The combination of extreme electronic and thermal properties found in synthetic diamond produced by chemical vapor deposition (CVD) is raising considerable excitement over its potential use as a semiconductor material. Experimental studies have demonstrated charge-carrier mobilities of >3000cm2V-1s-1 and thermal conductivities >2000 Wm-1K-1. The material has been predicted to have a breakdown field strength in excess of 10 MVcm-1. These figures suggest that, providing a range of technical challenges can be overcome, diamond would be particularly well suited to operation as a semiconductor material wherever high frequencies, high powers, high temperatures or high voltages are required. This proposal addresses the novel use of 'delta-doping' to realise such devices.In conventional device technology a major limitation to the magnitude of mobility values within a given semiconductor is the presence of ionised impurities which cause carrier scattering. However, it is these ionised impurities that are the origin of the free carriers within n- or p-doped material. It is the physical separation of the impurities from the free carriers, such that less scattering occurs and mobility values increase, that lies at the heart of recent improvements in high frequency device performance using III-V semiconductor technology. One approach to achieve this the formation of very thin, highly doped regions within a homostructure. Provided the doped, or d, layer is only a few atom layers thick, carriers will move in a region close to, but outside, this layer. The resultant separation between carriers and the donor/acceptor atoms that created them leads to enhanced mobility. The advantages offered by d doping in other systems will be valid for diamond, with the additional feature that the problem with the large activation energy of boron can be overcome, as very high concentrations are desirable in the d-layer. However, the molecular beam epitaxy (MBE) techniques that can be used for III-V semiconductor growth cannot be used with diamond; the need to use plasma-enhanced CVD processes significantly complicates the approach needed to realise atomic-scale modulation-doped diamond structures.While Si and GaAs devices dominate the solid-state microwave device market, they cannot match the power performance of the vacuum tube. One driver for diamond as a semiconductor stems from an interest in replacing vacuum tubes in niche applications. The development of a solid-state alternative would have many benefits including small size, low weight, low operational voltage (compared with vacuum tube devices), and greater robustness. Current vacuum tube designs, such as magnetrons, klystrons, and traveling-wave tubes (TWT) are usually bulky, often fragile, and expensive (with the exception of magnetrons for microwave ovens, which are manufactured in huge volumes and cost only $10-20/kW). If the intrinsic properties of diamond could be fully exploited through novel delta-doped device design and fabrication, it could compete not only with existing wide-bandgap devices (based on SiC and GaN) but also with TWTs in the entire radio frequency (RF) generation market up to 100 GHz. The control of power at high voltages is another potential use of the diamond devices that may arise from the proposed programme of study. Theoretically, a single diamond switch could be used to switch power at voltages approaching 50 kV. This is not currently achievable with any other electronic material.

Mitochondria are small bacteria like organelles contained inside everybody's cells. Often called the battery pack of a cell, they are responsible for taking the oxygen we breathe and using it to generate a molecule known as ATP, the unit of currency for energy production inside most living organisms. Mitochondria generate ATP using chemical reactions that push protons to one side of a small membrane inside the mitochondria. This generates an imbalance of electrical charge across the membrane called mitochondrial membrane potential (MMP), equivalent in strength to the electrical field required for a bolt of lightning to strike during a thunderstorm. This charge imbalance inside the mitochondria pushes protons back through a small protein motor on the membrane to generate ATP, giving cells the energy required to function in their day-to-day tasks. The importance of this little organelle should not be understated and it is widely held to have underpinned the evolution of all complex life on earth. Dysfunctional mitochondria can cause many problems for health and have been linked to a range of diseases such as Parkinson's, heart disease, cancer and obesity. A by-product of this energy creating process in mitochondria are molecules called free radicals. The presence of free radicals inside the body are commonly thought to be a bad thing. It is true that in some circumstances they cause damage to the body however, these free radicals are also involved in many different processes in the body that are vital for the maintenance of health. As such free radicals have to be carefully regulated such that they are not being produced at harmful levels, but in sufficient amounts to allow cells to function normally. Collectively, this balance of free radical production and MMP is referred to as the mitochondrial redox state. This redox state can be a very good indicator of whether a cell is healthy or is undergoing stress or dysfunction. For example, a hallmark of many cancers is 'the Warburg effect' in which cancer cells have a very different