The growth behavior of epitaxial ZrB2(0 0 0 1) films on Si(I 1 1) via the thermal decomposition of the unimolecular precursor Zr(BH4)(4) was studied in situ using low-energy electron diffraction and low-energy electron microscopy, and ex situ using cross-sectional transmission electron microscopy and atomic force microscopy. Under appropriate kinetic conditions, epitaxy was achieved in spite of the very large lattice mismatch between ZrB2(0 0 0 1) and Si(I 1 1). Our study followed the growth from the initial nucleation stage to the final epitaxial film at various growth temperatures. At 900degreesC, the growth of ZrB2(0 0 0 1) proceeded by the nucleation of two-dimensional islands. These islands eventually coalesced to form a smooth film with an RMS roughness of 0.9 nm. The interface between ZrB2(0 0 0 1) and Si(I 1 1) was modeled theoretically and the most favorable interface consisted of the ZrB2(0 0 0 1) growing on a Si(I 1 1)-(root3 x root3)B surface with the Zr-layer nearest to the interface and the B-layer on the top surface. (C) 2004 Elsevier B.V. All rights reserved.