SUBSTRATE-DEPENDENT SUBLIMATION KINETICS OF MESOSCOPIC ICE FILMS

We have measured the sublimation kinetics of 2-30 nm thick ice layers deposited in ultra high vacuum at 100 K, on different surfaces; Pt(111 ) and graphite (0001) surfaces with and without various pre-adsorbed m onolayers. The results reveal (i) a much more complex sublimation kine tics than expected for a simple molecular solid, and (ii) a strong inf luence of the underlying substrate on the kinetics. These features, wh ich are reproduced by computer simulations, are due to (i) a phase tra nsition from amorphous to crystalline ice during sublimation, and (ii) substrate dependent nucleation and growth of the ice layers, respecti vely. The results are correlated with the hydrophobicity-hydrophilicit y of the surfaces, and suggest a new method to characterize the wettin g properties of solid surfaces. It can be easily performed with state- of-the-art surface cleanliness control, contrary to conventional wetti ng methods. Applied to the present results, and those of Smith et al. in the preceding paper [Surf. Sci. 367 (1996) L13], this gives, in ord er of decreasing wetting of water; clean Pt(111)>clean Ru(001)>Cs cove red graphite>clean graphite>octane covered Pt(111)greater than or equa l to clean Au(111).