Atomic structure and crystallography of Mn silicide islands formed on an Si(1 1 1) surface was investigated. Mn with 8-10 MLs was deposited on an Si(1 1 1) 7 x 7 surface at room temperature by means of an ultrahigh vacuum molecular beam epitaxy, and then transferred to an ultrahigh vacuum transmission electron microscope (UHV-TEM) without exposure to air. Annealing at 400degreesC caused the round shaped silicide islands composed of MnSi with a size of several tens of nanometers to grow epitaxially. From transmission electron microscopy analysis, it was found that the crystallography of the islands matches with that of the Si(1 1 1) substrate with the relation (1 1 1)(Si)parallel to(1 1 1)(MnSi) and [(1) over bar 0 1](Si)parallel to[(1) over bar 2 (1) over bar](MnSi), but their interface was incommensurate. (C) 2002 Elsevier Science B.V. All rights reserved.