The diffusion of iodine implanted 6H-SiC has been investigated using Rutherford backscattering Spectrometry (RBS). SiC is used as the main barrier in the modern high temperature gas cooled reactors. An understanding of the transport behaviour of iodine in 6H-SiC will shed some light into SiC’s effectiveness in the retention of fission products. Room temperature iodine implantations were performed to a fluence of 1 x 1016 iodine ions per cm2. Iodine depth profiles were determined by Rutherford backscattering spectroscopy. Previous studies indicate that iodine diffusion cannot be detected for temperatures below 1000oC. Isochronal annealing experiments for 5 hours cycles were then performed starting from 1000oC. 5 hour annealing cycles at 1200oC and 1300oC were also performed. These relatively short annealing cycles were used to study the evolution of the iodine depth profiles and to determine the temperature where the first noticeable broadening of the iodine implanted profile is observed. Broadening of the iodine profile was initially observed at temperatures around 1200oC. Isothermal annealing cycles were then performed at this temperature of 1200oC where the broadening was first observed. The annealing experiments were performed for a total annealing time of 60 hours. Isothermal annealing experiments were also performed at a lower temperature of 1100oC also for a total annealing time of 60 hours. The experimental data was analyzed by fitting the iodine depth profiles to a Gaussian function using the GENPLOT program. Diffusion coefficients were obtained by comparing the full widths at half maximum, (FWHM) of the iodine profiles before and after annealing. Results for 1100oC show that the diffusion coefficient is below 10-21 m2 s-1 . Solving the diffusion equation numerically for this diffusion coefficient shows that the iodine does not traverse more than 2 ìm through SiC after annealing for one year. Intact SiC coatings which have a thickness of 35 ìm in the fuel particles will therefore be able to prevent iodine release from the particle at this temperature. Results for 1200oC show that the diffusion coefficient is in the order of 10-20 m2 s-1. The results also reveal that iodine loss through the front surface is relatively low with only 15% of iodine loss observed after annealing for a total time of 60 hours. Further indications of SiC ability to retain iodine are observed when an iodine peak is still present after annealing for 30 hours at a temperature of 1500oC. Radiation damaged produced during ion implantation was investigated by Rutherford backscattering in conjunction with channeling. The results of the RBS/channeling reveal that the room temperature implantations produce an amorphous layer from the surface up to a depth of 260 nm. Some epitaxial regrowth is observed starting at approximately 1000oC. / Dissertation (MSc)--University of Pretoria, 2011. / Physics / unrestricted

<p>The purpose of this thesis work was to find a way to measure basic light emission properties of nitrogen-and-boron-doped 6H-SiC, which are fabricated with a growth method developed at Linköping University. The research is in its initial phase and the light properties as well as optical measurement techniques are important. The aim is that the results of the measurements will provide feedback to the growth process what quality and doping levels that are required to get the maximum amount of light. The measurements were performed at the Laboratory of Lighting Technology, Technical University of Darmstadt, Germany.</p><p>Two measuring methods with different excitation sources were tested: a double monochromator and a setup using near UV-filters. While the double monochromator was able to project wavelengths in steps down to 0.5 nm with a high accuracy, the filters were only available in steps of 10 nm where the accuracy of the wavelength values varied. The double monochromator was chosen for the continuing measurements.</p><p>When using excitation light between 375-390 nm the emitted light was in the visible wavelength region. The light properties measured were the irradiance (measured in W/m²) and the peak wavelength were maximum luminescence occurred.</p><p>The result showed that sample 2-4 had a peak wavelength at approximately 580‑582 nm for the excitation wavelength 375 nm. For sample 5 the peak wavelength occurred at 582 nm at the excitation wavelength 390 nm. Sample 1, the unintentionally doped, did not show any measurable results as expected.</p><p>When irradiance of the excitation light was approx. 8 W/m² the irradiance at the peak of luminescence for the samples varied between 15.03-29.35 mW/m². The low values are believed to be the result of the emitted light scattering in all directions whereas the measurements are done in one direction and only from a small area of the sample.</p><p>The measurements has shown that it is possible to measure the light properties of the grown material even though the samples were not finalized (capsulated) LED’s. The results from the measurements are of interest for the continuing development of the material.</p>

