Comparison of the electrical properties and chemical stability of crystalline silicon(111) surfaces alkylated using Grignard reagents or Olefins with Lewis acid catalysts

Lauren J. Webb, Nathan S Lewis

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Abstract

Four methods were used to functionalize crystalline Si(111) surfaces with alkyl groups (CnH2n+1, n = 1, 2, 6, 8): chlorination with PCl5 followed by alkylation with CnH2n+1MgX (X = Cl, Br), chlorination with Cl2(g) followed by alkylation with CnH2n+1MgX, Lewis acid-mediated reduction of a terminal alkene, and anodization in diethyl ether containing 3.0 M CH3MgI. The chemical properties of each surface were characterized as a function of time exposed to air using X-ray photoelectron spectroscopy, and the electrical properties of the various surfaces were probed using time-resolved radio frequency (rf) photoconductivity decay methods. Both chlorination/alkylation routes produced alkylated Si surfaces that displayed low (-1) initial charge carrier surface recombination velocities (S); furthermore, the recombination velocities of these functionalized surfaces were stable during >600 h of exposure to air. Surfaces functionalized through this route also displayed a significantly lower rate of oxidation than did unalkylated, H-terminated or Cl-terminated Si(111) surfaces. In contrast, surfaces modified by the Lewis acid-catalyzed reduction of 1-hexene and 1-octene exhibited high S values (S > 400 cm s-1) when initially exposed to air and oxidized as rapidly as H-terminated Si(111) surfaces. Methyl-terminated Si(111) surfaces functionalized by anodization in a solution of CH3MgI in ether exhibited stable, albeit high, S values (460 cm s-1), indicating that the surface had been partially modified by the anodization process. The fractional monolayer coverage of oxide on the alkylated surface after exposure to air was determined for each functionalization technique. Although all four of the functionalization routes studied in this work introduced alkyl groups onto the Si surface, subtle changes in the extent and quality of the alkyl termination are significant factors in determining the magnitude and degree of chemical and electrical passivation of the resulting functionalized Si surfaces.

Original languageEnglish
Pages (from-to)5404-5412
Number of pages9
JournalJournal of Physical Chemistry B
Volume107
Issue number23
Publication statusPublished - Jun 12 2003

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Lewis Acids
Chemical stability
Alkenes
Silicon
alkenes
Olefins
reagents
Electric properties
electrical properties
Crystalline materials
catalysts
acids
Catalysts
Acids
silicon
chlorination
Chlorination
alkylation
Alkylation
air

