Surface science and kinetic modelling studies of the surface chemical mechanisms active during low pressure chemical vapor deposition (CVD) and chemical beam epitaxy (CBE) growth of Si from mono- and disilane are summarized. Time-of-flight direct recoiling (DR) is discussed as an in situ method to analyze the composition of the growth interface. Steady state measurements of surface hydrogen coverage (θH) are made by DR in situ during CBE Si growth from Si2H6 and SiH4, and are illustrated here. Key results using other experimental methods are briefly discussed. © 1992.