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

DG Sangiovanni and P Edstrom and L Hultman and I Petrov and JE Greene and V Chirita, SURFACE SCIENCE, 624, 25-31 (2014).

DOI: 10.1016/j.susc.2014.01.007

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. (C) 2014 Elsevier B.V. All rights reserved.

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