DNP-enhanced NMR surface characterization

通过这一奖项，化学测量和成像计划正在支持达特茅斯学院的Chandrasekhar Ramanathan的研究，以开发研究和了解表面物理和化学性质的新技术。许多重要的过程发生在材料的表面。例如，在太阳能转换过程中或在催化转化器中发生的催化作用发生在催化剂的表面。详细了解固体表面的结构及其与其他介质的界面对于开发新的催化剂和其他技术至关重要，例如可用于测量地下水污染或探测爆炸物的高灵敏度传感器。这项研究开发了基于核磁共振(磁共振成像背后的技术)的方法，并将该技术应用于小规模材料的研究。目标是以高空间分辨率表征这些表面的结构。然后，所产生的信息被用于选择性地激活表面上的特定位置，以改善其催化或传感性能。这项研究正在通过开发有用的新技术产生广泛的影响，这些技术将在许多领域有各种应用。它正在通过当地科学酒吧和咖啡馆的项目产生进一步的影响，这些项目旨在向广泛的社会受众传播所涉及的科学。人们正在开发核磁共振波谱方法来研究表面和界面的物理和化学性质。为了弥补核磁共振的低灵敏度，人们正在设计和优化动态核极化技术(DNP)，以最大限度地增强表面自旋物种的信号，并获得关于纳米和亚纳米尺度上自旋的局部空间有序的信息。特别是，对硅和二氧化硅微米和纳米颗粒中表面官能化基团的DNP使用内源和外源极化剂进行了比较。超极化与静态多脉冲核磁共振技术相结合，如多量子自旋计数实验，以探测这些系统中表面自旋的局部有序性。新开发的方法正在应用于纳米颗粒表面和原子薄层(如Langmuir-Blodgett或功能化石墨烯薄膜)等系统，使用内源和外源偏振剂。这些研究的目的是为了更好地定量估计猝灭区的大小、偏振转移率和关于局域DNP过程的原子能级细节。对这些现象的更好理解反过来可以使使用最优控制技术来选择性地激发和研究某些化学物种，从而使增强的选择性最大化。

With this award, the Chemical Measurement and Imaging program is supporting the research of Chandrasekhar Ramanathan of Dartmouth College to develop new techniques to study and understand the physical and chemical properties of surfaces. A number of important processes occur at the surface of materials. For example, catalysis?such as occurs in solar energy conversion processes or in catalytic converters?takes place on the surface of the catalyst. A detailed understanding of the structure of solid surfaces and their interfaces to other media is critical to the development of new catalysts and other technologies, such as highly sensitive sensors that can be used, for example, to measure groundwater contamination or detect explosives. This research develops methods based on nuclear magnetic resonance (the technology behind magnetic resonance imaging, or MRI) and applies that technique to the study of small-scale materials. The goal is to characterize the structure of these surfaces with high spatial resolution. The resulting information is then used to selectively activate specific sites on the surface to improve on their catalytic or sensing properties. The research is having a broad impact through the development of useful new technologies that will have a variety of applications in many areas. It is having a further impact through programs in local science pubs and cafes designed to communicate the science involved to a broad societal audience. Nuclear magnetic resonance (NMR) spectroscopic methods are being developed to study the physical and chemical properties of surfaces and interfaces. To compensate for the low sensitivity of NMR, dynamic nuclear polarization techniques (DNP) are being designed and optimized to both maximize the signal enhancements for surface spin species, as well as to obtain information about the local spatial ordering of the spins at nanometer and sub-nanometer length scales. In particular, the use of endogenous and exogenous polarizing agents for DNP of surface functionalized groups in silicon and silica micro- and nano-particles are being compared. Hyperpolarization is being combined with static multiple-pulse NMR techniques such as multiple-quantum spin counting experiments to probe the local ordering of the surface spins in these systems. The newly developed methods are being applied to systems such as nanoparticle surfaces and atomistically-thin layers such as Langmuir-Blodgett or functionalized graphene films, using both endogenous and exogenous polarizing agents. The goal of these studies is to get a better quantitative estimate of the size of the quenched region, the polarization transfer rates and atomic level detail about the local DNP process. A better understanding of these phenomena could, in turn, enable the use of optimal control techniques to selective excite and study certain chemical species, allowing selective maximization of enhancements.