Structure and morphology of epitaxially grown Fe3O4/NiO bilayers on MgO(001)

Crystalline Fe3O4/NiO bilayers were grown on MgO(001) substrates using reactive molecular beam epitaxy to investigate their structural properties and their morphology. The film thickness either of the Fe3O4 film or of the NiO film has been varied to shed light on the relaxation of the bilayer system. The surface properties as studied by x-ray photo electron spectroscopy and low energy electron diffraction show clear evidence of stoichiometric well-ordered film surfaces. Based on the kinematic approach x-ray diffraction experiments were completely analyzed. As a result the NiO films grow pseudomorphic in the investigated thickness range (up to 34nm) while the Fe3O4 films relax continuously up to the thickness of 50nm. Although all diffraction data show well developed Laue fringes pointing to oxide films of very homogeneous thickness, the Fe3O4-NiO interface roughens continuously up to 1nm root-mean-square roughness with increasing NiO film thickness while the Fe3O4 surface is very smooth independent on the Fe3O4 film thickness. Finally, the Fe3O4-NiO interface spacing is similar to the interlayer spacing of the oxide films while the NiO-MgO interface is expanded.Comment: 20 pages including 12 figure

Static magnetic proximity effect in Pt/Ni1−x_{1-x}Fex_x bilayers investigated by x-ray resonant magnetic reflectivity

We present x-ray resonant magnetic reflectivity (XRMR) as a very sensitive tool to detect proximity induced interface spin polarization in Pt/Fe, Pt/Ni$_{33}$Fe$_{67}$, Pt/Ni$_{81}$Fe$_{19}$ (permalloy), and Pt/Ni bilayers. We demonstrate that a detailed analysis of the reflected x-ray intensity gives insight in the spatial distribution of the spin polarization of a non-magnetic metal across the interface to a ferromagnetic layer. The evaluation of the experimental results with simulations based on optical data from ab initio calculations provides the induced magnetic moment per Pt atom in the spin polarized volume adjacent to the ferromagnet. We find the largest spin polarization in Pt/Fe and a much smaller magnetic proximity effect in Pt/Ni. Additional XRMR experiments with varying photon energy are in good agreement with the theoretical predictions for the energy dependence of the magnetooptic parameters and allow identifying the optical dispersion $\delta$ and absorption $\beta$ across the Pt L3-absorption edge

System Design Results for an Air Taxi Concept in HorizonUAM

Onboard systems such as flight controls, power supply and avionics are an integral part of the air taxi concept being studied in the HorizonUAM project. The aim of this presentation is to give an overview of the current status of the system design. A special focus has been on the full-electric flight control system containing the powertrain components and the power supply system including the thermal management. Based on a multirotor configuration with four main rotors and two push propellers, a safe powertrain architecture was developed and the associated components dimensioned. Simulation models were used to check the dimensioning results and to study the general dynamic behaviour of the mechanical and electrical components. Three different electrical power supply variants were examined: a battery-operated power supply, a fuel cell-based power supply and a hybrid-electric power supply based on both a battery and fuel cell system. Cooling concepts were successfully developed and analysed for these three power supplies. The system design results for the flight control and power supply were achieved in different parallel design streams. The basic feasibility of each system design was verified in each associated design stream. Although attempts have been made to make the same assumptions, this has not always been possible. Thus, the different system designs and models will be integrated and harmonized to achieve fully consistent design results in a future step

Development of a Safe Powertrain System Architecture for the HorizonUAM Air Taxi Concept

The German Aerospace Center project HorizonUAM encompasses numerous research areas regarding urban air mobility. Whithin this context, this presentation aims to explain the design process for deriving a safe all-electric multirotor propulsion system for one of the HorizonUAM air taxi concepts. The main challenges for the multirotor propulsion system are the highly demanding certification requirements, especially in terms of system reliability, which are laid down within the means of compliance of the EASA SC-VTOL. Using a model-based systems engineering design approach which follows the safety design methods of ARP4761, different multirotor propulsion system architectures were iteratively developed, analyzed and further optimized to meet the required system reliabilities. The result of one proposed powertrain propulsion architecture, incorporating 4 main rotors and two push propellers, is presented herein. In addition to the powertrain architecture design each powertrain component, like the electric motor, the motor controller as well as a gearbox, was sized and compared with current state of the art technology. To verify the dynamic behavior of the whole powertrain a simulation model was set up. It could be shown that the powertrain can be build up using currently commercially available components and that the rotor reaction times seem to be acceptable. However, due to the low rotational speeds of the rotors, it is highly advisable not to use a direct drive but rather a gearbox to avoid high thermal losses. In the next future step, the different system models, which were implemented will be integrated to achieve a holistic integrated system model

