One-dimensional materials have gained increasing attention in the last decades: from carbon nanotubes to ultrathin nanowires, to few-atom atomic chains, these can all display unique electronic properties and great potential for next-generation applications. The continuous downscaling of electronic devices stimulates the need for increasingly smaller building blocks, and exfoliable bulk materials could naturally provide a source for wires with well defined structure and electronics. In this thesis, we explore a database of 1D materials that could be exfoliated from experimentally known three-dimensional vdW compounds, searching metallic wires that could act as vias or interconnects for future downscaled electronic applications. The first part of this thesis is dedicated to the dynamical stability of 1D metallic systems. Metallic wires are particularly susceptible to dynamical instabilities, such as Peierls transitions and CDW, which lead to the opening of an electronic gap and transform the system into an insulator.
We carefully inspect phonon dispersions. An imaginary phonon signals the occurrence of a phase transition, suggesting that the system is driven towards a more stable phase.
Phonons are calculated using DFPT to evaluate their stability across the entire BZ. For the systems that do show unstable phonons, we aim to find their stable phase by exploiting the additional information provided by phonon eigenmodes. We identify several stable candidates, either in their configuration as is exfoliated from the three-dimensional parents or in a reconstructed superstructure. The portfolio of selected wires from the 1D database is then thoroughly explored from various perspectives. Alongside their vibrational properties and stability, electronic and mechanical properties are calculated from first-principles.
Band structures, DOS, and band gaps are determined to provide an exhaustive description of these systems, which will serve on one side to explore possible future applications in downscaled electronic devices, and on the other to reveal a wide variety of behaviours in real one-dimensional materials. We compute the Young's modulus to evaluate their strength and stiffness for potential applications in flexible electronics and strain engineering. In this regard, a consistent method for defining the volume of exfoliable wires is necessary, and we define it as the quantum volume enclosed by the electronic charge density. A separate chapter is dedicated to the most promising wires, namely those stable in their metallic or semi-metallic phase, with detailed characterisation and discussions of each one's particular features.
The last part of the thesis focuses on the thermodynamics of the exfoliable wires. We employ the stochastic self-consistent harmonic approximation to investigate vibrational properties, fully accounting for anharmonic and quantum effects.
We establish an effective protocol for applying SSCHA to one-dimensional materials, which includes the use of machine learning techniques, with neural network potentials.
Here, we examine their behaviours as a function of temperature and at the same time their anharmonicity, assessing the heat capacity and the linear thermal expansion coefficient for a few candidates within our portfolio of one-dimensional materials exfoliable from weakly-bonded parents.