Twig Ygal, Sorkin Anton, Cristea David, Feintuch Akiva, Blank Aharon
Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel.
Department of Chemical Physics, Weizmann Institute of Science, Rehovot 76100, Israel.
Rev Sci Instrum. 2017 Dec;88(12):123901. doi: 10.1063/1.5000946.
Electron spin resonance (ESR) is a spectroscopic method used to detect paramagnetic materials, reveal their structure, and also image their position in a sample. ESR makes use of a large static magnetic field to split the energy levels of the electron magnetic moment of the paramagnetic species. A strong microwave magnetic field is applied to excite the spins, and subsequently the ESR system detects their faint microwave signal response. The sensitivity of an ESR system is greatly influenced by the magnitude of the static field and the properties of the microwave resonator used to detect the spin signal. In general terms, the higher the static field (microwave frequency) and the smaller the resonator, the more sensitive the system will be. Previous work aimed at high-sensitivity ESR was focused on the development and testing of very small resonators operating at moderate magnetic fields in the range of ∼0.1-1.2 T (maximum frequency of ∼35 GHz). Here, we describe the design, construction, and testing of recently developed miniature surface loop-gap resonators used in ESR and operating at a much higher frequency of ∼95 GHz (W-band, corresponding to a field of ∼3.4 T). Such resonators can greatly enhance the sensitivity of ESR and also improve the resulting spectral resolution due to the higher static field employed. A detailed description of the resonator's design and coupling mechanism, as well as the supporting probe head, is provided. We also discuss the production method of the resonators and probe head and, in the end, provide preliminary experimental results that show the setup's high spin sensitivity and compare it to theoretical predictions.
电子自旋共振（ESR）是一种用于检测顺磁性材料、揭示其结构并成像其在样品中位置的光谱方法。ESR利用强静磁场来分裂顺磁性物质电子磁矩的能级。施加强微波磁场以激发自旋，随后ESR系统检测其微弱的微波信号响应。ESR系统的灵敏度受静磁场强度和用于检测自旋信号的微波谐振器特性的极大影响。一般来说，静磁场（微波频率）越高且谐振器越小，系统就越灵敏。以往针对高灵敏度ESR的工作重点是开发和测试在约0.1 - 1.2 T（最大频率约35 GHz）的中等磁场下工作的非常小的谐振器。在此，我们描述了最近开发的用于ESR且在约95 GHz（W波段，对应约3.4 T的磁场）的更高频率下工作的微型表面环形间隙谐振器的设计、构造和测试。由于采用了更高的静磁场，这种谐振器可以极大地提高ESR的灵敏度，并改善所得的光谱分辨率。提供了谐振器的设计和耦合机制以及支撑探头的详细描述。我们还讨论了谐振器和探头的生产方法，最后提供了初步实验结果，展示了该装置的高自旋灵敏度并将其与理论预测进行比较。
