Morphology of Monolayer MgO Films on Ag(100): Switching from Corrugated Islands to Extended Flat Terraces
The ability to engineer nearly perfect ultrathin oxide layers, up to the limit of monolayer thickness, is a key issue for nanotechnological applications. Here we face the difficult and important case of ultrathin MgO films on Ag(100), for which no extended and well-ordered layers could thus far be produced in the monolayer limit. We demonstrate that their final morphology depends not only on the usual growth parameters (crystal temperature, metal flux, and oxygen partial pressure), but also on aftergrowth treatments controlling so far neglected thermodynamics constraints. We thus succeed in tuning the shape of the oxide films from irregular, nanometer-sized, monolayer-thick islands to slightly larger, perfectly squared, bilayer islands, to extended monolayers limited apparently only by substrate steps.
SPM by CreaTec.
Jagriti Pal, Marco Smerieri, Edvige Celasco, Letizia Savio, Luca Vattuone, and Mario Rocca, Morphology of Monolayer MgO Films on Ag(100): Switching from Corrugated Islands to Extended Flat Terraces
Radio-Wave Oscillations of Molecular-Chain Resonators
We report a new type of nanomechanical resonator system based on one-dimensional chains of only 4 to 7 weakly coupled small molecules. Experimental characterization of the truly nanoscopic resonators is achieved by means of a novel radio-frequency scanning tunneling microscopy detection technique at cryogenic temperatures. Above 20 K we observe concerted oscillations of the individual molecules in chains, reminiscent of the first and second eigenmodes of a one-dimensional harmonic resonator. Radiofrequency scanning tunneling microscopy based frequency measurement reveals a characteristic length dependence of the oscillation frequency (between 51 and 127 MHz) in reasonable agreement with onedimensional oscillator models. Our study demonstrates a new strategy for investigating and controlling the resonance properties of nanomechanical oscillators.
SPM by CreaTec.
Stefan Müllegger, Mohammad Rashidi, Karlheinz Mayr, Michael Fattinger, Andreas Ney, and Reinhold Koch, Radio-Wave Oscillations of Molecular-Chain Resonators