Journal of Crystal Growth 270 (2004) 107–112 Thermochemical analysis of MgB 2 synthesis by molecular-beam epitaxy Jihoon Kim a, *, R.K. Singh a , J.M. Rowell a , N. Newman a, *, Lin Gu b , David J. Smith b,c a Department of Chemical and Materials Engineering, Arizona State University, Engineering Center G-wing 209, Tempe, AZ 85287-6006, USA b Center for Solid State Science, Arizona State University, Tempe, AZ 85287-1704, USA c Department of Physics and Astronomy, Arizona State University, Tempe, AZ 85287-1504, USA Received 25 September 2003; accepted 30 May 2004 Available online 28 July 2004 Communicated by L.F. Schneemeyer Abstract In this paper we report a study that correlates the properties of superconducting MgB 2 thin films with molecular- beam-epitaxy deposition parameters. We show the utility of using a thermochemical analysis of MgB 2 synthesis to predict optimal growth conditions. The growth of stoichiometric films with improved crystalline quality can be achieved at enhanced temperatures using high reactant fluxes. High B flux enhances the sticking coefficient of Mg and facilitates higher growth temperatures and improved structural and electrical properties. With a Mg flux of B16 ( A/s and a substrate temperature of 300  C, a superconducting transition temperature (T c ) of 37.7 K with a narrow transition width (DT c o1 K) was observed. Our work shows that a growth model must include the strong dependence of the Mg sticking coefficient on B flux. r 2004 Published by Elsevier B.V. PACS: 74.62.Bf Keywords: A1. Molecular beam epitaxy; B2. Superconducting materials 1. Introduction Magnesium diboride (MgB 2 ) with 39 K phonon- mediated superconductivity [1] has the potential to be used in several superconducting electronic devices applications currently dominated by low- T c materials [2–4]. The first step in the develop- ment of a MgB 2 technology is the synthesis of ARTICLE IN PRESS *Corresponding author. Tel.: +1-480-965-2094; fax: +1- 480-965-0037. E-mail addresses: jihoon.kim@asu.edu (J. Kim), nathan.newman@asu.edu (N. Newman). 0022-0248/$-see front matter r 2004 Published by Elsevier B.V. doi:10.1016/j.jcrysgro.2004.05.116