UC Riverside

Realistic implementation of graphene and carbon nanotubes (CNT) in energy devices and nano-electronics requires these carbon nanomaterials to have engineered architectures with sp2-hybridized carbon atoms as building blocks. Graphene-CNT hybrid structures will provide attractive material properties of both CNTs and graphene with the capability to develop into a variety of geometries. The first part of this dissertation presents a scalable approach for synchronous fabrication of multiple component carbon hybrids. Large and uniform graphene-CNT hybrid films are successfully synthesized via simultaneous CVD growth of graphene layers and CNTs on copper foil substrates. The graphene-CNT hybrids have tuneable nano-architectonics, which is essential for application-oriented design of hierarchical graphene structures. The unique mechanism of synchronized CVD growth of CNT and graphene contributed significantly to the composure of the final carbon structure. We also demonstrate the potential of Block Copolymer (BCP) self-assembly as a nano-fabrication and patterning tool. Block copolymers are employed as templates to fabricate desired arrays of catalyst particles for CVD growth. Thoughtful choices of constituent blocks, polymerization degree, and volume fractions in BCPs, enable us to modulate the size and the separation distance of micro/nano-domains in the coplymer templates. Such versatility provides us with a powerful tool to control the diameter and separation distance of grown CNTs in the pillared architectures, and eventually allows us to tune the surface area in the resulting carbon hybrids.

The metrology part of this work focuses on the utilization of fluorescence quenching microscopy (FQM) for quick visualization of doping in large-area graphene layers. Reactive ion plasma etching allows us to generate patterns of p-type CVD-grown graphene layers doped with fluorine. We specifically employ the dye 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) as the fluorescent agent. The emission of DCM is quenched to different extents by p-doped and non-doped regions of graphene. This provides the fluorescence-imaging contrast, which is critical for visualization/mapping of the doped regions in high-throughput metrology techniques. To determine the method's resolution and scalability strengths, we increased the complexity of the doping pattern and successfully reproduced the mapping results. Upon that, we conducted a comparative investigation on steady-state and time-resolved fluorescence parameters of dye-coated pristine graphene and fluorinated graphene, using bare glass as the control sample. Fluorometry results support the increasing trend observed in the quenching level of DCM dye, from control sample to doped graphene to pristine graphene. The variation in fluorescence quenching by graphene after it is doped is also predicted by theory, as discussed in this work. Due to its simplicity, high speed, and small footprint, segmented FQM can be employed to address the chronic need for a microscopy based graphene metrology capable of "seeing" the features that are processed.