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Silicon carbide/silicon rich carbide multilayers, aimed at the formation of silicon nanodots for photovoltaic applications, have been studied. The electrical properties have been investigated at the nano-scale by conductive Atomic Force Microscopy (c-AFM) and at macro-scale by temperature dependent conductivity measurements. The mixture is composed of highly conductive Si nanoclusters and moderately conductive SiC nanoclusters in a disordered matrix. The conduction mechanism takes place via band states induced by the disorder at the interface between nanodot clusters. Structural properties have been extracted by optical spectroscopy analyses. The results contribute to the understanding of the microscopical electronic mechanisms of the composite material, which is a candidate for third generation photovoltaics.

Abstract The effect of high temperatures as a degrading factor of rock materials is investigated in this study. Valdieri Marble samples, collected in a quarry in North-western Italian Alps, were subjected to thermal cycles (ranging from 105° to 600 °C) and to subsequent non-destructive and destructive laboratory tests with the aim of evaluating the variation of physical and mechanical properties as a function of temperature variations. Physical and mechanical measurements were complemented with microscopic observations on thin sections. The increase of crack density with temperature and the consequent porosity increases were found to be the main causes of degradation of physical and mechanical properties. In general, density, ultrasonic pulse velocity, wet electrical resistivity, uniaxial compressive strength and Young's moduli decrease as temperature increases. By contrast, peak strain and porosity increase. Correlations between temperature and physical-mechanical properties were proposed and compared to other relationships already established in scientific literature. A damage parameter to quantify the degradation of mechanical properties with temperature is also proposed.

AbstractMountain treelines are thought to be sensitive to climate change. However, how climate impacts mountain treelines is not yet fully understood as treelines may also be affected by other human activities. Here, we focus on “closed‐loop” mountain treelines (CLMT) that completely encircle a mountain and are less likely to have been influenced by human land‐use change. We detect a total length of ~916,425 km of CLMT across 243 mountain ranges globally and reveal a bimodal latitudinal distribution of treeline elevations with higher treeline elevations occurring at greater distances from the coast. Spatially, we find that temperature is the main climatic driver of treeline elevation in boreal and tropical regions, whereas precipitation drives CLMT position in temperate zones. Temporally, we show that 70% of CLMT have moved upward, with a mean shift rate of 1.2 m/year over the first decade of the 21st century. CLMT are shifting fastest in the tropics (mean of 3.1 m/year), but with greater variability. Our work provides a new mountain treeline database that isolates climate impacts from other anthropogenic pressures, and has important implications for biodiversity, natural resources, and ecosystem adaptation in a changing climate.

For layered oxide cathodes, aluminum doping has widely been shown to improve performance, particularly at high degrees of delithiation. While this has led to increased interest in Al-doped systems, including $\mathrm{LiNi_{0.8}Co_{0.15}Al_{0.05}O_{2}}$ (NCA), the aluminum surface environment has not been thoroughly investigated. Using hard x-ray photoelectron spectroscopy measurements of the Al 1s core region for NCA electrodes, we examined the evolution of the surface aluminum environment under electrochemical and thermal stress. By correlating the aluminum environment to transition metal reduction and electrolyte decomposition, we provide further insight into the cathode-electrolyte interface layer. A remarkable finding is that Al-O coatings in LiPF$_6$ electrolyte mimic the evolution observed for the aluminum surface environment in doped layered oxides. ECS transactions 80(10), 197 - 206 (2017). doi:10.1149/08010.0197ecst Published by Pennington, NJ

The optical and photovoltaic properties of Si NCs / SiC multilayers (MLs) are investigated using a membrane-based solar cell structure. By removing the Si substrate in the active cell area, the MLs are studied without any bulk Si substrate contribution. The occurrence is confirmed by scanning electron microscopy and light-beam induced current mapping . Optical characterization combined with simulations allows us to determine the absorption within the ML absorber layer, isolated from the other cell stack layers. The results indicate that the absorption at wavelengths longer than 800 nm is only due to the SiC matrix. The measured short-circuit current is significantly lower than that theoretically obtained from absorption within the ML absorber, which is ascribed to losses that limit carrier extraction. The origin of these losses is discussed in terms of the material regions where recombination takes place. Our results indicate that carrier extraction is most efficient from the Si NCs themselves, whereas recombination is strongest in SiC and residual a-Si domains . Together with the observed onset of the external quantum efficiency (EQE) at 700-800 nm, this fact is an evidence of quantum confinement in Si NCs embedded in SiC on device level.

The use of graphene as transparent conducting layer in devices that require high temperature processing is proposed. The material shows stability upon thermal treatments up to 1100 °C ifc apped with a sacrificial silicon layer. The use of Cu foil or evaporated Cu as catalysts in Catalytic-Chemical Vapor Deposition growth gives rise to graphene ofs imilar properties, which represents a promising result in view of its direct integration in microelectronic devices. Photovoltaic p-i-n thin film devices were fab- ricated on the as-deposited or annealed graphene membranes and compared with similar devices that incorporate as-deposited Indium Tin Oxide. No degradation in series resistance is observed for the annealed device. A 3.7% and 2.8% photovoltaic conversion efficiency is observed on the devices fabricated on as-transferred and on annealed graphene respectively. The major limitation derives from the high sheet resistance of the as-transferred state-of-the-art material. The results opens the way to the use of graphene in applications that require transparent conducting layers resistant to high temperature pro- cessing.

This research provides new techno-economic insights into integrating flexible combined-cycle gas turbines with post-combustion carbon capture and storage (CCGT-CCS) for low-carbon power systems. This study developed a versatile unit-commitment optimisation model of CCGT-CCS. This research highlights the model’s adaptability, accommodating diverse techno-economic configurations, feed gases (e.g., biomethane or fossil natural gas), carbon capture rates, and policy instruments. This generalisation empowers seamless application in various policy and market contexts, making the model a potent tool for researchers and policymakers. While the case study focuses on the UK, the findings are relevant for most low-carbon power systems with variable renewable supplies. Analysing the UK’s net-zero scenarios from 2030 to 2050, the economic viability of flexible CCGT-CCS was highlighted. Intertemporal flexibility proves highly valuable with greater electricity price volatility, with a total ROI range of 81–246 %, surpassing the CCGT-CCS plant’s ROI (7–64 %). A flexible solvent storage solution should be seen in the context of the overall system ‘flexibility’ requirements of a low-carbon power system. On a cost basis, solvent storage represents just a fraction of the capital costs of more “mainstream” energy storage technologies, such as lithium-ion batteries or hydro-pumped storage, while CCGT-CCS offers firm power. Overall, while seen as a rather technical solution, if abated fossil fuel generation is to be part of a future low-carbon power system, having this flexibility adds economic benefits not just to operators but also improves overall system security and complements high shares of variable renewables on the grid.