Au nanopatterns on glass substrate using block copolymer and their applications in transparent conducting electrode Md. Mahbub Alam a , Jin-Yeol Kim b , Woo-Gwang Jung b, ⁎ a Department of Arts and Sciences, Ahsanullah University of Science and Technology, 141–142 Love Road, Tejgaon, Dhaka-1208, Bangladesh b Department of Advanced Materials Engineering, Graduate School of Kookmin University, 861-1 Jeongneung-dong, Seongbuk-gu, Seoul, 136-702, Republic of Korea abstract article info Article history: Received 27 March 2011 Received in revised form 20 March 2012 Accepted 1 April 2012 Available online 6 April 2012 Keywords: Transparent conducting electrodes Block copolymers Pattering Transmittance Resistivity Scanning electron microscopy Gold High density Au nanostructures were fabricated using polystyrene-block-polymethylmethacrylate (PS-b- PMMA) copolymer on glass substrate for the preparation of electrode materials with good stability, high transparency and excellent conductivity. A 1 wt.% polymer solution in toluene was spin coated on glass sub- strate. Samples were baked for 48 h at 200 °C with a continuous flow of Ar. Patterned polymer film was obtained by removing the PMMA region through exposing ultraviolet irradiation and rinsing in acetic acid. Au thin films with several thicknesses were then deposited onto the patterned glass substrates by thermal evaporation or sputtering. Removing PS cylinders by sonicating in acetone resulted in Au nanopattern on glass substrates. The connecting gold film acts as conductor while the holes allow light pass through it and helps to be transparent. The transmittance with Au film thickness of 7 nm and 4 nm was found to be about 63% and 70%, respectively. The resistivity was in the range 10 -5 Ω cm–10 -6 Ω cm which is comparable with ITO (10 -3 Ω cm–10 -4 Ω cm). © 2012 Elsevier B.V. All rights reserved. 1. Introduction Block copolymer self-assembly has attracted significant interest in recent years, since the resultant bulk and thin film morphologies offer ideal platforms for the generation of nanoscopically ordered patterns in a range of the promising applications [1–5]. The self-assembly of block copolymer is a versatile way of preparing nanoparticles and controlling size, shape and location [6–8]. As for thin films, however, interfacial interactions play an important role in influencing the mor- phology and orientation of the block copolymer microdomains [9,10] allowing the desired nanopatterns or arrays [11–14]. One commonly studied diblock copolymer is polystyrene-b-polymethyl-methacrylate (PS-b-PMMA), which is valued for having both blocks present at the surface in the film [15–17]. It is generally accepted that perpendicular domain orientation in PS-b-PMMA films requires elimination of the preferential segregation of PMMA on the substrate–film interface. It was found that perpendicular and hybrid [10] morphologies can be obtained for certain film thickness ranges. There is a need in a number of different areas of fundamental sci- ence and applied technology for thin films those are both electrically conducting and optically transparent. Almost all practically electro- chromic devices must incorporate optically transparent electrodes. Indium-tin-oxide (ITO) is the most widely known and commonly used material of this kind because of its properties to offer transparen- cy in the visible range of the electromagnetic spectrum and also elec- trical conductivity [18–21]. Advantages of ITO are its low resistivity (10 -3 Ω cm–10 -4 Ω cm depending on the deposition method) and its high transparency in the visible region (80%–90% between 400 nm and 800 nm). Due to unique properties, ITO films have many applica- tions, such as solar cells [22], light emitting electrochemical cells [23] and flat panel displays [24,25]. A stable supply of ITO may be difficult to achieve for the recently expanding market for optoelectronic devices because of the cost and scarcity of indium, the principal material of ITO. The search for electrode materials with good stability, high transpar- ency and excellent conductivity is therefore a crucial goal for optoelec- tronics [26]. In our work, we have tried to make gold patterned glass electrode, where the gold pattern is connected throughout the substrate to act as a conductor. At the same time, the holes in the patterns help passing light through it to increase the transmittance of the substrate. 2. Experimental details Two different compositions of PS-b-PMMA block copolymer were used for patterning. One with Mn: PS (46100), PMMA (21000) and Mw/Mn: 1.09, having a PS volume fraction of 0.69 and in another Mn: PS (25000), PMMA (40000) and Mw/Mn: 1.07, having a PS volume frac- tion of 0.38 (Polymer Source Inc.). The substrates were ordinary glass microscope slides, of dimensions 2.5 cm×7.5 cm and thickness 1 mm. A 1 wt.% polymer solution in toluene was spin coated on glass sub- strates. The samples were then baked for 48 h with a continuous flow Thin Solid Films 520 (2012) 5161–5164 ⁎ Corresponding author. Tel.: +82 2 910 4643; fax: +82 2 910 4320. E-mail address: wgjung@kookmin.ac.kr (W.-G. Jung). 0040-6090/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2012.04.006 Contents lists available at SciVerse ScienceDirect Thin Solid Films journal homepage: www.elsevier.com/locate/tsf