Full Length Article Intrinsically water-repellent copper oxide surfaces; An electro- crystallization approach Raziyeh Akbari a,b , Gabriela Ramos Chagas b , Guilhem Godeau b , Mohammadreza Mohammadizadeh a , Frédéric Guittard b , Thierry Darmanin b,⇑ a Supermaterials Research Laboratory (SRL), Department of Physics, University of Tehran, North Kargar Av., P.O. Box 14395-547, Tehran, Iran b Université Côte d’Azur, NICE Lab, IMREDD, 06200 Nice, France article info Article history: Received 15 October 2017 Revised 13 December 2017 Accepted 21 February 2018 Keywords: Copper oxide Electrodeposition Hydrophobicity Crystals abstract Use of metal oxide thin layers is increased due to their good durability under environmental conditions. In this work, the repeatable nanostructured crystalite Cu 2 O thin films, developed by electrodeposition method without any physical and chemical modifications, demonstrate good hydrophobicity. Copper (I) oxide (Cu 2 O) layers were fabricated on gold/Si(1 0 0) substrates by different electrodeposition meth- ods i.e. galvanostatic deposition, cyclic voltammetry, and pulse potentiostatic deposition and using cop- per sulfate (in various concentrations) as a precursor. The greatest crystalline face on prepared Cu 2 O samples is (1 1 1) which is the most hydrophobic facet of Cu 2 O cubic structure. Indeed, different crystal- lite structures such as nanotriangles and truncated octahedrons were formed on the surface for various electrodeposition methods. The increase of the contact angle (h w ) measured by the rest time, reaching to about 135°, was seen at different rates and electrodeposition methods. In addition, two-step deposition surfaces were also prepared by applying two of the mentioned methods, alternatively. In general, the morphology of the two-step deposition surfaces showed some changes compared to that of one-step samples, allowing the formation of different crystallite shapes. Moreover, the wettability behavior showd the larger h w of the two-step deposition layers compared to the related one-step deposition layers. Therefore, the highest observed h w was related to the one of two-step deposition layers due to the cre- ation of small octahedral structures on the surface, having narrow and deep valleys. However, there was an exception which was due to the resulted big structures and broad valleys on the surface. So, it is possible to engineer different crystallites shapes using the proposed two-step deposition method. It is expected that hydrophobic crystallite thin films can be used in environmental and electronic applica- tions to save energy and materials properties. Ó 2018 Elsevier B.V. All rights reserved. 1. Introduction As communities grow around the globe, finding better ways to reduce pollution and fuel consumptions is more felt. Recently, water-repellent and hydrophobic surfaces have attracted substan- tial interests due to their excellent applications in environmental and industrial fields. However, hydrophobic surfaces have poten- tial applications as easy to clean, anti-bacteria, drag force reduc- tion, corrosion resistance and marine applications [1,2]. In fact, for a smooth surface, following the Young-Dupré equa- tion [3], h Y cannot ‘‘experimentally” exceed around 130°. Two developed version of the Young-Dupre equation (Wenzel [3] and Cassie-Baxter [4] equations) are very often used to predict the effect of surface roughening on the surface hydrophobicity. In the Wenzel state, the liquid penetrates in all the surface roughness, so the surface roughness can increase the surface hydrophobicity but only if h Y > 90° (intrinsically hydrophobic materials). For the Cassie-Baxter equation, there is some air trapped inside the surface roughness between the water droplet and the surface. With this equation, it is possible to increase the surface hydrophobicity whatever h Y if the surface structures present on the surface are able to trap some air. Different processes were employed in the literature to control the surface structures and energy [1,2,5,6]. The electrodeposition allows an easy and fast control of these properties allowing the for- mation of various surface morphologies, such as spheres [7], tubes [8–10] and fibers [11] in polymers, for example. Metals and con- ducting polymers can be deposited and the surface properties can be tuned, with many electrochemical parameters such as the https://doi.org/10.1016/j.apsusc.2018.02.205 0169-4332/Ó 2018 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: thierry.darmanin@unice.fr (T. Darmanin). Applied Surface Science 443 (2018) 191–197 Contents lists available at ScienceDirect Applied Surface Science journal homepage: www.elsevier.com/locate/apsusc