The reaction of ultrathin layers of Mo and Ti with Se as investigated, and significantly different reaction pathways were found.However, in both systems postdeposttion annealing results in smooth dichalcogenide films with specific thicknesses determined by e precursor. X-ray diffraction (XRD) patterns of as -deposited Mol Se films around a 1:2 ratio of Mo to Se contain weak, broad reflections from small and isolated MoSe2 crystallites that nucleated during deposition and a sharper intensity maximum resulting from the composition modulation created from the alternating deposition of Mo and Se layers. In contrast, as -deposited TilSe films around a 1:2 ratio of Ti to Se contain narrow and intense 001 reflections from TiSe2 crystallites and do not contain a Bragg reflection from the sequence of deposited TilSe layers. The as -deposited TiSe2 crystallites' have a larger c-axis lattice parameter than was previously reported for TiSe2, however, which suggests a poor vertical interlayer registry and/or, high defect densities including interstitial atoms. In-plane XRD patterns show the nucleation of both TiSe2 and Ti2Se during deposition, with the Ti2Se at the substrate. For both systems, annealing the precursors decreases the peak width and increases the intensity of reflections from crystalline TiSe2 and MoSe2. Optimized films consist of a single phase after the annealing and show clear Laue oscillations in the specular XRD patterns, which can only occur if a majority of the diffracting crystallites in the film consist of the same number of unit cells. The highest quality films was obtained when an excess of similar to 10% was dePosited in the Precursor, which presumably acts asa fluxsto facilitate diffusion of metal atoms to crystallite grovythfronts and compensates for Se loss to the open system during annealing.