Reproducible surface-enhanced Raman spectroscopy of small molecular anions

Abstract

A gold-coated silicon substrate having an array of pyramidal shaped holes is shown to provide a reproducible surface-enhanced Raman spectra (SERS) in a number of inorganic ions such as , , , and deposited on the substrate as 10⁻³ to10⁻⁴ molar aqueous solutions of their salts. Of particular interest is the observation of a SERS effect in , the anion of ammonium nitrate, a commonly used terrorist explosive, suggesting the potential for sensitive detection of this material. An unusual increase in the frequency of the bending mode frequency is observed in the SERS spectra of KNO₂. Density Functional Theory calculations of the frequencies of the normal modes of vibration of bonded to gold predict an upward shift of the frequencies compared with the calculated results for a free , suggesting a possible explanation for the shifts.

Keywords:

• surface-enhanced Raman spectroscopy
• inorganic ions
• ammonium nitrate
• gold substrate
• Density Functional Theory

Acknowledgement

This work was supported by the Army Armament Research, Development and Engineering Center, Picatinny, NJ, USA.