The electronic spin of the nitrogen vacancy (NV) center in diamond forms an
atomically sized, highly sensitive sensor for magnetic fields. To harness the
full potential of individual NV centers for sensing with high sensitivity and
nanoscale spatial resolution, NV centers have to be incorporated into scanning
probe structures enabling controlled scanning in close proximity to the sample
surface. Here, we present an optimized procedure to fabricate single-crystal,
all-diamond scanning probes starting from commercially available diamond and
show a highly efficient and robust approach for integrating these devices in a
generic atomic force microscope. Our scanning probes consisting of a scanning
nanopillar (200 nm diameter, $1-2\,\mu$m length) on a thin ($< 1\mu$m)
cantilever structure, enable efficient light extraction from diamond in
combination with a high magnetic field sensitivity
($\mathrm{\eta_{AC}}\approx50\pm20\,\mathrm{nT}/\sqrt{\mathrm{Hz}}$). As a
first application of our scanning probes, we image the magnetic stray field of
a single Ni nanorod. We show that this stray field can be approximated by a
single dipole and estimate the NV-to-sample distance to a few tens of
nanometer, which sets the achievable resolution of our scanning probes
Colloidal dispersions of Ni nanorods were synthesized by pulsed electrodeposition of Ni into nanoporous aluminum oxide layers followed by dissolution of the templates. Geometrical characterization of the nanorods by transmission electron microscopy and scanning electron microscopy allowed us to determine the average length (100-250 nm) and diameter (20-40 nm) of the rods and to estimate the thickness of the polyvinylpyrrolidone surfactant layer. Due to their acicular shape, nanorods of the given size are uniaxial ferromagnetic single domain particles and exhibit a distinct anisotropic polarizability. These two characteristic properties are the physical basis for magnetic field-dependent optical transmission and allow us to investigate the rotational diffusion of the nanorods in liquid dispersion. In the present study, we employed AC magnetization measurements, dynamical light scattering and optical transmission measurements in a rotating magnetic field to determine the rotational diffusion coefficient. The results from all three methods were consistent and agree with theory within a factor of 2.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.