Electric field and contact interactions of tip with adenine molecules on SrTiO3(100)-√5x√5 surfaces

We have performed tip-assisted migration of adenine molecules adsorbed on SrTiO3(100)-root 5 x root 5 surfaces with scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) conditions at room temperature. The migration with stepwise current control reveals the difference in binding energy of adenine molecules adsorbed on various sites on root 5 x root 5 surfaces. The adenine molecules easily migrate on the root 5 x root 5 surface at room temperature and settle down at the trap sites of Sr atoms remaining on the surface. Quantitative analysis of migration probability as a function of tunneling current (I) and tip bias voltage (V-t) shows that the electric field effect is dominant at V-t greater than or equal to 4 V or I greater than or equal to 70 pA, while contact interaction is dominant at 0 V < V-t less than or equal to 0.1 V for the tip-assisted migration in this system.