Influence of doping (Ti, V, Zr, W) and annealing on the sp2 carbon structure of amorphous carbon films

Abstract

The influence of the transition metal (Ti, V, Zr, W) doping on the carbon matrix nanostructuring during the thin film growth and subsequent annealing is investigated. Pure and metal-doped amorphous carbon films (a-C, a-C:Me) were deposited at room temperature by non-reactive magnetron sputtering. The carbon structure of as-deposited and post-annealed (up to 1300 K) samples was analyzed by X-ray diffraction (XRD) and Raman spectroscopy.The existence of graphene-like regions in a-C is concluded from a (10) diffraction peak. A comparison of the XRD and Raman results suggests that XRD probes only the small amount of 2-3 nm large graphene-like regions, whereas the majority of the sp 2 phase is present in smaller distorted aromatic clusters which are probed only by Raman spectroscopy. Annealing leads to an increase of the graphene size and the aromatic cluster size. During the carbon film growth the addition of metals enhances ordering of sp 2 carbon in sixfold aromatic clusters compared to a-C, Ti and Zr showing the strongest effect, W the lowest. This order qualitatively corresponds with the catalytic activity of the respective carbides found during graphitization of carbide-doped graphites published in the literature. With annealing, carbide crystallite formation and growth occurs in a-C:Me films, which destroys the initial carbon structure, reduces the size of the initially formed aromatic clusters and the differences in carbon structure introduced by different dopants. For high annealing temperatures the carbon structure of a-C:Me films is similar to that of a-C, and is determined only by the annealing temperature.2

Erosion of tungsten-doped amorphous carbon films in oxygen plasma

“…A quantitative analysis of the raw data is at present not possible because not only the optical constants but also the layer structure of the surface layer of the films change during the erosion and the corresponding film thicknesses and the optical constants of the different layers are presently unknown. Furthermore, amorphous carbon material prepared by magnetron sputtering of a graphite target consists of nano-graphite particles dispersed in an amorphous carbon matrix [12,25,26], and therefore it is strongly absorbing at the laser wavelength of 623.8 nm. As a consequence, time-resolved erosion rates could not be deduced from real-time ellipsometry measurements.…”

Retention and enrichment of tungsten-containing carbon films under deuterium beam impact

“…Since the specimens were heat treated at 1300 K, a-C and a-C:W have the same C structure [40]. Therefore, the influence of W is studied by comparing a-C:W with a-C and the influence of the C material is studied by comparing a-C with pyrolytic graphite.…”

Characterization of nano-structured W-, Ti-, V-, and Zr-doped carbon films

“…The analysis of the Raman spectra regarding the D to G peak intensity ratio indicates that small aromatic areas are present in the as-deposited films. Their size increases with annealing [48]. In addition, diffraction from graphene-like areas is observed with XRD (graphene peaks).…”

“…The spectra were recorded between 900 -1900 cm -1 with a Renishaw 1000 microscope using an argon ion laser at 514.5 nm. The resulting peak structures -known as D and G peak [53] -were fitted by an asymmetrical line shape of Breit-Wigner-Fano type [45,48]. The interpretation of the D to G intensity ratio as well as the peak width and shift is accordingly to [53].…”

“…These areas increase also in size with annealing. It is proposed that these graphene-like areas of 2-3 nm size are embedded in a matrix dominated by distorted aromatic ring systems [45,48].…”