Paper NM-TuP17
Surface Structure and Local Valence Electronic States of Si(110)-16×2 Surface after Exposure to Water: XPS and Auger-Photoelectron Coincidence Study

Tuesday, December 9, 2014, 4:00 pm, Room Mauka

Si(110)-16×2 is a favorable candidate for a next-generation semiconductor substrate because it takes a single domain (SD) structure with high hole-mobility, which is larger than that of the other Si crystal faces. Recently, Adatom-Buckling (AB) model has been proposed as the surface structure model for clean Si(110)-16×2 surface [1]. The AB model consists of five Si surface components of SC1: the buckled upper atoms, SC2: the unbuckled atoms and the second layer atoms with dangling bonds (DBs), SC3: the first layer and second layers atoms without DBs, SC4: the adatoms, and SC5: buckled lower atoms. In the AB model, the surface states S₁, S_2, S₃, and S₄ with binding energies of 0.2 eV 0.4 eV, 0.7 eV, and 1.0 eV are reported to be located at specific surface sites of SC4, SC1, SC5, and SC3, respectively [1]. However, the SD structure of Si(110)-16×2 disappears when it is exposed to atmospheric air. In this study, we investigated a water-terminated Si(110)-16×2 SD surface with XPS and Auger-photoelectron coincidence spectroscopy. Si-2p photoelectron spectra indicate that water is dissociatively adsorbed and forms Si-H and Si-OH components after exposure to water of 0.1 Langmuir (L). When Si(110)-16×2 surface is exposure to water form 1.0 L to 5.0 L, there is little change in these Si-2p intensity ratio. This result indicates that clean Si(110)-16×2 surface is saturated with water of less than 1.0 Langmuir (L). In addition, water is preferentially dissociative-adsorbed at surface components of the SC1, the SC2, and the SC3 on step edge of SD structure, but is hardly adsorbed at surface components of the SC4 and the SC5 on the terrace of the SD structure. The SD structure of Si(110)-16×2 surface after the exposure to water of 5.0 Langmuir is kept under ultra-high vacuums condition and atmosphere pressure of N₂ gas. This result indicates that Si(110)-16×2 SD surface is inactivated by water dissociative-adsorption. On the other hand, Si-L₂₃VV-Si-2p coincidence spectra suggest that the surface states S₁, S₂, S₃, and S₄ disappear after exposure to water. The valence band maximum energy of water adsorbed Si(110)-16×2 surface is shifted to deeper binding energy side in comparison with that of clean Si(110)-16×2 surface. The water adsorbed Si(110)-16×2 SD surface may be used as a unique semiconductor substrate.

[1] K. Sakamoto, M. Setvin, K. Mawatari, P. E. J. Eriksson, K. Miki, and R. I. G. Uhrberg, Phys. Rev. B 79, 045304 (2009).