C. Boragno

Self-organized metal nanowire arrays with tunable optical anisotropy

Here we report on the development of an unconventional approach for the physical synthesis of laterally ordered self-organized arrays of metallic nanowires supported on nanostructured dielectric templates. The method, based on a combination of nanoscale patterning of the glass substrate by ion beam sputtering with shadow deposition of the metal nanoparticles, provides a viable alternative to time consuming serial nanopatterning approaches. Far-field optical characterization demonstrates that the nanowire arrays exhibit tunable anisotropic properties in the visible range due to the excitation of localized plasmon resonances.

Patterning polycrystalline thin films by defocused ion beam: The influence of initial morphology on the evolution of self-organized nanostructures

We report on self-organized patterning of polycrystalline noble metal films, supported on dielectric substrates, by defocused Ar+ ion beam irradiation. The initial surface morphology affects the formation of nanostructures, forcing the growth of ripples with a lateral periodicity imposed by the pristine polycrystalline grain distribution. At the early stages, the self-organization process is dominated by the shadowing of taller grains, while a crossover to the conventional erosive regime, observed for single crystals, sets in at longer sputtering times. The grain boundaries, although providing an additional bias for diffusion of mobile defects, do not affect the propagation of nanoscale ripples across individual grains.

Elastically bounded flapping wing for energy harvesting

In this Letter, we present and discuss an energy harvesting device, based on a wing elastically bounded to a fixed support. Large amplitude and periodic oscillations can be induced when this system is subject to wind, if a few parameters are carefully set. A linear stability analysis as well as two-dimensional numerical simulations confirms the existence of instability regions in the parameter space. In order to harvest energy by using this system, different methods are considered. Preliminary results obtained by an electromagnetic coupling are presented.

Contact mechanics and friction of fractal surfaces probed by atomic force microscopy

We investigated the contact mechanics and friction forces between atomic force microscope (AFM) probes and self-affine fractal carbon films. We studied single-asperity contacts by means of conventional nanometric conical tips whilst custom-designed micrometric flat tips were adopted to form multiple junctions between the probe and the sample. By varying the externally applied load we found that the average frictional force follows a power-law behavior in the single-asperity regime and a linear behavior in the multi-asperity regime. The friction coefficient was the same for carbon specimens having different fractality. We also acquired quasi-static load–displacement curves on micrometric scale, revealing a strong dependence of the average indentation depth on the values of fractal parameters. A comparison of experimental data with contact theories for randomly rough surfaces is provided.

Friction force microscopy investigation of nanostructured carbon films

Frictional properties of nanostructured carbon-based films, obtained by deposition of supersonic carbon clusters, have been investigated by friction force microscopy under ambient conditions. The experiment was performed at low loads to avoid plastic deformation and wear of materials. By analysing the load-dependent measurements acquired on samples with different composition, we deduced that the Hertzian-plus-offset model can take into account the frictional behaviour of these materials. A strong dependence of adhesive forces on the specific surface location was observed. A quantitative comparison among these films and atom-assembled carbon compounds is finally presented.

Fabrication of stable nanopatterns on metals

Nanopatterns on metal surfaces can be easily created by ion sputtering. However, due to the fast diffusion processes characterizing these materials, the nanostructures are often unstable at room temperature and above. This effect prevents the use of such patterned substrates in nanotechnology applications. In this letter, we present a simple oxidation process able to stabilize these features durably. The method has been tested on Cu, but its generality suggests that it can be applied to many other metals.

C60 thin films on Ag(001): an STM study

Abstract The structure of submonolayer C60 films deposited on Ag(001) is studied as a function of the substrate temperature in the range 100–700 K. Morphological aspects such as island shape and preferential nucleation sites are in agreement with the theory of submonolayer deposition. A peculiar irreversible transition which leads to the onset of brightness differences between molecules of the same film is observed at around 300 K. This effect is ascribed to electronic differences due to non-equivalent orientation of the C60 molecules on the surface rather than to morphological differences induced by a surface reconstruction.

Amplified nanopatterning by self-organized shadow mask ion lithography

The self-organized formation of high aspect ratio dielectric nanostructures can be guided and sped-up recurring to a sacrificial metal film during ion beam sputtering. Following ion irradiation, the metal film evolves into a disconnected array of laterally ordered nanowires, which guide etching of the dielectric substrate. While the amplification rate of large scale features can be described simply in terms of the ratio of the sputtering yields of substrate and film, for small scale features the amplification rate depends on the interplay and lateral range of the smoothing and erosive mechanisms of the two materials.

Low-temperature static friction of N2 monolayers on Pb(111)

Using a quartz crystal microbalance technique, we have measured the interfacial viscosity of nitrogen monolayers deposited on very homogeneous Pb(111) surfaces. At temperatures below 15?K, no dissipation is detected, suggesting that the N2 films are rigidly coupled to the oscillating electrode. By raising the temperature close to 20?K, we find sliding of the nitrogen film for coverages above about 0.5?nominal layers. The observed temperature dependence is in good qualitative agreement with recent calculations on the static friction of a nitrogen slab in contact with a crystalline Pb substrate.

Wetting process in superhydrophobic disordered surfaces

A sessile (water) drop deposited onto a superhydrophobic surface can stay in two different regimes: the heterogeneous (or Cassie–Baxter) regime, where air or vapour is trapped at the interface, or the homogenous (or Wenzel) regime, where the interface is completely wet. Often, a spontaneous transition from the first to the second regime may occur in time. We report on a study of this phenomenon in a new kind of superhydrophobic surfaces, characterized by a relevant spatial disorder. The observed transition follows a behaviour quite different respect to the one measured in the commonly used periodic artificial arrays.