Annealing of CH3I films on TiO2(110) studied with TPD and UV-induced desorption

Annealing of CH3I films formed on TiO2(110) at 90 K has been investigated using thermal desorption and photodesorption. At a surface temperature of 90 K, the multilayer film of CH3I grows stochastically. Thermal desorption and photodesorption studies indicate that annealing a CH3I film at temperatures of 120–125 K for less than ∼12 min induces the desorption of weakly bound molecules and produces two CH3I phases on TiO2(110): a two-dimensional (2D) monolayer phase and a three-dimensional (3D) multilayer phase. After annealing at ∼125 K for 12 min, the 3D multilayer phase is completely desorbed and only the 2D monolayer phase is left on the TiO2(110) surface. This 2D layer has a saturation molecular density greater than that of the 1 ML film deposited at 90 K. When the annealing temperature is increased to above 130 K, the thermal stability of the 2D film increases and the number of the CH3I molecules left on the TiO2(110) surface decreases.