Damage microstructure evolution of helium ion irradiated SiC under fusion relevant temperatures

Abstract

In-situ transmission electron microscopy (TEM) with ion irradiation has been used to study the damage microstructure evolution of He ion irradiated 4-H SiC at nuclear fusion relevant temperatures. The SiC samples were irradiated with 20 keV He ions at 25, 400, 800 and 1200°C to a dose of 5.0 displacements per atom (DPA). At 25°C, the material fully amorphises at 1.5 DPA and no He bubble nucleation occurs up to the doses studied. At 400 and 800°C, He bubble nucleation occurs and the material remains crystalline. Bubble nucleation occurs at 2.0 DPA at 400°C but occurs at only 0.5 DPA at 1200°C. This is attributed the He atoms de-trapping from vacancies and migrating interstitially to larger He-vacancy clusters at higher temperatures, leading to faster nucleation of observable He bubbles. Helium platelets form at an irradiation temperature of 1200°C at 0.5 DPA showing a preference for nucleation between the {0001} basal planes.

Atomistic simulations of a helium bubble in silicon carbide

“…It is especially the case for high dose rates of incoming helium atoms combined with a restricted vacancy supply. In silicon carbide, several studies reported observations of helium-filled bubbles and platelets [4][5][6][7][8][9][10][11][12]. Such highly pressurized defects can significantly degrade the structural integrity of the host, a particularly annoying feature for a structural or confining material.…”

Low-temperature investigations of ion-induced amorphisation in silicon carbide nanowhiskers under helium irradiation

“…Closely related to the current work, He irradiation has been studied and reported to induce amorphisation in single crystalline SiC. Liu et al [48] using 70 keV He ions and Leclerc et al [14] using 50 keV He ions at room temperature reported amorphisation critical doses of 1.1 dpa and 1.3 dpa, respectively, whilst Harrison et al [26] under identical energy and temperature conditions. These observations indicate a better resistance of the NWs to amorphisation as compared to the foils at room temperature.…”

“…The foils were prepared from 4H-SiC wafers obtained from Cree Corporation, USA (Product code: W4NPE4C-Y200). Using an ultrasonic disc cutter, the wafer was cut into 3 mm discs which were mechanically polished to ⁓100 μm and dimpled to ⁓50 µm then ion-beam milled using a precision ion polishing system (PIPS) to a thickness range of 50-70 nm as described previously [26]. All the samples used were 4H-SiC with 99.9% purity.…”

Temperature dependence of elastic strain and damage build-up in He implanted AlN

“…The presence of bubbles is indeed only detected at 550°C. In the absence of mobile vacancies [5,30], this should result from the thermally activated detrapping of He atoms from small He-V complexes that migrate to larger and more stable complexes leading to faster nucleation and growth of visible bubbles at elevated temperature [56]. A thermally enhanced mechanism of trap mutation or loop punching could also contribute to this observation.…”