| Summary: | A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 5 September 2017. === Ultra-pure type II-a diamond was irradiated with 2,2 MeV of protons with a
fluence of 5:0 1017ions=cm2 at Universidad Autonoma de Madrid (UAM)
using the 5 MV Tandem accelerator at the Centre for Microanalysis of Ma-
terials (CMAM). Magnetic measurements before and after irradiation were
performed using the MPMS XL (5T) system that consists of the Super-
conducting Quantum Interference Device (SQUID) at the Consejo Superior
de Investigaciones Cient cas (CSIC). The sample was further characterised
using low temperature magnetic fi eld microscopy (MFM) and Raman Spec-
troscopy.
The magnetization curves of the pristine (un-irradiated) sample exhibited
an almost perfect diamagnetic signal which was independent of temperature.
The diamagnetic signal obtained was 4:75 107 emu=g and was in agreement
with that found in literature [1]. A very weak magnetic contribution was
observed at 4.2 K though not at room temperature in the pre-irradiation
measurements. The magnetization curves at 300 K and 4.2 K after ir-
radiation and the thermal cycle at 2 kOe exhibited a similar diamagnetic
behaviour to that of the pristine sample with a small and positive magnetic
contribution appearing above the previous diamagnetic background. The
main outcome of the irradiation seemed to be a paramagnetic contribution
but there were additional superparamagnetic and ferromagnetic-like contri-
butions which were also observed.
Raman spectra indicate graphitization on the irradiated area. An appar-
ent blueshit was observed in the main diamond peak that was relative to
1332 cm-1. The irradiated region that was not graphitized showed a little
disorder within the structure of diamond as expected on an area that was
heavily irradiated by protons. The damage was tens of microns into the
sample. The graphitized region showed the G-peak at around 1600 cm-1 of
the damaged diamond that is beyond the graphitization limit. The irradi-
ated region showed a mixture of the sp3 and sp2 orbitals that are related to
the peak at 1330 cm-1 of diamond and the 1580 cm-1 peak related to the G-
band of graphite. The sp2 orbitals corresponded to the micro-polycrystalline
graphite that is often seen in irradiated diamond. It has been previously ob-
served that the defects have a tendency of clustering into graphitic islands
and swell after high dose implantations.
Magnetic measurements show a decrease in the diamagnetic signal of the
sample showing that the irradiation has a ected the magnetic signal of the
sample. A magnetic signal was observed in the MFM image with a negative
contrast, this was observed by the darker regions relative to the pure dia-
mond corresponding to the graphitic/graphitized region in the topography
image. The negative contrast was not completely clear in the MFM image
but it can be observed that there is a change in contrast between the irra-
diated and un-irradiated region.
From the SQUID analyses, Raman measurements and MFM analysis, we
can safely conclude that the irradiation resulted in the mixture of sp2 and
sp3 orbitals that graphitized the irradiated surface. As it was concluded
from the Raman analyses, any magnetic signal measured over the graphi-
tized irradiated region is attributed to the ion induced modi cation of the
diamond structure. === LG2018
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