Step-flow growth mode is observed for 100 fs pulsed laser deposition (fsPLD) of Si on vicinal Si(100)-2X1, while the Volmer-Weber mode is observed for fsPLD of Si on Si(100)-1 X 1. Reflection high-energy electron diffraction (RHEED) is used to in situ monitor the dynamics of the film growth while ex situ atomic force microscopy (AFM) is used to observe the morphology of the grown film. For Si on Si(100)-2 X 1, the diffraction pattern's basic features remain unchanged during deposition, indicating step-flow growth. AFM shows smooth growth on flat terraces. However, for Si on Si(100)-1 X 1 two growth behaviors are observed. For a laser fluence of 1.9 J/cm(2) and a substrate temperature below similar to400degreesC, we observe a decay of the RHEED peaks until they completely disappear, indicating the loss of the long-range order in the grown film. Postdeposition analysis shows three-dimensional (3D) clusters associated with the Volmer-Weber growth mode. On the other hand, deposition above similar to400degreesC at the same laser fluence results in the decay and eventual disappearance of the reflection diffraction peaks accompanied by the evolution of a transmission pattern instead. Transmission patterns appear when the electrons are diffracted in a transmission mode through 3D crystallites. These crystallites are observed in the AFM images.