Immediate Product after Exposing Si(111)-7×7 Surface to O₂ at 300 K

Abstract

Using real-time O 1s X-ray photoelectron spectroscopy together with Si 2p X-ray photoelectron spectroscopy, the oxygen bonding configurations of oxides shortly after exposing the Si(111)-7×7 surface to O2 at 300 K are revealed. It is found that the ins structure firstly forms where one oxygen atom sits in the backbond of the silicon adatom. It is confirmed that the chemisorbed molecular oxygen, the so-called paul oxygen, is the adsorbate on top of the ins structure. It is also clarified that the ad–ins structure and the ins–tri structure, where ad means an oxygen atom adsorbed onto top of the silicon adatom and tri means the interstitial oxygen atom, appear after a short time. The results implying the presence of mobile O2 on the surface were obtained.

In situ synchrotron radiation photoelectron spectroscopy study of the oxidation of the Ge(100)-2 × 1 surface by supersonic molecular oxygen beams

“…The component γ seems to originate from the Ge-Ge dimer at the residual unoxidized area on the surface 42 and/or can be assigned to the oxide-related component normally observed in the oxidation of Si surfaces. 25,[43][44][45] The positions of the components related to suboxide states such as Ge 1+ and Ge 2+ were set to the positions reported by Schmeisser et al 28 Figure 5 shows the results of curve-fitting analysis, and the parameters obtained from the curve-fitting analysis are shown in Table I. Our analysis clearly revealed the Ge 1+ and Ge 2+ oxidation states at core-level shifts of 0.81 and 1.71 eV, respectively.…”

“…In this study, we carefully calibrated the oxygen coverage on the Ge(100) surface by referring to the results of oxygen uptake on the Si(111)-7 × 7 surface, where the relationship between the oxygen coverage and the intensity of the O 1s peak is well-understood. [25][26][27] This careful calibration allows us to assess the oxygen coverage in monolayer units (ML; 1 ML = 6.19 × 10 14 cm −2 , corresponding to the density of Ge atoms on the Ge(100)-1 × 1 surface). It was found that the final oxygen coverage was dependent on the incident energy of the oxygen, suggesting that the oxidation process can be activated by the translational energy of the O 2 molecules.…”

“…All of the experiments were performed in UHV using SUREAC2000 [25][26][27]32 constructed at the soft X-ray beamline, BL23SU, 33 at SPring-8, Hyogo, Japan. The SUREAC2000 is equipped with a supersonic O 2 beam generator and hemispherical electron energy analyzer (EA125-5MCD, Omicron Nanotechnology GmbH, Taunusstein, Germany) and lowenergy electron diffraction (LEED) facilities.…”

“…16 It is well known that core-level photoelectron spectroscopy is a powerful tool to give detailed information about the chemical environment and oxidation states of oxides at solid surfaces. [5][6][7][8][9][23][24][25][26][27] Schmeisser et al 28 and Kuhr and Ranke 29 reported Ge 3d core-level spectra for various oxygen exposures to a Ge(100) surface. Two chemically shifted components of Ge 3d, corresponding to Ge atoms with one or two oxygen ligands, were debated.…”

“…These findings are particularly interesting as the results of the chemical analysis of oxidized Ge(100) surfaces. However, although the peak positions attributed to Ge oxidation states were described in their core-level spectra, no detailed oxide-related components, which are widely reported in silicon oxidation studies, [23][24][25][26][27] were given as a function of the oxygen coverage in both papers.…”