Catalytic nanomotors: self-propelled sphere dimers.

Experimental and theoretical studies of the self-propelled motional dynamics of a new genre of catalytic sphere dimer, which comprises a non-catalytic silica sphere connected to a catalytic platinum sphere, are reported for the first time. Using aqueous hydrogen peroxide as the fuel to effect catalytic propulsion of the sphere dimers, both quasi-linear and quasi-circular trajectories are observed in the solution phase and analyzed for different dimensions of the platinum component. In addition, well-defined rotational motion of these sphere dimers is observed at the solution-substrate interface. The nature of the interaction between the sphere dimer and the substrate in the aqueous hydrogen peroxide phase is discussed. In computer simulations of the sphere dimer in solution and the solution-substrate interface, sphere-dimer dynamics are simulated using molecular-dynamics methods and solvent dynamics are modeled by mesoscopic multiparticle collision methods taking hydrodynamic interactions into account. The rotational and translational dynamics of the sphere dimer are found to be in good accord with the predictions of computer simulations.

Molecular mapping by low-energy-loss energy-filtered transmission electron microscopy imaging.

Structure-function relationships in supramolecular systems depend on the spatial distribution of molecules, ions, and particles within complex arrays. Imaging the spatial distribution of molecular components within nanostructured solids is the objective of many recent techniques, and a powerful tool is electron spectroscopy imaging in the transmission electron microscope (ESI-TEM) in the low-energy-loss range, 0-80 eV. This technique was applied to particulate and thin film samples of dielectric polymers and inorganic compounds, providing excellent distinction between areas occupied by various macromolecules and particles. Domains differentiated by small changes in molecular composition and minor differences in elemental contents are clearly shown. Slight changes in the molecules produce intensity variations in molecular spectra that are in turn expressed in sets of low-energy-loss images, using the standard energy-filtered transmission electron microscopy (EFTEM) procedures. The molecular map resolution is in the nanometer range and very close to the bright-field resolution achieved for the same sample, in the same instrument. Moreover, contrast is excellent, even though sample exposure to the electron beam is minimal.