Physical properties of pulse electrodeposited lead sulfide thin films

• Cuboctahedral morphology was proposed and verified for the pulse electrodeposited PbS crystals.
• Stability of the PbS nanoparticles was due to the arrangement of Pb and S atoms causing low surface energy.
• Band gap of the PbS film showed the effect of nanograins.
• PbS films composed of nanograins in the range 2–20 nm were pulse-electrodeposited.

PbS thin films were deposited on transparent conducting substrates by pulse electrodeposition. Stoichiometric and highly adherent films were obtained by optimizing the deposition parameters such as pulse duration, deposition and dissolution potentials. Structural properties of the films were studied using XRD, and HRTEM techniques. The film consists of nanocrystals with size in the range 2–20 nm. Using atomic resolution images an atomic model with cuboctahedral morphology was proposed for the PbS crystals. The stability of the PbS nanoparticles was attributed to the surface configuration of Pb and S atoms causing low surface energy. SEM and AFM surface analysis indicated a uniform and void free surface with agglomerations of crystals with an average size in the order of 250 nm. Appearance of the 2LO mode in the Raman spectra revealed good crystalline quality of the film, and the characteristic bands were assigned in agreement with the mineral galena. The XPS spectrum in the binding energy region of sulfur shows the presence of S in 2 different environments; S 2p3/2 at 160.4 eV which is due to the sulfur in sulfide (PbS), and a second peak at higher binding energy of 161.64 eV which can be due to Pb–S–O and the Pb 4f7/2 peak at binding energy 138 eV indicate the presence of traces of PbO. However, Raman and XRD analysis showed no evidence of PbO and PbSO3. From the transmittance spectrum the band gap of the film was estimated as 0.74 eV. The resistivity of the film was 2 × 104 ohm-cm and the films were photosensitive.