Public defence in Advanced Materials and Photonics, M.Sc.(Tech.) Mikko Turunen

The title of the thesis: Engineering the Optical Properties of Semiconducting Two-Dimensional Materials 

Doctoral student: Mikko Turunen
Opponent: Prof. Antonio Polimeni, Sapienza Università di Roma, Italy
Custos: Prof. Zhipei Sun, Aalto University School of Electrical Engineering, Department of Electronics and Nanoengineering

After discovery of graphene twenty years ago, two-dimensional (2D) materials have emerged as one of the most prominent material platforms for optoelectronic applications. Owing to their unique atomic level thickness, they have demonstrated exquisite physical properties and offer interesting means for miniaturization of optoelectronic devices. Especially 2D transition metal dichalcogenides (TMDs) have raised attention owing to their special physical properties, including bright photoluminescence, strong spin–orbit coupling, and high optical nonlinearity. In addition, 2D TMDs have been demonstrated to host single-photon emitters, which are highly important for quantum photonics. However, the single-photon emitters do not fulfill the coherence requirements to make the emitted photons indistinguishable, which is highly required for many quantum photonic application. 

This thesis investigates means to control the optical properties of 2D TMDs to improve their applicability using optical modification and atomic layer deposition (ALD). The used optical modification method includes illumination of 2D TMD sample with femtosecond laser pulses. This modification method changes the optical response of the sample and creates three-dimensional structures on the illuminated area. In addition, the ALD of TiO2 on top of 2D TMD has a significant influence on its optical properties. These changes are caused by the chemical effects, dielectric screening, and strain arising from the ALD process. Nevertheless, it was also observed that covering the 2D TMD sample with hexagonal boron nitride, the chemical effects can be mitigated. 

The results presented in thesis provide information about the fundamental physical properties of 2D TMDs and facilitate the integration of these materials into real-world applications, such as single-photon emitters. Furthermore, the results provide useful insights for the rapidly evolving field of 2D materials, paving the way for further advancements.

Keywords: two-dimensional materials, transition metal dichalcogenides, optical modification, atomic layer deposition

Thesis available for public display 10 days prior to the defence at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/

Contact:

Doctoral theses in the School of Electrical Engineering: https://aaltodoc.aalto.fi/handle/123456789/53

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