Vibrational density of states and thermodynamics at the nanoscale: the 3D-2D transition in gold nanostructures.

Surface enhanced Raman scattering (SERS) is generally and widely used to enhance the vibrational fingerprint of molecules located at the vicinity of noble metal nanoparticles. In this work, SERS is originally used to enhance the own vibrational density of states (VDOS) of nude and isolated gold nanoparticles. This offers the opportunity of analyzing finite size effects on the lattice dynamics which remains unattainable with conventional techniques based on neutron or x-ray inelastic scattering. By reducing the size down to few nanometers, the role of surface atoms versus volume atoms become dominant, and the "text-book" 3D-2D transition on the dynamical behavior is experimentally emphasized. "Anomalies" that have been predicted by a large panel of simulations at the atomic scale, are really observed, like the enhancement of the VDOS at low frequencies or the occurrence of localized modes at frequencies beyond the cut-off in bulk. Consequences on the thermodynamic properties at the nanoscale, like the reduction of the Debye temperature or the excess of the specific heat, have been evaluated. Finally the high sensitivity of reminiscent bulk-like phonons on the arrangements at the atomic scale is used to access the morphology and internal disorder of the nanoparticles.

In-plane organization of silicon nanocrystals embedded in SiO2 thin films.

Nanofabrication of buried structures with dimensions below 5 nm and with controlled 3D-positioning at the nanoscale was attempted to open new routes to future nanodevices where single nanostructures could be systematically interfaced. A typical example is ultralow-energy ion beam synthesis where already the depth positioning of embedded arrays of silicon nanocrystals can be finely controlled with nanometric precision. In this study, we investigated for the first time the control of the in-plane organization of the nanocrystals using a legitimate patterning option for microelectronic industries, self-assembled block-copolymer. The compatibility with the ultralow-energy ion beam synthesis process of polymeric nanoporous films used as mask was demonstrated together with the capability to control in 3D the organization of Si nanocrystals. The resulting nano-organization consists in a hexagonal array of 20 nm wide nanovolumes containing on average 8 nanocrystals embedded at a controlled depth within a silica matrix.

Extraction of the characteristics of Si nanocrystals by the charge pumping technique.

In this paper, the characteristics of silicon nanocrystals used as charge trapping centers in memory devices are examined using the two-level charge pumping (CP) technique performed as a function of frequency and energy filtered transmission electron microscopy (EFTEM). The parameters extracted from the two methods such as the depth location, density and effective diameter of the nanocrystals are in good quantitative agreement. These results validate the charge pumping approach as a non-destructive powerful technique to access most of the properties of nanocrystals embedded in dielectrics and located at injection distances from the substrate surface not limited to the direct tunneling regime.

The synthesis of single layers of Ag nanocrystals by ultra-low-energy ion implantation for large-scale plasmonic structures.

Single layers of silver (Ag) nanoparticles embedded in silica (SiO2) have been fabricated by ultra-low-energy ion implantation. The distance between the Ag particles and the free SiO2 surface is controlled with nanometer precision. Raman scattering and reflectivity measurements strongly correlate to transmission electron microscopy analyses, allowing the use of these non-invasive techniques to monitor structural and dynamical properties. These results open up new opportunities to manipulate electromagnetic near-field interactions on wafer-scale plasmonic devices.