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Abstract
Vanadium nitride (VN) has been identified as a promising material for numerous applications including electrochemical nitrogen reduction reaction (eNRR). For such applications, catalyst nanoengineering will help to experimentally test its theoretically predicted eNRR activity, but the majority of investigated VN catalysts are prepared by fabrication methods that do not allow for nanoengineering to the required degree. Herein, we report on a new metalorganic chemical vapor deposition (MOCVD) process for the growth of high quality, facetted and crystalline VN thin films relevant for eNRR applications. N,N’-diisopropylformamidinato [V(dpfamd)3] was identified as a promising precursor as it possesses favorable thermal properties relevant for MOCVD. The application of [V(dpfamd)3] in a MOCVD process with NH3 as co-reactant yielded crystalline VN thin films on Si substrates with high compositional purity. With the potential of using the catalytic activity of VN towards eNRR, the structure-property correlation is of relevance and in this context, the thin films were subjected to complementary analysis including X-ray diffraction (XRD), Rutherford backscattering spectrometry in combination with nuclear reaction analysis (RBS/NRA), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Based on the observation of the significant influence NH3 has on the growth characteristics, we conducted first principles density functional theory (DFT) simulations of the precursor reactivity in the absence and presence of NH3 towards VN, supporting experimental findings of energetically more favorable decomposition of [V(dpfamd)3] to VN in the presence of NH3. Process transfer from Si to conductive Ti substrates, relevant for prospective electrochemical testing, revealed comparable VN thin film properties rendering these films promising for further investigation of eNRR applications in follow up studies.
Supplementary materials
Title
Supporting Information Document
Description
Figure S1. The configurations of key steps along the decomposition pathway in the absence of NH3 and presence of NH3
Figure S2. XPS high resolution core level spectra of C1s for VN film on Si grown at 500 °C and at 700 °C.
Figure S3. Normalized EDX spectra measured in TEM at different positions of VN grown on Si at 500 °C and 700 °C
Figure S4. Enlarged view of the XRD measurement of the VN thin film grown at 700 °C for 2θ from 33° to 55°.
Figure S5. XPS high resolution core level spectra of C 1s for VN film on Ti (a) grown at 500 °C and at 700 °C.
Figure S6. Normalized EDX spectra measured in TEM
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