Researcher:
Kumar, Baskaran Ganesh

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Baskaran Ganesh

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Kumar

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Kumar, Baskaran Ganesh

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2018 - 20209

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Researcher Of Publications: search.filters.isAuthorOfPublication.028e2e82-3ed5-458e-85a1-89b5d6630e08

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Now showing 1 - 9 of 9
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    Silk as a biodegradable resist for field-emission scanning probe lithography
    (Institute of Physics (IOP) Publishing, 2020) Sadeghi, Sadra; Rangelow, Ivo W.; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; N/A; N/A; Department of Electrical and Electronics Engineering; Alaca, Burhanettin Erdem; Kumar, Baskaran Ganesh; Melikov, Rustamzhon; Doğru-Yüksel, Itır Bakış; Nizamoğlu, Sedat; Faculty Member; Other; PhD Student; PhD Student; Faculty Member; Department of Mechanical Engineering; Department of Electrical and Electronics Engineering; Koç University Surface Science and Technology Center (KUYTAM) / Koç Üniversitesi Yüzey Teknolojileri Araştirmalari Merkezi (KUYTAM); N/A; N/A; N/A; N/A; College of Engineering; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; 115108; N/A; N/A; N/A; 130295
    The patterning of silk allows for manufacturing various structures with advanced functionalities for optical and tissue engineering and drug delivery applications. Here, we propose a high-resolution nanoscale patterning method based on field-emission scanning probe lithography (FE-SPL) that crosslinks the biomaterial silk on conductive indium tin oxide (ITO) promoting the use of a biodegradable material as resist and water as a developer. During the lithographic process, Fowler-Nordheim electron emission from a sharp tip was used to manipulate the structure of silk fibroin from random coil to beta sheet and the emission formed nanoscale latent patterns with a critical dimension (CD) of similar to 50 nm. To demonstrate the versatility of the method, we patterned standard and complex shapes. This method is particularly attractive due to its ease of operation without relying on a vacuum or a special gaseous environment and without any need for complex electronics or optics. Therefore, this study paves a practical and cost-effective way toward patterning biopolymers at ultra-high level resolution.
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    Radiative energy transfer in color-conversion LEDs
    (Optica Publishing Group (formerly OSA), 2018) N/A; N/A; Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; N/A; Department of Electrical and Electronics Engineering; Melikov, Rustamzhon; Press, Daniel Aaron; Kumar, Baskaran Ganesh; Sadeghi, Sadra; Nizamoğlu, Sedat; PhD Student; Researcher; Other; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; N/A; 130295
    We developed a matrix method that calculates and reveals all the radiative energy transfer processes of absorption, reabsorption, inter-absorption and their iterative and combinatorial interactions in down-conversion layer of a light-emitting diode.
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    Stokes-shift-engineered indium phosphide quantum dots for efficient luminescent solar concentrators
    (American Chemical Society (ACS), 2018) Ow-Yang, Cleva W.; N/A; N/A; N/A; Department of Electrical and Electronics Engineering; N/A; Department of Electrical and Electronics Engineering; Sadeghi, Sadra; Jalali, Houman Bahmani; Melikov, Rustamzhon; Kumar, Baskaran Ganesh; Aria, Mohammad Mohammadi; Nizamoğlu, Sedat; PhD Student; PhD Student; PhD Student; Other; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; N/A; N/A; 130295
    Luminescent solar concentrators (LSCs) show promise because of their potential for low-cost, large-area, and high-efficiency energy harvesting. Stokes shift engineering of luminescent quantum dots (QDs) is a favorable approach to suppress reabsorption losses in LSCs; however, the use of highly toxic heavy metals in QDs constitutes a serious concern for environmental sustainability. Here, we report LSCs based on cadmium-free InP/ZnO core/shell QDs with type-II band alignment that allow for the suppression of reabsorption by Stokes shift engineering. The spectral emission and absorption overlap was controlled by the growth of a ZnO shell on an InP core. At the same time, the ZnO layer also facilitates the photostability of the QDs within the host matrix. We analyzed the optical performance of indium-based LSCs and identified the optical efficiency as 1.45%. The transparency, flexibility, and cadmium-free content of the LSCs hold promise for solar window applications.
