Thin films composed of Au nanoparticles embedded in AlN: Influence of metal concentration and thermal annealing on the LSPR band

doi:10.1016/j.vacuum.2018.09.013

Vacuum

Volume 157, November 2018, Pages 414-421

https://doi.org/10.1016/j.vacuum.2018.09.013 Get rights and content

Highlights

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Nanocomposite films containing Au dispersed in AlN were deposited by sputtering.
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Au nanoparticles growth was promoted by thermal annealing.
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Au nanoparticles dispersed in the AlN matrix induced plasmonic responses.
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LSPR bands appeared at 500 °C, positioned in the range 520–540 nm.

Abstract

Nanocomposite thin films, with noble nanoparticles dispersed in a dielectric matrix, are known to present unique optical properties. Based on the Localized Surface Plasmon Resonance (LSPR) phenomenon, these “nanoplasmonic” materials are the basis of a wide range of technological applications, namely (bio)molecular LSPR-sensors. They are regulated by the concentration, size, shape and distribution of the nanoparticles and dielectric environment properties. In this work, the possibility of using aluminium nitride (AlN) as a host dielectric matrix for LSPR films was evaluated. For this purpose, nanocomposite Au:AlN films were prepared by magnetron sputtering, followed by thermal annealing to promote the growth of the nanoparticles. Three sets of films were deposited with atomic Au concentrations of 2.2, 4.4 and 6.0 at.%. LSPR bands appeared from the temperature of 500 °C, with resonance positions of 520–540 nm. The films showed potential to be tested in LSPR-sensing applications due to their optical responses.

Graphical abstract

Introduction

Nanocomposite materials containing plasmonic metallic nanoparticles, such as Au or Ag, dispersed in a dielectric matrix have been receiving special attention in several areas of science and technology [[1], [2], [3], [4], [5], [6], [7], [8]]. Most of the applications are based on the Localized Surface Plasmon Resonance (LSPR) phenomenon, which arise from the interaction of the noble nanoparticles with an incident electromagnetic field [9], resulting in charge density oscillations confined in the metallic nanoparticles. This effect can give rise to strong absorption bands and the enhancement of the electromagnetic field near the nanoparticles [[10], [11], [12], [13], [14]]. Due to these unique optical properties, nanoplasmonic materials have been widely studied [[15], [16], [17], [18], [19], [20], [21], [22]]. Furthermore, their optical responses can be tailored by geometric characteristics (size, shape and distribution) of the nanoparticles and dielectric properties of the host matrix, presenting tuneable LSPR bands within the visible range. For that reason, this type of plasmonic thin films are being designed and produced to be used in a wide range of technological applications [[23], [24], [25], [26], [27], [28], [29]], particularly in plasmonic sensing such as the detection of gas molecules and biological agents [[30], [31], [32]].

In recent works, it was shown that the production of Au:TiO₂ films by reactive magnetron sputtering (using a composite Ti-Au target) followed by post-deposition heat-treatment is a straightforward way to obtain nanoplasmonic thin films, where Au nanoparticles are embedded in the TiO₂ matrix [5,22,33]. It was possible to obtain well defined Transmittance LSPR (T-LSPR) bands, associated to Au nanoparticles’ growth and coalescence, highly dependent of the deposition conditions and heat treatment temperatures [9,22,[33], [34], [35], [36], [37], [38]].

Envisaging the development of optical sensors based on LSPR effect, different sets of nanoplasmonic Au:AlN films, with variable Au concentrations, were prepared using a similar experimental procedure as the Au:TiO₂ system The plasmonic metal concentration and annealing temperature were both changed in order to study their influence on the structural and morphological properties of the films. The chemical composition and structural changes (induced by thermal annealing at different temperatures) were then correlated with the optical response (transmittance and reflectance) and LSPR behaviour of the films.

Section snippets

Experimental details

The different sets of Au:AlN films were prepared by reactive DC magnetron sputtering using an aluminium target (200 × 100 × 6 mm³) with 99.8% purity. Small Au disks (pellets) with 99.99% purity, each one with surface area of 16 mm² and 0.5 mm thick, were symmetrically placed on the preferential erosion zone of the Al target. In order to increment the atomic concentration of the noble metal in the matrix, the films were deposited with three different fluxes of sputtered Au atoms, by simply

Deposition rate

The deposition process depends on several factors (applied current, working and reactive gas partial pressures, etc.) that can influence the deposition kinetics and, consequently, the characteristics and properties of the thin films produced [39,[42], [43], [44], [45]]. In this particular case it is of primordial importance to understand the influence of the area of the Au pellets in the evolution of the deposition (growth) rate of the films. The results are plotted in Fig. 2.

The deposition

Conclusions

In order to study the influence of Au concentration and annealing temperature on the structure, morphology and optical behaviour of Au:AlN nanoplasmonic thin films, three different sets of films were prepared. The films were deposited by reactive DC magnetron sputtering using an aluminium target with small Au pellets on its preferential erosion zone and posteriorly submitted to in-air thermal treatments at different temperatures.

Regarding the characteristics of the deposition process, the

Conflicts of interest

The authors certify that there is no conflict of interest regarding this study.

Acknowledgements

This work is financed by National Funds through FCT - Portuguese National Funding Agency for Science, Research and Technology, in the framework of the project PTDC/FIS-NAN/1154/2014 (FCT Projet 9471-RIDTI Reforçar a Investigação, o Desenvolvimento Tecnológico e a Inovação), co-financed by FEDER (POCI-01-0145-FEDER-016902). This research was also sponsored by FCT in the framework of the Strategic Funding UID/FIS/04650/2013. The authors also acknowledge project CICECO-Aveiro Institute of

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Thin films composed of Au nanoparticles embedded in AlN: Influence of metal concentration and thermal annealing on the LSPR band

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Experimental details

Deposition rate

Conclusions

Conflicts of interest

Acknowledgements

Mater. Lett.

Thin Solid Films

Compos. B Eng.

Thin Solid Films

Surf. Coating. Technol.

Surf. Coating. Technol.

Thin Solid Films

Vacuum

Appl. Surf. Sci.

Thin Solid Films

Thin Solid Films

Nucl. Instrum. Methods Phys. Res. Sect. B Beam Interact. Mater. Atoms

Appl. Surf. Sci.

Surf. Coating. Technol.

Electronic properties of gold thin films studied by electron energy loss spectroscopy

Gold Bull.

Electron-phonon coupling dynamics in very small (between 2 and 8 nm diameter) Au nanoparticles

J. Chem. Phys.

The incorporation of noble metal nanoparticles into host matrix thin films: synthesis characterisation and applications

J. Mater. Chem.

Optical properties and refractive index sensitivity of reactive sputtered oxide coatings with embedded Au clusters

J. Appl. Phys.

Broadband optical absorption caused by the plasmonic response of coalesced Au nanoparticles embedded in a TiO2 matrix

J. Phys. Chem. C

Interparticle coupling effect on the surface plasmon resonance of gold nanoparticles: from theory to applications

Chem. Rev.

Exploitation of localized surface plasmon resonance

Adv. Mater.

Advanced optical effective medium modeling for a single layer of polydisperse ellipsoidal nanoparticles embedded in a homogeneous dielectric medium: surface plasmon resonances

Phys. Rev. B Condens. Matter

Dispersion and damping of gold surface plasmon

Plasmonics

Theory of surface plasmons and surface-plasmon polaritons

Tuning of the surface plasmon resonance in TiO2/Au thin films grown by magnetron sputtering: the effect of thermal annealing

J. Appl. Phys.

Shape-controlled synthesis of gold and silver nanoparticles

Science