|Tipo di tesi||Tesi di laurea magistrale|
|Titolo||Step interaction at the GaAs b_2 (2×4) (001) surface: from a classical to a quantum-mechanical description|
|Titolo in inglese|
|Struttura||Dipartimento di Scienze Fisiche, Informatiche e Matematiche|
|Corso di studi||FISICA (D.M. 270/04)|
|Data inizio appello||2016-03-18|
|Disponibilità||Accessibile via web (tutti i file della tesi sono accessibili)|
We have compared the structural properties of two vicinal surfaces on the b_2 (2×4) reconstructed GaAs(001) surface misoriented towards the (111) surface. The calculations have been carried out using the open source suite QUANTUM ESPRESSO. Using an ab-initio approach based on the density functional theory we have calculated the elastic energy of the vicinal surfaces. To compare the results with classical models we have studied the variation of the energy of the system due to the presence of steps on the flat b_2 (2×4) reconstructed surface. We have focused our attention on the displacements of the ions in the surface layer and calculated the energy due to those displacements: we have named this energy as the elastic energy. We have tried to understand if the interaction between the step lines is repulsive or attractive. We have found different step-step elastic interactions: repulsive for the vicinal surfaces with steps Ab and attractive for the vicinal surfaces with steps Aa in contrast with the Marchenko-Parshin model which predicts always a repulsive interaction between like-oriented steps. The step interactions obtained from the complete calculation of the surface energies show an opposite behaviour revealing thus the importance of the charge redistribution that follows the ionic displacements. We have found that vicinal surfaces with steps Ab are less unstable than those with step Aa confirming the experimental observation.