Nano-manipulation of diamond-based single
E. Ampem-Lassen1, D. A. Simpson1*, B. C. Gibson1, S. Trpkovski1, F. M. Hossain1, S. T.
Huntington1, K. Ganesan2, L. C. L. Hollenberg1, and S. Prawer1
1Quantum Communications Victoria, School of Physics, The University of Melbourne, Parkville, 3010, Australia.
2Micro-Analitical Research centre School of Physics, The University of Melbourne, Parkville, 3010, Australia.
*Corresponding author: firstname.lastname@example.org
Abstract: The ability to manipulate nano-particles at the nano-scale is
critical for the development of active quantum systems. This paper presents
a new technique to manipulate diamond nano-crystals at the nano-scale
using a scanning electron microscope, nano-manipulator and custom tapered
optical fibre probes. The manipulation of a ~ 300 nm diamond crystal,
containing a single nitrogen-vacancy centre, onto the endface of an optical
fibre is demonstrated. The emission properties of the single photon source
post manipulation are in excellent agreement with those observed on the
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Diamond has a range of readily produced optical centres that can be utilised as single photon
sources (SPSs). Diamond based SPSs offer the unique advantage of long-term photo stability
at room temperature which has generated significant interest in areas such as quantum
information processing (QIP) [1-3]. Among the single photon emitters identified to date [4-9],
the nitrogen vacancy (N-V) centre remains the most studied and applicable for QIP. The N-V
centre has been identified in natural diamonds and can also be created synthetically using the
microwave plasma enhanced chemical vapour deposition (MPECVD) technique  or
through direct ion implantation . The ability to readily fabricate these single defect centres
has in recent times seen the commercialization of the first SPS based on the N-V defect in
diamond . However, fabricating these sources in desired locations and on particular
structures remains difficult due to the statistical nature of creating the atomic defect. The
demonstration of nano-scale magnetometry [13-16] and the possibility of de-coherence
imaging using single N-V centres opens up exciting opportunities in quantum imaging (QI)
. However, if these types of opportunities are to be explored the manipulation of single
quantum systems and sources is required. A previously reported method has been used to
manipulate nano-particles containing single photon emitters by combining an atomic force
microscope (AFM) with a scanning confocal optical microscope . This technique allows
the position and optical characteristics of the emitter to be measured simultaneously provided
the focused laser spot from the confocal microscope coincides with the AFM cantilever tip.
Combined AFM and confocal systems have been shown to be an effective tool in terms of
attaching single quantum emitters onto the AFM tip. However, the technique is limited to
substrates which are transparent and optically thin.
In this paper we present a technique for characterizing and manipulating isolated diamond
nano-particles containing single photon emitters. The nano-manipulation of single diamond
nano-crystals is achieved using a custom tapered optical fibre probe in a standard scanning
electron microscope (SEM) with a nano-manipulator. The technique offers the unique
advantage of being able to inspect and manipulate single diamond nano-crystals onto desired
substrates and waveguiding devices with nano-scale precision.
2. Experimental details
To correlate the position of a single diamond nano-crystal containing a single defect centre in
the SEM environment a marked silicon substrate was prepared using a focused ion beam
(FIB). The markers were milled using 30 keV Ga+ ions with a current of 7 nA to a depth of ~
3 µm to enable detection in the confocal microscope. The marked silicon substrate was then
ultrasonically seeded in a solution of methanol and commercial grade diamond powder (0-500
nm) known to contain appreciably high numbers of (N-V) defect centres. The diamond nano-
particles and subsequently rinsed in acetone, methanol and de-ionised water to remove the
unwanted larger and coagulated particles.
The marked region of the silicon substrate was characterised optically with an in-house
scanning confocal microscope. The room temperature luminescent properties of the emitting
centres were studied under continuous wave (CW) excitation at 532nm with a 100× 0.95 NA
microscope objective, providing a spatial resolution of ~ 400nm. The photo-luminescence
from the emitting crystals captured by the microscope objective was coupled into a standard
62.5/125 µm multimode optical fibre which acted as a pinhole to provide the confocallity of
the microscope. A 560nm long-pass and 650-750nm band-pass filter was used to remove the
unwanted pump excitation before being coupled into the fibre. The photon statistics of the
diamond emitters were characterised using a fibre based version of the Hanbury Brown and
Twiss (HBT) interferometer . The characteristic dip in the second order correlation
function at zero delay time enabled single N-V centres to be identified. The confocal images
of the marked silicon substrate were then used to correlate the position of the single N-V
centres in the SEM. The SEM was operated with a nano-manipulator containing a custom
tapered optical fibre probe with a tip size of ~ 50nm to manipulate the diamond nano crystals
. The probe was fabricated using a custom CO2 laser based fibre pulling system.
3. Results and discussion
The FIB marked silicon substrate used to correlate the position of the single photon emitters is
shown in Fig. 1.
Fig. 1: Focused ion beam (FIB) marked silicon substrate prior to diamond seeding. Note: the
depth of the milled markers was ~ 3 µm.
A fluorescence intensity confocal map of a 70×70 µm region of the seeded marked substrate
is shown in Fig. 2(a). The photon statistics of each fluorescent emitter were studied to identify
a single N-V centre. The fluorescent emitter highlighted in Fig. 2(a) was found to exhibit the
characteristic dip in the second order correlation function at the zero delay time (t=0) (see Fig.
2(d)), with a minimum g(2)(0) of 0,16 observed under 500 µW of excitation power at 532 nm.
