Graphene oxide based nanocomposite systems for Optical device applications

Abstract

Graphene oxide is a promising alternative to Graphene. Its low cost large scale production method make it favorable for semiconductor energy storage applications. But the optical bandgap of Graphene oxide is far greater than it is require to operate as a semiconductor in electronic devices. In this thesis we have designed and performed three different schemes to tailor the optical bandgap of Graphene oxide to make it usable in electronic industry. Firstly we have tried to control the oxidation of Graphene oxide during its synthesis. Reason behind this was to control the sp2/sp3 hybridization ratio of carbon. This was achieved with the help of reduced amount of Oxidizing agent during its synthesis. Absorption spectrophotometry shows the reduction in optical bandgap of the resultant material as the amount of oxidant is decreased. This decrease in sp2 /sp3 hybridization ratio was further confirmed with the help of Raman spectroscopy but this oxidation process is not even throughout the basil plane of graphene oxide flake. X-ray diffraction (XRD) analysis reveals the presence of un-oxidized graphitic domains all over the graphene oxide flake which in turn effects the exfoliation efficiency and hydrophilic properties of the resultant material. Limited range of optical band gap reduction and the reduced exfoliation efficiency caused by the un-oxidized graphitic domains rules out the feasibility of this process. To achieve better range in optical bandgap control another technique is opted that used 𝛼-Fe2O3 - Graphene oxide nanocomposite. XRD analysis reveals the in situ reduction of graphene oxide which drastically degrades the crystallinity of graphene oxide by introduction the lattice defects. To overcome this problem a novel synthesis process for Iron oxide-Graphene oxide nanocomposites named as “Wet impregnation method” is devised that uses pre-synthesized Iron oxide nanoparticles. XRD analysis of synthesized nanocomposites rules out the possibility off in situ reduction of graphene oxide. Optical bandgap measured with the help of absorption spectrophotometry reveals the linear decrease in optical bandgap as the loading of Iron oxide nanoparticles is increased from 0.25% to 7%. Morphology of these nanoparticles is probed with scanning electron microscopy (SEM) that rules out all the possibilities of agglomeration of iron oxide nanoparticles and coagulation of Graphene oxide sheets. EDX analysis and Elemental mapping shows the even distribution of iron oxide nanoparticles throughout the Graphene oxide sheets. In the last Raman and Photoluminescence spectroscopy is used to understand the electronic interaction among the constituents of the synthesized nanocomposites.