4-Aminothiophenol Photodimerization Without Plasmons

The photodimerization of 4-aminothiophenol (PATP) into 4,4’-dimercaptobenzene (DMAB) has been extensively utilized as a paradigm reaction to probe the role of surface plasmons in nanoparticle-mediated light-driven processes. Over the past 25 years, a lively debate about the reaction mechanism involved several research groups. Plasmon-mediated generation of energetic (hot) electrons and holes has been invoked as the main driving-force, although plasmonic heating has recently gained attention. However, either model and their combinations are not sufficient to explain some experimental observations and appear, in some cases, contradictory. No matter the differences, there is a general, firm consensus about the presence of plasmonic nanoparticles (Ag or Au), which has always been considered mandatory for triggering the photoconversion. Here I report the first observation of the PATP-to-DMAB photoreaction in the absence of any plasmonic mediators. In particular, neither plasmonic heating nor charge transfer from hot carriers were exploited. The reaction was observed to occur with different kinetics on plasmon-free TiO2 nanoparticles, as well as on self-standing droplets. Confocal microRaman spectroscopy enabled to investigate the reaction progress in different plasmon-free contexts, either aerobic or anaerobic, suggesting a new interpretation of the photodimerization process, based on direct laser-induced activation of singlet oxygen species. These results provide new insights in light-driven redox processes, elucidating the role of sample morphology, light and oxygen.

Investigations of proximity-induced superconductivity in the topological insulator Bi2Te3 by microRaman spectroscopy

We used the topological insulator (TI) Bi2Te3 and a high-temperature superconductor (HTSC) hybrid device for investigations of proximity-induced superconductivity (PS) in the TI. Application of the superconductor YBa2Cu3O7-δ (YBCO) enabled us to access higher temperature and energy scales for this phenomenon. The HTSC in the hybrid device exhibits emergence of a pseudogap state for T > Tc that converts into a superconducting state with a reduced gap for T < Tc. The conversion process has been reflected in Raman spectra collected from the TI. Complementary charge transport experiments revealed emergence of the proximity-induced superconducting gap in the TI and the reduced superconducting gap in the HTSC, but no signature of the pseudogap. This allowed us to conclude that Raman spectroscopy reveals formation of the pseudogap state but cannot distinguish the proximity-induced superconducting state in the TI from the superconducting state in the HTSC characterised by the reduced gap. Results of our experiments have shown that Raman spectroscopy is a complementary technique to classic charge transport experiments and is a powerful tool for investigation of the proximity-induced superconductivity in the Bi2Te3.

Assessing Thermal Maturity through a Multi-Proxy Approach: A Case Study from the Permian Faraghan Formation (Zagros Basin, Southwest Iran)

This study focuses on the thermal maturity of Permian deposits from the Zagros Basin, Southwest Iran, employing both optical methods (Thermal Alteration Index, Palynomorph Darkness Index, Vitrinite Reflectance, UV Fluorescence) and geochemical analyses of organic matter (Rock Eval Pyrolysis and MicroRaman spectroscopy) applied to the Faraghan Formation along two investigated Darreh Yas and Kuh e Faraghan surface sections. Furthermore, an integrated palynofacies and lithofacies analysis was carried out in order to integrate the few studies on the depositional environment. The Faraghan Formation, which is widely distributed in the Zagros area, generally consists of shale intercalated with sandstones and pebble conglomerates in the lower part, followed by a succession of sandstone, siltstone and shaly intercalations and with carbonate levels at the top. The integrated palynofacies and lithofacies data confirm a coastal depositional setting evolving upwards to a shallow marine carbonate environment upwards. Rock Eval Pyrolysis and Vitrinite Reflectance analysis showed that the organic matter from samples of the Darreh Yas and Kuh e Faraghan sections fall in the mature to postmature range with respect to the oil to gas generation window, restricting the thermal maturity range proposed by previous authors. Similar results were obtained with MicroRaman spectroscopy and optical analysis such as Thermal Alteration Index and UV Fluorescence. Palynomorph Darkness Index values were compared with Rock Eval Pyrolysis and vitrinite reflectance values and discussed for the first time in the late stage of oil generation.

Thermal Annealing and Phase Transformation of Serpentine-like Garnierite

This study deals with vibrational and crystallographic aspects of the thermally induced transformation of serpentine-like garnierite into quartz, forsterite, and enstatite occurring at about 620 °C. Powder specimens of garnierite have been annealed in static air between room temperature and 1000 °C. The resulting products from the transformations detected based on thermogravimetric and differential thermal analysis, have been extensively characterized via microRaman spectroscopy, and X-ray diffraction. Our study shows that serpentine-like garnierite consists of a mixture of different mineral species. Furthermore, these garnierites and their composition can provide details based on the mineralogy and the crystalline phases resulting from the thermal treatment.

