As discussed above, the nanowires are composed of assemblies Epigenetics inhibitor of Si nanocrystals and nanowires interconnected in a Si skeleton, the mean size of these nanocrystals being different along their length. The PL spectra from assemblies of Si nanocrystals are in general broad, and peak position depends

strongly on their size distribution and the chemical composition of their surface [21, 23–27]. Quantum confinement of the generated carriers is at the origin of the long decay times (in the several micrometer range) [25, 27]. The recombination mechanism depends on the structural and chemical composition of the nanocrystal surface. In hydrogen-terminated nanocrystals without important structural defects at their surface, free exciton recombination is in general observed [28, 29], while in oxidized nanocrystals, a significant Stokes shift is observed between the absorption and the PL band peak energy [27, 30, 31], attributed to an important pinning of the nanocrystal energy bandgap due to localized states at the interface of Si NCs with the surrounding SiO2 matrix [27, 30, 32, 33]. The same effect can be caused by structural defects at

the surface of the nanocrystals. Pump and probe measurements confirmed the above behavior [33]. The differences observed from the different samples investigated in this work can be explained, based on the above, by considering the size distribution selleck screening library of nanocrystals and the state of their surface. In the as-grown samples, a number of very tiny nanocrystals that are light emitting

are found at the surface the of larger nanocrystals. On the other hand, a lot of structural defects exist that quench luminescence (spectrum 1 in Figure 4). The tiny nanocrystals (slightly oxidized at ambient atmosphere) are removed by the first HF dip. In addition, some of the structural defects that quench PL are also smoothed out. This is why the PL signal from the SiNWs after the first HF dip is red-shifted compared to that obtained from the as-formed nanowires, and its intensity increases (spectrum 2 in Figure 4). The different surface chemistry of the as-formed and HF-treated NWs is confirmed by the FTIR results. In the HF-treated samples, the surface is hydrogen-terminated, while the as-grown sample and the sample after piranha cleaning show mainly Si-O and SiO-H bonds at the surface. The slightly oxidized NWs after piranha cleaning show a blueshift in PL due to a slight shift of the mean nanocrystal size by oxidation (spectrum 3, Figure 4). The find more increase in intensity is again attributed to a further smoothing of surface structural defects that quench PL. Furthermore, light emission from additional nanocrystals, which were dark before due to their large size and are now smaller after oxidation, contributes to the increased PL intensity.