Spontaneous synthesis of carbon nanowalls, nanotubes and nanotips using high flux density plasmas

Abstract

We have investigated the formation of various carbon nanostructures using extreme plasma fluxes up to four orders of magnitude larger than in conventional plasma-enhanced chemical vapor deposition processing. Carbon nanowalls, multi-wall nanotubes, spherical nanoparticles and nanotips are among the structures detected with electron microscopy methods. Precursor injection or surface pretreatment were not required for the synthesis of the nanostructures. Preliminary experiments with varied plasma composition, sample bias and surface temperature have demonstrated the potential for optimizing the growth of the nanostructures in the current experimental setup .

Fast nanostructured carbon microparticle synthesis by one-step high-flux plasma processing

“…This is in sharp contrast to the chemical synthesis routes, which often require several processing steps and the inevitable use of expensive chemical precursors [8][9][10]12,16]. Thirdly, the reported carbon microparticle processing rate is very high, up to 0.15 μm/s [31], which results in the full coverage of the sample surface by microparticles within the timeframe of a hundred seconds, which is a critical advantage in terms of the scalability of the process.…”

“…Although this setup is not optimized for industrial processing, is a convenient setup due to its extensive diagnostic suite and well characterized plasma. Previous work using this machine led to the understanding that the basic requisite of microparticles synthesis is a very high plasma density (>10 20 m -3 ) [31]. This extreme condition makes the plasma opaque for hydrocarbon molecules that are released by chemically sputtering from the graphite sample surface, i.e.…”

“…This induced recycling of hydrocarbon molecules leads 4 to reorganization of the plasma-exposed surface, and eventually to the appearance of microparticles on the surface. Yet, the mechanism that led to nucleation and its conditions remained unclear [31,37] and have not been thoroughly studied in these high density/flux conditions. Moreover, properties of the effective surface area and the pore size distribution, which is important for future applications, are unknown.…”

“…In these devices the particles are formed due to interaction of the plasma with the graphite tokamak wall and can pose safety hazards in terms of radioactivity and chemical reactivity [29,30]. Experiments on this type of dust formation have been conducted in linear plasma generators [31,32], that can simulate the extreme hydrogen (and isotopes) plasma conditions (ion flux of ~10 24 m -2 s -1 ) close to the tokamak walls.…”

“…i.e., no graphite surface pretreatment or chemical precursor gas injection is needed [31], taking advantage of natural hydrocarbon release. This is in sharp contrast to the chemical synthesis routes, which often require several processing steps and the inevitable use of expensive chemical precursors [8][9][10]12,16].…”