Femtosecond Laser Microfabrication of Glasses and 2D Materials for Photonics and Energy Storage
Time: Mon 2023-12-18 09.30
Subject area: Electrical Engineering
Doctoral student: Po-Han Huang , Mikro- och nanosystemteknik
Opponent: Professor Yves Bellouard, École polytechnique fédérale de Lausanne (EPFL), Neuchâtel, Switzerland
Supervisor: Professor Frank Niklaus, Mikro- och nanosystemteknik; Göran Stemme, Mikro- och nanosystemteknik; Kristinn Gylfason, Mikro- och nanosystemteknik
Femtosecond laser-based fabrication technologies have seen rapid developments in the past decades, thanks to the capability of femtosecond lasers to induce localized multiphoton absorption in materials. Multiphoton absorption can result in various material modifications that can be leveraged for additive and subtractive manufacturing. Their versatile applications have demonstrated the great potential of femtosecond lasers in advancing micro- and nano-fabrication. These include (1) multiphoton crosslinking enabling 3D printing with unprecedented patterning freedom and sub-micrometer resolution,(2) the formation of self-organized structures enabling the creation of multi-functional sub-wavelength patterns in solid materials, and (3) multiphoton ablation enabling precise sculpturing of wide-ranging materials. Nevertheless, there remains a large room to explore when it comes to available materials and achievable devices. This thesis aims to advance the applications of femtosecond lasers to glasses and 2D materials for the fabrication of advanced and integrated microdevices for photonics and energy storage. The first part of this thesis presents two approaches for 3D printing of inorganic glass. These approaches are based on two unusual observations in hydrogen silsesquioxane (HSQ) upon femtosecond laser exposure: (1) multiphoton crosslinking and (2) the formation of self-organized structures. The first work reports an approach for 3D printing of solid silica glass with sub-micrometer resolution by multiphoton crosslinking of HSQ. In contrast to the alternative methods, our approach does not require any thermal treatments, which offers desirable design fidelity and integration flexibility. The second work reports the possibility of inducing material modifications (1) and (2) in HSQ simultaneously. This possibility enables additive manufacturing of self-organized nanogratings, and thus, 3D printing of hierarchical structures made of Si-rich glass. In the third work, a protocol to perform the 3D printing on optical fiber tips is developed, which enables the fabrication of fiber-tip optical microdevices for sensing and beam shaping. The second part of this thesis presents the application of femtosecond lasers to fabricating on-paper microsupercapacitors (MSCs).MSCs are promising energy-storage microdevices for self-powering electronics, and paper substrates, yet vulnerable, are attractive for their sustainability and flexibility. The material and shape of MSCelectrodes play a crucial role in the energy-storage performance, and 2D materials have emerged as suitable candidate materials. In the last two works, a scalable approach for the precise micromachining of 2D-material electrodes by multiphoton ablation is developed, preserving their electrochemical performance and the integrity of the paper substrates.