Fundamental Research On Direct Fabrication Of Low Dimensional Nanomaterials On Si Substrates
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Continuous demand for improvements to reduced electronic sizes, increased processor density, and faster performance of electronics have led researchers to study low dimensional nanomaterials for their electrical properties and sizes to achieve these criteria. These specific examples of low dimensional structures are of particular interest in electronics applications due to their size and electrical properties as they display unique electrical characteristics suitable for electronics applications. In particular, Ni and Cu silicides have a long history in Si based electronics as contact materials and interconnects in CMOS technology. Recently silicides have been used to grow large scale, high quality graphene flakes and have been shown to protect a silicide layer from oxidation. However, previous research of graphene growth atop silicides has only occurred using metal substrates in the graphene growth, followed by silicidation after the graphene has been grown. This dissertation looks at the theoretical and experimental studies of graphene and other low dimensional layers on Si. DFT calculations were performed to study whether two dimensional layers such as graphene and silicene are stable atop silicides. The binding energy, band structure, and density of states were calculated and these calculations were used to study how the silicide interface may affect the electrical properties of the 2D layer on top. Exploratory research on the direct fabrication of graphene on Si using silicides is presented as a proof of concept experiment to directly integrate graphene on Si substrates without the transfer method. Additionally, quantum dot behavior of self-assembled Ni-Si quantum dots was studied on Si(111). Ni-Si QD structures on Si(111) form ring like structures similar to the √19×√19 reconstruction. Using scanning tunneling microscopy (STM), the electronic properties of these Ni-Si rings were studied and found to display negative differential resistance (NDR) and quantum resonance not previously observed. Finally, low temperature (55K) STM analysis of low dimensional Sn layers on Si(111) were shown not to form a silicide due to the low solubility between Sn and Si. This new phase is of interest due to conductance and topology images indicating charge ordering within a new 4√3x2√3 phase indicating the possibility of a charge density wave at lower temperatures providing further evidence towards Sn monolayers of Si acting as a topological insulator.
SubjectGraphene, silicides, low-dimension nanostructures, quantum dots, charge density, silicene, band gap, charge ordering