September

Picture of the Month - September 2018

Here you see current insights into the research of the LaMa groups. A collection of the former pictures can be found in the Gallery.

In-plane stress development in mesoporous thin films

The research area of mesoporous thin films became more popular in the last decade as these films enhance the material properties for several applications in (photo‑)catalysis, energy storage, photo-/electrochromics, thermal insulators or sensors. As there is still a lack of fundamental understanding the relationship between the pore structure and the mechanical properties of these mesoporous thin films, ordered mesoporous thin films of TiO₂ and Ce_xZr_1-xO₂ (x = 0, 0.5, 1) were prepared via an evaporation-induced self-assembly process (EISA) and subsequently investigated in terms of the developing intrinsic and residual in-plane stress. Within the cooperation with Kansai University (Osaka, Japan), these mechanical properties were determined by the curvature method which is based on the determination of the deflection of light due to concave or convex bending of the films on a substrate. This bending derives mainly from the difference of the thermal expansion coefficient α of the substrate and the film. Dense and mesoporous films were investigated in regards to the intrinsic stress during the heat treatment up to 500 °C yielding lower stress values for the PIB₅₀-b-PEO₄₅ templated film. A comparable behavior was observed for the residual stress at room temperature for several annealing temperatures indicating the distributed polymer and the corresponding mesopores act as relaxing agents for the system which was further verified by mesoporous Ce_xZr_1-xO₂ (x = 0, 0.5, 1) thin films. Our work reveals the increase in the residual in-plane stress during the pore collapse which lays the foundation for further understanding the stress-related mechanical properties of mesoporous thin films.

Recent publication:
P. Cop, S. Kitano, K. Niinuma, B. Smarsly, H. Kozuka, Nanoscale, 2018, 15, 7002–7015.
doi: 10.1039/C8NR00793D

This picture was submitted by Pascal Cop, group of Prof. Dr. Bernd Smarsly.