Scanning tunneling microscopy characterization and metallic nanocontacts for atomically precise graphene nanoribbons
As a potential candidate for replacing silicon (Si) as a next-generation semiconducting material, atomically precise graphene nanoribbons (GNRs) have been predicted to show very interesting electronic properties based on their geometries and their underlying substrates. Once the ribbons are synthesized, confirmation of their geometries and investigating their electronic properties are essential for further implementation in devices. This dissertation addresses investigations of three different solution-synthesized atomically precise GNRs by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). A dry contact transfer (DCT) technique was implemented for depositing GNRs onto various semiconducting substrates. Detailed STM and STS measurements of doublewide GNRs on InAs(110) and InSb(110) confirmed their geometries and revealed a 2 eV bandgap as well as the 3-D distribution of the local density of states. Computational modeling of the ribbon´s electronic structure showed good agreement with our experimental results, indicating a weak coupling between the InAs substrate and the GNR. STM studies of two additional types of GNRs, the extended chevron GNRs and the nitrogen-doped GNRs on InAs, demonstrate how structural modifications affect the properties of the ribbons including their bandgaps and interactions with the substrate. We also proposed a scheme of writing metallic hafnium diboride nanocontacts onto isolated GNRs using STM tip-assisted deposition for conducting transport measurements. In order to perform transport measurement in situ through sample biasing, we prefabricated an array of large metallic electrodes on Si and loaded it into the STM system. The material chosen, structural design and e-beam fabrication process are described in detail. The effect on thermal treatment to the formation of metal-silicide compounds was explored.
Scanning Tunneling Microscopy, Graphene Nanoribbons
University of Illinois - Urbana-Champaign
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University of Illinois at Urbana-Champaign