Structural and chemical evolution of single-wall carbon nanotubes under atomic and molecular deuterium interaction

Abstract

The interaction of atomic (D) and molecular (D 2 ) deuterium, as present in a (D + D 2 ) gas mixture, with single-wall carbon nanotubes (SWNTs) has been studied by means of a combination of scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The SWNT samples were exposed to the gas mixture, produced by thermal dissociation of D 2 on a hot W filament, its temperature, T W , being kept at 1020 and 1550 K for a deuterium pressure of 0.6 and 60 Pa, respectively. Prolonged interaction of the low-pressure (D + D 2 ) gas mixture produced at T W = 1020 K leads to a conglomeration of the SWNT bundles into larger diameter ropes of square and triangular cross-section, covered by nanoaggregates of graphite material. Both the coalescence of single SWNTs and a massive reconstruction of bundles of SWNTs into a ''coral reef''-like structure were found to occur after prolonged exposure of SWNTs to the high-pressure (D + D 2 ) gas mixture produced at T W = 1550 K. This structure is formed by the encapsulated Fe nanoparticles and deuterocarbon-like species appearing as a result of the deuterium interaction with the SWNT bundles accompanied by partial erosion of the SWNT material. The XPS valence-band spectra disclose electronic features characteristic for a hydrogen-plasma modified multi-wall carbon nanotube (MWNT)-like structure as a result of an intensive (D + D 2 ) induced transformation of the SWNTs into the ''coral reef''-like structure.

Integration of Carbon Nanotubes in an HFCVD Diamond Synthesis Process in a Methane-Rich H2/CH4 Gas Mixture

“…TEM analysis (Figure 7) was performed for the samples shown in Figure 5a,b, i.e., CVD treated at 28.6 vol.% CH 4 for 30 and 150 s (silicon substrates). Figure 7a shows a typical structure of a CNTs bundle containing SWCNTs; the same bundle structure was reported in other works [34,35]. In the sample in Figure 7b, both single nanotubes (Figure 7 (1)) and CNTs bundles (Figure 7 dash line) can be observed, and at 30 s a distinct crystal structure could still be traced in CNTs.…”

“…In the Raman spectra maps (not presented), two typical spectra were observed; the spectrum of an evenly distributed network of carbon nanotubes (Figure 8a), and the spectrum of a high-density agglomerations of nanotubes (Figure 8b). Figure 7a shows a typical structure of a CNTs bundle containing SWCNTs; the same bundle structure was reported in other works [34,35]. In the sample in Figure 7b, both single nanotubes (Figure 7 (1)) and CNTs bundles (Figure 7 dash line) can be observed, and at 30 s a distinct crystal structure could still be traced in CNTs.…”

Pilot Plant Scale Synthesis of CNS: Influence of the Operating Conditions

“…Of these five, the nanostructured carbon materials have sparked an increasing interest for chemists, physicists, and materials scientists worldwide . Because of their unique structural, mechanical, and electronic properties, there are numerous envisioned applications of nanostructured carbons including electrode materials for lithium ion batteries, gas storage media, catalyst supports, adsorbents, and electronic devices. − However, a targeted production of carbon nanospheres (CNSs) is only now starting to achieve a significant research activity. Their high surface chemical activity provided by the unclosed graphitic layers, which provides reactive “dangling bonds”, makes them suitable materials for catalysis and adsorption processes.…”

Hydrogen etching and cutting of multiwall carbon nanotubes

“…When the H dose and H-atom exposure temperature is increased, irreversible structural changes to the CNT structure can begin. 18 For example, Zhang et al 12 observed that when plasma power or H-exposure time was increased, CNTs were cut and etched. Rao et al 19 found that SWCNTs were easily etched by H 2 at 900°C but remained unaffected at 800°C.…”