SMALL VOLUME CHEMICAL BATH DEPOSITION OF Th-ALLOYED PbS FILMS

An addition of radioactive element such as thorium to thin films is expected to provide a unique path for studying radiation damage in materials. We developed a small volume chemical bath deposition (CBD) process for controlled alloying of PbS films with the stable isotope, ²³²Th. Small volume CBD technique is mandatory in order to decrease the use of Th precursor solution. In contrast to our previous work¹, we were able to drastically increase Th concentration in the films (up to ~10 at%). This was achieved by addition of sodium citrate into deposition solution, which extended Pb ions complexation in solution and allowed to obtain thicker films with higher Th concentration. Next, we developed small volume CBD process for controlled doping of PbS thin films with active ²²⁸Th isotope, altering deposition parameters such as temperature, pH, reagent concentrations and time.

The morphology and the thickness for all films were determined using scanning electron microscopy (SEM). X-ray photoelectron spectroscopy (XPS) depth profiles in ²³²Th-alloyed PbS films indicated homogeneous ²³²Th distribution in the films, and considerable amounts of oxygen were detected in the films as well. Presence of oxygen is explained by compensation of Pb²⁺ vacancies created in PbS lattice due to oxidation state difference between Pb²⁺ and Th⁴⁺ ions, by O^2- in the films. X-ray powder diffraction (XRD) of ²²⁸Th-doped films indicated a single phase material. Alpha-autoradiography confirmed homogeneous distribution of ²²⁸Th ions throughout the films. The resulting films show promise as a model system for the analysis of radiation damage in thin films.

References

¹ M. Biton, A. Shamir, M. Shandalov, N. Arad-Vosk, A. Sa’ar, E. Yahel, and Y. Golan, Thin Solid Films 556, 223 (2014).