Wear 244 (2000) 79–84 Naniondentation and scratch resistance testing on magnetic tape heads coated with ultra-thin amorphous carbon layers P. Lemoine a,* , J.F. Zhao a , J.P. Quinn a , A.A. Ogwu a , J.A. McLaughlin a , P. Maguire a , F. McGinnity b , X. Shi c a NIBEC, School of Electrical and Mechanical Engineering, University of Ulster at Jordanstown, Shore Road, Newtownabbey, Co Antrim BT37 OQB, Northern Ireland, UK b Seagate technology (Ireland), 1 Disc Drive, Springtown Ind. Estate, Londonderry BT48 OBF, Northern Ireland, UK c School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore Received 16 March 2000; received in revised form 31 May 2000; accepted 15 June 2000 Abstract We present results on nanoindentation and scratch testing on magnetic recording tape heads coated with sub-20 nm amorphous carbon layers, prepared by filtered cathodic deposition and plasma enhanced chemical vapour deposition. The hardness values of the coated devices are higher than that of the sputtered Al 2 O 3 substrate. The coatings do not reduce friction but improve the scratch resistance of the tape heads. Hardness, which shows some correlation with scratch resistance is a contributing factor, especially at high load where it reduces plastic ploughing of the substrate. For low scratching load, the wear seems to be influenced by the adhesive properties of the film/substrate interface. Smoother surfaces and smaller tip radius should improve the accuracy of the results. This could provide better insight into the failure mechanism of these ultra-thin overcoats. © 2000 Published by Elsevier Science S.A. Keywords: Ultra-thin films; Amorphous carbon; Nanoindentation; Scratch testing 1. Introduction The mechanical characterisation of films thinner than 50 nm is not merely of academic interest, it has now be- come a challenge for the industry. For instance, in the magnetic recording industry, the trends for increasing areal density push towards the development of sub-10 nm pro- tective coatings and such ultra-thin films remain difficult to characterise [1]. In the past 7 years, depth sensing indentation has been used to measure hardness (H) and Young’s Modulus (E) from load-displacement data [2,3]. Coupled with finite el- ement modelling, this technique permits the extraction of the E and H values of the thin film material from data obtained for the ‘film/substrate’ system [4]. For very hard coatings, such as tetragonal amorphous carbon produced by filtered cathodic arc deposition [5], these calculations are inaccurate, since the deformation of the diamond indenter tip is not fully accounted for, in the analysis method [6]. * Corresponding author. Tel.: +44-1232-36-89-40; fax: +44-1232-366-863. E-mail address: p.lemoine@ulst.ac.uk (P. Lemoine). However, the most important problem with the technique is its inability to deal with sub-50 nm films. Measurements have been carried out [7] but, at this level, the tip area function can only be estimated with relatively large errors. Environmental conditions, surface roughness and pile-up and sink-in effects, all adversely affect the accuracy of the results [8]. Optical techniques based on Brillouin scattering have been proposed but solely for the calculation of the E value [9]. In this context, there has been renewed in- terest in using semi-quantitative scratch testing techniques on ultra-thin films. Most studies focused on sub-20 nm thick amorphous carbon layers deposited onto magnetic discs [10] or model Al 2 O 3 -TiC and silicon substrates [11,12]. In this paper, we present initial results on nanoindentation and scratch testing of magnetic recording tape heads coated with various ultra-thin amorphous carbon layers. Our aim is to assess how effectively these experiments can differentiate between the various coated tape heads and to probe the link between hardness and scratch resistance for such ultra-thin layers. This preliminary study must be completed before examining the relationship between deposition conditions and tribological properties. 0043-1648/00/$ – see front matter © 2000 Published by Elsevier Science S.A. PII:S0043-1648(00)00439-7