Public defence in Engineering Physics, M.Sc. Marco Will

Title of the thesis: Dynamics and correlations in low-dimensional electrical systems

Doctoral student: Marco Will
Opponent: Senior Lecturer Sergey Kafanov, Lancaster University, UK
Custos: Professor Pertti Hakonen, Aalto University School of Science, Department of Applied Physics

Low-dimensional electrical systems are an important technology in the race for further miniaturization. Graphene, the two-dimensional wonder material, and its one-dimensional counterpart, the carbon nanotube (CNT), are particularly good examples of low-dimensional systems. They have excellent mechanical and electrical properties, as they are stronger than metal and are excellent conductors. Additionally, they are extremely lightweight. With these properties, it's only natural to use them as small mechanical resonators that can be read electrically.

Within the scope of this work graphene and CNT mechanical resonators are employed to explore different applications. For that purpose the experiments were conducted at low temperatures. At low temperatures, the ordering of He atoms on the surface of a CNT mechanical resonator was investigated, and a phase diagram was derived. Furthermore, combining graphene mechanical resonators with highly sensitive coplanar microwave cavities enables a wide range of experiments. To begin, investigating the quality factor, a quantification of sensitivity, of these mechanical resonators provides insight into future improvements to such systems. The exact loss channels are determined during a single experiment. Another experiment uses graphene as a nonlinear element, which, when combined with microwave pumping of the coplanar microwave cavity, acts as an amplifier for signals in the gigahertz range. This regime is particularly interesting at low temperatures because it is where many quantum experiments take place. In addition, experiments are being conducted to investigate the electrical noise in metal-contacted graphene. Similar to quality-factor measurements, these experiments provide insight into electrical losses, paving the way for potential improvements.

This thesis includes a variety of experiments involving graphene and carbon nanotubes, as well as their applications in conjunction with other low temperature and microwave technologies. Furthermore, the entire process is described, starting with simulation and progressing through fabrication, measurement, and data analysis. This makes this thesis both broad and relevant to anyone working in the field.

Key words: graphene, carbon nanotube, mechanical resonator, low temperature, coplanar wave guide cavity, amplifier, non-linear element, helium, superconductivity, fabrication, simulation, analysis, measurement 

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

Contact information:

Doctoral theses at the School of Science: https://aaltodoc.aalto.fi/handle/123456789/52