We realized the epitaxial growth of a Sr layer on Si(111) with an atomically abrupt heterointerface - in spite of its large lattice mismatch (12%) with Si - by introducing a monoatomic layer of H on Si. In order to identify the buried H, we carried out a combination analysis involving neutron reflectometry and resonant nuclear reaction of H-1(N-15,alpha gamma)C-12 analysis. We found different neutron reflectivity profiles resulting from a contrast variation between the H and D atoms at the buried heterointerface. Furthermore, the depth gamma-ray intensity profiles revealed that the H at the heterointerface acts as an effective buffer layer that enables it to manage the highly mismatched epitaxy on Si. (C) 2011 Elsevier B. V. All rights reserved.