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Clays are fine‐grained rocks that form in the presence of water. Their occurrence typically depends on a combination of geological setting and geochemical conditions. The widespread and diverse clay deposits identified on Mars indicate that the planet experienced multiple episodes of water activity, especially in the early period. The characterisation of Martian clays will reveal key information on geological history, the past climatic conditions and the overall habitability of Mars. Among the analytical techniques typically utilised for such mineralogical characterisation, Raman spectroscopy will be applied for the first time during several robotic exploration missions of Mars in the 2020s. In this study, various clay‐rich samples from Westerwald, Germany were analysed to help inform mission operations and interpretation of data returned by the miniaturised Raman instruments. The samples, as verified by infrared spectroscopy, constitute kaolinites, Al‐rich smectites and Fe/Mg‐rich smectites, which are relevant to the clay mineralogy expected at Martian landing sites (Jezero crater and Oxia Planum). Despite the levels of fluorescence experienced during Raman measurements of the clay‐rich powder samples when using a 532 nm laser, the Raman signatures of phyllosilicates were identified for kaolinite and several different types of smectite (e.g. montmorillonite, nontronite, saponite) in these complex dispersions. Following these measurements, identification of various accessory minerals disseminated in the clay matrix was also achieved using the micro‐Raman system. Finally, a brief discussion concerning the analytical strategies for successful clay analyses using miniaturised Raman instruments is provided. [ABSTRACT FROM AUTHOR]

Raman spectroscopy is a commonly applied technique for identifying the molecular nature of the constituents of solid samples. However, the quantification of the intensity associated with a particular molecular solute in solid dispersions requires analytical strategies to integrate the possible microheterogeneity in terms of composition. Many quantitative applications of solid dispersions rely on large spectral datasets. However, analytical procedures with limited data acquisition must be developed in preparation for future robotic planetary exploration missions or for field applications on earth, both of which involve miniaturised instrumentation. Based on statistical models, we evaluate the minimum number of spectra required to deliver robust data for quantitative measurements associated with differing concentrations of β‐carotene or L‐cysteine dispersed in gypsum. In this respect, reference materials were prepared, and we investigated an analytical methodology based on a large, automated multipoint scanning approach enabling the representative interrogation of the samples. We demonstrate from a comprehensive and reproducible model that the intensity associated with different organic contents within a mineral matrix can be estimated from a reduced number of spectra. Calibration curves were established for our reference dispersions of L‐cysteine in gypsum in the range 1–10 wt%, using both confocal benchtop and nonconfocal miniaturised portable instruments. We propose a reference system and a Raman analytical strategy, that is, adaptable for planetary exploration constraints, and which allows quantitative comparison of performance of instrumentation in terms of signal detection. [ABSTRACT FROM AUTHOR]

The Raman Laser Spectrometer (RLS) is one of the three Pasteur Payload instruments located within the rover analytical laboratory drawer (ALD), for ESA's Aurora exploration programme, ExoMars 2020 mission. The instrument will analyse the crushed surface and subsurface samples that are positioned below the Raman optical head by the ALD carousel. The RLS engineering and qualification model (EQM) was delivered to ESA at the end of 2017, after a wide technical and scientific test characterization campaign. The scientific campaign comprised instrument calibration and detailed evaluation of the scientific requirements and overall performance. For spectral calibration, continuous emission standard lamps (such as Hg‐Ar, Ne, and Xe) were utilized, as well as Raman spectra of pure liquids typically used as standards (cyclohexane and carbon tetrachloride (CCl4)). In addition, Raman spectra of the RLS calibration target (CT), a small disc of polyethylene terephthalate (PET) were obtained at various temperatures. This target, placed inside the rover, will be used for both Instrument health checks and calibration activities throughout Mars operations. For the scientific requirements and performance evaluations, several liquid and solid samples were analysed under a wide range of ambient conditions. The obtained spectral band parameters (peak position, relative peak intensity, peak width, and peak profile) were evaluated. Also, the instrument response (in terms of SNR) was characterized at different integration times and detector operating temperatures. In this paper, we provide a description of the development, verification, functional test, and overall scientific performance of the RLS instrument developed for ExoMars. Particular attention is placed on the performance of the EQM, which is the most representative instrument, in terms of engineering and functionality, of the flight model (FM) and in addition is used for performing all the mechanical, thermal, and radiation tests necessary for space qualification (for planetary applications). The data presented and analysed here, comprise part of the overall dataset obtained during the full instrument characterization campaign conducted at INTA before and during delivery and integration of the EQM in the rover ALD at TAS‐I facilities (Torino, Italy). The results obtained confirm that the full functionality and scientific performance of the RLS instrument was maintained after integration. [ABSTRACT FROM AUTHOR]

Graphene is a highly promising material in the development of new photodetector technologies, in particular due its tunable optoelectronic properties, high mobilities and fast relaxation times coupled to its atomic thinness and other unique electrical, thermal and mechanical properties. Optoelectronic applications and graphene-based photodetector technology are still in their infancy, but with a range of device integration and manufacturing approaches emerging this field is progressing quickly. In this review we explore the potential of graphene in the context of existing single photon counting technologies by comparing their performance to simulations of graphene-based single photon counting and low photon intensity photodetection technologies operating in the visible, terahertz and X-ray energy regimes. We highlight the theoretical predictions and current graphene manufacturing processes for these detectors. We show initial experimental implementations and discuss the key challenges and next steps in the development of these technologies. [ABSTRACT FROM AUTHOR]