F. Siviero

Cluster-Beam Deposition and in situ Characterization of Carbyne-Rich Carbon Films

Nanostructured carbon films produced by supersonic cluster beam deposition have been studied by in situ Raman spectroscopy. Raman spectra show the formation of a sp2 solid with a very large fraction of sp-coordinated carbyne species with a long-term stability under ultrahigh vacuum. Distinct Raman contributions from polyyne and cumulene species have been observed, as well as different stabilities under gas exposure. Our experiments confirm theoretical predictions and demonstrate the possibility of producing a carbyne-rich pure carbon solid. The stability of the sp2-sp network has important implications for astrophysics and for the production of novel carbon-based systems.

A portable ultrahigh vacuum apparatus for the production and in situ characterization of clusters and cluster-assembled materials

We present and discuss the design and operation of a compact ultrahigh vacuum compatible apparatus for the production and deposition of supersonic cluster beams. The apparatus is equipped with a pulsed microplasma cluster source capable of providing supersonic beams of high stability and intensity. The cluster mass distribution can be analyzed by a two-stage time-of-flight mass spectrometer. The transportability and versatility of the apparatus make the system well suited to perform in situ studies on both gas phase clusters and cluster assembled materials using different characterization facilities. The performances of the system have been tested by scanning tunneling microscopy and photoemission spectroscopy experiments on cluster-assembled carbon films.

Nanoscale and Mesoscale Properties of Nanostructured Carbon Films

Abstract A multi‐scale investigation of nanostructured carbon films has been performed by means of inelastic light scattering (Raman and Brillouin scattering). Carbon films with different nano‐ and mesostructure have been deposited from supersonic cluster beams in a low energy deposition regime by exploiting aerodynamic focusing effects. Acoustic phonon propagation in the porous amorphous structure, where disorder acts as a damping factor, is investigated by Brillouin scattering. Depending on the nano‐ and meso‐structure, acoustic phonons can either propagate along the medium, which acts as an elastic continuum at the meso‐scale (i.e., hundreds of nm), or turn to overdamped oscillations localized by the structural disorder. Nevertheless, we show that it is always possible to measure the elastic constants of thin and porous films, when other techniques (e.g., nano‐indentation) become critical. At the nano‐scale, Raman scattering measurements show the typical structure of an amorphous carbon, where the structural disorder is affected by the primeval cluster mass distribution. The synthesis of cluster‐assembled carbon films and the in situ Raman characterization in a UHV system allowed to observe the presence of a relevant fraction of sp 1‐hybridized carbon chains (also known as carbynoid structures) embedded in the sp 2 amorphous network.