Novel ultra-violet/blue optoelectronic materials and devices based on copper halides (CuHa)

Considerable research is being carried out in the area of wide band gap semiconductor materials for light emission applications in the UV/Blue (300-400 nm) spectral range. This project explores the novel use of the Copper Halides (CuHa), specifically γ-CuCl and γ-CuBr, I–VII wide band gap mixed ionic–electronic semiconducting materials with light emitting properties suitable for novel UV/blue light applications. This project details novel research carried out towards achieving single crystal growth of γ-CuCl from solution via Liquid Phase Epitaxy (LPE) based techniques. LPE growth runs are undertaken using an alkali halide flux compound (KCl) to depress the liquidus temperature of CuCl below its solid phase wurtzite-zincblende (β → γ) transition temperature for solution based epitaxy on lattice matched Si substrates (lattice constant of γ-CuCl (0.541 nm) is closely matched to that of Si (0.543 nm). Results show that the resulting KCl flux-driven deposition of CuCl onto the Si substrate has yielded superior photoluminescence (PL) and X-ray excited optical luminescence (XEOL) behaviour relative to comparatively observed spectra for GaN or polycrystalline CuCl. The resulting deposited material is a textured CuCl/K2CuCl3 polycrystalline intermix, with strong broad luminescence and novel luminescent characteristics not previously observed in CuCl. Difficulties inherent to LPE with CuCl/KCl melts, particularly with the CuCl/KCl eutectic system and the CuCl/Si surface reaction, are detailed. The use of γ-CuBr for thin film based blue light emitting devices is investigated. Its structural and physical properties allow for vacuum deposition on a variety of substrates and herein we report on the deposition of γ-CuBr on Si, glass and indium tin oxide coated glass substrates via vacuum evaporation with controllable film thickness from 100 to 500 nm. Temperature dependent photoluminescence characteristics of these γ-CuBr films on Si substrates reveal familiar Zf and I1 excitonic features. Work towards the development of a thin filmelectroluminescent device using a γ-CuBr active layer is outlined. Recently, dramatic improvements in the luminescent intensity of CuBr generated by the chemical interaction between CuCl films and KBr substrates have been demonstrated. The potential improvements in excitonic PL that can be gained from novel approaches to film preparation involving KBr and existing CuBr deposition techniques is promising. We report on the one such novel approach, the vacuum deposition of KBr spots (~30 µm radius) onto similarly deposited γ-CuBr epitaxial layer on a Si substrate. Post-deposition annealing of the samples at 220 °C in conjunction with a small CuBr flux from a target source leads to the formation of intermixed CuBr/ KBr microdots. PL characterisation reveals enhanced UV-Blue excitonic emission centered on the Zf free exciton peak at ~418 nm, far superior to Zf emission from γ-CuBr films deposited previously. An overview of the deposition process involving shadow masks to lay down an ordered array of KBr spots onto a γ-CuBr vacuum evaporated layer is presented, and the samples are characterised using XRD, EDX and spatially resolved room temperature PL

Modelling and Simulation of the Primary Power Distribution of a Lunar Habitat

A MATLAB/Simulink model of the Primary Power Distribution System of a lunar habitat is presented. The model can be adapted to multiple scenarios, and is able to interface with computer models of other habitat subsystems. A constant supply of power is considered regardless of the source and the time of the day, regulating the bus voltage when required. The electrical system of the International Space Station is used for reference and validation. The model has been tested in two scenarios representing two locations on the surface of the Moon.Peer ReviewedPostprint (published version

Additive manufacturing of Lunar Regolith Simulant using Direct Ink Writing

This work explores the use of a lunar regolith simulant as feedstock for the direct ink writing additive manufacturing process as an option to enable future lunar in-situ resource utilisation. The feasibility of this approach is demonstrated in a laboratory setting by manufacturing objects with different geometries, using methyl cellulose or sodium alginate as binding agents, water and lunar regolith simulant to create a viscous, printable ‘ink’. A custom three-axis gantry system is used to produce green bodies for subsequent sintering. The sintered objects are characterised using compressive strength measurements and scanning electron microscopy (SEM). It is proposed that the bioorganic compounds used in this work as additives could be produced in situ for a future lunar base through photosynthesis, utilising carbon dioxide exhaled by astronauts together with the available sunlight. Thus, all the components used for the dispersion – additive, water, and regolith – are available in situ. The compressive strength for sintered samples produced with this method was measured to be 2.4 MPa with a standard deviation of 0.2 MPa (n = 4). It is believed, based on the high sample porosity observed during SEM analysis, that the comparatively low mechanical strength of the samples is due to a low sintering temperature, and that the mechanical strength could be increased by optimising the sintering process further

Electroencephalography (EEG), electromyography (EMG) and eye-tracking for astronaut training and space exploration

The ongoing push to send humans back to the Moon and to Mars is giving rise to a wide range of novel technical solutions in support of prospective astronaut expeditions. Against this backdrop, the European Space Agency (ESA) has recently launched an investigation into unobtrusive interface technologies as a potential answer to such challenges. Three particular technologies have shown promise in this regard: EEG-based brain-computer interfaces (BCI) provide a non-invasive method of utilizing recorded electrical activity of a user's brain, electromyography (EMG) enables monitoring of electrical signals generated by the user's muscle contractions, and finally, eye tracking enables, for instance, the tracking of user's gaze direction via camera recordings to convey commands. Beyond simply improving the usability of prospective technical solutions, our findings indicate that EMG, EEG, and eye-tracking could also serve to monitor and assess a variety of cognitive states, including attention, cognitive load, and mental fatigue of the user, while EMG could furthermore also be utilized to monitor the physical state of the astronaut. In this paper, we elaborate on the key strengths and challenges of these three enabling technologies, and in light of ESA's latest findings, we reflect on their applicability in the context of human space flight. Furthermore, a timeline of technological readiness is provided. In so doing, this paper feeds into the growing discourse on emerging technology and its role in paving the way for a human return to the Moon and expeditions beyond the Earth's orbit

