Sputtering of chemisorbed gas (nitrogen on tungsten) by low-energy ions

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Abstract
Flash filament techniques and mass spectrometry have been used to measure sputtering yields for nitrogen chemisorbed on tungsten and bombarded with noble‐gas ions in the energy range up to 500 eV. The experimental results show that primarily nitrogen atoms rather than molecules are sputtered. Despite a high binding energy (∼6.7 eV/atom), we find high sputtering yields and low threshold energies. The results are found to be in reasonable agreement with simple theoretical estimates. It is sugguested that, in the investigated energy range, adsorbed nitrogen atoms are sputtered primarily as a consequence of direct knock‐on collisions with impinging and/or reflected noble‐gas ions. Estimates are also given for the yield of nitrogen atoms knocked off by sputtered tungsten atoms. This latter process is expected to dominate at much higher energies.