The purpose of this thesis work was to find a way to measure basic light emission properties of nitrogen-and-boron-doped 6H-SiC, which are fabricated with a growth method developed at Linköping University. The research is in its initial phase and the light properties as well as optical measurement techniques are important. The aim is that the results of the measurements will provide feedback to the growth process what quality and doping levels that are required to get the maximum amount of light. The measurements were performed at the Laboratory of Lighting Technology, Technical University of Darmstadt, Germany. Two measuring methods with different excitation sources were tested: a double monochromator and a setup using near UV-filters. While the double monochromator was able to project wavelengths in steps down to 0.5 nm with a high accuracy, the filters were only available in steps of 10 nm where the accuracy of the wavelength values varied. The double monochromator was chosen for the continuing measurements. When using excitation light between 375-390 nm the emitted light was in the visible wavelength region. The light properties measured were the irradiance (measured in W/m2) and the peak wavelength were maximum luminescence occurred. The result showed that sample 2-4 had a peak wavelength at approximately 580‑582 nm for the excitation wavelength 375 nm. For sample 5 the peak wavelength occurred at 582 nm at the excitation wavelength 390 nm. Sample 1, the unintentionally doped, did not show any measurable results as expected. When irradiance of the excitation light was approx. 8 W/m2 the irradiance at the peak of luminescence for the samples varied between 15.03-29.35 mW/m2. The low values are believed to be the result of the emitted light scattering in all directions whereas the measurements are done in one direction and only from a small area of the sample. The measurements has shown that it is possible to measure the light properties of the grown material even though the samples were not finalized (capsulated) LED’s. The results from the measurements are of interest for the continuing development of the material.

The solid-state interaction of palladium (Pd) with single crystal silicon carbide (6H- SiC) before and after annealing has been investigated using Rutherford backscattering spectrometry (RBS) in conjunction with RUMP simulation package, time-of-flight elastic recoil detector analysis (ToF-ERDA), glancing incident X-ray diffraction (GIXRD) and scanning electron microscopy (SEM). A thin layer of Pd (500 A) was deposited onto a clean 6H-SiC substrate at room temper- ature. The prepared difusion couples were then annealed in vacuum at different annealing temperatures for a maximum period of 1 h. The annealing temperature ranged from 2000C to 8000C. The composition of the as-deposited and the annealed samples was measured by using a He+ beam with an energy of 1.6 MeV. The ToF-ERDA measurements were per- formed on the as-deposited sample by using a high energy copper beam (about 30 MeV) for elemental depth distribution. The GIXRD measurements performed on the samples were able to identify the phases that form before and after annealing. The SEM micrograph obtained during this study gave some insight on the surface morphology of the samples before and after annealing. Our results obtained during this study showed that Pd reacts with SiC after annealing at 4000C resulting in the formation of metal-rich silicides and some unreacted Pd. Annealing at higher temperatures (5000C and 6000C) produced metal-rich silicides, which continued to grow until all the Pd has been consumed. Annealing at even higher temperatures (7000C and 8000C), the metal-rich silicides disappear and the silicon rich silicides start appearing. These appear by simply consuming the metal-rich silicides, resulting in the formation of two or more phases. The behaviour of the interaction between Pd with 6H-SiC is different than the Pd-Si system. The reaction temperature of the Pd/SiC are much more higher than those of the Pd/Si system. That is, Pd reacts with Si at temperatures as low as 2500C, while it starts to react with SiC at an annealing temperature of 4000C. In addition to this silicides such as Pd9Si2, Pd4Si form at the initial reaction temperature followed by the formation of the Pd2Si phase at the temperatures above 6000C for the Pd/SiC system. Meanwhile in the Pd/Si system the Pd2Si phase remains stable even after annealing at 8000C. No carbon compounds were observed in the temperature range used in this study and the formation of silicides were found to be accompanied by the formation of free carbon which remained immobile in the system. / Dissertation (MSc)--University of Pretoria, 2012. / Physics / unrestricted

Ce travail de thèse a porté sur l'étude de la croissance et des propriétés structurales et optiques des hétérostructures non-polaires de GaN/AlN plan m, déposées sur 6H-SiC plan m par épitaxie par jets moléculaires assistée par plasma d'azote.<br /><br />Nous avons tout d'abord étudié les couches épaisses d'AlN et de GaN. Les conditions de croissance de ces couches sont optimales en conditions riche métal. Toutes deux présentent des morphologies de surface anisotropes mais différentes l'une de l'autre avec une morphologie de type « tôle ondulée » pour l'AlN et « toît de tuiles » pour le GaN.<br />Nous nous sommes ensuite intéressés à la croissance d'hétérostructures de GaN/AlN. Nous avons démontré que la croissance de GaN en conditions riche N aboutit à la formation de puits quantiques de GaN tandis que la croissance en conditions riche Ga permet de former des fils ou des boîtes quantiques par le mode de croissance Stranski-Krastanow. Nous avons démontré que cette différence de morphologie pour les nanoobjets de GaN était liée à l'état de relaxation de la couche tampon d'AlN. Des études optiques ont mis en évidence une forte réduction du champ électrique interne dans les hétérostructures de GaN/AlN plan m.<br />Pour finir, nous avons étudié l'évolution de la morphologie des fils et des boîtes en fonction de la quantité de GaN déposée. Nous avons démontré l'existence d'une transition de forme ''boîtes-fils'' lorsque l'aire des boîtes excède une taille critique. Cette aire peut être contrôlée par la quantité de matière déposée mais également par la réalisation de superréseaux.

