Nanoscale femtosecond spectroscopy for materialscience and nanotechnology

The design and implementation of a novel facility to perform ultrafast spectroscopy and three-dimensional (3D) fabrication at the nanoscale is reported. Single and multiphoton femtosecond excitation coupled to a laser scanning confocal microscope and a photon counting streak camera system allows to perform photoluminescence (PL) spectroscopy with in-plane spatial resolution of the order of 100 nm and temporal resolution of similar to2 ps. The facility combines high performance imaging capabilities in 3D with high sensitivity detection system and time-resolution of the photoluminescence. Imaging and spectroscopy are performed on the same spatial position thus allowing a direct correlation of the morphological features with the spectroscopic properties. The use of a laser scanning confocal microscope gives the advantages of far-field microscopy (possible sample perturbation as in the case of near-field technique is prevented) with spatial resolution well below the diffraction limit, and fast laser scanning for fast data acquisition and lower sample photodegradation. A possible application of this optical nano-probe is in the spectroscopic investigation and imaging of the active areas of molecular electronic and optoelectronic devices, such as TFTs, LEDs and PVs cells. The morphology of active layers within working devices can be correlated to field distributions, charge flows, charge recombination and light emission. We show the potential of this novel experimental set-up for the study of organic, hybrid, biological nanostructures and nanodevices. (C) 2003 Elsevier Science B.V. All rights reserved.