5 research outputs found
Graphene-Induced Substrate Decoupling and Ideal Doping of a Self-Assembled Iron-phthalocyanine Single Layer
Iron-phthalocyanine molecules self-assemble on the moiré
pattern of graphene/Ir(111) as a flat and weakly interacting layer,
as determined by core-level photoemission and absorption spectroscopy.
The graphene buffer layer decouples the FePc two-dimensional structure
from the underlying metal; the electronic structure of the FePc molecular
macrocycles is preserved; and the Fe-L<sub>2,3</sub> edges present
narrower and slightly modified resonances at the FePc single-layer
coverage with respect to a thin film. The FePc layer induces a slight
electron doping to the Ir-supported graphene resulting in the Dirac
cone position expected for an ideal free-standing-like graphene layer
with the standard Fermi velocity
Formation of Hybrid Electronic States in FePc Chains Mediated by the Au(110) Surface
Iron–phthalocyanine (FePc) molecules deposited
on the Au(110)
surface self-organize in ordered chains driven by the reconstructed
Au channels. The interaction process induces a rehybridization of
the electronic states localized on the central metal atom, breaking
the 4-fold symmetry of the molecular orbitals of the FePc molecules.
The molecular adsorption is controlled by a symmetry-determined mixing
between the electronic states of the Fe metal center and of the Au
substrate, as deduced by photoemission and absorption spectroscopy
exploiting light polarization. DFT calculations rationalize this mixing
of the Fe and Au states on the basis of symmetry arguments. The calculated
electronic structure reproduces the main experimental spectral features,
which are associated to a distorted molecular structure displaying
a trigonal bipyramidal geometry of the ligands around the metal center
Energetics and Hierarchical Interactions of Metal–Phthalocyanines Adsorbed on Graphene/Ir(111)
The adsorption of metal–phthalocyanine
(MPc) layers (M =
Fe, Co, Cu) assembled on graphene/Ir(111) is studied by means of temperature-programmed
X-ray photoemission spectroscopy (XPS) and near-edge X-ray absorption
fine structure (NEXAFS). The balance between interaction forces among
the organometallic molecules and the underlying graphene gives rise
to flat-lying molecular layers, weakly interacting with the underlying
graphene. Further MPc layers pile up face-on onto the first layer,
up to a few nanometers thickness, as deduced by NEXAFS. The FePc,
CoPc, and CuPc multilayers present comparable desorption temperatures,
compatible with molecule–molecule interactions dominated by
van der Waals forces between the π-conjugated macrocycles. The
MPc single layers desorb from graphene/Ir at higher temperatures.
The CuPc single layer desorbs at lower temperature than the FePc and
CoPc single layers, suggesting a higher adsorption energy of the FePc
and CoPc single layers on graphene/Ir with respect to CuPc, with increasing
molecule–substrate interaction in the order <i>E</i><sub>CuPc</sub> < <i>E</i><sub>FePc</sub> ∼ <i>E</i><sub>CoPc</sub>
Structural Phases of Ordered FePc-Nanochains Self-Assembled on Au(110)
Iron-phthalocyanine molecules deposited on the Au(110)
reconstructed
channels assemble into one-dimensional molecular chains, whose spatial
distribution evolves into different structural phases at increasing
molecular density. The plasticity of the Au channels first induces
an ordered phase with a 5×5 symmetry, followed by a second long-range
ordered structure composed by denser chains with a 5×7 periodicity
with respect to the bare Au surface, as observed in the low-energy
electron-diffraction (LEED) and grazing incidence X-ray diffraction
(GIXRD) patterns. The geometry of the FePc molecular assemblies in
the Au nanorails is determined by scanning tunneling microscopy (STM).
For the 5×7 phases, the GIXRD analysis identifies a “4-3”
rows profile along the [001] direction in the Au surface and an on-top
FePc adsorption site, further confirmed by density functional theory
(DFT) calculations. The latter also reveals the electronic mixing
of the interface states. The chain assembly is driven by the molecule–molecule
interaction and the chains interact with the Au nanorails via the
central metal atom, while the chain–chain distance in the different
structural phases is primarily driven by the plasticity of the Au
surface
An Advanced Lithium-Ion Battery Based on a Graphene Anode and a Lithium Iron Phosphate Cathode
We report an advanced lithium-ion
battery based on a graphene ink
anode and a lithium iron phosphate cathode. By carefully balancing
the cell composition and suppressing the initial irreversible capacity
of the anode in the round of few cycles, we demonstrate an optimal
battery performance in terms of specific capacity, that is, 165 mAhg<sup>–1</sup>, of an estimated energy density of about 190 Wh kg<sup>–1</sup> and a stable operation for over 80 charge–discharge
cycles. The components of the battery are low cost and potentially
scalable. To the best of our knowledge, complete, graphene-based,
lithium ion batteries having performances comparable with those offered
by the present technology are rarely reported; hence, we believe that
the results disclosed in this work may open up new opportunities for
exploiting graphene in the lithium-ion battery science and development