Full Length ArticleClustering of gold particles in Au implanted CrN thin films: The effect on the SPR peak position
Graphical abstract
Introduction
Transition metal nitrides, such as chromium-nitride (CrN), have been widely studied in the past both from fundamental and technological point of view due to the attractive combination of physical and chemical properties [1], [2]. CrN coatings, depending on their microstructure, exhibit favorable corrosion and oxidation resistance, high hardness and wear behaviour [3], [4]. CrN is used as a coating material for corrosion resistance and in metal forming and plastic moulding applications [5]. Also, it is often used on medical implants and tools as well as a valuable component in advanced multicomponent coating systems, such as CrAlN [6]. Recent studies [7], [8], [9], [10] have indicated that the presence of carbon or additional transition metals (W, V, Nb, Al) may change the mechanical properties dramatically and enhance the hardness of CrN coatings. In particular, addition of soft metals such as Ag within the CrN matrix has been observed to result in substantial improvement of tribological properties of CrN coatings for both ambient and vacuum environments at high temperatures [11].
Nowadays, noble metal nanoparticles (NPs), such as gold, silver and copper nanoparticles have attracted interest, because of their unique photonic, electronic and catalytic properties [12], [13]. The origin of these unique properties is the surface plasmon resonance (SPR) effect, which corresponds to a collective excitation of the free electrons localized at the surfaces of metal structures [14], [15]. This strong absorption band, usually found in the UV–vis range, is governed by the noble metal NPs morphology, namely their size and shape, as well as of the dielectric function of the surrounding medium [13], [16]. Numerous works have been dedicated to researching nanocomposite materials, which consist of noble metal particles (Ag, Au) and dielectric matrices (SiO2, ZnO, TiO2) [17], [18], [19], the films being obtained by different methods, such as sol-gel, electrochemical methods, reactive magnetron co-sputtering and ion implantation. In contrast to this, only a few studies have been performed related to the formation of embedding metallic nanoparticles in non-dielectric matrices [20], [21]. Here, the efforts were mostly focused on studying the improvement of corrosion and antibacterial properties of these layers and very little is known about the dependence of the optical properties on the structural and morphological evolutions of these nanocomposites.
In various respects, the present work is an extension of our previous optical and microstructural analyses of CrN and TiN thin films irradiated with different ions (Ar+, Xe+ and Ag+) [21], [22], [23], [24]. It was shown that the optical properties of the Ar+ or Xe+-irradiated nitride thin films can be varied due to the formation of implantation induced damage, but no substantial changes of the optical constants were observed. In contrast to this, absorption properties of TiN layers irradiated with Ag ions exhibit a contribution by the SPR effect due to the presence of silver NPs. Led by these considerations, we have carried out a series of experiments, where the CrN layers were irradiated with 150 keV Au+ ions. The aim was to determine the complex dielectric function of Au+-irradiated CrN films based on experimental results by spectroscopic ellipsometry. The influence of ion fluence and particles (Ps) clustering on the optical response of Au particles was investigated.
Section snippets
Experimental
Optimal conditions for producing layers of stoichiometric CrN phase have been achieved using d.c. reactive sputtering by properly tuning the N2 pressure, deposition rate, as well as the CrN film thickness and substrate temperature. We used a Balzers Sputtron II system with Cr target of 99.9% purity, Ar for sputtering and reactive N2 gas. The base pressure in the chamber was around 1 × 10−4 Pa, the argon and nitrogen partial pressures during deposition were 1 × 10−1 Pa and 5 × 10−2 Pa, respectively. The
Structure and phase characterization
The elemental composition, measured by RBS on as deposited chromium-nitride layers under given deposition conditions, confirmed a homogeneous Cr and N concentration over the whole layers depth, with a Cr/N ratio ∼1. [25]. Starting from these results, we determined the evaluation of the Au depth distribution within CrN layers after 150 keV Au+ ions irradiation. Fig. 1a shows a typical RBS spectrum of a CrN film implanted with a nominal Au+ ion fluence of 3.2 × 1016 cm−2. It can be seen that the Au
Conclusions
Au particles were formed in CrN layers by using ion implantation process. The concentration of gold in the layers was varied by using different ion fluences from 2 × 1016 cm−2 to 4.1 × 1016 cm−2. The films revealed significant changes of the optical properties with regard to the complex dielectric function due to the contribution of a SPR peak, characteristic for Au particles. The shift of the peak position to longer wavelengths was attributed to the coalescence of Au Ps‘ and, moreover, to the Au
Acknowledgements
This work was supported by the Ministry of Education and Science of the Republic of Serbia (Project No. III 45005) and by the German-Serbian DAAD bilateral collaboration (Project No. 451-03-01038/2015-09118/18). We would like to thank Igor Peterka for his assistance at 500 kV ion implanter in Belgrade, and Ulrich Barth for his help during the RBS experiments in Jena.
References (41)
- et al.
A comparative study of CrNx coatings Synthesized by dc and pulsed dc magnetron sputtering
Thin Solid Films
(2009) - et al.
Cutting performance of CrN and Cr-Si–N coated end-mill deposited by hybrid coating system for ultra-high speed micro machining
Surf. Coat. Technol
(2008) - et al.
Surface treatment selections for automotive applications
Surf. Coat. Tehnol.
(2005) - et al.
Investigation of the properties of Al1-xCrxN coatings prepared by cathodic arc evaporation
Surf. Coat. Tehnol.
(2005) - et al.
Tribological enhancement of CrN coatings by niobium and carbon ion implantation
Surf. Coat. Tehnol.
(2004) - et al.
The effects of MEVVA ion implantation on the tribological properties of PVD-TiN films deposited on steel substrates
Surf. Coat. Tehnol.
(2002) - et al.
Tribological property enhancement of CrN films by metal vapor vacuum arc implantation of Vanadium and Carbon ions
Thin Solid Films
(2008) - et al.
Thermal stability of Al–Cr–N hard coatings
Scripta Mater.
(2006) - et al.
CrN–Ag nanocomposite coatings: Tribology at room temperature and during a temperature ramp
Surf. Coat. Technol
(2010) - et al.
Nanoparticle plasmonics: going practical with transition metal nitrides
Mater. Today
(2015)