Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Towards optimized surface $\delta$-profiles of nitrogen-vacancy centers
  activated by helium irradiation in diamond   The negatively-charged nitrogen-vacancy (NV) center in diamond has been shown
recently as an excellent sensor for external spins. Nevertheless, their optimum
engineering in the near-surface region still requires quantitative knowledge in
regard to their activation by vacancy capture during thermal annealing. To this
aim, we report on the depth profiles of near-surface helium-induced NV centers
(and related helium defects) by step-etching with nanometer resolution. This
provides insights into the efficiency of vacancy diffusion and recombination
paths concurrent to the formation of NV centers. It was found that the range of
efficient formation of NV centers is limited only to approximately $10$ to
$15\,$nm (radius) around the initial ion track of irradiating helium atoms.
Using this information we demonstrate the fabrication of nanometric-thin
($\delta$) profiles of NV centers for sensing external spins at the diamond
surface based on a three-step approach, which comprises (i) nitrogen-doped
epitaxial CVD diamond overgrowth, (ii) activation of NV centers by low-energy
helium irradiation and thermal annealing, and (iii) controlled layer thinning
by low-damage plasma etching. Spin coherence times (Hahn echo) ranging up to
$50\,$ $\mu$s are demonstrated at depths of less than $5\,$nm in material with
$1.1\,\%$ of $^{13}$C (depth estimated by spin relaxation (T$_1$)
measurements). At the end, the limits of the helium irradiation technique at
high ion fluences are also experimentally investigated.

26
The categories of this paper are: bayes-an
31
The categories of this paper are: ao-sci
7
The categories of this paper are: hep-th
32
The categories of this paper are: atom-ph
1
The categories of this paper are: cs
36
The categories of this paper are: cmp-lg
2
The categories of this paper are: math
3
The categories of this paper are: physics
8
The categories of this paper are: hep-ex
22
The categories of this paper are: chao-dyn
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The categories of this paper are: q-fin
27
The categories of this paper are: comp-gas
6
The categories of this paper are: astro-ph
10
The categories of this paper are: q-bio
30
The categories of this paper are: q-alg
16
The categories of this paper are: stat