WP 4

Advanced quality control


M 4.1 Description of the effects of fluorination conditions on the composition and structure of graphene-containing materials

WP4 is aimed at successful fulfillment of WP1, WP2, WP3. Special achievements within this WP: we were able to visualize basal plane patterns of fluorinated graphite as well as the bilayer structure of IFGC (intercalated fluorinated graphite compounds).

The structure of room-temperature produced intercalated graphite fluoride compounds has been elucidated by means of solid-state NMR and DFT calculations. Based on the observations in the present study, the following conclusions are drawn regarding: (a) the character of the guest −host matrix interactions, (b) the structure of the carbon matrix, and (c) fluorine distribution in the layer. The interaction between the intercalated acetonitrile and the C2Fx matrix has been found to be of van der Waals nature. It has been confirmed that the room-temperature synthesis of graphite fluoride results in the planar configuration of the carbon sheets because only carbon atoms in sp2 hybridization (i.e., graphitic carbon) and carbon atoms bonded to fluorine have been detected in the 13C NMR spectra. Moreover, no signature of the presence of the pristine graphite sheets has been found, demonstrating that all carbon sheets were fluorinated. However the presence of graphite-like domains has been proven in the material with the lowest fluorination degree. A combination of 19F solid-state NMR and DFT calculations of 19F absolute shielding allowed classifying and quantifying the structural motives obtained upon fluorination. Thus, it has been established that all possible fluorination motives (including CF chains of both zigzag and armchair configurations as well as fluorinated cyclohexane rings and isolated CF pairs) may exist in the materials.

M 4.2: Structural and magnetic quality of the fluorographite inclusion compounds

A series of layered inclusion compounds based on fluorinated graphite C2F (x) (xa parts per thousand currency sign1) was obtained by a room temperature synthesis. Inclusion compounds (intercalates) of fluorinated graphite matrix were n-hexane and dichloromethane, i.e., organic guest molecules that differ in size and symmetry. The changes in C2F (x) stoichiometry are shown to have a decisive effect on magnetic properties of produced complexes. The spin concentration decreases with the increase of fluorine content in fluorocarbon matrix. All samples have groups of correlated spins; at the temperatures 1.75-5 K nonlinear magnetization is observed, indicating a high-spin state. Application of the Langevin formula shows that the clusters consist of 10-20 interacting spins.

Intercalated compound of graphite fluoride with n-heptane has been synthesized at room temperature using a multi-stage process including fluorination by a gaseous BrF3 and a set of intercalant exchange reactions. The guest molecules interact with the graphite fluoride layers through the van der Waals forces. Since the distance between the filled layers is 1.04 nm and the unfilled layers are separated by similar to 0.60 nm, the obtained compound can be considered as a stack of the fluorinated graphenes. These fluorinated graphenes are large in area making it possible to study local destruction of the a conjugated system on the basal plane. It was shown that fluorine atoms form short chains, while non-fluorinated sp(2) carbon atoms are organized in very narrow ribbons and aromatic areas with a size smaller than 3 nm. These pi electron nanochains and nanoislands preserved after the fluorination process are likely responsible for the value of the energy gap of the compound of similar to 2.5 eV. Variation in the size and the shape of pi electron regions within the fluorinated graphene layers could be a way for tuning the electronic and optical characteristics of the graphene-based materials.

We developed an accurate measurement and a quantitative analysis of electron-beam-induced displacements of carbon atoms in single-layer graphene.We directly measure the atomic displacement(‘‘knock-on’’) cross section by counting the lost atoms as a function of the electron-beam energy and applied dose. Our analysis shows that a static lattice approximation is not sufficient to describe knock-on damage in this material, while a very good agreement between calculated and experimental cross sections is obtained if lattice vibrations are taken into account. While the results on graphene will be important for HRTEM studies of this material and related ones (especially carbon nanotubes), the generalized insights to radiation damage mechanisms should be more generally applicable to any material where knock-on damage is important.