Abstract
We fabricated self-assembled silver nanoisland films using a recently developed technique based on out-diffusion of silver from an ion-exchanged glass substrate in reducing atmosphere. We demonstrate that the position of the surface plasmon resonance of the films depends on the conditions of the film growth. The resonance can be gradually shifted up to 100 nm towards longer wavelengths by using atomic layer deposition of titania, from 3 to 100 nm in thickness, upon the film. Examination of the nanoisland films in surface-enhanced Raman spectrometry showed that, in spite of a drop of the surface-enhanced Raman spectroscopy (SERS) signal after the titania spacer deposition, the Raman signal can be observed with spacers up to 7 nm in thickness. Denser nanoisland films show slower decay of the SERS signal with the increase in spacer thickness.PACS78.67.Sc (nanoaggregates; nanocomposites); 81.16.Dn (self-assembly); 74.25.nd (Raman and optical spectroscopy)
Highlights
Metal island films (MIFs) have attracted significant attention due to the strong surface plasmon resonance (SPR) effect in these nanoislands
Structure and optical absorption of initial MIF atomic force microscope (AFM) studies of silver out-diffusion (SOD) MIF samples allowed concluding that depending on the mode of SOD we can fabricate MIFs consisting of tiny, nearly isolated silver nanoislands (Figure 1a), bigger islands which can be placed very closely (Figure 1b), and partly coagulated nanoislands (Figure 1c)
The performed studies demonstrate that silver nanoisland films formed using out-diffusion of silver from glass substrates during thermal processing in hydrogen atmosphere can be effectively used in SERS measurements
Summary
Metal island films (MIFs) have attracted significant attention due to the strong surface plasmon resonance (SPR) effect in these nanoislands. The main reason for this intensity enhancement is the electromagnetic (EM) enhancement mechanism prevailing over the chemical enhancement (CHEM) by several orders of magnitude [3]. This is because the EM enhancement is proportional to about the forth power of the SPR-increased local electric field input in Raman scattering, i.e., in the analyzed media adsorbed difference in metal nanoislands and nanoparticles used in the experiment, these results can hardly be compared, and they contradict the data obtained in SERS experiments using MIFs covered with non-ALD spacers [14]. It is worth to note that dielectric-capped isolated metal nanospheres have already demonstrated their effective applicability in photovoltaics [15] and SERS [16]
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