The high performance, at relatively low energy cost in today's field effect transistors (FETs), is achieved by decades long optimization of electrical contacts that has allowed the miniaturization of the semiconductor channel down to nanoscale dimensions. However, decreasing dimensions of the devices leads to power dissipation in the off state (leakage current) and other detrimental consequences that are collectively referred to as short channel effects. Emergent semiconductors, such as MoS2, that are naturally atomically thin can in principle mitigate several concerns related to short channel effects. In FETs with atomically thin body (ATB) channels, the charge carriers are confined within the sub 1nm thick semiconductor so that application of gate voltage influences all the carriers uniformly. This prevents leakage currents and allows the FETs to be sharply turned on or off. The fact that atomically thin individual layers of bulk-layered materials can be isolated necessitates the absence of dangling bonds in 2D semiconductors, which means that surface roughness effects are minimized. Recent research in FETs suggests that such ATB materials could be one pathway towards future energy efficient electronics that can operate down to milli volts using the current CMOS manufacturing platform. While the benefits of 2D semiconductor FETs in addressing short channel effects are obvious, they still possess lower performance compared to state-of-the-art silicon and III-V semiconductor analogues due the high contact resistance. To reap the benefits of ultra-short channel (sub 10 nm node) and tunnel FETs, contact resistances must be reduced down to the quantum limit. The contact resistance acts as a severe source-choke. This leads to degradation in the performance of the transistor, because the current depends very strongly on the effective gate voltage at the source injection point. The high contact resistance between metals and 2D semiconductors is a major barrier to their implementation in high performance short channel electronics. This proposal aims to pioneer low electrical resistance contacts on atomically thin body (ATB) transition metal dichalcogenide (TMD) semiconductors to enable the exploration of fundamental phenomena that is currently limited by poor contacts - with the motivation to understand key processes that underpin the behavior of short channel and tunnel field effect transistors so that devices with unprecedented energy efficiency and performance can be realized. The proposal builds on the our recent breakthrough on van der Waals contacts on ATB semiconductors published in Nature (April 2019) and strategic investments in the Materials for Energy-Efficient ICT theme at Cambridge through the Sir Henry Royce Institute. Our ambition is to realize low resistance contacts on ATB semiconductors that will allow a broad range of device communities to address and overcome the long-standing challenge of making good electrical contacts on low dimensional materials. The proposed work will underpin and impact ongoing programmes and initiatives aligned with several EPSRC priority areas. This includes adaptation of low resistance contacts for in operando characterization of battery materials using microelectrochemical cells and low resistance contacts for organic semiconductors and perovskites. This proposal aims to bring a step-change and establish an internationally leading programme in low resistance contacts for high-performance electronics based on ATB semiconductors that will add value and connect a broad range of communities. The proposed work will open up new pathways for achieving in-depth fundamental knowledge of physics of novel devices based on ATB materials to accelerate their development towards technological readiness and commercialization in higher value-added products.

The process of translating new materials into practical devices of benefit to society typically requires substantial time and capital investment. By virtue of their unique geometries and material properties, devices based on nanomaterial structures have unique (opto)electronic characteristics enabling applications not possible with conventional bulk materials. When creating a device based on an individual nanostructure, that structure's exact position needs to be known. Fabricating and measuring nanoscale devices is notoriously labour-intensive, involving searching and alignment before manual routing of electrode layout, or manually performing pick-and-place to transfer these nanostructures onto existing electrode configurations. In a research setting, this need for human intervention is a significant bottleneck that slows the development of new nanomaterials-enabled technologies. Worse still, the slow throughput of this approach precludes its application in any manufacturing setting. We have developed a three-pronged approach - together known as NanoMation - to remove the human intervention required during inspection, research and manufacturing. The first is a system of fiducial markers, "LithoTags", which are optimised for lithography processing - photo-, electron beam-, or nanoimprint lithography. These markers can be easily read by automated microscopy processes. The second is a computer-vision system that can find, sort and filter nanostructures depending on desired properties. Third is a system of computer-adjustable electrode designs where a machine-learning algorithm automatically routes the supporting electrodes to form an entire circuit. These processes will enable a rapid transition from individual prototype devices to high performance integrated systems (e.g. single-unit nanomaterial photodetectors, transistors, or LEDs respectively - to image sensors, integrated circuits, and displays).

