Introduction
The last 15 years the attention of material scientists is drawn to the world of 2D materials in particular to find candidates for spin-related applications. Heterostructure based on Me-porphyrin deposited on 2D materials can be found very promising because of variety of possible spin states and their low degeneracy with large distance between metallic centres preventing chemical interactions of the ions together with possible quantum entanglement of close to degeneracy localized spin states.
Graphene is one of the most popular planar material due to high charge carrier mobility, low hyperfine interaction as well as low intrinsic spin-orbital interaction.1 Due to its unique electronic structure (e.g. Dirac cone presence) graphene is a very promising material for spintronics applications. Taking into account the absence of spin-polarization, graphene can play a significant role as a part of novel heterostructures being the material that do not change the magnetic properties of other components allowing advanced transport properties.2 Interfaces based on graphene/hBN
have mobilities and carrier inhomogeneities that are almost an order of magnitude higher than devices based on SiO2.3,4 Due to simplicity of fabrication and opportunity to synthesize high-squared sheets, graphene is going to be the most popular material related to electronics in near future.5
A strong band gap dependence of narrow armchair graphene nanoribbons (AGNR) upon the edge effectswas demonstrated. 6–8 It was found that the band gap decreases almost inversely upon the effective widths of the ribbons until reaching a vanishing value for 2 nm width nanoribbons.6,7,9,10 The AGNR lattices belong to three groups of width-dependent small, medium, and large energy band gaps with N = 3p + 2, 3p + 1, and 3p , respectively, where p is a positive integer equal to the number of carbon dimers oriented perpendicular to the ribbon. 7,9,10 In fact, for p =11 (AGNR-11) the number of hexagonal rings perpendicular to the main axis of ribbon is equal to 9. The AGNR-11 satisfactory reproduces the electronic structure of graphene (close to zero narrow band gap of 0.05 eV with band structure resembles Dirac cone) in the vicinity of the Fermi level.6–8,10
Porphyrin belongs to a rich family of organic molecules that are of great interest in chemistry and physics. Due to presence of the active site in the centre of the molecule it can be filled by different transition metal (TM) ions. The TM-porphyrin complexes (TMP) demonstrate wide variety of spin and electronic properties.11,12The TM ions (Fe, Mg, Co) implemented in porphyrin determine particular biological roles in living cells forming the hemes, the chlorophylls and the cobalamins.13 Graphene-based heterostructures with absorbed molecules with non-zero spin-polarized open shell electronic structure gain popularity in recent years.14,15Spin-polarized molecules in contact with graphene constitute a tantalizing approach towards organic spin electronics because of the reduced conductivity mismatch at the interface15,16and high catalytic activity17. TMP/AGNR weakly bounded complexes may be considered as promising heterostructures for spin-related and quantum applications.
There are a lot of publications devoted to Me-porphyrin properties18,19, but the question about the migration pathway of the complexes on graphene surface is still open. Keeping in mind isotropic structure, flat potential energy profile and passivity of graphene surface, one can consider rotation and migration degrees of freedom of Me-porphyrin complexes on it. This paper is aimed to shed a light at the migration and rotation pathways of Fe-porphyrin (FeP) at AGNR surface, to determine the spin states of Fe ion in FeP complex (FeP/AGNR), and to locate its favourable coordinations relatively AGNR and to characterize migration potential energy pathways.