The reaction chemistry of H-terminated crystalline Si(111) and Si(100) surfaces in CH3OH, CD3OD, CF3(CH2)3OH, C4H9OH, and C4D9OD solutions containing ferrocenium (Fc+)-BF4, I2, or Br2 was monitored using X-ray photoelectron (XP) spectroscopy and infrared (IR) spectroscopy. Addition of the one-electron oxidant Fc+, or addition of the oxidizing species I2 or Br2, produced diagnostic changes in the IR spectra that clearly indicated formation of surficial Si-OR groups. XPS data confirmed the conclusions of the IR studies: Under our reaction conditions, no detectable reaction occurred without the presence of the oxidant. The data are consistent with oxidative activation of the surficial Si-H bonds toward nucleophilic attack by the alcohols. The reaction chemistry was generally similar on (111)-and (100)-oriented Si surfaces, although some differences were observed in the ratio of reaction products on the two different surface orientations. Alkoxylated surfaces were also prepared by a two-step process in which the surface was first chlorinated and then reacted with LiOCH3, LiOCD3, or LiO(CH2)3CF3. The data indicate that formation of silicon-halogen bonding alone is not sufficient to provide a robust correlation between the electronic and chemical properties of such crystalline Si surfaces and that formation of silicon-alkoxyl bonds is a common motif for surfaces often used in electronic and electrochemical studies of Si.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films
- Materials Chemistry