Research Centre in Physics of Matter and Radiation (PMR), University of Namur (FUNDP), rue de Bruxelles 61, 5000 Namur, Belgium.
Chemphyschem. 2010 Feb 22;11(3):607-15. doi: 10.1002/cphc.200900733.
Polarisation-dependent sum frequency generation (SFG) spectroscopy is used to investigate the orientation of molecules on metallic surfaces. In particular, self-assembled monolayers (SAMs) of dodecanethiol (DDT) and of p-nitrothiophenol (p-NTP), grown on Pt and on Au, have been chosen as models to highlight the ability of combining ppp and ssp polarisations sets (representing the polarisation of the involved beams in the conventional order of SFG, Vis and IR beam) to infer orientational information at metallic interfaces. Indeed, using only the ppp set of data, as it is usually done for metallic surfaces, is not sufficient to determine the full molecular orientation. We show here that simply combining ppp and ssp polarisations enables both the tilt and rotation angles of methyl groups in DDT SAMs to be determined. Moreover, for p-NTP, while the SFG active vibrations detected with the ppp polarisation alone provide no orientational information, however, the combination with ssp spectra enables to retrieve the tilt angle of the p-NTP 1,4 axis. Though orientational information obtained by polarisation-dependent measurements has been extensively used at insulating interfaces, we report here their first application to metallic surfaces.
偏振相关和频发生（SFG）光谱学被用来研究分子在金属表面的取向。特别是，选择了在 Pt 和 Au 上生长的十二硫醇（DDT）和对硝基硫酚（p-NTP）的自组装单层（SAM）作为模型，以突出结合 ppp 和 ssp 偏振集（代表 SFG、Vis 和 IR 光束的偏振）的能力，以推断金属界面处的取向信息。实际上，仅使用通常用于金属表面的 ppp 数据集不足以确定完整的分子取向。我们在这里表明，简单地结合 ppp 和 ssp 偏振即可确定 DDT SAM 中甲基的倾斜和旋转角度。此外，对于 p-NTP，虽然单独用 ppp 偏振检测到的 SFG 活性振动没有提供任何取向信息，但是与 ssp 光谱的组合可以恢复 p-NTP 1,4 轴的倾斜角度。尽管通过偏振相关测量获得的取向信息已在绝缘界面上得到广泛应用，但我们在此报告了它们在金属表面的首次应用。
