On the Electrochemical Growth of a Crystalline p-n Junction From Aqueous Solutions.

Our society largely relies on inorganic semiconductor devices which are, so far, fabricated using expensive and complex processes requiring ultra-high vacuum equipment. Here we report on the possibility of growing a p-n junction taking advantage of electrochemical processes based on the use of aqueous solutions. The growth of the junction has been carried out using the Electrochemical Atomic Layer Deposition (E-ALD) technique, which allowed to sequentially deposit two different semiconductors, CdS and Cu2S, on an Ag(111) substrate, in a single procedure. The growth process was monitored in situ by Surface X-Ray Diffraction (SXRD) and resulted in the fabrication of a thin double-layer structure with a high degree of crystallographic order and a well-defined interface. The high-performance electrical characteristics of the device were analysed ex-situ and show the characteristic feature of a diode.

Interplay between abiotic and microbial biofilm-mediated processes for travertine formation: Insights from a thermal spring (Piscine Carletti, Viterbo, Italy).

Active hydrothermal travertine systems are ideal environments to investigate how abiotic and biotic processes affect mineralization mechanisms and mineral fabric formation. In this study, a biogeochemical characterization of waters, dissolved gases, and microbial mats was performed together with a mineralogical investigation on travertine encrustations occurring at the outflow channel of a thermal spring. The comprehensive model, compiled by means of TOUGHREACT computational tool from measured parameters, revealed that mineral phases were differently influenced by either abiotic conditions or microbially driven processes. Microbial mats are shaped by light availability and temperature gradient of waters flowing along the channel. Mineralogical features were homogeneous throughout the system, with euhedral calcite crystals, related to inorganic precipitation induced by CO2 degassing, and calcite shrubs associated with organomineralization processes, thus indicating an indirect microbial participation to the mineral deposition (microbially influenced calcite). The microbial activity played a role in driving calcite redissolution processes, resulting in circular pits on calcite crystal surfaces possibly related to the metabolic activity of sulfur-oxidizing bacteria found at a high relative abundance within the biofilm community. Sulfur oxidation might also explain the occurrence of gypsum crystals embedded in microbial mats, since gypsum precipitation could be induced by a local increase in sulfate concentration mediated by S-oxidizing bacteria, regardless of the overall undersaturated environmental conditions. Moreover, the absence of gypsum dissolution suggested the capability of microbial biofilm in modulating the mobility of chemical species by providing a protective envelope on gypsum crystals.

Flux measurements of benzene and toluene from landfill cover soils.

Carbon dioxide and CH(4), C(6)H(6) and C(7)H(8) fluxes from the soil cover of Case Passerini landfill site (Florence, Italy) were measured using the accumulation and static closed chamber methods, respectively. Results show that the CH(4)/CO(2), CH(4)/C(6)H(6) and CH(4)/C(7)H(8) ratios of the flux values are relatively low when compared with those of the 'pristine' biogas produced by degradation processes acting on the solid waste material disposed in the landfill. This suggests that when biogas transits through the cover soil, CH(4) is affected by degradation processes activated by oxidizing bacteria at higher extent than both CO(2) and mono-aromatics. Among the investigated hydrocarbons, C(6)H(6) has shown the highest stability in a wide range of redox conditions. Toluene behaviour only partially resembles that of C(6)H(6), possibly because de-methylation processes require less energy than that necessary for the degradation of C(6)H(6), the latter likely occurring via benzoate at anaerobic conditions and/or through various aerobic metabolic pathways at relatively shallow depth in the cover soil where free oxygen is present. According to these considerations, aromatics are likely to play an important role in the environmental impact of biogas released into the atmosphere from such anthropogenic emission sites, usually only ascribed to CO(2) and CH(4). In this regard, flux measurements using accumulation and static closed chamber methods coupled with gas chromatography and gas chromatography-mass spectrometry analysis may properly be used to obtain a dataset for the estimation of the amount of volatile organic compounds dispersed from landfills.

Origin and distribution of thiophenes and furans in gas discharges from active volcanoes and geothermal systems.

The composition of non-methane organic volatile compounds (VOCs) determined in 139 thermal gas discharges from 18 different geothermal and volcanic systems in Italy and Latin America, consists of C(2)-C(20) species pertaining to the alkanes, alkenes, aromatics and O-, S- and N-bearing classes of compounds. Thiophenes and mono-aromatics, especially the methylated species, are strongly enriched in fluids emissions related to hydrothermal systems. Addition of hydrogen sulphide to dienes and electrophilic methylation involving halogenated radicals may be invoked for the formation of these species. On the contrary, the formation of furans, with the only exception of C(4)H(8)O, seems to be favoured at oxidizing conditions and relatively high temperatures, although mechanisms similar to those hypothesized for the production of thiophenes can be suggested. Such thermodynamic features are typical of fluid reservoirs feeding high-temperature thermal discharges of volcanoes characterised by strong degassing activity, which are likely affected by conspicuous contribution from a magmatic source. The composition of heteroaromatics in fluids naturally discharged from active volcanoes and geothermal areas can then be considered largely dependent on the interplay between hydrothermal vs. magmatic contributions. This implies that they can be used as useful geochemical tools to be successfully applied in both volcanic monitoring and geothermal prospection.

