Public defence in Advanced Materials and Photonics, M.Sc. Suvi-Tuuli Varjamo

The title of the thesis: Optical Modification of 2D Materials 

Thesis defender: Suvi-Tuuli Varjamo
Opponent: Prof. Zhiwen Liu, The Pennsylvania State University, US
Custos: Prof. Zhipei Sun, Aalto University School of Electrical Engineering

Two-dimensional (2D) materials, such as graphene, are materials with atomic thickness and remarkable optical and electrical properties. They have been extensively studied for over 20 years and show real promise for miniaturized applications in almost every impactful field, including microchip fabrication, medical sensing and even quantum solutions. 2D materials may hold the key to extending Moore’s law, which predicts the doubling of microcircuit components every other year, enabling smaller and more efficient devices. 

However, scaling up the production and modification of 2D materials in an eco-friendly and cost-effective way remains a major challenge. The standard 2D material device flow includes material fabrication (chemical or mechanical), polymer masking for patterning, etching to remove excess areas, and thin film deposition for electrodes or other functional layers. Achieving high-performance applications also demands precise control over physical and chemical properties, such as charge carrier concentration. In an ideal scenario, nearly all of these steps could be achieved using laser-based techniques, offering an efficient and accessible solution. This dissertation explores light-based techniques for the fabrication and modification of two-dimensional (2D) materials, with a particular emphasis on the controlled introduction of beneficial laser-induced structural defects. This ‘optical defect engineering’ is demonstrated to create band gap states that significantly enhance the nonlinear optical properties of semiconducting 2D materials. Additionally, the simultaneous laser irradiation of 2D material heterostructures, which are stacked layers of different 2D materials, induces distinctive structural transformations. These changes not only improve the optical response but also lead to profound alterations in the electronic performance of the heterostructures. 

This thesis deepens the understanding of laser-induced modifications in 2D materials and introduces scalable, cost-effective optical methods for their precise engineering. These techniques offer a promising route to integrate 2D materials into advanced technologies, ranging from environmental sensing to quantum devices, while also enabling faster, smaller, and more efficient systems with reduced fabrication complexity.

Keywords: two-dimensional materials, optical modification

Thesis available for public display 7 days prior to the defence at Aaltodoc. 

Contact: suvi-tuuli.varjamo@aalto.fi