Dellafossite CuAlO2 film growth and conversion to Cu–Al2O3 metal ceramic composite via control of annealing atmospheres

In this work we demonstrate simple techniques to form well crystallised CuAlO2 powders and thick films from CuO and boehmite or alumina, using a novel molten salt painting process. We examine the formation mechanism using X-ray diffraction, scanning electron microscopy, energy dispersive X-ray 15 spectroscopy and in situ high temperature X-ray diffraction and find that the annealing atmosphere plays a critical role. From this we develop a method to create Cu-Al2O3 conductive metal-ceramic composite materials with novel morphologies via the thermal decomposition of CuAlO2 precursor films

Dislocation loops as a mechanism for thermoelectric power factor enhancement in silicon nano-layers

A more than 70% enhancement in the thermoelectric power factor of single-crystal silicon is demonstrated in silicon nano-films, a consequence of the introduction of networks of dislocation loops and extended crystallographic defects. Despite these defects causing reductions in electrical conductivity, carrier concentration, and carrier mobility, large corresponding increases in the Seebeck coefficient and reductions in thermal conductivity lead to a significant net enhancement in thermoelectric performance. Crystal damage is deliberately introduced in a sub-surface nano-layer within a silicon substrate, demonstrating the possibility to tune the thermoelectric properties at the nano-scale within such wafers in a repeatable, large-scale, and cost-effective way

Spatially resolved investigation of the optical and structural properties of CuCl thin films on Si

CuCl thin films grown on (100) Si by thermal evaporation are studied by means of low temperature photoluminescence (PL) and reflectance spectroscopies. Spatially and wavelength resolved room temperature cathodoluminescence (CL) imaging of the surface of the CuCl samples in a scanning electron microscope (SEM) has also been performed. The reflectance spectra are modeled using a dielectric response function with various models involving dead layers and reflected waves in the thin film and the exciton-polariton structure obtained is compared to other studies of CuCl. The modeling is shown to match the experimental data quite well when a dead layer is included at the air/CuCl and CuCl/Si interfaces. Some inconsistencies between the CL spectra and those measured by PL and reflectance have been observed. The effects of changing the accelerating voltage of the probe from 10 keV to the range 1-5 keV to allow depth analysis of the CL are reported, in order to pinpoint the spatial origin of the CL emission within the thin film

Regolith and Radiation: The Cosmic Battle

This chapter discusses regolith utilization in habitat construction mainly from the point of view of radiation protection of humans on missions of long duration. It also considers other key properties such as structural robustness, thermal insulation, and micrometeoroid protection that all have to be considered in parallel when proposing regolith-based solutions. The biological hazards of radiation exposure on the Moon are presented and put in the context of lunar exploration-type missions and current astronaut career dose limits. These factors guide the research in radiation protection done with lunar regolith simulants, which are used in research and development activities on Earth due to the reduced accessibility of returned lunar samples. The ways in which regolith can be used in construction influence its protective properties. Areal density, which plays a key role in the radiation shielding capacity of a given material, can be optimized through different regolith processing techniques. At the same time, density will also affect other important properties of the construction, e.g. thermal insulation. A comprehensive picture of regolith utilization in habitat walls is drawn for the reader to understand the main aspects that are considered in habitat design and construction while maintaining the main focus on radiation protection

Topology Optimization of Compliant Mechanisms as a Design Method to Improve Hardware Performance in Lunar Dust Environment

The experience from the Apollo missions showed that Lunar regolith particles are exceptionally sharp, electrostatically charged, adhesive, and pose a significant risk to mission hardware by entering gaps between the elements of mechanisms and can cause damage especially where rigid body relative displacements occur. The present work presents an alternative approach for the design of hardware that will operate on the Lunar surface. The authors propose the use of compliant mechanisms to produce monolithic mechanisms that are intrinsically resilient to Lunar dust. To support the design of compliant mechanisms topology-optimisation based design methods are here proposed. Topology optimization focuses on optimizing material distribution for a given design space and boundary conditions with the goal of maximizing the performance of the design. Achieving topologically optimized compliant mechanisms, so far, has proven to be challenging, especially when compared to static structures, and the use of commercial software does not automatically translate in ease of use. In this work, several MATLAB routines that can support topology optimisation of compliant mechanisms are explored. The advantages and disadvantages of each routine are highlighted and their application to a compliant force inverter is presented

Implicit lunar dust mitigation technology: compliant mechanisms

The finest fraction of the lunar regolith, namely the lunar dust, poses a challenge for hardware design and lunar operations. The Apollo missions experienced equipment malfunctions and failures due to dust interactions with hardware. In this work we focus on the problems related to the clogging of rigid body mechanisms. We explain the causes of the problem and propose a solution consisting of replacing traditional mechanisms with compliant mechanisms. There are multiple methods for synthesizing compliant mechanisms, but two approaches are most commonly used: analytical design and topology optimization. In this paper using a compliant gripper as an example, the suitability of these methods to design compliant mechanisms used in extra-vehicular activities is investigated. In doing so, the feasibility of using complaint mechanisms in the lunar equipment as part of dust mitigation strategies for surface projects is also demonstrated