NV centers in a diamond are proving themselves to be good building blocks for
quantum information, electron spin resonance (ESR) imaging, and sensor applications.
The key feature of the NV is that it has an electron spin that can be polarized and read
out at room temperature. The readout is optical, thus the magnetic field imaging can also
be done easily. Magnetic field variation with feature sizes below 0.3 microns cannot be
directly resolved, and so in this region magnetic resonance imaging must be employed.
To realize the full sensitivity of NV diamond, the spin transition linewidth must be as
narrow as possible. Additionally, in the case of NV ensembles for micron-sized
magnetometers, there must be a high concentration of NV. To this end three techniques
are explored: (1) Electron paramagnetic resonance (EPR) imaging with microwave field
gradients, (2) Magic angle rotation of magnetic field, and (3) TEM irradiation to
optimize the yield of NV in a diamond.
For the EPR imaging demonstration a resonant microwave field gradient is used
in place of the usual DC magnetic gradient to obtain enough spatial resolution to resolve two very close "double NV" centers in a type Ib bulk diamond. Microfabrication
technology enabled the micron-size wire structure to sit directly on the surface of
millimeter-scale diamond plate. In contrast to conventional magnetic resonance imaging
pulsed ESR was used to measure the Rabi oscillations. From the beating of Rabi
oscillations from a "double NV," the pair was resolved using the one-dimension EPR
imaging (EPRI) and the spatial distance was obtained.
To achieve high sensitivity in nitrogen-doped diamond, the dipole-dipole
coupling between the electron spin of the NV center and the substitutional nitrogen (14N)
electron must be suppressed because it causes linewidth broadening. Magic angle
spinning is an accepted technique to push T2 and T2
* down toward the T1 limit. An
experiment was performed using the HPHT diamond with a high concentration of
nitrogen, and a rotating field was applied with a microfabricated wire structure to reduce
line broadening. In this experiment, ~50% suppression of the linewidth was observed
and the effective time constant T2* improved from 114 ns to 227 ns.
To achieve the highest possible sensitivity for micro-scale magnetic sensors the
concentration of NV should be large. Since the unconverted N are magnetic impurities
they shorten T2 and T2*, giving a tradeoff between NV (and therefore N) concentration
and sensitivity. To construct a damage monitor, a type Ib HPHT sample was irradiated
with electrons from a transmission electron microscope (TEM) and the effects on the
ESR transition were seen well before physical damage appeared on the diamond and
thus this proved to be a sensitive metric for irradiation damage.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2010-05-7728 |
| Date | 2010 May 1900 |
| Creators | Kim, Changdong |
| Contributors | Hemmer, Philip R. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | thesis, text |
| Format | application/pdf |
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