Variable-temperature scanning tunneling microscopy investigation of CH3ONO adsorbed on Ag(1 1 1)

Variable-temperature scanning tunneling microscopy (VT-STM) was used to image the CH3ONO–Ag(1 1 1) vacuum–solid interface held at 45, 105 and 160 K. With a few exceptions, atomic resolution is not achieved and only steps and terraces are resolved on the clean substrate. Images taken after dosing CH3ONO at 105 K where multilayers are not formed, reflect the presence of highly mobile two-dimensional (2D) islands. Streaks in these images indicate motion of CH3ONO with the STM tip as it is scanned. Island sizes range from 1×1 nm at low exposures to 10×10 nm at higher submonolayer exposures. The largest islands are generally located at the lower edges of steps. The images taken after lowering the temperature to 45 K show clear evidence for conversion of the 2D fluid-like islands into three-dimensional solids that form as ridges along steps on the Ag(1 1 1) surface. The ridges are ∼1 nm wide and 0.1 nm higher than the terrace connected to the upper step edge. Upon rewarming to 105 K, these ridges slowly form 2D islands on terraces. Upon heating to 160 K there is, as expected from temperature programmed desorption, no evidence for adsorbed CH3ONO.