mechanism for generating energy which implies a change in the function of mitochondria in growing tumours. Researchers have long been interested in how to better understand mitochondria. However, the technologies we use today have certain limitations; one example is the toxic side effects of different chemicals and invasive probes used to measure MMP. In this work we will develop a new technology that can non-destructively study mitochondria more accurately than existing methods to increase our understanding of these organelles and help develop treatments for diseases more effectively. Our approach is based on a peculiar property of pink diamond that will allow us to use a light microscope to study MMP and free radical production in living cells. Pink diamonds obtain their pinkness due to the presence of Nitrogen impurities lodged in the diamond's usually pure carbon structure. These impurities absorb green light and re-emit red/pink light. Physicists have discovered in the last 10 years that the intensity of this light can be used to measure electromagnetic fields very accurately (~250,000 times smaller than the electric field present in mitochondria) and at very short length scales (about 1 million times smaller than the width of a human hair). Our proposed work involves patterning very thin slabs of diamond with a uniform surface layer of these impurities. Then using a series of controlled pulses of green light, we can take pictures of the red/pink fluorescence using a camera and reconstruct a spatial heat map of electric fields and free radicals produced by mitochondria in cells growing on the diamond surface. We predict this new technology could overcome many of the disadvantages of currently used techniques, and will be able to provide new information about how mitochondria work. This could then lead to new and effective treatments for different diseases for the benefit of all.

Recent advances in the growth and processing of electronic diamond have provided a glimpse into the potential device performance and applications that this exciting material system can provide. Unique and highly desirable material properties such as large bandgap, high intrinsic mobility and very high thermal conductivity deem diamond the ultimate material for high power/high frequency device realisation. This combined with ultra small feature processing potential, points towards an ultra short gate length FET technology as the obvious choice for the application of such a unique material system. For this work it is proposed that 10nm T-gate diamond FETs be investigated leading to a device technology that can satisfy the expanding demand for high power / high frequency operation. In particular this technology finds application in increasing the source power of Terahertz imaging systems, which currently are of great interest for security and medical imaging applications. This prime goal of the proposed research is accomplishable using high quality diamond material supplied by U.K. based company Element 6 and use of the extensive fabrication and characterisation facilities at the University of Glasgow. In particular, access to the ultra-high resolution capabilities of the recently commissioned Vistek VB6 electron beam lithography tool, provides a direct route to the realisation of such ultra-small dimension devices.

The high breakdown voltage and large sheet carrier density of GaN based HEMTs provide major advantages for rf and microwave systems owing to their power handling capability. These advantages have also underpinned the emergence of GaN based components for low frequency power electronics. The latter is a major growth area as energy efficiency and sustainability become critical factors in the design of electrical systems. The overwhelming cause for reduced electrical power efficiency in active electronic components and systems is unwanted increases in operating temperature, which degrade power gain in amplifiers, the internal quantum efficiency of light emitting diodes and power conversion efficiency of diode lasers. As an example of the impact device heating on system efficiency, about 70% of the electrical power consumed by mobile telephone transmitter is wasted as heat owing to Joule heating in the electronics and consequent reductions in power gain of its constituent transistors. The most effective way to limit the temperature rise of a semiconductor device is to introduce high-thermal conductivity heat spreading layers as close as possible to its active region, for example over the top of the device or growing the device structure on a thermally conducting substrate. Typically GaN based HEMTs of the type used in rf circuits and high power electronics are grown on SiC or increasingly Si wafers substrates. Whilst SiC is a better thermal conductor than Si, polycrystalline or crystalline diamond are far superior, better even than metals. Recently GaN HEMT grown on crystalline diamond substrates have been recently demonstrated. However, the small size (5 x 5 mm) of current crystalline diamond (PD) substrates and their high cost prohibit this ideal approach. Thus, a polycrystalline diamond substrate offers the best solution. The calculations show that the larger thermal conductivity of polycrystalline diamond could bring to power HEMT performance compatible or better than that on SiC or Si substrates. To date, the most widely investigated method of exploiting PD substrates in GaN power HEMT technology has been to grow the III-Nitride layers on a Si substrate, then transfer the epitaxy