Surface noise is a detrimental issue for sensing devices based on shallow nitrogen vacancy (NV) color center diamonds. A recent experiment indicates that electric field noise is significant compared to magnetic field noise. They also found that the electric field noise can be reduced with a protective surface layer, though the mechanism of noise reduction is not well understood. We examine the effect of a protective surface layer on the noise spectrum, which is caused by surface charge fluctuations. We use the fluctuation-dissipation theorem to calculate and analyze the noise spectrum for six different surface layer materials typically used for NV center diamond devices. We find that four parameters largely affect the noise spectrum: effective relaxation time, effective loss tangent, power law exponent of the noise spectrum, and layer thickness. Our results suggest that a surface covering layer is indeed useful for decreasing surface noise, but which material is most suitable depends on the device operational frequency range.
This is an Accepted Manuscript for the Microscopy and Microanalysis 2020 Proceedings. This version may be subject to change during the production process.
A subset of isotopically “presolar” carbon
particles
extracted from the Murchison meteorite contain signatures expected
of particles formed in the atmosphere of red giant stars. Some of
these micron-size particles have spherical cores that show diffraction
rings from atom-thick graphene, possibly formed by solidification
of liquid carbon at low pressure. Electron phase-contrast transmission
electron microscopy (TEM) images suggest that these cores originate
from supercooled carbon droplets that formed graphene sheets on randomly
oriented 5-membered loops. In addition to presolar data, laboratory
synthesis in an “evaporating carbon oven” creates similar
core-rim structures by slow cooling of carbon vapor. In research studies,
it was shown that 5-membered loops are essential to the initiation
of carbon nanotubes on catalyst particles. In addition to offering
this experimental context, we present density functional theory (VASP)
computer simulations suggesting that 5-member loops are more likely
than 6-member loops in a solidifying carbon melt. These things suggest
that 5-member loops compete effectively as nucleation seeds for explaining
the faceted pentacones inferred from TEM images of presolar particle
cores. In that context, pent-first nucleation (along with the crowding
of growing sheets by nearby liquid atoms) may reduce the chances of
graphite layer formation and lead to unprecedented diffusion barrier
properties for this composite material.
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