Thulani Thokozani Hlatshwayo

Surface and interface structural analysis of W deposited on 6H–SiC substrates annealed in argon

A study of a tungsten (W) thin film deposited on a single crystalline 6H–SiC substrate and annealed in Ar at temperatures of 700 °C, 800 °C, 900 °C and 1000 °C for 1 hour was conducted. The subsequent solid state reactions, phase composition and surface morphology were investigated by Rutherford backscattering spectrometry (RBS), grazing incidence X-ray diffraction (GIXRD) and scanning electron microscopy (SEM) analysis techniques. RBS analysis of as-deposited samples indicated the presence of W and oxygen in the as-deposited thin film, the GIXRD analysis of the as-deposited film showed the presence of W, WO3, W5Si3 and WC. RBS results of the sample annealed at 700 °C indicated interaction between W and SiC with the formation of a reaction zone. The GIXRD analysis indicated the presence of W5Si3, WO3, SiO2, W2C and WC in the W–SiC reaction zone (RZ) after annealing at 700 °C. At temperatures of 800 °C to 1000 °C, the W–SiC samples did not show any new phase formation from the GIXRD patterns, while the RBS results indicate an increase in the RZ width which meant further reactions were taking place. An increase in the peak intensities of the GIXRD patterns was observed due to a change in the polycrystalline nature of the W film to a more crystalline structure. SEM micrographs of the as-deposited samples indicated that the W thin film had a uniform surface with small grains. Annealing at 700 °C and above led to the formation of large crystals. The large crystals formed were randomly orientated; it was observed that an increase in annealing temperature led to an increase in the film crystal size forming pores between crystals.

Effect of Xe ion (167 MeV) irradiation on polycrystalline SiC implanted with Kr and Xe at room temperature

The effect of swift heavy ion (Xe 167 MeV) irradiation on polycrystalline SiC individually implanted with 360 keV Kr and Xe ions at room temperature to fluences of 2 × 1016 cm−2 and 1 × 1016 cm−2 respectively, was investigated using transmission electron microscopy (TEM), Raman spectroscopy and Rutherford backscattering spectrometry (RBS). Implanted specimens were each irradiated with 167 MeV Xe+26 ions to a fluence of 8.3 × 1014 cm−2 at room temperature. It was observed that implantation of 360 keV Kr and Xe ions individually at room temperature amorphized the SiC from the surface up to a depth of 186 and 219 nm respectively. Swift heavy ion (SHI) irradiation reduced the amorphous layer by about 27 nm and 30 nm for the Kr and Xe samples respectively. Interestingly, the reduction in the amorphous layer was accompanied by the appearance of randomly oriented nanocrystals in the former amorphous layers after SHI irradiation in both samples. Previously, no similar nanocrystals were observed after SHI irradiations at electron stopping powers of 33 keV nm−1 and 20 keV nm−1 to fluences below 1014 cm−2. Therefore, our results suggest a fluence threshold for the formation of nanocrystals in the initial amorphous SiC after SHI irradiation. Raman results also indicated some annealing of radiation damage after swift heavy ion irradiation and the subsequent formation of small SiC crystals in the amorphous layers. No diffusion of implanted Kr and Xe was observed after swift heavy ion irradiation.

Surface and interface reaction analysis of Zr films deposited on 6H-SiC after thermal annealing

Zr films (130 nm) were deposited on a 6H-SiC substrate at room temperature by sputter deposition. The interface solid-state reactions due to high vacuum thermal annealing between 600 °C and 850 °C for 30 min were investigated by Rutherford backscattering spectrometry (RBS) and X-ray diffraction (XRD). The surface morphology evolution due to thermal annealing was investigated and quantified using atomic force microscopy (AFM) and secondary electron microscopy (SEM). RBS analysis indicated that the as-deposited sample had a thin intermixed region consisting of ZrC and Zr2Si. The phases formed at each temperature were identified by XRD analysis. At temperatures of 700 °C and above, Zr reacted with the SiC substrate and formed a mixed layer of Zr carbide (ZrC) and Zr silicides (Zr2Si, ZrSi2 and Zr5Si3). The surface morphology from SEM analysis revealed a homogeneous Zr surface which varied with annealing temperature with the appearance of clusters on the Zr surface. AFM analysis revealed that the RRMS surface roughness decreased from the as-deposited value of 1.65 nm after annealing at 700 °C and then increased at higher temperatures due to coalescing of the surface granules in the Zr layer. It has also been demonstrated that the obtained experimental results between Zr and SiC have a good correlation with the ternary EHF model with regards to initial phases formed in the interface.

Comparative study of the effect of swift heavy ion irradiation at 500 °C and annealing at 500 °C on implanted silicon carbide

Transmission electron microscopy (TEM), Raman spectroscopy and Rutherford Backscattering Spectrometry (RBS) were used to characterize polycrystalline SiC specimens individually implanted with 360 keV I+ or Kr+ ions at room temperature and thereafter either irradiated with 167 MeV Xe to a fluence of 5 × 1013 cm−2 at 500 °C or annealed at 500 °C under vacuum. Implantation of I and Kr resulted in an amorphous layer about 196 and 230 nm from the surface respectively. Randomly oriented SiC nanocrystallites nucleated and grew within the layer after both treatments. These nanocrystallites were more pronounced on the SHI irradiated at 500 °C as compared to the annealed samples. Raman results supported these observations. No diffusion or redistribution of the implanted ion species could be detected by RBS.

Diffusion of Silver in Single Crystalline 6H-SiC

In a modern high-temperature nuclear reactor, safety is achieved by encapsulating the fuel elements by CVD-layers of pyrolytic carbon and silicon carbide (SiC) to prevent the fission products release. Some studies have raised doubts on the effectiveness of SiC layer as a diffusion barrier to fission fragments due to 110m Ag released from the coated particle at high temperatures ranging from 1500°C to 1600°C [1].Copyright