The products of decomposition by the hot wire technique of disilane, germane and mixtures of these gases on a Si(001) surface held at 620 K are analysed using high-resolution electron energy loss spectroscopy. Silicon monohydride (Si–H) is detected for decomposed Si 2H 6 on Si(001), and both Si–H and Ge–H are present on Si 1− x Ge x /Si(001) ( x<0.5). In contrast, no hydride is detected on a pure Ge surface prepared in the same experimental conditions. From that, it is deduced that a Ge–H phase is stabilized at 620 K due to the presence of the neighboring silicon atoms in the alloys. Further room-temperature exposure to atomic hydrogen reveals additional hydrogen adsorption on Ge atoms. Short- versus long-range interaction mechanisms are discussed to explain the present observations.