Available online at ScienceDirect. Materials Today: Proceedings 2 (2015 )

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deposited by pulsed laser Mirza Khurram Baig a, Shahid Atiq a *, Shazia Bashir b, Saira Riaz a, Shahzad Naseem a a Centre of Excellence in Solid State Physics, University of the Punjab, Quaid-e-Azam

1 Available online at ScienceDirect Materials Today: Proceedings 2 (2015 ) International Conference on Solid State Physics 2013 (ICSSP 13) Thickness dependent optimization of 1-5 phase of SmCo thin films deposited by pulsed laser Mirza Khurram Baig a, Shahid Atiq a *, Shazia Bashir b, Saira Riaz a, Shahzad Naseem a a Centre of Excellence in Solid State Physics, University of the Punjab, Quaid-e-Azam campus, Lahore-54590, Pakistan b Centre for Advanced Studies in Physics, Government College University, Lahore-54000, Pakistan Abstract In this work an effort has been made to deposit SmCo thin films on single crystal Si(100) substrates using pulsed laser deposition technique. The substrate temperature was fixed at 400 C and number of laser pulses were varied in order to get thin films of different thicknesses. Effect of laser shots on the crystal structure evolution, composition of the deposited material and film thickness have been explored. A slight variation in the Sm and Co contents was observed in thin films grown by varying the number of laser shots, which ultimately resulted in the development of 1:5 phase of SmCo thin films Elsevier Elsevier Ltd. Ltd. All All rights rights reserved. reserved. Selection and and Peer-review under under responsibility of the of Committee the Committee Members Members of International of International Conference Conference Solid State on Solid Physics State Physics 2013 (ICSSP 13). Keywords: SmCo thin films; Pulsed laser deposition; Magnetic properties * Corresponding author. Tel.: address: satiq.cssp@pu.edu.pk Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of the Committee Members of International Conference on Solid State Physics 2013 (ICSSP 13) doi: /j.matpr

2 Mirza Khurram Baig et al. / Materials Today: Proceedings 2 ( 2015 ) Introduction During the last few decades, SmCo has gained enormous attention of scientific community due to its well-suited magnetic properties required for permanent magnetic storage media. However, there has been a continuous quest for the defect-free growth of these films [1]. Few techniques are there for well-oriented growth of SmCo films but pulsed laser deposition (PLD) has emerged as a relatively more effective technique that warrants growing thin films on a variety of substrates [2]. In addition, the possibility to grow thin magnetic films on even insulator substrates has triggered the interest with the aim to develop components for many modern day applications [3]. One of the added advantages of SmCo-based magnetic thin films is their thermal stability enough to produce continuous magnetic fields with no energy consumption that can be employed for biasing the magnetic detectors for electronic industry in particular [4, 5]. This enables SmCo thin films for consideration as a promising candidate for structured microelectromagnetic devices [6, 7]. In this context, it is inferred that deposition of SmCo thin films in phase pure form is essential to exploit its potential applications. In the present work, we focus on the phase optimization of pulsed laser deposited SmCo thin films on single crystal Si(100) substrates. Thickness of the films was varied by varying the number of laser shots. The subsequent effect on the structural and compositional properties has been reported [8]. 2. Experimental Details SmCo thin films were deposited on single crystal Si(100) substrate by PLD. The frequency doubled Nd: YAG laser with the wavelength of 532 nm, pulse duration of 6 ns, repetition rate of 10 Hz and max pulse energy of 150 mj with circular beam size of 8 mm was used as a source of irradiation. Laser beam hit the SmCo target paced in the ultrahigh vacuum chamber at an angle of 45. Five samples of SmCo thin films were deposited on Si(100) wafers using various laser shots from 1000 to 5000, by ablating the laser beam on SmCo 5 target, while keeping the substrate temperature constant at 400 C [6]. X-ray diffraction (XRD) was utilized for the investigation of crystal structure. Structural morphology and compositional analysis were carried out using a scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX), respectively. 3. Results and Discussion Fig. 1 shows the diffraction patterns of the thin films deposited on Si(100) substrate using 1000, 2000, 3000, 4000 and 5000 laser shots at a fixed substrate temperature of 400 C. The diffraction patterns were obtained using XRD. Amorphous behavior of SmCo thin films have mainly been reported for the as-deposited thin films [9]. Therefore, in the present case, the substrate temperature was fixed at 400 C for the phase stabilization. The samples deposited with 1000 and 2000 laser shots mainly showed amorphous behavior as no prominent peak relating to the any phase of SmCo was witnessed. When the number of laser shots was increased to 3000, i.e. for a relatively thicker deposition, a small peak at about 2θ = 68.8 related to (301) plane of SmCo 5 was evident. This peak was well-matched with ICSD reference code [6].

