Nickel-based
nanostructured materials have gained widespread attention,
particularly for energy-related applications. Employing chemical vapor
deposition (CVD) for NiO necessitates suitable nickel precursors that
are volatile and stable. Herein, we report the synthesis and characterization
of a series of new nickel β-ketoiminato complexes with different
aliphatic and etheric side chain substitutions, namely, bis(4-(isopropylamino)-pent-3-en-2-onato)nickel(II)
([Ni(ipki)2], 1), bis(4-(2-methoxyethylamino)pent-3-en-2-onato)nickel(II)
([Ni(meki)2], 2), bis(4-(2-ethoxyethylamino)pent-3-en-2-onato)nickel(II)
([Ni(eeki)2], 3), bis(4-(3-methoxy-propylamino)-pent-3-en-2-onato)nickel(II)
([Ni(mpki)2], 4), and bis(4-(3-ethoxypropylamino)pent-3-en-2-onato)nickel(II)
([Ni(epki)2], 5). These compounds have been
thoroughly characterized with regard to their purity and identity
by means of nuclear magnetic resonance spectroscopy (NMR) and electron
impact mass spectrometry (EI-MS). Contrary to other transition metal
β-ketoiminates, the imino side chain strongly influences the
structural geometry of the complexes, which was ascertained via single-crystal
X-ray diffraction (XRD). As a result, the magnetic momenta of the
molecules also differ significantly as evidenced by the magnetic susceptibility
measurements employing Evan’s NMR method in solution. Thermal
analysis revealed the suitability of these compounds as new class
of precursors for CVD of Ni containing materials. As a representative
precursor, compound 2 was evaluated for the CVD of NiO
thin films on Si(100) and conductive glass substrates. The as-deposited
nanostructured layers were stoichiometric and phase pure NiO as confirmed
by XRD, Rutherford backscattering spectrometry (RBS), and nuclear
reaction analysis (NRA). X-ray photoelectron spectroscopy (XPS) indicated
the formation of slightly oxygen-rich surfaces. The assessment of
NiO films in electrocatalysis revealed promising activity for the
oxygen evolution reactions (OER). The current densities of 10 mA cm–2 achieved at overpotentials ranging between 0.48 and
0.52 V highlight the suitability of the new Ni complexes in CVD processes
for the fabrication of thin film electrocatalysts.
A series of six cobalt ketoiminates, of which one was previously reported but not explored as a chemical vapor deposition (CVD) precursor, namely, bis(4-(isopropylamino)pent-3-en-2-onato)cobalt(II) ([Co( pki)], 1), bis(4-(2-methoxyethylamino)pent-3-en-2-onato)cobalt(II) ([Co(meki)], 2), bis(4-(2-ethoxyethylamino)pent-3-en-2-onato)cobalt(II) ([Co(eeki)], 3), bis(4-(3-methoxy-propylamino)pent-3-en-2-onato)cobalt(II) ([Co(mpki)], 4), bis(4-(3-ethoxypropylamino)pent-3-en-2-onato)cobalt(II) ([Co(epki)], 5), and bis(4-(3-isopropoxypropylamino)pent-3-en-2-onato)cobalt(II) ([Co( ppki)], 6) were synthesized and thoroughly characterized. Single-crystal X-ray diffraction (XRD) studies on compounds 1-3 revealed a monomeric structure with distorted tetrahedral coordination geometry. Owing to the promising thermal properties, metalorganic CVD of CoO was performed using compound 1 as a representative example. The thin films deposited on Si(100) consisted of the spinel-phase CoO evidenced by XRD, Rutherford backscattering spectrometry/nuclear reaction analysis, and X-ray photoelectron spectroscopy. Photoelectrochemical water-splitting capabilities of spinel CoO films grown on fluorine-doped tin oxide (FTO) and TiO-coated FTO revealed that the films show p-type behavior with conduction band edge being estimated to -0.9 V versus reversible hydrogen electrode. With a thin TiO underlayer, the CoO films exhibit photocurrents related to proton reduction under visible light.
Transition metal ferrites, such as CoFe2O4 (CFO) and NiFe2O4 (NFO), have gained increasing attention as potential materials for supercapacitors. Since chemical vapor deposition (CVD) offers advantages like interface quality to the underlying substrates and the possibility for coverage of 3D substrates, two CVD processes are reported for CFO and NFO. Growth rates amount to 150 to 200 nm h−1 and yield uniform, dense, and phase pure spinel ferrite films according to X‐ray diffraction (XRD), Raman spectroscopy, Rutherford backscattering spectrometry and nuclear reaction analysis (RBS/NRA) and scanning electron microscopy (SEM). Atom probe tomography (APT) and synchrotron X‐ray photoelectron spectroscopy (XPS) give insights into the vertical homogeneity and oxidation states in the CFO films. Cation disorder of CFO is analyzed for the first time from synchrotron‐based XPS. NFO is analyzed via lab‐based XPS. Depositions on conducting Ni and Ti substrates result in electrodes with pseudocapacitive behavior, as evidenced by cyclovoltammetry (CV) experiments. The interfacial capacitances of the electrodes are up to 185 µF cm−2.
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