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

由于核衰变释放出高能粒子，所以放射性很容易被探测到。事实上，它最初是在照相胶片被这种粒子偶然曝光时发现的。现代电子探测器非常灵敏，甚至可以从几个放射性原子中检测出放射性，从而使“放射性示踪”技术成为可能，在这种技术中，用放射性原子标记的化学物质可以通过化学、物理和生物过程进行跟踪。这是医学成像技术的基础，如正电子发射断层扫描（PET）。在这里，放射性衰变仅仅报告了放射性标记物种的位置。然而，某些类型的放射性可以给出放射性探针原子的局部环境的更详细的图像，这是β探测核磁共振（ß-NMR）的基础，这是该提议所基于的技术。**放射性衰变检测使ß-NMR成为研究材料局部原子性质的一种异常敏感的手段。然而，进行这样的测量是复杂的。所使用的放射性离子的半衰期必须很短，大约几秒钟或更短，因此必须在使用前立即制造。位于温哥华UBC的加拿大核与粒子物理国家实验室TRIUMF的ISAC设施提供了这种短寿命放射性离子束。我们的主要探测器是锂的重同位素8Li（半衰期848毫秒）。世界上只有少数实验室可以制造这样的光束，但更多的实验室正在建设中。我们在TRIUMF的努力引领了世界ß-NMR的发展，基于我们的成功，其他实验室现在正在寻求跟随。**这种测量的难度和复杂性意味着我们将ß-NMR的使用限制在它唯一能够解决的问题上。ß-NMR的一个关键功能是能够将放射性探针植入材料的不同深度。虽然有许多强大的“表面”探测器，即材料的最上层原子层，但很少有探测器可以研究材料在表面以下深度的函数。然后，我们的主要动机是使用ß-NMR来研究表面和界面效应，这些效应会在几纳米（10亿分之一米）到几百纳米的深度尺度上引起对固体中深度依赖现象的理解不足，这是现代电子技术的一个重要范围。**金属/半导体、金属/聚合物或电极/电解质等不同材料之间的界面对各种设备至关重要。随着设备进一步小型化，接近纳米技术的极限，设备中的每个原子都靠近一个界面。然而，界面效应还没有被很好地理解。该提议旨在利用ß-NMR的深度分辨能力来研究界面问题。**具体来说，我们将研究可能成为下一代技术基础的新材料，例如拓扑绝缘体和相关电子导体，它们具有独特的电磁特性，可用于新型器件，可以避开传统半导体器件的基本限制。我们将研究纳米结构的催化金属和锂离子导体中的界面效应，目的是更好地理解基础知识，并实现新一代电池技术，这对便携式设备日益增长的能源需求至关重要。我们还将探索ß-NMR在聚合物和生物化学中无法用其他方式解决的某些问题上的新应用。**加拿大将受益于引领世界先进材料研究，其成果将导致更好的基础理解，从而优化当前技术并开发全新技术。

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.