The advances in materials science allow the synthesis of novel materials in small dimensions penetrating well into the nano-scale in a progressively increasing controllable manner. With the size of matter shrinking towards the nanoscale, the properties (mechanical, thermal optical etc.) change quantitatively (i.e. decreasing number of atoms) and qualitatively. For example, it is found that fundamental interaction mechanisms like the electron-electron or the electron-phonon interaction in metals is accelerated in Gold nanocrystals when their sizes decreases to few nanometers . Scientists are now able to alter the dimensionality and the shape of the nanocrystal (e.g. spheres, nanocubes, nanorods, nanodisks, nanodots) where the degree of confinements changes from the dielectric regime to the quantum confinement regime.
Our first ultrafast time-resolved measurements in Sn nanocrystals (Fig. 2) (nanorods and nanospheres) show a dependence of the ultrafast properties on the shape of the confinement. We observe a coherent oscillation corresponding to the “breathing” vibration of the nanocrystals in the acoustic frequency regime where the frequency of this lattice deformation depends on the shape of the confinement (cylinder vs sphere).
Synthesis of more extended nanonstructures can result in complex three-dimensional systems with nano- and meso-porous properties. An interesting example is the 3-dimensional networks that are composed of Au nanospheres -as the building block- that agglomerate and finally give the complex interwoven nanostructure as shown in Fig. 3. Applications of these complex nanosystems may include switches and elements in nanocircuits, catalysts and components in solar cells. Our recent results by pump-probe spectroscopy have shown that the transport of the laser-deposited energy in the porous system is slower than its bulk counterpart, thus introducing the porosity as a significant parameter in the ultrafast optoelectronic response of such systems .
Ongoing research investigates the ultrafast response of hybrid nanoparticles that combine magnetic with plasmonic response.Collaborators
A. G. Kanaras, Physics & Astronomy, University of Southampton, Southampton SO17 1BJ, Hants, England.