Thermal Conductivity Degradation and Microstructural Damage Characterization in Low-Dose Ion Beam-Irradiated 3C-SiC (original) (raw)
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Raman spectroscopy study of heavy-ion-irradiated α-SiC
Journal of Physics: Condensed Matter, 2006
Raman spectroscopy was used to investigate the structure of ion-irradiated α-SiC single crystals at room temperature and 400 • C. Irradiations induce a decrease of the Raman line intensities related to crystalline SiC, the appearance of several new Si-C vibration bands attributed to the breakdown of the Raman selection rules, and the formation of homonuclear bonds Si-Si and C-C within the SiC network. For low doses, the overall sp 3 bond structure and the chemical order may be almost completely conserved. By contrast, the amorphous state shows a strong randomization of the Si-Si, Si-C and C-C bonds. The relative Raman intensity decreases exponentially versus increasing dose due to the absorption of the irradiated layer. The total disorder follows a sigmoidal curve, which is well fitted by the direct impact/defect stimulated model. The chemical disorder expressed as the ratio of C-C bonds to Si-C bonds increases exponentially versus the dose. A clear correlation is established between the total disorder and the chemical disorder. The increase of temperature allows the stabilization of a disordered/distorted state and a limitation of damage accumulation owing to the enhancement of the dynamic annealing.
Study of damage in ion-irradiated α-SiC by optical spectroscopy
Journal of Physics: Condensed Matter, 2006
UV-visible absorption and Raman scattering spectroscopy were used to investigate the effects of 4 MeV Xe-ion and 4 MeV Au-ion irradiations on α-SiC single crystals. The evolution of transmission spectra upon irradiation evidences an increase of the optical absorption. The optical band-gap energy decreases versus fluence, which is linked to band-gap closure attributed to the creation of localized states into the forbidden energy band. A strong effect of the irradiation temperature is observed as a result of dynamic annealing enhanced by the temperature increase. The Urbach energy increases versus fluence due to disorder accumulation in the damaged layer. Comparison of Urbach energy and disorder parameters extracted from Raman spectra shows that the Urbach energy is sensitive to the disorder induced by the accumulation of point defects.
Applied Physics A, 2018
At moderately elevated temperatures, radiation defects in SiC exhibit pronounced dynamic annealing, which remains poorly understood. Here, we study 3C-SiC bombarded at 100 • C with pulsed beams of 500 keV Ar ions. Radiation damage is monitored by a combination of X-ray diffraction, Raman scattering, and ion channeling. Similar damage buildup behavior but with different defect relaxation time constants, ranging from ∼ 1 to ∼ 6 ms, is observed for the different types of lattice defects probed by these techniques. A correlation between relaxation times and the nature of the defects is proposed. These results reveal additional complexity of radiation defect dynamics in SiC and demonstrate that results of different defect characterization techniques are needed for a better understanding of dynamic annealing processes in solids.
Optical spectroscopy study of damage induced in 4H-SiC by swift heavy ion irradiation
Journal of physics. Condensed matter : an Institute of Physics journal, 2012
Single crystals of 4H-SiC were irradiated with swift heavy ions (332 MeV Ti, 106 MeV Pb and 2.7 GeV U) in the electronic energy loss regime. The resulting damage was investigated with UV-visible optical absorption spectroscopy and micro-Raman spectroscopy. The evolution of the Raman data with fluence shows an accumulation of isolated point defects without amorphization of the material and a partial recrystallization of the structure, but only at the lowest fluence. Furthermore, the longitudinal optical phonon-plasmon coupling mode disappears upon irradiation, suggesting a strong perturbation of the electronic structure. This evolution is consistent with the optical bandgap decrease and the Urbach edge broadening that was also previously observed for the irradiation with 4 MeV Au ions.
Thermal conductivity degradation induced by point defects in irradiated silicon carbide
Applied Physics Letters, 2011
Irradiations are known to decrease the thermal conductivity of ceramics. This phenomenon is tackled by molecular dynamics simulation of the thermal resistance of point defects in cubic silicon carbide. The additional thermal resistivity due to point defects proves to vary linearly with their concentration. Large variations in the proportionality coefficient with the nature of the defects are observed. From these calculations, an approximate scale for the concentration of vacancies in irradiated SiC is built.
