The doctoral dissertation in the field of Physics will be examined at the Faculty of Science, Forestry and Technology, Joensuu campus.
What is the topic of your doctoral research? Why is it important to study the topic?
The topic of my doctoral research is engineering terahertz (THz) Components: Synergy of Geometry and Material Properties. Terahertz (THz) technology holds immense promise for applications in imaging, spectroscopy, sensing, and high-speed wireless communication.
However, the development of efficient, compact, and tunable THz components is hindered by the lack of naturally responsive materials in this spectral range. This research addresses these challenges by engineering metasurfaces and layered structures, particularly using graphene to manipulate THz waves with high precision. The work demonstrates broadband transparent and absorptive metasurfaces, tunable graphene-based devices, and novel THz calibration sources.
These innovations pave the way for next-generation THz systems with enhanced performance, robustness, and scalability for real-world applications in biomedicine, security, stealth technologies, electromagnetic compatibility, and environmental monitoring.
What are the key findings or observations of your doctoral research?
The key findings of my research demonstrate how engineered metasurfaces and graphene-based structures can overcome limitations in terahertz (THz) technology. Key findings include: development of broadband transparent metasurfaces using anapole resonances for low-loss THz transmission, realization of near-perfect THz absorption with random graphene metasurfaces, robust even with fabrication imperfections, demonstration of how dielectric substrates influence graphene’s electronic properties, enabling tunable device performance, creation of a blackbody radiation source for precise calibration, and observation of nonlinear THz responses in hybrid graphene-gold metasurfaces.
This work introduces scalable, tunable, and efficient THz components using novel material geometry synergies. It offers practical solutions for THz imaging, sensing, and wireless communication, and provides new tools for THz metrology. The findings are valuable for both scientific advancement and real-world applications.
How can the results of your doctoral research be utilised in practice?
The results of this research can be applied in several practical domains. The broadband transparent metasurfaces can enhance THz imaging systems by reducing signal loss and improving resolution. The graphene-based absorbers offer robust, scalable solutions for THz detectors, sensors, and stealth technologies, even under fabrication imperfections. The blackbody-like THz emitter provides a reliable calibration source for THz and far-infrared devices, essential for metrology and spectroscopy.
Additionally, the demonstrated tunability of graphene on different dielectric substrates enables the design of adaptive THz components for high-speed wireless communication, environmental sensing, and biomedical diagnostics. These innovations support the development of compact, efficient, and reconfigurable THz systems for both scientific and industrial applications.
What are the key research methods and materials used in your doctoral research?
This research combined theoretical modeling, nanofabrication, and experimental characterization to develop advanced terahertz (THz) components. Key methods included electron-beam lithography, atomic layer deposition, and chemical vapor deposition (CVD) for fabricating metasurfaces and graphene-based structures. Graphene was synthesized on copper foils and transferred using wet-transfer techniques. Characterization tools included terahertz time-domain spectroscopy (THz-TDS), scanning electron microscopy (SEM), Raman spectroscopy, and four-probe for sheet resistance measurements. Theoretical analysis employed the Drude model and transfer matrix method to extract material parameters. These methods enabled the design and validation of tunable, efficient, and scalable THz devices for imaging, sensing, and communication applications.
The doctoral dissertation of Isaac Appiah Otoo, MSc, entitled Engineering THz components: synergy of geometry and material properties will be examined at the Faculty of Science, Forestry and Technology, Joensuu campus. The opponent will be Professor Tapio Fabritius, University of Oulu, and the custos will be Professor Polina Kuzhir, University of Eastern Finland. Language of the public defence is English.
For more information, please contact:
Isaac Appiah Otoo, [email protected], tel. +358 417 401 061
