Carbon materials are of outstanding interest for use in energy sources. One of the latest achievements in improving their specific characteristics is the doping of carbon materials with various heteroatoms. However, the mechanisms that lead to improved performance remain unexplored. In this study, we investigated the influence of structural defects and incorporated heteroatoms on the oxygen reduction reaction (ORR) of highly oriented pyrolytic graphite and carbon nanowalls. Controllable modification in DC plasma in an atmosphere of nitrogen, oxygen and air was used for the incorporation of heteroatoms. We found that treatment in the air atmosphere leads to the formation of most active sites due to incorporation of heteroatoms and partial amorphization of material surface. The DFT calculations reveal these active sites can't be amplified by substitution to nitrogen atom due to insignificant sorption energy difference of *OOH group compared with undoped carbon. Existed material's structural defects and appeared after the treatment also make a significant contribution to the obtained ORR characteristics. Plasma-assisted treatment under air conditions can be used for carbon nanomaterials modification for ORR application.

Методом химического осаждения из газовой фазы в разряде постоянного тока были получены пленки углеродных наностенок разной толщины. Впервые проведено измерение теплопроводности полученных структур с использованием метода третьей гармоники (3-омега) в диапазоне температур от 280 до 310 К. Показана зависимость теплопроводности стенок от их толщины. При толщине пленки 1 мкм значение теплопроводности углеродных наностенок составляет 6.9 Вт м-1 К-1. Полученные результаты необходимы для конструирования электрооптических приборов на основе углеродных наностенок.

Carbon nanowall films with different thicknesses have been obtained by chemical deposition from a gas phase in a dc discharge. The thermal conductivity of the resulting structures has been measured for the first time using the 3ω method in the temperature range of 280–310 K. It has been shown that the thermal conductivity of walls depends on their thickness. The thermal conductivity of 1-μm carbon nanowalls is 6.9 W m –1 K –1 . The results obtained in this work are necessary to design electro-optical devices based on carbon nanowalls.

Nonlinear electrical properties, such as negative differential resistance (NDR), are essential in numerous electrical circuits, including memristors. Several physical origins have been proposed to lead to the NDR phenomena in semiconductor devices in the last more than half a century. Here, we report NDR behavior formation in randomly oriented graphene-like nanostructures up to 37 K and high on-current density up to 10^5 A/cm^2. Our modeling of the current-voltage characteristics, including the self-heating effects, suggests that strong temperature dependence of the low-bias resistance is responsible for the nonlinear electrical behavior. Our findings open opportunities for the practical realization of the on-demand NDR behavior in nanostructures of 2D and 3D material-based devices via heat management in the conducting films and the underlying substrates.

We report an approach to stabilize the electrochemical performance of silicon- and germanium-based thin film anodes by using carbon nanowall matrices.

We observed that thermally treated carbon nanowalls serve efficiently as templates governing the formation of quasiperiodic patterns for nanoparticles deposited. Here we report self-assembled quasi-regular structures of diverse nanoparticles on a freestanding multilayer graphene-like material, i.e. carbon nanowalls. Metallic (Ag, Al, Co, Mo, Ni, and Ta) and semiconductor (Si) nanoparticles form coaxial polygonal closed loop structures or parallel equidistant rows, which evolve upon further deposition into bead-like structures and, finally, into nanowires. Weakly bonded nanoparticles decorate atomic steps, wrinkles and other extended defects on the carbon nanowalls as a result of anisotropic diffusion of atoms or clusters along the hexagonal sp(2)-carbon network followed by their aggregation and agglomeration. The decorated carbon nanowalls are found to be promising materials for surface enhanced Raman scattering (SERS) analysis.

The optical properties of carbon nanowall (CNW) films in the visible range have been studied and reported for the first time. Depending on the film structure, ultra-low total reflectance up to 0.13% can be reached, which makes the CNW films a promising candidate for the black body-like coating, and thus for a wide range of applications as a light absorber. We have estimated important trends in the optical property variation from sample to sample, and identified the presence of edge states and domain boundaries in carbon nanowalls as well as the film mass density variation as the key factors. Also we demonstrated that at much lower film thickness and density than for a carbon nanotube forest the CNWs yield one order higher specific light absorption.

Catalyst-free growth of nanocrystalline carbon films on silicon substrates under direct current glow discharge in a mixture of hydrogen and methane was studied by scanning and transmission electron microscopy, Raman spectroscopy, as well as X-ray photoelectron and near edge X-ray absorption fine structure spectroscopy (BESSY II, Berlin). The in-time development of the film structure on a carbided silicon substrate includes the formation of diamond-like particles, ultra-thin graphite flakes parallel to the surface, carbon nanowalls nucleated on the stacked flakes and their growth accompanied by a permanent decrease of the structural defect density, and finally nanotube nucleation at the nanowall edges. Based on the observation of the carbon nanotube/nanowall linear size variation in time and using the calculated binding energies and the diffusion thresholds obtained from the literature, we propose that direct attachment of the CH3 radicals to the carbon nanowall edge is the predominant mechanism and the rate-limiting step of its growth, whereas carbon nanotube growth is controlled by radicals diffusing along its outer surface.

