Surface-Enhanced Infrared Spectroscopy: A Comparison of Metal Island Films with Discrete and Nondiscrete Surface Plasmons

Abstract

A study of the surface-enhanced infrared absorption (SEIRA) spectroscopy of para-nitrobenzoic acid (PNBA) adsorbed on thermally evaporated silver films has been conducted to determine the effect of film architecture on the magnitude of the SEIRA enhancement. Ordered arrays of uniformly sized silver nanoparticles, termed periodic particle arrays (PPAs), were prepared on several different infrared transparent substrates (germanium, silicon, and mica) by nanosphere lithography (NSL). It was found that the ordered arrays deposited by NSL produced well-defined and intense surface plasmon resonance (SPR) bands in the infrared at frequencies between 1500 and 4000 cm−1. The peak frequency of these infrared SPR bands depended on the array architecture and the substrate material. By appropriate design of the nanoparticle array, the infrared SPR band can be made to be coincident with the SEIRA sensitive infrared bands of the PNBA. The trends in the infrared SPR peak frequencies and band shapes were consistent with predictions from electrodynamic theory. The SEIRA responses per unit area of deposited metal obtained with the PPA-type films were at best comparable to results obtained with disordered silver and gold films deposited on the same substrate materials by thermal evaporation (i.e., in the absence of any NSL masking spheres). The results of this study are most consistent with theories and models that attribute SEIRA to the dielectric constant and optical extinction spectrum of the metal film.

Influence of Single Use and Combination of Reductants on the Size, Morphology and Growth Steps of Gold Nanoparticles in Colloidal Mixture

“…Therefore, this band might be red-shifted, however, this was not detectable with our UV-vis instrument [40]. As a matter of support to this assumption, some previous reports [41,42] also claimed that very large nanoparticles absorb and scatter light in the near-infrared and mid-infrared region of the spectrum. On the other hand, TEM could provide further hints on the formation of expected flower-like nanocrystals.…”

Ultra-sensitive vibrational spectroscopy of protein monolayers with plasmonic nanoantenna arrays

“…The enhanced signal mainly comes from a small quantity of molecules at the close vicinity of the N 2 nanorod tips (n ϭ 63 is the number of rows and columns). Second, in contrast to the studies conducted with self-assembled monolayers (SAMs) (7)(8)(9)(10)(11)(12)(13), here the protein molecules are physisorbed (see SI Text), which results in the following differences. (i) Unlike the SAMs, the transition dipole moments of the physisorbed proteins have no fixed orientation with respect to the metal surface normal.…”

“…The plasmonic enhancement of optical near fields can also be extended to the infrared frequencies enabling dramatic signal enhancement in infrared (IR) spectroscopy. In analogy to SERS, this method is called surface enhanced infrared absorption (SEIRA) spectroscopy (7)(8)(9)(10)(11)(12)(13)(14). Until recently, the bulk of SEIRA studies have revolved around enhancements achieved via chemically prepared or roughened metal surfaces (7)(8)(9)(10)14).…”

“…Furthermore, plasmonic resonances in these structures can be tuned to the spectral regions of interest with high spatial reproducibility. Recently, enhanced absorption signals have been observed from individual nanoantennas (8,(11)(12)(13). However, surprising new phenomena arise as a result of the collective resonant excitation of the nanoantenna ensembles.…”

Surface plasmonic contribution to SEIRA and asymmetrical band

“…Presuming that the cause of an asymmetrical band is not the Fano effect, it is necessary to consider what caused the asymmetrical band. At present, generally an asymmetrical band is thought to originate in Surface Plasmon (SP) [12,36]. SP is collective oscillation of the free-electron localized in the surface.…”