Ab initio and classical molecular dynamics simulations of N-2 desorption from TiN(001) surfaces

作者：Sangiovanni D G^*; Edstrom P; Hultman L; Petrov I; Greene J E; Chirita V

来源：Surface Science, 2014, 624: 25-31.

DOI：10.1016/j.susc.2014.01.007

• N-2 desorption
• Surface diffusion
• Nitrides
• Molecular dynamics simulations
• Density functional theory
• Vacancy formation

Ab initio molecular dynamics simulations based on density functional theory show that N adatoms are chemisorbed in threefold sites close to a N surface atom and between the two diagonally opposed neighboring Ti surface atoms on TiN(001). The most probable N adatom reaction pathway, even in the presence of nearby N adatoms, is for the N adatom and N surface atom pair to first undergo several exchange reactions and then desorb as a N-2 molecule, resulting in a surface anion vacancy, with an activation barrier E-des of 1.37 eV and an attempt frequency A(des) = 3.4 x 10(13) s(-1). E-des is essentially equal to the N adatom surface diffusion barrier, E-s= 139 eV, while As is only three to four times larger than A(des), indicating that isolated N adatoms migrate for only short distances prior to N-2 desorption. The probability of N-2 desorption via recombination of N adatoms on TiN(001) is much lower due to repulsive adatom/adatom interactions at separations less than similar to 3 angstrom which rapidly increase to similar to 2 eV at a separation of 1.5 angstrom. We obtain good qualitative and quantitative agreement with the above results using the modified embedded atom method potential to perform classical molecular dynamics simulations.

• 出版日期2014-6