Three-dimensional atom-probe tomography was utilized to study the distribution of M (M = Pt or Pd) after silicidation of a solid-solution Ni 0.95M0.05 thin-film on Si(100). Both Pt and Pd segregate at the (Ni1.xMx)Si/Si(100) heterophase interface and may be responsible for the increased resistance of (Ni1.xMx)Si to agglomeration at elevated temperatures. Direct evidence of Pt short-circuit diffusion via grain boundaries, Harrison regime-B, is found after silicidation to form (Ni0.99Pt0.01)Si. This underscores the importance of interfacial phenomena in stabilizing this low-resistivity phase, providing insights into the modification of NiSi texture, grain size, and morphology caused by Pt. The relative shift in work function between as-deposited and annealed states is greater for Ni(Pt)Si than for NiSi as determined by Kelvin probe force-microscopy. The nickel monosilicide/Si heterophase interface is reconstructed in three-dimensions and its chemical roughness is evaluated.