We report a detailed study using reflection absorption infrared (RAIR), temperature-programmed reaction (TPR), Auger electron (AES) spectroscopies, and low-energy electron diffraction (LEED) of the interaction and thermolytic reactions of disilane on a Cu(111) surface. Disilane adsorbs dissociatively on Cu(111) at temperatures as low as 90 K. At low coverages Si-Si and Si-H bond scissions yield two adsorbed fragments which are identified as being the SiH fragment and adsorbed H atoms, respectively. Low fluxes of disilane (less than or equal to 5 x 10(12) molecules/s) favor the formation of these dissociative adsorption products. Using higher fluxes, the exposures lead to the concomittant formation of SiH2 and SiH3 moieties. The yields of these later species depend very sensitively on both the absolute and relative surface coverages of Si and H. The decomposition processes of adsorbed SiH3 and SiH2 are characterized strongly by coverage dependent kinetics. The SiH3 species is stable over a limited temperature range (T < 150 K); upon heating it undergoes sequential Si-H bond cleavages to form a surface bound monohydride. The dihydride is stable to similar to 180 K. The monohydride decomposes at higher temperatures (T > 250 K), leaving behind surface bound Si. The recombinative desorption of dihydrogen occurs at similar to 300 K. This bimolecular process competes with another associative reaction which leads to the formation and desorption of silane (T similar to 230 K) from the surface. The amount of Si deposited on the surface depends sensitively on the surface temperature and the magnitude of the disilane exposure. A high coverage silicide surface phase is readily formed above the dihydrogen desorption temperature. This thin film is characterized by an ordered (root 3 x root 3)R30 degrees overlayer structure which is thermally stable over a wide range of temperatures. At higher temperatures, where atomic mobilities are higher, the growth of multilayer intermetallic thin films can be effected.