Absorption spectroscopy of gold nanoisland films: optical and structural characterization

Abstract

Nanoisland films prepared by annealing thin gold films at high temperatures were imaged using scanning electron microscopy (SEM) and atomic force microscopy, and optically characterized through absorption spectroscopy. Thin gold films of effective thicknesses 2, 5 and 7 nm annealed at 500, 700 and 900 degrees C were fabricated and studied experimentally. The measured absorption characteristics in support of theoretical calculations showed that the shapes of gold islands were partial spheres. The position of the peak absorption wavelength measured with s-polarized light or at normal incidence confirmed that the island shape grew from a near-hemisphere towards a sphere with increasing annealing temperature. The SEM images confirmed that the size of islands increased from 15 nm in diameter to 40 nm in diameter as film thickness increased from 2 to 5 nm. The affect of the index of the substrate material on absorption characteristics were also studied by comparing the absorption spectra of gold island films on quartz and LaSF15 glass substrates. The use of gold nanoisland films for preparing localized surface plasmon resonance substrates was suggested as they held advantages over the gold colloid films.

Optical Properties of Gold Nanoparticle Assemblies on a Glass Surface

“…Obviously, the shape of dimers and aggregates that differs from spherical can be the reason for shifting of plasmon resonances. Similar shifting of plasmon resonances in both red and blue wavelength directions in dependence on the changing of the nanoparticle shape was observed earlier [52].

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Reduced photoconductivity observed by time-resolved terahertz spectroscopy in metal nanofilms with and without adhesion layers

“…The 8nmAu spectrum contains two prominent absorption regions; one at wavelengths below ~ 500 nm from interband electronic transitions (d-band to s/p band above the Fermi level), the other between ~ 500 nm to the NIR from an intraband transition that excites the metallic electrically conductive electrons of the s/p band (surface plasmon resonance, SPR). 15–17 This is consistent with previously published spectra for a high electrical conductivity gold film at a thickness greater than the percolation limit. 18,19 Less information has been published about the optical properties of titanium nanofilms, but the absorbance spectrum of 8nmTi is qualitatively similar.…”

Excitation of multiple dipole surface plasmon resonances in spherical silver nanoparticles

“…The absorption band can therefore be attributed to a dipole LSPR, red-shifted from the calculated value due to the presence of the substrate, interactions between the NPs, and the deviation of the NP shape from a perfect sphere. 22,23 The absence of any further absorption bands is expected for Ag NPs of this size, and indicates that no higher order LSPR modes are excited. 24 The absorption spectra of thin-films consisting of the Ag NP layer covered by 6 to 30 nm of SubPc are shown in Fig.…”