Vacuum 72 (2004) 225–232 Gas scattering effects and microstructural evaluation of electron beam evaporated titanium coatings in neon and argon at different gas pressures J.C. Avelar-Batista a, *,A.D.Wilson b,w ,A.Davison a ,A.Matthews c,z ,K.S.Fancey a a Research Centre in Surface Engineering, Department of Engineering, University of Hull, Cottingham Road, Hull, HU6 7RX, UK b Sport Carrier Limited, Sywell Road, Park Farm South, Wellingborough, NN8 6XD, UK c Department of Engineering Materials, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield, S1 3JD, UK Received 14 May 2003; received in revised form 16 July 2003; accepted 16 July 2003 Abstract Titanium coatings were deposited on stainless steel and glass substrates by electron beam evaporation in vacuum (4  10 4 Pa) and at different neon and argon gas pressures (from 0.33 to 2.00Pa). The effect of background gas pressure and type on film microstructure was evaluated by scanning electron microscopy (SEM). Since it was not feasible to maintain a constant evaporation rate for all runs, the ‘deposition efficacy’, a parameter defined as the ratio between coating thickness and mass of material evaporated, was statistically modelled using non-linear regression analysis to determine the effects of gas scattering. The results revealed that neon and argon promote similar scattering of the titanium vapour and this may point to a lower likelihood of gas-phase metal cluster formation in neon. The coating microstructure was found to change from a tapered grain structure, obtained under vacuum conditions, to a facetedoneatlowgaspressure(0.33Pa),becomingmoreporousasgaspressureincreased.Foragivengaspressure,no significant differences could be observed in coating microstructure between the use of argon or neon. These findings maybesignificantwhenconsideringtheuseofneonasanalternativegastoargon,forimprovingreactivegasionisation (through Penning mechanisms) in Plasma-Assisted Physical Vapour Deposition. r 2003 Elsevier Ltd. All rights reserved. Keywords: Evaporation; Titanium; Argon; Neon; Coating microstructure; Statistical modelling; Gas scattering effects 1. Introduction The transport of evaporated or sputtered materials through the gas phase, from the eva- porative source to the substrate, has been mod- elled by several investigators using Monte-Carlo simulations [1–5] or analytical approaches [6–11]. In all transport models, the evaporant flux to the substrate is mainly limited by collisions with the background gas. The energy of the evaporant flux ARTICLE IN PRESS *Corresponding author. Tel.: +44-1482-465072; fax: +44- 1482-466477. E-mail address: j.c.avelar-batista@hull.ac.uk (J.C. Avelar-Batista). w Presentaddress:SportCarrierLtd,SywellRoad,ParkFarm South, Wellingborough, NN8 6XD, UK. z Present address: Department of Engineering Materials, University of Sheffield, Sir Robert Hadfield Building, Mappin Street, Sheffield, S1 3JD, UK. 0042-207X/$-see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0042-207X(03)00144-1