Self‐assembly Mechanism and Chiral Transfer in CuO Superstructures

Chiral inorganic superstructures have received considerable interest due to the chiral communication between inorganic compounds and chiral organic additives. However, the demanding fabrication and complex multilevel structure seriously hinder the understanding of chiral transfer and self‐assembly mechanisms. Herein, we use chiral CuO superstructures as a model system to study the formation process of hierarchical chiral structures. Based on a simple and mild synthesis route, the time‐resolved morphology and the in situ chirality evolution could be easily followed. The morphology evolution of the chiral superstructure involves hierarchical assembly, including primary nanoparticles, intermediate bundles, and superstructure at different growth stages. Successive redshifts and enhancements of the CD signal support chiral transfer from the surface penicillamine to the inorganic superstructure. Full‐field electro‐dynamical simulations reproduced the structural chirality and allowed us to predict its modulation. This work opens the door to a large family of chiral inorganic materials where chiral molecule‐guided self‐assembly can be specifically designed to follow a bottom‐up chiral transfer pathway.National Natural Science Foundation of China http://dx.doi.org/10.13039/501100001809Helmholtz-OCPC Postdoc ProgramPeer Reviewe

Battery-Electric Powertrain System Design for the HorizonUAM Multirotor Air Taxi Concept

The work presented herein has been conducted within the DLR internal research project HorizonUAM, which encompasses research within numerous areas related to urban air mobility. One of the project goals was to develop a safe and certifiable onboard system concept. This paper aims to present the conceptual propulsion system architecture design for an all-electric battery-powered multirotor electric Vertical Takeoff and Landing (eVTOL) vehicle. Therefore, a conceptual design method was developed that provides a structured approach for designing the safe multirotor propulsion architecture. Based on the concept of operation the powertrain system was initially predefined, iteratively refined based on the safety assessment and validated through component sizing and simulations. The analysis was conducted within three system groups that were developed in parallel: the drivetrain, the energy supply and the thermal management system. The design process indicated that a pure quadcopter propulsion system can merely be designed reasonably for meeting the European Union Aviation Safety Agency (EASA) reliability specifications. By adding two push propellers and implementing numerous safety as well as passivation measures the reliability specifications defined by EASA could finally be fulfilled. The subsequent system simulations also verified that the system architecture is capable of meeting the requirements of the vehicle concept of operations. However, further work is required to extend the safety analysis to additional system components as the thermal management system or the battery management system and to reduce propulsion system weight.Comment: 38 pages, 27 figures, CEAS Aeronautical Journal Special Issue "HorizonUAM - Opportunities and Challenges of Urban Air Mobility

UAM Vehicle Design with Emphasis on Electric Powertrain Architectures

The research on the system architecture of Urban Air Mobility (UAM) vehicles is a vital part within the DLR internal project HorizonUAM. One of the project goals in HorizonUAM is the development of a system concept for an air taxi. This includes research on safe and certifiable onboard systems. The aim of this article is to present results and findings with emphasis on electric powertrain architectures in the multirotor air taxi design. A preliminary design methodology was developed therefor, which enables the examination of full-electric, turbo-electric and hybrid-electric powertrains. This methodology was used in a design study to investigate the influence of different powertrain architectures on the multirotor design. Different evaluation parameters, parameter sweeps and technology exploration of batteries and fuel cell systems were applied to analyze and evaluate their impact on the UAM vehicle design. The main design drivers are the mass of the energy sources and the overall powertrain efficiency, which have a direct impact on the evaluation parameters like power and energy efficiency, maximum take-off mass, and payload fraction. The study showed that different powertrain architectures could lead to opposite vehicle design criteria. Therefore, a clear solution for an advantageous powertrain architecture could not be found. Hybrid-electric solutions, e.g. fuel cell and battery systems or parallel hybrid-electric systems, offer the possibility of increasing efficiency in different flight phases through suitable power management while increasing system complexity. The disadvantage of a high battery mass of a full-electric solution could thus be at least partially reduced

Impact of Different Powertrain Architectures on UAM Vehicle Concepts

The research on the system architecture of Urban Air Mobility (UAM) vehicles is a vital part inside the DLR internal project HorizonUAM. One of the project goals in HorizonUAM is the development of a system concept for an air taxi. For this purpose, research is also carried out in the area of safe and certifiable onboard systems. The aim of this article is to give an overview of the previous results and findings. The system and safety challenges in the design of onboard systems with a focus on electrical powertrain systems are described. A developed preliminary design method enables full, turbo and hybrid electric drive systems to be examined in UAM vehicle design. This methodology was used in a study to investigate the influence of different powertrain architectures on the multirotor design. Here, the basic feasibility of the multirotor designs with different powertrain systems could be determined. For this purpose, the battery weight and the overall efficiency of the powertrain system were identified as design driver. There is still a need for further research into drives with fuel cell systems