Experimental determination of the particle reflection coefficients of low-energy (100-1500 eV) ³He and ⁴He atoms from the (110) plane of tungsten

The particle reflection coefficients (R_N) for low-energy (100-1500 eV) implanted ³He and ⁴He atoms were determined employing the atom-probe field-ion microscope (FIM) technique. The implantations were made in situ at 60 K with the ion beam parallel to the [110] direction, within ±5°, of tungsten; the atom-probe FIM analysis were also performed at 60 K. At this temperature both the ³He and ⁴He atoms, as shown in our earlier work, are completely immobile. After an implantation, to a given fluence, the value of the particle retention coefficient (T_N) was determined directly from the total measured number of helium atoms retained in the range profile that was parallel to the [110] direction. Then the value of R_N was calculated from the relationship R_N = 1-T_N. The experimental value of R _N decreases from ∼0.85 to ∼0.25, as the energy of the incident helium ion beam increases from 100 to 1500 eV. The results are compared with values of R_N calculated employing Biersack's and Haggmark's TRIM program; the calculated values are in fair agreement with the experimental data between 300 and 1500 eV.