High Ionic Charges in Field-Evaporating5dTransition Metals

An energy-focused time-of-flight atom probe has been used in a search for highly charged ions of field-evaporating $5d$ transition metals. Maximum abundances of mostly new ion species were 1×${10}^{-5\mathrm{}}$ for ${\mathrm{W}}^{6+}$, 2.3×${10}^{-4\mathrm{}}$ for ${\mathrm{W}}^{5+}$, 2×${10}^{-4\mathrm{}}$ for ${\mathrm{Ta}}^{5+}$, 6.7×${10}^{-3\mathrm{}}$ for ${\mathrm{Hf}}^{4+}$, 2×${10}^{-2\mathrm{}}$ for ${\mathrm{Re}}^{4+}$, 5×${10}^{-5\mathrm{}}$ for ${\mathrm{Ir}}^{4+}$, 5×${10}^{-2\mathrm{}}$ for ${\mathrm{Pt}}^{3+}$, and 6×${10}^2$ for ${\mathrm{Au}}^{3+}$. Thus for the group Hf, Ta, and W, all $6s$ and $5d$ electrons may be coming off, while for Re to Au, at most only the $6s$ electron(s) and one pair of $5d$ electrons are removed.