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.