Effect of Substrate Temperature on Growth Bi1.6Pb0

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ScienceDirect Energy Procedia 36 (2013) 881 – 887

TERRAGREEN13 INTERNATIONAL CONFERENCE

Effect of Substrate Temperature on Growth Bi1.6Pb0.4Sr2Ca2Cu2.4 Zn0.6O10 Thin Films Prepared by Pulsed Laser Deposition. Ghazala Y.Hermiza,* , Mahdi H. Suhaila and Suzan M.Shakoulib a

b

Department of Physics, College of Science University of Baghdad, Baghdad ,Iraq Department of Physics, College of education University of Mustansiriyah , Baghdad ,Iraq

____________________________________________________________________ Abstract Bi1.6Pb0.4Sr2Ca2Cu2.4Zn0.6O10 superconducting pellet was prepared by solid state reaction. The epitaxial growth of Bi1.6Pb0.4Sr2Ca2Cu2.4Zn0.6O10 films has been realized on Si (111) by pulse laser deposition (PLD) using Nd: YAG laser with 532 nm, pulse duration of about 7 nsec and a current density (0.4 – 8) J/cm2, at different substrate temperature 300, 320, 350 and 400 oC. All samples annealed at 820oC in vacuum furnace employing oxygen atmosphere with flow rate 2 lit/min and heating rate 15oC/min. The structure and morphology of the prepared samples was obtained by using x-ray diffractometer (XRD) and atomic force microscopy (AFM). The lattice constants of thin films samples were calculated using inter planer distance and Miller indices of the strong peaks in the XRD patterns. It has been observed that the enhancement of the transition temperature (Tc) for obtained films increase in Tc with the enhancement of substrate increase with increase of substrate temperature (Ts). The temperature could be explained to increasing the mobility of clusters and subsequently enhance the critical temperature. Open access © The Authors. Published by Elsevier © 2013 2013 The Authors. Published byLtd. Elsevier Ltd.under CC BY-NC-ND license. Selection and/or peer-review under responsibility of the TerraGreen Academy Selection and/or peer-review under responsibility of the TerraGreen Academy. Keywords: Substrate temperature; PLD;, Thin film superconductors

______________________________________________________________________ 1.

Introduction

Bi-based superconductor compounds of the form Bi2Sr2Can-1CunO10, where n=1, 2, 3 gives the number of CuO2 layers, have been studied extensively by many groups. The superconducting phases in this material, known as (2201),(2212) and (2223) ,for n=1,2,3 with the critical temperature of 10-20K,6085K and 110K ,respectively [1] .According to previous studies, the n =2 phase was found more stable and more easily obtained than the 2223 phase. The later phase can be obtained in stable form by doping the structure with a small amount of Pb. The Pb atoms are thought to reside at the Bi sites in the structure [2] _________________________________ *Corresponding author. .:E-mail address [email protected]:

1876-6102 © 2013 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license.

Selection and/or peer-review under responsibility of the TerraGreen Academy doi:10.1016/j.egypro.2013.07.101

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Ghazala Y. Hermiz et al. / Energy Procedia 36 (2013) 881 – 887

