Continuous-time core-level photon-stimulated desorption spectroscopy for monitoring soft x-ray-induced reactions of molecules adsorbed on a single-crystal surface

Abstract

Continuous-time core-level photon-stimulated desorption ͑PSD͒ spectroscopy was proposed for monitoring the soft x-ray-induced reactions of molecules adsorbed on a single-crystal surface. Monochromatic synchrotron radiation was used as a soft x-ray light source in the photon-induced reactions of CF 3 Cl adsorbed on a Si͑111͒-7 ϫ 7 surface at 30 K and also as a probe for studying the produced fluorination states of the bonding surface Si atom in the positive-ion PSD spectroscopy. The F + PSD spectrum was obtained by monitoring the F + signal as a function of incident photon energy near the Si͑2p͒ edge ͑98-110 eV͒. Sequential F + PSD spectra were measured as a function of photon exposure at four adsorbate coverages ͑the first dose= 0.3ϫ 10 15 molecules/ cm 2 , the second dose= 0.8ϫ 10 15 molecules/ cm 2 , the third dose= 2.2 ϫ 10 15 molecules/ cm 2 , and the fourth dose= 3.2ϫ 10 15 molecules/ cm 2 ͒. For the first and second CF 3 Cl-dosed surfaces, the sequential F + PSD spectra show the variation of their shapes with photon exposure and indicate the formation of surface SiF species. The sequential F + PSD spectra for the third and fourth CF 3 Cl-dosed surfaces also show the variation of their shapes with photon exposure and depict the production of surface SiF and SiF 3 species.

X-Ray-Induced Changes to Passivation Layers of Lithium-Ion Battery Electrodes

“…Soft X-rays are common photon sources for these experiments as much of the theoretical interest involves excitation of core-levels with electron-binding energies in the sub-keV range. Chou and Wen note, however, that while many soft X-ray sources and their characteristic photon flux densities are generally assumed to cause negligible changes to the adsorbate in PSD studies, particular systems can exhibit variation in chemical-bonding structure, especially when high-intensity SR is used [23]. When hard X-ray sources are used, in addition to the MGR and KF model mechanisms, escaping photoelectrons contribute to a high-energy secondary electron background.…”

Monochromatic soft-x-ray-induced reactions of CF2Cl2adsorbed on Si(111)-7 × 7 studied by continuous-time photon-stimulated desorption spectroscopy near the F(1s) edge

“…It is well known that the excitations of the core-level electrons by the tunable soft x-ray photons of synchrotron radiation (SR) can cause the site-specific chemical reactions of adsorbed species [1][2][3][4][5][6][7]. Several experiments on SR-stimulated processes [8][9][10][11][12][13][14][15] on semiconductor surfaces have been performed, and understanding the basic mechanisms responsible for the photochemical reactions of adsorbates on a semiconductor surface has become a very important research work [16][17][18][19][20][21][22][23][24][25][26][27].…”

“…As a result, a dramatic change in a series of PSD spectra, which are measured one by one via repeating the incident photon energy scan, will be observed. The method to obtain the series of PSD spectra was called continuous-time PSD spectroscopy in our previous work [23]. Since a PSD spectrum can provide information on the local bonding and electronic structure of the surface, continuous-time PSD spectroscopy can be used to investigate the variation of the surface chemical bonding structure-the disappearance of a specific state and the production of a new bonding structure during irradiation by incident photons.…”

“…In our previous experiment [23], the continuous-time core-level PSD spectroscopy was used to study the monochromatic soft x-ray photochemistry of Freon-13 (CF 3 Cl) adsorbed on Si(111)-7 × 7 near the Si(2p) edge (98-110 eV). We found that a sequential F + PSD spectrum depicts the variation of their shapes with photon exposure, indicating that the adsorbed CF 3 Cl molecules are dissociated and the surface species SiF and SiF 3 are produced.…”