PhD defense – Luigi Matera

On Friday, November 27, at 15 h (TRT Auditorium), Luigi Matera will defend his PhD thesis titled “Control of the metal-insulator transition in rare-earth nickelate thin films toward infrared camouflage applications”, supervised by Manuel Bibes and Lucía Iglesias.

Jury members:

Giampiero Gerini, Principal scientist at TNO and professor at TU Eindhoven, Examiner and Chair
Sylvia Matzen, Professor at Université Paris-Saclay, C2N, Examiner
Francisco Rivadulla, Professor at University of Santiago de Compostela, CIQUS, Reviewer
Beatriz Noheda,  Professor at University of Groningen, Reviewer

Abstract: 

Camouflage is a key survival strategy in nature. It is found across a wide range of environments and species, from the body shape of stick insects to the dynamic colour changes of cuttlefish. Inspired by these strategies, humans have developed camouflage technologies for a wide range of applications. Historically, camouflage has been strongly associated with military applications. In recent decades, major advances in sensing and imaging technologies have extended camouflage strategies across multiple regions of the electromagnetic spectrum. Among these, infrared imaging has become particularly relevant because, unlike imaging in the visible range, it relies on the thermal radiation naturally emitted by anybody at finite temperature.

Among the different approaches developed for thermal infrared camouflage, thermochromic materials have attracted considerable interest owing to their ability to undergo large and reversible changes in their optical properties with temperature. In particular, these materials can be engineered to decrease their emissivity as temperature increases, compensating for the natural increase in thermal radiation and thereby realizing so-called Zero Differential Thermal Emitters (ZDTEs), for which the emitted radiative power remains approximately constant over a finite temperature range. Among the materials considered for this application,

rare-earth perovskite nickelates are particularly promising. These correlated oxides exhibit a rich phase diagram and a metal-insulator transition (MIT) arising from the strong coupling between their electronic and structural degrees of freedom. The MIT can therefore be tuned through external parameters such as chemical composition and strain, enabling a concomitant control of their optical properties.

This thesis focuses on the growth and optimization of rare-earth nickelate thin films for the realization of a room-temperature ZDTE. To this end, Sm1 – xNdxNiO3 thin films were grown by pulsed laser deposition, and their metal-insulator transition was engineered to occur close to room temperature. Their electrical, structural, and optical properties were investigated across the MIT, revealing the strong influence of epitaxial strain on the transition and providing the basis for its active control. Preliminary results using a piezoelectric substrate further demonstrate the possibility of actively modifying the structural, electrical, and optical properties of nickelate films at room temperature, paving the way toward actively tunable nickelate-based infrared camouflage devices, extending the concept of thermal camouflage beyond passive ZDTEs.