Yang, Wei-ChenHore, Dennis K.2020-01-042020-01-0420172017Yang, W. & Hore, D. K. (2017). Determining the orientation of chemical functional groups on metal surfaces by a combination of homodyne and heterodyne nonlinear vibrational spectroscopy. The Journal of Physical Chemistry C, 121(50), 28043- 28050. DOI: 10.1021/acs.jpcc.7b09730https://doi.org/10.1021/acs.jpcc.7b09730http://hdl.handle.net/1828/11454We illustrate how phase-sensitive sum-frequency generation spectroscopy may be used to determine the polar orientation of organic species on metals, where there is a significant electronic contribution to the second-order signal. It turns out that traditional direct heterodyne schemes, as would be applied to the same molecules on dielectric substrates, are challenging to use here as a result of the large resonant/nonresonant amplitude ratio that diminishes the phase contrast observed in tuning through the vibrational mode. This is demonstrated in a variety of experimental surfaces that illustrate all limiting cases. We propose a scheme that can overcome this challenge and thereby determine the chemical functional group orientation through a combination of the homodyne spectrum and some phase information from a heterodyne approach.enMetalsNonlinear opticsOscillationPolarity AlkylsPostprint