Photochromic polyurethanes showing a strong change of transparency and refractive index

Photochromic polymers have been studied as rewritable systems for optical elements with tunable transparency in the visible and refractive index in the NIR. Six diarylethene monomers have been synthesized to give thin films of photochromic polyurethanes. The absorption properties of the monomers in solution and of the corresponding polymeric films have been evaluated showing that a transparency contrast in the visible spectrum of the order of 103can be obtained by a suitable choice of the chemical structure and illumination wavelength. The change in the refractive index in the NIR have been determined by ellipsometry showing changes larger than 10-2. A trend of this variation with the absorption properties has been also highlighted. Fresnel lenses working on the basis of both a change of the transparency and the refractive index (amplitude and phase) have been demonstrated

Structural and electronic properties of anisotropic ultrathin organic films from dichroic resonant soft x-ray reflectivity

We developed a quantitative approach for the determination of molecular arrangement and electronic structure in anisotropic organic ultrathin films based on the measurement of polarized reflectivity at the carbon K-edge. The reflectivity spectra were fitted to a parameterized model calculation. The method was applied to a self-assembled monolayer of 1,4-benzenedimethanethiol on gold. To simulate reflectivity, the organic anisotropic film was described by a dielectric tensor, obtained by ab initio calculations for the single molecule and suitable rotations to describe the molecular organization in film domains. Film structure was obtained though the best fit of the simulation to the experiment. Results were consistent with a monolayer-thick film composed of domains of molecules with in-plane isotropic distribution of orientations. In each domain, molecules adopted a standing configuration, with a tilt of 28° relative to the substrate normal. Information on the modification of the molecular electronic states due to chemical bonding was derived

Fabrication of Gold-Coated Ultra-Thin Anodic Porous Alumina Substrates for Augmented SERS

Anodic porous alumina (APA) is a nanostructured material used as a template in several nanotechnological applications. We propose the use of APA in ultra-thin form (<100 nm) for augmented surface-enhanced Raman scattering (SERS). Here, the effect of in-depth thinning of the APA nanostructures for possible maximization of SERS was addressed. Anodization was carried out on ultra-thin films of aluminum on glass and/or silicon, followed by pore-opening. Gold (Au) was overcoated and micro‑Raman/SERS measurements were carried out on test target analytes. Finite integration technique simulations of the APA-Au substrate were used both for the experimental design and simulations. It was observed that, under optimized conditions of APA and Au thickness, the SERS enhancement is higher than on standard APA-Au substrates based on thin (~100 nm) APA by up to a factor of ~20 for test molecules of mercaptobenzoic acid. The agreement between model and experimental results confirms the current understanding of SERS as being mainly due to the physical origin of plasmon resonances. The reported results represent one step towards micro-technological, integrated, disposable, high-sensitivity SERS chemical sensors and biosensors based on similar substrates

Yeast Cytochrome c adsorption on SiO2/Si substrates studied by in situ spectroscopic ellipsometry

none4Chiara Toccafondi;Ornella Cavalleri;Francesco Bisio;Maurizio CanepaToccafondi, Chiara; Cavalleri, Ornella; Bisio, Francesco; Canepa, Maurizi

Fabrication of Gold-Coated Ultra-Thin Anodic Porous Alumina Substrates for Augmented SERS

Anodic porous alumina (APA) is a nanostructured material used as a template in several nanotechnological applications. We propose the use of APA in ultra-thin form (<100 nm) for augmented surface-enhanced Raman scattering (SERS). Here, the effect of in-depth thinning of the APA nanostructures for possible maximization of SERS was addressed. Anodization was carried out on ultra-thin films of aluminum on glass and/or silicon, followed by pore-opening. Gold (Au) was overcoated and micro‑Raman/SERS measurements were carried out on test target analytes. Finite integration technique simulations of the APA-Au substrate were used both for the experimental design and simulations. It was observed that, under optimized conditions of APA and Au thickness, the SERS enhancement is higher than on standard APA-Au substrates based on thin (~100 nm) APA by up to a factor of ~20 for test molecules of mercaptobenzoic acid. The agreement between model and experimental results confirms the current understanding of SERS as being mainly due to the physical origin of plasmon resonances. The reported results represent one step towards micro-technological, integrated, disposable, high-sensitivity SERS chemical sensors and biosensors based on similar substrates

Biomedical applications of anodic porous alumina

In the last decade, the number of possible biological and biomedical applications suggested in the literature for anodic porous alumina has increased significantly. Here we shortly review the existing literature and show the most recent and successful directions taken by research in this area. In particular, the use of anodic porous alumina as a substrate for bioassays or biosensing in living cells, mostly based on surface-enhanced Raman scattering, seems to be promising

Photochromic and photomechanical responses of an amorphous diarylethene-based polymer: a spectroscopic ellipsometry investigation of ultrathin films

This work deals with very thin (14-40 nm) films of a polyester containing diarylethene units in the main chain spin cast on a silicon wafer. By irradiation with UV light the colourless form turns blue due to the appearance of a strong absorption band centred at about 600 nm. The coloured state is thermally stable and the backward conversion can be triggered with visible light. Comparison of broadband (245-1700 nm) spectroscopic ellipsometry data with simulations based on an isotropic, Kramers???Kronig consistent, multiple-resonance model allowed us to determine the complex index of refraction n of the film in its blue and colourless forms. The refractive index of the blue phase neatly exceeds that of the transparent form for wavelengths in the NIR. In particular, out of resonance, at lambda 1700 nm, DeltaRe(n) 0.05. Parallel to the DeltaRe(n) increase, the analysis of ellipsometry data suggests a decrease of the film thickness (about 1.5%) during the transition from the open (transparent) to the closed (coloured) form