3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Physical properties of nanostructures induced by irradiation in diamond(2017) Makgato, Thuto NelsonWe investigate the interaction of slow highly charged ions (SHCIs) with insulating type-Ib diamond (111) surfaces. Bismuth and Xenon SHCI beams produced using an Electron Beam Ion Trap (EBIT) and an Electron Cyclotron Resonance source (ECR) respectively, are accelerated onto type Ib diamond (111) surfaces with impact velocities up to 0.4 Bohr. SHCIs with charge states corresponding to potential energies between 4.5 keV and 110 keV are produced for this purpose. Atomic Force Microscopy analysis (AFM) of the diamond surfaces following SHCI impact reveals surface morphological modi cations characterized as nanoscale craters (nano-craters). To interpret the results from Tapping Mode AFM analysis of the irradiated diamond surfaces we discuss the interplay between kinetic and potential energy in nanocrater formation using empirical data together with Stopping and Range of Ions in Matter (SRIM) Monte Carlo Simulations. In the case of irradiation induced magnetic e ects in diamond, we investigate the magnetic properties of ultra-pure type-IIa diamond following irradiation with proton beams of 1-2 MeV energy. SQUID magnetometry of proton irradiated non-annealed diamond indicates formation of Curie type paramagnetism according to the Curie law. Raman and Photoluminescence spectroscopy measurements show that the primary structural features created by proton irradiation are the centers: GR1, ND1, TR12 and 3H. The Stopping and Range of Ions in Matter (SRIM) Monte Carlo simulations together with ii iii SQUID observations show a strong correlation between vacancy production, proton uence and the paramagnetic factor. At an average surface vacancy spacing of 1-1.6 nm and bulk (peak) vacancy spacing of 0.3-0.5 nm Curie paramagnetism is induced by formation of ND1 centres with an e ective magnetic moment eff (0.1-0.2) B. Post annealing SQUID analysis of proton irradiated diamond shows formation temperature independent magnetism with magnetic moment 6-7 emu superimposed to Curie-type paramagnetism. The response of ultra-pure type-IIa single crystal CVD diamond following 2.2 MeV proton micro-irradiation is further investigated using Atomic Force, Magnetic Force and Electrostatic Force Microscopy (AFM, MFM and EFM) under ambient conditions. Analysis of the phase shift signals using probe polarization dependent magnetization measurements and comparison of the MFM and EFM signals at zero electrical bias, show that measured force gradients originate from a radiation induced magnetic response in the micro-irradiated regions in diamond.Item Magnetic properties in diamond induced by proton irradiation(2017) Mdhluli, Joyful ElmaUltra-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.