Thin films composed of Ag nanoclusters dispersed in TiO2: Influence of composition and thermal annealing on the microstructure and physical responses

Abstract

Thin films composed of Ag nanoclusters dispersed in TiO 2 : influence of composition and thermal annealing on the microstructure and physical responses, Applied Surface Science (2015), http://dx.doi.org/10.1016/j.apsusc. 2015.08.148 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Ag fractals formed on top of a porous TiO2 thin film

“…Furthermore, the same annealed sample shows a significant drop in the transmittance spectrum in the infrared region (1200–2500 nm), a clear evidence of a significant increase on its opacity and absorbing nature. Anyway, the semi‐transparent character of the as‐deposited sample was actually expected taking into account some recent studies of the group . The reflectance spectrum also reveals the signature of the onset of interband transition involving d‐electrons in Ag , clearly visible for a wavelength value close to 320 nm.…”

“…The preparation of the thin films was carried out in two steps, where the first corresponded to their preparation by reactive DC magnetron sputtering, without external heating . A titanium target (200 × 100 × 6 mm 3 , 99.8% purity), containing Ag ”pellets” placed on its preferred erosion zone, was sputtered by applying a current density of 100 Am –2 , in an Ar/O 2 (partial pressure ratio: 7/1) plasma atmosphere (working pressure: 4.5 × 10 –1 Pa), during 90 min.…”

“…However, the reflectance is far below the unit for both as‐deposited and annealed samples, which might result from two main reasons: (i) non‐specular scattering and (ii) discontinuity of the metallic structure, i.e., its fractal geometry. Well defined shapes of Ag clusters would manifest themselves by their characteristic spectral features, for instance, spherical NPs (not too small) would show LSPR close to 400 nm , which would be split into two distinct resonances in nanorods. Fractal aggregates incorporate a plenitude of shapes and spatial scales and therefore their spectral response is very broad and almost featureless, as predicted theoretically and shown experimentally for specially prepared agglomerates of Ag NPs .…”

“…The XRD analysis of the films was performed in a Bruker D8 Discover, using copper radiation (Cu K α ) in grazing incidence mode ( ϑ = 2°). The as‐deposited sample is amorphous , but as soon as it is subjected to annealing treatment, the Ag diffusion throughout the host matrix occurs, and crystalline Ag domains are formed . The Ag clusters crystallized in a face centered cubic (fcc) structure (COD card No.…”

“…In a previous work, X‐ray photoelectron spectroscopy (XPS) analysis was performed in Ag:TiO 2 films, and from those results it was possible to claim that Ag surface is most probably oxidized (see Ref. ). This conclusion is based on the negative shift (Δ E = –0.37 eV) observed for the Ag‐3d 5/2 peak, in comparison to metallic silver (368.27 eV) .…”