Non-covalent Modification of Graphene and MoS2 Synthesis and Characterization of Charged Molecules and Two-Dimensional Materials

Doctoral thesis, 2020

Graphene is a material of superlatives. It has unique properties, which are explored in various areas of interdisciplinary research. Graphene can improve the properties of other materials or even give them new functions and is therefore a suitable candidate for different sensor applications. While covalent functionalization of graphene comprises the outstanding properties of graphene, non-covalent modification of graphene does not affect the outstanding properties of graphene. Next to graphene there are other two-dimensional materials such as molybdenum disulfide in the focus of research, which increases the scope of applications for two-dimensional materials.
 
This thesis presents the synthesis of a series of neutral and charged π-conjugated systems with a different amount of either benzimidazole or pyridine moieties. The molecules differ in the size of their π-conjugated system, the amount of charges, and the counter ions. Selected molecules were used to non-covalently functionalize either graphene or molybdenum disulfide. The new two-dimensional materials were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy, photoluminescence spectroscopy, atomic force microscopy and Time-of-Flight secondary ion mass spectrometry. Both, neutral and charged molecules can interact with graphene/ molybdenum disulfide via intermolecular forces. Computational studies support experimental observations and helped to gain more insight about the intermolecular attraction between the π-conjugated systems and graphene. Lastly, the non-covalently functionalized graphene was used to fabricate FET-devices, which showed strong p-doping of the underlying graphene by the π-conjugated systems.
 
To summarize, we showed the non-covalent functionalization of graphene and molybdenum disulfide with π-conjugated molecules and the influence of structural and electrochemical parameters on the interaction with graphene or molybdenum disulfide. The results presented in this thesis can be the basis of novel sensors on the nanoscale such as a pH-meter or a humidity sensors.