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The evolution of the helium-related defect in polycrystalline tungsten was studied by Doppler Broadening Positron Annihilation Spectroscopy and Scanning Electron Microscope as functions of annealing temperature and implantation fluence. The experimental results showed that the defect type was not changed at lower annealing temperature, and the decline of S parameter manifested that the lower temperature annealing led the decrease of defect concentration. In addition there existed the same defect type with the increment of the implantation fluence, thus the rise of S parameter implied the increase of the defect concentration.

W/Cu multilayer nanofilms and pure W nanofilms were prepared in pure Ar and He/Ar mixing atmosphere by radio frequency magnetron sputtering method. The defect evolution of the samples was characterized by Doppler broadening positron annihilation spectroscopy (DB-PAS).The results show that plenty of defects can be produced by introducing helium (He) into W/Cu multilayer nanofilms. With the natural storage time increasing, the helium located in the near surface of W/Cu multilayer nanofilm would be released gradually and induce the coalescence of the helium related defects due to the diffusion of the helium and defects. In addition, the pure W nanofilms were irradiated by 30 keV helium ions and 40 keV hydrogen (H) ions in sequence at room temperature. From the DB-PAS analysis, it can be shown that a large number of vacancy-type defects are produced due to the He and/or H irradiation. H ions would be trapped by He related defects and produced He-H-V complexes.

The microstructure of He+-irradiation induced defects in tungsten was studied as functions of annealing temperature by means of scanning electron microscope (SEM) and Doppler broadening positron annihilation spectroscopy (DB-PAS). The results show that the S parameter become higher after helium implanted in tungsten. When the annealing temperature increases to 923 K, plenty of large size of holes and new types of defects could be found in this sample.

Molecular dynamics (MD) simulations are performed on the diffusion and coalescence of helium in tungsten. A new method for determining the effective capture radii (ECRs) and the dissociation energies of helium-related defects is proposed in this work. It is observed that the ECR of an interstitial helium atom trapping helium interstitials (denoted as He–Hen, n = 1–3) decreases with increasing temperature, except for He–He2 at T D3 > D4 at T < 500 K, which can be attributed to the disordered structure of He5. The Arrhenius relation describes the diffusion of Hen well in the temperature range from 300 K to 550 K, whereas the diffusion is not a standard thermally activated process at higher temperatures. Taken together, these results help elucidate the initial stage of helium bubble formation in tungsten as well as the requirements of long-term evolution methods such as KMC or RT models.

Cu/W multilayer nanofilms are prepared in pure Ar and He/Ar mixing atmosphere by the rf magnetron sputtering method. The cross-sectional morphology and the defect distribution of the Cu/W multilayer nanofilms are characterized by scanning electron microscopy and Doppler broadening positron annihilation spectroscopy. The results show that plenty of point defects can be produced by introducing He during the growth of the multilayer nanofilms. With the increasing natural storage time, He located in the near surface of the Cu/W multilayer nanofilm at room temperature could be released gradually and induce the segregation of He-related defects due to the diffusion of He and defects. However, more He in the deep region spread along the interface of the Cu/W multilayer nanofilm. Meanwhile, the layer interfaces can still maintain their stability.

Various helium-containing titanium films were deposited on Si substrates by magnetron sputtering under different helium/argon (He/Ar) ambiances. Helium concentrations and corresponding depth profiles in the Ti films are obtained by elastic recoil detection analysis (ERDA). X-ray diffraction (XRD) measurements are carried out to evaluate the crystallization of the titanium films. Vacancy-type defects and their depth profiles were revealed by slow positron beam analysis (SPBA). It is found that the defect-characteristic parameter S rises with the increment of the He/Ar flow ratios. The variation of.. indicates the formation and evolution of various He-related defects, with uniform distribution into the depth around 400 nm.

Helium-containing titanium films were prepared on Si substrates with various biases applied by magnetron sputtering under stable He/Ar ambiance. Rutherford backscattering and elastic recoil detection analyses are used to measure the thickness of the He-Ti films and the helium depth profile, respectively. Experiments of x-ray diffraction and variable energy positron annihilation spectroscopy are carried out to investigate the microstructures of titanium films and the corresponding helium-related defects developed. The behavior of the implanted He, the microstructure of the He-Ti film and the formation of He-related defects all are affected by the substrate biases applied.

Based on Monte Carlo simulations, we describe a mechanism, i.e., cascade-coalescence, to provide an explanation on the novel growth of gas bubbles in materials that has been observed in experiments and cannot be explained on the basis of the classical Smoluchowski theory and its variants. It is found that as the concentration and the average size of the bubbles reaches certain critical point, the cascade-coalescence is a dominant mechanism and leads to explosive growth of bubbles. The critical point for the cascade-coalescence happening can be evaluated by a scaling parameter determined by the average radius and concentration of the bubbles. This mechanism can be also used to explain the sudden release of gas atoms from thin films that can be measured in thermal desorption spectrometry in annealing experiments.

In this paper, we analyze and compare electrical compensation and deep level defects in semi-insulating (SI) materials prepared by Fe-doping and high temperature annealing of undoped InP. Influence of deep level defects in the SI-InP materials on the electrical compensation has been studied thermally stimulated current spectroscopy (TSC). Electrical property of the Fe-doped SI-InP is deteriorated due to involvement of a high concentration of deep level defects in the compensation. In contrast, the concentration of deep defects is very low in high temperature annealed undoped SI-InP in which Fe acceptors formed by diffusion act as the only compensation centre to pin the Fermi level, resulting in excellent electrical performance. A more comprehensive electrical compensation model of SI-InP has been given based on the research results.