L. Chaltel Lima

Properties of PbS: Ni2

The growth of nanocrystalline PbS films by chemical bath deposition (CBD) onto glass at temperature 𝑇=20±2∘C is presented in this research. We report on the modification of structural, optical, and electrical nanostructures due to in situ Ni-doping. The morphological changes of the layers were analyzed using SEM, AFM, and TEM. XRD spectra displayed peaks at 2θ = [26.00, 30.07, 43.10, 51.00, 53.48], indicating growth on the zinc blende face. The grain size determined by X-rays diffraction of the undoped samples was ∼36 nm, whereas with the doped sample was 3.2–5 nm. By TEM, the doped PbS was found crystalline films in the range 3.5–5 nm. Optical absorption (OA), and forbidden bandgap energy (𝐸𝑔) shift disclose a shift in the range 2.1–3.8 eV. Likewise, the dependence of 𝐸𝑔 with the radius size and interplanar distance of the lattice is discussed. Raman spectroscopy (RS) exhibited an absorption band ∼135 cm−1 displaying only a PbS ZB structure. The thermal energy for the films was determined from the slope of dark conductivity (DC) and the energy was estimated to be 0.15 to 0.5 eV.

Influence of L-Tryptophan on Growth and Optical Properties of PbS Nanocrystalline Thin Films

The growth through the green chemical bath of PbS doped systematically with the biomolecule L-tryptophan led to growth of hybrid, inorganic-organic, nanocrystalline thin films onto glass slides at . The thickness was found in the range of 230–140 nm. Morphological changes were analyzed using atomic force microscopy (AFM). FTIR (Fourier-transform infrared spectroscopy) spectra showed broad absorption bands located at ~3450 cm−1 attributed to stretching of the H2O molecules and two small absorption bands located at ~2285 cm−1 and ~2918 cm−1 along with a strong band at ~1385 cm−1 assigned to vibration modes corresponding to ions. In the patterns of X-ray diffraction (XRD), the cubic phase was identified in all the samples according to the angular positions , 30.13°, 43.08°, 51.91°, 53.60°, 6251°, 68.98°, and 71.15°. Using the Scherrer formula on the XRD patterns, the grain size (GS) was determined; for the undoped sample, ~42 nm was found, whereas for the doped samples, ~42–22 nm was found. The electronic charge distribution of L-tryptophan was determined using the molecular electrostatic potential (MEP) to understand the decrease on the GS associated with the interaction of π electrons from conjugated rings and amino-acid functional groups. The absorbance spectra in doped films showed excitonic peaks at ~1.8–2.1 eV associated to a higher energy of the 1Sh → 1Sh and 1Ph → 1Pe electronic transitions. Through optical absorption, a shift for the band gap energy was observed from ~1.4 eV for the undoped sample and ~2.1–2.3 eV for the doped films, respectively. Such behaviour is generally associated with the GS decrease and the effect of quantum confinement; a simple model by calculating changes in Gibbs free energy (ΔG°) for growth of nanocrystals is presented.