Electron spin resonance imaging with AFM using near field microwave techniques

An unpaired electron possess two quantum states when external magnetic field presents. The energy gap between two quantum states increases linearly with the applied external magnetic field strength. The electron spin resonance (ESR) peaks at the moment that the microwave wave photo energy is exactly equal to the electron energy gap. Previous researches demonstrated spatially resolved electron spin resonances using evanescent microwave magnetic-dipole probe at 3.7 GHz on the ruby surface. The minimum number of detected electron spin centers was in the range of 20,000 to 30,000. This paper is to present a new ESR detection technique by integrating the atomic force microscopy (AFM) with near field microwave probe. With smaller probe tips, the spatially confined magnetic field is expected to increase the sensitivity of ESR detections. Both AFM and near field microwave probe techniques are non-destructive and non-invasive measurement techniques. Thus, the new technique will be a powerful instrument for many applications that include the detection of material defect pockets, detecting free radicals in biological tissues, and the analysis of structure and dynamics of biomembranes. Our ultimate objective is to spatially detect single electron spin center and use the single electron as one quantum bit in future spintronic devices.