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    Effective neural photostimulation using indium-based type-ii quantum dots
    (American Chemical Society (ACS), 2018) Şahin, Mehmet; Ow-Yang, Cleva W.; N/A; N/A; N/A; N/A; Department of Electrical and Electronics Engineering; Department of Chemical and Biological Engineering; Department of Electrical and Electronics Engineering; Jalali, Houman Bahmani; Aria, Mohammad Mohammadi; Dikbaş, Uğur Meriç; Sadeghi, Sadra; Kumar, Baskaran Ganesh; Kavaklı, İbrahim Halil; Nizamoğlu, Sedat; PhD Student; PhD Student; Master Student; PhD Student; Other; Faculty Member; Faculty Member; Department of Chemical and Biological Engineering; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; College of Engineering; N/A; N/A; N/A; N/A; N/A; 40319; 130295
    Light-induced stimulation of neurons via photoactive surfaces offers rich opportunities for the development of therapeutic methods and high-resolution retinal prosthetic devices. Quantum dots serve as an attractive building block for such surfaces, as they can be easily functionalized to match the biocompatibility and charge transport requirements of cell stimulation. Although indium based colloidal quantum dots with type-I band alignment have attracted significant attention as a nontoxic alternative to cadmium-based ones, little attention has been paid to their photovoltaic potential as type-II heterostructures. Herein, we demonstrate type-II indium phosphide/zinc oxide core/shell quantum dots that are incorporated into a photoelectrode structure for neural photostimulation. This induces a hyperpolarizing bioelectrical current that triggers the firing of a single neural cell at 4 mu W mm(-2), 26-fold lower than the ocular safety limit for continuous exposure to visible light. These findings show that nanomaterials can induce a biocompatible and effective biological junction and can introduce a route in the use of quantum dots in photoelectrode architectures for artificial retinal prostheses.
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    Quantum dot white leds with high luminous efficiency
    (Optical Soc Amer, 2018) N/A; Department of Electrical and Electronics Engineering; N/A; N/A; N/A; Department of Electrical and Electronics Engineering; Sadeghi, Sadra; Kumar, Baskaran Ganesh; Melikov, Rustamzhon; Aria, Mohammad Mohammadi; Jalali, Houman Bahmani; Nizamoğlu, Sedat; PhD Student; Other; PhD Student; PhD Student; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; N/A; N/A; 130295
    Colloidal quantum dots (QDs) have attracted significant attention in the last three decades due to high quantum yield (QY) and tunable electronic properties via quantum confinement effect and material composition. However, their utilization for efficient solid-state lighting sources has remained a challenge due to the decrease of QY from the synthesis batch in the liquid state to the host matrix in the solid state, which is also known as the host material effect. Here, we suppress the host material effect by simple liquid-state integration in light-emitting diodes (LEDs) that lead to a luminous efficiency of 64 lm/W for red, green, blue (RGB)-based and 105 lm/W for green, blue (GB)-based white light generation. For that, we maximized the QY of red- and green-emitting QDs by optimizing synthesis parameters and integrated efficient QDs with QY up to 84% on blue LED dies in liquid form at appropriate injection amounts for high-efficiency white lighting. Liquid-state integration showed two-fold and six-fold enhancement of efficiency in comparison with incorporation of QDs in polydixnethylsiloxane film and close-packed formation, respectively. Our theoretical calculations predicted that the luminous efficiency of liquid QD-LEDs can reach over 200 lm/W. Therefore, this study paves the way toward ultra-high-efficiency QD-based lighting.
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    Eco-friendly silk-hydrogel lenses for LEDs
    (Optica Publishing Group (formerly OSA), 2018) N/A; N/A; Department of Electrical and Electronics Engineering; Department of Electrical and Electronics Engineering; N/A; N/A; N/A; N/A; Department of Electrical and Electronics Engineering; Melikov, Rustamzhon; Press, Daniel Aaron; Kumar, Baskaran Ganesh; Doğru-Yüksel, Itır Bakış; Sadeghi, Sadra; Chirea, Mariana; Yılgör, İskender; Nizamoğlu, Sedat; PhD Student; Researcher; Other; PhD Student; PhD Student; Researcher; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; Graduate School of Sciences and Engineering; College of Engineering; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Sciences; College of Engineering; N/A; N/A; N/A; N/A; N/A; N/A; 24181; 130295
    In this study, silk fibroin in hydrogel form is analyzed as an eco-friendly alternative to conventional polymers for lens applications in light-emitting diodes. The intensity profile was controlled via dome- and crater-type lenses.
