The novel method of modifying Si surfaces by using a CdF2 molecular beam was proposed. Si(I 1 1) surfaces exposed to a CdF2 molecular beam at 400 ° C exhibited very smooth surfaces, and the surfaces were found to have different properties from those obtained by the conventional thermal flush method through reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM) observation. CaF2 layers grown on the substrates modified by the treatment using a CdF2 molecular beam exhibited very smooth surfaces and good crystallinity. © 2005 Elsevier B.V. All rights reserved.