Van der Waals two-color infrared photodetector

With the increasing demand for multispectral information acquisition, infrared multispectral imaging technology that is inexpensive and can be miniaturized and integrated into other devices has received extensive attention. However, the widespread usage of such photodetectors is still limited by the high cost of epitaxial semiconductors and complex cryogenic cooling systems. Here, we demonstrate a noncooled two-color infrared photodetector that can provide temporal-spatial coexisting spectral blackbody detection at both near-infrared and mid-infrared wavelengths. This photodetector consists of vertically stacked back-to-back diode structures. The two-color signals can be effectively separated to achieve ultralow crosstalk of ~0.05% by controlling the built-in electric field depending on the intermediate layer, which acts as an electron-collecting layer and hole-blocking barrier. The impressive performance of the two-color photodetector is verified by the specific detectivity (D*) of 6.4 × 109 cm Hz1/2 W−1 at 3.5 μm and room temperature, as well as the promising NIR/MWIR two-color infrared imaging and absolute temperature detection.

Modelling and optimization of magnesium alloy milling parameters

In the pursuit to lighter, less consuming products, manufacturers, especially in aviation and automotive industries, are turning more and more to using lightweight alloys such as the ones based on magnesium. Higher requirements for increased productivity have led to concepts like high-speed machining (HSM), high feed machining (HFM) or high-efficiency machining. Tighter regulations concerning requiring for more environmentally friendly industrial processes led to limitations in the use of cooling liquids and a search for cooling methods with less impact (dry cutting, cryogenic cooling, near dry machining and others). Better machining processes can only be achieved by modelling and optimization. This paper briefly presents the results obtained by our research team concerning the modelling and optimization attempts on face milling of magnesium alloys using different methods: design of experiments (e.g. factorial design, response surface method), fuzzy logic or neural networks.

Sustainable Processes in Aluminium, Magnesium, and Titanium Alloys Applied to the Transport Sector: A Review

The reduction of consumption and pollutant emissions is a top priority for the transport sector. One working line is the substitution of conventional structural materials with lightweight materials such as metallic alloys of aluminium, titanium, and/or magnesium. For this reason, and considering that the number of related articles is lower than the existing number of other structural lightweight materials, it is considered very convenient and helpful to carry out a systematic analysis of their latest trends through Open Access literature. A methodology adapted from the PRISMA statement is applied, in order to guarantee unbiasedness and quality in selecting literature and research. The final selection is made up of the 40 most cited research papers from 2015–2020, with an average of 20.6 citations per article. Turning and drilling are the most trending machining processes, and there is particular interest in the study of sustainable cooling, such as dry machining, cryogenic cooling, and MQL. In addition, another trending topic is multi-materials and joining dissimilar materials with guarantees. Additive manufacturing has also been identified as an increasingly trending theme, appearing in 18% of the selected studies. This work is complemented with summary tables of the most cited Open Access articles on sustainable machining and cooling, multi-materials or hybrid components, and additive manufacturing.

Conceptual Design, Sizing and Performance Analysis of a Cryo-Electric Propulsion System for a Next-Generation Hydrogen-Powered Aircraft

In this paper, we present a comprehensive sizing and performance analysis framework for a disruptive cryo-electric propulsion system intended for a hydrogen-powered regional aircraft. The main innovation lies in the systematic treatment of all the electrical and thermal components to model the overall system performance. One of the main objectives is to study the feasibility of using the liquid hydrogen (LH\textsubscript{2}) fuel to provide cryogenic cooling to the electric propulsion system, and thereby enable ultra-compact designs. Another aim has been to identify the optimal working point of the fuel cell to minimize the overall propulsion system's mass. The full mission profile is evaluated to make the analysis as realistic as possible. Analyses are done for three different 2035 scenarios, where available data from the literature are projected to a baseline, conservative, and optimistic scenario. The analysis shows that the total propulsion system's power density can be as high as 1.63 kW/kg in the optimistic scenario and 0.79 kW/kg in the baseline scenario. In the optimistic scenario, there is also sufficient cryogenic cooling capacity in the hydrogen to secure proper conditions for all components, whereas the DC/DC converter falls outside the defined limit of 110 K in the baseline scenario.

