Ionization of Al recoiled and sputtered from Al(100)

The absolute ionization probability of energetic $(>500\mathrm{eV})$ particles recoiled from Al(100) by 2 and $5\mathrm{keV}$ ${\mathrm{Xe}}^{+}$ bombardment was measured with time-of-flight spectroscopy. These values were then used to calibrate the energy and angular distributions of low-energy $(10–600\mathrm{eV})$ sputtered ions collected with an electrostatic analyzer. The independent-particle model of nonadiabatic surface-atom charge exchange, which is typically used to analyze single scattering events, was applied to the ion fractions of the recoiled and sputtered atoms. The model describes all the experimental data from a few eV to the keV range if a different surface electronic temperature is used for recoiling and sputtering. This suggests that the ionization process depends on the instantaneous surface condition at the time of ion emission.

Figure 1

(Color online) TOF spectra of energetic Al atoms recoiled from Al(100) by the impact of $5\mathrm{keV}$ ${\mathrm{Xe}}^{+}$ ions. The exit angles are along the [001] azimuth and at (a) 57° and (b) 78° with respect to the surface normal.

Figure 2

(Color online) The ionization probability ${\mathrm{P}}^{+}$ measured by TOF for Al atoms recoiled by 2 and $5\mathrm{keV}$ ${\mathrm{Xe}}^{+}$ ions shown as a function of the perpendicular component of the Al exit velocity $v_{\perp }$. The calculated probability is shown by a solid line for $T_e=0\mathrm{K}$ and by a dashed line for $T_e=1250\mathrm{K}$.

Figure 3

(Color online) The ionization probability measured by TOF for Al atoms recoiled by $5\mathrm{keV}$ ${\mathrm{Xe}}^{+}$ shown vs iodine-induced work-function change for two values of $v_{\perp }$.

Figure 4

(Color online) The ionization probability ${\mathrm{P}}^{+}$ of sputtered Al shown as a function of the perpendicular component of the exit velocity $v_{\perp }$. The squares were taken from Ref. 10 and calibrated by our TOF data, and the triangles are from our measurements. The values of ${\mathrm{P}}^{+}$ calculated from Eq. (1) are shown by a solid line for $T_e=0$ and by a dashed line for $T_e=1250\mathrm{K}$.