Revisiting thin film of glassy carbon

Abstract

Glassy carbon (GC) is a chemically stable form of fully sp 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 o C which is not compatible with the silicon substrate for example. This opens for glassy carbon the way to microengineering applications (mechanics, electronics.. .). A particular attention is paid to characterize the vitreous carbon. In the literature, the vitreous nature of a 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 pyro-carbon, 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.

Preparation and Carbonization of Glucose and Pyromellitic Dianhydride Crosslinked Polymers

“…The D-band at c.a. 1620 cm −1 , attributed to a maximum in the vibrational density of states, is absent due to the very small graphitic domains as usually found in defective graphitic carbons [44,48]. Furthermore, a broad low frequency shoulder of the D-band observed at c.a.…”

Vitreous Carbon, Geometry and Topology: A Hollistic Approach

“…Raman features are compatible with a 3D amorphous structure in the as-deposited film. After several laser shots, the film presents the features of GLC (corroborated by other spectroscopic tools, see below): (a) un-irradiated carbon; (b) 5 shots; (c) 10 shots; (d) 100 shots; (e) 200 shots; and (f) 1000 shots [ 46 ].…”

“…Details are given elsewhere [ 46 ]. Carbon thin films (in the broadest sense a film of thickness less than 100 nm) were deposited by pulsed laser deposition ( PLD ) at room temperature by means of a pulsed KrF excimer laser (Lambda Physik; = 248 nm; pulse duration = 20 ns; and repetition rate f = 10 Hz).…”

“…Figure 5 summarises all the features that corroborate the thin film GLC structure. To guide the eye, the GLC films are compared with a commercial GLC sample obtained by high-temperature pyrolysis (see details in [ 46 ]). The presence of precursors (see XPS spectra) in the as-deposited sample ensures a non-graphitisation route during laser annealing.…”

“…( F ) The TEM observation showing the open structure with a “spaghetti tangle” in GLC (c). The figures are taken from [ 46 ]. Reproduced with permission from Diaf, Phys.…”