Pulsed Laser Deposition (PLD) is a physical vapor deposition (PVD) technique based on the evaporation of material by using a pulsed, highly energetic laser beam focused inside a vacuum chamber to strike a target of the desired composition. This versatile technique may be applied to profoundly different materials such as, metals, insulators, semiconductors and high-Tc superconductors. With the use of PLD, the stoichiometric transfer of these materials from a multicomponent target to a film on a substrate can be obtained entirely. Under the right experimental conditions, PLD also offers the potential for epitaxial thin film growth. In the previous decades, various fabrication techniques of the BSCCO 2212 and 2223 superconductor thin film developed [3]. Among them, the pulse laser deposition (PLD) technique was found to be most favorable, and has been regarded as a versatile method to grow ceramic thin films. Laser evaporation offers the particular advantages that one may deposited films rapidly and without the need for sophisticated rate control and high vacuum equipment. Many researchers [3-5] have been working on this technique because the application of high Tc superconductors in microelectronics depends on the availability of high quality superconducting thin films. It has been found that the nominal composition and thermal treatment parameters such as annealing time, heat rate and substrate temperature play an important role in the formation of high Tc phases. Kim et al. [3] deposited thin films of Bi-Sr-CaCu-O on (100) cubic zirconia by laser ablation from a bulk superconducting target of nominal composition BiSrCaCu2Ox. They indicated that the film quality is affected by the substrate temperature and the annealing processes. The influence of the composition on the crystallographic properties of deposited Mg (M) O with (M=Al, Cr, Ti, Y, and Zr) films was studied by Saraiva et al [6]. using dual reactive magnetron sputtering to predict the stoichiometry of the deposited coatings, an analytical relation that states the deposition rate varies inversely as the square of the target-substrate distance was used [6]. Effect of annealing on superconducting properties of Bi1.6Pb0.4Sr2Ca2Cu2.2Zn0.8O10 thin films by pulsed laser deposition was investigated by Malike et al.[7]. Their results demonstrate that the transition temperature are related to the phase's evolution and formation of intergrowth, however nearly pure 2223 phases were grown when the annealing temperature is equal to 820 °C and 860 °C. On the other side enhancement of the annealing temperature above 860 °C leads to the increases of low phase and disappear of high phase. In this paper, studies were carried out to reveal the role of substrate temperature on the surface morphology, structure and electrical properties of the Bi1.6Pb0.4Sr2Ca2Cu2.4Zn0.6O10 superconducting thin films. The substrate temperature plays a great role of linking the crystalline orientations of both the substrate crystal and the film. 2.

Experimental work

Bi1.6Pb0.4Sr2Ca2Cu2.4Zn0.6O10 pellet was prepared by solid state reaction. The conventional preparation of the bulk involves mixing together the oxides, carbonates or nitrates of the constituent elements, the mixture was milled in agate mortar for 1h to obtain a fine particle size and heating them to 810oC (calcinations) to initiate the reaction for 24 h in order to get oxides from fly to off carbonates, nitrate, alkaline oxides through calcinations reaction, the production power mill for 30 minute, pressing the mixture at 0.5 GPa as a pellet shape with thickness for 3mm, 14mm diameter. A pellet enters to furnace for sintering about 140 h at 860oC. A pellet was use as a target to grow a thin film at an optimal Si (111) with different substrate temperature (300, 320, 350 and 400oC) by PLD technique. PLD using Nd: YAG laser with 532 nm, pulse duration of about 7 nsec and a current density (0.4 – 8) J/cm2 was use with an oxygen back ground pressure of 2×10-3 mbar, number of pulses is 150 pulses. Energy density was focused on the target to generate plasma plume. Distance between target and substrate was 5cm. system was mounted in vacuum chamber 10-5 mbar. All samples annealed at 820oC in vacuum furnace employing oxygen atmosphere with flow rate 2 lit/min with heating rate 15oC/min .The BiPbSrCaCuZnO nanostructure film has been measured by an optical interferometric method [8]. Then realized the

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electrical resistivity measurement (using four – probe) which is important study in superconductivity in order to evaluate the critical temperature Tc through measure the resistivity ρ as a function of temperature using this equation

U

bt V d I

(1)

Where b is width of sample (1cm), thickness (184.2±10 nm) depend on the number of pulses, d is distance between two point measure voltages (29.27x10-6 m), I is current flow through film surface (0.05 mA). The structure of the prepared samples was obtained by using x-ray diffractometer (XRD) type (Philips) with the CuKα source. The lattice constants of thin films samples were calculated using inter planer distance d, and Miller indices h,k and l values of strong peaks in the XRD patterns according to:

1 d2

h2 k 2 l2 ( ) 2 a2 c

(2)

Bragg law was used to find the lattice parameter c by taking the Miller indices of adjacent peak. The morphologies of the film were measured by atomic force microscopy (AFM) type origin USA Model AA300-CSPM. 3.

Results and discussion

Fig (1) shows the resistivity as a function of temperature for films of Bi1.6 Pb0.4Sr2Ca2Cu2.4Zn0.6O10 deposited at variable substrate temperature. It is found from this figure that the transition from normal state resistance to superconducting is not sharp and has tails, this may be attributed to the fluctuation of the oxygen content in grains and existence of multi phases 2223, 2212 and impurity phases as it is observed in the results of the x-ray diffraction.

