New Model of the Initial Stages of Si(111)-(7×7) Oxidation

Determination of the bonding configuration of the metastable molecular oxygen adsorbed on a Si(111)-(7×7) surface

“…In studies based on density-functional theory ͑DFT͒ calculations, 1,2 it was stated that the metastable oxygen has an atomic oxygen configuration. These DFT calculations 1,2 reinterpreted the earlier spectroscopic [3][4][5][6][7][8][9][10] and microscopic [11][12][13][14][15][16] results in which the metastable oxygen was reported to be a molecular species, a so-called molecular precursor. The absence of the molecular precursor was supported by a Cs ion scattering experiment.…”

“…Oxygen atoms are reported to first adsorb into the back bonds of the adatoms and then on top of them by scanning tunneling microscopy ͑STM͒. [12][13][14][15] The STM results indicate that the atomic oxygen species has the ''insϫn-ad'' or ''ins ϫn'' (nϭ1, 2, and 3͒ configuration on a Si(111)-(7ϫ7) surface. Each insϫn-ad configuration is expected to have two O 1s components with rather different binding energies (Ͼ2.5 eV) by the DFT calculation.…”

“…This number is different from that used for the previous models, i.e., only two oxygen atoms with different chemical environments have been considered for the atomic configuration 1,2,17 and the molecular precursor. [3][4][5][6][7][8][9][10][11][12][13][14][15][16] This obvious conflict calls for an urgent and careful reinvestigation of the structural model of the metastable species, which is essential for the understanding of the oxidation process of Si on an atomic level. Since the long debate principally originates from the uncertainty in the number of oxygen atoms composing the metastable species, a probe sensitive to the chemical environments of the oxygen atoms is required.…”

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

“…[3][4][5][6][7] These reports indicate that metastable oxygen is formed by a secondary reaction process and that the oxidation path should be different from the paths suggested based on the metastable species as a precursor with either molecular paul [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] or atomic ins-ad and ins ϫ3-ad configurations [23][24][25] ͑Fig. 1͒ in the former studies.…”

Photoemission study of metastable oxygen adsorbed on aSi(111)−(7×7)surface

“…From a scientific point of view, the presence of the metastable oxygen has particularly attracted a deep interest in the initial oxidation stage of the Si͑111͒-͑7 ϫ 7͒ surface. This metastable species, which has a finite lifetime and disappears after annealing the sample at 600 K, was observed in various spectroscopic [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] and microscopic studies, [17][18][19][20] and it has also been treated theoretically. 3,[21][22][23][24] Despite these extensive research efforts, a complete picture of the processes determining the lifetime has not yet been obtained.…”