Nano-patterning and characterization of functional materials

In this thesis, the nano-patterning and characterization of various materials for the fabrication of carbon-based devices are presented. In the first part, the fabrication and characterization process of 2D-materials such as graphene and hBN are described in details. The exfoliation process and the necessary tools for the selection of high-quality graphene monolayers were optimized and was shown that a theoretically calculated contrast value of 0.05 corresponds to a graphene monolayer. These results were confirmed experimentally by Raman spectroscopy. The optical characterization methods were extensively used onto hBN. During this study, an oscillating behavior of the signal intensity to the flake thickness was observed. Further optical investigation was carried out on hBN flakes for the characterization of naturally-occurring sharp optical emissions.

A dry-transfer process for 2D materials using stamp stacks was developed and used for the fabrication of heterostructures, which were subsequently also optically characterized. 

Additionally, using a dual beam FIB-SEM setup, important progress was achieved in the nano-patterning of diamond. Employing the method of electron-beam-induced etching (EBIE) a record patterning resolution of 10 nm was achieved. The limits of this method were tested by attempting to fabricate a nanometer-sized diamond tip. Furthermore, it was shown that a threshold dose of 0.01 pC/μm2 of Ga+ is sufficient for the removal of the surface conductivity of the hydrogen-terminated diamond. The Ga+-beam was also employed for the deterministic creation of single emitters in diamond and hBN films. Subsequent photoluminescence and HBT-characterization confirmed the success of the experiment on the hBN flakes.

Finally, the aforementioned findings were combined in the fabrication of a carbon-based field-effect transistor (FET) device. The device was based on the transfer of a hBN/graphene/hBN heterostructure onto diamond, resulting in a normally-off, lateral FET structure with the diamond’s 2DHG as the conductive channel, hBN the dielectric and graphene as the gate electrode.


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