Kulkarni, G. U.

Low cost, rapid synthesis of graphene on Ni: An efficient barrier for corrosion and thermal oxidation

2014-01-01T00:00:00Z

Low cost, rapid synthesis of graphene on Ni: An efficient barrier for corrosion and thermal oxidation Mogera, Umesha; Kurra, Narendra; Radhakrishnan, Dhanya; Narayana, Chandrabhas; Kulkarni, G. U. Graphene because of its inert and impermeable nature holds a great promise as a protective coating against corrosion and oxidation. It is envisioned that graphene coated metals will be increasingly used in metal and electronic industries. To date, mainly expensive chemical vapor deposition methods are being employed for its synthesis over large area involving hydrogen at high reaction temperatures. Here we report, a simple and rapid method of Joule heating a Ni foil coated with naphthalene in rotary vacuum to produce graphene without hydrogen gas. The graphene thus grown protects the Ni surface against corrosion and oxidation even at elevated temperatures. This synthetic approach has a great potential for widespread use as it is low cost and adaptable to metal surfaces of complex curvatures. (C) 2014 Elsevier Ltd. All rights reserved. Restricted Access

All-Solution-Processed, Ambient Method for ITO-Free, Roll-Coated Tandem Polymer Solar Cells using Solution-Processed Metal Films

2014-01-01T00:00:00Z

All-Solution-Processed, Ambient Method for ITO-Free, Roll-Coated Tandem Polymer Solar Cells using Solution-Processed Metal Films Angmo, Dechan; Dam, Henrik F.; Andersen, Thomas R.; Zawacka, Natalia K.; Madsen, Morten V.; Stubager, Jorgen; Livi, Francesco; Gupta, Ritu; Helgesen, Martin; Carle, Jon E.; Larsen-Olsen, Thue T.; Kulkarni, G. U.; Bundgaard, Eva; Krebs, Frederik C. A solution-processed silver film is employed in the processing of top-illuminated indium-tin-oxide (ITO)-free polymer solar cells in single-and double-junction (tandem) structures. The nontransparent silver film fully covers the substrate and serves as the bottom electrode whereas a PEDOT:PSS/Ag grid forms the semitransparent top electrode. All layers are roll-coated/printed on a flexible substrate by using only two techniques: slot-die coating for up to 11 consecutive layers and flexo-printing for the last Ag grid layer. The slot-die coated Ag film is compared to an evaporated Ag film in terms of surface morphological and topographical properties and to ITO in terms of flexibility. The slot-die coated Ag film demonstrates extremely low roughness (a root-mean-square roughness of 3 nm was measured over 240 x 320 mu m(2) area), is highly conductive (< 1 Omega/square), highly flexible, and cost-effective in comparison to other reported metal films applied in polymer solar cells. Such properties result in high fill factors exceeding 50% in both single and tandem structures on large-area devices (1 cm(2)) and the corresponding efficiencies exceed 2%. Restricted Access

Cellphone Camera Imaging of a Periodically Patterned Chip as a Potential Method for Point-of-Care Diagnostics

2014-01-01T00:00:00Z

Cellphone Camera Imaging of a Periodically Patterned Chip as a Potential Method for Point-of-Care Diagnostics Gupta, Ritu; Reifenberger, Ronald G.; Kulkarni, G. U. In this study, we demonstrate that a disposable chip periodically patterned with, suitable ligands, an ordinary cellphone camera, and a simple pattern recognition software, can potentially be used for quantitative diagnostics. A key factor in this demonstration is the design of a calibration grid around the chip that, through a contrast transfer process, enables reliable analysis of the images collected under variable ambient lighting conditions. After exposure to a dispersion of amine terminated silica beads used as analyte mimicking pathogens, an epoxy-terminated glass substrate microcontact printed with octadecyltrichlorosilane (250 mu m periodicity) developed a characteristic pattern of beads which could be easily imaged with a cellphone camera of 3.2 MP pixels. A simple pattern recognition algorithm using fast Fourier transform produced a quantitative estimate of the analyte concentration present in the test solution. In this method importantly, neither the chip fabrication process nor the fill-factor of the periodic pattern need be perfect to arrive at a conclusive diagnosis. The method suggests a viable platform that may potentially find use in fault-tolerant and robust point-of-care diagnostic applications. Restricted Access

Digital grayscale printing for patterned transparent conducting Ag electrodes and their applications in flexible electronics

2014-01-01T00:00:00Z

Digital grayscale printing for patterned transparent conducting Ag electrodes and their applications in flexible electronics Gupta, Ritu; Hosel, Markus; Jensen, Jacob; Krebs, Frederik C.; Kulkarni, G. U. Grayscale (halftone) laser printing is developed as a low-cost and solution processable fabrication method for ITO-free, semi-transparent and conducting Ag electrodes extendable over large area on a flexible substrate. The transmittance and sheet resistance is easily tunable by varying the grayscale value of the color fill between 10% to 20%. The operation of electrodes is demonstrated by fabricating a transparent push button, an electrochromic window and a solar cell. Restricted Access