Number 225 (Story #1), May 8, 1995 by Phillip F. Schewe and Ben Stein ROOM-TEMPERATURE ICE. Microscopic images of water condensing and evaporating can be rendered with an atomic force microscope (AFM) operating in a novel mode. Normally it is difficult to study thin liquid films at a surface with an AFM because capillary forces will cause liquid molecules to wet the probe tip, throwing off the measurements. Miquel Salmeron at LBL gets around this problem by backing off the tip to an altitude of 20 nm above the sample. He charges up the tip (made conducting by a thin coating of Pt). Because of the sharpness of the probe, the electric field is concentrated around the tip apex; this polarizes the atoms in the insulating substrate beneath. By monitoring the polarization force as the tip is scanned across the surface, a topographic map of a water layer on a mica substrate can be made. The name for this new technique is polarization force microscopy. The LBL researchers studied wetting in two humidity regimes. Below 25% humidity a uniform layer of water forms. This water layer is still fluid. For humidity above 25%, a different sort of wetting takes place, one in which water islands having polygonal shapes form, apparently oriented by the underlying mica substrate. That is, the water possesses crystalline structure and is, in effect, a type of ice. The LBL experiments is carried out at room temperature; further research will study the effect of temperature on the water crystal formation. (J. Hu et al., Science, 14 April 1995.)