First-principles Calculation Of ES Barriers And Effects On Metallic Nanorods

In the recent two decades,owing to the wide application of metallic nanorods in the surface-enhanced Raman scattering,biological detection and biological therapy,more and more researchers have paid their attentions on them.And the seed solution synthesis and electrochemical synthesis were used to fabricate the metallic nanorods in the early stage.But these methods are completed and there are some toxic residues on the metallic nanorods surface.The physical vapor deposition(PVD)based on glancing angle deposition has been used in the fabrication of metallic nanorods during a decade.Compared with former two methods,PVD method is more convenient to control the metallic nanorods morphological directly and it has been caught more and more attention by researchers.During the metallic nanorods synthesis by PVD,the Ehrlich-Schwoebel(ES)barrier has played an important role and there are lots of works about it.Firstly,we calculated the two-dimensional(2D)ES barrier and three-deminsional(3D)ES barrier on Ag(111)by first principles calculation and CI-NEB method.It is found the 2D ES barrier and 3D ES barrier are 0.19 eV and 0.48 eV,respectively.And after analyze the electron distributions,it is found that the 2D ES barrier and 3D ES barrier comes from the bonding weakening of exchange atoms during the exchange diffusion.Furthermore,because of more worse of bonding weakening of exchange atoms,the 3D ES barrier is larger than the 2D ES barrier.Then,the 2D metallic nanorods Monte Carlo model was built in this paper.By using this model of growth simulation and results analysis,it is found that the 2D ES barrier promotes the steps formation and growth and 3D ES barrier promotes the multiple layers steps formation and growth.They promote the film vertical growth and cause the metallic nanorods formation and growth.And we simulated the metallic nanorods growth in the different temperature,deposition rates and glancing angle by this model.After analyzed the simulation results,it is found that the temperature weaken the ES barrier effects,with the temperature increasing,the step numbers and sum of steps height are decreasing and it hinders the metallic nenorods formation and growth.There are adverse results of the deposition rates and glancing angle and they enlarge the ES barrier effects.With increasing of deposition rates or glance angle,he step numbers and sum of steps height are also increasing and it promote the metallic nanorods formation and growth.Finally,considered the trend of metallic nanorods synthesis,we put forward an controlled synthesis method based on substrate pre-treatment method and PVD.In ordered to valid it,the 3D metallic nanorods Monte Carlo model was built.After the growth simulation and results study,the pre-deposited seeds can control the metallic nanorods distribution and the diameter of metallic nanorod is irrelevant with the size of pre-deposited seeds.Besides it,after growth simulation under numerous growth conditions with different temperature,deposition rates and glancing angle,it is found that there is a linear relation between the diameter and separation of pre-deposited seeds,the diameter increase with increasing of separation.