Investigation of irradiation effects induced by self-ion in 6H-SiC combining RBS/C, Raman and XRD
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2012
Single crystals of 6H-SiC were irradiated at room temperature and 670 K with 4 MeV C ions at two fluences: 10 15 and 10 16 cm À2 (0.16 and 1.6 dpa at the damage peak). Damage accumulation was studied by a combination of X-ray diffraction (XRD), Raman spectroscopy and Rutherford backscattering spectrometry in channelling geometry (RBS/C) along the [0 0 0 1] direction. The irradiated layer is found to be composed of a low damage region up to 1.5lmfollowedbyaregionwherethedisorderlevelishigher,consistentwithSRIMpredictions.Atroomtemperatureandlowfluence,typically1015cmAˋ2,thestraindepthprofilefollowsthedpadepthdistribution(withamaximumvalueof1.5 lm followed by a region where the disorder level is higher, consistent with SRIM predictions. At room temperature and low fluence, typically 10 15 cm À2 , the strain depth profile follows the dpa depth distribution (with a maximum value of 1.5lmfollowedbyaregionwherethedisorderlevelishigher,consistentwithSRIMpredictions.Atroomtemperatureandlowfluence,typically1015cmAˋ2,thestraindepthprofilefollowsthedpadepthdistribution(withamaximumvalueof2%). The disorder is most likely due to small defect clusters. When increasing the fluence up to 10 16 cm À2 , a buried amorphous layer forms, as indicated by e.g. Raman results where the Si-C bands become broader or even disappear. At a higher irradiation temperature of 670 K, amorphization is not observed at the same fluence, revealing a dynamic annealing process. However, results tend to suggest that the irradiated layer is highly heterogeneous and composed of different types of defects.
Microstructural development in cubic silicon carbide during irradiation at elevated temperatures
Journal of Nuclear Materials, 2006
Microstructural development in chemically vapor-deposited (CVD) high-purity beta-SiC during neutron and self-ion irradiation at elevated temperatures was studied. The CVD SiC samples were examined by transmission electron microscopy following neutron irradiation to 4.5-7.7 • 10 25 n/m 2 (E > 0.1 MeV) at 300 and 800°C and 5.1 MeV Si 2+ ion irradiation up to 200dpaat600−1400°C.Theevolutionofvariousirradiation−produceddefectsincludingblackspotdefects,dislocationloops,networkdislocations,andcavitieswascharacterizedasafunctionofirradiationtemperatureandfluence.Itwasdemonstratedthattheblackspotdefectsandsmalldislocationloopscontinuetodominateatrelativelylowtemperatures(<200 dpa at 600-1400°C. The evolution of various irradiation-produced defects including black spot defects, dislocation loops, network dislocations, and cavities was characterized as a function of irradiation temperature and fluence. It was demonstrated that the black spot defects and small dislocation loops continue to dominate at relatively low temperatures (<200dpaat600−1400°C.Theevolutionofvariousirradiation−produceddefectsincludingblackspotdefects,dislocationloops,networkdislocations,andcavitieswascharacterizedasafunctionofirradiationtemperatureandfluence.Itwasdemonstratedthattheblackspotdefectsandsmalldislocationloopscontinuetodominateatrelativelylowtemperatures(<800°C), whereas they grow into Frank faulted loops and finally develop into dislocation networks at a higher temperature (1400°C). Substantial cavity formation on grain boundaries and stacking faults was confirmed after ion irradiation at 1400°C. These observations were discussed in relation with the known irradiation phenomena in SiC, such as low temperature swelling and cavity swelling.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2014
Implantation with 1 MeV N ions was performed at room temperature in n-type 4H-SiC (0 0 0 1) at four implantation fluences (or doses in dpa (displacements per atom) at the damage peak) of 1.5 Â 10 13 (0.0034), 7.8 Â 10 13 (0.018), 1.5 Â 10 14 (0.034), and 7.8 Â 10 14 (0.178) ions/cm 2 , respectively. The evolution of disorder was studied using Rutherford backscattering spectrometry in channeling mode (RBS-C), Raman spectroscopy, and optical transmission. The disorder in the Si sub-lattice was found to be less than 10% for the dpa of 0.0034 and 0.0178 and increased to 40% and 60% for the dpa of 0.034 and 0.178 respectively. The normalized Raman intensity I n , shows disorder of 41%, 69%, 77% and 100% for the dpa of 0.0034, 0.0178, 0.034 and 0.178, respectively. In this paper, the characterization of the defects produced due to the nitrogen implantation in 4H-SiC are presented and the results are discussed.
Disorder induced in silicon carbide by heavy-ion irradiation
Philosophical Magazine Letters, 2021
The decrease of crystal phonon peak intensities in Raman spectra of silicon carbide after heavy-ion irradiation is analyzed in relation to band-gap shrinkage and Urbach edge increase arising from accumulation of lattice disorder. The discrepancy on amorphous fractions deduced from Raman spectroscopy and Rutherford backscattering-channeling spectroscopy is addressed by taking into account the point defect formation and amorphization by displacement damage. A new analysis of Raman data is provided on the basis of the scattered light self-absorption due to damage build-up.