Abstract
Lattice mismatch between lead and copper is approximatively 36%, but why does the STM data show that lead atoms substitute for copper atoms, instead of adsorption on the surface. In order to answer this question, Density Functional Theory was used in this thesis to verify the stable structure of lead on copper (110) surface in different coverage by comparing lead substitution and lead adsorption models. Since the total the number of atoms in both lead substitution and lead adsorption models are different we use formation energy to determine the stability of the two model. The simulation results show that the coverage 0.8, p(5×1) unit cell, of substitution case is the most stable one among all of models; the formation energy of the Pb substitution models is 0.03 eV lower than the Pb adsorption model. The same trend is observed in the cases of the coverage equal to 0.75, p(12×1) unit cell, and 0.778,p(9×1) unit cell: the Pb substitution for Cu is more stable than the Pb adsorption case. In addition, with the increase of the Pb coverage, we have found the difference of formation energy between the Pb substitution and adsorption models increases slightly. We also examine their charge density and the outcomes disclose that there is no charge transfer between the lead and copper atoms. Concerning their bond length variation, the bond distances between Cu and Pb is almost the same under the three coverage models; the Pb-Pb bond length decreases with the increase of Pb coverage on Cu (110) surface. We found that the Pb-Pb bond length of substitution model is larger than the Pb-Pb bond length of adsorption model. Keyword: Density Functional Theory, Cu surface, Pb atom, adsorption, substitution