The influence of potassium on the growth of ultra-thin films of para-hexaphenyl on muscovite mica(001)

Abstract

The interaction of potassium with mica(001) and its influence on the subsequent film growth of para-hexaphenyl (6P) was studied by Auger electron spectroscopy, thermal desorption spectroscopy, and atomic force microscopy (AFM). Freshly cleaved mica is covered with 0.5 monolayer (ML) of potassium. By intentional potassium deposition in ultra-high vacuum a saturation of 1 ML can be achieved, which is stable up to 1000 K. Additional potassium desorbs at around 350 K. The film morphology of 6P on mica(001) is significantly influenced by the potassium monolayer. On the freshly cleaved mica surface, which contains 1/2 ML of K, 6P forms needle-like islands which are composed of lying molecules. On the fully potassium covered mica surface 6P grows in form of dendritic islands, composed of standing molecules. The reason for this change is attributed to the removal of lateral electric fields which exist on the freshly cleaved mica surface, due to the specific arrangements of the atoms in the surface near region of mica.