A. Manuaba

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.

Characterization of ion implanted silicon by ellipsometry and channeling

Abstract A correlation between the amount of disorder measured by channeling and the trajectory of measured ellipsometric angles (ψ, Δ) is reported. The implantation was performed by 11 B + , 28 Si + , 31 P + , 40 Ar + , 72 Ge + , 75 As + , 209 Bi + ions at room temperature. For fully amorphous samples the thickness data were obtained from channeling and the complex refractive index from a 145 nm thick amorphous layer. These experimental values were used to compute a theoretical curve in the ψ-Δ plane. The good agreement between the theoretical curve and experimental data provides a fast and non-destructive and non-contact method for estimating the thickness of an amorphous layer. For buried and partially disordered layers a qualitative interpretation of different trajectories depending on the ion species and other implantation condition such as energy and dose in the ψ-Δ plane can be given, in certain cases, on the basis of channeling measurements. It is also pointed out that plasma stripping, removes the polymerized hydrocarbon film without affecting the disordered layer, plays an important role in preparing implanted samples for ellipsometry.

Improved depth resolution of channeling measurements in Rutherford backscattering by a detector tilt

Abstract An optimized geometry for Rutherford scattering and channeling is described giving an enhanced depth resolution (40–50 A). Tis resolution was achieved by a second particle detector mounted at such an angle that it would accept scattered ions emerging at glancing angles only (tilted detector). The method was shown to bring advantages of regular RBS (easy to find major channels) and glancing angle geometry (≈ tenfold enhanced depth resolution, but restricted possibility to align the crystal) to a useful compromise in investigating thin disordered structures on single crystals or, say, depth dependence of lattice location, of foreign atoms. Comparative spectra on annealing of lattice detects and location of implanted Sb in Si are presented.

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.

Three-dimensional scanning of ion-implanted porous silicon

Abstract As it was recently shown, the porosity of porous Si gradually decreases under ion implantation, until the sample completely transforms into a compact material. To determine the underlying elementary process, we measured the degree of densification along the ion track. Different types of porous Si layers were implanted from the side of the samples parallel to the surface by 4.0 MeV 4 He + ions. The implanted lateral spots were scanned three-dimensionally by Rutherford backscattering spectrometry (RBS) microprobe using 2 MeV 4 He + ions. Results obtained for columnar and spongy type porous Si samples clearly indicate that the densification occurs most intensively in a narrow depth region around the penetration depth of the ions, i.e., it is mainly caused by ion cascades. Based on this phenomenon, production of deeply buried narrow compact layers in porous materials seems to be accessible.

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.

Densification and noble gas retention of ion-implanted porous silicon

Abstract To investigate the gas retention behaviour of porous materials, 500 keV He and 100 keV Ar ion implantations were carried out into porous silicon samples of columnar structure. Samples of different porosities were irradiated using a current density of ∼ 6 × 10 12 ions/cm 2 /s up to a fluence of 10 × 10 17 and 10.3 × 10 16 ions/cm 2 , for He + and Ar + , respectively. The quantity of the retained gas was determined by Rutherford backscattering spectrometry (RBS). It was found that in contrast to the case of compact materials, the gas retention is negligible for the lowest fluence implantations (∼ 5 × 10 16 and ∼ 1 × 10 15 ions/cm 2 , for He and Ar respectively). At higher fluences the retention rate gradually increases, approaching the rate of full retention. For He implantation the retention behaviour shows a strong porosity dependence. The above phenomenon is accompanied by the densification of the material as it was observed by scanning electron microscope on the fractured samples and also indicated by the gradual depression of the whole implanted area according to surface profiler measurements. The densification grows until the whole implanted layer (from the surface to the implanted range) almost completely transforms into compact material. Possible mechanisms responsible for the above phenomena are also discussed.

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.