Keynote Lectures:

Title:         Tuning of ultrafast optical and electrical properties of graphene oxide through thermal annealing and infrared radiation for optoelectronic and photonics devices
Authors:    P K Datta, S Bhattacharya, A. C. Das, R. Maiti, T. K. Sinha, A. Midya, S. K. Ray
Abstract:   Graphene is an atomically thin two-dimensional (2D) carbon allotrope which consists of sp2 – hybridized carbon atoms. Graphene has been proved to be a substantial candidate for laser mode locker, higher harmonic generation and optical frequency mixer due to its large nonlinear optical susceptibility. But the challenges faced in many applications of graphene based materials are the solubility, the absence of bandgap and the difficulty to fabricate it in large scales. Whereas Graphene Oxide (GO), a strongly hydrophilic intermediate product to form graphene chemically, has attracted attention among the researchers due to its low-cost processing, large-scale production, solvent and substrate compatibility and the ease of functionalization in order to obtain certain novel properties. GO can be considered as pristine graphene decorated with oxygen functional groups. Thus, it is possible to tune the optical and electrical property of GO by tailoring the band gap through reduction. To have a precise control over optical and electrical property non-hazardous thermal annealing and infrared radiation have been deployed as reduction techniques. Characterization of reduced graphene oxide (RGO) by means of Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and UV-Visible absorption measurements confirm an efficient reduction. Non-linear optical properties of colloidal aqueous solution of GO and RGO reduced with increasing exposure time of IR radiation are measured using single beam open aperture Z-Scan technique in femtosecond regime. Depending on the intensity, both saturable absorption and two-photon absorption effects are found to contribute to the non-linearity of all the samples. The reason of tunable NLO properties is explained using amorphous carbon model. Transient absorption spectroscopy with optical pump and white light supercontinuum probe is used to find the electron dynamics of gradually reduced graphene oxide which in turn cause the optical nonlinearity. Variation in wavelength dependent ultrafast carrier dynamics is observed with increasing reduction of GO. We have used Terahertz time domain spectroscopy to monitor a highly efficient one pot method for effective and controlled aerobic reduction of laboratory prepared graphene oxide (GO) ink in a fast (<10 min.), room temperature, non-hazardous condition. The home made THz TDS study shows tunability in electrical and optical behavior of the RGO films (e.g., conductivity, electromagnetic induction (EMI) shielding effectiveness and transmission etc.). The talk will present transient absorption, THz-TDS and Z-scan data to establish the physical processes for the tenability of optical and electrical properties of grapheme oxide with degree of reduction.

Pages:       006-006

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