Browsing by Author "Sridhara, N."

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    Design and development of ITO/Ag/ITO spectral beam splitter coating for photovoltaic-thermoelectric hybrid systems
    (Elsevier Ltd, 2017) Sibin, K.P.; Selvakumar, N.; Kumar, A.; Dey, A.; Sridhara, N.; Shashikala, H.D.; Sharma, A.K.; Barshilia, H.C.
    ITO/Ag/ITO (IAI) multilayer coatings were designed for spectral beam splitter applications and these coatings were deposited on glass substrates by magnetron sputtering method. The thicknesses of the component layers, namely, Ag and ITO were varied to achieve high visible transmittance, high NIR-IR reflectance and optimum cut-off wavelength. The optimized ITO/Ag/ITO exhibits high visible transmittance (?88%) and high NIR-IR reflectance (>90%) with an optimum cut-off wavelength (?900 nm). A novel chemical etching method was used to improve the transmittance of the plain glass substrate. The optimized IAI multilayer coating deposited on single side etched glass substrate resulted in increase in transmittance (?91%), which is due to the nano-porous morphology of the etched glass substrate. The angular and polarization dependence studies of IAI multilayer coatings were also studied in detail. © 2016 Elsevier Ltd
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    Development of Multifunctional Thin Film Based X-Ray Intensity Filters for Space-Based Payloads
    (Springer New York LLC barbara.b.bertram@gsk.com, 2019) Prajwal, K.; Dey, A.; Sudhakar, M.; Nandi, A.; Esther, A.C.M.; Sridhara, N.; Yougandar, B.; Kumar, P.; Arya, S.; Rajendra, A.
    We report the development, thorough characterizations and space worthiness studies of multifunctional aluminized film as x-ray intensity filter for space-based payloads, suitably designed to place in Sun–Earth Lagrangian (L1) point. The L1 point is the ideal location for uninterrupted observation of Sun to study the solar flares in hard x-rays. For our specific purpose, we make use of two different types of x-ray detectors (e.g., CdTe and CZT) which are generally used for hard x-ray studies in the energy band of 5 to 200 keV. Further, these aforesaid two detectors require specified thermal control characteristic for optimal performance. Aluminization of Kapton films is proposed which would satisfy the thermo-optical and x-ray transmission requirements of the proposed payload. The developed aluminized films are thoroughly studied by field emission scanning electron microscopy and atomic force microscopy techniques for micro-structural characteristic, x-ray diffraction for phase purity, nanoindentation for mechanical integrity at micro-structural length scale and spectrophotometer for thermo-optical properties. X-ray transmission test is carried out with two radioactive sources, namely 55Fe and 241Am, with various aluminized Kapton layer combinations. Finally, space worthiness of the aluminized Kapton films is examined by accelerated environments, e.g. humidity, thermal cycling and thermo-vacuum tests. © 2019, ASM International.
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    Development of reflective co-sputtered nanostructured metallic films
    (Taylor and Francis Ltd., 2021) Prajwal, K.; Priyanka, G.L.; Hasan, M.A.; Carmel Mary Esther, A.; Sridhara, N.; Rajendra, A.; Arya, S.B.; Dey, A.
    DC magnetron co-sputtering technique is utilised to develop reflective Ag- and Al-based metal films co-sputtered with Ni deposited on quartz glass substrates. The sputtered films are characterised by field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques to investigate microstructure, topology and phase analysis, respectively. Further, average thermo-optical properties such as solar reflectance, absorptance and IR emittance and electrical property such as sheet resistance of the deposited films are evaluated. The reflectance property as a function of wavelength is also investigated. Sputtered Ag and Al films show high (>93%) reflectance, however, co-sputtered Al + Ni and Ag + Ni offer comparatively lesser value, e.g. 45% and 73%, respectively. The significant lower reflectance of Al + Ni is possibly due to the presence of higher amount of Ni in the film and the formation of intermetallic compounds. © 2020 Institute of Materials, Minerals and Mining Published by Taylor & Francis on behalf of the Institute.
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    Environmental stability of transparent and conducting ITO thin films coated on flexible FEP and Kapton® substrates for spacecraft applications
    (Elsevier B.V., 2018) Sibin, K.P.; Mary Esther, A.C.; Shashikala, H.D.; Dey, A.; Sridhara, N.; Sharma, A.K.; Barshilia, H.C.
    Acquiring good adhesion of ITO thin films on polymer substrate is a major concern, especially for space related applications. Delamination of ITO coating on these polymers can seriously damage the spacecraft. This paper presents the development of highly transparent and conducting ITO thin films on as-received and surface treated fluorinated ethylene propylene (FEP) and Kapton® substrates by reactive direct current magnetron sputtering. Stability of the ITO coating on FEP and Kapton® substrates was studied in simulated space environments. Environmental tests such as: relative humidity, thermal cycling and thermo vacuum were performed. Thermo-optical properties and sheet resistance of ITO coated FEP and Kapton® substrates were studied before and after environmental tests. Optimized ITO coating with thickness of ~ 15 nm on FEP and Kapton® substrates showed sheet resistance in the range of 2–4 k?/sq. with high average transmittance and high IR emittance. Adhesion of ITO coating on FEP substrate was improved by Ar plasma etching. X-ray photoelectron spectroscopy and field emission scanning electron microscopic studies of etched FEP substrate showed defluorination and high roughness of the etched surface which helped for better adhesion of ITO coating. We demonstrated that ITO coated plasma etched FEP substrate showed no change in the sheet resistance and thermo-optical properties. Moreover, ITO coated etched FEP substrate showed good environmental stability than ITO coated untreated FEP substrates. © 2017 Elsevier B.V.
