D. Garoli

Nanoporous gold plasmonic structures for sensing applications

The fabrication, characterization and functionalization of periodically patterned nanoporous gold layers is presented. The material shows plasmonic properties in the near infrared range, with excitation and propagation of surface plasmon polaritons. Functionalization shows a marked enhancement in the optical response in comparison with evaporated gold gratings, due to a great increase of the active surface. Due to its superior response, nanoporous gold patterns appear promising for the realization of compact plasmonic platforms for sensing purposes.

Sunscreen tests: Correspondence between in vitro data and values reported by the manufacturers

BACKGROUNDnIn vitro sunscreen tests are diffusively used to test both the sun protection factor (SPF) and the photo-stability of filters. Spectrophotometric measurements of the absorbance of ultraviolet radiations through a sunscreen applied on a suitable substrate allow a rapid evaluation of its protection factor both at short and long wavelength ultraviolet radiation (UVB and UVA).nnnOBJECTIVESnThe objective of this study has been to demonstrate if Teflon can be adopted as substrate both for SPF evaluation and photo-stability tests. Moreover, we have investigated if there is a correspondence between in vitro SPF measurements and values reported by manufacturers on sunscreens.nnnMATERIAL AND METHODSnTeflon has been used to perform several photo-stability tests by irradiating the filters with different wavebands and analyzing the combined effect of UV and infrared (IR) light. Similar analyses have been carried out using PMMA Plates, which is the standard substrate for UVA in vitro test.nnnRESULTSnWe have demonstrated that it is possible to establish a good correspondence between in vitro SPF and values reported by manufacturers on sunscreens. We have also verified that the in vitro/label SPF correlation curve depends on the quantity of product applied while this does not seem to be true for other parameters like Critical Wavelength and UVA ratio. With regard to photo-stability studies, our results indicate for the first time that IR irradiation may have a role on photo-degradation.nnnCONCLUSIONSnThe results show that there is a good correlation between the in vitro SPF determined by the present method and the SPF reported by the manufacturer. The compatibility of the results obtained using Teflon and PMMA Plates demonstrates that Teflon can be utilized for both SPF determination and photo-stability tests.

Effectiveness of different substrate materials for in vitro sunscreen tests.

BACKGROUNDnIn vitro measurements of sunscreen products are used to assess their reliability in terms of photoprotection and photo-stability.nnnOBJECTIVEnIn this study, several substrates have been fully characterized for in vitro sunscreen testing.nnnMETHODSnThe following different substrates have been utilised in the study: roughened PMMA plates, Transpore, Vitro-Skin, roughened quartz plate and a laboratory prepared roughened PTFE plate. The suitability of these substrates for SPF evaluation has been investigated by performing total absorbance measurements of seven sunscreen products with different SPF values produced by the same manufacturer.nnnRESULTS AND CONCLUSIONSnApplication of sunscreen products on Transpore, roughened quartz plate, PMMA, PTFE and Vitro-Skin was performed efficiently. With regard to photo-stability of the substrate materials, only PMMA plate, PTFE and roughened quartz plate showed to be photo-stable after UV irradiation. With regard to SPF tests, our results indicate that Transpore, roughened quartz plate and Vitro-Skin are preferable to assess SPF values because of a better correlation between in vitro and in vivo measurements. Our study also confirms that an initial calibration must be performed for sunscreen products labelled with different SPF values. Finally, the results of our measurements demonstrate that, although a correlation between in vitro and in vivo SPF results can be established, it is never exactly 1:1.

In vitro evaluation of sunscreens: an update for the clinicians.

Topical sunscreens contain molecules or molecular complexes that can absorb, reflect, or scatter UV photons. Evaluation of the efficacy of sunscreen products has been made through the Sun Protection Factor (SPF), a mean of quantitatively assessing in vivo the degree of protection offered by sunscreen products against solar radiation. In vivo evaluation of SPF has several drawbacks. First of all, this evaluation method is expensive in terms of money and time. Moreover, it raises several ethical issues concerning the potential damage to skin volunteers. Several in vitro techniques have been developed, but at present there is no broadly accepted method. In this paper, we will discuss some of the recent advances concerning the in vitro evaluation of sunscreens which would be acceptable for replacing in vivo assays.