High pressure serpentinization and abiotic methanogenesis in metaperidotite from the Appalachian subduction, northern Vermont

&lt;p&gt;Serpentinization is the process of hydroxylation of olivine-rich ultramafic rocks to produce minerals such as serpentine, brucite, magnetite, and may release H&lt;sub&gt;2&lt;/sub&gt;. The hydrogen produced through serpentinization reactions can be involved in abiotic reaction pathways leading to the genesis of abiotic light hydrocarbons such as methane (CH&lt;sub&gt;4&lt;/sub&gt;). Examples of this phenomenon exist at the seafloor, such as at the serpentinite-hosted Lost City hydrothermal field, and on land in ophiolites at relatively shallow depths. However, the possibility for serpentinization to occur at greater depths, especially in subduction zones, raises new questions on the genesis of abiotic hydrocarbons at convergent margin and its impact on the deep carbon cycle. High-pressure ultramafic bodies exhumed in metamorphic belts can provide insights on the mechanisms of high-pressure serpentinization in subduction zones and on the chemistry of the resulting fluids. This study focuses on the ultramafic Belvidere Mountain complex belonging to the Appalachian belt of northern Vermont, USA. Microstructures show overgrowth of olivine by delicate antigorite crystals, suggesting olivine serpentinization at high-temperature consistent with the subduction evolution of the Belvidere Mountain complex. &amp;#160;Fluid inclusion trails cross-cutting the primary olivine relicts &amp;#160;suggest their formation during the antigorite serpentinization event. MicroRaman spectroscopy on the fluid inclusions reveals a CH&lt;sub&gt;4&lt;/sub&gt;-rich gaseous composition, with trace of N&lt;sub&gt;2&lt;/sub&gt;, NH&lt;sub&gt;3&lt;/sub&gt; and S-H compound. Moreover, the precipitation of daughter minerals of lizardite and brucite in the fluid inclusions indicate the initial presence of H&lt;sub&gt;2&lt;/sub&gt;O in the fluid. Secondary olivine is observed at the rim of pseudomorphosed primary pyroxenes (bastite), and has higher forsterite (Fo&lt;sub&gt;95&lt;/sub&gt;) content with respect to the primary olivine (Fo&lt;sub&gt;92&lt;/sub&gt;), suggesting either a syn-serpentinization olivine precipitation in the subduction zone, or a successive partial dehydration of the antigorite during metamorphism. Decreasing oxygen fugacity during serpentinization and related abiotic reduction of carbon at high-pressure conditions is proposed at the origin of methane in the fluid inclusions. This potentially places the Belvidere Mountain complex as an example of deep serpentinization related to high-pressure genesis of abiotic methane.&lt;/p&gt;

Strange polymorphs and where to find them: a melt inclusion story

&lt;p&gt;Small portions of pristine melt with diameters of 2 to 50&amp;#181;m are increasingly recognized as a rather common occurrence in high grade metamorphic terranes which experienced melting. Their study delivers crucial chemical information on partial melts at depth. But they are also unique &quot;natural experimental charges&quot; where the behaviour of the silicate melt can be investigated, directly in the natural rocks, under P-T-t conditions which cannot be completely reproduced in the laboratory.&lt;/p&gt;&lt;p&gt;Each nanogranitoid case study has consistently shown H&lt;sub&gt;2&lt;/sub&gt;O-bearing, silica and alkali-rich melt. However, rather than a classic granitoid assemblage consisting mainly of quartz and feldspar(s), on cooling these isolated melt droplets produce a plethora of mineral phases identified via microRaman spectroscopy that are rarely &amp;#8211;or never- observed as rock-forming minerals. Cristobalite (tetragonal) and tridymite (orthorhombic) are often present as SiO&lt;sub&gt;2&lt;/sub&gt; polymorphs, and hexagonal kokchetavite as a polymorph of KAlSi&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;8&lt;/sub&gt;. NaAlSi&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;8&lt;/sub&gt; occurs as orthorhombic kumdykolite, whereas CaAl&lt;sub&gt;2&lt;/sub&gt;Si&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;8 &lt;/sub&gt;may occur either as monoclinic svyatoslavite or trigonal dmisteinbergite. Two presently unidentified phases have been also recognized via Raman and analysed via electron microprobe. One has the main peak at 426-430 cm&lt;sup&gt;-1&lt;/sup&gt; and has the composition of a granitic glass, whereas the second has a main peak at 412 cm&lt;sup&gt;-1&lt;/sup&gt; and a variable composition depending on the inclusion in which it occurs. As their main peaks occur in the same region of most tectosilicates, it is likely that they are two new polymorphs of feldspar, to the best of our knowledge never reported before. These polymorphs have been so far identified in inclusions mainly hosted in garnet, zircon and, in one case, sapphirine and trapped under an extremely variable range of metamorphic conditions (from low P migmatites to UHP eclogites) in very different rock types (metagranitoids, metasediments, mafic and ultramafic rocks).&lt;/p&gt;&lt;p&gt;Microstructures confirm that all of these phases crystallize directly from the trapped melt on cooling, independently of the internal P of the inclusions or the original conditions of melt entrapment. They appear to be the result of metastability in the inclusions, possibly during rapid crystallization of a melt, not caused by rapid cooling but by the peculiar undercooled and supersaturated conditions achieved on cooling by a melt confined in a small cavity (Ferrero &amp; Angel, 2018). According to this possibility, these polymorphs can be regarded as kinetically stabilized, yet possibly thermodynamically metastable, phases as recently proposed by Zolotarev et al. (2019) for dmisteinbergite. A preliminary crystallization experiment on a haplogranitic melt at undercooled conditions however failed to reproduce such phases. Another possibility is that under natural cooling the confined inclusions experience underpressurization, and the system (i.e. the trapped melt) reacts crystallizing phases, i.e. the polymorphs, less dense than their common counterparts. This would result in the decreasing of the P gradient between inclusions and surrounding rock, equivalent to reducing the free energy of the system.&lt;/p&gt;&lt;p&gt;References&lt;/p&gt;&lt;p&gt;Ferrero, S. &amp; Angel, R. 2018. JPet 59, 1671&amp;#8211;1700.&lt;/p&gt;&lt;p&gt;Zolotarev, A.A. et al. 2019. Minerals&amp;#160; 9, 570.&lt;/p&gt;

