We report a direct and fast synthesis route to grow boron-carbon-nitrogen layers based on microwave-assisted plasma enhanced chemical vapour deposition (PECVD) by using methylamine borane as a single source molecular precursor. This easy and inexpensive method allows controlled and reproducible growth of B-C-N layers onto thin Cu foils. Their morphological, structural, chemical, optical and transport properties have been thoroughly characterized by a number of different microscopies, transport and spectroscopic techniques. Though disorder and segregation into C-rich and h-BN-rich domains have been observed in ultrathin flat few layers, high doping levels have been reached, inducing strong modifications of the electronic, optical and transport properties of C-rich and h-BN-rich phases. This synthesis procedure can open new routes towards the achievement of homogeneous highly mixed ternary B-C-N phases.

Ultrathin B-C-N layers grown on Ti substrates are investigated as efficient anodes for electrochemical water splitting. A fast and direct synthetic route has been used, based on plasma-enhanced chemical vapour deposition with Methylamine Borane as a singlesource molecular precursor. The effect of growth time on the morphological and structural properties and on the chemical composition of the layers has been investigated by scanning electron microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy and transmission electron microscopy coupled with electron energy loss spectroscopy. Flat B-C-N layers on top of an amorphous titanium oxide layer present at the Ti surface have been obtained by using short growth times, while longer growth times give rise to core/ shell structures formed by vertical wall B-C-N layers and titanium carbonitride phases. The obtained layers present enhanced electrocatalytic activity for the oxygen evolution reaction in alkaline aqueous solutions. Moreover, owing to their ultrathin nature, the B-C-N layers preserve the photocurrents of the underlying titanium oxide layer, acting as transparent electrodes with

Heterostructures formed by ultrathin borocarbonitride (BCN) layers grown on TiO2 nanoribbons were investigated as photoanodes for photoelectrochemical water splitting. TiO2 nanoribbons were obtained by thermal oxidation of TiS3 samples. Then, BCN layers were successfully grown by plasma enhanced chemical vapour deposition. The structure and the chemical composition of the starting TiS3, the TiO2 nanoribbons and the TiO2-BCN heterostructures were investigated by Raman spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. Diffuse reflectance measurements showed a change in the gap from 0.94 eV (TiS3) to 3.3 eV (TiO2) after the thermal annealing of the starting material. Morphological characterizations, such as scanning electron microscopy and optical microscopy, show that the morphology of the samples was not affected by the change in the structure and composition. The obtained TiO2-BCN heterostructures were measured in a photoelectrochemical cell, showing an enhanced density of current under dark conditions and higher photocurrents when compared with TiO2. Finally, using electrochemical impedance spectroscopy, the flat band potential was determined to be equal in both TiO2 and TiO2-BCN samples, whereas the product of the dielectric constant and the density of donors was higher for TiO2-BCN.

Tuning the electrocatalytic properties of MoS 2 layers can be achieved through different paths, such as reducing their thickness, creating edges in the MoS 2 flakes, and introducing S-vacancies. We combine these three approaches by growing MoS 2 electrodes by using a special salt-assisted chemical vapor deposition (CVD) method. This procedure allows the growth of ultrathin MoS 2 nanocrystals (1−3 layers thick and a few nanometers wide), as evidenced by atomic force microscopy and scanning tunneling microscopy. This morphology of the MoS 2 layers at the nanoscale induces some specific features in the Raman and photoluminescence spectra compared to exfoliated or microcrystalline MoS 2 layers. Moreover, the S-vacancy content in the layers can be tuned during CVD growth by using Ar/H 2 mixtures as a carrier gas. Detailed optical microtransmittance and microreflectance spectroscopies, micro-Raman, and X-ray photoelectron spectroscopy measurements with sub-millimeter spatial resolution show that the obtained samples present an excellent homogeneity over areas in the cm 2 range. The electrochemical and photoelectrochemical properties of these MoS 2 layers were investigated using electrodes with relatively large areas (0.8 cm 2 ). The prepared MoS 2 cathodes show outstanding Faradaic efficiencies as well as long-term stability in acidic solutions. In addition, we demonstrate that there is an optimal number of Svacancies to improve the electrochemical and photoelectrochemical performances of MoS 2 .

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