Plasmonic Gradient Effects on High Vacuum TipEnhanced Raman Spectroscopy

Tip-enhanced Raman spectroscopy (TERS) [ 1–14 ] is a high-sensitivity optical analytical technique with nanoscale resolution beyond the diffraction limit of light. As a plasmon antenna controlled by tunneling current or bias voltage, a sharp metal tip is used to create a “hot site” to excite the localized surface plasmons and consequently enhance the electromagnetic fi eld and Raman signals in the vicinity of the tip apex. In order to conduct spectral measurements that are sensitive to ambient conditions for a variety of specimens, the use of an ultra-high vacuum (UHV) environment is mandatory. [ 10,12 ] To obtain higher effi ciency of collecting Raman signals, the objective had been put into the vacuum chamber and near the tip and the substrate in our novel designed high vacuum TERS (HV-TERS). [ 13 ]