Title: Nanosheets and Nanostructured Thin Films of Metal Oxides for Practical Applications
Speaker: Dr. Mahmut Aksit
Date/Time: 14 December 2015, 14:40
Place: FENS L030
Abstract: Two-dimensional (2D) inorganic materials present exciting opportunities for new scientific and technological breakthroughs. In this seminar, novel fabrication and characterization techniques will be presented for metal oxide 1) nanosheets and 2) nanostructured thin films with the motivation of advancements in thermoelectrics, flexible electronics, optoelectronics and thermal engineering: 1) Metal oxide nanosheet stacks of NaxCoO2 and KxCoO2.yH2O are fabricated using a novel bottom-up method based on sol-gel chemistry, E-field induced kinetic demixing and high temperature heat treatment. The nanosheet thicknesses can be 10–100 nm while their lengths can measure up to 1.8 mm long. The stacked nanosheets are readily delaminated into very large (<350 µm long, ~100 nm thick) free-standing 2D crystals. Both NaxCoO2 and KxCoO2.yH2O nanosheets are electrically conductive and show ductility. Thermoelectric efficiency of bulk NaxCoO2 is expected to improve in the nanosheet form due to phonon confinement and scattering.2) Novel p-type TCO thin films of Ca3Co4O9 nanoplates are produced using a sol-gel and spin coating based process. The process parameters can be varied to produce transparent conducting oxide (TCO) thin films with sheet resistance (SR) as low as 5.7 kΩ/sq (ρ ≈ 57 mΩ·cm) or with average visible range transparency as high as 67%. The figure of merit (FOM) for the top-performing Ca3Co4O9 thin film (151 MΩ-1) is higher than FOM values previously reported in the literature for all other solution processed, p-type TCO thin films and higher than most others prepared by physical and chemical vapor deposition.
Bio: Mahmut Aksit obtained his B.S. in Materials Science and Engineering from SabanciUniversity in 2008. He went on to pursue graduate studies at Cornell University under the guidance of Professor Richard Robinson and was awarded his Ph.D. in Materials Science and Engineering in 2014. Mahmut’s Ph.D. research involved novel synthesis/characterization methods and applications for metal oxide nanosheets and low temperature (<0.4 K) phonon transport experiments/simulations on Si nanosheets. His work on “Scalable nano-manufacturing of millimeter long NaxCoO2 Nanosheets” was published as a front cover article in Journal of Materials Chemistry (2012) and highlighted by R&D Magazine (2012). The same work was also highlighted by U.S. Department of Energy in two separate articles entitled “Metal Oxide Nanosheets: Graphene's Inorganic Cousin” (Office of Basic Energy Sciences, January 2012) and “Thin Oxides, Thick Prospects” (Frontiers in Energy Research, July 2012). Mahmut is currently employed as a Senior Materials Chemist in 3M Company’s Central Materials Research Laboratory and his research in 3M focuses on applications of nanomaterials in color displays and high-voltage insulators.