The imaging and control of self-assembled, physisorbed monolayers have been the subject of numerous scanning tunneling microscopy and atomic force microscopy investigations. The successful interpretation of the structures observed in scanning probe images of molecules self-assembled at liquid-solid and gas-solid interfaces has benefited greatly from recent experimental and theoretical work. These studies are converging on a general tunneling mechanism that accounts for the images of weakly bound, insulating adsorbates. Experiments in which the dynamical behavior of these monolayers has been monitored as a function of time both statically and after the introduction of an external perturbation are described, and novel studies of the selective control of monolayer structure that make use of internal and external electric fields, photons, and solvent coadsorption are reviewed.

Scanning tunneling microscopy (STM) has been used to study the chiral molecules (R)/(S)-2-bromohexadecanoic acid at the liquid/solid interface. When adsorbed onto the basal plane of graphite, these molecules segregate on the surface into domains of pure R or S enantiomers. The atomic resolution obtained in the STM images of these species allows a direct assignment of the chirality of individual molecules.

When used in conjunction with "chemical marker groups" (functionalities such as -Br and -COOH), scanning tunneling microscopy is a powerful tool for studying the properties of liquid-solid interfaces. Chemical markers serve as "flags" for the identification of interfacial structures, allowing, for example, the absolute chirality of optically active molecules self-assembling on a graphite surface to be determined. Subtle changes in the orientation of these chemical functionalities that affect the long-range order of interfacial films have also been observed and explored. Finally, alterations in self-assembly resulting from variations in adsorbate or substrate structure can be deduced by taking advantage of these STM "flags".

Irrigation drainage and industrial wastewaters often contain elevated levels of toxic oxyanions and oxycations such as selenate, chromate, and uranyl. A potential remediation method is to react contaminated water with zero-valent iron, which transforms the mobile contaminants into immobile forms. In this work, iron foil was exposed to aqueous solutions containing the relevant ions, and the reacted surfaces were characterized by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). STM images collected in situ show that the protrusions on the foil surface associated with iron oxides are smoothed out by the reaction. XPS indicates that partially reduced Se(IV) and Cr(III) are adsorbed on the surface, while uranium is deposited as U(VI), i.e., without reduction. More Se and Cr are deposited when the atmospheric gases are removed from solution because of the elimination of a competing process in which dissolved O2 increases the thickness of the iron oxide overlayer to the point where the reduction reaction is quenched. The amount of U deposited is greatly increased when the atmospheric gases are removed because of the elimination of dissolved CO2, which can form carbonate complexes with uranium.