Nucleation, growth and hydrogen resistance of multi-layer graphene

This thesis describes exploratory materials research on thin graphene films for the final use as mask protecting membranes, so called pellicles, in Extreme UV photolithography. This application imposes challenging material properties, which directed the research on few steps of nanoscale membrane technology: in term this should deliver typically few tens of nanometer thick and tens of square centimeter large films which can withstand chemically active H-environments. The thesis addresses the improved growth of graphene films as well as the control of defect-induced degradation.
The graphene growth studies dealt with the use of Mo thin films and transformed Mo2C catalysts, produced using different deposition methods, in an attempt to understand the correlation to multilayer graphene (MLG) growth on these catalysts. Most notably, the density of the Mo thin films was found to be the most critical material property for graphene growth, where only low-density Mo films showed graphene growth. These Mo films are formed pinholes upon annealing, which are triggered the MLG growth. The pinholes created an interface with the under-layer oxide, which is investigated as next step.
The underlying oxide, is known to alter the chemical reaction pathways in catalysis. To evaluate its impact on graphene synthesis, an artificial interface between underlayer SiO2 and pinhole-free Mo was fabricated. The results have shown the requirement of an Mo2C/SiO2 interface for MLG growth. A chemical model for MLG nucleation is presented and critical steps of this model is tested. The results confirmed the bifunctional role of the Mo2C/SiO2 interface on MLG growth.
In order to improve the chemical resistivity of graphene films against the chemically active H radicals a passivation method has been explored. It is known that H radicals start etching graphene from defect sites. The investigated etch mitigation method involves the selective passivation of the MLG at defects using atomic layer deposition (ALD) of a H- resistant material, being Al2O3. The etch rate in an H-radical environment has been characterized, with and without ALD passivation process applied. The results have shown that the etching of graphene layers were reduced significantly by using this selective ALD passivation with Al2O3.