The feasibility of a new, non-chemical methodology for synthesizing PGM-free materials based on Fe was evaluated using XPS, Raman, and electrochemistry [1]. Vertically aligned carbon nanotubes were chosen as a model material to minimize non-graphitic contributions, enabling the preparation of nitrogen-free materials adaptable to common carbon powders. By employing nitrogen ion implantation via a Kaufman ion source and Fe evaporation in a UHV chamber, surface chemistry comparable to chemical methods was achieved. XPS and Raman demonstrated the formation of N-C bonds and Fe-containing active sites without high-temperature pyrolysis. This method enhanced pyridinic N moieties crucial for stabilizing Fe-Nx sites, resulting in electrochemically active materials with improved oxygen electrocatalysis. This physics-based approach shows promise for preparing efficient N-free electrocatalysts for energy applications without extensive post-treatments.

References:
[1] V.C.A. Ficca et al Non-Chemical Route to PGM-Free via N+ Ion Implantation in Vertically Aligned Carbon Nanotubes, Adv. Funct. Mater. Doi: 10.1002/adfm.202413308

Within the PTOLEMY and ANDROMEDA projects, aiming at developing new instruments for Dark Matter (DM) and neutrino detection [1], vertically highly aligned multi-wall carbon nanotubes (CNTs) are grown in the INFN-Sapienza Titan lab. Here, the study of anisotropic damage under noble gases ion bombardment (few keV energy [2]) is investigated, by micro-spectroscopy analysis on the top and on the lateral side of the CNT arrays [3].

We observe a negligible anisotropy at the sample surface (by surface-sensitive XPS) while a mass-dependent damage is brought to light along the body of the CNTs (by the bulk-sensitive Raman spectroscopy).

References:
1) Ptolemy collaboration, Journal of Cosmology and Astroparticle Physics 07, 047 (2019); Pandolfi et al., Nucl. Inst. and Meth. in Phys. Research A 1050, 168116 (2023) 

2)  D’Acunto et al., Carbon 139, 768 (2018); Ripanti et al., Journal of Physical Chemistry C  123, 20013 (2019) 

3) Tayyab et al., Nanomaterials 14, 77 (2024) 

Strain engineering of two-dimensional semiconductors, such as MoS2, is a powerful strategy to modify their electronic and optical properties. Thanks to the controlled buckling of MoS2 prior to transfer we can induce wrinkles in the transferred material which act as local uniaxial strain profiles. In this work we study the effects of uniaxial strain in monolayer and trilayer MoS2 using spatially resolved Raman and photoluminescence spectroscopy. X-ray photoemission spectroscopy (XPS) is used to assess the quality of the material. The two XPS spectra of Mo3d and S2p core levels show that the mechanically exfoliated ultrathin material does not suffer damage during the process. From the Raman map a maximum strain of 1.2% on the wrinkle can be calculated while the photoluminescence map shows an anti-funneling effect on the wrinkle, which act as an exciton repulsion center and inhibits their radiative recombination.

Alkali metal deposition is an effective way to increase graphene (Gr) metallicity by enhancing its low density of state at the Fermi level, leading to a strong modification of the electronic and vibrational spectrum. In this work we investigate the effect of potassium (K) doping of Gr by comparing a fully free-standing Nanoporous graphene architecture (NPG) and supported graphene flakes via photoemission spectroscopy and micro-Raman. Due to the failure of the adiabatic Born-Oppenheimer approximation and the removal of the Kohn anomaly upon doping, the Gr G Raman mode is split into an uncharged (G1) and charged (G2) peak. The 2D mode is suppressed at high coverages due to the increased electron scattering rate while the intercalation of the K adatom in Gr flakes is also deduced from the modification of the 2D mode line-shape.

Moreover, thanks to the high spatial resolution of the micro-Raman apparatus, Gr flakes mappings were performed to study the diffusion process of the K adatom. Lastly, the correlated photoemission spectroscopy performed on NPG highlights a broad asymmetry of the C1s core level at increasing K doping,

signature of the presence of a π*-plasmon mode induced by the increased electron charge density.

The Group is currently involved in the synthesis and characterization of low-dimensional nanomaterials based on carbonaceous structural units, heteroatoms like S, N, B, and P, and non-platinum group transition metals. This class of materials, called platinum-group-metal-free (PGM-free), are electrocatalysts capable of catalyzing specific reactions critical for technological application in the energetic sector.

Group: E. Placidi, V.C.A. Ficca

References:
1) Chem. Eng. Journal, in press (2023). [IF 16]

2) Appl. Catalysis B: Env. 237 (2018) 699–707. [IF 14] 

2) Electrochimica Acta. 391 (2021) 138899. [IF 7] 

3) J. Power Sources 550 232135 (2022) [IF 9]

The adsorption of hydrogen on graphene (Gr) is expected to modify its electronic properties leading to an energy gap opening, obtaining 2D “graphane”, promising for a widespread number of applications, from integration in advanced 2D devices to hydrogen storage. The adsorption of the isotope deuterium (D) on fully free-standing Gr was obtained by molecular cracking in ultra-high-vacuum on nano-porous graphene (NPG), constituted by a single to a few veils of smoothly rippled Gr, reaching nearly 50 at.% D upload [1] and 90 at.% H [2], achieving a low-defect free-standing 2D 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 formation, and by Raman spectroscopy, pointing to remarkably clean and low-defect production of graphane [1], corresponding to a double-sided coordinated graphene [2]. Deuteration is demonstrated to be highly homogeneously distributed on graphane, as brought to light by the combined optical and electron spectro-microscopy study wholly carried out in ultra-high vacuum conditions at the SmartLab [1].

References:
1) Nanomaterials 12, 2613 (2022) 

2) Nano Letters 22, 2971 (2022)