Revisiting thin film of glassy carbon

Abstract

Glassy carbon (GC) is a chemically stable form of fully $s{p}^{2}$-bonded carbon with locally ordered domains. GC is the intermediate material between graphite and diamond combining various properties such as high temperature resistance, hardness, good electrical conductivity, low density, low gases and liquids permeability, and excellent resistance to a wide range of aggressive chemical environments. These characteristics make it a very promising material for many applications, but unfortunately it is not widely used because of the high temperatures required for its synthesis. In this work, synthesis of glassy carbon thin films by means of laser ablation of carbon targets under vacuum or in gaseous helium, followed by a nanosecond laser irradiation of the deposited films, is presented. In particular, it is demonstrated that the amorphous structure of a thin film can be efficiently modified to the one of glassy carbon film by nanosecond UV laser irradiation. This method is valuable to prepare thin films similar to commercial glassy carbon with a completely different route which does not require the application of temperature beyond $1000{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ which is not compatible with the silicon substrate for example. This opens for glassy carbon the way to microengineering applications (mechanics, electronics,$\ensuremath{\cdots}$). Particular attention is paid to characterize the vitreous carbon. In the literature, the vitreous nature of carbon layers is often highlighted on the basis of Raman spectroscopy measurements. However, as the Raman spectrum of glassy carbon is similar to that of pyrocarbon, multiwall carbon nanotubes, or functional graphene, this technique is not sufficient to safely characterize a carbonaceous material with a high degree of allotropy. To clear up any doubts, additional characterization methods, such as x-ray spectroscopy, transmission electron microscopy, and Rutherford backscattering spectrometry, are discussed here.