Low energy electron induced chemistry: CH3Cl on Ag(111)

X. L. Zhou, P. M. Blass, B. E. Koel, J. M. White

Research output: Contribution to journalArticle

25 Scopus citations

Abstract

The chemistry, induced by 50 eV electrons, of CH3Cl on clean, Cl-covered and D-covered Ag(111) at 100 K has been studied using TPD, XPS, UPS and Δφ. Electron induced dissociation (EID) occurs very efficiently with an initial total cross section of, at most, (5.5±0.5)×10-16 cm2 for 1 ML CH3Cl coverage. For coverages up to 1 ML, CH3 and C2H5 radicals, some CH4 and C2H6 and, perhaps, some C2H4 molecules desorb during EID; very few Cl-containing species desorb. At the surface, the following are synthesized and retained: H and Cl atoms; CHx (x = 2,3), -C2H5 and, possibly, =CHCH3 and -CH=CH2 fragments; an and C2H4 molecules. The relative concentrations of these species depend on electron fluence (EF) and CH3Cl coverage. In TPD, CH3Cl and C2H4 desorb molecularly; H atoms and hydrocarbon frragments react to produce H2, CH4, C2H4, C2H6, C3H6, C3 H8, C4H8 and C4H10 below 300 K; the only higher temperature product is AgCl, which desorbs at 750 K. No dehydrogenation occurs during TPD. Preadsorbed Cl has a dramatic influence; compared to 1 ML CH3Cl on clean Ag(111), the production of saturated hydrocarbons, CH4, C2H6 and C3H8, is suppressed and the desorption of olefins shifts to lower temperatures. When D is preadsorbed, EID leads to TPD of partially deuterated, saturated hydrocarbons CH3D, CH2D2, C2H4D2, C2H5D, C3H5 D3, C3H6D2 and C3H7D. For multilayers (3-10 ML), desorption of H2, CH3, CH4, C2H4, C2H5, C2H6, C Cl, HCl and CH3Cl is observed during EID. The TPD products appearing below 300 K are desorption-limited HCl, C2H4, C3H6 and C4H8, and reaction-limited H2, CH4, C2H4, C2H6, C3H6 and C3H8. A strongly bound CxHyClz (x > 1) is formed during EID; it decomposes to form HCl, H2 and surface carbon above 400 K. AgCl continues to appear at high temperatures but the amount drops as the initial multilayer CH3Cl coverage increases.

Original languageEnglish (US)
Pages (from-to)427-451
Number of pages25
JournalSurface Science
Volume271
Issue number3
DOIs
StatePublished - 1992
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry

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