Nanocrystalline diamond coating of fusion plasma facing components Samuele Porro a, ⁎, Gregory De Temmerman b , Steve Lisgo b , Phillip John a , Isaela Villalpando a , Jerry W. Zimmer c , Bob Johnson c , John I.B. Wilson a a Heriot-Watt University, Engineering and Physical Sciences, Riccarton, Edinburgh EH144AS, UK b UKAEA Euratom Fusion Association, Culham Science Centre, Oxfordshire OX143DB, UK c sp3 Diamond Technologies, 2220 Martin Ave., Santa Clara, CA 95050, United States abstract article info Available online 12 January 2009 Keywords: Nanocrystalline diamond film Hot-filament CVD Fusion Nanocrystalline diamond layers were deposited by hot-filament CVD on several substrates including molybdenum tiles and foils, graphite blocks and silicon wafers. The structural characterisation of the deposited layers, achieved by SEM, AFM, Raman and X-ray photoelectron spectroscopies, showed the typical features of nanocrystalline diamond. A nanocrystalline diamond coated molybdenum tile was exposed to a fusion grade deuterium plasma in the MAST tokamak, with a plasma current of 700 kA, core electron temperature of about 0.6 keV, and total exposure time of about 1 s. The diamond coating showed good resistance to the extremely harsh conditions of the fusion plasma edge. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The chemical vapour deposition of micro and nanocrystalline diamond, carried out by different techniques including microwave plasma and hot-filament, has been the subject of many research works aiming for a large range of applications, such as micro/ nanoelectromechanical systems, aerospace and biomedical engineer- ing, electrochemistry, tribological and electronic applications that require very smooth films, and harsh environment applications [1–7]. Compared to the other CVD techniques, the hot-filament process presents many advantages, such as the possibility of depositing thick layers on large areas (over 1000 cm 2 ), the possibility of coating various types of substrates including metals, uniformity of tempera- ture over the substrate surface, high film uniformity, etc. [8,9]. The outstanding physical and mechanical properties of CVD diamond, such as high radiation resistance, high atomic density, low thermal expansion, high thermal conductivity and chemical stability in the presence of hydrogen plasma, could make it an ideal candidate for a thin film coating on fusion relevant materials for application in tokamak fusion reactors. Fusion plasma facing components must withstand extremely high temperatures, high fluxes of charged and neutral species and plasma pressure transients. At the same time they should not retain a large quantity of tritium as compared to graphite or carbon fibre composite (CFC) or absorb other plasma constituents, whilst minimising surface erosion by chemical sputtering that can contaminate the plasma [10]. Graphite and other carbon-based materials are widely used in nowadays tokamaks because of carbon high resilience to thermal loads owing to its lack of a liquid phase (it simply sublimates). This makes carbon very forgiving to transient events such as those which occur in tokamaks (ELMs, disruptions) [11–13]. However, carbon has two main limitations which obviate its use in a fusion reactor: its reactivity towards hydrogen isotopes and the related chemical erosion pose a serious problem for the lifetime of carbon plasma-facing materials under bombardment by high fluxes of hydrogen plasma [14,15]. The chemical erosion and co-deposition also rise the problem of the tritium inventory in the machine. Tokamaks which have turned from carbon walls to metal walls have seen a huge reduction of the deuterium inventory [16]. CFC materials suffer from severe degrada- tion of their mechanical and thermal properties under high fluence neutron irradiation at fusion neutron energies [17]. This work describes the growth of nano and microcrystalline diamond by hot filament chemical vapour deposition (HFCVD) and the structural characterisation of deposited layers. Diamond thin films were deposited on different substrates, including silicon, graphite and molybdenum. The first encouraging results of nanocrystalline diamond exposure to deuterium plasma in the MAST tokamak [18] during a preliminary test will also be presented. The experiment was carried out with a nanocrystalline diamond coated Mo tile exposed in the edge plasma. In this paper, we will focus on the results of the characterisation of nano-sized diamond layers. 2. Experimental The hot filament system used in this work is a Model 650 CVD Diamond Deposition System from sp3 Diamond Technology. A brief Diamond & Related Materials 18 (2009) 740–744 ⁎ Corresponding author. E-mail address: S.Porro@hw.ac.uk (S. Porro). 0925-9635/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2009.01.006 Contents lists available at ScienceDirect Diamond & Related Materials journal homepage: www.elsevier.com/locate/diamond