In this paper, we make use of the hydrogen passivation concept to demonstrate that the pyrolysis of disilane (Si2H6) results in two silicon atoms and all six hydrogen atoms remaining on the surface and silane (SiH4) produces one silicon atom and four hydrogen atoms on the surface, The dominant reaction pathways an identified and implications for Si film growth are discussed. The adsorption kinetics and subsequent dissociation of silane, disilane and germane during gas source molecular beam epitaxy on the Si(0 0 1) surface are studied in situ using modulated beam mass spectrometry (MBMS), temperature programmed desorption (TPD) and reflection high-energy electron diffraction (RHEED). These were also combined with the growth of various epitaxial layers involving repeated cycles of silane or disilane adsorption and hydrogen desorption with the Layer thicknesses determined ex situ using X-ray diffraction (XRD) rocking curve measurements and computer simulations.