Indian Journal of Pure & Applied Physics Vol. 57, August 2019, pp. 605-606 Low energy ion beam study on Co/CoO thin films Deepak Kumar & A S Bhattacharyya* Department of Nano Science and Technology, Central University of Jharkhand, Brambe 835 205, India Computer simulation using SRIM software has been done for ion beam irradiation of different metal ions on Co/CoO thin film which is an FM/AFM system. The films have been experimentally deposited by magnetron sputtering and subjected to low energy ion beams (LEIB) of different energies and fluences. The variation of Si ion energy led to different ion distribution profiles which could be correlated with the morphological changes like dewetting occurring at the surface. Such phenomenon is potentially important for making spintronic devices in future. Keywords: Low energy ion beam (LEIB), FM/AFM system, SRIM, Dewetting 1 Introduction Ion beam irradiation is an effective means of studying the morphological changes occurring in thin films. Surface energy changes as well as displacement of atoms due to localized heating can bring about interesting phenomena which can lead to possible patterning and device fabrication in the future. Film thickness and temperature affect the Co nanoparticles size and uniformity formed by dewetting. Co films have been found to undergo dewetting on annealing. These Magnetic metal nanoparticle arrays are used in magnetic recording and carbon or semiconductor nanotubes. Other means of obtaining patterned nanoparticle arrays are by lithography, spin-coating, droplet drying, dip-coating, or LB methods 1, 2 . 2 Experimental Details Co/CoO thin films were deposited by magnetron sputtering. Thickness of each film was 25 nm. The films were then irradiated with Si and Ar ions at different fluences and energies. Scanning electron microscopy (SEM) and magnetic force microscopy (MFM) measurements were performed to study the changes in morphology and magnetic structure that occurred with the irradiation while SQUID and PPMS measurements were performed to study temperature and magnetic field dependence of dc magnetization. 3 Results and Discussion Due to Si ion irradiation at 50 keV on the Co/CoO sample, the phenomenon of ion-beam-induced dewetting occurred. Due to larger surface free energy of Co compared to CoO, globule-like structures, as shown in the SEM image Fig. 1, have formed. This phenomenon resulted in the loss of connectivity between the different regions and as a result the ferromagnetic property got lost and the Co clusters act as separate entities with no interaction between each other. The phenomenon known as ion-beam- induced dewetting. Superparamagnetism was observed for Co/CoO films, which were irradiated with 200 keV Ar ions at a fluence of 10 15 ions/cm 2 . Blocking temperature around 300 K was obtained from the measured ZFC-FC magnetization 3,4 . Simulation studies using SRIM was done with Si (27.977 amu) ions of 40 keV energy irradiated on Co/CoO bilayers of thickness 100 Å each as shown in ————— *Corresponding author (E-mail: arnab.bhattacharya@cuj.ac.in) Fig. 1 – SEM image of ion beam induced dewetting caused by Si ions on Co/CoO bilayer 4 .