Adsorption and thermal reaction of short-chain iodoalkanes on Ge(100)

P. Y. Chuang, W. L. Lee, T. F. Teng, Y. H. Lai, W. H. Hung

Research output: Contribution to journalArticle

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Abstract

The adsorption and thermal decomposition of iodoalkanes CH3I, C2H5I, and C4H9I on Ge(100) were studied with temperature-programmed desorption (TPD) and X-ray photoelectron spectra (XPS) using synchrotron radiation. At 105 K, the iodoalkanes adsorb both molecularly and dissociatively on Ge(100); the shorterchain iodoalkane dissociates to form a surface alkyl and an I adatom to a greater extent. The chemisorbed iodoalkane gradually dissociates to form a surface alkyl and an I adatom in a temperature range 200-370 K. At 720 K, most surface CH3 desorbs directly from the surface, and other surface CH3 radicals undergo disproportionation to desorb as CH4. Surface C 2H5 and C4H9 mostly undergo β-hydride elimination to desorb as C2H4 and C 4H8 at ̃550 K, respectively. The temperature for C4H9 to react is slightly lower than that for C 2H5 because the C4H9 chain exhibits a stronger interaction with the surface than C2H5. The I adatom can react with a H atom liberated during decomposition of a surface alkyl and subsequently desorbs as molecular HI in two temperature regimes, ̃650 and ̃720 K. Some I adatoms are removed from the surface via direct desorption in atomic form at 720 K. On annealing to 770 K, the Ge surface becomes free of I adatom but retains a deposit of residual C as adatoms. According to our data, the temperature of fabrication and operation of a Ge-based device with the alkyl monolayer is suggested to be not higher than 530 K.

Original languageEnglish
Pages (from-to)17447-17454
Number of pages8
JournalJournal of Physical Chemistry C
Volume113
Issue number40
DOIs
Publication statusPublished - 2009 Oct 21

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Adatoms
Adsorption
adsorption
adatoms
desorption
temperature
Hot Temperature
decomposition
Temperature
Temperature programmed desorption
Photoelectrons
Synchrotron radiation
Hydrides
hydrides
thermal decomposition
elimination
Monolayers
Desorption
synchrotron radiation
photoelectrons

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Energy(all)
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films

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Adsorption and thermal reaction of short-chain iodoalkanes on Ge(100). / Chuang, P. Y.; Lee, W. L.; Teng, T. F.; Lai, Y. H.; Hung, W. H.

In: Journal of Physical Chemistry C, Vol. 113, No. 40, 21.10.2009, p. 17447-17454.

Research output: Contribution to journalArticle

Chuang, P. Y. ; Lee, W. L. ; Teng, T. F. ; Lai, Y. H. ; Hung, W. H. / Adsorption and thermal reaction of short-chain iodoalkanes on Ge(100). In: Journal of Physical Chemistry C. 2009 ; Vol. 113, No. 40. pp. 17447-17454.
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AB - The adsorption and thermal decomposition of iodoalkanes CH3I, C2H5I, and C4H9I on Ge(100) were studied with temperature-programmed desorption (TPD) and X-ray photoelectron spectra (XPS) using synchrotron radiation. At 105 K, the iodoalkanes adsorb both molecularly and dissociatively on Ge(100); the shorterchain iodoalkane dissociates to form a surface alkyl and an I adatom to a greater extent. The chemisorbed iodoalkane gradually dissociates to form a surface alkyl and an I adatom in a temperature range 200-370 K. At 720 K, most surface CH3 desorbs directly from the surface, and other surface CH3 radicals undergo disproportionation to desorb as CH4. Surface C 2H5 and C4H9 mostly undergo β-hydride elimination to desorb as C2H4 and C 4H8 at ̃550 K, respectively. The temperature for C4H9 to react is slightly lower than that for C 2H5 because the C4H9 chain exhibits a stronger interaction with the surface than C2H5. The I adatom can react with a H atom liberated during decomposition of a surface alkyl and subsequently desorbs as molecular HI in two temperature regimes, ̃650 and ̃720 K. Some I adatoms are removed from the surface via direct desorption in atomic form at 720 K. On annealing to 770 K, the Ge surface becomes free of I adatom but retains a deposit of residual C as adatoms. According to our data, the temperature of fabrication and operation of a Ge-based device with the alkyl monolayer is suggested to be not higher than 530 K.

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