PHILOSOPHICAL MAGAZINE LETTERS,JUNE 2004 VOL. 84, NO. 6, 395–403 In-situ stress measurement during the deposition of CN x thin films by unbalanced magnetron sputtering; formation of high levels of stress with 28 eV ion irradiation I. F. Brunellyô, L. Pichonz , N. Hellgren‰, Zs. Cziga¤ nyy , J. Neidhardty and L. Hultmany yThin Film Physics Division, Department of Physics (IFM), Linko¨ping University, S-581 83 Linko¨ping, Sweden zLaboratoire de Me´tallurgie Physique, UMR 6630-CNRS, Universite´ de Poitiers, UFR Sciences SP2MI, Te´le´port 2, Boulevard Pierre et Marie Curie, BP 30179, 86962 Futuroscope, Chasseneuil Ce´dex, France §Materials Research Laboratory, University of Illinois, 104 S. Goodwin Ave., Urbana, IL 61801, USA [Received in final form 14 March 2004 and accepted 12 April 2004 ] Abstract Stress development during growth of CN x films by unbalanced magnetron sputtering has been investigated with an in-situ laser deflection technique. The stress is initially tensile, then it becomes compressive, reaching a maximum of as much as 7 GPa. These are anomalously high stress levels compared with pure carbon, considering the low ion energies (28 eV) and ion-to-neutral arrival rate ratio (<1) employed. This phenomenon is explained by the formation of a fullerene-like microstructure and nitrogen substitution at the growth surface. An accompanying increased reactivity of carbon atoms promotes sp 3 bonding or other cross-linking of curved basal planes with resulting film densification. } 1. Introduction The recently discovered fullerene-like CN x phases or compounds are formed by incorporating nitrogen into graphite sheets, which induces bending and curvature by pentagon formation (Sjo¨stro¨m et al. 1995, Hellgren et al. 1999), hence the term fullerene-like. The reactivity of carbon atoms around the nitrogen increases, thus promoting sp 3 cross-linking of carbon between the fullerene-like features (Stafstro¨m 2000). Similarly, aza-fullerene C 59 N molecules are known to exhibit a radical nature owing to nitrogen incorporation, leading to the formation of dimers (Brown et al. 1996). Fullerene-like CN x is a material of great scientific and technological interest, because it has high fracture toughness and extremely high elasticity. The orientation, radius of curvature of the basal planes and the degree of cross-linking between them define the structure and properties of the material. It deforms elastically over a wide range due to bending and buckling of the atomic sheets. The comparatively low ôAuthor for correspondence. Email: ian.brunell@tiscali.co.uk. Present address: 98 Plymyard Avenue, Bromborough, Wirral CH62 6BR, UK. Philosophical Magazine Letters ISSN 0950–0839 print/ISSN 1362–3036 online # 2004 Taylor & Francis Ltd http://www.tandf.co.uk/journals DOI: 10.1080/09500830410001716140