Reflectance measurements and optical constants in the extreme ultraviolet-vacuum ultraviolet regions for SiC with a different C/Si ratio

Reflectance versus incidence angle measurements have been performed from 5 to 152 nm on samples of SiC with a different C/Si ratio deposited with rf magnetron sputtering. The optical constants of the material at different wavelengths have been determined by using a curve-fitting technique of reflectance values versus incidence angle. Complementary measurements of the incident beam polarization, film thickness, surface roughness, and stoichiometry were performed to complete the analysis of the samples.

Extraordinary optical transmission in one-dimensional gold gratings: near- and far-field analysis

One-dimensional arrays of nanoslits fabricated on silicon nitride membranes show extraordinary optical transmission. Optical characterization techniques have been used to characterize the transmission spectra and the near-field optical configuration. Experimental results have been compared with numerical simulations in order to elucidate the different modes of light propagation. Near- and far-field optical distribution is studied as a function of the polarization of light.

Optical constants in the EUV soft x-ray (5÷152 nm) spectral range of B4C thin films deposited by different deposition techniques

B4C optical coating represents, together with Ir, Pt, SiC, one of best choice for high reflectance in the extreme ultraviolet region (EUV 160-30 nm). This material is also used in multilayer for soft X-ray applications, such as Si/B4C or W/B4C, or as interlayer in Mo/Si multilayer to avoid interdiffusion also because of its high thermal stability. Our work concerns on B4C thin films deposited on Si [100] substrates by means of three different deposition techniques: RF plasma magnetron sputtering, e-beam evaporation, pulsed laser ablation (PLD). We performed reflectance vs incidence angle measurements from 5 nm to 152 nm on different samples deriving the optical constants with a least-square fitting method. Complete films characterization have been carried out with compositional (XPS), structural (XRD) and morphological (AFM, SEM) analyses.

Sub-wavelength confinement of the orbital angular momentum of light probed by plasmonic nanorods resonances

We discuss how the topological charge of an OAM-carrying plasmon (Plasmonic Vortex) can be probed by monitoring the near-field response of plasmonic nanostructures suitably arranged inside a Plasmonic Vortex Lens. The turning on or off of four gold nanorods, detected by a Scanning Near field Optical Microscope (SNOM), acts as a fingerprint of the OAM state of the PV at the nanoscale. Different configurations are studied numerically, the integrated structure is fabricated and near field characterization is performed for a particularly meaningful case.

Space applications of Si/B4C multilayer coatings at extreme ultra-violet region; comparison with standard Mo/Si coatings

In the extreme ultra-violet region, multilayer coatings are the only technique to obtain high reflectivity in normal incidence optical configurations. The interference process which regulates periodic multilayers behavior offers narrow-band spectral filtering without the use of additional filters, fact that makes these coatings particularly suitable for lines emission observations. Despite the large amount of possible materials combinations, Mo/Si multilayers are the standard choice for space research on plasma physics in the 13 - 30 nm spectral region. In this work Si/B4C is presented as an alternative material couple for the 30.4 nm selection. Attractive features are the better spectral purity and the second order reflectivity reduction. A possible application to the Sounding CORonagraph Experiment is described as an example. B4C thin films have been used to characterize this material in terms of optical constants in the 40 nm - 150 nm spectral region where, currently, only few data are available.

Wedge nanostructures for plasmonic nanofocusing

We report numerical and experimental results on the optical response of transparent metal coated wedges arrays for plasmonic nanofocusing. Light normally impinging from the dielectric side is coupled to Surface Plasmon Polaritons (SPPs) at the oblique metal-air interfaces. A dielectric phase shifter has been implemented in the structure in order to allow constructive interference of SPPs at the wedge apex. Finite Elements simulations were used to design the system. Focused Ion Beam (FIB) milling, chemical etching and replica molding were used for the fabrication. NSOM and Raman measurements demonstrate that plasmonic nanofocusing actually takes place in the structure.