The measured single photon emission rate was ~ 270 kHz under the same excitation
conditions. After the initial optical characterization, the sample was placed into the SEM for
inspection and manipulation. The properties of silicon are such that the substrate does not
experience significant charging in the SEM when operated with 10 keV electrons at 50 pA.
The fabricated optical probe however does suffer from charging due to insulating nature of
silica. Therefore, to avoid the charge related issues, the optical probe was coated with a thin
layer of carbon ~ 10 nm. The areas of the marked substrate were compared to the confocal
images to correlate the position of the single N-V emitter. Figure 2(b) shows the SEM image
of a marked region of the substrate.
Fig. 2: (a) Confocal map of a 70×70 µm area of the marked and seeded silicon substrate. (b)
SEM image of the same 70×70 µm region of a marked and seeded silicon substrate (c) The
photo-luminescence spectrum of the fluorescence emitter identified in (a). (d) The photon
statistics of a single N-V centre identified in (a) measured at room temperature with 500 µW
excitation power at 532 nm.
Once the position of the single emitting centre was identified, the tapered probe was
manipulated to pick the diamond nano-crystal from the substrate. A strong electrostatic
Delay time (ns)
20 µm 20 µm
attraction between the tip and diamond nano-particle firmly holds the particle in place
allowing the probe to be re-positioned to another location where the particle is required to be
placed. It is worth mentioning here that several steps had to be taken to manipulate the single
emitter onto a waveguiding structure in the form of a single mode optical fibre (3M FS-SN
3224). Firstly, in order to identify the core region of an optical fibre in the SEM, the end face
was etched in 25% hydrofluoric (HF) acid for 2 minutes . Secondly, the bulk of the
optical fibre is made up of SiO2 which suffers from significant charging in the SEM, to
eliminate these effects the optical fibre was coated with a thin layer of carbon ~ 10 nm. The
emitter was manipulated to a region outside the core to avoid the unwanted fluorescence
background from co-dopants such as germanium and fluorine . Figures 3(a)-(c) illustrate a
sequence of SEM images taken before and after the manipulation of the SPS, with the
corresponding confocal image of the endface of the optical fibre shown in Fig. 3(d).
Fig. 3: (a) SEM image of a single diamond nano-crystal (~ 300 nm) being removed from the
marked silicon substrate. (b) SEM image of the tapered probe with the diamond nano-crystal
attached and positioned above the optical fibre endface. (c) SEM image of the single emitting
diamond nano-crystal positioned in the region outside the fibre core. (d) Confocal image of the
fibre endface after manipulation and 1 hour anneal at 650 °C in air.
After manipulation, the thin layer of carbon coating applied to the endface of the optical fibre
the sample was removed by annealing the fibre at 650 °C in air using an 1100 Quartz Tube
furnace for 1 hour. To confirm that the manipulated N-V centre was not damaged or degraded
in the process, the centre was characterized again using the same experimental configuration
and compared with the results in Fig. 2 obtained on the silicon substrate. A confocal map of
the post annealed fibre endface is shown in Fig. 3(d) which clearly identifies the single N-V
emitter outside the core region of the fibre. It is worth mentioning here that the fluorescence
from the core region of the fibre is not observed in the confocal map as the etched region of
the core is beyond the depth of field (DOF) of the microscope objective. Although perhaps
the most striking feature of the confocal image is the contrast between the SPS and its
surroundings. In the 17 x 17 µm scan, the single N-V centre is the only notable fluorescing
object, allowing it to be easily identified. The photon statistics from the single centre after
manipulation are shown in Fig. 4(a) and the measured single photon emission rate as a
function of incident pump power is shown in Fig. 4(b). The performance characteristics of the
centre are in excellent agreement with those obtained on the original silicon substrate. The
autocorrelation function minimum at the zero delay time, g(2)(0), was measured to be 0.16
before and after manipulation and the measured single photon emission rate was within 5% of
the rate obtained on the original substrate. These results confirm that the manipulation
technique does not degrade the performance of the single photon source.
Fig. 4: (a) The photon statistics of the single N-V centre on the endface of the optical fibre
measured at room temperature with 500 µW excitation power at 532 nm. (b) Single photon
emission rate as a function of incident pump power.
This technique opens up the possibility to manipulate single photon sources onto structures
such as mirrors, nano-wires and cavities which can all act to enhance the emission properties
[21-23]. Furthermore, the ability to nano-manipulate single quantum systems could prove
advantageous in realizing QIP and QI applications. Although the sample preparation can be
laborious, economies of scale can be achieved since a single seeded substrate contains
numerous single defect N-V centres.
A novel technique for manipulating single diamond nano-crystals, containing single N-V
defect centres, was presented. The technique maintains the performance characteristics of a
single N-V centre in a 300 nm diamond crystal before and after manipulation. The ability to
inspect the nano-particles throughout manipulation process provides an important adjunct to
existing methods for analyzing and manipulating single photon sources. Manipulating these
types of quantum systems onto nanostructures and other plasmonic and cavity devices is the
goal of future work.
The authors acknowledge Dr. Sergey Rubanov for helpful discussions regarding the operation
of the FIB/SEM. This project was supported by Quantum Communications Victoria, which is
funded by the Victorian Government's Science, Technology and Innovation initiative.
Delay time (ns)
0 2040 6080
Incident Pump Power (?W)
200 300400 500
Emission Rate (kHz)