to carrier substrate and finally bonding the device layers to the PD wafer. The procedure involves two wafer bonding steps, a process that requires minimal wafer bow if breakage is to be avoided, something that is difficult to achieve owing to the lattice mismatch between Si and III-Nitride materials. There is also a tendency for the final structure to delaminate and despite several years of development by companies like Group4Labs, SOITEC and Nitronex, commercial products are still not established. To overcome these difficulties, an alternative approach has been developed by the Applicants in collaboration with Element 6. Briefly, this involves forming a composite structure comprising a thin layer of Si on a thicker layer of polycrystalline diamond, intimately contacted without wafer bonding. The upper Si surface is suitable for immediate III-Nitride growth. More information is given in section 3. One patent application has already been filed (world wide) and a second is in preparation; in both instances Bath has assigned its rights to Element 6. Independently of Element 6 and other parties, Bath has developed methods for growing III-Nitride hetero-epitaxy on these complex Si/PD substrates. The results of applying these methods to realise high quality III-Nitride epitaxial layers on Si/PD substrates has recently been reported in ICNS9, critical details in the process were not disclosed and thus the opportunity exists to create an intellectual property portfolio covering the realisation of device grade III-Nitride epitaxial films on Si/PD heat extracting substrates to complement the very separate existing IP covering the manufacture of the latter. The new knowledge will be owned in its entirety with the University of Bath.

Atoms and molecules are very well described by quantum mechanics, but what about much larger things? Erwin Schrödinger pointed out that cats have never been shown to exist in a quantum superposition, but recent experiments are pushing back the boundaries of which objects have been shown to do this. The strongest tests require a large mass in a superposition for a long time with a large superposition distance. The superposition distance is the distance between the two components of the superposition. Pioneering experiments have been done with superconductors, superfluids and vibrating cantilevers but the most macroscopic superposition state created so far is a variant of the famous two-slit experiment for molecules made of 2000 atoms. Our project has the ambitious goal of testing whether levitated nanodiamonds made up of more than a million times more atoms can display this quantum behaviour. The most exciting thing about this experimental frontier is that it could, in 10-15 years, lead to a test of quantum gravity. Einstein's general relativity explains gravity and is needed to make GPS work, but we don't know how to combine it with quantum mechanics to explain the gravitational effects produced by a quantum object. Successfully combining these two most fundamental theories of physics would produce a theory of quantum gravity, which has been sought for 100 years. Theories of quantum gravity such as string theory and loop quantum gravity have been proposed, but suffer from a lack of empirical evidence. Physicists such as Stephen Hawking and Roger Penrose worked on black holes and showed they are fertile playgrounds to constrain theories of quantum gravity, but black holes are not practical to experiment on. A new proposal from us and others shows a way to test one key aspect of quantum gravity with a lab experiment on a table-top. The idea is to create two of the nanodiamond Schrödinger cats and see how they interact gravitationally. This project is only possible thanks to the advances already demonstrated by the quantum technology community, and indeed this research will, in time, lead to a new class of more sensitive sensors that would be used to detect acceleration, rotation, tilt, gravity and magnetic fields. Having already published our descriptions for how to test macroscopic quantum mechanics and quantum gravity, we will now transform our preliminary experiments to begin the delivery of these proposals. To reach large superposition distances and long durations we will use diamond nanoparticles (around 800 nm across) containing a single nitrogen vacancy centre (NVC). This follows our proposals which provide a clear route to achieve a superposition distance of over 1000 nm, although our initial experiments will only reach 0.1 pm. Nanodiamonds have been levitated in vacuum using optical traps by us and others, as well as in Paul traps and magnetic traps. We showed that the heating of the diamond by the trapping beam in an optical trap in vacuum is a serious obstacle. To get around this we developed (with collaborator Oliver Williams) large quantities of high-purity nanodiamonds, and have now switched to using a magnetic trap as this further minimises the heating of the levitated diamond. A magnetic trap also provides the inhomogeneous magnetic field which is required to couple the spin to the motion. The core idea is to put the NVC electron spin into a spin superposition because the inhomogeneous magnetic field then provides a superposition of forces on the diamond leading to a spatial superposition. To evidence this, we will then flip the spin to recombine the superposition components for matter-wave interferometry and repeat the interferometry as a function of experimental tilt with respect to gravity to search for interference fringes.