Currently, X-ray photoelectron spectroscopy (XPS) is widely used to characterize the nanostructured material surface. The ability to determine the atom distribution and chemical state with depth without the sample destruction is important for studying the internal structure of the coating layer several nanometers thick, and makes XPS the preferable tool for the non-destructive testing of nanostructured systems. In this work, ultra-soft X-ray spectroscopy methods are used to study hidden layers and interfaces of pyrolytic tungsten carbide nanoscale coatings on the multi-walled carbon nanotube (MWCNT) surfaces. XPS measurements were performed using laboratory spectrometers with sample charge compensation, and Near Edge X-ray Absorption Fine Structure (NEXAFS) studies using the Russian–German dipole beamline (RGBL) synchrotron radiation at BESSY-II. The studied samples were tested by scanning and transmission electron microscopy, X-ray diffractometry, Raman scattering and NEXAFS spectroscopy. It was shown that the interface between MWCNT and the pyrolytic coating of tungsten carbide has a three-layer structure: (i) an interface layer consisting of the outer graphene layer carbon atoms, forming bonds with oxygen atoms from the oxides adsorbed on the MWCNT surface, and tungsten atoms from the coating layer; (ii) a non-stoichiometric tungsten carbide WC_1-x nanoscale particles layer; (iii) a 3.3 nm thick non-stoichiometric tungsten oxide WO_3-x layer on the WC_1-x/MWCNT nanocomposite outer surface, formed in air. The tungsten carbide nanosized particle’s adhesion to the nanotube outer surface is ensured by the formation of a chemical bond between the carbon atoms from the MWCNT upper layer and the tungsten atoms from the coating layer.

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. REFERENCES