Maria Grazia Betti

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(-1), of an estimated energy density of about 190 Wh kg(-1) 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.

Core-shell photoabsorption and photoelectron spectra of gas-phase pentacene: experiment and theory.

The C K-edge photoabsorption and 1s core-level photoemission of pentacene (C22H14) free molecules are experimentally measured, and calculated by self-consistent-field and static-exchange approximation ab initio methods. Six nonequivalent C atoms present in the molecule contribute to the C 1s photoemission spectrum. The complex near-edge structures of the carbon K-edge absorption spectrum present two main groups of discrete transitions between 283 and 288 eV photon energy, due to absorption to pi* virtual orbitals, and broader structures at higher energy, involving sigma* virtual orbitals. The sharp absorption structures to the pi* empty orbitals lay well below the thresholds for the C 1s ionizations, caused by strong excitonic and localization effects. We can definitely explain the C K-edge absorption spectrum as due to both final (virtual) and initial (core) orbital effects, mainly involving excitations to the two lowest-unoccupied molecular orbitals of pi* symmetry, from the six chemically shifted C 1s core orbitals.

Pentacene self-aggregation at the Au(110)-(1×2) surface: growth morphology and interface electronic states

Abstract We present an investigation of the growth morphology and electronic properties of pentacene (C 22 H 14 ) deposited in situ on the (1×2)-reconstructed Au(110) surface, in ultra-high-vacuum conditions, at different substrate temperatures. Atomic force microscopy (AFM) investigates evidence of the growth of pentacene in linear stripes preferentially oriented along the [001] direction, on a first thin film phase. Low Energy Electron Diffraction (LEED) data reveal a clear (1×3) periodicity induced by the thin film phase, which is stable up to 500 K. The long range periodicity of this 2D ordered phase is improved at higher substrate temperature, due to higher diffusion of the pentacene oligomers, while stripes become more disordered. The electronic properties of the interface are studied by means of high-resolution UV photoelectron spectroscopy, bringing to light the Au–Pentacene interaction electronic levels leading to the formation of the ordered phase.

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 E(CuPc) < E(FePc) ~ E(CoPc).

Adsorption of pentacene on filled d-band metal surfaces: Long-range ordering and adsorption energy

The growth of pentacene on suitable metallic templates is studied by means of low-energy electron diffraction and ultraviolet photoelectron spectroscopy. Highly ordered pentacene single layers can be prepared by deposition on filled d-band metal templates kept at 370 K. The presence of the steps for the Cu(119) vicinal surface and of the Au troughs for the Au(110)-(1 x 2) surface allows the formation of commensurate long-range ordered structures with (3 x 7) and (3 x 6) periodicities, respectively. A detailed analysis of the molecular induced electronic states evolution is performed for different growth morphologies. The adsorption energy of the ordered molecular single layers on the Au(110) surface is lower (1.90 eV) than on the Cu vicinal surface (2.36 eV), where the steps enhance the molecule adsorption energy.

Metal-phthalocyanine ordered layers on Au(110): Metal-dependent adsorption energy

Iron-phthalocyanine and cobalt-phthalocyanine chains, assembled along the Au(110)-(1×2) reconstructed channels, present a strong interaction with the Au metallic states, via the central metal ion. X-ray photoemission spectroscopy from the metal-2p core-levels and valence band high-resolution ultraviolet photoelectron spectroscopy bring to light signatures of the interaction of the metal-phthalocyanine single-layer with gold. The charge transfer from Au to the molecule causes the emerging of a metal-2p core level component at lower binding energy with respect to that measured in the molecular thin films, while the core-levels associated to the organic macrocycle (C and N 1s) are less influenced by the adsorption, and the macrocycles stabilize the interaction, inducing a strong interface dipole. Temperature Programmed Desorption experiments and photoemission as a function of temperature allow to estimate the adsorption energy for the thin-films, mainly due to the molecule-molecule van der Waals interaction, while the FePc and CoPc single-layers remain adsorbed on the Au surface up to at least 820 K.

Azimuthal dependence of reflection high resolution electron energy loss of Si(111)(2×1)

Abstract High Resolution Electron Energy Loss Spectroscopy has been used, with low energy of the primary beam and azimuthal resolution, to study the anisotropy of surface dielectric properties of Si(111)(2 × 1), in the range of the surface electronic excitations. By eliminating the effect of the kinematic prefactor, we are able to obtain from the data the surface Loss Function. Its dependence on q ∥ and ω is discussed in term of a model of surface dielectric function.

Molecular gap and energy level diagram for pentacene adsorbed on filled d-band metal surfaces

The authors present a combined photoemission and scanning-tunneling spectroscopy study of the filled electronic states, the molecular energy gap, and the energy level diagram of highly ordered arrays of pentacene deposited on the Cu(119) vicinal surface. The states localized at the interface are clearly singled out, comparing the results at different pentacene thicknesses and with gas-phase photoemission data. The molecular gap of 2.35eV, the hole injection barrier of 1.05eV, and the electron injection barrier of 1.30eV determine the energy level diagram of the states localized at the pentacene molecules.

Graphene-Induced Magnetic Anisotropy of a Two-Dimensional Iron Phthalocyanine Network

A single layer of flat-lying iron phthalocyanine (FePc) molecules assembled on graphene grown on Ir(111) preserves the magnetic moment, as deduced by X-ray magnetic circular dichroism from the Fe L2,3 edges. Furthermore, the FePc molecules in contact with the graphene buffer layer exhibit an enhancement of the magnetic anisotropy, with emergence of an in-plane easy magnetic axis, reflected by an increased orbital moment of the FePc molecules in contact with the C atoms in the graphene sheet. The origin of the increased magnetic anisotropy is discussed, considering the absence of electronic state hybridization, and the breaking of symmetry upon FePc adsorption on graphene.

Interaction of iron phthalocyanine with the graphene/Ni(111) system.

Summary Graphene grown on crystalline metal surfaces is a good candidate to act as a buffer layer between the metal and organic molecules that are deposited on top, because it offers the possibility to control the interaction between the substrate and the molecules. High-resolution angular-resolved ultraviolet photo electron spectroscopy (ARPES) is used to determine the interaction states of iron phthalocyanine molecules that are adsorbed onto graphene on Ni(111). The iron phthalocyanine deposition induces a quenching of the Ni d surface minority band and the appearance of an interface state on graphene/Ni(111). The results have been compared to the deposition of iron phthalocyanine on graphene/Ir(111), for which a higher decoupling of the organic molecule from the underlying metal is exerted by the graphene buffer layer.