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

We focus the apparent contrast of water islands formed at ionic crystal surfaces in air at room temperature RT.using the non-contact monitoring mode of a scanning force microscope SFM.. Their apparent heights of water islands formed on LiF 001., CaF2 111.and BaF2 111.surfaces have been measured to be about 2, 1 and 1 nm, respectively. The water growth of a NaF 001.surface 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. The apparent height of water films is shown to be strongly modified by the dielectric constant of sample and water, and the true thickness of water islands is discussed. q1999 Elsevier Science B.V. All rights reserved