Structure and electronic properties of fluorographene and fluorographite crystals

The paper presents the study of the structure and electronic properties of two-dimensional and three-dimensional crystals composed of monolayers of graphene polymorphs L$_6$, L$_{4-8}$, L$_{3-12}$, L$_{4-6-12}$, L$_{5-7}$ functionalized by fluorine atoms with various types of attachment of fluorine atoms. It reveals that the interlayer distances in the studied crystals vary within a wide range from 4,73 to 5,96 Å and volumetric densities vary from 2,43 to 3,98 g/cm$^3$. The value of the band gap in three-dimensional fluorographite crystals is on average 0,4 eV less than the band gap in the corresponding two-dimensional fluorographenes. The studied three-dimensional structures demonstrated a pattern: with an increase in the interlayer distance, the energy of the interlayer interaction decreases, and the volumetric density increases. The band gap of the fluorographenes and fluorographites decreases with an increase of sublimation energy. The paper establishes a correlation between the degree of C-C bond length variation of and the presence or absence of repulsive flagpole forces between the attached fluorine atoms. It proves that during functionalization, the values of the average C-C bond length increase for monolayers L$_6$, L$_{4-8}$, L$_{3-12}$, L$_{4-6-12}$ and L$_{5-7}$. The values of the average lengths of C-C bonds practically do not change during the formation of fluorographite from fluorographene. The variation of C-C bond lengths in fluorographites is minimal for F-L$_6$ T1 and equal to 0,2 %, while the maximum is observed for F-L$_{4-6-12}$ T1, which is 10,7 %.