嵌入电子自旋退相干作为基质材料结构的指示剂
Embedded electron spin decoherence as indicator of the matrix material structure
摘要：
本文从理论和实验两方面研究了嵌入电子自旋退相干表征基体材料结构的问题。用核自旋浴模型和集团关联展开方法进行的理论计算表明，基体材料单晶取向间退相干时标极值的位置与最近邻质子偶极耦合的位置相吻合。这一发现证实了单晶脉冲EPR实验进行$γ$辐照的丙二酸（MA）。在多晶基体材料中的电子自旋退相干衰减轮廓是从作为在斐波那契网格上的采样取向的平均值的取向依赖性获得的。此外，从理论上指出，进一步去除核自旋浴中的晶体有序性可以减小多晶值的退相干时间尺度。实验验证了这一预测的哈恩回波时间衰减尺度在一个新的无定形多晶型的MA，获得第一次通过机械研磨。因此，嵌入的电子自旋退相干可以被看作是研究基体材料的结构和/或结构变化的定量指标。
英文摘要：
In this work the problem of characterizing matrix material structure from embedded electron spin decoherence is studied both theoretically and experimentally. Theoretical calculation using nuclear spin bath model and cluster correlation expansion method shows that the positions of decoherence time scale extremums among single crystal orientations of the matrix material coincide with those of the nearest neighbour proton dipolar couplings. This finding is confirmed by single crystal pulsed EPR experiment performed on $γ$-irradiated malonic acid (MA). Electron spin decoherence decay profile in polycrystalline matrix material is obtained from the orientation dependence as an average over sampled orientations on a Fibonacci grid. In addition, it is pointed out theoretically that a further removal of crystal ordering in the nuclear spin bath can reduce decoherence time scale from the polycrystalline value. This prediction is verified experimentally by the Hahn echo time decay scale in a new amorphous polymorph of MA, obtained for the first time by mechanical milling. Thus the embedded electron spin decoherence can be viewed as a quantitative indicator for studying structures and/or structure changes of the matrix material.
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