45 research outputs found
Spin properties of dense near-surface ensembles of nitrogen-vacancy centres in diamond
We present a study of the spin properties of dense layers of near-surface
nitrogen-vacancy (NV) centres in diamond created by nitrogen ion implantation.
The optically detected magnetic resonance contrast and linewidth, spin
coherence time, and spin relaxation time, are measured as a function of
implantation energy, dose, annealing temperature and surface treatment. To
track the presence of damage and surface-related spin defects, we perform in
situ electron spin resonance spectroscopy through both double electron-electron
resonance and cross-relaxation spectroscopy on the NV centres. We find that,
for the energy (~keV) and dose (~ions/cm)
ranges considered, the NV spin properties are mainly governed by the dose via
residual implantation-induced paramagnetic defects, but that the resulting
magnetic sensitivity is essentially independent of both dose and energy. We
then show that the magnetic sensitivity is significantly improved by
high-temperature annealing at C. Moreover, the spin properties
are not significantly affected by oxygen annealing, apart from the spin
relaxation time, which is dramatically decreased. Finally, the average NV depth
is determined by nuclear magnetic resonance measurements, giving
-17~nm at 4-6 keV implantation energy. This study sheds light on the
optimal conditions to create dense layers of near-surface NV centres for
high-sensitivity sensing and imaging applications.Comment: 12 pages, 7 figure
Spatial mapping of band bending in semiconductor devices using in-situ quantum sensors
Band bending is a central concept in solid-state physics that arises from
local variations in charge distribution especially near semiconductor
interfaces and surfaces. Its precision measurement is vital in a variety of
contexts from the optimisation of field effect transistors to the engineering
of qubit devices with enhanced stability and coherence. Existing methods are
surface sensitive and are unable to probe band bending at depth from surface or
bulk charges related to crystal defects. Here we propose an in-situ method for
probing band bending in a semiconductor device by imaging an array of
atomic-sized quantum sensing defects to report on the local electric field. We
implement the concept using the nitrogen-vacancy centre in diamond, and map the
electric field at different depths under various surface terminations. We then
fabricate a two-terminal device based on the conductive two-dimensional hole
gas formed at a hydrogen-terminated diamond surface, and observe an unexpected
spatial modulation of the electric field attributed to a complex interplay
between charge injection and photo-ionisation effects. Our method opens the way
to three-dimensional mapping of band bending in diamond and other
semiconductors hosting suitable quantum sensors, combined with simultaneous
imaging of charge transport in complex operating devices.Comment: This is a pre-print of an article published in Nature Electronics.
The final authenticated version is available online at
https://dx.doi.org/10.1038/s41928-018-0130-
A graphene field-effect transistor as a molecule-specific probe of DNA nucleobases
© 2015 Macmillan Publishers Limited. All rights reserved. Fast and reliable DNA sequencing is a long-standing target in biomedical research. Recent advances in graphene-based electrical sensors have demonstrated their unprecedented sensitivity to adsorbed molecules, which holds great promise for label-free DNA sequencing technology. To date, the proposed sequencing approaches rely on the ability of graphene electric devices to probe molecular-specific interactions with a graphene surface. Here we experimentally demonstrate the use of graphene field-effect transistors (GFETs) as probes of the presence of a layer of individual DNA nucleobases adsorbed on the graphene surface. We show that GFETs are able to measure distinct coverage-dependent conductance signatures upon adsorption of the four different DNA nucleobases; a result that can be attributed to the formation of an interface dipole field. Comparison between experimental GFET results and synchrotron-based material analysis allowed prediction of the ultimate device sensitivity, and assessment of the feasibility of single nucleobase sensing with graphene
On the creation of near-surface nitrogen-vacancy centre ensembles by implantation of type Ib diamond
Dense, near-surface (within 10 nm) ensembles of nitrogen-vacancy (NV) centres
in diamond are rapidly moving into prominence as the workhorse of a variety of
envisaged applications, ranging from the imaging of fast-fluctuating magnetic
signals to the facilitation of nuclear hyperpolarisation. Unlike their bulk
counterparts, near-surface ensembles suffer from charge stability issues and
reduced NV formation efficiency due to the diamond surface's role as a vacancy
sink during annealing and an electron sink afterwards. To this end, work is
ongoing to determine the best methods for producing high-quality ensembles in
this regime. Here we examine the prospects for creating such ensembles
cost-effectively by implanting nitrogen-rich type Ib diamond with electron
donors, aiming to exploit the high bulk nitrogen density to combat
surface-induced band bending in the process. This approach has previously been
successful at creating deeper ensembles, however we find that in the
near-surface regime there are fewer benefits over nitrogen implantation into
pure diamond substrates. Our results suggest that control over diamond surface
termination during annealing is key to successfully creating high-yield
near-surface NV ensembles generally, and implantation into type Ib diamond may
be worth revisiting once that has been accomplished.Comment: 7 pages, 3 figure