Crystalline nickel and copper possess bcc lattices, the parameters of which are 1.2 and 1.35% smaller than that of diamond. Heteroepitaxial Ni and Cu films have been grown by magnetron sputtering on polished and then thermally annealed and etched {100} and {110} surfaces of natural diamond. The films exhibit island morphology and possess a highly perfect crystalline structure.

Reference EPFL-ARTICLE-184204doi:10.1038/490331aView record in Web of Science Record created on 2013-02-27, modified on 2017-07-13

Ir layers were deposited on single-crystal diamond using magnetron sputtering at substrate temperatures ranging from 830 to 1150 °C. The grown films have high adhesion to diamond and a low surface roughnessRq= 4–6 nm according to the AFM measurements. Crystalline perfection of Ir layers was investigated using x-ray diffraction and heteroepitaxial growth of Ir on diamond was confirmed. Because the lattice parameters of Ir and diamond are significantly different (7.65%) and because the deposition temperature of Ir is low in comparison with its melting point (2443 °C), diffraction reflections of the films are similar to analogous reflections of diamond, but wider. The films consist of elongated crystallites of length 10–100 nm. By broadening the reciprocal lattice points, we conclude that the level of microstresses in the Ir films increases as the substrate temperature during deposition of Ir films on the (0 0 1) diamond substrate increases, and that the level of microstresses decreases for the films on the (0 1 1) substrate. Simultaneously, the misorientation of Ir crystallites on the (0 1 1) substrate also decreases with increasing temperature.

New method for nucleation of different nanocrystalline carbon films upon monocrystalline Si substrate was proposed. The process is based on a combination of microwave and radio frequency plasma assisted chemical vapor deposition methods. Potential of the method for nucleation was demonstrated by deposition of nanocrystalline diamond film in pure microwave plasma in one process, immediately after "seeding" procedure. The method was also used for growth of nanocrystalline graphite (NCG) films, which are currently under intensive investigation due to their exceptional electronic properties, particularly fine electron emission characteristics. Deposited NCG films have demonstrated remarkable electron field emission properties having current density of up to 10 A/cm2. The films have also possessed good adhesion to silicon substrate. Carbon films and nucleation layer were characterized by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy.

A new method is proposed for the synthesis of nanostructured zinc oxide (ZnO) films in propane that is used as a source of reactive carbon and carrier gas. The growth of films consisting of columnar ZnO structures under these conditions takes place at a relatively low temperature (about 630°C) of the evaporator.

The morphology of a nanocrystalline graphite field-emission cathode based on a polycrystalline diamond grid has been studied in order to elucidate the nature of electron-emitting centers. Ribbonlike and cylindrical carbon nanostructures have been found on the emitter surface, which possess greater aspect ratios as compared to those of graphite microedges forming the cathode surface.

Electron field emission properties of nanocrystalline graphite (NCG) films, grown by plasma enhanced chemical vapor deposition method on conductive Si substrates without using of any catalyst, were investigated. Current-voltage characteristics were measured in pulse-periodic regime. It was shown that grown NCG films can operate at field emission current density up to 10 A/cm(2). It was found that NCG films contain, along with the normally oriented to the substrate nanoflakes, carbon whiskers consisted of graphene nanoribbons and nanowires with length considerably higher than of the nanoflakes.

New method of Si wires synthesis by magnetron sputtering of solid target as a Si source is described. This method is simple, safe and cheaper in comparison with Chemical Vapor Deposition (CVD). Influence of silicon atom flow rates (target sputtering rate) and substrate temperature on the growth of different Si structures were studied. It was found that Si wires have different morphology, which depends on the Si flux and substrate temperature.

Boron doped polycrystalline diamond films were grown using MW PE CVD method. Optical emission spectra (OES) of MW-plasma in the region from 200 nm to 800 nm during boron doped polycrystalline diamond films growth were in situ investigated. Raman spectroscopy method was used for morphology investigation of grown polycrystalline diamond films. Also, absorption spectroscopy method was used for optical properties investigation of all grown films.

Nanocrystalline films of zinc oxide deposited by rf magnetron sputtering are used as a working material of UV detectors. The photoelectric performance of UV detectors versus ZnO deposition conditions is studied. The influence of the surface topology of the UV detectors on their efficiency is examined with an atomic force microscope.