In this study, we show from helium (He) plasma irradiation to tantalum and iron surfaces that morphology changes in nanoscale occur on the both metals. In particular, from systematic irradiation experiments, it is identified that fuzzy nanostructures are grown on the both metals. The necessary conditions for the morphology changes are discussed based on the experimental results in terms of the helium migration, the physical sputtering, and the shear modulus of materials. Because oxides or oxinitrides of iron and tantalum are thought of as visible light responsive photocatalytic materials, the present work shows wide potential of usage of plasmas as a tool to tailor photocatalytic materials.

Using a magnetron sputtering device operating in helium, fibre-form ‘fuzz’ has been grown on tungsten samples in the presence of a significant auxiliary source of depositing tungsten. In this system, fuzzy tungsten was grown over a range of helium ion fluences, , sample temperatures and helium ion energies, but with operator control over the tungsten atom-to-helium ion arrival rate ratio at the sample (from 0.003 to 0.009). In the presence of tungsten deposition, it appears that the fuzz growth has two distinct stages: at low to intermediate helium ion fluence the fuzzy layer thickness follows the expected diffusive law augmented by approximately the ‘effective’ thin film thickness of deposited tungsten; at high fluences the fuzz thickness increases very steeply with . These observations are explained through the increase in the porosity of the fuzzy layer as it reaches thicknesses larger than ∼1 m. It was observed that during the second phase of fuzz growth the thickness was highly dependent on both the sample temperature and the tungsten atom-to-helium ion arrival rate ratio. For the same helium ion exposure, an increase in the sample temperature from 1050 to 1150 K lead to a six-fold increase in the fuzzy layer thickness, whilst increasing the tungsten atom-to-helium ion arrival rate ratio over the full range produced a two-fold increase in the thickness. Microscopy and electron diffraction studies of the grown structures show clearly helium bubbles within polycrystalline tendrils.

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Isolated regions of nano-tendril bundles (NTBs) have been grown on tungsten surfaces exposed to low-pressure direct-current helium plasma discharges operating with the addition of impurity gases, including neon, argon, nitrogen and residual air. Through the variation of impurity gas partial pressures and bombarding ion energies, threshold conditions and operational ranges for the growth of NTB's have been investigated. It was found that increasing the vacuum base-pressure from ~10 −5 to ~10 −4 Pa during the experiment could give rise to NTB formation without the need for other additional gases. In general, the required impurity gas ratio and the incident ion energy necessary to form these structures was found to vary across the range of different additional gas species, with a key parameter being the net erosion yield (Y) due to ion bombardment, Y ~ 10 −2 -10 −3 , with the morphology altering with changing net erosion yield. It is predicted that erosion-deposition processes, acting upon existing He-induced morphology changes, are the precursors for NTB growth.