The use of efficient wavelength-shifters from the vacuum-ultraviolet to the photosensor's range of sensitivity is a key feature in detectors for Dark Matter search and neutrino physics based on liquid argon scintillation detection. Thin film of Tetraphenyl-butadiene (TPB) deposited onto the surface delimiting the active volume of the detector and/or onto the photosensor optical window is the most common solution in current and planned experiments. Detector design and response can be evaluated and correctly simulated only when the properties of the optical system in use (TPB film + substrate) are fully understood. Characterization of the optical system requires specific, sometimes sophisticated optical methodologies. In this paper the main features of TPB coatings on different, commonly used substrates is reported, as a result of two independent campaigns of measurements at the specialized optical metrology labs of ENEA and University of Tor Vergata. Measured features include TPB emission spectra with lineshape and relative intensity variation recorded as a function of the film thickness and for the first time down to LAr temperature, as well as optical reflectance and transmittance spectra of the TPB coated substrates in the wavelength range of the TPB emission.

We present a Bell-type polarization experiment using two independent sources of polarized optical photons, and detecting the temporal coincidence of pairs of uncorrelated photons which have never been entangled in the apparatus. Very simply, our measurements have tested the quantummechanical equivalent of the classical Malus' law on an incoherent beam of polarized photons obtained from two separate and independent laser sources greatly reduced in intensities.The outcome of the experiment gives evidence of violation of the Bell-like inequalities. Drawing the conclusions of the present work, we invoke the distinction between the concepts of state-preparation and measurement to understand this result.

The fascinating properties of two dimensional (2D) crystals have gained increasing interest for many applications. In this regard, the synthesis of a 2D silicon structure, namely silicene, is attracting great interest for possible development of next generation micro-and nano-electronic devices. The main difficulty in working with silicene remains its strong tendency to oxidation when exposed to air as a consequence of its relatively highly buckled structure. In this work, we univocally identify the Raman mode of air-stable low-buckled silicene nanosheets synthesized on highly oriented pyrolytic graphite (HOPG) located at 542.5 cm-1. The main focus of this work is Raman spectroscopy and mapping analyses in combination with ab initio calculations. Scanning tunneling microscopy images reveal the presence of a patchwork of Si three-dimensional (3D) islands and contiguous Si areas presenting a honeycomb atomic arrangement, rotated by 30° with respect to the HOPG substrate underneath, with a lattice parameter of 0.41 ± 0.02 nm and a buckling of the Si atoms of 0.05 nm. Raman analysis supports the coexistence of 3D silicon clusters and 2D silicene structures. The Raman shift of low-buckled silicene on an inert substrate has not been reported so far and it is completely different from both; the one calculated for freestanding silicene and the experimental ones measured for silicene grown on Ag(111) surfaces. Our experimental results are perfectly reproduced by our ab initio calculations of silicene nanosheets. This leads us to the conclusion that the precise value of the observed Raman shift crucially depends on the strain induced between the silicene nanosheets and the graphite substrate.

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