NanoStructures at Surfaces
Department of Physics - Sapienza University of Rome
Research at the NanoStructures at Surfaces laboratory is focused on electronic and magnetic properties at the nanoscale. Graphene and 2D materials, carbon-based nanostructures, molecular spin interfaces, low dimensional magnetic systems are prototypes to enlighten the effects of reduced symmetry and dimension. State-of-the-art on-campus high energy-resolution photo-electron spectroscopy techniques and synchrotron-radiation based spatially-resolved spectroscopies compared with theoretical modeling unable to tune the electronic and magnetic properties of nanostructures at surfaces for desired functions .
RESEARCH HIGHLIGHTS
March 2022
"Graphane": Highly-Hydrogenated Double-Sided Free-Standing Graphene Free-standing graphene has been converted into pure "graphane", where each C atom is sp3 bound to a hydrogen atom. Here, we obtain an unprecedented high level of hydrogenation (≈90% of sp3 bonds) by exposing fully free-standing nanoporous samples constituted by a single to a few veils of smoothly rippled grapheneto atomic hydrogen in ultrahigh vacuum. Such a controlled hydrogenation of high-quality and high specific-area samples converts the original conductive graphene into a wide gap semiconductor, as monitored by photoemission spectromicroscopy and confirmed by theoretical predictions. The calculated band structure unequivocally identifies the achievement of a stable, double-sided fully hydrogenated configuration, with gap opening and no trace of π states, in excellent agreement with the experimental results. ~ Nano Letters 22, 2971 (2022)
July 2022
Graphane: Homogeneous Deuterium Adsorption on Free-Standing Graphene The adsorption of hydrogen isotopes in graphene is expected to modify its electronic properties leading to an energy gap opening, thereby rendering graphene promising for a widespread of applications. Deuterium (D) adsorption on free-standing graphene was obtained molecular cracking in ultra-high-vacuum on nanoporous graphene (NPG) sample. With this method we could reach nearly 50 at.% D upload in graphene, higher than that obtained by other deposition methods so far, towards low-defect and free-standing D-graphane. That evidence was deduced by X-ray photoelectron spectroscopy of the C 1s core level, showing clear evidence of the D-C sp3 bond, and Raman spectroscopy, pointing to remarkably clean and low-defect production of graphane and showing a high homogeneity of deuteration. Moreover, ultraviolet photoelectron spectroscopy showed the opening of an energy gap in the valence band. ~ Nanomaterials 12, 2613 (2022); Nanomaterials 11, 130 (2021)
January 2021
Tuning the Magnetic Coupling of a Molecular Spin Interface via Electron Doping The magnetic response of molecular spin interfaces has been mastered by tuning the occupancy of the molecular orbitals, which carry the spin magnetic moment, by electron doping. The control of the the magnetization direction and magnitude of a molecular spin network has been achieved via alkali doping of manganese phthalocyanine (MnPc) molecules assembled on cobalt intercalated under a graphene membrane. The antiparallel magnetic alignment of the MnPc molecules with the underlying Co layer can be switched to a ferromagnetic state by electron doping. This new molecular spin configuration can be aligned by an external field, almost independently from the hardmagnet substrate effectively behaving as a free magnetic layer. ~ Nano Letters 21, 666-672 (2021)
January 2021
Magnetic response and electronic states of well defined Graphene/Fe/Ir(111) heterostructure Magnetic Fe layers sandwiched between graphene (Gr) and Ir(111), avoiding Fe-C solubility and Fe-Ir intermixing, has been achieved with atomic controlled Fe intercalation at moderate temperature below 500 K. Upon intercalation of a single ordered Fe layer in registry with the Ir substrate, an intermixing of the Gr bands and Fe d states breaks the symmetry of the Dirac cone, with a downshift in energy of the apex by about 3 eV, and well-localized Fe intermixed states induced in the energy region just below the Fermi level. First principles electronic structure calculations show a large spin splitting of the Fe states, resulting in a majority spin channel almost fully occupied and strongly hybridized with Gr π states. X-ray magnetic circular dichroism on the Gr/Fe/Ir heterostructure reveals an ordered spin configuration with a ferromagnetic response of Fe layer(s), with enhanced spin and orbital configurations with respect to the bcc-Fe bulk values. The magnetization switches from a perpendicular easy magnetization axis when the Fe single layer is lattice matched with the Ir(111) surface to a parallel one when the Fe thin film is almost commensurate with graphene. ~ Physical Review Materials 5, 014405 (2021)
October 2020
Strong ferromagnetic coupling and tunable easy magnetization directions of FeCo layer(s) intercalated under graphene Element-sensitive hysteresis loops unveil a strong ferromagnetic coupling between Fe and Co, and Fe behaves as a strong ferromagnet, with the highest magnetic moment among 3d alloys. This is a significant step towards the control at the atomic scale of the magnetic response in low dimensional 3d transition metal alloys, with tunable easy-magnetization direction, enhanced spin moments and magnetic anisotropy, in a protected spin architecture thanks to the 2D graphene cover ~ Applied Surface Science 527, 146599 (2020)
