Room-temperature graphitization in a solid-phase reaction

Abstract

The spontaneous graphitization for C films containing Ni NPs was attributed mainly to the increased solubility for metallic Ni NPs, and was enhanced at the deposition temperature of 50 °C.

One-step synthesis of spontaneously graphitized nanocarbon using cobalt-nanoparticles

“…Although the distinct 2D peak was not observable in the Raman spectrum of the background-like region, the Raman spectrum for this region was different from the amorphous carbon film [26]. Also, the spectrum for the background-like region was quite similar to the spectra reported previously for partially graphitized samples [16,17]. The intensity ratios of D and G peaks (I D /I G ) were calculated to be ~ 0.79 and 0.92 for the flake-like and background-like regions, respectively.…”

“…The graphitization mechanism will be discussed later in detail. The present observations suggest that the spontaneous graphitization of a-C catalyzed by Co NPs occurs even at RT, similar to the case of Ni NPs [17].…”

“…Recently, Asaka et al have demonstrated the spontaneous local graphitization at RT for an amorphous carbon film deposited onto NaCl substrates with a pre-deposition of Ni NPs [16]. In our previous paper also, we have demonstrated the local graphitization of amorphous carbon films containing Ni NPs which were deposited on insulator substrates by a simple one-step magnetron sputtering of a C-Ni target at RT [17]. So, the catalyst in NP form must be promising for the low-temperature graphitization in the solid-phase reaction.…”

“…The mechanism of the graphitization of NPs-carbon composite films at RT and the negative effect of the oxide in the graphitization were discussed elsewhere for Ni NPs [17]. In brief, with a decrease in particle size, in general, the melting point decreases while the carbon solubility increases [29][30][31].…”

“…In brief, with a decrease in particle size, in general, the melting point decreases while the carbon solubility increases [29][30][31]. For NPs-carbon composite films, due to the decrease in melting point, the situation of C atoms would be similar to that at high temperatures even at RT, namely C atoms readily displace to form sp 2 bonding [16,17]. In the film deposition process, agglomeration of NPs would occur, and the solubility of C would slightly decrease with increasing NP size in the agglomeration process, yielding a graphitized layer behind the trace of moving agglomerated NPs.…”