Role of Nitrogen and Oxygen in Capacitance Formation of Carbon Nanowalls.

Supercapacitors based on carbon nanomaterials are attracting much attention because of their high capacitance enabled by large specific surface area. The introduction of heteroatoms such as N or O enhances the specific capacitance of these materials. However, the mechanisms that lead to the increase in the specific capacitance are not yet well-studied. In this Letter, we demonstrate an effective method for modification of the surface of carbon nanowalls (CNWs) using DC plasma in atmospheres of O2, N2, and their mixture. Processing in the plasma leads to the incorporation of ∼4 atom % nitrogen and ∼10 atom % oxygen atoms. Electrochemical measurements reveal that CNWs functionalized with oxygen groups are characterized by higher capacitance. The specific capacitance for samples with oxygen reaches 8.9 F cm-3 at a scan rate of 20 mV s-1. In contrast, the nitrogen-doped samples demonstrate a specific capacitance of 4.4 F cm-3 at the same scan rate. The mechanism of heteroatom incorporation into the carbon lattice is explained using density functional theory calculations.

Self-assembled nanoparticle patterns on carbon nanowall surfaces.

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.

Carbon nanowalls: the next step for physical manifestation of the black body coating.

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.

Nanocrystalline graphite films nucleation by the radio frequency bias pretreatment.

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.