The next generation of MEMS is NEMS - nano-electro-mechanical systems, and the most promising candidate for NEMS membranes are graphene and 2-dimensional (2-D) materials. 2-D materials exhibit a unique combination of superlative properties such as high stiffness, low bending modulus, high elasticity, low mass per unit area, low thickness and high electrical conductivity. This allows for the development of NEMS membranes that can achieve behaviour that are typically considered conflicting in traditional MEMS devices and membranes, such as both high resonance frequency and high deflection amplitude. A number of 2-D NEMS devices have been demonstrated on the lab scale, including pressure, touch and mass sensors, microphones, self-sustained oscillators, quantum Hall devices, RF front-end filters, switches, photonic modulators and more. These novel NEMS devices will find applications in future robotics, electronics, healthcare, automotive, aerospace and more. The transition from lab-scale devices to large-scale manufacturing of 2-D NEMS has to overcome a number of critical challenges. Some of these challenges, such as minimising nanoscale defects and improving device yield and performance, have been addressed by employing few-layer graphene or graphene-polymer heterostructure membranes. However, there is still one key outstanding challenge in the future manufacturing of novel 2-D NEMS devices. It is well known that 2-D layers possess significant built-in tensile and compressive stresses which are both arbitrarily distributed as well as difficult to control. These arise both from the way that they are grown and the the way that they are transferred from one surface to another during NEMS manufacturing. In the nano-manufacturing of 2-D NEMS devices, it is essential that these built-in stresses are rendered uniformly within each device and across all devices. This will be accomplished in this project by developing a new process that will apply a well-controlled biaxial tensile strain to the 2-D membrane during the transfer from the parent to the target NEMS substrate. Not only will this strain ensure that the suspended membranes are uniform across all devices, the resulting pre-tension will also increase the stiffness of the membrane, and consequently the resonance quality factor of the resulting NEMS device. Furthermore, the static and dynamic sensitivity of the device and its resonance frequency can be tuned by controlling the pre-tension. It is also essential that this applied strain, and the residual strain in the resulting membrane, are monitored in real-time. In this project, we will implement in-situ strain monitoring based on the fact that the strain in 2-D materials can be detected as shifts in their signature Raman spectroscopy peaks. This project will enable the UK to take the lead in wafer-scale and roll-to-roll 2-D NEMS manufacturing, building on the UK's existing strengths in MEMS foundries, printed electronics, 2-D material production, and sensors and actuators. This in turn will strongly reinforce the health of a wide range of other manufacturing sectors including sensors, healthcare, communications, automotive and aerospace. 2-D NEMS will enable various next-generation devices and technologies that will transform our society to be more productive, connected, healthy and resilient.

Semiconductor nanowires (NWs) of group III-V materials have emerged over the past decade as promising ingredients for nanoscale devices and interconnects. NWs offer great opportunities for nanoscale optoelectonic devices, including field-effect transistors, lasers, photodetectors and single-electron memory devices. In addition, NWs are ideal ingredients for next-generation solar cells as they are typically single crystal hexagonal rods of around 5nm in diameter and a few microns length, thus offering excellent conduction pathways to photo-generated charges. III-V semiconductors currently hold the efficiency records of light to electrical power conversion efficiency for conventional planar solar cells, yet they are generally only used in specialised applications such space missions and in solar concentrator arrays owing to their high production cost. The ability to make cheaper, and more efficient solar panels will change the economics in favour of photovoltaics and see a much larger proportion of electricity generation from solar cells. Nanowires are relatively cheap to produce as their growth substrates need not be single crystals and can be recycled. Furthermore the nanoscale geometry of nanowires can be easily manipulated to minimise reflective loss of incident sunlight. However, while early results on NW photovoltaics have been highly promising, these also highlighted that the application of NWs in solar cells crucially relies on electrically doping them accurately and reproducibly. Thus the inability to reliably dope nanowires has become the major obstacle to developing and exploiting any new nanowire based devices. Attaining such control is crucial as it allows directional charge flow along intended device routes. In this research programme we will attack this major obstacle using two a two-fold approach. (1) We will exploit novel techniques of modulation doping in core-shell nanowires to achieve reliable nanowire doping and surface trap passivation; and (2) We will explore alternatives to doping by developing methods to channel charge flow based on interfacial charge transfer at built-in