Title: Intentional vacuum annealing induced, surfactant-initiated surprising carbon doping @ zinc oxide decorated graphitic carbon nano fiber hybrid thin films for Interfacial Stress-Grading Applications

Biography:

G.R. Dillip is an INSPIRE Faculty in the Solid State and Structural Chemistry Unit, Indian Institute of Science, India. Previously, he was worked as an Assistant Professor in the School of Mechanical Engineering, Yeungnam University, South Korea. He finished his Ph.D. Degree in Physics from Sri Venkateswara University, India in 2013 and after that he joined at Yeungnam University, South Korea. He has authored ~40 scientific articles in various reputed International Journals, a Book Chapter and also presented his work in both National and International Conferences and participated in several Workshops. He also registered a Korean Patent. His research interests include various defect-mediated studies of carbon based metal oxide nanocomposites/hybrids for energy-related applications (such as Supercapacitors/Batteries) and also rare-earth doped optical materials for solid state lighting devices.

Abstract

The efficiency of the high-power, high-voltage (HV) insulation system is currently approaching a saturation level due to the limited availability of the high-quality resistive stress-grading material that can withstand ever-increasing applied voltage at very low insulation-wall thickness. A unique non-rectifying, non-linear current-voltage characteristic is observed in ZnO nanoparticle-anchored carbon nanofiber (ZnO-CNF) hybrid thin film devices, which has novel applications in non-linear stress-grading materials for high-voltage devices and overvoltage protectors in multifunctional electronic circuits. A simple chemical precipitation method is used to fabricate the hybrid films, followed by vacuum-annealing at elevated temperatures. Interestingly, the organic surfactant (Triton X-114), used as binder during the film deposition, manifests unintentional carbon-doping into ZnO lattice, which leads to a conductivity inversion of ZnO from n-type in lower-temperature (300 ºC) annealed hybrid into p-type in the higher-temperature (600 ºC) annealed film. The novelty of this work is that, the CNF-ZnO interface acts as a metal-semiconductor (M-S) junction, where high conducting CNF acts as the metal and ZnO NPs as the semiconducting (n- or p-type) counterpart (denoted as MCNF-Sn/p-ZnO junction). The band-energy calculations have revealed that the barrier height at the MCNF-Sn/p-ZnO junction is quite low to manifest non-rectifying characteristics (i.e. the I-V curves are near-symmetric in both forward and reverse directions). Additionally, a large number of C-atoms (from the surfactant) are not only doped into the ZnO lattice, but also reside at the ZnO-CNF interface as trap states. Electrical characterizations reveal that the CNF-ZnO interfaces act as a metal-semiconductor junction with low barrier height, leading to non-rectifying junction properties. Also the surfactant-induced C-atoms create trap-states at the interface which ‘emit’ the trapped charges via interfacial field-assisted tunneling, thus imposing non-linearity (in both forward and reverse directions) on the I-V curves.