In this thesis the chemical and physical interactions of both single-layer and multi-layer graphene are experimentally investigated.
'Graphene is a promising material for optical uses, says Baibhav Mund. 'It may protect sensitive optic surfaces because of its high optical transmission, chemical and mechanical stability, and its very special thin layer characteristics.'
Lifetime tests and new experimental characterization techniques were performed during this PhD work. Oxidation studies showed that single-layer graphene degradation is most likely to occur at point defects and grain boundaries. 'When properly used, single layer graphene is a good candidate for optical layer protection still,' Baibhav says. 'We showed that a low defect density is paramount.'
Further, it was shown that multi-layer graphene can be resistant to oxidation when dosed with H2O, as exposed to EUV radiation in the presence of even up to 1 x 10-3 mbar of H2.
Baibhav: 'Because of the morphology we could argue that the only way for EUV-induced chemistry to take place, would be through either EUV photons, or photoelectrons generated from graphene.
Baibhav'' s NWO-funded PhD work was also funded by ASML and Zeiss Optical and Optoelectronic Technology.
'I learnt a lot working in two worlds, academic and industry, at the same time,' Baibhav shares. 'I got to learn the research approach at ASML by performing experiments there, and by close collaboration with my daily supervisor. Experimenting at Mesa+ was of extra value by being able to design unique characterization experiments, using the equipment of the Nanolab and the expertise available at Mesa.'
Baibhav: 'We had biannual meetings, discussing the progress of the work in an open atmosphere. I also learnt that writing public and internal reports is quite different from writing academic articles to be published in renowned journals. We managed to publish on some fundamental physical phenomena and on surface science.'
For example, Scanning Electron Microscopy (SEM) images showed that multi-layer graphene contains holes of < 50 nm diameter. These holes increase in number after exposure to EUV. 'Transferred multilayer graphene is shown to be more susceptible to oxidation, by formation of keto-enol groups when compared to As-grown multi-layer graphene,' Baibhav concludes.
Multi-layer graphene was further investigated, as a diffusion barrier for atomic hydrogen and compared to sputter-deposited amorphous carbon of similar thickness.
Experiments demonstrated that etching of graphene by atomic hydrogen is considerably slower than etching of an amorphous carbon film of similar thickness. As a final sub-study, Ruthenium was investigated as a protective material with respect to photochemistry of carbon and oxygen containing molecules, notably CO2.
'After my Defense I would like to pursue a job in industry,' Baibhav says. 'I now have a good impression how R&D in a company such as ASML takes place, and how industrial research and academic research may benefit and strengthen one another. I like to widen my scope in a future job. I hope to use the experience gained during this four years.'