Pramfin.a - J. Phys., Vol. 30, No. 5, May 1988, pp. L463-L467. © Printed in India.

Monitoring of thin layer deposits of high temperature superconducting materials by energy-dispersive X-ray fluorescence technique (EDXRF)

MADAN LAL and R K C H O U D H U R Y Nuclear Physics Division, Bhabha Atomic Research Centre, Bombay 400085, India

MS received 16 February 1988; revised 21 March 1988

Abstract. We present here a method for rapidly monitoring the composition of samples deposited on a substrate. This was applied to the case of superconducting material YBa2Cu307 deposited by laser evaporation on quartz plates. The aim of this study was to achieve the right composition of the deposited material so as to have it superconducting at high temperatures. The monitoring was done by comparing the X-ray spectrum obtained by EDXRF technique of the deposited film with the spectrum of the original superconducting material. By this method of signature analysis it was possible to arrive at the laser beam parameters which give the elemental composition of the deposited material almost as same as that of the original material. The optimization was done by changing the laser power and pulse width and monitoring the X-ray fluorescence spectra as a function of the beam parameters.

Keywords. High temperature superconductivity; YBa2Cu3OT; thin film laser deposition; energy-dispersive X-ray fluorescence analysis.

PACS No. 73"60

A number of techniques such as X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS) etc have been employed to characterize the surface properties of deposited materials. Recently to determine the composition of deposited film obtained from high Tc superconducting material, the Rutherford backscattering (Dijkkamp et a11987) and XPS (Jin et al 1987) have been employed. In order to determine rapidly the elemental composition or thickness of one or more elements deposited on any substrate, EDXRF has been widely applied (Huang and Parrish 1979; Laguitton 1977; Stine and Leidl 1974; Gianelos 1974; Lal and Choudhury 1987) due to the advantage of its high sensitivity and ease of analysis. This method has an added advantage of being non-destructive which is an essential requirement for many applications.

Recently there have been significant developments in the area of high temperature superconducting materials and one of the compounds showing superconducting behaviour at high temperatures is YBa2Cu3OT. For many applications such as junction devices, accelerator cavities, etc., the material used is required to be in the form of a thin film, with superconducting properties. Various methods such as multi-target evaporation (Laibowitz et al 1987), sputtering (Kawasaki et al 1987), plasma spraying (Elam et al 1987) and laser beam (Dijkkamp et al 1987) are being tried for obtaining thin film deposits of required composition.

We report here the results of thin films prepared by laser evaporation. The film was prepared on quartz plates placed in ~ 10-4 torr oxygen using a Nd-Yag laser beam (Chaddah et al 1987). The film thickness obtained was in the range of 1.0 micron.

L463

L464 Madan Lal and R K Choudhury

The EDXRF set-up (Lal et al 1979) employed for monitoring these films comprises of a high resolution lithium drifted silicon Si(Li) detector along with the radioisotope sources of l ° 9 C d (20mc) and 241Am (100mc) for excitation of characteristic X-rays. The sources are mounted in an annular geometry as shown in figure 1. The signals of the X-rays detected by the Si(Li) detector are amplified by high resolution electronics and the spectrum is stored in the multichannel analyser. The original superconducting material was ground into a fine powder and mixed with a binder material for preparing a thin sample on a filter paper backing. The X-ray spectra of a few such samples were taken to act as reference. The spectra obtained from the deposited film of the superconducting material were compared with the reference spectra by taking the ratios of the intensities of k~ lines of Y, Ba and Cu elements. A number of samples prepared by laser evaporation were analysed by changing the laser beam parameters. The laser beam power was varied (Chaddah et al 1987) from 1-10joules per pulse and pulse width from 1-10 msec. Ba and Y concentrations were monitored with the 241Am source and Y and Cu concentrations with the l°9Cd source. The results of the series of runs are summarized in table 1. Figures 2 and 3 show the spectra obtained after the optimum laser parameters were achieved to give almost the same composition as that of the original material of YBazCu30 7. It is seen that the elemental composition of the deposited thin film is almost similar to that of the original superconducting material. Whether or not the deposited film is in superconducting phase can be ascertained by carrying out further work regarding the lattice structure and taking p-T measurements of these films.

Sornple

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Table i. Intensity ratios of X-ray Dines of Cu, Y and Ba of thin film sample of YBa2Cu30 ~.

Sample no. CuK,/YK, BaKJYK,

1 2"02 4-0"24 16"52 + 3.5 2 1"08 ± 0'07 8"95 4- 1" 1 3 1"01 +0-06 9"98_+ 1'0 4 0'75 _+ 0"02 7"50 __+ 0'35 5 0-51 ± 0,02 7.09 + 0.5{) 6 0"57 ± 0.{)2 6-83 _+ 0-33

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L466 Madan Lal and R K Choudhury

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ChQnnel No. • Figure 3. X-ray spectra of thin samples of superconducting material and its deposited thin film excited by l°9Cd.

Monitoring of thin layer deposits by EDXRF L467

References

Chaddah P, Nathan T P S, Goswami G L, Kumar D and Malik M K 1987 Proc. Solid State Physics Symposium C30 248

Dijkkamp D, Wu X D, Ogale S B, Inam A, Chase E W, Miceli P, Tarascon J M and Venkatesan T June 1987 Proc. Int. Conf. on Novel mechanisms of superconductivity (ed.) V Z Kresin (Berkeley, Ca: LBL, University of California)

Dijkkamp D, Venkatesan T, Wu X D, Shaheen S A, Jisrawi N, Min-Lee Y H, McLean W L and Croft M 1987 Appl. Phys. Lett. 51 819

Elam W T, Kirkaland J P, Neiser R A, Skelton E F, Sampath S and Herman H 1987 Advanced ceramic materials (special issue) Vol. 2, No. 3B, 41 l

Gianelos J 1974 Adv. X-ray Anal. 17 325 Huang T C and Parrish W 1979 Adv. X-ray Anal. 22 43 Jin B Y, Lee S J, Song S N, Hwu S J, Thul J, Poeppelmeier K R and Ketterson J B 1987 Advanced ceramic

materials (special issue) Vol. 2, No. 3B, 436 Kawasaki M, Funakashi M, Nagata S, Fueki K and Koinuma H 1987 Jpn. J. Appl. Phys. 26 L388 Laguitton D 1977 X-ray Spectrometry Vol. 6, No. 4 p. 187 Laibowitz R B, Koeh R H, Chaudhari P and Gambino R J 1987 Phys. Rev. B35 8821 Lal M, Bhatia P L, Kataria S K 1979 Proc. Nuclear Phys. and Solid State Phys. (India) B22 327 Lal M, and Choudhury R K 1987 National symposium on advances in surface treatment of metals,

ASTOM-87, BARC, Bombay, p. 472 Stine P A and Leidl S J 1974 Adv. X-ray Anal. 17 48 Turner N H and Colton R J 1982 Anal. Chem. Rev. 54 2983