Observation of two metastable oxygen species adsorbed on aSi(111)−(7×7)surface: Reinterpretation of the initial oxidation process

Abstract

Using high-resolution core-level photoemission measurements, we show that two different metastable species exist on a Si(111)-(7ϫ7) surface, instead of only one as suggested in the literature. One metastable species has a finite lifetime and is composed of both molecular and atomic oxygen. The other one, which is formed by atomic oxygen only, is stable in terms of time at 300 and 100 K but disappears after annealing at 600 K. The present study reconciles the inconsistent former results and provides a detailed atomic-level understanding of the complex initial oxidation process of this surface.

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

“…Concerning the O 1s XPS profiles of the oxidized Si(111) surface, it is well known that XPS profile is composed of several components. 6,[18][19][20][21][22][23] In order to decompose the O 1s XPS profiles, the Voigt function is used, where the FWHM of the Lorentzian function is considered to be 0.2 eV. [19][20][21][22][23] The width of the Gaussian function is used to be 0:95 AE 0:05 eV, which is determined by the fitting result of the symmetric peak observed just after the oxidation.…”

“…6,[18][19][20][21][22][23] In order to decompose the O 1s XPS profiles, the Voigt function is used, where the FWHM of the Lorentzian function is considered to be 0.2 eV. [19][20][21][22][23] The width of the Gaussian function is used to be 0:95 AE 0:05 eV, which is determined by the fitting result of the symmetric peak observed just after the oxidation. We found Relative binding energy (eV) that this initial peak was mainly observed.…”

“…Contrary to this expectation, recent studies have confirmed that paul oxygen is the adsorbate on Si adatoms with the oxygen atoms at the backbond, which might be either an ins structure or an insÂ2 structure. [19][20][21][22][23][24][25][26][27][28] Moreover, another research group has reported that the dissociative O 2 adsorption firstly occurs to form an ins structure and then an ad-ins structure. [19][20][21][22][23][24][25][26][27][28][29][30][31] In this manner, a missing piece for understanding the structures of the initial oxides and their formation processes remains.…”

“…[19][20][21][22][23][24][25][26][27][28] Moreover, another research group has reported that the dissociative O 2 adsorption firstly occurs to form an ins structure and then an ad-ins structure. [19][20][21][22][23][24][25][26][27][28][29][30][31] In this manner, a missing piece for understanding the structures of the initial oxides and their formation processes remains. Furthermore, the question of whether or not paul oxygen is the precursor prior to O 2 dissociation on an oxygen-free Si adatom has not been solved yet.…”

Chemical and kinetic insights into the Thermal Decomposition of an Oxide Layer on Si(111) from Millisecond Photoelectron Spectroscopy

“…An estimated O coverage of 1.4 ML (1 ML = 7.68 × 10 14 atoms/cm 2 ) was obtained. The O 1 s spectrum at 45 L (Figure S2(b) of the SI) shows clearly the absence of molecular metastable oxygen 67 , 68 , observed at much lower exposure (~1 L).…”