Detailed synchrotron radiation photoemission studies of Yb/Hg 1-xCdxTe junctions as a function of Yb coverage were performed at room temperature. Photoemission from physisorbed xenon after cooling the sample to 35 K was also used to examine the local overlayer work function and the development of interface morphology. For Yb coverages less than 6 Å, the data provide evidence for the lateral growth of islands consisting of Yb-Te reaction products involving divalent Yb, and an associated Hg depletion within an 18-Å-thick near-surface layer. Upon island coalescence at an Yb coverage of 6 Å, the formation of a metallic Yb-rich layer at the surface is observed. This layer traps Hg atoms diffusing across the interface through the formation of an Yb-Hg alloy, and is responsible for the nonmonotonic behavior of the Hg interface concentration as a function of Yb coverage.