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
In several upcoming rheological approaches, including methods of micro- and nanorheology, the measurement geometry is of critical impact on the interpretation of the results. The relative size of the probe...
Inspired by chains of ferrimagnetic nanocrystals (NCs) in magnetotactic bacteria (MTB), the synthesis and detailed characterization of ferrimagnetic magnetite NC chain-like assemblies is reported. An easy green synthesis route in a thermoreversible gelatin hydrogel matrix is used. The structure of these magnetite chains prepared with and without gelatin is characterized by means of transmission electron microscopy, including electron tomography (ET). These structures indeed bear resemblance to the magnetite assemblies found in MTB, known for their mechanical flexibility and outstanding magnetic properties and known to crystallographically align their magnetite NCs along the strongest <111> magnetization easy axis. Using electron holography (EH) and angular dependent magnetic measurements, the magnetic interaction between the NCs and the generation of a magnetically anisotropic material can be shown. The electro-and magnetostatic modeling demonstrates that in order to precisely determine the magnetization (by means of EH) inside chain-like NCs assemblies, their exact shape, arrangement and stray-fields have to be considered (ideally obtained using ET).
The
rotation of Ni nanorods, dispersed in dilute and semidilute
poly(ethylene oxide) solutions, is investigated. Ni nanorods with
similar diameter but different lengths are synthesized using the anodic
aluminum oxide template method and characterized by transmission electron
microscopy and static magnetic field-dependent optical transmission
(SFOT) of linearly polarized light. The rotational motion of nanorods,
determined by oscillating magnetic field-dependent optical transmission
(OFOT) measurements, is analyzed to retrieve the local dynamic modulus
of the polymer solution. The effect of probe size relative to intrinsic
length scales of the polymer solution is systematically investigated
by variation of the nanorod size, polymer molar mass, and concentration.
A significant decrease in the zero-shear rate viscosity is observed
in the semidilute entangled regime, which depends on the hydrodynamic
length of the nanorods, L
h, and polymer
radius of gyration, R
g, but not on PEO
concentration. The relative viscosity can be approximated by η
0
OFOT/η
0
macro = exp ( – 5.6R
g/L
h). The macroscopic dynamic
modulus of the entangled polymer solutions is measured by small-amplitude
oscillatory shear. The local dynamic modulus, obtained from nanorod
oscillation measurements, exhibits systematic changes with decreasing
size of the probe particles, which indicate entanglement reduction
as the physical origin of the size effect in this particular particle/polymer
system.
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