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Hypogenic caves, developed by sulphuric acid speleogenesis, are known all over the world among which the Santa Cesarea Terme caves have been included. They are four submerged caves, located along a coastal carbonate sector in Southern Italy and hosting the outflow of coastal springs of thermal mixed waters (from 21 to 33 °C). These waters derive from the mixing of three water end members: the fresh pure groundwater of a wide karstic aquifer, the deep sulphur thermal water and the seawater. This cave system represents an almost unique case of hypogenic sea caves in carbonate environment. The thermal mixed waters have a different effect on the surrounding rocks of the caves, influencing the sulphuric acid speleogenetic process within the whole cave system. To understand the complex and overlapping natural processes acting on the development of these coastal caves, a multidisciplinary study has been carried out. This study has integrated all the data resulting from different methods and technologies, merging morphology, structural geology, hydrogeology, hydrogeochemistry and mineralogy. This multidisciplinary study has allowed to define the main geochemical processes acting within these caves, including the cave development and the formation of the mineral concretions. After the introduction of H2S in the thermal waters, formed by the reduction of sulphates in the sedimentary deposits crossed at depth in the offshore, the oxidation occurs within the caves, producing sulphuric acid. Favoured by upwelling deep-seated thermal flows, this acid dissolves the limestone, with condensation corrosion process that involve replacement of limestone rock with gypsum. This process has resulted to be more active and remarkable within the Gattulla Cave, one of the Santa Cesarea Terme sea caves.

A study of the structural, optical and electrical properties of synthetic and natural melanin by means of X-ray diffraction, absorption and photocurrent techniques is reported. The model of the natural melanin film as a network of nano-aggregates of polymeric units based on the indolic structure is proposed to explain the X-ray diffraction results. The shape of the absorption spectra is similar to that of amorphous and disordered semiconductors, with a very strong, broad band UV and visible absorption and an optical gap value of about 0.5 eV. Photosensitivity to sun spectra has been demonstrated by photoconductivity measurements of synthetic melanin pellets under AM1 light source illumination.

Undoped CdSe and CdSe:Zn thin films have been grown on silicon substrate by using pulsed laser deposition technique. The electrical, structural and optical properties have been investigated. The films grow crystalline and highly oriented. Electrical measurements show that they are n-type doped. The reflectivity and photoluminescence are consistent and point out that the undoped CdSe film present excitonic features at low temperature, differently from CdSe:Zn films, whose spectral features are related to band–band transition. The luminescence efficiency of CdSe:Zn persists up to room temperature, whereas the luminescence of undoped CdSe is scarcely visible above 250 K.

InP films have been deposited on amorphous sapphire substrate by means of the metallorganic chemical vapour deposition technique with and without PH3/H-2 plasma preactivation. Polycrystalline materials, having average grain sizes of about 40 nm, which, however, vary according to the growth parameters, were obtained. The structural and compositional disorder strongly influence the optical and electrical properties. The most structurally disordered films present the largest photoluminescence (PL) efficiency and a blue-shift of the whole PL spectra. Radiative recombinations of carriers confined in crystallites having the smallest sizes are proposed to explain such an anomalous behaviour. The temperature dependence of the bandgap follows the well known phenomenological models except for the hydrogenated samples, in which a blue-shift of the intrinsic luminescence band is observed with increasing temperature. This anomalous effect is related to phonon-assisted transitions between nanoclusters with different sizes. Electrical conductivity measurements show different conductivity mechanisms in two different ranges of temperature. In particular, for temperatures lower than 200 K the conduction mechanism is due to a variable-range hopping process.

The structural and optical properties of CdS x Se 1− x alloy films, deposited on Si(111)-oriented substrates by the laser ablation technique, have been investigated. The films grow highly oriented in the hexagonal phase and the lattice constant c of the ternary alloy follows Vegard's rule. The exciton line recombination is well resolved in the PL spectra of each film alloy from 10 up to 300 K. The temperature dependence of the excitonic energy indicates that both acoustic and optical phonons contribute to the thermal shrinkage of the band gap: in particular, the acoustic phonon contribution is larger in ternary compounds than in the binary ones.

Thin films of n-type CdSe have been grown on a quartz substrate by laser ablating a target obtained by mixing CdSe and metallic In powders. The effects of different doping concentration of In have been investigated. X-ray diffraction spectra show that at low In density only the CdSe lattice is present in the deposited film, whereas CdIn2Se4 and InSe compounds are deposited at higher In concentration. Band gap narrowing and band tails are observed in the absorption spectra when the In concentration increases. Photoluminescence spectra show band-band recombinations from 10 K to room temperature.

ZnSe films have been deposited by pulsed laser ablation technique on Al 2 O 3 (0 0 0 1)-oriented substrates at different temperatures and pulsed laser fluence. The films grow highly oriented according to the (1 1 1) direction of the ZnSe cubic lattice. The best structural quality is obtained for film deposited at 400–450 °C and relatively high laser fluence. The good optical quality of the films is revealed by the presence of several features well resolved in the reflection spectra. The energy gap E g values, obtained as fitting parameters of the optical spectra, indicate the presence of a residual bidimensional compressive stress in the ZnSe layers.