PhD Thesis Defense by Houyem Trabelsi, predoctoral researcher at IMB-CNM
Supervisors:
- Prof. Khaled Alouani (University of Tunis El Manar, UTM)
- Dr. Stella Vallejos Vargas (IMB-CNM-CSIC)
Members of the Jury:
- Hager Maghraoui Meherzi, Professor at FST President
- Yasser Ben Amor, Professor at CNRSM Institut Reporter
- Mounir Ferhi, Professor at CNRSM Institut Reviewer
- Jesús Lozano Rogado, Professor at University of Extremadura Reviewer
Type of thesis: Cotutela PhD between the Universitat Autònoma de Barcelona (UAB) and the University of Tunis El Manar (UTM), Tunisia
About the thesis
Metal sulfide (MS) thin films have attracted significant attention due to their remarkable
electrical and optical properties. Extensive research has focused on their synthesis through
various precursors and deposition techniques. Among these, the use of transition metal
complexes as single-source precursors (SSPs) offers a promising and efficient route for MS thin
film processing. This approach integrates all required elements within a single molecular entity,
simplifying the synthesis process, and enhancing control over growth parameters. Aerosol-
assisted chemical vapor deposition (AACVD) is particularly well-suited for depositing films
from SSPs, it operates under atmospheric pressure, accommodates non-volatile precursors, and
provides excellent scalability for large-area applications.
Beyond their synthesis, the integration of nanostructured MS thin films into electronic devices,
particularly gas microsensors, has gained increasing interest. Their high surface area, strong
surface reactivity, and ability to function effectively at room temperature (RT) make them
excellent candidates for gas sensing applications. These sensor devices hold great potential
across diverse fields, including healthcare diagnostics, industrial process monitoring, food
safety, agriculture, and air quality assessment.
Among MS-based gas sensors, CuxS and ZnS stand out as promising semiconductors with
outstanding optoelectronic properties; however, their gas sensing behavior have been relatively
underexplored, making them ideal target materials for this work. In this context, my thesis
advances the state of the art by: (i) synthesizing a new copper SSP precursor, [Cu(Et4P2S2)Cl]2,
optimized for AACVD; (ii) developing novel AACVD routes for depositing Cu2S thin films
with particle- and flake-type nanostructures and (iii) establishing a new AACVD codeposition
route for the growth of ZnS nanoleaves, with all depositions carried out at relatively low
temperatures (below 500 °C).
Furthermore, this thesis demonstrates the gas sensing capabilities of Cu2S and ZnS thin films,
representing a novel contribution to the field of gas sensor research. Cu2S was found to be
particularly suitable for chemoresistive gas sensing, operating effectively at RT under
photoactivation and showing high selectivity toward NO2, while exhibiting negligible responses
to ethanol, toluene, and hydrogen. In contrast, ZnS films were more appropriate for optical gas
sensing, benefiting from their strong UV absorbance. ZnS sensors displayed higher sensitivity
to NO2 and toluene, with measurable cross-sensitivity to ethanol, hydrogen, and carbon
monoxide. The effect of humidity was significant for ZnS, leading to the formation of a ZnO
overlayer, on its surface, whereas Cu2S sensors maintained stable under humid conditions.