Monocrystalline Si NPs are observed with a lattice space of 0.31 nm corresponding to the Si (111) plane. Their diameter is mainly ranging from 4 to 8 nm with the presence of few smaller and larger NPs. This size distribution has been confirmed on functionalized AZD2014 ic50 Si NPs dispersed in squalane by DLS measurement (Figure 1B). We observe an almost monodisperse size distribution centered at 7 nm with a standard deviation of 2 nm. The efficiency of the functionalization step (Si-C18H37)

has been checked by FTIR analysis of Si NPs before and after reaction. As can be deduced from Figure 2, the surface of initial Si NPs is mainly covered by a native oxide layer giving a large characteristic SiO2 band (Si-O-Si symmetric and asymmetric stretching mode) centered at 1,100 cm−1. Nevertheless, the presence of H at the surface is also clearly evidenced by SiHx waging and rolling modes around 650 cm−1, Oy-SiHx waging around 850 cm−1, SiHx stretching modes at 2,090 cm−1, and Oy-SiHx stretching around 2,230 cm−1. After the functionalization, (i) the SiO2 band is no longer detected selleck compound which confirms the success of the HF washing step to remove the oxide layer, and (ii)

the different Si-H and O-Si-H related bands disappear. At the same time, characteristic bands of ν as (CH3) at 2,962 cm−1, ν as (CH2) at 2,925 cm−1, ν s (CH2) at 2,853 cm−1, and δ (CH2) at 1,467 cm−1 rise. These data prove the efficient replacement of the Si-H and Si-O bonds by the alkyl chains (C18H37). After this essential step that leads to a good dispersion of the Si NPs in nonpolar liquid, their luminescence properties were studied. Figure 1 Transmission electron microscopy image and DLS measurement. (A) TEM image of Si powder initially suspended in ethanol

and deposited on a graphite grid. (B) DLS of functionalized Si NPs dispersed in squalane. Figure 2 FTIR analysis of Si NPs before and after functionalization. very Si-C18H37 means Si NPs functionalized by the C18H37 group (black curve), and Si-H means Si NPs without any chemical modification (red curve). Figure 3 shows temperature-dependent fluorescence spectra of Si NP colloidal suspension in squalane with a concentration C equal to 1 mg/mL. Excitation energy is fixed at the maximum of the excitation spectra (3.94 eV). Figure 3 Temperature-dependent fluorescence spectra of Si NP colloidal suspension in squalane with a concentration of 1 mg/mL. The PL intensity of the Si NPs decreases in the chosen temperature range (from 303 to 383 K). In static conditions, this intensity variation can be used to design a sensitive temperature sensor, but many other parameters can influence the PL intensity in dynamic conditions of a mechanical contact (concentration gradient in the lubricant, pressure variation, nanoparticle flows, etc.).