Effect of temperature on NH3 reactivity with Si(100) 2 x 1

Initially clean, (2 x 1)-reconstructed Si(100) surfaces were exposed to NH3, until saturation, at sequentially increased temperatures of up to 600degreesC. The resulting surfaces have been studied by low energy electron diffraction (LEED) and by photoemission yield and Auger electron spectrometries (PYS and AES). The room temperature saturation - for which NH3 is adsorbed in a dissociated form as NH2 and H, either of them bonded to a single Si dimer - remains essentially unchanged up to 250degreesC. Beyond 250degreesC, NH radicals form and replace the Si dimers by flat Si-NH-Si bridges along the surface, which ends up being stabilized by a full monolayer of such bridges at 400-450degreesC. Beyond that starts the actual nitridation process which concerns deeper Si layers.