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    Structural control of InP/ZnS core/shell quantum dots enables high-quality white LEDs
    (Iop Publishing Ltd, 2018) Ow-Yang, Cleva W; Department of Electrical and Electronics Engineering; N/A; N/A; N/A; N/A; Department of Electrical and Electronics Engineering; Kumar, Baskaran Ganesh; Sadeghi, Sadra; Melikov, Rustamzhon; Aria, Mohammad Mohammadi; Jalali, Houman Bahmani; Nizamoğlu, Sedat; Other; PhD Student; PhD Student; PhD Student; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; N/A; N/A; N/A; N/A; 130295
    Herein, we demonstrate that the structural and optical control of InP-based quantum dots (QDs) can lead to high-performance light-emitting diodes (LEDs). Zinc sulphide (ZnS) shells passivate the InP QD core and increase the quantum yield in green-emitting QDs by 13-fold and redemitting QDs by 8-fold. The optimised QDs are integrated in the liquid state to eliminate aggregation-induced emission quenching and we fabricated white LEDs with a warm, neutral and cool-white appearance by the down-conversion mechanism The QD-functionalized white LEDs achieve luminous efficiency (LE) up to 14.7 lm W-1 and colour-rendering index up to 80. The structural and optical control of InP/ZnS core/shell QDs enable 23-fold enhancement in LE of white LEDs compared to ones containing only QDs of InP core.
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    PublicationOpen Access
    Unravelling radiative energy transfer in solid-state lighting
    (American Institute of Physics (AIP) Publishing, 2018) Department of Electrical and Electronics Engineering; Melikov, Rustamzhon; Press, Daniel Aaron; Kumar, Baskaran Ganesh; Sadeghi, Sadra; Nizamoğlu, Sedat; PhD Student; PhD Student; Faculty Member; Department of Electrical and Electronics Engineering; College of Engineering; Graduate School of Sciences and Engineering; N/A; N/A; N/A; N/A; 130295
    Today, a wide variety of organic and inorganic luminescent materials (e.g., phosphors, quantum dots, etc.) are being used for lighting and new materials (e.g., graphene, perovskite, etc.) are currently under investigation. However, the understanding of radiative energy transfer is limited, even though it is critical to understand and improve the performance levels of solid-state lighting devices. In this study, we derived a matrix approach that includes absorption, reabsorption, inter-absorption and their iterative and combinatorial interactions for one and multiple types of fluorophores, which is simplified to an analytical matrix. This mathematical approach gives results that agree well with the measured spectral and efficiency characteristics of color-conversion light-emitting diodes. Moreover, it also provides a deep physical insight by uncovering the entire radiative interactions and their contribution to the output optical spectrum. The model is universal and applicable for all kinds of fluorophores.
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    PublicationOpen Access
    Silk-based aqueous microcontact printing
    (American Chemical Society (ACS), 2018) Department of Electrical and Electronics Engineering; N/A; Department of Physics; Department of Molecular Biology and Genetics; Kumar, Baskaran Ganesh; Melikov, Rustamzhon; Aria, Mohammad Mohammadi; Yalçın, Aybike Ural; Begar, Efe; Sadeghi, Sadra; Güven, Kaan; Nizamoğlu, Sedat; PhD Student; PhD Student; Faculty Member; Faculty Member; Department of Electrical and Electronics Engineering; Department of Physics; Department of Molecular Biology and Genetics; College of Engineering; Graduate School of Sciences and Engineering; N/A; N/A; N/A; N/A; N/A; N/A; 52290; 130295
    Lithography, the transfer of patterns to a film or substrate, is the basis by which many modern technological devices and components are produced. However, established lithographic approaches generally use complex techniques, expensive equipment, and advanced materials. Here, we introduce a water-based microcontact printing method using silk that is simple, inexpensive, ecofriendly, and recyclable. Whereas the traditional microcontact printing technique facilitates only negative lithography, the synergetic interaction of the silk, water, and common chemicals in our technique enables both positive and negative patterning using a single stamp. Among diverse application possibilities, we exemplify a proof of concept of the method through optimizing its metal lift-off process and demonstrate the fabrication of electromagnetic metamaterial elements on both solid and flexible substrates. The results indicate that the method demonstrated herein is universally applicable to device production and technology development.