Synthesis and analysis of metallic Zn phase rich ZnO oxide films for the photocatalytic water treatment technologies Martynas Lelis a,⇑ , Simona Tuckute a , Sarunas Varnagiris a , Marius Urbonavicius a , Kristina Bockute a,b , Giedrius Laukaitis a,b a Lithuanian Energy Insitute, 3 Breslaujos st., Kaunas LT-44403, Lithuania b Kaunas University of Technology, 50 Studentu st., Kaunas LT-51368, Lithuania article info Article history: Received 30 November 2019 Received in revised form 12 February 2020 Accepted 8 March 2020 Available online xxxx Keywords: ZnO Self-doped Mixed phase Magnetron sputtering Plasma emission Photocatalyst abstract In this study ZnO based photocatalyst films were deposited using magnetron sputtering with in-situ con- trol of the physical vapor phase composition. Precise monitoring and control of Zinc, Argon and oxygen content in plasma phase allowed to identify small range of parameters which led to the formation of sam- ples in the intermediate zone between metallic Zn and stoichiometric ZnO. Photocatalytic tests have demonstrated that in such samples metallic zinc up to some extent improves the photocatalytic effi- ciency of ZnO oxide. The relationship between magnetron sputtering process parameters and film prop- erties are provided and their influence to the photocatalytic activity of the films is discussed. Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the E-MRS Fall Meeting, 2019. 1. Introduction ZnO is one of the most researched photocatalyst materials [1]. Advantageous properties of pristine ZnO and its significant activity under UV light excitation has been recognized by many groups [2– 4]. Unfortunately, pristine ZnO has relatively wide band gap (3.4 eV) and this limits ZnO applications for the daylight assisted photocatalysis [5]. In order to overcome this limitation various approaches have been tried. Studies showed that ZnO doping (with metal [6,7] and non-metal [8,9] dopants), dye-sensitization [10], semiconductor coupling [11] and other approaches [12,13] are capable to lower the band gap of ZnO and make it responsive at visible light spectra. Accordingly, interest in ZnO based photocatal- ysis is still rising exponentially [14] and ZnO remains one of the most promising materials for the daylight assisted photocatalytic water cleaning. Majority of the ZnO synthesis methods can be classified into two categories: i) chemical methods and ii) physical methods. The former one is appreciated for its relative simplicity, easy scal- ability and ability to produce different shapes and forms of ZnO powders [15]. Also, it is successfully used to add various dopants and sensitize with dyes [16]. From notable shortcomings chemical methods suffers from the inability to overcome thermodynamic limitations of material mixing and naturally imminent formations of specific phases. Moreover, some of the chemical methods used for the ZnO synthesis and modification are criticized for the envi- ronmental issues caused by the toxicity of the reactants or reaction by-products [17,18]. On the other hand, most of the physical meth- ods are less attractive for the high mass throughput-oriented pow- der synthesis but are far more superior for the ZnO synthesis in films and coatings form [19]. Later forms are especially attractive for the easier photocatalyst withdrawal during repetitive contam- inated water photocatalytic cleaning processes [20]. But the big- gest advantage of physical methods is the possibility to overcome traditional thermodynamical limitations and to produce metastable materials [21]. At the same time, it offers wider possi- bilities to create controllable interfaces and heterojunctions which are beneficial for the charge separation [22]. Among other physical methods magnetron sputtering stands up as a well proven mature technology whose expediency has been recognized by both small scale oriented scientific research as well as large scale industrial production [23–25]. ZnO film deposition by magnetron sputtering is done by using either ZnO or metallic Zn sputtering targets. When ZnO target is used zinc oxide deposi- tion by magnetron sputtering can be done using just nobel Ar gas. However, some of the oxygen can be lost during the sputtering process therefore in order to maintain the stoichiometry of zinc https://doi.org/10.1016/j.matpr.2020.03.197 2214-7853/Ó 2020 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the E-MRS Fall Meeting, 2019. ⇑ Corresponding author. E-mail address: martynas.lelis@lei.lt (M. Lelis). Materials Today: Proceedings xxx (xxxx) xxx Contents lists available at ScienceDirect Materials Today: Proceedings journal homepage: www.elsevier.com/locate/matpr Please cite this article as: M. Lelis, S. Tuckute, S. Varnagiris et al., Synthesis and analysis of metallic Zn phase rich ZnO oxide films for the photocatalytic water treatment technologies, Materials Today: Proceedings, https://doi.org/10.1016/j.matpr.2020.03.197