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

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Abstract
The particle reflection coefficients (RN ) 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 (TN ) 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 RN was calculated from the relationship RN = 1−TN. The experimental value of RN 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 RN 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.