CFx thin solid films deposited by high power impulse magnetron sputtering: Synthesis and characterization

Abstract

atmosphere. The fluorine content of the films was controlled by varying the CF 4 partial pressure from 0 mPa to 110 mPa at a constant deposition pressure of 400 mPa and a substrate temperature of 110 ºC. The films were characterized regarding their composition, chemical bonding and microstructure as well as mechanical properties by applying elastic recoil detection analysis, Xray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, and nanoindentation. First-principles calculations were carried out to predict and explain Fcontaining carbon thin film synthesis and properties. By geometry optimizations and cohesive energy calculations the relative stability of precursor species including C 2 , F 2 and radicals, resulting from dissociation of CF 4 , were established. Furthermore, structural defects, arising from the incorporation of F atoms in a graphene-like network, were evaluated. All as-deposited CF x films are amorphous. Results from X-ray photoelectron spectroscopy and Raman spectroscopy indicate a graphitic nature of CF x films with x ≤ 0.23 and a polymeric structure for films with x  0.26. Nanoindentation reveals hardnesses between ~1 GPa and ~16 GPa and an elastic recovery of up to 98 %.

CF : A first-principles study of structural patterns arising during synthetic growth

“…As reported in our previous work, the precursors with major impact during magnetron sputtered deposition of CF x films (in CF 4 /Ar atmosphere) are the CF, and the CF 2 radicals, the C 2 dimers, and to a lesser extent, the free C and F atoms, and the CF 3 radicals [18].…”

“…In contrast to all the patterns A, B, and C which, as certified by cohesive energy gains ΔE coh/at in the range of ~0.2 -0.4 eV ( Table 1 but it is also below 0.1 eV/at and thus closer to the thermal energies ~0.04 eV at temperatures (100 -200 °C) typical for the CF x growth environment [18].…”

“…1f). The size of each model system employed here was chosen based on our experience in systematic studies of defects in graphene-like networks [4,6], including in CF x [18] and was equal or larger than was used by others for similar material systems and properties addressed at a similar level of theory [31,32]. In contrast to what happens in other carbon-based compounds where the dopant element differs less radically from carbon in its bonding properties (e.g.,…”

“…This cohesive energy gain is only slightly lower than the cohesive energy gain of 0.405 eV/at associated to large N-member ring defects suggesting a comparable prevalence of these two types of defects. The one-dimensional chains resulting from the branching defect, besides being unique to CF x (when compared to CN x , CP x , and CS x ), also bear resemblance with short polymeric chains [33] expected to play a major role in softer CF x films with polymeric character featuring F concentrations above ~25 at.% [18]. However, even if more F atoms are incorporated in the one-dimensional chains resulting from branching, for stochastic reasons it can not be expected that the chain will exhibit any strictly repeating C n F m -unit-cell (where m, n are integers) like in conventional polymers [33].…”

“…In order to understand and control the process of F-incorporation in CF x films, we carried out SGC calculations to predict and explain the relative stability of precursor species resulting from dissociation of the CF 4 molecules used as a fluorine source. Also some typical structural defects resulting from the incorporation of F atoms in a perfect hexagonal carbon (graphene-like) network were assessed [18]. Such defects clearly distinguish CF x from other carbonbased nanostructured compounds such as CN x [4] and CP x [6].…”