NaCl islands on Ag(111) are investigated by low temperature scanning tunneling microscopy and spectroscopy. The thermodynamically stable growth mode consists of bilayer-high rectangular-shaped islands that are (100) terminated with a large band gap. Deviations from this bulk-like (100) growth are induced by surface defects as intrinsic step edges and point defects in the supporting Ag( 111) surface. The interface between NaCl(100) and Ag( 111) induces an interface state that is completely depopulated with its onset at (92 ± 4) meV. The influence of the Ag surface-induced defects on the interface state is discussed.

The submonolayer growth of NaCl bilayer high-rectangular shaped islands on Ag(111) is investigated at around room temperature by using low temperature scanning tunneling microscopy. The growth at the step edges is preferred. Two kinds of islands are observed. They either grow with their non-polar edge at the step edge of Ag(111) or the islands overgrow in a carpet-like mode with the polar direction parallel to the edge. In the latter case, the Ag step is rearranged and considerable, while the NaCl layer is bent. This study clarifies the nature of the interaction of an alkali halide nanostructure with a metal step edge.

We investigate astraphloxine, an industrial dye, on two metal surfaces, Au(111) and Ag(111). Low-temperature scanning tunneling microscopy with submolecular resolution in comparison to semiempirical calculations reveal that only two of the nine possible conformers of this molecule are adsorbed. The two conformers adsorb via one of their indol groups, which serves as a platform that decouples the rest of the molecule from the surfaces. A change from one to the other conformer is demonstrated by injecting inelastic electrons from the tunneling tip selectively into individual molecules.

Determination of the exact structure of individual molecules is the ultimate goal of high-resolution microscopy. However, the resolution of scanning tunneling microscopy (STM) is intrinsically limited to the extent of molecular orbitals, which frequently do not differ for small changes in the molecular conformation. Here we use the position of water molecules during the first hydration steps of an azobenzene derivative on Au(111) to determine not only the orientation of the end groups with respect to the phenyl rings but also the orientation of the two phenyl rings with respect to the azo group. We investigate the co-adsorption of 4,4'-hydroxy-azobenzene and water molecules on Au(111) by low-temperature STM. The water molecules are attached exclusively to the hydroxyl end groups of the azobenzene derivatives. Predominantly the trans-azobenzene molecule with the two hydroxyl groups pointing into opposite directions is adsorbed. As corroborated by the attachment of a single water molecule to 4-anilino-4'-nitro azobenzene on the same inert surface, the method is generally applicable for structure determination of molecules with appropriate end groups. Our study thus gives unprecedented information about the intramolecular orientation based on the first real space observation of the hydration of a functional molecule.

Mobile molecules crossing freely underneath the scanning tip of a scanning tunneling microscope create a uniform diffusive noise, making the identification of single molecules on the surface a challenge. We demonstrate the possibility of detecting mobile molecules on a surface by scanning tunneling microscopy and reveal how the diffusive noise is created. Additionally, we show that a molecule caught in the tip–sample junction allows us to explore the potential energy surface of the system. Finally, voltage pulses disturb the mobile molecules, causing the loss of that ability. They also allow the creation of islands on the surface. Most of the investigations were done for Co- and Cu-phthalocyanine (Pc) on Ag(100). However, the concept is limited to neither Pc molecules nor Ag(100), as shown for a different organic molecule, astraphloxin, on Cu(111).