semiconductor heterojunctions. We will tackle these aims with a broad team of experts on both nanowire growth technology and advanced spectroscopic analysis. Relatively few techniques are suitable for assessing the carrier concentration in nanowires, owing to their geometry. We will explore nanowires developed through a range of routes, using a powerful combination of spectroscopic methods based on Optical Pump Terahertz Probe spectroscopy and time- and spatially-resolved photoluminescence spectroscopy. This spectroscopic methodology benefit from being a non-contact method, i.e. the physical observables derived from the measurement are not obscured by variations in the contacts, but reflect the intrinsic properties of the nanowire ensemble. Through these cutting-edge analytical techniques we will advance both of the current leading approches to bottom-up growth of single crystal semiconductor nanowires, which are molecular beam epitaxy (MBE) and metal organic chemical vapour deposition (MOCVD). Having leading research groups on both MBE (Australian National University) and MOCVD (Ecole Polytechnique Federale de Lausanne) growth as partners on this project will allow for the first time a direct comparison of their different approaches to nanowire doping. Through this joint-up approach, we will establish general nanowire design parameters that give a crucial boost to the growth and implementation of semiconductor nanowires in nanoscale optoelectronics devices and next-generation solar cells.

This proposal aims to bring to the UK an amazing microscope which will provide new and powerful capability in understanding the properties of light emitting materials and devices. These materials are key to many technologies, not only technologies that utilise the light emission from materials directly (such as energy efficient light bulbs based on light emitting diodes) but also a range of other devices which utilise the same family of materials such as solar cells and electronic devices for power conversion. Some of these technologies are in current use, but their efficiency and performance can be enhanced by achieving a better understanding of the relevant materials. Other target technologies are further from the market, but may represent the building blocks of our future security and prosperity. For example, the new microscope will provide information about light sources which emit one and only one fundamental particle of light (photon) on demand. Such "quantum light sources" are a potential building block for quantum computers and for quantum cryptography schemes which represent the ultimate in secure data transfer. How will the new microscope allow us to advance the development of all these technologies? It is based on a scanning electron microscope, which utilises an electron beam incident on a sample surface to achieve resolutions almost three orders of magnitude better than can be achieved using a standard light microscope. It thus accesses the nanometre scale, which is vital to addressing modern day electronic devices. Standard electron microscopy accesses the topography of a surface, but the incoming electron beam also excites some of the electrons within the material under examination into states with a higher energy. When these electrons relax back down to their usual low energy state, light may be given out, and the colour and intensity of that light is incredibly informative about the properties of the material under examination. This light emission can be mapped on a scale of ~10 nanometres so that nanoscale structures ranging from defects to deliberately engineered quantum objects can be addressed. This technique is known as cathodoluminescence, and has been in use for many years. The new capability of our proposed system is that it will map not only the colour and intensity of the light emission, but also allow us to measure the timescales on which an electron relaxes back down to its low energy state. We use the phrase "in the blink of an eye" to describe something that happens extraordinarily quickly. A real eye blink takes at least 100 milliseconds, whereas the relevant timescales for the electron to return to its low energy state could be almost 10 billion times quicker than this! The new microscope will be able to measure processes occurring on this time scale, by addressing how long after an electron pulse excites the material a photon is emitted. It will even be able to distinguish between photons with different wavelengths (or colours) being emitted on different time scales. Crucially, coupling this time-resolved capability with the ability to vary the temperature, we will be able to infer not only the time scales on which electrons relax to low energy sites emitting a photon, but also the time scales by which electrons reduce their energy by other, non-light-emitting routes. These non-light-emitting processes are what limit the efficiency of light emitting diodes, for example. Overall, across a broad range of materials, we will build up an understanding of how electrons interact with nanoscale structure to define a material's electrical and optical properties and hence what factors limit or improve the performance of devices. The proposed system will be the most advanced in the world, and will give UK researchers working on these hugely important photonic and electronic technologies a global advantage in developing new materials, devices and ultimately products.