Fig 1: ρ-T curves of Bi1.6Pb0.4Sr2Ca2Cu2.4Zn0.6O10 thin films deposited at Ts: (a) 300°C, (b)320°C, (c)350°C and, (d)400°C

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Fig.(2) shows the Tc obtained under different substrate temperature 300, 320, 350 and 400 oC . The transition temperature as a function of substrate temperature was 95, 97, 110 and 112 K respectively. The reason of increase Tc with the enhancement of substrate temperature could be explained as follows: the heat increase the energy of adsorbed species over surface, and interact among themselves which lead to form clusters, these clusters collide with other to form bigger and becomes thermodynamically stable and grown in number as well as in size, this lead to increasing the mobility of clusters and subsequently enhance the critical temperature. Indeed heat treatment under high pressure of O2 enhances Tc and improve the homogeneity of the crystals as indicated by [9]

116

Tc(K)

112 108 104 100 96 92 300

320

340 360 TS (oC)

380

400

420

Fig.2: Transition temperature as a function of substrate temperature

Fig.(3) Shows XRD patterns for films of Bi1.6Pb0.4Sr2 Ca2 Cu2.4 Zn0.6 O10 deposited at different substrate temperature. It has been observed that the intergrowth phase of 2212 and 2223 are obtained with the variation of the substrate temperature as pointed out by Ranno et al. [10]. Indeed increase Ts does not causes re-evaporation of Bi in the films and thus leads to grow phase is between 2212 and 2223 , also film begin to melt away and drives the calcium atoms to the 2212 phase , where, there exists a deficiency of calcium, there by forming the 2223 phase. X-ray diffraction patterns and Miller indices for specimens under study exhibit tetragonal structure, the indices in the patterns are taking and compared with, Primo et al. [11] and Koyama et al. [12]. The lattice constants at different substrate temperature are listed in Table 1. It is interesting to note from this table, there is an increase in lattice parameter (a) with the increases of substrate temperature up to 350oC, while lattice constant (c) is nearly constant (from 320 oC to 400 oC). This behavior could be explained as follows: increases of the substrate temperature will increase the velocity of the particles traveling to the surface, this allowed enough time for cluster to form .These nanoclusters, once attached to the film surface, would serve two possible purpose :( 1) they act themselves as seeding sites for island growth. (2) These larger species would certainly cause more strain on the film surface which lead to increase the growth in (a) parameter.


Fig.3: The XRD pattern of Bi1.6 pb0.4Sr2 Ca2 Cu2.4 Zn0.6 O10 thin films deposited at Ts300, 320, 350 and, 400°C

Table 1: a and c lattice constants for Bi1.6Pb0.4Sr2Ca2Cu2.4Zn0.6 O10 thin films deposited under different substrate temperature

Ts(oC)

a (nm)

c (nm)

300 320

3.99 4.49

37.33 36.96

350

4.62

36.96

400

4.62

36.96

885

886


Fig (4) shows the three dimensional views AFM of Bi1.6 Pb0.4Sr2 Ca2 Cu2.4 Zn0.6 O10 thin films deposited at Ts equal to 300, 320, 350 and, 400°C. From the AFM image, some out-growths exist on the surface of film. The width of the surface pits (average diameter), mean surface roughness (Ra) and the root mean square deviation value (RMS) of the samples carried out from AFM images are shown in Table (2). The film showed a rough surface. This mode may be correlated to the existence of clusters in the plasma. This can be explained by the different epitaxial growth modes with strong chemical bonds or weak physical interactions with Si (111). It has been observed that the interaction of film with substrate or the starting atomic layer of BiPbSrCaCuZnO may change with substrate temperature [14].

Ts=300oC

Ts=320oC

Ts=350oC

Ts=400oC

Fig. 4: AFM of Bi1.6Pb0.4Sr2Ca2Cu2.4Zn0.6O10 thin films deposited at Ts 300, 320, 350 and, 400°C

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Table 2 :width of the surface pits (average diameter), average surface roughness and root mean square deviation of Bi1.6Pb0.4Sr2Ca2Cu2.4 Zn0.6 O10 thin films deposited at different substrate temperature.

