Optically monitored wet‐chemical preparation of SEIRA active Au nanostructures

Abstract

The growth process of spherical substrate-bound Au nanoparticles (AuNP) was investigated with in situ visible (VIS) spectroscopy, in situ Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM). In the VIS spectra, the redshift and broadening of the AuNP's surface plasmon resonance could be observed, as the size of the AuNP increased. FTIR spectra showed the increasing IR absorption of the surrounding water molecules because of the surface-enhanced infrared absorption (SEIRA), as well as plasmon absorption. IR spectra of adsorbates were further used to compare the SEIRA activity of the resulting Au films.

Plasmons in nanoscale and atomic-scale systems

“…Also, nanofilms with a random morphology and high surface roughness provide extremely high enhancement of optical absorption by molecular vibrations in a broad spectral range [13,14,[71][72][73][74]. This phenomenon has been known since the discovery of SEIRA in the early 1980s and has recently achieved worldwide success because the broadband plasmon resonance matches the absorption band of the molecular analytes.…”

“…This phenomenon has been known since the discovery of SEIRA in the early 1980s and has recently achieved worldwide success because the broadband plasmon resonance matches the absorption band of the molecular analytes. Vacuum deposition is a conventional preparation method of these analytes, although wet-chemical deposition has recently been developed as a quick and inexpensive method for fabricating high-sensitivity SEIRA films [13,14,75]. These films are more convenient for enhanced vibrational spectroscopy compared with chip-based sensor devices fabricated by lithography.…”

“…First, the nanoparticles are adsorbed and immobilized onto an aminosilane-treated substrate via Langmuir kinetics to form a submonolayer-saturated film [76][77][78]. Then gold nanoparticles are produced by electroless deposition [13,14]. As the islands grow, they interconnect and spread laterally.…”

“…As shown in figure 10(a), the absorption intensity from a single monolayer of octadecanthiol is high as 16.5% for a near-percolated Au film. This value is one order of magnitude larger than that of the spherical Au nanoparticles and two orders of magnitude larger than that of the flat Au surface [13,14]. …”

“…We present results obtained from both top-down lithographically fabricated micro/nanostructures as well as bottom-up self-assembled nanoscale and atom-scale structures. For example, lithographically fabricated nanorod and nanoparticle antennas as well as gap-tuned random nanoislands have been successfully adopted to optimize the enhancement of vibrational signals by tuning the structural parameters [12][13][14]. Even in atom-scale metallic objects, such as atomic sheets and atomic wires, plasmons can be confined and can propagate [15][16][17]; moreover, they can exhibit standing-wave antenna resonance [15].…”