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

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title = "Comparison of the electrical properties and chemical stability of crystalline silicon(111) surfaces alkylated using Grignard reagents or Olefins with Lewis acid catalysts",
abstract = "Four methods were used to functionalize crystalline Si(111) surfaces with alkyl groups (CnH2n+1, n = 1, 2, 6, 8): chlorination with PCl5 followed by alkylation with CnH2n+1MgX (X = Cl, Br), chlorination with Cl2(g) followed by alkylation with CnH2n+1MgX, Lewis acid-mediated reduction of a terminal alkene, and anodization in diethyl ether containing 3.0 M CH3MgI. The chemical properties of each surface were characterized as a function of time exposed to air using X-ray photoelectron spectroscopy, and the electrical properties of the various surfaces were probed using time-resolved radio frequency (rf) photoconductivity decay methods. Both chlorination/alkylation routes produced alkylated Si surfaces that displayed low (-1) initial charge carrier surface recombination velocities (S); furthermore, the recombination velocities of these functionalized surfaces were stable during >600 h of exposure to air. Surfaces functionalized through this route also displayed a significantly lower rate of oxidation than did unalkylated, H-terminated or Cl-terminated Si(111) surfaces. In contrast, surfaces modified by the Lewis acid-catalyzed reduction of 1-hexene and 1-octene exhibited high S values (S > 400 cm s-1) when initially exposed to air and oxidized as rapidly as H-terminated Si(111) surfaces. Methyl-terminated Si(111) surfaces functionalized by anodization in a solution of CH3MgI in ether exhibited stable, albeit high, S values (460 cm s-1), indicating that the surface had been partially modified by the anodization process. The fractional monolayer coverage of oxide on the alkylated surface after exposure to air was determined for each functionalization technique. Although all four of the functionalization routes studied in this work introduced alkyl groups onto the Si surface, subtle changes in the extent and quality of the alkyl termination are significant factors in determining the magnitude and degree of chemical and electrical passivation of the resulting functionalized Si surfaces.",
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N2 - Four methods were used to functionalize crystalline Si(111) surfaces with alkyl groups (CnH2n+1, n = 1, 2, 6, 8): chlorination with PCl5 followed by alkylation with CnH2n+1MgX (X = Cl, Br), chlorination with Cl2(g) followed by alkylation with CnH2n+1MgX, Lewis acid-mediated reduction of a terminal alkene, and anodization in diethyl ether containing 3.0 M CH3MgI. The chemical properties of each surface were characterized as a function of time exposed to air using X-ray photoelectron spectroscopy, and the electrical properties of the various surfaces were probed using time-resolved radio frequency (rf) photoconductivity decay methods. Both chlorination/alkylation routes produced alkylated Si surfaces that displayed low (-1) initial charge carrier surface recombination velocities (S); furthermore, the recombination velocities of these functionalized surfaces were stable during >600 h of exposure to air. Surfaces functionalized through this route also displayed a significantly lower rate of oxidation than did unalkylated, H-terminated or Cl-terminated Si(111) surfaces. In contrast, surfaces modified by the Lewis acid-catalyzed reduction of 1-hexene and 1-octene exhibited high S values (S > 400 cm s-1) when initially exposed to air and oxidized as rapidly as H-terminated Si(111) surfaces. Methyl-terminated Si(111) surfaces functionalized by anodization in a solution of CH3MgI in ether exhibited stable, albeit high, S values (460 cm s-1), indicating that the surface had been partially modified by the anodization process. The fractional monolayer coverage of oxide on the alkylated surface after exposure to air was determined for each functionalization technique. Although all four of the functionalization routes studied in this work introduced alkyl groups onto the Si surface, subtle changes in the extent and quality of the alkyl termination are significant factors in determining the magnitude and degree of chemical and electrical passivation of the resulting functionalized Si surfaces.

AB - Four methods were used to functionalize crystalline Si(111) surfaces with alkyl groups (CnH2n+1, n = 1, 2, 6, 8): chlorination with PCl5 followed by alkylation with CnH2n+1MgX (X = Cl, Br), chlorination with Cl2(g) followed by alkylation with CnH2n+1MgX, Lewis acid-mediated reduction of a terminal alkene, and anodization in diethyl ether containing 3.0 M CH3MgI. The chemical properties of each surface were characterized as a function of time exposed to air using X-ray photoelectron spectroscopy, and the electrical properties of the various surfaces were probed using time-resolved radio frequency (rf) photoconductivity decay methods. Both chlorination/alkylation routes produced alkylated Si surfaces that displayed low (-1) initial charge carrier surface recombination velocities (S); furthermore, the recombination velocities of these functionalized surfaces were stable during >600 h of exposure to air. Surfaces functionalized through this route also displayed a significantly lower rate of oxidation than did unalkylated, H-terminated or Cl-terminated Si(111) surfaces. In contrast, surfaces modified by the Lewis acid-catalyzed reduction of 1-hexene and 1-octene exhibited high S values (S > 400 cm s-1) when initially exposed to air and oxidized as rapidly as H-terminated Si(111) surfaces. Methyl-terminated Si(111) surfaces functionalized by anodization in a solution of CH3MgI in ether exhibited stable, albeit high, S values (460 cm s-1), indicating that the surface had been partially modified by the anodization process. The fractional monolayer coverage of oxide on the alkylated surface after exposure to air was determined for each functionalization technique. Although all four of the functionalization routes studied in this work introduced alkyl groups onto the Si surface, subtle changes in the extent and quality of the alkyl termination are significant factors in determining the magnitude and degree of chemical and electrical passivation of the resulting functionalized Si surfaces.

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