Graphene oxide nano-filler based experimental dentine adhesive. A SEM / EDX, Micro-Raman and microtensile bond strength analysis

Aim: The study aimed to assess graphene oxide (GO) adhesive and its dentin interaction using scanning electron microscopy (SEM), MicroRaman spectroscopy and Microtensile bond strength (μTBS). Materials and Methods: Experimental GOA and control adhesives (CA) were fabricated. Presence of GO within the experimental adhesive resin was assessed using SEM and Micro-Raman spectroscopy. Ninety specimens were prepared, sixty teeth were utilized for μTBS, twenty for SEM analysis of interface for CA and GOA and ten were assessed using microRaman spectroscopy. Each specimen was sectioned and exposed dentine was conditioned (35% phosphoric acid) for 10 s. The surface was coated twice with adhesive (15 s) and photopolymerized (20 s). Composite build-up on specimen was photo-polymerized. Among the bonded specimens, thirty specimen were assessed using Micro-Raman spectrometer, SEM and energy dispersive X-ray spectroscopy (EDX), whereas remaining specimens were divided in to three sub-groups ( n = 10) based on the storage of 24 h, 8 weeks and 16 weeks. μTBS testing was performed at a crosshead speed of 0.5 mm/min using a microtensile tester. The means of μ-tbs were analyzed using ANOVA and post hoc Tukey multiple comparisons test. Results: No significant difference in μTBS of CA and GOA was observed. Storage time presented a significant interaction on the μTBS ( p < 0.01). The highest and lowest μTBS was evident in CA (30.47 (3.55)) at 24 h and CA (22.88 (3.61)) at 18 weeks. Micro-Raman analysis identified peaks of 1200 cm-1 to 1800 cm1, D and G bands of GO nanoparticles in the resin. Uniform distribution of graphene oxide nanoparticles was present at the adhesive and hybrid layer. Conclusion: GO showed interaction within adhesive and tooth dentin similar to CA, along with formation of hybrid layer. In ideal conditions (absence of nanoleakage), graphene oxide modified adhesive shows comparable bond strength and durability of resin dentine bond.

Bioinspired self-similar all-dielectric antennas: probing the effect of secondary scattering centres by Raman spectroscopy

The role of secondary scattering centres in surface light management of self-similar optical antennas is investigated by microRaman spectroscopy.

An Alternative Scenario on the Origin of Ultra-High Pressure (UHP) and Super-Reduced (SuR) Minerals in Ophiolitic Chromitites: A Case Study from the Mercedita Deposit (Eastern Cuba)

The origin of the assemblage of ultra-high pressure (UHP), super-reduced (SuR) and several crustally derived phases in ophiolitic chromitites is still hotly debated. In this paper, we report, for the first time, this assemblage of phases in ophiolitic chromitites of the Caribbean. We studied the Mercedita chromitite deposit in the eastern Cuban ophiolitic complexes. The mineral phases were characterized using microRaman spectroscopy, energy-dispersive spectroscopy with a scanning electron microscope (SEM-EDS), X-ray microdiffraction and electron microprobe analyses. Mineral concentrates were prepared using hydroseparation techniques. We have identified oriented clinopyroxene lamellae in chromite, oriented rutile lamellae in chromite, moissanite hosted in the altered matrix of the chromitite, graphite-like amorphous carbon, corundum and SiO2 hosted in healed fractures in chromite grains, and native Cu and Fe–Mn alloy recovered in heavy-mineral concentrates obtained by hydroseparation. This assemblage may correspond to UHP-SuR conditions, implying recycling of chromitite in the mantle or formation of the chromite grains at deep mantle depths, followed by emplacement at a shallow level in the mantle. However, the chromitite bodies contain gabbro sills oriented parallel to the elongation of the chromitite lenses, and these show no evidence of HP/UHP metamorphism. Therefore, the identified “exotic” phases may not be indicative of UHP. They formed independently as oriented clinopyroxene lamellae in chromite during cooling (clinopyroxene and rutile), in super-reduced microenvironments during the serpentinization processes, and by transference of subducted crustal material to the mantle wedge via cold plumes.