Tabby graphene: Dimensional magnetic crossover in fluorinated graphite

Abstract

Tabby is a pattern of short irregular stripes, usually related to domestic cats. We have produced Tabby patterns on graphene by attaching fluorine atoms running as monoatomic chains in crystallographic directions. Separated by non-fluorinated sp 2 carbon ribbons, sp 3-hybridized carbon atoms bonded to zigzag fluorine chains produce sp 2-sp 3 interfaces and spin-polarized edge states localized on both sides of the chains. We have compared two kinds of fluorinated graphite samples C2Fx, with x near to 1 and x substantially below 1. The magnetic susceptibility of C2Fx (x < 1) shows a broad maximum and a thermally activated spin gap behaviour that can be understood in a two-leg spin ladder model with ferromagnetic legs and antiferromagnetic rungs; the spin gap constitutes about 450 K. Besides, stable room-temperature ferromagnetism is observed in C2Fx (x < 1) samples: the crossover to a three-dimensional magnetic behaviour is due to the onset of interlayer interactions. Similarly prepared C2Fx (x ≈ 1) samples demonstrate features of two-dimensional magnetism without signs of high-temperature magnetic ordering, but with transition to a superparamagnetic state below 40 K instead. The magnetism of the Tabby graphene is stable until 520 K, which is the temperature of the structural reconstruction of fluorinated graphite.

Bromine polycondensation in pristine and fluorinated graphitic carbons

“…The content of carbon was determined by CHNS ana-regions, which grow with an increase of the fluorination level. [6][7][8][9][10] At low coverage, recent first-principle calculations demonstrated the tendency of stripe-like patterns to form along armchair and zigzag directions. 54 Therefore to simulate substrates of fluorinated graphene and its interface with bromine, we considered zigzag chains of fluorinated carbon atoms alternated with 10 chains of bare sp 2 -hybridized carbon atoms.…”

“…We note that the Br-related Raman spectra are almost the same for the samples with zero and low-fluorination levels. This can be understood from the heterogeneous distribution of fluorine patterning of graphene planes, 9,10,[50][51][52][53] indicating that the bromine signal is coming from species adsorbed on the non-fluorinated regions.…”

“…Partially fluorinated graphite with a stoichiometry close to C 2 F has a patchwork fluorine pattern on the basal planes composed of non-fluorinated gra-phene nanoregions, which are separated by sp 3 -hybridized carbon atoms bonded to zigzag fluorine chains. [6][7][8][9][10] Covalent functionalization of the carbon surface can drastically change the electronic structure of the material. Fluorination of graphite layers and metallic CNTs opens a band gap, which can be tuned by tailoring the content and distribution of fluorine.…”

Photolysis of Fluorinated Graphites with Embedded Acetonitrile Using a White-Beam Synchrotron Radiation

“…The distance between fluorinated layers varies from ~0.6 to ~1.5 nm depending on the size and packing of the guest molecules [7]. A very weak (if any) interaction between the layers causes a two-dimensional (2D) magnetic behavior of these materials [8]. Their exfoliation in appropriate solvents allows producing thin films of the fluorinated graphene layers [9], which are promising materials for gas sensors and energy applications [9,10].…”

Fluorine patterning of graphene: Effects of fluorine content and temperature

“…Theoretical approaches to study FG structures are density functional theory (DFT) and molecular dynamics (MD) simulations. DFT calculations allow to accurately determine the energy of specific structures, such as various conformations of fully FG [19], fluorinated or bare carbon chains, roads and quantum dots [10], specific pairs and triples and their impact on the surroundings [9,10], evenly distributed fluorine [20], periodic patterns [21] and manually set patterns [18,22,23]. Such information gives opportunity to study the thermodynamically most stable structures and can help to establish fluorination mechanisms, but it can hardly predict structural variations under different synthesis conditions.…”