Ultra miniature resonators for electron spin resonance: Sensitivity analysis, design and construction methods, and potential applications

Abstract

This paper describes a recently developed new family of miniature surface resonators, used for electron spin resonance spectroscopy and imaging. The first part of the paper provides a detailed description of the operational principles of the surface resonators. It also includes sensitivity analysis for a variety of configurations with inner dimensions ranging from 150 μm down to 2 μm, operating at the Ku, Q, and W frequency bands. Most of the data presented here is based on theoretical predictions; however, some of it is accompanied by experiential results for verification. The second part of the paper describes a new type of double-surface microresonator and its production method. This new configuration enables an efficient coupling of the microwave energy from millimetre-sized microstrip lines to micron structures even at relatively low frequencies. The resonator is analysed both theoretically and experimentally – exhibiting ultra-high spin sensitivity. The conclusion of the two parts of the paper is that micron-scale surface microresonators may achieve spin sensitivity of a few thousands of spins in one second of acquisition time for special samples, such as phosphorous-doped ²⁸Si, at cryogenic temperatures. However, further miniaturization below 1–2 microns does not seem to be beneficial, sensitivity-wise. In addition to their high spin sensitivity, these resonators have a huge conversion factor, reaching in some cases to more than 500–1000 G of microwave magnetic field with input power of 1 W. Some possible applications of these unique capabilities are also described herein.

Keywords:

• EPR
• ESR
• microresonators
• imaging
• sensitivity

Acknowledgements

This work was partially supported by grant #213/09 from the Israeli Science Foundation, grant #201665 form the European Research Council (ERC), and by the Russell Berrie Nanotechnology Institute at the Technion. We acknowledge Dr. Graham Smith and his team from St. Andrews for their help with the network analyser measurements at W band. The help and support of Arkady Gavrilov and Avshalom Shai from the Technion's Micro-Nano Fabrication Unit are greatly appreciated.