Analysis of the NdBa 2 Cu 3 O x thin film growth mechanism by time of flight mass spectrometry of the laser plume
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Analysis of the NdBa2 Cu3 Ox thin film growth mechanism by time of flight mass spectrometry of the laser plume M. Badaye, K. Fukushima, and T. Morishita Superconductivity Research Laboratory, International Superconductivity Technology Center, 10-13 Shinonome, 1-chome, Koto-ku, Tokyo 135, Japan (Received 19 April 1995; accepted 16 January 1996)
Time of flight (TOF) spectroscopic measurements are used to diagnose the laser-generated plume of ceramic NdBa2 Cu3 Ox targets. We have been able to directly correlate the laser-deposited films’ properties such as superconductivity, crystallinity, and orientation with plasma properties. Study of the TOF spectra shows that at laser fluences greater than 3 Jycm2 the plume become Nd-rich, and this leads to a low Tc in the deposited film. We have also shown the effect of target density on the energy of the plume species, and through energy considerations we have explained the observed change in the crystalline orientation of films from c- to a-orientation with increasing the target density. Finally, we have examined the oxidation mechanism of NdBa2 Cu3 Ox thin films, and have shown that highly energetic atomic oxygens have a prevailing role in oxidizing our laser-deposited thin films.
I. INTRODUCTION
Pulsed laser deposition (PLD) of high quality NdBa2 Cu3 Ox (NBCO) thin films was previously reported by our group.1,2 In the course of the film optimization process, we observed various trends in variations of our films’ properties, some of which could not be fully explained. The time of flight mass spectroscopy (TOF-MS) is a powerful technique frequently used to analyze the laser-generated plasmas from high temperature superconducting (HTS) ceramic targets. Because of the complexity of multicomponent plasmas involved in the laser ablation of HTS materials, a direct correlation between the TOF-MS results and the film’s properties has rarely been made.3 In this paper we have used TOF-MS to analyze the growth trends observed in Refs. 1 and 2. Specifically, we have investigated the effect of laser fluence, target density, and the ambient oxygen pressure on the laser plume properties. These plasma properties are then related to the film’s composition, orientation, and superconducting properties. II. EXPERIMENTAL
The experimental procedures for depositing NBCO thin films were reported previously.1,2 We used an ArF excimer laser having a wavelength of 193 nm, and a pulse duration of 16 ns. The TOF experiments were carried out using a reflectron type spectrometer.4 This apparatus is made of a sample chamber and a drift chamber, separated by a small orifice. The sample chamber, containing the ablation target, closely emulates the actual thin film deposition chamber. The orifice between the two chambers is located where the substrate would 1072
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J. Mater. Res., Vol. 11, No. 5, May 1996
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be in the deposition chamber. Being used as extraction aperture, this orifice experiences exactly the sa
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