Neutralization effects in the electron-stimulated desorption of molecules covalently bonded to metal oxide surfaces

Todd R. Hayes; John F. Evans

doi:10.1016/0039-6028(85)90441-8

Neutralization effects in the electron-stimulated desorption of molecules covalently bonded to metal oxide surfaces

Todd R. Hayes, John F. Evans

Chemistry & Biochemistry

Research output: Contribution to journal › Article › peer-review

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Abstract

TiO₂ and SiO₂ surfaces were chemically modified via covalent attachment of a variety of organosilane molecules, and electron stimulated desorption from these surfaces was examined. The study focussed on, but was not limited to, bound trimethylsilyl and tri(methyl-d₃)silyl groups. Relative parent and fragment secondary ion yields are strongly dependent upon the substrate material. The significantly lower ion yields found in the case of modified TiO₂ are explained by the relative positions of the TiO₂ valence band and the ionization potentials of (CH₃)₃Si. and CH₃. radicals, such that resonance neutralization of near-surface (CH₃)₃Si⁺ ions is energetically favorable. Such neutralization processes are energetically unfavorable at the SiO₂ surface. Total dissociation cross sections (1.0 keV electron bombardment) were measured for trimethylsilyl groups bound to these surfaces. The cross section was found to be a factor of 3.7 lower for modified TiO₂ than for modified SiO₂. This difference does not appear to be explicable in terms of differences between the secondary electron yields of the two substrates, but may instead be an indication that "recapture" (neutralization processes involving bond reformation) occurs with significant probability at the tiO₂ surface.

Original language	English (US)
Pages (from-to)	466-484
Number of pages	19
Journal	Surface Science
Volume	159
Issue number	2-3
DOIs	https://doi.org/10.1016/0039-6028(85)90441-8
State	Published - Aug 2 1985

Bibliographical note

Funding Information:
The bulk of this work was performed at the University of Minnesota Regional Instrumentation Facility for Surface Analysis, which is funded by the National Science Foundation under grant CHE: 7916206. We would like to thank Dr. M. Knotek, Sandia Laboratories, Albuquerque. NM, for performing preliminary ESD threshold energy measurements and for helpful discussions. T.R.H. is grateful to the Dow Chemical Company and the Procter and Gamble Company for financial support during this work. The Physical Electronics Division of Perkin-Elmer Corporation provided both financial support for T.R.H. and aided in the design and production of the reactor for surface chemical modification.

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title = "Neutralization effects in the electron-stimulated desorption of molecules covalently bonded to metal oxide surfaces",

abstract = "TiO2 and SiO2 surfaces were chemically modified via covalent attachment of a variety of organosilane molecules, and electron stimulated desorption from these surfaces was examined. The study focussed on, but was not limited to, bound trimethylsilyl and tri(methyl-d3)silyl groups. Relative parent and fragment secondary ion yields are strongly dependent upon the substrate material. The significantly lower ion yields found in the case of modified TiO2 are explained by the relative positions of the TiO2 valence band and the ionization potentials of (CH3)3Si. and CH3. radicals, such that resonance neutralization of near-surface (CH3)3Si+ ions is energetically favorable. Such neutralization processes are energetically unfavorable at the SiO2 surface. Total dissociation cross sections (1.0 keV electron bombardment) were measured for trimethylsilyl groups bound to these surfaces. The cross section was found to be a factor of 3.7 lower for modified TiO2 than for modified SiO2. This difference does not appear to be explicable in terms of differences between the secondary electron yields of the two substrates, but may instead be an indication that {"}recapture{"} (neutralization processes involving bond reformation) occurs with significant probability at the tiO2 surface.",

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note = "Funding Information: The bulk of this work was performed at the University of Minnesota Regional Instrumentation Facility for Surface Analysis, which is funded by the National Science Foundation under grant CHE: 7916206. We would like to thank Dr. M. Knotek, Sandia Laboratories, Albuquerque. NM, for performing preliminary ESD threshold energy measurements and for helpful discussions. T.R.H. is grateful to the Dow Chemical Company and the Procter and Gamble Company for financial support during this work. The Physical Electronics Division of Perkin-Elmer Corporation provided both financial support for T.R.H. and aided in the design and production of the reactor for surface chemical modification.",

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N2 - TiO2 and SiO2 surfaces were chemically modified via covalent attachment of a variety of organosilane molecules, and electron stimulated desorption from these surfaces was examined. The study focussed on, but was not limited to, bound trimethylsilyl and tri(methyl-d3)silyl groups. Relative parent and fragment secondary ion yields are strongly dependent upon the substrate material. The significantly lower ion yields found in the case of modified TiO2 are explained by the relative positions of the TiO2 valence band and the ionization potentials of (CH3)3Si. and CH3. radicals, such that resonance neutralization of near-surface (CH3)3Si+ ions is energetically favorable. Such neutralization processes are energetically unfavorable at the SiO2 surface. Total dissociation cross sections (1.0 keV electron bombardment) were measured for trimethylsilyl groups bound to these surfaces. The cross section was found to be a factor of 3.7 lower for modified TiO2 than for modified SiO2. This difference does not appear to be explicable in terms of differences between the secondary electron yields of the two substrates, but may instead be an indication that "recapture" (neutralization processes involving bond reformation) occurs with significant probability at the tiO2 surface.

AB - TiO2 and SiO2 surfaces were chemically modified via covalent attachment of a variety of organosilane molecules, and electron stimulated desorption from these surfaces was examined. The study focussed on, but was not limited to, bound trimethylsilyl and tri(methyl-d3)silyl groups. Relative parent and fragment secondary ion yields are strongly dependent upon the substrate material. The significantly lower ion yields found in the case of modified TiO2 are explained by the relative positions of the TiO2 valence band and the ionization potentials of (CH3)3Si. and CH3. radicals, such that resonance neutralization of near-surface (CH3)3Si+ ions is energetically favorable. Such neutralization processes are energetically unfavorable at the SiO2 surface. Total dissociation cross sections (1.0 keV electron bombardment) were measured for trimethylsilyl groups bound to these surfaces. The cross section was found to be a factor of 3.7 lower for modified TiO2 than for modified SiO2. This difference does not appear to be explicable in terms of differences between the secondary electron yields of the two substrates, but may instead be an indication that "recapture" (neutralization processes involving bond reformation) occurs with significant probability at the tiO2 surface.

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Neutralization effects in the electron-stimulated desorption of molecules covalently bonded to metal oxide surfaces

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