Materiali bidimensionali e stratificati: dai framework metallorganici ai dicalcogenuri di metalli di transizione

Research in two-dimensional (2D) and layered materials has emerged as a pivotal frontier in materials science and nanotechnology, holding immense promise for advancing a multitude of technological applications. These materials, characterized by their atomically thin nature and peculiar electronic, optical, and mechanical properties, have opened up new avenues for innovation in fields such as electronics, energy storage, photonics, and beyond. As we delve deeper into the exploration of these materials, we uncover opportunities to engineer novel devices, enhance energy efficiency, and push the boundaries of fundamental scientific understanding. In this thesis we analyse three inherently two-dimensional systems. On one hand, the focus is on the identification of new systems for heterogeneous catalysis, and on the other hand, the investigation of temperature-driven phase transitions in a prototypical layered material. These systems are investigated through a combination of first-principles and machine learning computational methods, and the results are compared with various experimental findings. The first part is dedicated to a self-assembled Cobalt Tetra-Pyridyl-Porphirins (CoTPyP) layer on graphene/iridium(111). In this context, akin to many biological molecules, a metal atom is encapsulated within a well-defined chemical environment. This metallic center acts as a single-atom catalyst for heterogeneous catalysis. The addition of further Co atoms, that occupy intermolecular sites, leads to a surprisingly drastic rearrangement of CoTPyPs on the surface with the formation of a 2D metal-organic framework. The structural and electronic properties of these systems are presented, shedding light on the mechanisms underlying the self-assembly process and the substantial structural changes that occur. Particular attention is given to the two inequivalent (intra and intermolecular) Co metal centers, highlighting their inherent differences which result in a different chemical reactivity. This reactivity is explored by showcasing the capacity of the most active site, nestled within the molecule core, to facilitate the formation and stabilization of the OOH-H2O complex. Additionally, the adsorption of CO on both Co species will be discussed. Secondly, our attention is directed towards the investigation of transition metal dichalcogenides (TMDs), a diverse class of layered inorganic materials that, under ambient conditions, exhibit a variety of polytypic structures. In many cases, these structures are stabilized by periodic lattice distortions (PLD), resulting in the formation of charge density waves (CDWs). In this context, we focus on the phase transitions occurring at different temperatures in two specific TMDs: vanadium ditelluride (VTe2) and tungsten ditelluride (WTe2). VTe2, in its layered bulk form, assumes a normal 1T phase at high temperatures. However, upon cooling, it undergoes a phase transition to a CDW phase 1T" at around 475K. A combination of DFT phonon calculations and pump-and-probe experiments is employed to demonstrate the presence of two phonon modes coupled to the CDW phase. Furthermore, the profound modifications induced in the electronic band structure during this phase transition is illustrated. As an initial step towards a more comprehensive, temperature-dependent exploration of phase transitions in TMDs, we consider a WTe2 monolayer, which is stable at room temperature in the 1T’ phase. A first-principle interatomic potential suitable for classical molecular dynamics simulations has been developed. Its accuracy is validated through comparisons with phonon calculations performed using fine displacement methods and ab-initio approaches.