In this work the long-term antibacterial activity of silver doped titania coatings is studied systematically as a function of the titania layer structure (with and without molecular template) and the amount and physical properties of the silver dopant. Silver was incorporated in two different ways into the titania sol-gel films, either by co-deposition, i.e., adding the silver ions directly to the precursor sol of the layer or by postsynthetic impregnation of the mesoporous titania coating. The structure and morphology of the layers were investigated using transmission and scanning electron microscopy, whereas the silver content was determined by Rutherford backscattering spectrometry. Antibacterial properties against Escherichia coli bacteria were studied by colony forming unit assay and agar diffusion method. It was found that directly after preparation, all composite coatings show antibacterial activity both in the dark and under visible light illumination. The antibacterial activity of the co-deposited samples vanished after the first use despite their high and constant remaining silver content (2.597 at%). This type of coating was not effective in agar diffusion tests at all. The antibacterial activity of the impregnated coatings with lower silver contents (0.596 at% and 1.961 at%), however, showed long-lasting antibacterial effect both in the colony forming unit assay and in agar diffusion tests as well. This can be attributed to the fact that the silver content is distributed over the mesoporous network of the titania coating and is effective during the long-term tests. Fig. 2 Toluene adsorption-desorption isotherms at 294 K and normalized pore radius distribution of (a and b) TiO 2 , (c and d) pTiO 2 , and (e and f) TiO 2 -AgNO 3 type titania coatings determined by ellipsometric porosimetry.This journal is

Porous silicon layers were prepared by electrochemical etching of p-type single-crystal Si (c-Si) of varying dopant concentration resulting in gradually changing morphology and nanocrystal (wall) sizes in the range of 2–25nm. We used the model dielectric function (MDF) of Adachi to characterize these porous silicon thin films of systematically changing nanocrystal size. In the optical model both the surface and interface roughnesses have to be taken into account, and the E0, E1, and E2 critical point (CP) features are all described by a combination of several lineshapes (two-dimensional CP, excitonic, damped harmonic oscillator). This results in using numerous parameters, so the number of fitted parameters were reduced by parameter coupling and neglecting insensitive parameters. Because of the large number of fitted parameters, cross correlations have to be investigated thoroughly. The broadening parameters of the interband transitions in the measured photon energy range correlate with the long-range order in the crystal. The advantage of this method over the robust and simple effective medium approximation (EMA) using a composition of voids and c-Si with a nanocrystalline Si reference [Petrik et al., Appl. Surf. Sci. 253, 200 (2006)] is that the combined EMA+MDF multilayer method of this work provides a more detailed description of the material and layer structure.

The optical properties of p-type, n-type and nominally undoped (Al x Ga! -Jyln! _ y P layers have been determined in a wide spectral range. The layers under study have been chosen with compositions and dopant concentrations which make them interesting for their use in III-V multijunction solar cells. The layers have been measured by variable angle spectroscopic ellipsometry and, irrespective of composition and doping, their optical response has been modelled using the same model dielectric function consisting of two asymmetric Tauc-Lorentz oscillators and a 3D-M 0 Adachi term. The results show that transition energy values change with layer composition, whilst for layers of the same material (i.e. GalnP or AllnP), the band-gap transition energy E 0 shows a strong dependence on the order parameter. The refractive indexes and extinction coefficients deduced from the ellipsometric data have been used to fit reflectance measurements for the same layers and an excellent agreement has been achieved, thus validating the model dielectric function proposed for this kind of materials.

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