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Register a new userNanofriction behavior of cluster-assembled carbon films
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Added by
Alessandro Podesta'
Publication date
2002
fields
Physics
and research's language is
English
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We have characterized the frictional properties of nanostructured (ns) carbon films grown by Supersonic Cluster Beam Deposition (SCBD) via an Atomic Force-Friction Force Microscope (AFM-FFM). The experimental data are discussed on the basis of a modified Amontons law for friction, stating a linear dependence of friction on load plus an adhesive offset accounting for a finite friction force in the limit of null total applied load. Molecular Dynamics simulations of the interaction of the AFM tip with the nanostructured carbon confirm the validity of the friction model used for this system. Experimental results show that the friction coefficient is not influenced by the nanostructure of the films nor by the relative humidity. On the other hand the adhesion coefficient depends on these parameters.
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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 showing a long-term stability under ultra high vacuum. Distinct Raman contribution from polyyne and cumulene species have been observed. The long-term stability and the behavior of carbyne-rich films under different gas exposure have been characterized showing different evolution for different sp configurations. Our experiments confirm theoretical predictions and demonstrate the possibility of easily producing a stable 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.
We report the experimental and theoretical investigation of the growth and of the structure of large carbon clusters produced in a supersonic expansion by a pulsed microplasma source. The absence of a significant thermal annealing during the cluster growth causes the formation of disordered structures where sp2 and sp hybridizations coexist for particles larger than roughly 90 atoms. Among different structures we recognize sp2 closed networks encaging sp chains. This nutshell configuration can prevent the fragmentation of sp species upon deposition of the clusters thus allowing the formation of nanostructured films containing carbynoid species, as shown by Raman spectroscopy. Atomistic simulations confirm that the observed Raman spectra are the signature of the sp/sp2 hybridization characteristic of the isolated clusters and surviving in the film and provide information about the structure of the sp chains. Endohedral sp chains in sp2 cages represent a novel way in which carbon nanostructures may be organized with potential interesting functional properties.
In this work we report on the controlled fabrication of a self-assembled line network in highly epitaxial BiFeO3 thin films on top of LaAlO3 in the kinetically limited grown region by RF sputtering. As previously shown in the case of manganite thin films, the remarkable degree of ordering is achieved using vicinal substrates with well-defined step-terrace morphology. Nanostructured BiFeO3 thin films show mixed-phase morphology. Besides typical formation following (100) and (010) axes, some mixed phase nanodomains are detected also in-between the regular line network. These particular microstructures open a playground for future applications in multiferroic nanomaterials.
Deposition of clusters from the gas phase is becoming an enabling technology for the production of nanostructured devices. Supersonic clusters beam deposition (SCBD) has been shown as a viable route for the production of nanostructured thin films. By using SCBD and by exploiting aerodynamical effects typical of supersonic beams it is possible to obtain very high deposition rates with a control on neutral cluster mass distribution, allowing the deposition of thin films with tailored nanostructure. Due to high deposition rates, high lateral resolution, low temperature processing, SCBD can be used for the integration of cluster-assembled films on micro- and nanofabricated platforms with limited or no post-growth processing. Here we present the industrial opportunities for batch fabrication of gas sensor microarrays based on transition metal oxide nanoparticles deposited on microfabricated substrates.
Schwarzites are 3D crystalline porous materials exhibiting the shape of Triply Periodic Minimal Surfaces (TPMS). They possess negative Gaussian curvature, created by the presence of rings with more than six sp2-hybridized carbon atoms. Recently, new routes to their synthesis have been proposed. Due to its foam-like structure, schwarzites are interesting for mechanical energy absorption applications. In this work, we investigate through fully atomistic reactive molecular dynamics the mechanical response under ballistic impacts of four structures from primitive (P) and gyroid (G) families (two structures within each family). The two structures in the same family differ mainly by the ratio of hexagons to octagons, where this ratio increases the flatness of the structures. Although the penetration depth values are higher in the flatter structures (P8bal and G8bal), the absorbed kinetic energy by them is considerably higher, which yields them a better energy-absorption performance.
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