Apparent contrast of molecularly thin films of water at ionic crystal surfaces

We focus the apparent contrast of water islands formed at ionic crystal sur faces in air at room temperature (RT) using the non-contact monitoring mode of a scanning force microscope (SFM). Their apparent heights of water isla nds formed on LiF(001), CaF2(111) and BaF2(111) surfaces have been measured to be about 2, 1 and I nm, respectively. The water growth of a NaF(001) su rface has two phases (phase I and phase II). The apparent heights of phase I and phase II have been measured to be about 2 and 1.5 nm, respectively. T he apparent height of water films is shown to be strongly modified by the d ielectric constant of sample and water, and the true thickness of water isl ands is discussed. (C) 1999 Elsevier Science B.V. All rights reserved.