This collaborative research award provides funding for understanding and controlling the key factors in the local nanoscale thermal reduction of graphene oxide. In particular, the combination of computational modeling with experiments will give access to the efficiency and rate of the local thermal reduction during the thermochemical nanolithography process, and to the ultimate writing speed and resolution of this technique. The reduced form of graphene oxide (GO) is an attractive alternative to graphene for producing large-scale flexible conductors, supercapacitors, mechanical resonators, and for creating devices that require an electronic gap. Thermochemical nanolithography is a new nanofabrication technique in which heated probe tips can be used to locally control and tune the reduction of GO and pattern nanoscale regions of reduced GO within a GO sheet at speeds of several µm/s, with a resolution of 12 nm. The goal is the transition of this technology to arrays of several cantilevers with hot tips for parallel writing, and the integration of reduced GO nanostructures into field effect transistors prototypes.
The research will contribute to elucidate at the atomic-scale the structural properties of GO, the mechanisms driving the reduction process, and the physical-chemical transformations resulting from local heat transfer. This novel understanding will be converted into a modeling scheme to be used to engineering the nano-patterning process. This study will improve the community?s understanding of nanoscale processes and potentially provide inexpensive and robust tools to decrease the cost of nano-manufacturing. Since this project will be developed in close collaboration with an Italian group of the Politecnico of Milano, it will enable exchange of graduate students. In the current climate of outsourcing and globalization of economy, international training is an essential component for the education of our next generation of leaders.
In this research project we have explored the potential of a new lithography technique invented at Georgia Tech by the PIs of this proposal, called Thermochemical nanolithography (TCNL). TCNL employs heated nano-size tips to induce local thermally activated chemical reactions to change the chemical functionality of surfaces, or obtain new nanostructures. During the development of this NSF project we have demonstrated the ability to reduce graphene oxide at the nanoscale by using TCNL. The resulting nanostructures have a conductivity that can be tuned over 4 orders of magnitude. Furthermore, we have demonstrated the ability of TCNL to create chemical gradients with sub-100 nm resolution, and to fabricate complex nanostructures of ferroelectric/piezoelectric PZT and PTO ceramics. More recently, we have worked on the parallelization of TCNL by fabricating and using arrays with 5 tips. Furthermore, by combining experiments and density functional theory investigations we have discovered a new method to produce graphene oxide films. Ultra-thin epitaxial graphene oxide (EGO) films with a controlled number of layers were obtained by a mild Hummers oxidation of epitaxial graphene grown on silicon carbide substrates. EGO films possess the following attributes. (1) EGO synthesis is rapid (~2 hours), the chemical oxidation process does not change the number or disrupt the order of the graphene layers, and the oxide films exhibit reproducible chemical and structural features. (2) Pristine graphene and EGO films exhibit comparable vertical inter-layer structural quality (coherence lengths and interlayer registry). (3) EGO films are extremely smooth over the entire SiC substrate area, do not present holes or edges and they are uniform, showing no propensity to exfoliate. In total this project has led to 15 publications and one book chapter. The PI of this proposal has been founder and co-organizer of the "Southeast Workshop Series on Soft Materials", yearly since 2008, attracting more than one hundred people each time. Outreach activities have included public presentations, career panels, work with an elementary school, and more recently the foundation of the "Women in Physics (WiP)" association. This research activity has involved post-doctoral associates, and graduate students. All the post-doctoral fellows who have worked in our laboratory hold now permanent or tenure track positions in research institutions. Three students obtained a PhD from Georgia Tech. One is now employed in Industry and two are pursuing post-doctoral research. In particular one of these students, a US citizen, is now working with our collaborators at IBM in Zurich.