Conceptual Design, Sizing and Performance Analysis of a Cryo-Electric Propulsion System for a Next-Generation Hydrogen-Powered Aircraft

In this paper, we present a comprehensive sizing and performance analysis framework for a disruptive cryo-electric propulsion system intended for a hydrogen-powered regional aircraft. The main innovation lies in the systematic treatment of all the electrical and thermal components to model the overall system performance. One of the main objectives is to study the feasibility of using the liquid hydrogen (LH\textsubscript{2}) fuel to provide cryogenic cooling to the electric propulsion system, and thereby enable ultra-compact designs. Another aim has been to identify the optimal working point of the fuel cell to minimize the overall propulsion system's mass. The full mission profile is evaluated to make the analysis as realistic as possible. Analyses are done for three different 2035 scenarios, where available data from the literature are projected to a baseline, conservative, and optimistic scenario. The analysis shows that the total propulsion system's power density can be as high as 1.63 kW/kg in the optimistic scenario and 0.79 kW/kg in the baseline scenario. In the optimistic scenario, there is also sufficient cryogenic cooling capacity in the hydrogen to secure proper conditions for all components, whereas the DC/DC converter falls outside the defined limit of 110 K in the baseline scenario.

Physics of Nanostructure Design for Infrared Detectors

Infrared detectors and focal plane array technologies are becoming ubiquitous in military, but are limited in the commercial sectors. The widespread commercial use of this technology is lacking because of the high cost and large size, weight and power. Most of these detectors require cryogenic cooling to minimize thermally generated dark currents, causing the size, weight, power and cost to increase significantly. Approaches using very thin detector design can minimize thermally generated dark current, but at a cost of lower absorption efficiency. There are emerging technologies in nanostructured material designs such as metasurfaces that can allow for increased photon absorption in a thin detector architecture. Ultra-thin and low-dimensional absorber materials may also provide unique engineering opportunities in detector design. This chapter discusses the physics and opportunities to increase the operating temperature using such techniques.

Determination of the through-plane profile of vanadium species in hydrated Nafion studied with micro X-ray absorption near-edge structure spectroscopy – proof of concept

Vanadium-ion transport through the polymer membrane results in a significant decrease in the capacity of vanadium redox flow batteries. It is assumed that five vanadium species are involved in this process. Micro X-ray absorption near-edge structure spectroscopy (micro-XANES) is a potent method to study chemical reactions during vanadium transport inside the membrane. In this work, protocols for micro-XANES measurements were developed to enable through-plane characterization of the vanadium species in Nafion 117 on beamline P06 of the PETRA III synchrotron radiation facility (DESY, Hamburg, Germany). A Kapton tube diffusion cell with a diameter of 3 mm was constructed. The tube diameter was chosen in order to accommodate laminar flow for cryogenic cooling while allowing easy handling of the cell components by hand. A vertical step size of 2.5 µm and a horizontal step size of 5 µm provided sufficient resolution to resolve the profile and good statistics after summing up horizontal rows of scan points. The beam was confined in the horizontal plane to account for the waviness of the membrane. The diffusion of vanadium ions during measurement was inhibited by the cryogenic cooling. Vanadium oxidation, e.g. by water radiolysis (water percentage in the hydrated membrane ∼23 wt%), was mitigated by the cryogenic cooling and by minimizing the dwell time per pixel to 5 ms. Thus, the photo-induced oxidation of V3+ in the focused beam could be limited to 10%. In diffusion experiments, Nafion inside the diffusion cell was exposed on one side to V3+ electrolyte and on the other side to VO2 +. The ions were allowed to diffuse across the through-plane orientation of the membrane during one of two short defrost times (200 s and 600 s). Subsequent micro-XANES measurements showed the formation of VO2+ from V3+ and VO2 + inside the water body of Nafion. This result proves the suitability of the experimental setup as a powerful tool for the determination of the profile of vanadium species in Nafion and other ionomeric membranes.