3 5584 Mirza Khurram Baig et al. / Materials Today: Proceedings 2 ( 2015 ) Fig. 1. XRD Patterns of SmCo thin films with varying laser shots

4 Mirza Khurram Baig et al. / Materials Today: Proceedings 2 ( 2015 ) Fig. 2. SEM images and relevant EDX spectra of SmCo thin films deposited for various No of Laser shots (a) 1000, (b) 2000, (c) 3000, (d) 4000, and (e) 5000 Therefore, the thin film samples were identified to have hexagonal structure with space group P6/mmm, space group number 191. The corresponding lattice parameters were noted to be a = b = Å and c = Å. When the films were deposited with increased number of laser shots, i.e and 5000 pulses, the intensity of this peak increased further, indicating the improved crystallinity of the deposited SmCo films. The preferred orientation of the SmCo 5 phase for the last three samples could be attributed to the high fluence of laser shots, well suited for the phase stabilization [7]. With increasing laser shots and hence the film thickness, (301) peak relating to SmCo 5 becomes visible and stronger. Film thickness of the samples evaluated by spectroscopic ellipsometry increased from 25 to 67 nm as the number of laser pulses was increased from 1000 to EDX spectra of all the samples deposited by varying the number of laser shots have been shown in Fig. 2. In the spectra, a sharp peak indicates the presence of silicon whereas small and wide peaks originate from the Sm and Co elements. Table 1 provides the variation in Sm and Co concentrations in the samples deposited with 1000, 2000, 3000, 4000 and 5000 laser shots. The data reveals that as the number of laser shots is increased, the at% and wt% of Sm is increased while that of Co is decreased. From this trend, it is also evident that the composition of the third sample which was deposited by using 3000 laser shots, keeping substrate temperature of 400 C bears the composition well-matched to that of 1:5 phase of SmCo. SEM images of SmCo thin films have been shown in the left side of Fig. 2. The micrographs mainly reveal a smooth, uniform and homogenous film surfaces. Grain boundaries were not detected on most of the film surfaces however, some large sized agglomerated grains were observed on the film surfaces. It has been understood that

5 5586 Mirza Khurram Baig et al. / Materials Today: Proceedings 2 ( 2015 ) these grains might have been ablated from the target surface as stray particles and ultimately deposited on the film surface during the post deposition environment [10]. Table 1. at% and wt% of Sm and Co in the pulsed laser deposited thin film samples Element Composition of SmCo film samples wt% at% wt% at% wt% at% wt% at% wt% at% Sm Co Conclusions SmCo thin films of varying thicknesses have been deposited by PLD on Si (100) substrate. The substrate temperature was kept constant at 400 C, while laser pulses were varied from 1000 to 5000 shots. The diffraction analysis reveals the amorphous nature of the films deposited at 1000 and 2000 laser shots. Whereas, the films deposited using increased number of laser pulses, showed a peak related to (301) plane of 1:5 phase of SmCo. The SEM micrographs reveal mainly a uniform surface with some large grains, attributed to molten droplets ejected due to hydrodynamic sputtering. The EDX analysis was performed to determine the Sm and Co contents in at% and wt%. References [1] T. Speliotis, D. Niarchos, J. Magn. Magn. Mater (2005) 290. [2] L. Allocca, U. Gambardella, A. Morone, M. Valentino, Proc. of SPIE 6985 (2008) 69850F-1 [3] L. Allocco, C. Bonavolonta, A. Giardini, T. Lopizzo, A. Morone, M. Valentino, M.F. Verrastro, V. Viggiano, Proc. of SPIE 6879 (2008) 68791I. [4] T. Speliotis, D. Niarchos, J. Phys.: Conf. Ser. 10 (2005) 175. [5] N. Powers, M.L. Yan, L. Gao, S.H. Liou, D.J. Sellmyer, J. Appl. Phys. 91 (2002) [6] L. Allocca, C. Bonavolota, A. Giardini, T. Lopizzo, A. Morone, M. Valentino, M.F.Verrastro, V. Viggiano, Phys. Scr. 78 (2008) [7] C.J. Yang, C.Y. You, Z.D. Zhang, J.S. Han, J. Kor. Phys. Soc. 42 (2003) 401. [8] E. Pina, F.J. Palomares, M.A. Garcia, F. Cebollada, A. de-hoyos, J.J. Romero, A. Hernando, J.M. Gonzalez, J. Magn. Magn. Mater (2005) 290. [9] C. You, Z. Zhang, X. Sun, C.J. Yang, W. Liu, X. Zhao, J. Mater. Sci. Technol. 23 (2007) 521. [10] B.D. Chirsey, G.K. Hubler, Pulsed laser deposition of thin films, John Wiley & Sons, New York, 1994

Formation of Droplets on Thin Film Surface in Pulsed Laser Deposition Using Metal Targets*

[Quarterly Journal of Japan Welding Society, Vol. 21, No. 3, pp. 338-343 (2003)] Formation of Droplets on Thin Film Surface in Pulsed Laser Deposition Using Metal Targets* by Salim MUSTOFA**, TSUYUGUCHI