Effect of Temperature and Surface Properties on the Growth of Crystalline Multilayers of Methanol on Copper

Abstract

Surface impurities can have a significant effect on the initial adsorption of adsorbates to a substrate. When the adsorbate is a hydrogen-bonding molecule, such as methanol, its ability to form hydrogen-bonded structures and networks on the surface may be affected as well. Here, polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) is used to explore how the surface properties and temperature affect the growth and structure of crystalline multilayer ices of methanol. Differences in the PM-IRRAS spectra for methanol films grown on bare Cu(111) and oxygen-precovered Cu(111) (Cu(111)/O) at two different adsorption temperatures (120 and 140 K) reveal that different structures of methanol ices are obtained under each set of conditions. The methanol-Cu(111) interaction is relatively weak. Methanol molecules form long-range hydrogen-bonded structures on Cu(111) at both 120 and 140 K. The preadsorption of oxygen on Cu(111) increases the interaction of methanol with the surface; at 120 K, the methanol molecules form hydrogen bonds with the surface, while at 140 K, the methanol molecules are dissociated into methoxy and water. In both cases, the formation of long-range hydrogen-bonded structures is hindered, and the subsequently adsorbed layers of methanol are relatively disordered. The most ordered methanol ices are grown on Cu(111) at 140 K, while the most disordered methanol ices are grown on Cu(111)/O at 120 K.