Antireflection coating with enhanced anti-scratch property from nanoporous block copolymer template Wonchul Joo, Youngsuk Kim, Sangshin Jang, Jin Kon Kim ⁎ National Creative Research Center for Block Copolymer Self-Assembly, Department of Chemical Engineering and Polymer Research Institute, Pohang University of Science and Technology, Pohang, Kyungbuk 790-784, Republic of Korea abstract article info Article history: Received 1 March 2010 Received in revised form 18 September 2010 Accepted 5 January 2011 Available online 19 January 2011 Keywords: Antireflection coating Block copolymer Anti-scratch We prepared a sponge-like nanoporous silica film with a dense skin layer by the infiltration of silica precursor into nanoporous polystyrene-block-poly(methyl methacrylate) copolymer template followed by calcinations at high temperature. This film showed not only excellent antireflection at visible light wavelength range but also very good resistance to scratching compared with antireflection materials made of polymeric film. We expect that this film could be used for antireflection film with anti-scratching property for flat panel displays or touch panels. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Light reflection at the interface between a transparent substrate and a transmitted medium is inevitable because of the rapid change in the refractive index (n) from air to the substrates [1,2]. This disturbing light reflection can cause a “ghost image” or blurring of viewed images on a flat panel display or light loss which can cause low efficiency of a solar cell. This light reflection loss is avoided by using antireflection (AR) film with a proper n and a judicious control in the thickness (d) [1]. To remove light reflection completely at the interface, two requirements should be satisfied [1]: n f =(n s n o ) 1/2 , with n f , n s , and n o being the n of an AR film, a substrate, and a transmitted medium, respectively, and n f d =4λ for d of the AR film and target wavelength of light (λ). For instance, for zero reflectance at 550 nm, the values of n and d of the AR film on the glass substrate should be 1.23 and 112 nm, respectively. However, because most organic or inorganic materials have n higher than 1.23, AR film should be achieved by introducing porous structure into the film [1]. Porous polymer films have been extensively employed for AR films. Steiner and coworkers introduced porous structure by using polysty- rene/polymethyl methacrylate (PS/PMMA) blend followed by removing the PMMA [2]. Some research groups fabricated AR films by colloidal assembly [3,4], layer-by-layer assembly [5,6], nanoimprinting method [7], and plasma treatment on polymer surface [8]. Others prepared a polymeric nanorod array based on anodized alumina template [9,10]. Although these methods are easy and versatile, porous polymer films have very poor thermal stability. Also, it shows poor anti-scratch property which is very important for a flat panel display. To increase the anti-scratch property as well as to enhance thermal stability, inorganic materials should be used. Hattori [11] and Tao [12] showed that an array of silica spheres with an appropriate diameter satisfying the quarter-wave optical thickness, exhibited good AR. However, because of the difficulty in controlling the pore volume fraction and the final thickness, multiple process steps of the layer-by- layer deposition were employed. Other research groups [13,14] prepared a regularly patterned surface on a silicon substrate by using reactive ion etching with the aid of an etchant mask and this showed good AR and Saarikoski et al. [15] prepared nanoporous anodized aluminum oxide layer on a polycarbonate surface; but these methods need a patterned mask in addition to the use of a high vacuum. In this study, we prepared a nanoporous silica film with enhanced anti-scratch property based on a nanoporous block copolymer template. The template was fabricated by spin-coating of polysty- rene-block-poly(methyl methacrylate) copolymer (PS-b-PMMA) on a glass substrate without thermal annealing, followed by removing PMMA block [16]. Then, silica precursor was infiltrated into the nanoporous template and calcined at high temperature. The fabricat- ed nanoporous silica film showed good AR at visible wavelength range and high anti-scratch property confirmed by a pencil hardness test. 2. Experimental section 2.1. Materials and fabrication PS-b-PMMA with a number average molecular weight of 98,200 and a polydispersity of 1.13 was purchased from Polymer Source Inc. Thin Solid Films 519 (2011) 3804–3808 ⁎ Corresponding author. E-mail address: jkkim@postech.ac.kr (J.K. Kim). 0040-6090/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2011.01.107 Contents lists available at ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf