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Growth kinetics of MgB2 layer and interfacial MgO layer during ex situ annealing of amorphous boron film

Published online by Cambridge University Press:  01 October 2004

Hyun-Mi Kim
Affiliation:
School of Materials Science and Engineering and Nano Systems Institute-National Core Research Center, Seoul National University, Seoul 151-742, Korea
Sung-Soo Yim
Affiliation:
School of Materials Science and Engineering and Nano Systems Institute-National Core Research Center, Seoul National University, Seoul 151-742, Korea
Ki-Bum Kim*
Affiliation:
School of Materials Science and Engineering and Nano Systems Institute-National Core Research Center, Seoul National University, Seoul 151-742, Korea
Seung-Hyun Moon
Affiliation:
School of Materials Science and Engineering, Seoul National University, Seoul 151-742, Korea
Young-Woon Kim
Affiliation:
School of Materials Science and Engineering, Seoul National University, Seoul 151-742, Korea
Dae-Hwan Kang
Affiliation:
Korea Institute of Science and Technology, Thin Film Materials Research Center, Seoul 136-791, Korea
*
a) Address all correspondence to this author. e-mail: kibum@snu.ac.kr
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Abstract

This paper describes the growth kinetics of an interfacial MgO layer as well as those of an MgB2 layer during ex situ annealing of the evaporated amorphous boron (a-B) film under Mg vapor overpressure. A thin MgO layer is formed at the interface between a-B and Al2O3 substrate before the formation of crystalline MgB2 layer and the interfacial layer is epitaxially related with Al2O3 substrate (MgO (111)[110] // Al2O3 (0001)[1100]). The interfacial MgO layer continues to grow during the annealing, and its apparent growth rate is about 0.1 nm/min. The analysis of MgB2 layer growth kinetics using cross-sectional transmission electron microscopy reveals that there exist two distinct growth fronts at both sides of an MgB2 layer. The growth kinetics of the lower MgB2 layer obeys the parabolic rate law during the entire annealing time. The growth of the upper MgB2 layer is controlled by the surface reaction between out-diffused boron and Mg vapor up to 10 min, resulting in a rough surface morphology of MgB2 layer. By considering the mass balance of Mg and boron during ex situ annealing, we obtained the diffusivities of Mg and boron in MgB2 layer which were in the same order range of approximately 10−12 cm2/s.

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Articles
Copyright
Copyright © Materials Research Society 2004

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References

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Growth kinetics of MgB2 layer and interfacial MgO layer during ex situ annealing of amorphous boron film
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