Experimental mechanistic investigation of the nanostructuring of tungsten with low energy helium plasmas

Fiflis, P.; Connolly, N.; Ruzic, D. N.

doi:10.1016/j.jnucmat.2016.10.015

Cited by 33 publications

(29 citation statements)

References 21 publications

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“…A similar result has recently been reported by Fiflis [17], where a thin tungsten coating was applied to a molybdenum wire and the entire structure was subjected to conditions where a fuzzy W surface should form. Even though the experiment utilized two different elements, the result also showed the motion of the substrate material up through the surface layer toward the tips of the tendrils.…”

Section: Dynamics Of Tungsten Atomssupporting

confidence: 84%

Motion of W and He atoms during formation of W fuzz

Doerner¹,

Nishijima²,

Krasheninnikov³

et al. 2018

Nucl. Fusion

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Measurements are conducted to identify the motion of tungsten and helium atoms during the formation of tungsten fuzz. In a first series of experiments the mobility of helium within the growing fuzz was measured by adding 3 He to the different stages of plasma exposure under conditions that promoted tungsten fuzz growth. Ion beam analysis was used to quantify the amount of 3 He remaining in the samples following the plasma exposure. The results indicate that the retention of helium in bubbles within tungsten is a dynamic process with direct implantation rather than diffusion into the bubbles, best describing the motion of the helium atoms. In the second experiment, an isotopically enriched layer of tungsten (~92.99% 182 W) is deposited on the surface of a bulk tungsten sample with the natural abundance of the isotopes. This sample is then exposed to helium plasma at the conditions necessary to support the formation of tungsten 'fuzz'. Depth profiles of the concentration of each of the tungsten isotopes are obtained using secondary ion mass spectrometry (SIMS) before and after the plasma exposure. The depth profiles clearly show mixing of tungsten atoms from the bulk sample toward the surface of the fuzz. This supports a physical picture of the dynamic behavior of helium bubbles which, also, causes an enhanced mixing of tungsten atoms.

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Section: Dynamics Of Tungsten Atomssupporting

confidence: 84%

Motion of W and He atoms during formation of W fuzz

Doerner¹,

Nishijima²,

Krasheninnikov³

et al. 2018

Nucl. Fusion

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“…Samples were exposed to a helicon source helium plasma (MORI 200). Plasma conditions for He ion exposure were similar to those of previous investigation for growth of tungsten and palladium nanostructures with slight variations: input RF power of 700 W, a magnetic field strength of 57 Gauss, a base pressure of 4 mTorr, and helium pressure of 100 mTorr measured by a convectron gauge (Graville Phillips 375). An external bias voltage of −50 to −140 V was applied to the sample to control the incident ion energy, as well as a tunable resistively heating AC current supplied by a variac.…”

Section: Methodsmentioning

confidence: 79%

“…The experiment setup for the He ion irradiation of the Ti substrate is shown in Figure . A Ti substrate sample (Alfa Aesar, 99% purity) with 1.3 cm (width) × 4.4 cm (length) × 0.05 cm (thickness) was supported by two copper tubes.…”

Section: Methodsmentioning

confidence: 99%

“…Energetic He ion (>20 eV) bombardment at 1000–2000 K leads to a formation of fuzz like structures on the surface of tungsten . Other metals such as titanium, copper, and aluminum exhibits similar transformations of their morphologies under He ion bombardment . One can tune the generated morphology and their properties by controlling the incident ion energy as well as the temperature of the target metal .…”

Section: Introductionmentioning

confidence: 99%

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Enhanced effect of a plasma‐irradiated titanium substrate on the photocatalytic activity of a TiO₂ film

Zhu

Kalathiparambil

Sun

et al. 2018

Plasma Processes & Polymers

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To improve the photocatalytic activity of TiO 2 film, Ti substrates are irradiated by He ions with different incident ion energy, temperature, and fluence. Anatase TiO 2 films are then coated on the plasma-irradiated substrates via chemical vapor deposition followed by calcination. Photocurrent tests and photocatalytic oxidation (PCO) of formaldehyde are used to assess photocatalytic performance. The optimal plasmairradiated samples showed a four times higher photocurrent and a three fold increase in the rate constant of the PCO reaction compared to the TiO 2 coated, untreated control sample. It is found that the enhanced photocatalytic activity and photocurrent are related to the changes of Ti crystal structure and surface morphology through plasma irradiation. K E Y W O R D Sion bombardment, photocatalytic activity, plasma treatment, TiO 2 film, Ti substrate

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“…The interaction with the electric field from the plasma present could accelerate this. However, two studies have shown that electric field variation has no effect on fuzz growth [30,31], so this mechanism has been rejected.…”

Section: Electrostatic Growthmentioning

confidence: 99%

A review of late-stage tungsten fuzz growth

Wright

2022

Tungsten

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Tungsten will be used as the plasma-facing divertor material in the International Thermonuclear Experimental Reactor (ITER) fusion reactor. Under high temperatures and high ion fluxes, a ‘fuzz’ nanostructure forms on the tungsten surface with dramatically different properties and could contaminate the plasma. Although simulations and experimental observations have provided understanding of the initial fuzz formation process, there is debate over whether tungsten or helium migration is rate-limiting during late-stage growth, and the mechanisms by which tungsten and helium migrations occur. Here, the proposed mechanisms are considered in turn. It is concluded that tungsten migration occurs by adatom diffusion along the fuzz surface. Continual helium migration through the porous fuzz to the tungsten bulk is also required for fuzz growth, for continued bubble growth and rupture. Helium likely migrates due to ballistic penetration, although diffusion may contribute. It is difficult to determine the limiting process, which may switch from helium penetration to tungsten adatom diffusion above a threshold flux. Areas for further research to clarify the mechanisms are then considered. A greater understanding of the fuzz formation mechanism is key to the successful design of plasma-facing tungsten components, and may have applications in forming porous tungsten catalysts.

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Experimental mechanistic investigation of the nanostructuring of tungsten with low energy helium plasmas

Cited by 33 publications

References 21 publications

Motion of W and He atoms during formation of W fuzz

Motion of W and He atoms during formation of W fuzz

Enhanced effect of a plasma‐irradiated titanium substrate on the photocatalytic activity of a TiO₂ film

A review of late-stage tungsten fuzz growth

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Experimental mechanistic investigation of the nanostructuring of tungsten with low energy helium plasmas

Cited by 33 publications

References 21 publications

Motion of W and He atoms during formation of W fuzz

Motion of W and He atoms during formation of W fuzz

Enhanced effect of a plasma‐irradiated titanium substrate on the photocatalytic activity of a TiO2 film

A review of late-stage tungsten fuzz growth

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Enhanced effect of a plasma‐irradiated titanium substrate on the photocatalytic activity of a TiO₂ film