Single-Digit Nanofabrication Technologies for Tailoring Graphene into Functional Nanostructures
Monday, April 11, 1127 Kemper Hall, 11:00am-12:00pm
Speaker: Xiaogan Liang
Staff Scientist, Nanofabrication Facility Group, The Molecular Foundry
Host: Professor Richard Kiehl
Recently, graphene has been extensively studied as a material for making future electronic and energy devices. In comparison with conventional semiconductors, graphene exhibits exceptional properties, such as pronounced ambipolar effect, high carrier mobility, a stable 2D crystal structure, and potential to realize ballistic transport at room temperature. Potential electrical and electronic applications include bio/chemical sensors, semiconductor devices, transparent conductors, and energy conversion/storage devices, etc.
However, two of the challenges for scale-up applications are incorporating graphene over large areas and patterning nanostructures to achieve desirable electronic characteristics. Several approaches have been attempted to produce graphene for large area electronics, including epitaxial growth on catalytic metals, thermal decomposition of SiC, solution-based deposition, and mechanical cleavage, etc. At the same time, efforts have been made to tailor graphene sheets into nanoscale features (e.g. nanoribbons, quantum dots, and nanomeshes, etc.).
At LBNL, my research team is developing novel nanofabrication technologies to address these two challenges simultaneously. One of recent progresses is the development of a novel transfer-printing technology, which uses a combination of electrostatic exfoliation with micro and nano lithographically patterned graphite to produce pristine graphene features and fabricate electronic nanodevices. With this method, we have successfully demonstrated the printing of ordered graphene features ranging from 10s µm to sub-10 nm over large areas. Especially, we fabricated hexagonal graphene nanomeshes (GNMs) with sub-10 nm ribbon width. Graphene field-effect transistors (GFETs) made from GNMs exhibit very different electronic characteristics in comparison with unpatterned GFETs even at room temperature. We observed multi-plateaus in the drain current – gate voltage dependence as well as an enhancement of ON/OFF current ratio with reduction of the average ribbon width. These effects are attributed to the formation of electronic subbands and a bandgap in GNMs. Such mesoscopic graphene structures can serve as not only a solution to open a bandgap, directly benefiting the electronic applications of graphene, but also an important basis upon which superlattices consisting of various graphene structures could be constructed.
Finally, the future perspectives in terms of research trend and application opportunities will also be presented in the talk.
Dr. Xiaogan Liang is currently working as a Staff Scientist (PI) at The Molecular Foundry, Lawrence Berkeley National Laboratory. His current research interests are focused on nanoimprint lithography, graphene-based nanoelectronics, nanofluidics, block copolymer self-assembly, and organic photovoltaics. Dr. Liang has coauthored 23 journal publications and more than 20 conference presentations, and has 4 pending patents. Xiaogan Liang is the member of Sigma Xi and IEEE.
Dr. Liang obtained a BS in Physics from Peking University, a MS in Condensed Matter Physics from Chinese Academy of Sciences, and a Ph.D. in Electrical Engineering from Princeton University.