High-field Dynamic Nuclear Polarization using Spin Probes and Intrinsic Defects at Local Interfaces of Polymers and Solids

在加州大学圣巴巴拉分校化学系化学测量和成像项目的支持下，Song-I Han教授和她的团队正在开发新的仪器和方法，用于高磁场核磁共振（NMR），以探测复杂和非均相材料的详细微观结构，例如多相嵌段共聚物或非晶硅。常规核磁共振波谱的灵敏度不足以在必要的亚纳米尺度上探测表面或界面的微观结构性质。韩教授通过开发新的动态核极化（DNP）放大核磁共振仪器和7特斯拉的方法来解决这一挑战，通过低温冷却和从极化电子自旋到核自旋的极化转移，将信号增强多达五个数量级。该方法的一个独特而关键的方面是利用战略电子自旋探针，特别是通过化学功能化定位，或对材料的功能或故障至关重要的内在顺磁缺陷。韩教授正在为自制光谱仪增加并发连续波和脉冲电子顺磁共振（EPR）检测功能，以通过核和电子自旋探针提供完整的材料表征。高场DNP方法可能会对广泛的功能和非均相材料的研究产生重大影响，例如各种多相聚合物体系或非晶和晶体Si基光伏材料，其界面性质或本征顺磁中心是其功能或故障的核心。通过为本科生提供研究机会和支持追求高水平科学事业的女科学家的专业发展，加强了教育影响。

With support from the Chemical Measurement and Imaging program in the Division of Chemistry, Prof. Song-I Han and her group at the University of California - Santa Barbara are developing new instrumentation and methodologies for high magnetic field nuclear magnetic resonance (NMR) to probe the detailed microstructure of complex and heterogeneous materials, e.g. of multiphase block copolymers or amorphous silicon. The sensitivity of conventional NMR spectroscopy is insufficient to probe the microstructural properties at the surface or interface at the necessary sub-nanometer length scale. Prof. Han addresses this challenge by developing novel dynamic nuclear polarization (DNP)-amplified NMR instrumentation and methods at 7 Tesla that enhance signals by up to five orders of magnitudes through cryogenic cooling and polarization transfer from polarized electron spins to nuclear spins. A unique and crucial aspect of the approach is utilization of strategic electron spin probes specifically located through chemical functionalization, or intrinsic paramagnetic defects that are critical to the function or malfunction of the materials. Prof. Han is adding concurrent continuous wave and pulsed electron paramagnetic resonance (EPR) detection capabilities to a home-built spectrometer to provide complete materials characterization through the nuclear and electron spin probes. The high field DNP approach may have high impact on the study of a wide range of functional and heterogeneous materials, e.g. a variety of multiphase polymer systems or amorphous and crystalline Si based photovoltaic materials, whose interfacial properties or intrinsic paramagnetic centers lie at the core of their function or malfunction. Educational impact is enhanced by provision of research opportunities for undergraduate students and by supporting professional development for women scientists pursuing high level science careers.