When CaF2 molecules are deposited on Si(1 1 4)-2 x 1 held at 500 degrees C, two kinds of isolated and symmetric Casilicide units are initially formed. With increasing CaF2 deposition to 0.4 ML, instead of the terrace being filled with them, a trench composed of (1 1 3) and (1 1 7) facets appears on the surface as a result of substrate etching induced by dissociated F atoms. Selectively on this (1 1 3) facet, a 2 x 2 CaF overlayer is formed uniformly. In the present studies, using scanning tunneling microscopy and synchrotron photoemission spectroscopy, the origins of such isolation of Ca-silicide units on the (1 1 4) terrace as well as selective adsorption of CaF on the (1 1 3) facet have been disclosed. (C) 2015 Elsevier B.V. All rights reserved.