Multistage order-disorder surface transition of Si(111)root 3 x root 3-ag surface with defects

We report a remarkable series of structural changes newly predicted for a Si(111)root3 x root3-Ag surface with defects. Monte Carlo simulations based on the results of first-principles calculations show that in a particular configuration of a few defects, a wide region undergoes disorder --> order --> disorder --> order structural changes with the decrease of temperature. We call this series of changes multistage order-disorder surface (MODS) transition, which is able to be observed by scanning tunneling microscopy (STM) as a series of clear changes of the image.