E. Kótai

Hydrogen and deuterium measurements by elastic recoil detection using alpha particles

Abstract This paper presents recoil cross sections for both H and D for alpha particle bombardment in the energy range of 1.6 to 3.4 MeV. For hydrogen and deuterium, a non-Rutherford cross-section was found. For deuterium, a resonance at 2.15 MeV with fwhm of 75 keV was obtained. Calculations were carried out to find the geometrical arrangement where the maximum information concerning the probing depth can be obtained in the energy range of 1–10 MeV. In contrast to the generally accepted 30° scattering angle, another configuration is suggested.

Cross section measurements of the 1H(4He, 4He)1H elastic recoil reaction for ERD analysis

Abstract The non-Rutherford differential cross section of the 1H(4He, 4He)1H reaction utilized in elastic recoil detection (ERD) analysis has been measured in the 0.9–3.4 MeV energy and 16°–41° recoil angle range. The results for the differential recoil cross section vs energy (lab) and recoil angle were fitted on a second-order surface, yielding d σ d ω = 89.1E 2 − 0.119θ 2 − 455.7E + 10.2θ−1.38θE + 693 , where E is the energy [MeV], θ the recoil angle [deg] and d σ d ω the differential cross section [10−31 m2/sr], all in the laboratory system.

Comparative study on Fe32Ni36Cr14P12B6 metallic glass and its polycrystalline modification bombarded by 2000 keV helium ions with high fluence

Abstract Surface deformations on both amorphous and polycrystalline alloys of METGLASS 2826A caused by high dose bombardment of helium ions of energy 2 and 3.52 MeV were examined by RBS analysis and SEM. Both observations confirm that the resistance of the amorphous form against flaking is 70% higher. The morphology of the metallic glass surface after flaking is characterized by a wave-like structure. For higher energy bombardment and higher current density the surface deformations are characterized by competition of two processes, i.e. exfoliation and flaking presumably due to temperature effects.

Investigations on blistering and exfoliation in gold by 3.52 MeV helium ions

Abstract The mechanism of blister formation on a cold-rolled gold target by 3.52 MeV helium ion bombardment was investigated. The critical dose was found to be 6 × 10 17 He + /cm 2 under the experimental condition used. To study the inner morphology of the blisters, they were opened mechanically. Based on these observations several new features are reported. A speculative model of high-energy blister formation is discussed, based on the fact that the diameter increases in discontinuous steps. It is pointed out that in MeV energy region this formation could be exfoliation rather than blistering confirming the previous investigations.

Formation of GdSi2 under UHV evaporation and in situ annealing

GdSi2 was prepared under ultrahigh vacuum conditions. Prior to processing, a clean interface was produced using diluted HF dipping. It is pointed out that the ‘‘critical temperature’’ for formation published earlier is probably an artifact and correlation between the interface native oxide and the critical temperature is established.

An investigation of ion-bombarded silicon by ellipsometry and channeling effect

Abstract Both ellipsometry and channeling measurements were applied to investigate how the surface layer of single crystal silicon becomes amorphous when subjected to implantation of different doses. The characteristic behaviour of ellipsometric parameters is reported in correlation with the increasing amount of buried disorder. The transition between the partially disordered and the fully amorphous phase is a breaking point on the ψ-Δ-plot. The ellipsometric parameters of the highest dose implants, where only the thickness of the amorphous layer increases, follow the theoretical spiral curve. Besides in the case of fully amorphous layers, the ellipsometry is a fast and non-destructive method with which to estimate the thickness of these films.

Damage accumulation in nitrogen implanted 6H-SiC: Dependence on the direction of ion incidence and on the ion fluence

The influence of crystallographic orientation and ion fluence on the shape of damage distributions induced by 500keV N+ implantation at room temperature into 6H‐SiC is investigated. The irradiation was performed at different tilt angles between 0° and 4° with respect to the ⟨0001⟩ crystallographic axis in order to consider the whole range of beam alignment from channeling to random conditions. The applied implantation fluence range was 2.5×1014–3×1015cm−2. A special analytical method, 3.55MeV He+4 ion backscattering analysis in combination with channeling technique (BS∕C), was employed to measure the disorder accumulation simultaneously in the Si and C sublattices of SiC with good depth resolution. For correct energy to depth conversion in the BS∕C spectra, the average electronic energy loss per analyzing He ion for the ⟨0001⟩ axial channeling direction was determined. It was found that the tilt angle of nitrogen implantation has strong influence on the shape of the induced disorder profiles. Significantl...

Exfoliation on stainless steel and inconel produced by 0.8-4 MeV helium ion bombardment

Abstract In order to try and outline the energy dependence of surface deformations such as exfoliation and flaking on candidate CTR first-wall materials, stainless steel and two types of inconels were bombarded by 0.8, 1 and 4 MeV helium ions. All the bombarded spots could be characterized by large exfoliations covering almost the total implanted area. No spontaneous rupture was observed except on one type of inconel where flaking took place right after reaching the critical dose. After mechanical opening of the formations, similar inner morphology was found as in our previous studies on gold [5,6].

Surface deformations and gas escape process studied by quasi-simultaneous multiple-energy He irradiation

Abstract Single crystal silicon wafer covered by Al foil of thickness 5 μm was irradiated quasi-simultaneously by multiple-energy He ions up to the fluence level of 3.3 × 10 19 ions/cm 2 . The implantation was performed by 3.5 MeV 4 He + through a moving Al absorber foil in such a way that a nearly uniform He distribution was obtained extending in both Si and Al to depth intervals of 1.9 × 10 19 Si/cm 2 and of 1.5 × 10 19 Al/cm 2 , respectively. During irradiation the evolution of the He concentration-depth profile was studied in situ by 3 MeV proton RBS analysis. It was found that the He concentration in the Al cover foil, after reaching a maximum value of 30 at.% began to decrease. This accelerated re-emission process was initiated near the inter-boundary surface and extended inward gradually. No significant He escape was observed from the Si up to the applied dose, so at the end of the implantation a He concentraton of 80 at.% has been reached. Exposing both inter-boundary surfaces to SEM, flaking from numerous spots was observed on the Al but not on the Si where only one crater was found. After mechanically breaking the implanted Si wafer and Al cover foil it could be seen on the fracture surfaces that regions containing a large amount of He acquire a sponge-like structure. Channels and large cavities were also observed in this region of the broken Si produced as cracks of interconnected He bubbles. The appearance of the flaking processes clearly demonstrates that even with such a depth distribution the He implanted in the materials in spite of re-emission may reach the critical value for blistering or flaking. The critical concentrations required for the observed surface deformation together with the thickness of the flaked layers evaluated from RBS and SEM observations are discussed.

Flaking and wave-like structure on MeV energy high-dose 4He + bombarded silicon

Abstract In previous work different types of metallic glasses were irradiated under the same experimental conditions by 1 or 2 MeV 4 He + ions up to a fluence of 10 18 ions/cm 2 . It was found that, at a critical dose, flaking occurred and on the flaked surface a wave pattern consisting of periodical elevations was observed. The appearance of this pattern was independent of the material composition and the manufacturing technology of the target as well as on the applied He + energy provided the current was kept low to avoid beam heating effects. Surprisingly a similar pattern was also observed in the present work on the flaked surface of single crystal silicon after irradiation with MeV energy He + ions up to the same fluence. Consequently it is suggested that this pattern is not related to amorphous structure, as was previously thought to be the most probable, but rather seems to be a more general phenomenon. Possible mechanisms of the formation are discussed.