The interface produced by vapor deposition of Mn on the MoS2 (0001) surface has been studied in situ by high-resolution photoelectron spectroscopy using synchrotron radiation. The evolution of the Mo 3d, Mn 3p, and S 2p core levels and of the valence-band spectra during growth of thin films (10–58 A) is consistent with partial conversion of the Mn overlayer to MnS via the overall reaction 2Mn + MoS2 →2MnS + Mo. The persistence of the substrate components of the Mo 3d and S 2p spectra for thicknesses = 35 A are consistent with the Volmer-Weber growth mode. Annealing a 58-A film to 770 K resulted in an overlayer film consisting mostly of MnS coexisting with some metallic Mn. Analysis of the Mo 3d core levels indicates the production of a MoS2(0001) surface with S vacancy defects. Annealing to temperatures between 850 and 1040 K drove the reaction to completion (as shown by the valence band and Mn 3p core level spectra). Annealing of the sample to 1130 K resulted in uncovering the MoS2 (0001) surface due to breakup of the reacted layer. In addition, low-energy electron diffraction indicated the formation of (0001)-2 X 2 regions on the surface. This surface structure is interpreted in terms of an ordered, MoS2_ xsulfur vacancy defect structure rather than a Mn-Mo-S compound. © 1989, American Vacuum Society. All rights reserved.