Water adsorption on aBaF2(111) surface in air observed with force microscopy

We present the dynamical behavior of water adsorption of a ${\mathrm{BaF}}_2$(111) surface in air observed with force microscopy. The profile from the ${\mathrm{BaF}}_2$(111) surface has exhibited water droplets with small contact angles on exposure to air with a relative humidity of 70%. As time passes, such droplets are plentifully formed and, as a result, turn into a uniform film showing about 1 nm in thickness. We confirm that the saturated adsorption volume of water on the surface depends on the relative humidity and increases with an increase of the relative humidity. Moreover, the force between a tip and the sample surface is measured and discussed.