Development and Application of Depth-Resolved beta-Detected Nuclear Magnetic Resonance to electronic, ionic and molecular phenomena in the Solid State

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Radioactivity is easy to detect since the nuclear decay emits high energy particles. In fact, it was first discovered by the accidental exposure of photographic film by such particles. Modern electronic detectors are extremely sensitive and can detect radioactivity from even a few radioactive atoms, enabling *radiotracer* techniques, where a chemical species, tagged with a radioactive atom, is followed through chemical, physical and biological processes. This is the basis for medical imaging techniques, such as Positron Emission Tomography (PET). Here, radioactive decay merely reports the location of the radiolabelled species. Certain kinds of radioactivity, however, can give a much more detailed picture of the local environment of the radioactive probe atom, a property that is the basis of beta-detected nuclear magnetic resonance (ß-NMR), the technique on which this proposal is based.**Detection by radioactive beta decay makes ß-NMR an exceptionally sensitive means to study the local atomic properties of materials. However, it is complicated to carry out such measurements. The radioactive ions used necessarily have very short halflives on the order of seconds or less, so they must be made immediately before being used. The ISAC facility at TRIUMF, Canada's national lab for nuclear and particle physics, located at UBC in Vancouver, provides beams of such short-lived radioactive ions. Our main probe is a heavy isotope of Li, 8Li (halflife 848 milliseconds). Only a few other labs in the world can make such beams but more are being constructed. Our efforts at TRIUMF lead the world in the development of ß-NMR, and based on our success, other labs are now looking to follow.**The difficulty and complexity of such measurements means that we restrict the use of ß-NMR to problems that it is uniquely capable of addressing. A key capability of ß-NMR is the ability to implant the radioactive probe at different depths in a material. While there are many powerful probes of the *surface*, the top atomic layer, of a material, there are very few that can study materials as a function of depth below a surface. Our main motivation then is to use ß-NMR to study surface and interface effects that give rise to poorly understood depth-dependent phenomena in solids on depth scales of a few nanometers (1 billionth of a meter) to a few hundred nm, an important range for modern electronic technology.**Interfaces between dissimilar materials like metal/semiconductor, metal/polymer or electrode/electrolyte are crucial to all sorts of devices. As devices are further miniaturized towards the limit of *nanotechnology*, every atom in the device is near an interface. However, interface effects are not well understood. This proposal aims to study interface problems using the depth-resolved power of ß-NMR.**Specifically, we will study new materials that may be the basis for next generation technologies, e.g. topological insulators and correlated electronic conductors that have unique electromagnetic properties for new types of devices that may sidestep fundamental limitations of conventional semiconductor devices. We will study nanostructured catalytic metals and interface effects in Li ion conductors, with the aim of a better fundamental understanding and enable new generations of battery technology, crucial for the increasing energy demands of portable devices. We will also explore new applications of ß-NMR to polymers and certain problems in biochemistry that cannot be addressed in other ways.**Canada will benefit by leading the world in advanced materials research with outcomes that lead to a better fundamental understanding that will afford optimization of current technologies as well as development of radically new ones.