SSL Seminar Series 2005 No.1

Date: March 3 (Thursday), 2005
Time: 3:30-4:30pm
Venue: Physics Resource Room (Blk S13 # 02-16)

Speaker: Dr. Wang XueShen
Title: Driving forces behind the formation of a superstructure on Ru(0001)


Periodic structures on surfaces, such as surface reconstructions, have been used as self-assembled nano-scale templates to facilitate fabrication of other nanostructures. Recently, we observed a superstructure of period ~ 3.2 nm on Ru(0001) after Ge deposition and annealing. Here, we first explore the formation of 2D periodic structures by Wigner crystallization of surface accumulated charge that can be stable near room temperature. If the surface segregation of impurity atoms, driven by reduction of surface energy, is accompanied with charge transfer, the surface density of impurity and charge will reach an optimal value in thermal equilibrium due to the balance between surface energy reduction and Coulomb energy increase. Within certain charge density range, Wigner crystallization can occur for the segregated charge on the surface, and subsequently the segregated atoms may also form a periodic superstructure. But the Wigner crystallization mechanism cannot explain some aspects of our experimental results, and similar superstructure also forms with other adsorbates on Ru(0001). We will also explore other mechanisms related to surface states on Ru(0001).