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Plasmonic Gradient Effects on High Vacuum Tip‐Enhanced Raman Spectroscopy
Author(s) -
Sun Mengtao,
Zhang Zhenglong,
Chen Li,
Sheng Shaoxiang,
Xu Hongxing
Publication year - 2014
Publication title -
advanced optical materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.89
H-Index - 91
ISSN - 2195-1071
DOI - 10.1002/adom.201300296
Subject(s) - raman spectroscopy , overtone , materials science , plasmon , molecular physics , spectroscopy , electric field , field (mathematics) , optics , optoelectronics , chemistry , physics , spectral line , mathematics , quantum mechanics , astronomy , pure mathematics
Experimental evidence is given of the breakdown of Raman selection rules in high vacuum tip‐enhanced Raman spectroscopy (HV‐TERS), where molecular Raman‐active, IR‐active, and overtone modes are simultaneously observed in situ, due to the strong tip‐enhanced near‐field gradient effects. Theoretical calculations firmly support our experimental multipole vibrational observation, and the ratio of the near‐field gradient term over electric field term is dependent on both the ratio of∂ E β γ∂ r∂ E β γ∂ rE βE βand the ratio ofA α , β γA α , β γα α βα α β, which are dependent on the physical structure of TERS and the molecular structure, respectively, in HV‐TERS. When the molecule is symmetric along the tip axis, the strongest near‐field gradient effect in HV‐TERS can be obtained. These experimental findings can promote an understanding of the unexpected “additional Raman peaks” in HV‐TERS and provide a promising technique for ultrasensitive molecular spectroscopy.