Vibrational Activity Change of Self-Assembled Monolayers upon Chemical Attachment and Nanoscale Block Revealed by Surface Enhanced Raman Spectroscopy

The origin of weak ambiguous vibrational modes in surface enhanced Raman scattering (SERS), i.e., from the high-order effect or symmetry change using 1,4-benzenedithiol (BDT) as a probe, is investigated.Weak ambiguous vibrational modes are caused by symmetry change rather than high-order effect.The experimental method can be extended, e.g., to similar systems excited by lasers with different wavelengths, or microelectronic junctions bridged by organic molecules.