Anisotropy of Chemical Bonding in Semifluorinated Graphite C₂F Revealed with Angle-Resolved X-ray Absorption Spectroscopy

Abstract

Highly oriented pyrolytic graphite characterized by a low misorientation of crystallites is fluorinated using a gaseous mixture of BrF(3) with Br(2) at room temperature. The golden-colored product, easily delaminating into micrometer-size transparent flakes, is an intercalation compound where Br(2) molecules are hosted between fluorinated graphene layers of approximate C(2)F composition. To unravel the chemical bonding in semifluorinated graphite, we apply angle-resolved near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and quantum-chemical modeling. The strong angular dependence of the CK and FK edge NEXAFS spectra on the incident radiation indicates that room-temperature-produced graphite fluoride is a highly anisotropic material, where half of the carbon atoms are covalently bonded with fluorine, while the rest of the carbon atoms preserve π electrons. Comparison of the experimental CK edge spectrum with theoretical spectra plotted for C(2)F models reveals that fluorine atoms are more likely to form chains. This conclusion agrees with the atomic force microscopy observation of a chain-like pattern on the surface of graphite fluoride layers.

A backside fluorine-functionalized graphene layer for ammonia detection

“…The simulation of X-ray emission and absorption spectra of fluorinated graphite C 2 F obtained under the same conditions as the original samples used in this study revealed that fluorine atoms prefer to form chains on the basal plane sequentially linking with the opposite sides. 27,34 Removal of fluorine atoms from one side leaves three backside fluorine atoms in the meta-position of two adjacent hexagons as presented in the C 73 F 3 H 21 model. The relative arrangement of five fluorine atoms in the C 73 F 5 H 21 model was set to occupy the para-or meta-positions in relation to each other.…”

“…26 As the result of covalent attachment of fluorine atoms to both sides of a graphene sheet, the plate thickness increased by at least two times. 27 For the sensor preparation, the plate was split into flakes with a typical size of about 2.5 Â 5 mm 2 . Optical microscopy analysis showed that the detached flakes have multilayered structure and uniform bronze coloring (Fig.…”

Revealing distortion of carbon nanotube walls via angle-resolved X-ray spectroscopy

“…The sp 2 -hybridized carbon materials possess anisotropy of chemical bonding that results in different probability of an X-ray transition depending on symmetry (p or s) of the initial (XFS) or final (NEXAFS) state and orientation of these states with respect to the polarization of the emitted or incident beam. Owing this, an angular variation of the spectral components was observed for graphite [23,24], functionalized graphite and graphene [25,26], and multi-walled CNTs [27,28]. A plotting of the experimentally derived intensity ratios of p and s (or p* and s*) components versus takeoff (or incidence) angle of the X-ray beam allows numerically evaluating the order of graphite crystallites [29] and CNTs [30e32] in samples and the height of out-of-plane graphene corrugation after sample transferring to a substrate [33].…”

Extra electronic outer-shell peculiarities accessible under a joint XPS and DFT study

“…DFT calculations have found this structure to be energetically most favourable, 20 whereas experimental data indicate another C 2 F configuration. 21 Moreover, the common feature of each phase is the presence of fluorinated and unfluorinated carbons, which determines the DOS structure in similar energy regions. The empty space of 40 Bohr in the Z-direction was accepted to neglect the interaction between the slabs.…”