Optical Materials 108 (2020) 110415 Available online 26 September 2020 0925-3467/© 2020 Elsevier B.V. All rights reserved. Fabricating multilayer antirefective coating for near complete transmittance in broadband visible light spectrum Rupali Patel a , Nainesh Patel b, * , Nicola Bazzanella c , Antonio Miotello c a Department of Physics, NES Ratnam College, University of Mumbai, Bhandup (West), Mumbai, 400078, India b Department of Physics, University of Mumbai, Vidyanagari, Santacruz (East), Mumbai, 400098, India c Department of Physics, Universit` a Degli Studi di Trento, I-38123, Povo, Trento, Italy A R T I C L E INFO Keywords: Antirefective coating Multilayer Refractive index RF-magnetron sputtering Near-zero transmittance ABSTRACT To extract maximum performance out of the certain optical devices it is highly desirable to use completely transparent window in a broad wavelength range. In search of large-scale applicable antirefective (AR) coating for such window, herein we report the design and fabrication of multilayer coating with the aim to reduce the refection of the window in the entire visible light range. Systematic selection of material and thickness of each layer was performed based on the criteria fulflled by refractive index to obtain zero refection. Low refractive index material like MgF 2 is deposited by e-beam technique to obtain single-layer AR coating. While Al 2 O 3 and ZrO 2 , deposited by RF-magnetron sputtering, with MgF 2 are used to develop multilayer AR coating. Scanning electron microscope image along with elemental line scan obtained along the cross-section of the coating verifed the thickness and composition of each layer. Deposition of four-layer AR coating (MgF 2 /Al 2 O 3 /ZrO 2 /MgF 2 ) on both side of quartz window with optimized thickness showed considerable reduction in the refection to 0.6% at 550 nm. The average transmittance of 99.1% was recorded in the broadband of visible spectrum in the range of 450–750 nm wavelength. With near to complete transmission, the present AR coating holds encouraging pros- pect for implementing in windows of digital display, photovoltaic module, and other optoelectronic devices. 1. Introduction Ever increasing demand of optical and optoelectronic devices has driven the scientifc community to identify the effective strategies to maximize light transmission and receiving effciency. In this context, protective window with high optical transparency plays a pivotal role. For example the ultimate effciency of photovoltaic module will depend on the refection property of the cover glass from where minimum of 4% of incident light across the solar spectrum is refected back and lost. Space exploration through telescope receives a very minute optical signal which cannot be afforded to be attenuated through the window. Among others, refection losses through the lenses of cameras and mi- croscopes affect the quality of images. Generally, antirefective (AR) coatings and pattern on the windows and lenses are used to avoid such shortfall [1,2]. In addition to accomplish minimum refection, AR coating also need to be effective in broadband spectrum, independent on the angle of incidence, and should be ultra thin [3,4]. Single-layer AR coating, with refractive index value between that of air and of the window material, and with thickness of one quarter of wavelength of interest, reduces the refection at that wavelength [5]. However, practically such material does not exist in the nature thus MgF 2 having low refractive index close to the ideal value is used for single layer coating. Materials with high porosity and low density were also applied for such single-layer AR coating with limited success [6–8]. Combination of two materials with different refractive index has also been tested in two-layer AR coating which manages to reduce the refection of only specifc wavelength [2,9]. In order to further broaden the bandwidth of the spectrum, multilayer AR coatings have been realized from materials having refractive index greater than that of the window [10–16]. By proper selection of the material with required refractive index and tuning the thickness, the multilayer coating can minimize the summation of overall refection vectors [17]. The combi- nation of TiO 2 and SiO 2 is most commonly used for multilayer AR coating [18–22], while Al 2 O 3 having refractive index of 1.62 close to glass is rarely been studied along with ZrO 2 [9,14,23]. Both these ma- terials have been limited to the designing stage [9,23] even if refractive index of both these materials perfectly satisfy the condition of refractive index required to achieve zero refection for multilayer coating. * Corresponding author. E-mail addresses: naineshp@physics.mu.ac.in, nainesh11@gmail.com (N. Patel). Contents lists available at ScienceDirect Optical Materials journal homepage: http://www.elsevier.com/locate/optmat https://doi.org/10.1016/j.optmat.2020.110415 Received 3 July 2020; Received in revised form 5 September 2020; Accepted 7 September 2020