A New Variable Temperature Solution-Solid Interface Scanning Tunneling Microscope
Hipps, K. W.
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Scanning tunneling microscopy (STM) has been widely used to investigate surface structures and electronic properties of adsorbed species on surfaces and also for observing chemical reactions on surfaces. The technique can be used in various environments such as vacuum, air and solution. Among these environments, ultrahigh vacuum (UHV)-solid and solution-solid (SS) interfaces get the most attention. If we compare sample preparation procedures for these two environments, it is much easier to prepare samples and take measurements at the SS interface, although STM images in UHV generally show higher resolution. If the sample cannot be evaporated without decomposition, SS interface studies may be the only choice. Generally, studies in UHV require that the molecules of interest be vapor deposited – which is impossible for many compounds. No matter how the sample is prepared, by the nature of the experiment, UHV studies are not compatible with chemical equilibrium involving material transport to and from the surface. SS interface studies, on the other hand, are easily adaptable to equilibrium studies. In SS studies, one can change the solvent in order to tune molecule-solvent and substrate-solvent interactions at the SS interface, thereby changing the ordering and structure of the adsorbed species. Gyarfas et al. demonstrated that the length of the alkane chain in different alkanoic solvents had a role in determining the surface structure of coronene on gold . The repair of defects in self assembled layers at the SS interface can be promoted if there is a dynamic exchange between molecules on the surface and in the solution phase .