)2 ⋅ TMEDA, Co(tfac)2 ⋅ TMEDA and Co(hfac)2 ⋅ TMEDA with different degree of fluorination were thermochemically evaluated and used as precursors for the MOCVD growth of cobalt monoxide thin films. The influence of the degree of fluorination of the cobalt precursors on impurities (carbon, nitrogen, and fluorine) in the CoO films and the influence of these impurities on the electrocatalytically activity for the oxygen evolution reaction (OER) in alkaline media was investigated in detail.