<p>The goal of the project work has been to study the symmetry of the phonons in 4H and 6H-SiC for different measuring geometries by using two experimental techniques, Raman and infrared absorption (IR) spectroscopy, and a theoretical model. The Raman spectra were measured in different scattering configurations in order to obtain experimental data for detailed investigation of the phonon symmetries.</p><p>The gross features of the spectra obtained in different geometries can be explained using general group-theoretical arguments. Using a lattice-dynamics model, we have also calculated the angular dependence of the phonon energies near the centre of the Brillouin zone, as well as the phonon displacements in some high-symmetry directions. The theoretical results are used to interpret the Raman lines in different configurations, and it was possible to estimate that if ionicity of the bonding of 12% is taken in the theoretical model for 4H-SiC, the splitting of the polar TO mode and the shift of the polar LO mode observed in our spectra are well reproduced theoretically. It was also observed that these polar modes have to be classified as longitudinal and transversal with respect to the direction of phonon wave vector, while the rest of the modes remain longitudinal or transversal with respect to the c-axis of the crystal. The Raman lines in the case of 4H SiC have been tentatively labelled with the irreducible representations of the point group of the crystal (C6v).</p>

The goal of the project work has been to study the symmetry of the phonons in 4H and 6H-SiC for different measuring geometries by using two experimental techniques, Raman and infrared absorption (IR) spectroscopy, and a theoretical model. The Raman spectra were measured in different scattering configurations in order to obtain experimental data for detailed investigation of the phonon symmetries. The gross features of the spectra obtained in different geometries can be explained using general group-theoretical arguments. Using a lattice-dynamics model, we have also calculated the angular dependence of the phonon energies near the centre of the Brillouin zone, as well as the phonon displacements in some high-symmetry directions. The theoretical results are used to interpret the Raman lines in different configurations, and it was possible to estimate that if ionicity of the bonding of 12% is taken in the theoretical model for 4H-SiC, the splitting of the polar TO mode and the shift of the polar LO mode observed in our spectra are well reproduced theoretically. It was also observed that these polar modes have to be classified as longitudinal and transversal with respect to the direction of phonon wave vector, while the rest of the modes remain longitudinal or transversal with respect to the c-axis of the crystal. The Raman lines in the case of 4H SiC have been tentatively labelled with the irreducible representations of the point group of the crystal (C6v).

In this thesis work several manufacturing methods for graphene is discussed followed by an indepth study of graphene grown by a high temperature sublimation method (sublimation of siliconcarbide). The graphene surfaces studied have been grown by Graphensic AB, both graphenegrown on the Si-face and the C-face of the silicon carbide were studied. Six graphene samplesgrown 4H-SiC substrates were examined for homogeneity and surface morphology as well assome surface roughness parameters using Atomic Force Microscopy (AFM). The graphene wasstudied to get a better understanding of the surfaces and the growth mechanisms to improvemanufacturing parameters while also being informative for graphene sample customers. Anadditional graphene sample grown on 6H-SiC epitaxial layer was also studied to get a betterunderstanding of the sublimation mechanism. If graphene could be manufactured in a cheaprepeatable way the applications are endless and a new era of technology could emerge muchlike the silicon era that began several decades ago. In this thesis work the results are presentedas topography images as well as tables and histograms in the results section. The growth onthe Si-face is found to be well ordered when compared to the C-face which shows signs of alargely complex growth. The graphene on the Si-face lies on top of silicon carbide steps like acarpet with a buer layer interface against the silicon carbide. On the C-face this buer layeris not present but the graphene is deformed by buckling which is suspected to originate fromdierences in thermal properties between the graphene and the C-face. The in uence of AFMsettings for characterization of graphene while using intermittent mode have been evaluated andrecommendations are given. Finally a method for evaluating the homogeneity of the graphenelm is proposed but is in need of further verication.