New Techniques for Determining Electronic
Properties of Nitrogen Doped Carbon
Nanospheres
Vincent Marsicano, Jonathan Keartland, William Wright,
and Neil Coville
DST/NRF Centre of Excellence in Strong Materials
School of Physics, WITS
School of Chemistry, WITS
Introduction Part 1
• Carbon nanomaterials are of great scientific and
technological interest at present due to their wide
applicability.
• Carbon nanospheres (CNS) were produced using a
horizontal CVD reactor.
• CNS of known dopant level were characterized using
Electron Paramagnetic Resonance (EPR)
• Nitrogen content of unknown samples was determined
using an EPR spectrometer
Electron Magnetic Resonance
• EMR (also known as ESR and EPR) experiment was
performed using the Bruker Spectrometer shown below.
The experiment was performed in CW mode.
Horizontal CVD reactor
XPS Determination of N dopant
SDA = 0% Nitrogen
SDB = 0.4% Nitrogen
SDC = 2.5% Nitrogen
SDD = 5% Nitrogen
EPR Data of Selected Samples
EPR spectra of three Ndoped
CNS
obtained.
Signal strength is based on
many parameters, both of
the spectrometer and the
samples.
3450
3460
3470
3480
3490
Magnetic Field (G)
3500
3510
Samples
are
carefully
weighed to calculate the
number of paramagnetic
sites present per gram of
sample.
EPR Spectrometer Calibration
EPR Spectrometer Calibration Curve
4000
Arbitrary Units per gram
3500
3000
2500
2000
1500
1000
500
0
0
2
Nitrogen Concentration (%)
4
6
Composite EPR Spectrum of SDD and DPPH
3410
3420
3430
3440
3450
3460
Magnetic Field
3470
3480
A
Composite
EPR
spectrum of N-doped
CNS sample (SDD) and
the
EPR
reference
standard (DPPH) that we
used to determine the gfactor. Deconvolution of
the two spectra allows
one to determine the g
value of the original
signal.
3490
EPR Spectrometer Calibration
Electron g Value vs Sample Nitrogen Concentration
• The g Value
increases with
increased
nitrogen
concentration.
2.00270
g Value
2.00268
2.00266
2.00264
hν=gμB
2.00262
2.00260
-1
0
1
2
3
Nitrogen Content (%)
4
5
6
Unknown Sample Characterisation
• SD1 = C2H2 at 900oC for 2 hours.
• SD2 = C2H2 at 900oC for 1.5 hours.
• SD3 = Collected from quartz tube
• SD4 = Collected from quartz boat
•
•
•
•
SD1 = 1.710% ± 0.503%
SD2 = 1.737% ± 0.509%
SD3 = 3.362% ± 1.101%
SD4 = 3.446% ± 0.986%
Unknown Sample Characterisation
Electron g Value vs Sample Nitrogen Concentration
2.00285
• SD1 = 2 hours.
• SD2 = 1.5 hours.
SD4
2.00280
g Value
2.00275
2.00270
SD1
• SD3 = quartz tube
• SD4 = quartz boat
SD2
2.00265
SD3
2.00260
2.00255
-1
0
1
2
3
Nitrogen Content (%)
4
5
6
Introduction Part 2
• Determination of Electronic Transport Properties of
CNS are criticical to their deployment in industry.
• Doping contributes significantly to the transport
properties of these materials.
• Resistivity of the bulk CNS samples was determined
using the Van der Pauw technique.
• Sample chambers were designed and built in-house with
the use of open source communities.
Open Source Technologies
• Open Source technologies were extensively deployed in
the production of these results.
Slic3r
• The experiments were conducted with significant time
and cost saving.
Van der Pauw Greek Cross Cell
Van der Pauw Square Cell
Hall Effect Cell
RepRap Ormerod Printer
Computer Controlled 4 Channel
Physical Relay Multiplexer
SDD
SDC
SDB
SDA
Temperature Dependance of the Resistivity of Carbon
Microspheres of Variying Nitrogen Dopant
Concentrations Determined with a Greek Cross Cell
VDP Results
0.0012
0.0011
Resistivity decreases
with Nitrogen
Dopant level.
Resistivity (Ohm.m)
0.001
0.0009
Metal-Insulator
transition likely caused
by contacts.
0.0008
0.0007
0.0006
50
100
150
200
Temperature (K)
250
300
350
SDD
SDC
SDB
SDA
Temperature Dependance of the Resistivity of Carbon
Microspheres of Variying Nitrogen Dopant
Concentrations Determined with a Square Cell
VDP Results
0.0012
Incraesing dopant
level increases the
semiconducting
behaviour.
0.001
Resistivity (ohm.m)
0.0008
0.0006
VRH and FIT likely
models for conduction.
0.0004
0.0002
RH ≈ -1.1537e-07
0
50
100
150
200
Temperature (K)
250
300
350
Conclusions
• N-doped CNS have been successfully produced using a
horizontal CVD reactor.
• The nitrogen is strongly paramagnetic indicating that the nitrogen
is in substitutional sites
• EPR can be used as a characterisation technique for determining
dopant level.
• Open source technologies allow for substantial cost savings in
producing research.
• Developing an MPRI “open source” community to improve
sharing of ideas and technologies is imperative to increase
research output.
Acknowledgements
Thanks are due to the following:
• DST/NRF CoE in Strong Materials, the School of
Physics for support.
• School of Physics
• Prof. Jonathan Keartland
• Open Source Communities Mentioned