Comprehensive characterization at nanoscale is needed to create novel nanostructures for high efficiency solar cells. To produce consistent results, wide-ranging characterization procedures for integrated nanostructures have been developed. Characterization of a novel nanowire, nanotube and nanocable system includes: chemical, electrochemical, structural, optical and electrical characterization of nanostructures in relation with growth conditions. We present here results on Au and CdTe/Au system that help understanding how surface composition and properties are modified in this system. New challenges in structural characterization were also identified and improved sample preparation techniques were developed.

We studied the optical properties of silicon nanocrystals incorporated into colloidal and solgel matrices. The silicon nanocrystals are produced by ultrasonic dispersion of porous silicon layers. We report results on the dependence of the photoluminescence (PL) spectra with excitation intensity. The PL shows a blue peak (at ∼ 415-460 nm.) and a red peak (at ∼ 680 nm). This PL spectrum shows a remarkable dependence on the excitation intensity. As the intensity is increased, the blue peak grows at the expense of the red. A model is suggested for this behavior. We also report on the excitation intensity dependence and the emission wavelength dependence of the PL decay at low (1 kHz) and high (82 MHz) repetition rates of optical excitation. When low repetition rate excitation is used, the PL decay times are all exponential, short (ns), and appear to vary little with emission wavelength. This sharply contrasts with what is observed in porous silicon. With high repetition rate excitation, both red and blue peaks show long (100's ns) and short (ps-ns) lifetime components. We contrast the different optical properties of these silicon nanocrystals with that observed in porous silicon.