Range profiles of low-energy (100 to 1500 eV) implanted3He and4He atoms in tungsten II. Analysis and discussion

Abstract

Abstract The identifiable sources of possible systematic errors in the measurement of the mean range (x) and the straggling (Δx) of the 3He and 4He range profiles, reported on in the previous paper (Amano, Wagner and Seidman 1981, Part I) are modelled mathematically and the resulting expressions numerically evaluated. The evaluations show that these possible sources of systematic errors are not of significant magnitude to affect the range parameters x and Δx. The role of the transfer of energy, either indirectly or directly, from the incoming beam of helium ions to those helium atoms that had already been implanted is also considered as a possible source of systematic error. It is shown that there is a possibility of radiation-induced diffusion or the simple displacement of helium atoms—as a result of helium-helium collisions—at an implantation energy of 100 eV and a fluence of 4 × 1015 cm−2; however, the magnitude of this effect is probably not large enough to have a major effect on the detailed shape of the profiles. It is also demonstrated—employing a simple Monte Carlo simulation procedure—that for the sample sizes we employed in our experimental work (Part I) the integral profiles are characterized with a reasonable degree of statistical significance. The experimental results presented in Part I are compared with the calculated results of Biersack's and Haggmark's TRIM simulation program; this program is based on a Monte Carlo simulation procedure for an amorphous solid. There is qualitative agreement between the experimental and calculated values of the range parameters but not quantitative. In general, the experimental values of the dimensionless range parameters—for both 3He and 4He—are greater than the calculated values. The possible sources of this discrepancy are attributed to: (1) the use of the Molière interatomic potential in the TRIM program; and (2) possible low-energy channelling effects along the [110] direction of tungsten. Simple expressions are given for the experimental range-energy data and the effective-stopping powers of both 3He and 4He in tungsten in the energy range 100 to 1500 eV.