Continuous tuning of the plasmon resonance frequency of porous gold nanoparticles by mixed oxide layers
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Continuous tuning of the plasmon resonance frequency of porous gold nanoparticles by mixed oxide layers Laura Juhász1,2 · Bence Parditka1 · Péter Petrik3 · Csaba Cserháti1 · Zoltán Erdélyi1
© The Author(s) 2020
Abstract Porous gold nanoparticles (PGNs) are very popular due to their high surface/volume ratio, moreover they have stronger plasmonic properties than their solid counterparts. These properties make the porous gold nanoparticles very useful for lots of applications, for instance chemical sensors, cancer therapy applications. For applications, however, it is indispensable that the resonance frequency (RF) of a plasmonic structure to be tuneable. In this work we show that the RF can be set in a wide range as desired by coating the PGNs by mixed oxide layers. By changing the composition of the coating layer, that is the mixture ratio, the RF can be shifted practically continuously in a wide range determined by the refractive index of the used oxides. As a demonstration, PGNs were coated with mixed alumina-titania oxide layers (5–7 nm) using plasma-enhanced atomic layer deposition method. The oxide layer, beside as a tuning tool, also stabilises the structure of the PGNs when are exposed to elevated temperature. This is shown by the influence of the temperature (from 350 ◦ C up to 900 ◦ C ) on the morphology, and as a consequence the optical extinction spectra, of the oxide coated PGNs. Keywords Porous gold nanoparticle · Local surface plasmon resonance · Mixed oxide coating · Plasma enhanced atomic layer deposition · Tuning the plasmon resonance frequency
1 Introduction Surface Plasmon (SP)[1] resonance is a collective oscillation of conduction electrons excited by the electromagnetic field of light. In the case of metallic nanoparticles (NPs), the electron oscillations induced electric field around the NP opens the possibility to manipulate visible and near infrared light on the nanoscale[1, 2]. This property makes the NPs popular in a wide range of fields, including biomedical, energy, environment protection, sensing, information technology[1, 3] and even in analytical applications such as surface-enhanced Raman spectroscopy (SERS)[3, 4] which is based on the phenomenon of the largely increased Raman * Csaba Cserháti [email protected] 1
Department of Solid State Physics, Faculty of Science and Technology, University of Debrecen, P.O. Box 400, 4002 Debrecen, Hungary
2
Doctoral School of Physics, University of Debrecen, Egyetem sqr. 1, 4032 Debrecen, Hungary
3
Institute of Technical Physics and Materials Science, Centre for Energy Research, P.O.Box 49, 1525 Budapest, Hungary
scattering, accomplished by placing the investigated molecules on the surface of the NPs. Two kinds of optical excitations can occur: propagating surface plasmons and localized ones. Localized surface plasmons (LSP) are excited at metal-nanoparticle/dielectric interfaces[5, 6]. The resonance energy of these excitations are extremely sensitive to the composition, size, shape and the dielectric function o
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