Characterization of Pb24Te76 quantum dot thin film synthesized by inert gas condensation

•Pb24Te76 nanocrystalline film was successfully prepared by inert gas condensation.•Heat-treatment for 5 h at 473 K is suitable to make change in particle size (Ps).•The nanostructure films consider air-stable and thermal-stable below 473 K.•The changes of particle size affecting electrical and optical properties of films.•The band gap is blue shifted with decreasing particle size (Ps).

Air-stable and thermal-stable lead telluride quantum dot was successfully prepared on glass substrate by inert gas condensation (IGC) method. Argon (Ar) is the inert gas used during deposition process with a constant flow rate of 3 × 10−3 Torr. The effect of heat-treatment process at different times was studies for structure, optical and electrical properties for nanocrystalline thin films. The structures of the as deposited and heat-treated films were investigated using grazing incident in-plane X-ray diffraction (GIIXD). The GIIXD pattern showed nanostructure face centered cubic structure of PbTe thin films. The energy dispersive X-ray analysis (EDX) of as deposited PbTe thin film was carried out and showed that the atomic ratio of Pb/Te was 24/76. The particle size of the as deposited PbTe film and after stored it in an unhumid atmosphere are 6.8 ± 0.3 nm and 7.2 ± 0.3 nm respectively as estimated form TEM image (i.e. in the same level of particle size). However, the particle size was changed to be 11.8 ± 0.3 nm after heat-treated for 5 h at 473 K. These particle size values of PbTe thin film are smaller than its Bohr radius. The estimated value of optical band gap Eg decreased from 1.71 eV for the as deposited film to 1.62 eV for film heat-treated (5 h at 473 K). The dc electrical conductivity is increased with raising temperature in the range (303–473 K) for all thin films under investigation. The deduced activation energy decreased from 0.222 eV for as deposited sample to 0.125 eV after heat-treated at 473 K for 5 h.

Graphical abstractTransmission electron microscope (TEM) micrograph of as deposited Pb24Te76 thin film; it shows a homogenous distribution of a spherical shape of nanoparticles over wide range. The particle size of nanoparticles can be estimated from the micrograph image which in turn plays an important factor affecting all physical properties. This particle size does not show assignable change after stored for 200 days in room temperature and heat-treated for 3, 4 h at 473 K. This means that thin film is air and thermal-stable. The defined diffracted rings observed in the diffracted pattern indicating that, the film have crystalline structure nature.Figure optionsDownload full-size imageDownload as PowerPoint slide