Microscopic imaging has increased our understanding of the world and has been responsible for numerous scientific achievements, from the discovery of microbes in biology to imaging atoms in physics. With the development of spintronics and micromagnetic devices, there is an increasing demand for nanometer-scale imaging to detect quantum features of materials such as electron spins, magnetic domain structure in ferromagnets, and magnetic vortices in superconductors. This is often accomplished by combining traditional microscopy methods, like scanning tunneling microscopy and atomic force microscopy (AFM), with magnetic sensors to generate "scanning magnetometry probes" capable of nanoscale imaging and sensing. However, these probes frequently demand ultrahigh vacuum conditions and extremely low temperatures, and their spatial resolution is restricted by probe size.
Nitrogen-vacancy (NV) centers in diamond (defects in diamond structure caused by nitrogen atoms close to "vacancies" created by missing atoms) have received a lot of attention in this respect. The NV pair, it turns out, may be used in conjunction with AFM to do local magnetic imaging and can function at ambient temperature and pressures. However, the fabrication of these probes requires sophisticated processes that do not provide much control over the probe form and size. A new study led by Associate Professor Toshu An of the Japan Advanced Institute of Science and Technology (JAIST) and Yuta Kainuma, a Ph.D. student at JAIST, in collaboration with researchers from Kyoto University, Japan, and the National Institute of Advanced Industrial Science and Technology, Japan, addressed this issue by fabricating NV-hosting diamond probes using a novel technique combining laser cutting and focused ion beam (FIB) processing that enabled both a high NV-hosting diamond probe This research was published in Volume 130, Issue 24 of the Journal of Applied Physics and was made accessible online on December 28, 2021.
To begin, the scientists implanted nitrogen ions into the bulk diamonds to produce N-V centers. They next polished the opposing surface and used laser cutting to create several rod-shaped pieces. They connected one of the diamond rods to the tip of an AFM probe and utilized FIB processing to shape the diamond rod's front surface into the final probe form. "Gallium ions are used in FIB to form the probe. These ions, however, can cause vacancies in the diamond lattice, changing the charge state of the NV defect. To circumvent this, we milled a donut-shaped pattern around the core of the probe to protect the NV center "Dr. An elaborates. The final probe was a micropillar consisting of 103 NV centers with a diameter of 1.3 µm and a length of 6 µm.
The scientists used the probe to scan the periodic magnetic domain structure in a magnetic tape. Dr. An says, "We photographed the stray magnetic fields from the magnetic domain structure by mapping the photoluminescence intensity at a given microwave frequency and the resonance frequencies in the optically recorded magnetic resonance spectra." The researchers believe that the new production approach will widen the use of quantum imaging probes. "In recent years, innovative technology has been developed in order to alleviate environmental and energy concerns and achieve human society's long-term prosperity. In the future, quantum measurement and sensing technology are projected to totally change the system that maintains social infrastructure. In this sense, our manufacturing process might aid in the realization of nano-scale quantum imaging "Dr. An adds.
Journal Information: Yuta Kainuma et al, Scanning diamond NV center magnetometer probe fabricated by laser cutting and focused ion beam milling, Journal of Applied Physics (2021). DOI: 10.1063/5.0072973