Vibrational Sum-Frequency Spectroscopic Investigation of the Structure and Azimuthal Anisotropy of Propynyl-Terminated Si(111) Surfaces

Abstract

Vibrational sum-frequency generation (VSFG) spectroscopy was used to investigate the orientation and azimuthal anisotropy of the C-H stretching modes for propynyl-terminated Si(111) surfaces, Si-C≡C-CH 3 . VSFG spectra revealed symmetric and asymmetric C-H stretching modes in addition to a Fermi resonance mode resulting from the interaction of the asymmetric C-H bending overtone with the symmetric C-H stretching vibration. The polarization dependence of the C-H stretching modes was consistent with the propynyl groups oriented such that the Si-C≡C bond is normal to the Si(111) surface. The azimuthal angle dependence of the resonant C-H stretching amplitude revealed no rotational anisotropy for the symmetric C-H stretching mode and a 3-fold rotational anisotropy for the asymmetric C-H stretching mode in registry with the 3-fold symmetric Si(111) substrate. The results are consistent with expectation that the C-H stretching modes of a -CH 3 group are decoupled from the Si substrate due to a -C≡C-spacer. In contrast, the methyl-terminated Si(111) surface, Si-CH 3 , was previously reported to have pronounced vibronic coupling of the methyl stretch modes to the electronic bath of bulk Si. Vacuum-annealing of propynyl-terminated Si(111) resulted in increased 3-fold azimuthal anisotropy for the symmetric stretch, suggesting that removal of

Vibrational Sum Frequency Generation Spectroscopy Measurement of the Rotational Barrier of Methyl Groups on Methyl-Terminated Silicon(111) Surfaces

“…In contrast, vibrational sum frequency generation (VSFG) spectroscopy has provided information about the covalently attached functional groups on methylterminated 28 and propynyl-terminated Si(111) substrates. 29 Along with the 3-fold anisotropy of the Si(111) surface probed by SHG spectroscopy, a 3-fold rotational anisotropy of covalently attached methyl and propynyl groups has been observed by VSFG spectroscopy, corroborating the proposition by Yamada et.al. 5 that the orientation of the methyl groups is interlocked at the interface because of steric interactions with the neighboring ligands.…”

“…Several groups have studied the 3-fold azimuthal anisotropy of Si(111) surfaces by second harmonic generation (SHG) spectroscopy. − SHG probes the electronic resonances of the Si substrate and therefore is not sensitive to the attached chemical groups. In contrast, vibrational sum frequency generation (VSFG) spectroscopy has provided information about the covalently attached functional groups on methyl-terminated and propynyl-terminated Si(111) substrates . Along with the 3-fold anisotropy of the Si(111) surface probed by SHG spectroscopy, a 3-fold rotational anisotropy of covalently attached methyl and propynyl groups has been observed by VSFG spectroscopy, corroborating the proposition by Yamada et.al .…”

Effect of Surface Hydration on Antifouling Properties of Mixed Charged Polymers

“…SFG theories, experimental details, and data analysis have been extensively reported and will not be repeated. − Our SFG equipment and data collection method were published before. , SFG is a second-order nonlinear optical phenomenon where a signal is generated with a frequency equaling to the summation of the two incident lights’ frequencies. The SFG selection rule determines that SFG signal can only be generated from a medium with no inversion symmetry.…”

Small Polarons and Surface Defects in Metal Oxide Photocatalysts Studied Using XUV Reflection–Absorption Spectroscopy

“…An array of established and emerging techniques exist that provide time-resolved and surface sensitive measurements of catalytic interfaces. These include sum frequency generation spectroscopy, − second harmonic generation spectroscopy, two photon photoemission spectroscopy, , time and angle resolved photoemission spectroscopy, − transient grating spectroscopy, and attenuated total reflectance spectroscopy . While XUV reflection–absorption spectroscopy complements these existing tools, it also provides several unique advantages for probing surface dynamics.…”