Study of water droplets and films on graphite by noncontact scanning forcemicroscopy

The scope of the noncontact scanning force microscopy technique concerning the analysis of fragile and weakly attached samples is shown by proving its ability to investigate the water-graphite interface. After a macroscopic q uantity of purified water has been shacked out from the graphite surface, a noncontact image taken in air at a relative humidity value of 60% reveals nanodroplets attached to the steps. In a high relative humidity atmosphere (>90%), water adsorbs on the surface forming flat rounded islands of 5 nm i n height that transform to 2 nm high islands when the relative humidity sta bilizes to 90%. This process is induced by the presence of the scanning tip . Desorption of the water present on the surface is achieved after the expo sure of the sample to a dry atmosphere for several hours. The adsorption-de sorption cycle is reversible.