Lead sulfide (PbS) nanoparticles were synthesized by chemical methods with different sizes and different capping ligands (oleic acid, myristic acid, and hexanoic acid), avoiding ligand exchange procedures, to study the effect of characteristics of the capping ligands on their energy levels and band gap values. Experimental results (UV–vis–NIR, Fourier transform infrared, and Raman spectroscopies, cyclic voltammetry, transmission electron microscopy, and electron energy loss spectroscopy) showed a marked influence of the capping ligand nature on the electro-optical properties of PbS nanoparticles with a very similar size. Differences were observed in the atomistic arrangement on the nanoparticle surface and phonon vibrations with the different capping ligands. These observations suggest that the electro-optical properties of PbS nanoparticles are not only determined by their size, through quantum confinement effects, but also strongly affected by the atomistic arrangement on the nanoparticle surface, which is determined by the capping ligand nature.

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In this contribution, we report on the microscopic and spectroscopic characterization of lead chalcogenide nanoparticles. PbSe and PbTe nanoparticles were synthesized by chemical methods, using different molar ratios of Pb, Se, and Te precursors and varying the reaction time. These nanoparticles were characterized by means of transmission electron microscopy and their related techniques: electron diffraction, energy dispersive X-ray spectroscopy (EDXS), electron energy loss spectroscopy (EELS), and aberration corrected scanning transmission electron microscopy (AC-STEM), to obtain information related to their morphology, crystal structure, and composition. They were also characterized by means of Fourier transform infrared (FTIR) absorption spectroscopy to assess the functional groups found on the surface of the nanoparticles, depending on the synthesis conditions. The results obtained showed that the synthesized nanoparticles always display a higher concentration of Pb compared to that of the chalcogen. Moreover, the final concentration of Pb depended on the original ratio between the Pb precursor and the chalcogen precursor used in the synthesis. These variations in the composition influenced the FTIR absorption characteristics of the nanoparticles. EDXS, EELS, and AC-STEM results indicate that this excess of Pb is located on the surface of the nanoparticles, particularly in the amorphous capping layer. These results as well as those obtained from FTIR spectroscopy suggest that the protective layer is mostly made of lead oleate.