Photon-exposure-dependent photon-stimulated desorption for obtaining photolysis cross section of molecules adsorbed on surface by monochromatic soft x-ray photons

Journal Article · Sun Dec 07 04:00:00 EST 2008 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.3026598· OSTI ID:21254934

Chou, L -C; Jang, C -Y; Wu, Y -H; Tsai, W -C; Wang, S -K; Chen, J; Chang, S -C; Liu, C -C; Shai, Y; Wen, C -R ^[1]

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1. Department of Physics, National Cheng Kung University, Tainan 70101, Taiwan (China)

Photon-exposure-dependent positive- and negative-ion photon-stimulated desorption (PSD) was proposed to study the photoreactions and obtain the photolysis cross sections of molecules adsorbed on a single-crystal surface by monochromatic soft x-ray photons with energy near the core level of adsorbate. The changes in the F{sup +} and F{sup -} PSD ion yields were measured from CF{sub 3}Cl molecules adsorbed on Si(111)-7x7 at 30 K (CF{sub 3}Cl dose=0.3x10{sup 15} molecules/cm{sup 2}, {approx}0.75 monolayer) during irradiation of monochromatic soft x-ray photons near the F(1s) edge. The PSD ion yield data show the following characteristics: (a) The dissociation of adsorbed CF{sub 3}Cl molecules is due to a combination of direct photodissociation via excitation of F(1s) core level and substrate-mediated dissociation [dissociative attachment and dipolar dissociation induced by the photoelectrons emitting from the silicon substrate]. (b) the F{sup +} ion desorption is associated with the bond breaking of the surface CF{sub 3}Cl, CF{sub 2}Cl, CFCl, and SiF species. (c) the F{sup -} yield is mainly due to DA and DD of the adsorbed CF{sub 3}Cl molecules. (d) The surface SiF is formed by reaction of the surface Si atom with the neutral fluorine atom, F{sup +}, or F{sup -} ion produced by scission of C-F bond of CF{sub 3}Cl, CF{sub 2}Cl, or CFCl species. A kinetic model was proposed for the explanation of the photolysis of this submonolayer CF{sub 3}Cl-covered surface. Based on this model and the variation rates of the F{sup +}/F{sup -} signals during fixed-energy monochromatic photon bombardment at 690.2 and 692.6 eV[near the F(1s) edge], the photolysis cross section was deduced as a function of energy.

• OSTI ID: 21254934
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 21 Vol. 129; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
CROSS SECTIONS
DESORPTION
DISSOCIATION
FLUORINE
FLUORINE IONS
MONOCHROMATIC RADIATION
MONOCRYSTALS
PHOTOLYSIS
PHOTONS
SILICON
SILICON COMPOUNDS
SOFT X RADIATION
SURFACES