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

Abstract

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.

Fluorinated β-diketonate complexes M(tfac)2(TMEDA) (M = Fe, Ni, Cu, Zn) as precursors for the MOCVD growth of metal and metal oxide thin films

“…Synthesis of M(tfac) 2 (TMEDA) (M ¼ Fe 1, Ni 2, Cu 3, Zn 4) 1-4 were synthesized according to a previously reported synthesis protocol for Co(tfac) 2 (TMEDA) with minor modications. 11 2.8 mL (23.3 mmol) of Htfac was added dropwise to a solution of 0.94 g NaOH in 50 mL deionized water and stirred for 20 min 11.73 mmol of the corresponding metal salt (2.33 g FeCl 2 $4H 2 O, 2.79 g NiCl 2 $6H 2 O, 2.00 g CuCl 2 $2H 2 O, 1.60 g ZnCl 2 ) was dissolved separately in 75 mL water and then added dropwise to the previously prepared aqueous solution of Na(tfac). The reaction mixture was stirred for another 30 min and then 1.8 mL (11.93 mmol) of TMEDA was added.…”

“…1–4 were synthesized according to a previously reported synthesis protocol for Co(tfac) 2 (TMEDA) with minor modifications. 11 …”

“…A large number of rst-row transition metal complexes of the type M(hfac) 2 (TMEDA) have been prepared and used as precursors for the deposition of transition metal oxide lms. 12a-g In remarkable contrast to widely applied M(acac) 2 (TMEDA) and M(hfac) 2 (TMEDA) complexes, the corresponding M(tfac) 2 (-TMEDA) complexes have received far less attention, and within the rst-row transition metals only manganese, iron and cobalt complexes have been applied for the deposition of Mn 3 O 4 , 13 CoO, 11 We recently demonstrated that the sublimation temperature of different uorinated cobalt acetylacetonate complexes largely depends on the degree of uorination. In addition, using these complexes as precursors in MOCVD processes demonstrated that the amount of uorine-containing impurities in the resulting material lms can be tailored by the degree of uorination.…”

“… 10 A comparable thermal behaviour was recently reported for Co(acac) 2 and Co(acac) 2 (TMEDA). 11 The volatility of these compounds can be further improved by replacing the CH 3 groups with electron-withdrawing CF 3 groups. A large number of first-row transition metal complexes of the type M(hfac) 2 (TMEDA) have been prepared and used as precursors for the deposition of transition metal oxide films.…”

“…In addition, using these complexes as precursors in MOCVD processes demonstrated that the amount of fluorine-containing impurities in the resulting material films can be tailored by the degree of fluorination. 11 These fluorine-containing impurities can have either positive 16 a , b or have no 11 effect on the physical and chemical properties of the resulting material films. In addition to the impurity content, the ligand design directly influences the possible formation of corrosive or toxic decomposition products such as hydrogen fluoride.…”