Expanding the Environmental Frontiers of Operando Metrology for Advanced Device Materials Development

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Lord Kelvin famously stated "when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind". This holds none more true than for nanotechnology today. Emergent materials such as 2D transition metal dichalcogenide (TMD) compounds offer exciting, wide opportunities from novel (opto-) electronic devices to energy storage and catalytic energy conversion. For the latter, TMDs materials like MoS2 have shown high catalytic activity and offer large potential as earth abundant electro-catalysts to for instance convert waste CO2 into industrially relevant chemicals/fuels and to generate hydrogen sustainably, i.e. processes of utmost significance as strategies for a sustainable, clean future economy. However, TMD catalysts can undergo significant chemical and structural changes during reactions, and the mechanisms that give the high catalytic activity remain largely unknown. Our knowledge is currently equally meagre in terms of materials synthesis. There is very little understanding how TMDs actually grow and hence how the structure and properties of these materials can be scalably controlled. These challenges and lack of understanding are common to numerous emerging materials. One key reason for this is that they typically can only be resolved and adequately characterised at a "post-mortem" stage, and we are left to speculate what mechanisms actually govern growth or material functionality at industrially relevant "real-world" conditions.This proposal aims at true operando characterisation of novel materials like TMDs under industrially relevant reactive atmospheres at elevated temperatures, to have a transformative impact on their future use by developing a fundamental understanding of their design and functionality. Our focus will be on electron microscopy and spectroscopy, in particular scanning electron microscopy and X-ray photoelectron spectroscopy, which are among the most wide-spread and versatile characterisation techniques in modern science, used across all disciplines in academia and industry. They are endowed with high (near-)surface sensitivity, making them powerful tools for analysing the structure and chemistry of surfaces and interfaces. However, low-energy electrons are also strongly scattered by gas molecules, and therefore all these techniques are conventionally performed under high vacuum or restricted environmental conditions. We propose new environmental cell approaches that can be flexibly implemented for the many electron-based techniques to overcome these restrictions, and enable direct characterisation at high spatial and/or chemical resolution across an unprecedented range of industrially relevant process conditions for temperatures as high as 1000C and in reactive gaseous or liquid environments. The proposal builds on recent strategic equipment investment at Manchester, Cambridge and the Diamond Light Source/Harwell, and together with market-leading industrial partners our vision is to pioneer versatile approaches that open up new correlative, multi-modal operando probing capability applicable to a wide range of fields including organic semiconductors, battery/energy research, catalysis and life sciences. This will also link to simulation and theory to achieve new levels of understanding and predictive power. Applied to TMD materials, this capability will allow us to directly interrogate TMD nucleation and growth at industrially relevant reactor conditions, to develop new manufacturing processes including for so far largely unexplored metallic compounds. This will further allow us for the first time to systematically study model TMD catalysts under reaction conditions. In particular, we propose to explore metallic TMDs like NbS2, as unlike to semiconducting MoS2, their catalytic activity could extend over the entire basal plane, opening new directions to design novel electro-catalysts with low overpotential and high current densities.