The mechanism of amine formation on Si(1 0 0) activated with chlorine atoms

The dissociation of NH3 on a Si(1 0 0) surface activated with Cl atoms was investigated using X-ray photoelectron spectroscopy. Gas phase UV-Cl2 (0.1-10 Torr Cl2 for 10-600 s under 1000 W Xe lamp illumination) completely replaced the H-termination on aqueous-cleaned Si(1 0 0) with 0.82 ± 0.06 ML of Cl at 298 K. A single spin-orbit split Cl 2p doublet indicated that the Cl atoms were bound to Si dimer atoms, forming silicon monochloride (Cl-Si-Si-Cl). Exposing the Cl-terminated surface at 348 K to NH3 (1-1000 Torr for 5-60 min) replaced one Cl atom with one N atom up to a coverage of 0.33 ± 0.02 ML. Cl atoms lowered the activation energy barrier for reaction to form a primary amine (Si-NH2). Oxygen was coadsorbed due to competition by H2O contamination. The presence of Cl on the surface even after high NH3 exposures is attributed to site blocking and electrostatic interactions among neighboring Cl-Si-Si-NH2 moieties. The results demonstrate a low temperature reaction pathway for depositing N-bearing molecules on Si surfaces.