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The La Fossa volcano on the Island of Vulcano, Italy, showed signs of more energetic fumarolic–solfataric activity during 2021. Several increases in volcanic gas emissions and seismicity, namely, "crisis," punctuated the passive degassing at Vulcano that had ensued after the last 1888–1890 vulcanian eruption. Most of the gases (i.e., up to 90%) were emitted at the crater cone while the diffuse degassing of CO2 at Vulcano Porto accounted for more than 10% of the volcanic emissions. Two anomalous degassing zones at the base of the volcanic cone (i.e., Palizzi and Faraglione) showed notable changes in the gas output during the volcanic crisis. In these zones, increases of soil CO2 flux (φCO2) had several practical implications other than of volcanological interest, owing to the risk related to people's exposure to volcanic gas emissions. The results of this study reveal variations of the average φCO2 from 74 g m−2 d−1 during September 2021 to 370 g m−2 d−1 in November 2021, which were 27% and 538% higher than the statistical background since 1988 (φCO2 ≈ 58 g m−2 d−1), respectively. These observations helped in volcanic surveillance at Vulcano. The soil CO2 partitioning determined using both φCO2 and carbon isotope measurements, helped track changes in the volcanic CO2 output from 9.97 · 104 to 101.15 · 104 kg d−1. Estimates for volcanic CO2 suggest that the instability of a magmatic body caused a transition from background fumarolic–solfataric activity toward an unrest event after September 2021. Plain Language Summary: A noticeable increase in volcanic outgassing occurred at Vulcano, Italy, in 2021. Although the volcano has not achieved critical conditions to produce an eruption, the soil CO2 emissions have prevented access into some zones of the island, due to the volcanic risk known as the gas hazard. Specialized instruments such as fluxmeters and spectrophotometers were used to measure the soil CO2 flux and the carbon isotopes of CO2 during four soil gas surveys. To understand why the volcanic system evolved toward a period of unrest, we modeled our measurements using mass balance calculations. We find that the CO2 increase, almost 10 times its baseline, was most likely due to the instability of a magmatic body within the mantle to crustal boundary known as the Moho discontinuity. Because of this magmatic instability, the volcanic CO2 emissions resumed in some zones of the island where volcanic activity had been dormant for decades. The resumption of volcanic degassing in a short period had not been recorded before at Vulcano, and it is important to understand its cause because future changes in magmatic activity might produce larger CO2 emissions that will have the added risk of gas hazards as well as that of an explosion. Key Points: Diffuse degassing surveys help track transition toward volcanic unrest periodsCarbon isotope composition allows quantification of the volcanic CO2 emitted by soilsSignificant changes in volcanic outgassing state caused increases in soil CO2 emissions and gas hazard at Vulcano—Italy—during 2021 [ABSTRACT FROM AUTHOR]

A novel Micro-Raman technique was designed and used to detect extended defects in 4H-SiC homoepitaxy. The technique uses above band-gap high-power laser densities to induce a local increase of free carriers in undoped epitaxies (n<1016 at/cm-3), creating an electronic plasma that couples with the longitudinal optical (LO) Raman mode. The Raman shift of the LO phononplasmon- coupled mode (LOPC) increases as the free carrier density increases. Crystallographic defects lead to scattering or recombination of the free carriers which results in a loss of coupling with the LOPC, and in a reduction of the Raman shift. Given that the LO phonon-plasmon coupling is obtained thanks to the free carriers generated by the high injection level induced by the laser, we named this technique induced-LOPC (i-LOPC). This technique allows the simultaneous determination of both the carrier lifetime and carrier mobility. Taking advantage of the modifications on the carrier lifetime induced by extended defects, we were able to determine the spatial morphology of stacking faults; the obtained morphologies were found to be in excellent agreement with those provided by standard photoluminescence techniques. The results show that the detection of defects via i-LOPC spectroscopy is totally independent from the stacking fault photoluminescence signals that cover a large energy range up to 0.7 eV, thus allowing for a single-scan simultaneous determination of any kind of stacking fault. Combining the i-LOPC method with the analysis of the transverse optical mode, the micro-Raman characterization can determine the most important properties of unintentionally doped film, including the stress status of the wafer, lattice impurities (point defects, polytype inclusions) and a detailed analysis of crystallographic defects, with a high spectral and spatial resolution. [ABSTRACT FROM AUTHOR]