For the Jayich Lab’s Quantum Sensing Group at the University of California, Santa Barbara, we developed a custom solution for their challenging nanometer-scale positioning requirements regarding the development of magnetic sensors in a cryogenic environment. Our CPSHR high resonance positioning stage is used to create a very stable atomic force microscope inside a closed-cycle cryostat. In this page their experiment is explained.
The development of magnetic sensors with improved sensitivity is important for studies in a wide range of fields, including solid state physics, new materials synthesis, and biomedicine. There are a number of systems where state-of-the art magnetic sensors are insufficient in terms of their spatial resolution and operating temperature range. The nitrogen-vacancy (NV) defect center in diamond has the potential to enable nanoscale magnetometry in a large class of problems where there are no current magnetic measurement solutions.
Scanning electron microscope image of a typical diamond cantilever fabricated for magnetometry. The density of NV centers is chosen to yield on average approximately one NV center per pillar.
While NVs have promising characteristics for magnetometry, the vast majority of studies have focused on NV centers in bulk diamond, which are not easily amenable to a small movable probe. The critical piece of the puzzle in realizing NV based magnetic imaging with nanoscale spatial resolution is to fabricate diamond cantilevers with high quality, shallow NVs with long spin coherence times near the tip. This will allow for precise nanoscale positioning of the NV center relative to a sample using standard atomic force microscopy techniques.
A nanofabricated single-crystal diamond cantilever is used as the probe tip in a custom-built low temperature atomic force microscope, as seen schematically in figure 1. The atomic force microscope is comprised of a six degree-of-freedom coarse positioning stage from Janssen Precision Engineering that allows for independent alignment of both the tip to the sample, and also the confocal microscope objective to the tip. The RMS vibration between the tip and the sample in the vertical direction with the fridge running is 0.72 nm, measured with a tapping mode technique.
1) Schematic of the low temperature NV scanning magnetometry measurement. The diamond cantilever is patterned with an array of pillars that host NV centers, of which only one is addressed optically. Both the NV center and sample are housed in a closed-cycle cryostat with a base temperature of 6 K.
A representative low temperature NV magnetometry measurement is shown in figure 2, displaying contours of equal magnetic field magnitude at the surface of a hard disk. Contours appear as a reduction in NV fluorescence because, when the resonant condition of applied microwave field and magnetic field is met, the spin of the NV center is driven between a bright and dark fluorescence state.
2) Low temperature NV magnetometry image of the bits of a hard disk at 6 K. The dark contours in the image correspond to locations where the stray field from the hard disk has a magnitude of 5.3 G (resonant with a 2892.7 MHz RF field) along the axis of the NV center.
The custom CPSHR which is driven with 6 PiezoKnobs in total is build into the experiment setup as can be seen in the two pictures below. For more about this custom development click here