Infrared study of SiH₄-adsorbed Si(100) surfaces: Observation and mode assignment of new peaks

SiH_n adspecies on Si(100)-2 × surfaces adsorbed with SiH₄ have been studied using multiple-internal-reflection infrared spectroscopy. In addition to the stretching modes of SiH, SiH₂, and SiH₃ known to be present on H-terminated Si surfaces, three new peaks were observed at 2036, 2060-2064, and 2077 cm^-1. By observing the change of the peak intensities before and after the 300°C annealing as well as the effects of polarized radiation, the stretching modes at 2060-2064 cm^-1 were concluded to be related to step-edge monohydrides, while the one at 2077 cm^-1 was considered to be related to the monohydride at a dimer whose counterpart is -SiH₃. Moreover, the SiH₂ vibration is assigned to the bridging dihydrides between dimers, which is different from the one on HF-treated Si(100) known to be formed by breakage of the dimer bonds. These stretching modes are closely related to the presence of Si adatoms on the surface, providing new convenient probes for studying surface chemistry during epitaxy using SiH₄ or Si₂H₆.