Rapid communication Swift heavy ion induced modifications in structural, optical & magnetic properties of pure and V doped ZnO films G. Jayalakshmi a , K. Saravanan b , S. Balakumar c , T. Balasubramanian a, * a Thin Film Laboratory, Department of Physics, National Institute of Technology, Thuvakudi, Tanjore Road, Tiruchirappalli 620015, India b Institute of Ion Beam Physics and Materials Research, Helmholtz Zentrum Dresden Rossendorf, 01328 Dresden, Germany c National Centre for Nanoscience and Nanotechnology, University of Madras, Chennai 25, India article info Article history: Received 17 November 2012 Received in revised form 15 February 2013 Accepted 21 February 2013 Keywords: Swift heavy ion Irradiation Defects Room temperature ferromagnetism abstract The effect of swift heavy ion irradiation on structural, optical and magnetic properties of pure ZnO, Zn 0.95 V 0.05 O and Zn 0.90 V 0.10 O films prepared by RF sputtering are studied. X-ray diffraction (XRD) analysis reveals no significant change in the ZnO crystal structure except a small change in intensity and peak broadening on irradiation. Raman spectra reveal the degradation of crystalline quality upon ion irradiation. Atomic force microscopy (AFM) study shows the formation of smaller sized nanostructures on ion irradiation. Photoluminescence (PL) spectra of ZnO films reveal the increase of defects such as oxygen vacancy in the films upon ion irradiation. The irradiated V doped ZnO films exhibit room tem- perature ferromagnetic behaviour. An increase in oxygen vacancy on ion irradiation together with V ion concentration favours enhanced ferromagnetic behaviour in irradiated V doped ZnO films. Ó 2013 Elsevier Ltd. All rights reserved. Semiconductors and magnetic materials are the basis of most of today’s technological devices [1]. For instance, the coexistence of both charge and spin degrees of freedom are exploited into the semiconductor materials has become a goal of spintronics in order to create a future generation of devices being smaller, more versatile and robust [2]. The doping of transition metal (TM) ions such as V, Cr, Fe, Co and Ni into host semiconductor is the con- ventional method for integrating spin related information in non- magnetic systems which are called dilute magnetic semi- conductors (DMSs) [3]. Among the semiconductors, ZnO is the semiconductor of the choice for fabrication of spintronic devices due to its high solubility for TM ions and exhibiting room temperature ferromagnetism (RTFM) [4]. Despite some initial promising results, the presence of RTFM in ZnO is still under debate [5]. The segregation of transition element clusters, secondary phases and defects generated during the film growth leads to controversial interpretations of the origin of ferromagnetism [6]. Some of the recent experimental predictions suggest that structural defects influence ferromagnetic ordering in oxide DMS [7,8]. As a consequence, the origin of ferromagnetism is still under debate. Swift heavy ion (SHI) irradiation can generate controlled defects in ZnO nanostructures that can tune the materials properties [9]. When SHI penetrates a solid, it slows via two processes: the direct transfer of energy to the target atoms through elastic collisions i.e., nuclear energy loss (S n ) and electronic excitation and ionization of target atoms by inelastic collisions i.e., electronic energy loss (S e ). The values of S e and S n of 50 MeV Ag ions in ZnO films are 11.15 keV/nm and 0.1508 keV/nm, respectively calculated using SRIM 2008 code [10]. Since the value of S e is much higher than the value of S n , the energy deposited by SHI beam is ascribed to the electronic energy process. As a consequence of large amount of energy deposition with short span of time, molten zone is formed along the ions trajectory. This molten zone solidifies within pico seconds. As a result of the rapid quenching of the material, nano- crystallization may take place within the matrix [11]. As the thickness of the target (w150 nm) is much smaller as compared to the range (w9.14 mm) of Ag ions, the projectile Ag ions were not implanted in the presently studied ZnO films. Hence, the changes in the material properties are expected to be the introduction of structural defects during the passage of energetic ions. In the present work, the effect of 50 MeV Ag ions with 1  10 12 ions/cm 2 fluence on pure and V doped ZnO has been investigated with an objective to study the role of defects in determining the magnetic properties of ZnO films. The pure and V doped ZnO thin films have been grown on sapphire substrate by RF magnetron sputtering. The deposition parameters and conditions have already been reported [5]. SHI irradiation on pure and V doped ZnO films were carried out with 50 MeV Ag ions using the 6 MV Tandetron accelerator at Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum * Corresponding author. Tel.: þ91 431 2503603; fax: þ91 431 25001133. E-mail address: bala@nitt.edu (T. Balasubramanian). Contents lists available at SciVerse ScienceDirect Vacuum journal homepage: www.elsevier.com/locate/vacuum 0042-207X/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.vacuum.2013.02.014 Vacuum 95 (2013) 66e70