|Tipo di tesi||Tesi di laurea magistrale|
|Titolo||Phosphorene as a possible solid lubricant: An ab initio comparative study with graphene and molybdenum disulfide|
|Titolo in inglese|
|Struttura||Dipartimento di Scienze Fisiche, Informatiche e Matematiche|
|Corso di studi||PHYSICS – FISICA (D.M.270/04)|
|Data inizio appello||2018-10-25|
|Disponibilità||Accessibile via web (tutti i file della tesi sono accessibili)|
Lo spreco di energia e i costi ambientali associati all'attrito e all'usura ha innescato una grande attività di ricerca per trovare nuovi materiali lubrificanti. I materiali 2D hanno recentemente attirato crescente attenzione come alternativa ecologica agli additivi per lubrificanti nell'olio di base e come rivestimenti sottili per ridurre l'usura e l'attrito delle interfacce solide.
The waste of energy and environmental costs associated to friction and wear has triggered a great research activity in the search for novel lubricant materials. 2D materials have recently attracted increasingly attention as environmental-friendly alternative to lubricants additives in base oil and as thin coatings to reduce the wear and friction of solid interfaces. Phosphorene, a single layer of black phosphorus, is attracting interest as alternative to graphene for technological applications, especially for those requiring semiconducting properties. However, phosphorene also possesses a great potential for (nano)tribological applications due to its layered structure and for the capability of phosphorus to reduce friction and adhesion in iron/steel contacts. In fact, phosphorus is a key element in lubricant additives used in engine oils. In spite of these promising characteristics, the lubricating properties of phosphorene have not been investigated so far. In the present work we consider phosphorene as a possible solid lubricant and calculates its tribological properties by means of a computational ab initio approach. First, the electronic and structural properties of phosphorene are studied as a function of the number of layers. Then, the interlayer binding energy and shear strength are evaluated for different interlayer orientations. A structural superlubricity is identified for a perpendicular layer orientation. In the second part of the work, the capability of phosphorene to lubricate iron is evaluated and compared to those of two well known solid lubricants: graphene and MoS2. The tribochemistry of MoS2 on iron is studied here for the first time. The results indicate that iron interfaces lubricated by a single layer of phosphorene present lower adhesion and friction than those lubricated by graphene and MoS2. Instead, the bilayer intercalation produces similar effects for all the considered materials. The optimal properties of phosphorene are due to its layers structure, consisting of two atomic planes of phosphorus. The separation of these planes is observed once the single layer is intercalated within iron. Therefore, a single phosphorene layer can fully passivate the metal interface, producing lubricant effects that in other 2D materials can only be obtained with bilayer films. The present study provides new fundamental insights into the structural, electronic, and tribological properties of phosphorene. Such understanding, together with a comparison with graphene and MoS2 can open the way to the application of phosphorene as solid lubricant.