室温下金刚石粉末DNP采用调频法

IF 1.8 3区 化学 Q4 CHEMISTRY, PHYSICAL Solid state nuclear magnetic resonance Pub Date : 2022-12-01 DOI:10.1016/j.ssnmr.2022.101833
Daphna Shimon , Kelly Cantwell , Linta Joseph , Chandrasekhar Ramanathan
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引用次数: 1

摘要

动态核极化(DNP)是利用微波辐照将电子自旋的极化转移到核自旋,从而增强核磁共振信号的一种方法。在大多数情况下,使用单色连续波(MCW)毫瓦辐照。最近,一些研究小组已经表明,毫瓦辐射的频率调制可以导致DNP增强的额外增加,而不是MCW获得的。频率调制对固体效应(SE)和交叉效应(CE)的影响已经在20 K以下的温度下用稳定的有机自由基4-羟基TEMPO (TEMPOL)进行了研究。在此,除了SE和CE外,我们还讨论了调频对室温13C-DNP下金刚石粉末的Overhauser效应(OE)和截断CE (tCE)的影响。我们最近发现,由于金刚石晶体内P1(取代氮)环境的非均质性,金刚石粉末可以同时表现出多种DNP机制。我们探讨了定义频率调制的两个参数:(i)调制频率,fm(微波频率变化的速度)和(ii)调制幅度,Δω(微波频率变化的幅度)如何影响通过每种机制获得的增强。在DNP过程中进行频率调制不仅可以提高DNP的增强效果,而且还提供了一种控制哪一种DNP机制最活跃的方法。通过选择适当的调制参数,我们可以选择性地增强某些机制,同时抑制其他机制。
本文章由计算机程序翻译,如有差异,请以英文原文为准。

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Room temperature DNP of diamond powder using frequency modulation

Dynamic nuclear polarization (DNP) is a method of enhancing NMR signals via the transfer of polarization from electron spins to nuclear spins using microwave (MW) irradiation. In most cases, monochromatic continuous-wave (MCW) MW irradiation is used. Recently, several groups have shown that frequency modulation of the MW irradiation can result in an additional increase in DNP enhancement above that obtained with MCW. The effect of frequency modulation on the solid effect (SE) and the cross effect (CE) has previously been studied using the stable organic radical 4-hydroxy TEMPO (TEMPOL) at temperatures under 20 K. Here, in addition to the SE and CE, we discuss the effect of frequency modulation on the Overhauser effect (OE) and the truncated CE (tCE) in the room-temperature 13C-DNP of diamond powders. We recently showed that diamond powders can exhibit multiple DNP mechanisms simultaneously due to the heterogeneity of P1 (substitutional nitrogen) environments within diamond crystallites. We explore how the two parameters that define the frequency modulation: (i) the Modulation frequency, fm (how fast the microwave frequency is varied) and (ii) the Modulation amplitude, Δω (the magnitude of the change in microwave frequency) influence the enhancement obtained via each mechanism. Frequency modulation during DNP not only allows us to improve DNP enhancement, but also gives us a way to control which DNP mechanism is most active. By choosing the appropriate modulation parameters, we can selectively enhance some mechanisms while simultaneously suppressing others.

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来源期刊
CiteScore
5.30
自引率
9.40%
发文量
42
审稿时长
72 days
期刊介绍: The journal Solid State Nuclear Magnetic Resonance publishes original manuscripts of high scientific quality dealing with all experimental and theoretical aspects of solid state NMR. This includes advances in instrumentation, development of new experimental techniques and methodology, new theoretical insights, new data processing and simulation methods, and original applications of established or novel methods to scientific problems.
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