Analysis of mass transport in ionic liquids: a rotating disk electrode approach.

Ionic Liquids are a promising alternative to water electrolytes for the electrodeposition of metals. These solvents have a much larger electrochemical window than water that expands the potential of electrodeposition. However, mass transport in Ionic Liquids is slow. The slow mass transport dramatically affects the rate of reactions at the solid-liquid interface, hampering the exploitation of Ionic Liquids in high-throughput electrodeposition processes. In this paper, we clarify the origin of such poor mass transport in the diffusion-advection (convection) regime. To determine the extent and the dynamics of the convection boundary layers, we performed Rotating Disk Electrode (RDE) experiments on model reactions along with the finite element simulation. Both the experiments and the finite element modelling showed the occurrence of peaks in the RDE curves even at relatively high rotation rates (up to 2000 rpm). The peak in the RDE is the fingerprint of partial diffusion control that happens for the relative extent of the diffusion and convection boundary layers. In looking for a close match between the experiments and the simulations, we found that the ohmic drop plays a critical role and must be considered in the calculation to find the best match with the experimental data. In the end, we have shown that the combined approach consisting of RDE experiments and finite elements modelling providing a tool to unravel of the structure of the diffusion and convection boundary layers both in dynamic and stationary conditions.

Spectroscopic study of volcanic ashes.

Volcanic ashes particles are subjected to substantial modification during explosive eruptions. The mineralogical and compositional changes have important consequences on the environment and human health. Nevertheless, the relationship between the speciation of iron (Fe) and the mineralogical composition and particle granulometry of the ashes, along with their interaction with water, are largely unknown. In particular, the Fe oxidation state and the possible formation of new Fe-bearing phases in presence of S, Cl, and F in the plume are key points to assess the impact of the ashes. Fragmental material ejected during volcanic activity (tephra) in 2013, was collected on the Mt. Etna (Italy) and investigated using a multi-technique approach that included conventional Electron Paramagnetic Resonance (EPR), high field EPR (HFEPR), EchoEPR, and Fe K-edge X-ray Absorption Spectroscopy (XAS). These element-selective techniques allowed obtaining a detailed information on the oxidation state and coordination environment of Fe, and of its speciation in the ash samples as a function of the granulometry. A complex mineralogical assemblage, consisting of variable amounts of nanometric crystalline Fe inclusions in a glass matrix, and of Fe-oxides and Fe-sulfur phases was revealed. A risk assessment of the ashes is attempted.

Mathematical model for volcanic harmonic tremors.

Harmonic tremors consist in the release of infrasonic energy associated with volcanic activity. The typical frequency range of harmonic tremors is 0.1-12 Hz. We suppose that the harmonic tremors are due to the formation of bubbles entrapped in cavities that oscillate converting thermal energy into mechanic energy. Reproducing the natural phenomenon through an experimental apparatus, we propose here a mathematical model to describe the oscillatory mechanism and to detect the frequency as a function of the main physical parameters. We show that the frequency obtained through the model is in agreement with the one obtained through experimental measurements and with the data available from the literature, proving the consistency of the proposed model.

Chemical variability of artificial stone powders in relation to their health effects.

The occurrence of highly severe silica-related diseases among the resin- and silica-based artificial stone workers was claimed, associated to an extremely short latency. High levels of exposure and intrinsic properties of AS are thought to modulate the development of silicosis and auto-immune diseases. This study compares parent materials and processed dusts, to shed light on changes of AS occurring in the manufacturing process, through an XRF, EPR and XAS investigation. We point out the extremely wide variability of the materials, the occurrence of chemical signatures impressed by the processing techniques, and the unprecedented generation of stable radicals associated to the lysis of the Si-O chemical bond inside the resin coated respirable crystalline silica. These results suggest that the AS processing in industrial stone workshops can create respirable dusts with peculiar physical and chemical properties, to be correlated to the observed clinical evidences.

Green and scalable synthesis of nanocrystalline kuramite.

