DIFFER: Publications
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Impact of pi-Conjugated Linkers on the Effective Exciton Binding Energy of Diketopyrrolopyrrole-Dithienopyrrole Copolymers
No full textImplications of thermo-chemical instability on the contracted modes in CO2 microwave plasmas
Get PDFUnderstanding and controlling contraction phenomena of plasmas in reactive flows is essential to optimize the discharge parameters for plasma processing applications such as fuel reforming and gas conversion. In this work, we describe the characteristic discharge modes in a CO2 microwave plasma and assess the impact of wave coupling and thermal reactivity on the contraction dynamics. The plasma shape and gas temperature are obtained from the emission profile and the Doppler broadening of the 777 nm O(5S ← 5P) oxygen triplet, respectively. Based on these observations, three distinct discharge modes are identified in the pressure range of 10 mbar to atmospheric pressure. We find that discharge contraction is suppressed by an absorption cut-off of the microwave field at the critical electron density, resulting in a homogeneous discharge mode below the critical transition pressure of 85 mbar. Further increase in the pressure leads to two contracted discharge modes, one emerging at a temperature of 3000 K to 4000 K and one at a temperature of 6000 K to 7000 K, which correspond to the thermal dissociation thresholds of CO2 and CO respectively. The transition dynamics are explained by a thermo-chemical instability, which arises from the coupling of the thermal-ionization instability to heat transfer resulting from thermally driven endothermic CO2 dissociation reactions. These results highlight the impact of thermal chemistry on the contraction dynamics of reactive molecular plasmas.</p
From Geometry to Activity: A Quantitative Analysis of WO3/Si Micropillar Arrays for Photoelectrochemical Water Splitting
Get PDFThe photoelectrochemical (PEC) activity of microstructured electrodes remains low despite the highly enlarged surface area and enhanced light harvesting. To obtain a deeper understanding of the effect of 3D geometry on the PEC performance, well‐defined WO3/n‐Si and WO3/pn‐Si micropillar arrays are fabricated and subjected to a quantitative analysis of the relationship between the geometry of the micropillars (length, pitch) and their PEC activity. For WO3/n‐Si micropillars, it is found that the photocurrent increases for WO3/n‐Si pillars, but not in proportion to the increase in surface area that results from increased pillar length or reduced pillar pitch. Optical simulations show that a reduced pillar pitch results in areas of low light intensity due to a shadowing effect. For WO3/pn‐Si micropillar photoelectrodes, the p–n junction enhances the photocurrent density up to a factor of 4 at low applied bias potential (0.8 V vs RHE) compared to the WO3/n‐Si. However, the enhancement in photocurrent density increases first and then decreases with reduced pillar pitch, which scales with the photovoltage generated by the p–n junction. This is related to an increased dead layer of the p–n junction Si surface, which results in a decreased photovoltage even though the total surface area increases.</p
Development of a real-time algorithm for detection of the divertor detachment radiation front using multi-spectral imaging
Get PDFIn this paper we present a novel algorithm to extract the optical plasma boundary and radiation front for detached divertor plasmas. We show that reliable detection of the divertor leg and radiation front is possible using lightweight image processing tools. Using a non-tomographic approach, the detected divertor leg and radiation front can be mapped to the poloidal plane. This approach is fast and accurate enough for real-time control purposes, allowing in particular real-time plasma shape and detachment control, and post-shot detachment physics and dynamics analysis.</p
Eco-efficiency analysis of plasma-assisted nitrogen fixation
No full textAn eco-efficiency analysis has been conducted, as a sustainability performance indicator, by combining the life cycle costs (LCC) and the environmental impacts of diverse plasma-assisted ammonia and nitric acid synthesis routes, for which a detailed process design for small-scale production has been previously reported. The proposed design of the specific plasma processes involves new upstream and downstream activities, which are independent of conventional natural resources and comprise less equipment. In the context of this study, the impact of the product yield and plasma power consumption on the eco-efficiency profiles of the selected plasma processes is evaluated and benchmarked against that of the established synthesis pathways. Results show a relatively improved environmental profile of the plasma-assisted NH3 (5% NH3 yield), considering a power consumption of 17.2 g NH3 kWh-1 and energy recovery of 5%, against that of the contemporary production route. In the case of the plasma-assisted HNO3 (6% NO yield) synthesis, incorporating a power consumption of 7.77 kWh kg-1 NO and a 20% energy recovery, a better ecological footprint is displayed as compared to the conventional chemical process. Both plasma processes are characterized by higher LCC than the conventional ones, with the plasma-assisted nitric acid displaying a more competitive LCC profile. A clear contribution of the utilities (upstream and downstream equipment) to both the environmental and cost benefits is shown, and the plasma plant is the enabler of such integration. The contribution is related to both the number reduction of equipment (process simplification) and improved operation (process intensification). Given the outcomes of this study, the concept of developing modular plants incorporating the plasma technology and renewable energy sources -e.g. wind power- for synthesizing ammonia and nitric acid demonstrates promising potential and promotes a new window of opportunities for future sustainable decentralized fertilizer production; such as distributed production at the farm site, with the opportunity to react immediately to weather changes and to local conditions (soil, climate, crops, farming business model)
Performance of transition metal-doped CaCO3 during cyclic CO2 capture-and-release in low-pressure H2O vapour and H2O plasma
Get PDFThe effects of transition metal doping of calcium carbonate on the subsequent performance of the material during CO2 release and recapture have been evaluated for calcination under low-pressure (~0.1 mbar) water vapour and water plasma conditions. The initial samples were prepared by precipitation method from analytical grade carbonate, calcium and transition metal (Fe, Co, Zn, Cu and Ni) containing precursors. The release-recapture properties of the sorbents were monitored over five cycles involving calcination at 1200 K and carbonation at 825 K. The most noteworthy effects were observed for the Zn-doped samples, which exhibited rapid CO2 recapture. Calcination in H2O plasma was tested to evaluate the potential for in-situ material processing as a means to counteract material degradation. The impact of plasma exposure during calcination on the looping performance was mixed and dependent on the specific sample composition. The performance of the Zn-doped CaCO3 was consistently improved by plasma calcination, yielding high uptake and better retention of carrying capacity over the five cycles. All samples exhibited a deterioration in carrying capacity over repeated cycles. The Zn-doped samples also performed best in this respect (least loss of carrying capacity). The beneficial effects of Zn-doping were dependent on the Zn-content of the precursor solutions used for material synthesis.</p
Hydrogen diffusion out of ruthenium - an ab initio study of the role of adsorbates
No full textHydrogen permeation into mirrors used in extreme ultraviolet lithography results in the formation of blisters, which are detrimental to reflectivity. An understanding of the mechanism via which hydrogen ends up at the interface between the top ruthenium layer and the underlying bilayers is necessary to mitigate the blistering damage. In this study, we use density functional theory to examine the ways in which hydrogen, having entered the near-surface interstitial voids, can migrate further into the metal or to its surface. We show that with hydrogen and tin adsorbed on the ruthenium surface, diffusion to the surface is blocked for interstitial hydrogen in the metal, making diffusion further into the metal more likely than out-diffusion. The dependence on surface conditions matches and confirms similar findings on hydrogen permeation into metals. This suggests control and modification of surface conditions as a way to influence hydrogen retention and blistering
Organic Photodetectors and their Application in Large Area and Flexible Image Sensors: The Role of Dark Current
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