The fitting results for the different samples resulted in a PL decay time in the range of 19 to 23 μs and a constant β in the range of 0.85 to 0.95. The PL results are discussed in detail in the ‘Discussion’ section. The differences in the PL behavior of the different samples can be explained by taking into account
that the studied samples constitute very complicated systems of nanowires composed of nanocrystals of different sizes and different surface chemical compositions that, in addition, present different structural defects at their surface. Depending on the chemical treatment, the mean size of the nanocrystals composing the nanowires and their surface chemical composition are different. Moreover,
the number and nature of the structural defects change. Both surface composition and structural defects introduce states in the nanocrystal energy bandgap that influence the PL selleckchem recombination mechanism. In addition, the porous Si layer underneath the SiNWs contributes to the PL signal. The above will be discussed in detail for each sample in the ‘Discussion’ section. FTIR analysis The surface composition of the four different samples was characterized by FTIR find more Saracatinib transmittance analysis. The results are depicted in Figure 5. The spectra of the as-grown and the piranha-treated samples are similar, showing the characteristic asymmetric stretching signals of the Si-O-Si bridge between 1,000 and 1,300 cm−1, with a strong band at 1,080 cm−1 and a shoulder at 1,170 cm−1. Furthermore, a strong broad signal between 3,000 and 3,650 cm−1 is present, attributed to the stretching signal of the SiO-H bond . Finally, the peak at 626 cm−1 is in general attributed to the Si-H bond . However, since no other vibrations of the Si-H bond are present, this peak can be attributed to the wagging vibration mode of the OSi-H bond. On the other hand, the FTIR transmittance spectra after the
first and the second HF dip (Figure 4, spectra 2 and 4) do not show any significant surface oxide signature, since the surface oxide has been removed by the HF. The characteristic asymmetric stretching signals of the Si-O-Si bridge between 1,000 and 1,300 cm−1 and the wagging and stretching points of O3Si-H at 847 and 2,258 Fossariinae cm−1 are too weak. Instead, the transmittance peaks due to different vibration modes of the SiHx bond (the wagging and stretching vibration modes of Si-H bond at 623 and 2,112 cm−1, and the wagging, scissors, and stretch vibration modes of Si-H2 bond at 662, 908, and 2,082 cm−1) respectively  are too strong, corresponding to the hydrogen signature at the SiNW surface. These results are exactly what one could expect from a Si surface after the above chemical treatments. Figure 5 FTIR transmittance spectra of SiNWs.