The new generation of solar cells aims to overcome many of the issues created by silicon-based devices (e.g., decommissioning, flexibility and high-energy production costs). Due to the scarcity of the resources involved in the process and the need for the reduction of potential pollution, a greener approach to solar cell material production is required. Among others, the solvothermal approach for the synthesis of nanocrystalline Cu-Sn-S (CTS) materials fulfils all of these requirements. The material constraints must be considered, not only for the final product, but for the whole production process. Most works reporting the successful synthesis of CTS have employed surfactants, high pressure or noxious solvents. In this paper, we demonstrate the synthesis of nanocrystalline kuramite by means of a simpler, greener and scalable solvothermal synthesis. We exploited a multianalytical characterization approach (X-ray diffraction, extended X-ray absorption fine structure, field emission scanning electron microscopy, Raman spectroscopy and electronic microprobe analysis (EMPA)) to discriminate kuramite from other closely related polymorphs. Moreover, we confirmed the presence of structural defects due to a relevant antisite population.

Determination of organic acids in plants of Silene paradoxa L. by HPLC.

According to the general behavior that organic acids steadily bind metals, a specific and highly reproducible HPLC separation method with photodiode array detection has been improved for their determination and quantification in biological materials. The separation was carried out on an Alltima C-18 reverse phase column. The mobile phase was 125 mM KH2PO4, adjusted to pH 2.5 with concentrated H3PO4, and optimum separation efficiency was obtained by using a 2 mL min(-1) flow rate. Detection wavelength for quantitative measurement was 210 nm. The run time of each sample was 20 min, with a spectra collection frequency of 5 spectra s(-1). Organic acids were identified by comparing the retention times of the samples against retention times of the standards and confirmed with spectral (190-700 nm) signature. Because organic acids could steadily bind metals in plant tissues and due to the strong matrix effect observed, the addition method was applied for quantitative analysis and its performance evaluated.

Operando SXRD study of the structure and growth process of Cu2S ultra-thin films.

Electrochemical Atomic Layer Deposition (E-ALD) technique has demonstrated to be a suitable process for growing compound semiconductors, by alternating the under-potential deposition (UPD) of the metallic element with the UPD of the non-metallic element. The cycle can be repeated several times to build up films with sub-micrometric thickness. We show that it is possible to grow, by E-ALD, Cu2S ultra-thin films on Ag(111) with high structural quality. They show a well ordered layered crystal structure made on alternating pseudohexagonal layers in lower coordination. As reported in literature for minerals in the Cu-S compositional field, these are based on CuS3 triangular groups, with layers occupied by highly mobile Cu ions. This structural model is closely related to the one of the low chalcocite. The domain size of such films is more than 1000 Å in lateral size and extends with a high crystallinity in the vertical growth direction up to more than 10 nm. E-ALD process results in the growth of highly ordered and almost unstrained ultra-thin films. This growth can lead to the design of semiconductors with optimal transport proprieties by an appropriate doping of the intra metallic layer. The present study enables E-ALD as an efficient synthetic route for the growth of semiconducting heterostructures with tailored properties.

Physico-chemical properties of quartz from industrial manufacturing and its cytotoxic effects on alveolar macrophages: The case of green sand mould casting for iron production.

Industrial processing of materials containing quartz induces physico-chemical modifications that contribute to the variability of quartz hazard in different plants. Here, modifications affecting a quartz-rich sand during cast iron production, have been investigated. Composition, morphology, presence of radicals associated to quartz and reactivity in free radical generation were studied on a raw sand and on a dust recovered after mould dismantling. Additionally, cytotoxicity of the processed dust and ROS and NO generation were evaluated on MH-S macrophages. Particle morphology and size were marginally affected by casting processing, which caused only a slight increase of the amount of respirable fraction. The raw sand was able to catalyze OH and CO2(-) generation in cell-free test, even if in a lesser extent than the reference quartz (Min-U-Sil), and shows hAl radicals, conventionally found in any quartz-bearing raw materials. Enrichment in iron and extensive coverage with amorphous carbon were observed during processing. They likely contributed, respectively, to increasing the ability of processed dust to release CO2- and to suppressing OH generation respect to the raw sand. Carbon coverage and repeated thermal treatments during industrial processing also caused annealing of radiogenic hAl defects. Finally, no cellular responses were observed with the respirable fraction of the processed powder.

Degradation of C2-C15 volatile organic compounds in a landfill cover soil.

The composition of non-methane volatile organic compounds (hereafter VOCs) in i) the cover soil, at depths of 30, 50 and 70 cm, and ii) gas recovery wells from Case Passerini landfill site, (Florence, Italy) was determined by GC-MS. The study, based on the analysis of interstitial gases sampled along vertical profiles within the cover soil, was aimed to investigate the VOC behaviour as biogas transits from a reducing to a relatively more oxidizing environment. A total of 48 and 63 different VOCs were identified in the soil and well gases, respectively. Aromatics represent the dominant group (71.5% of total VOC) in soil gases, followed by alkanes (6.8%), ketones (5.7%), organic acids (5.2%), aldehydes (3.0%), esters (2.6%), halogenated compounds (2.1%) and terpenes (1.3%). Cyclics, heterocyclics, S-bearing compounds and phenols are