Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Caesium nanostructures

Nanostructures through direct deposition of cold Caesium atoms were grown onto a surface. This is a challenging and complex task for several reasons: Caesium is highly reactive in air, hence UHV operation of the whole experiment (manipulation, deposition, investigation) is required; the use of a laser cooled atom beam implies deposition in a sub-thermal regime, that, in principle, is remarkably different with respect to conventional experiments, where effusive beams are used. As a consequence, poor knowledge of the specific diffusion and growth phenomena expected in this regime can be retrieved in the literature.

The cold atomic beam of the apparatus is produced continuously out of a pyramidal magneto-optical trap (MOT) for Caesium atoms, a specific configuration of mirrors mounted as a hollow pyramid, with a small apical aperture. Direct deposition of the cold Caesium atoms onto a surface was carried out, combined with in-situ microscopic diagnostics through UHV Scanning Tunnelling Microscopy. Direct deposition of cold Caesium atoms in the presence of standing wave optical mask was carried out by using HOPG substrates. It must be noted that, observation of a regular array of Caesium nanolines is made difficult due to the relatively small dimensions of the atomistically flat regions of the substrate. As a consequence, we concentrated our efforts so far in the investigation of single, isolated lines. Their alignment relative to the substrate is in perfect agreement with the expectations (i.e., structures are orthogonal to the standing wave direction), and their space extension appears in some images quite remarkable (almost continuous lines are observed with a length in the mm range). Besides continuous line, also structures composed of isolated mutually aligned atoms, as well as zig- zag lines have been imaged, with a typical height corresponding to that of a few atoms.

Further work will be devoted to clarify the role of process parameters and of substrate features in determining the shape of the deposits. The final assessment of the lateral resolution requires further work, including the use of different substrates and a comprehensive investigation of the role of the process parameters, yet the present preliminary data indicate a lateral confinement of the deposited atoms within a transverse size of the order of 10 nm, and a negligible contribution from background (unfocused) atoms, at least for the process parameters explored so far.

Informazioni correlate

Reported by

Universita di Pisa
L. Pontecorvo 3
56122 Pisa
See on map