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    Highly transparent and conducting ITO/Ag/ITO multilayer thin films on FEP substrates for flexible electronics applications
    (Elsevier B.V., 2017) Sibin, K.P.; Srinivas, G.; Shashikala, H.D.; Dey, A.; Sridhara, N.; Sharma, A.K.; Barshilia, H.C.
    Transparent and conducting ITO/Ag/ITO (IAI) multilayer coatings were deposited on glass and flexible fluorinated ethylene propylene (FEP) substrates by reactive sputtering using metallic In:Sn (90%:10%) and Ag targets at room temperature. Middle Ag layer thickness was optimized to obtain maximum figure of merit (?) and the optimum Ag layer thickness was found to be ~13 nm. The optimized IAI multilayer on glass substrate showed transmittance of ~88.6% and sheet resistance of ~7.1 ?/sq. The transmittance increased to ~91.4% for the IAI multilayer deposited on one side etched glass. The optimized IAI multilayer coating was also deposited on flexible FEP substrates. The electrical, optical, structural and morphological properties of IAI deposited on glass and FEP substrates were compared. IAI deposited on FEP substrate showed transmittance of ~90.2% at ? = 550 nm, sheet resistance of ~6.9 ?/sq. and figure of merit of ~52 × 10?3 ??1. Bending test of IAI deposited FEP proved the high flexibility of IAI multilayer for the flexible transparent electrode applications. Solar selectivity study of IAI on FEP substrate showed it can effectively reflect the higher wavelength region of solar spectrum and can be used as a flexible solar spectrum segregator. Optical haze measurements of IAI coated glass and FEP show that high haze value can be achieved by increasing the roughness on non-coated side of the FEP substrate. © 2017
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    Optical and electrical properties of ITO thin films sputtered on flexible FEP substrate as passive thermal control system for space applications
    (Elsevier, 2016) Sibin, K.P.; Swain, N.; Chowdhury, P.; Dey, A.; Sridhara, N.; Shashikala, H.D.; Sharma, A.K.; Barshilia, H.C.
    ITO thin films were deposited on flexible fluorinated ethylene propylene (FEP) substrates by pulsed direct current reactive magnetron sputtering system using an In:Sn (90%-10% wt.) alloy target. The influence of the deposition parameters (argon and oxygen flow rates, and substrate temperature) and effect of coating thickness on the optical, electrical, structural and microstructural properties of ITO thin films deposited on FEP was investigated. The thickness of the ITO coatings was varied from 5 to 180 nm. The optimized ITO coating (10 nm thick) exhibited high IR emittance (79%) on FEP substrate with high average solar transmittance (94.0%) and moderate sheet resistance (3 k?/sq.). We also investigated in detail the angular dependence of reflectance as well as haze factor of thin ITO coatings. Our results suggest that 10 nm thick ITO coating exhibits an average haze factor of 8.6%. The high value of IR emittance, moderate sheet resistance and high solar transmittance along with low haze factor indicate the suitability of ITO thin films on FEP substrates as flexible optical solar reflector for space applications. © 2015 Elsevier B.V. All rights reserved.
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    Optical and electrical studies of sputter-deposited transparent and conducting ITO/Ag/ITO multilayer on Kapton® substrate for transparent flexible electronic applications
    (Elsevier Ltd, 2018) Sibin, K.P.; Srinivas, G.; Shashikala, H.D.; Dey, A.; Sridhara, N.; Sharma, A.K.; Barshilia, H.C.
    Transparent and conducting thin films on flexible substrates have enormous applications in the areas of space, solar, displays, etc. We hereby report the sputter deposition of transparent and conducting ITO/Ag/ITO (IAI) thin films on commercially available flexible Kapton® substrate at a lower substrate temperature. IAI multilayer has been deposited by magnetron sputtering system using an alloy In:Sn (90% :10%) and Ag targets at room temperature without breaking the vacuum. The optimized IAI coating shows high transmittance (∼81.3 % at γ= 650 nm) along with very low resistance (8.36 ω/). Optical haze value of IAI on Kapton was measured and found to be <7%. The figure of merit of IAI coating on Kapton® has been calculated using the Haacke's formula π = r10/Rs. At γ= 650 nm π = 15 × 10 ω was observed. Our findings give worthful insight into the sputter deposition of transparent conducting IAI coating on flexible Kapton® substrate for flexible electronics applications. © 2017 Elsevier Ltd. All rights reserved.
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    Optical and electrical studies of sputter-deposited transparent and conducting ITO/Ag/ITO multilayer on Kapton� substrate for transparent flexible electronic applications
    (2018) Sibin, K.P.; Srinivas, G.; Shashikala, H.D.; Dey, A.; Sridhara, N.; Sharma, A.K.; Barshilia, H.C.
    Transparent and conducting thin films on flexible substrates have enormous applications in the areas of space, solar, displays, etc. We hereby report the sputter deposition of transparent and conducting ITO/Ag/ITO (IAI) thin films on commercially available flexible Kapton� substrate at a lower substrate temperature. IAI multilayer has been deposited by magnetron sputtering system using an alloy In:Sn (90% :10%) and Ag targets at room temperature without breaking the vacuum. The optimized IAI coating shows high transmittance (?81.3 % at ?= 650 nm) along with very low resistance (8.36 ?/). Optical haze value of IAI on Kapton was measured and found to be <7%. The figure of merit of IAI coating on Kapton� has been calculated using the Haacke's formula ? = r10/Rs. At ?= 650 nm ? = 15 � 10 ? was observed. Our findings give worthful insight into the sputter deposition of transparent conducting IAI coating on flexible Kapton� substrate for flexible electronics applications. � 2017 Elsevier Ltd. All rights reserved.