En las fronteras de la Materia Condensada

The Si(001) surface reconstructs forming buckled dimer rows in order to reduce the surface energy. These dimer rows are stable up to 1463K, close to the temperature at which the surface becomes rough. Therefore the surface dimers are considered as building units on Si(001). In a clean area of the surface, far from defects, the principal movement of surface dimers consists of a flipping or vibration between two equivalent buckling angles. The dimers that are close to a surface defect usually present three possible local minima, two of them buckled, with positive and negative buckling angles, and the third, symmetric.
According to previous high temperature molecular dynamics studies surface dimers participate strongly in ad-atom and ad-dimer diffusion on Si(001), through concerted motions and atom exchanges. Therefore the dimer dynamics and its modification at different local environments could strongly affect the surface diffusion, and consequently the epitaxial growth. Motivated by the above mentioned importance of surface dynamics, and also by recent experimental STM results which show large differences in the flipping energy barriers (of about 0.1 eV) depending on the local environment, we have performed a detailed study of the dimer dynamics at finite temperature near surface defects.
We have found Some similarities in the dynamics between dimers close to single dimer vacancies (SDV), steps, and steps with kinks. First neighbors of a SDV, upper step B edge dimers, and dimers close to kinks in step A have similar local environment. Therefore all tend to flip faster, and spend most of the time symmetric. On the other hand, second neighbors of a SDV, upper step A edge dimers, and dimers close to kinks in step B tend to flip slower.