Studying adsorption with graphene
DOI: 10.1063/1.3541955
Under ambient conditions, water vapor in the air coats most solid surfaces. Although adsorbed water layers, called adlayers, are typically only a few molecules thick, they often determine the surface behavior of solids (see the article by Peter Feibelman in PHYSICS TODAY, February 2010, page 34 ). Despite the adlayers’ importance, determining their microscopic structure has been elusive because they are highly delicate and dynamic at room temperature.
James Heath’s team at Caltech has developed a new method to visualize elusive water adlayers under ambient conditions: using graphene, an impervious sheet of carbon just one atom thick, as an ultrathin coating to seal and lock the adlayers in position. The structure of the layers can then be measured using conventional atomic force microscopy.
Shown here is an atomic force micrograph, 14 µm across, of water adlayers trapped under a graphene sheet. Under ambient conditions, the first adlayer forms atomically flat islands (lightest blue), typically tens of nanometers across. Remarkably, the islands are icelike at room temperature: Their facets have preferred angles near 120°, and each island has the same height (0.37 nm) as a single bilayer of crystalline ice. At high humidity levels, a second layer of water coats the first, also as ice. At even higher humidity levels, additional layers of water coat the surface as droplets. (K. Xu, P. Cao, J. R. Heath, Science 329, 1188, 2010.)
Under ambient conditions, water vapor in the air coats most solid surfaces. Although adsorbed water layers, called adlayers, are typically only a few molecules thick, they often determine the surface behavior of solids (see the article by Peter Feibelman in PHYSICS TODAY,
To submit candidate images for Back Scatter, visit http://www.physicstoday.org/backscatter.html .
