The electronic structure and morphology of ultrathin MgO films epitaxially grown on Ag(001) were investigated using low-temperature scanning tunneling spectroscopy and scanning tunneling microscopy. Layer-resolved differential conductance (dI/dU) measurements reveal that, even at a film thickness of three monolayers, a band gap of about 6 eV is formed corresponding to that of the MgO(001) single-crystal surface. This finding is confirmed by layer-resolved calculations of the local density of states based on density functional theory.

Considerable progress has been made recently, using scanning tunnelling microscopy (STM), scanning tunnelling spectroscopy (STS) and local density functional theory (DFT), in examining the atomic structure and electronic properties of ultrathin insulating films. This article reviews pertinent results to date with special emphasis on ultrathin MgO films on Ag(001) surfaces. Using STS, the layer-by-layer resolved electronic structure up to 3 ML shows that the band gap of about 6 eV at the MgO surface develops within the first 3 ML confirmed by local density of states (LDOS) calculations. Using model calculations, the atomic species observed in STM on the MgO film are unambiguously identified. These results underline the importance of a combination of local spectroscopy, scanning probe techniques and local density of states calculations for the understanding of matter on the microscopic level.

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Scanning tunneling microscopy at low temperature reveals that upon dissociative adsorption of oxygen on Ag(001) “hot” adatoms have separated in a far-ranged transient motion to two different intrapair distances around 2 and 4 nm, corresponding to 7 and 14 surface lattice constants, respectively. Manipulation experiments on oxygen atoms displaying different contrasts in the images and model calculations suggest that the transient motion ends up not only in the stable fourfold hollow site but also in two metastable sites.

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The optical properties of indium islands on GaAs(001) surfaces have been studied by reflectance anisotropy spectroscopy as a function of metal coverage. A large optical anisotropy is observed, which shows an oscillatory behavior and scales with the island size: mean island sizes determined by scanning electron microscope correspond to the wavelengths where extremes in the optical anisotropy arise. We explain this behavior by surface plasmon resonances of the island structure which induce a huge optical anisotropy related to the anisotropic shape and distribution of the In islands. Model calculations of the reflectance anisotropy spectroscopy signal based on a layer system where the island film is represented by an effective medium consisting of ellipsoidal metal particles in a vacuum matrix reproduce the main oscillation and support our conclusion

The deep biomedical knowledge reached in the past decades in many fields of medicine and biology has been accompanied by continuous technological progress in measurement instrumentation and analysis techniques. This development is important also to improve the characterization and the understanding of the interactions between nanoparticles and biological liquids, due to emerging applications such as drug delivery, bioimaging, biosensing, diagnostics and photothermal therapy. In this study, we characterize the interaction between mouse serum and gold nanoparticles (NPs) and nanorods (NRs) by Modulated 3D Cross-correlation Dynamic Light Scattering (DLS), in order to demonstrate that this technique can be applied to the investigation of complex biological liquids. The analysis of the size distribution of the hydrodynamic radius reveals three different contributions from particles motion, associated to rotation, translation and agglomerates. Moreover, we show that the interaction between Au NPs or NRs and mouse serum depends on the aspect ratio of the Au particles. These results are promising for deepening the knowledge on proteins-nanoparticles interaction, for laboratory-based experiments as well as for sensing and diagnostic applications and nanoparticles based medical therapy.