NEXAFS and XPS Studies of Cr/MWCNT Composites

Abstract

Nanocomposites obtained by MOCVD through deposition of pyrolytic chromium layers of different thickness on the outer surface of multi-walled carbon nanotubes (MWCNTs) using the “Barkhos” chromium-organic liquid were studied.. These pyrolytic Cr coatings have high microhardness, heat resistance, hydrophobicity, and chemical resistance to hydrochloric and sulphuric acids and alkali melt.
The unique physical properties of chromium coatings as well as chemical resistance in a wide temperature range and large external surface of MWCNTs offer great opportunities for the possible applications of the studied nanocomposites. An important problem in this case is the determination of the mechanisms of chromium adhesion to the chemically inert surface of MWCNTs.
A promising method of studying the interface between the MWCNT surface and the coating layer is ultra-soft X-ray spectroscopy in the NEXAFS 1s carbon ionization threshold region. However, there are practically no publications on such studies for chromium compounds due to the superposition of the structure of NEXAFS Cr2p absorption spectra on the NEXAFS C1s ionization threshold region. In the present paper, nanocomposites were studied by the total electron yield method using the unique technique of suppressing and measuring the contribution of multiple orders near the C1s absorption edge.
The studies of the nanocomposite (pyrolytic Cr)/MWCNT performed by NEXAFS and XPS methods showed: (i) the initial MWCNT features are preserved in the composite spectrum; (ii) there is no signifi cant destruction of the outer layers of MWCNTs; (iii) the interface between the MWCNT and the pyrolytic chromium coating is a multilayer structure. This structure includes the outer surface of the MWCNT, the atoms of which form С–О and C–Cr bonds with the pyrolytic chromium coating, chromium carbide monolayer, and the chromium oxide (Cr2O3) coating layer. The effective thickness of the chromium
oxide and chromium carbide coating layers is 1.5 and 0.3 nm respectively, were determined for the studied samples.

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