Amorphous LaAlO3 thin films have been deposited by laser molecular beam epitaxy system on Si substrate with an abrupt interface. The formation of the interface between LaAlO3 and silicon was investigated in detail using high-resolution transmission electron microscopy and Xray photoelectron spectroscopy. When several atomic-thick LaAlO3 film was deposited at low temperature and subsequently annealed at high vacuum, a stable Si-La-Al-O silicate thin layer was formed. Using this very thin film as a buffer layer, LaAlO3 films can be deposited with an atomically defined interface at the high temperature and oxygen pressure conditions. With good understanding of the formation mechanism for the interfacial structure, we can control the interface between high-k oxide and Si substrate via optimized deposition parameters and specific growth sequences. (c) 2006 Elsevier B.V. All rights reserved.