• GIRIDHAR U KULKARNI

      Articles written in Bulletin of Materials Science

    • Twisted multilayer graphene exhibiting strong absorption bands induced by van Hove Singularities

      UMESHA MOGERA GIRIDHAR U KULKARNI

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      Twisted bilayer graphene exhibits several angle-dependent properties due to the emergence of the van Hove Singularities in its density of states. Among them, twist-angle-dependent optical absorption has gained a lot of attention due to its presence in the visible spectral region. However, observation of such absorption is experimentally tricky due to large transmittance. In this study, we use highly decoupled twisted multilayer graphene to observe such absorption in thevisible region using a simple spectrometer. A large number of twisted graphene layers in the system enable observation of such absorption evident in the visible region; the absorption band position correlates with the twist angle measuredusing selective area electron diffraction pattern as well as predictions from theory. While the Raman spectra were akin to those of the decoupled graphene system, at specific twist angle of $\sim$13$^{\circ}$, the spectrum contained clear signatures of G-band enhancement.

    • A spring network simulation in three dimensions for designing optimal crack pattern template to fabricate transparent conducting electrodes

      SUPTI SADHUKHAN ANKUSH KUMAR GIRIDHAR U KULKARNI SUJATA TARAFDAR TAPATI DUTTA

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      Desiccation cracks in colloids are of the order of µm width or less. Therefore, such connected crack networks in a desiccating colloidal film can provide a very fine template for the fabrication of transparent conducting surfaces by vapour deposition of a metal onto the crack network (Rao $et al$ 2014 $Adv. Mater. Interfaces$ 1 140009). The colloidal layer is removed leaving a connected metallic network invisible to the eye. So the surface becomes conducting, while retaining its transparency. The challenge lies in maximizing electrical conductivity while retaining the transparency as far as possible. An optimal combination of the system parameters, which affect the morphology of the crack network is necessary to meet this challenge. In this work, we simulate crack pattern in desiccating colloidal films in three dimensions using a spring network model. We look for the optimal combination of system parameters, such as film thickness, material stiffness and polydispersity, which can produce the best template for producing a conducting network on transparent surfaces.

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