300

Width of surface pits (nm) 107.49

Average surface roughness(Ra) (nm) 8.9

root mean square deviation (RMS)(nm) 12.9

320

164.23

12.6

16.2

350

105.30

2.72

3.57

400

69.19

1.8

2.32

Ts(oC)

4.

Conclusion

Bi1.6Pb0.4Sr2Ca2Cu2.4Zn0.6O10 pellet was prepared by solid state reaction. A pellet with thickness for 3mm and 14mm diameter was use as a target to grow a thin film at an optimal Si (111) at different substrate temperature (300, 320, 350 and 400oC) by PLD technique. It has been observed that the intergrowth phase of 2212 and 2223 are obtained with the variation of the substrate temperature. AFM results reveal individual epitaxial domains posses. This was explaining by the different epitaxial growth modes with strong chemical bonds or weak physical interactions with Si (111). We can also be conclude that the increase of the substrate temperature lead to increases the growth in (a) parameter and enhance the activation energy of substrate atoms, which assist to attach the ablated atoms and subsequently increase the transition temperature. References [1] Tarascon JM and Page YLe. Crystal substructure and physical properties of the superconducting phase Bi 4(Sr,Ca)6Cu4O16+x Phys Rev B,1988,37;9382-9389 [2] Maeda A, Hase M, Tsukada I, Noda K, Takebayashi S and Vchinokura K. Physical properties of Bi2Sr2Can-1CunOy (n=1,2,3).Phys Rev B 1990; 41: 6418–6434 . [3] Kim BF, Bohandy J, Phillips TE, Green WJ, Agostinelli E, Adrian FJ and Moorjani K. Superconducting thin films of Bi-SrCa-Cu-O obtained by laser ablation processing. Appl Phys Lett 1988; 53: 321-323. [4]Katase T, Hiramatsu H, Kamiya T and Hosono H. Thin film growth by pulsed laser deposition and properties of 122-type ironbased superconductor Ae (Fe1−xCox)2As2 (AE=alkaline earth) Supercond Sci Technol 2012; 25:084015 . [5]Jannah AN, Halim SA , Abdullah H . Superconducting properties of BSCCO thin films by pulsed laser deposition. European Journal of Scientific Research 2009;29:438-446. [6]Saraiva M, Georgieva V, Mahieu S, Van Aeken K, Bogaerts A, and Depla D. Compositional effects on the growth of Mg„M…O films.J Appl Phys 2010;107:034902. [7] Malike S, Suhail MH, Hermiz GY, Haider AJ. Effect of annealing on superconducting properties of Bi1.6Pb0.4Sr2Ca2Cu2.2Zn0.8O10 thin films by pulsed laser deposition. Iraqi Journal of Phys 2011;9:8-13. [8] Hecht E.Optical interferometery , New York: Wiely; 1998. [9] Giannini E, Gladyshevskii R, Clayton N, Musolino N, Garnier V, Piriou A and Flükiger R. Growth, structure and physical properties of single crystals of pure and Pb-doped Bi-based high Tc superconductors Current Appl Phys 2008; 8:115-119. [10] Ranno L, Martinez G D, Perriere J, and Barboux P. Phase intergrowth in Bi2Sr2Can-1CunOy thin films. Phys Rev B 1993; 48:13945-13948 13945(1993). [11] Primo V, Sapina F, Sanchis MJ, Ibanez R, Beltran A and Beltran D, A new improved synthesis of the 110 K bismuth superconducting phase: freeze-drying of acetic solutions. Mater Lett 1992 ; 15:149-155. [12] Koyama S, Endo U and Kawai T. Preparation of Single 110 K Phase of the Bi-Pb-Sr-Ca-Cu-O Superconductor. Jap J Appl Phys 1988;27: L1861-L1863. [13]Gao J, Tang WH and Chi TC. Enhanced initial epitaxy of YBa2Cu3Oy ultrthin films grown on YSZ substrates by using a new buffer layer of Nd2CuO4 .Physica C 2000;330:33-38. [14]OhkuboM, Brecht E, Linker G, Geerk J and Meyer O. Different epitaxial growth modes of Bi2Sr2Ca2Cu3Oxon MgO. Appl Phys let 1996;69: 574-576.