FACULTY OF TECHNOLOGY AND SOCIETY | Seminar
Licentiate seminar – Sana Khayyamifar

As demand for wearable devices grows, the need for sustainable and reliable energy sources becomes increasingly important. Materials designed for skin contact must be non-toxic, environmentally friendly, affordable, and stable. Both mechanical and chemical stability are essential: they must adhere to flexible substrates, withstand  bending, and remain unchanged under prolonged exposure to air, moisture, and skin-like environments.

The thesis evaluates the stability of amorphous TiNiSn thin films for flexible thermoelectric applications. Mechanical performance was assessed by comparing surface morphology before and after bending. Only minor cracking at high bending angles was observed, indicating good flexibility.

Chemical stability was investigated using X-ray photoelectron spectroscopy at MAX IV Laboratory. Air exposure caused oxidation of Ti and Sn, while Ni remained inert. Simulated skin-contact conditions, using hydrogen peroxide and tryptophan in water under short- and long-term exposure, led to increased oxidation and reduced metallic species, revealing how the material evolves in reactive environments.

Computational analysis supported these findings by examining adhesion to flexible substrates (paper, silk, Kapton) and ductility via Cauchy pressure. The simulations reproduced the observed oxidation behaviour, showing strong interactions between Ti/Sn and oxygen, while Ni remained largely inert.

Overall, amorphous TiNiSn combines mechanical flexibility with predictable chemical behaviour, making it a promising candidate for flexible thermoelectric devices. Its stability and non-toxic composition highlight its potential for safe, sustainable wearable technologies.