Nanoscale Manipulation of Surfaces and Interfaces: Engineering Electrical Properties Through Nanofabrication
Smith, Gregory J.
University of Kansas
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Nanotechnology interest and research has increased dramatically over the last decade, but there remain fundamental limitations and barriers to the fabrication of ever smaller devices. To overcome these limitations, new nanofabrication methods and novel nanoscale systems must be explored. To form nanoscale systems, we must have the ability to electrically interconnect various nanoscale parts. To do that, methods must be developed to form nanowires and nanofeatures in a very controlled fashion with arbitrary shapes. It should be noted, however, that materials' properties can change at nanoscale sizes, so these nanowires and nanofeatures themselves must be studied to ensure they function as designed. Materials with unique electronic properties and low dimensionalities, like graphene and carbon nanotubes also need to be studied for potential use in nanoscale devices. Graphene has been found to be electronically tunable by doping, causing it to be able to function as a semiconductor or as a metallic conductor. Understanding this doping interaction will help in the design and implementation of novel nanoscale systems and devices. The first part of this work puts forth a method for fabricating metallic nanofeatures into self-assembled monolayer resists. An atomic force microscope (AFM) is used with methods called nanoetching and grafting and oxidative lithography to form patterned nanofeatures down to 20 nm in width. Nanoetching and grafting involve using the AFM tip to directly remove molecules and replace them with new ones, creating a nanopattern. Oxidative lithography uses a conductive AFM tip as a tiny electrode to write nanopatterns into surfaces by very localized electrochemical oxidation. These nanopatterns are then exposed to an electroless copper plating solution, which selectively plates copper right onto those nanopatterns, to form copper nanofeatures. These are characterized with the AFM that helped form them. With this AFM based method, features of any shape can potentially be formed, providing a way to wire up more complex nanodevices and circuitry. The second part investigates the interaction between graphene-like materials and adsorbates. These interactions are becoming increasingly important as these materials become incorporated into more devices. There has been much study recently focused on graphene and graphene-like materials, such as carbon nanotubes and graphite. Graphene is of particular interest because of its low dimensionality, being a two-dimensional sheet of sp2 hybridized carbon atoms, and its unique properties. It is tough and flexible, but what is most interesting is that its electronic properties are very tunable. Adsorbates can dope it p-type or n-type, so it behaves more like a semiconductor or a metal, respectively. In this work, azulene derivatives and gold nanoparticles are studied as potential adsorbates on graphene-like materials. Azulene molecules themselves have very tunable HOMO and LUMO levels, and it could be possible to dope graphite-like materials in different fashions with different types of azulenes. Gold nanoparticles can also be tunable with size and shape, and their ability to dope graphene-like materials is of interest. Using an AFM technique called surface potential mapping, the electrostatic potential of azulenes adsorbed onto graphite was studied. It was found that azulene and azulene compounds with electron withdrawing groups at the 1 and 3 positions were more negative in the potential than the graphite, indicating they were pulling electrons out of the material. An azulene compound with electron donating groups at the 1 and 3 positions was positive in potential with respect to the graphite surface, indicating donation of electrons to the graphite. This is good evidence that azulenes can be tunable dopants for modifying the properties of graphene-like materials. Using AFM based techniques, this work advances methods to form and electrically characterize nanoscale metallic features and decorated graphene-like materials that could have important applications as nanotechnology moves forward into complex nanodevice fabrication. It also gives insight into a novel system, azulenes on a graphene-like material, at a nanoscale level of resolution. Study of nanosystems like these is integral to the advancement of nanotechnology as a whole.
- Chemistry Dissertations and Theses 
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