700 keV Ni +2 ions induced modification in structural, surface, magneto-optic and optical properties of ZnO thin films M. Fiaz Khan a , K. Siraj a,⇑ , M.S. Anwar b , M. Irshad a , J. Hussain c , H. Faiz a , S. Majeed a , M. Dosmailov d , J. Patek d , J.D. Pedarnig d , M.S. Rafique a , S. Naseem e a Laser and Optronics Centre, Department of Physics, University of Engineering and Technology, Lahore, Pakistan b Department of Physics, Syed Babar Ali School of Science and Engineering, Lahore University of Management Sciences (LUMS), Opposite Sector U, D.H.A. Lahore 54792, Pakistan c National Centre for Physics, Islamabad, Pakistan d Institute of Applied Physics, Johannes Kepler University Linz, Austria e Center of Excellence in Solid State Physics, University of Punjab, Lahore, Pakistan article info Article history: Received 14 July 2015 Received in revised form 8 December 2015 Accepted 8 December 2015 Available online 21 December 2015 Keywords: Nickel ion irradiation ZnO thin films XRD Microrods Optical properties abstract We investigate the effect of 700 keV Ni +2 ions irradiation at different ion fluences (1  10 13 ,1  10 14 , 2  10 14 ,5  10 14 ions/cm 2 ) on the structural, surface, magneto-optic and optical properties of ZnO thin films. The X-ray diffraction (XRD) results show improved crystallinity when ion fluence is increased to 2  10 14 ions/cm 2 , while deterioration is observed at the highest ion fluence of 5  10 14 ions/cm 2 . Scanning electron micrographs (SEM) show the formation of small grains at ion fluence 1  10 13 ions/ cm 2 , micro-rods at fluences 1  10 14 and 2  10 14 ions/cm 2 and ultimate fracturing of thin film surface at ion fluence 5  10 14 ions/cm 2 . Faraday rotation measurements are also performed and show a decrease in Verdet constant from 53 to 31 rad/(T-m) when irradiated at 1  10 13 ions/cm 2 , increasing up to 45 rad/ (T-m) at 2  10 14 ions/cm 2 , and then decreasing again to 36 rad/(T-m) at 5  10 14 ions/cm 2 . The optical band gap energy of the films is determined using spectroscopic ellipsometry, which shows an increase in optical band gap energy (E g ) from 3.04 eV to 3.19 eV when the fluence increases to 2  10 14 ions/ cm 2 and a decrease to 3 eV at fluence 5  10 14 ions/cm 2 . We argue that these properties can be explained using ion heating effect of thin films. Ó 2015 Elsevier B.V. All rights reserved. 1. Introduction There exists a continued interest in zinc oxide thin films owing to its attractive properties and promising applications. Its wide band gap (3.37 eV), high excitonic binding energy (60 meV), semi- conducting, piezoelectric, optical and magnetic properties have all been exploited for use in optoelectronic devices (blue/UV LED’s, photodetectors, optical windows for solar cells etc), gas and chemical sensors, telecommunication devices, acoustic resonators, surface acoustic waves, spintronic and magneto-optical devices [1–10]. There exist several techniques for the fabrication of ZnO thin films, such as pulsed laser deposition, thermal sputtering, mag- netron sputtering, sol–gel, physical vapor deposition, molecular beam epitaxy and electro-deposition, etc. [11–17]. An important technique that has been reported to synthesize high quality films is pulsed laser deposition [18]. The properties of these films can be subsequently tailored, for example, doping with metallic ions, electron irradiation, ion irradiation, etc. [3,19,20]. Ion irradiation (Co, Mn, Fe, Cr, etc.) [21–23] of ZnO thin films is particularly plau- sible technique for impurity doping and deliberate production of defects, which facilitate modifying the structural, electrical, optical and magnetic properties with high spatial selectivity [24]. During ion penetration in solids, ions loose energy by means of two mechanisms. First is nuclear energy loss, which occurs due to direct transfer of recoil energy to target atoms through elastic col- lisions. The second is electronic energy loss, occurring due to elec- tronic excitation and ionization through inelastic collisions. The second mechanism is prominent when thickness of the target material is smaller than the range of the incident ion (linear energy transfer). The ion energy transfer to the medium is responsible for defects and heat production in the material [25]. Subsequently, the thermal energy generated provides the activation energy required for substitution of metallic ions to the host ions. There are a number of experiments on implanting ZnO with low energy (<200 keV) ions [26,27] etc. but the studies on optical and especially magneto-optical properties (Eg, Verdet’s constant etc.) http://dx.doi.org/10.1016/j.nimb.2015.12.010 0168-583X/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: khurram.uet@gmail.com (K. Siraj). Nuclear Instruments and Methods in Physics Research B 368 (2016) 45–49 Contents lists available at ScienceDirect Nuclear Instruments and Methods in Physics Research B journal homepage: www.elsevier.com/locate/nimb