The leitmotif was the investigation of phosphorene imagined as a 2D-extended atomic platform for chemical and physical functionalizion in view of its use for devices. The starting point was the synthesis of high quality crystalline black phosphorus (bP). These crystals provided few-layers bP after exfoliation, both in solution or by micromechanical methods. An efficient liquid exfoliation method by bP sonication in dimethylsulfoxide was estabished.
We contributed to a deeper knowledge of bP either as the bulk material or as its exfoliated product: (i) a new phase in the high-pressure phase diagram of bP was described; (ii) exfoliated bP could be decorated by nanoparticles of different metals with significant applications in catalysis and higher stability. The performance of the material in the catalytic hydrogenation of paradigmatic refractory substrates (i.e. the reduction of chloronitroarenes to chloroanilines) was proved to be quite effective and comparable with other state-of-the-art Pd heterogenised catalysts. In particular, once decorated with Pd nanoparticles, we were able to get a confirmatory evidence about the existence of genuine covalent P-Pd bonding interactions.
The phosphorene functionalization with a variety of metal fragments was carefully modelled in silico and evaluated in comparison with the highly reactive P4 allotrope. Physical measurements about weak-localization in bP flakes showed a behavior similar to that previously observed in quasi-one-dimensional systems (nanotubes or metallic nanowires). This was attributed to the strong crystalline anisotropy of bP. By scanning tunnelling microscopy (STM), we were able to directly observe the thermal desorption under ultra-high vacuum conditions and to determine the anisotropic crater alignment with respect to the crystallographic axes of the bP flake, as along the zigzag direction, solving a literature controversy.
The embedding of exfoliated bP in a polystyrene matrix by a solvent blending or direct exfoliation of bP in a polymeric solution, followed by in situ radical polymerization in the liquid monomer (methyl methacrylate, MMA), conferred an improved air and moisture stability to the new assembled hybrid materials. From the resultant heterostructures, the preparation of bP-based devices was anticipated, and effective devices were fabricated from PMMA/bP hybrid materials without the need of a protective atmosphere. Transport measurements demonstrated the electronic-grade quality of the resulting bP flakes.
During the project, 20 papers were published in international journals, and other will be submitted in due time. The results were regularly presented in both national and international scientific meetings, workshops and congresses. Three project workshops were organized. The first was held in Florence at the beginning of the project, while the second was organized in Rome at the headquarters of the Italian National Research Council in 2017. The last one took place as Symposium T “2D Semiconductors: Applications and Perspectives” of the E-MRS, European Materials Research Society Spring Meeting held in Nice, France in May 2019. The first meeting was intended as a sort of “call to arms” for the Italian community active in the area of 2D-materials, paving the way to the birth of several sounds collaborations between chemists and physicists. This idea was later consolidated in the second “Phosphorene day” in Rome and finally opened to the international community of 2D-materials in the closing symposium, which was purposefully organized within the framework of the E-MRS convention just before the closing of the project.
