Wavelength dependent second harmonic generation: a new spectroscopic tool for the study of interfaces

The adsorption of n‐hexadecane thiol on gold in ethanol has been examined by wavelength dependent second harmonic generation (SHG). In addition to the amplitude, the phase of the second harmonic signal has been measured. At fundamental wavelengths of 1064 nm and 532 nm the temporal dependence of the SH signal reveals that the second order susceptibility is linearly related to the thiol coverage. Between 610 nm and 660 nm a dramatic variation of the time dependent second harmonic signal both in magnitude and in phase is observed due to a coverage dependent resonance. The results demonstrate the potential of second harmonic generation as a spectroscopy for monitoring the effect of adsorbates on the electronic properties of surfaces