Charge exchange and excitation in collision at medium energy (2-30 keV). Experiment and simulation

Abstract

ions were scattered from an amorphous silicon surface (a:Si) at relatively low incident energy (2-30 keV) to investigate the charge exchange processes and the electronic excitation mechanisms. The study was carried out as a function of several experimental parameters: primary energy , incidence angle and scattering angle . We show in this study that neutralization in the subsurface region of Si plays a significant role. The electron spectra show the same predominant autoionizing peaks as observed in scattering from metallic surfaces and the core rearrangement mechanisms used for explaining the conversion are still valid. The conversion efficiency is an increasing function of the incidence angle and a decreasing one of the beam energy in the 1-5 keV range; however this efficiency remains nearly constant at higher energies. This behaviour is attributed to a direct production of states not assisted by core rearrangement processes.

Dissociation and Charge Transfer of H2O on Cu(110) Probed in Real Time Using Ion Scattering Spectroscopy

“…In our calculations, γ = 0.00364 (1.5 × 10 14 /s) is used, a value that is very close to that (1.8 × 10 14 /s) presented in ref , which indicates that the value is reasonable. The widths used in our calculation are Γ ⊥ ( z ) = 12 exp­[−0.96­( z + 0.716)] and Γ ∥ ( z ) = 2.9 exp­[−1.05­( z + 0.716)] that are obtained from the literature .…”

Anomalous Positive Ion Formation in Negative Ion Collisions with HOPG

“…In principle, the positive ion fraction in these studies at large energies , can be understood in terms of the exponential dependence of the inverse of exit angle for a given energy. , It is associated with the survival probability of positive ions during Auger and/or resonant neutralization along the outgoing trajectory proposed by Hagstrum . As we can see, the first two mentioned studies, , as well as ours, are different from other studies. , The descending rate of positive-ion fraction as a function of incident angle cannot be well explained by the exponential scaling as mentioned above. As a consequence, the reason for new findings about the dependence of positive-ion fraction on incident velocity and angle will be discussed in details in the next section.…”

“…Moreover, the increase is faster at small exit angles, and starts to slow down at high exit angles. It is consistent with many previous observations. − , However, this trend is not consistent with our experimental data as shown in Figures and . Moreover, as discussed above, the survival probability related to is close to 1 due to the negligible v c .…”

“…It is also found that the descending rate of the Ne + fraction scattering from an amorphous silicon surface gradually decreases when the incident angle increases. 42 However, for F − and Cl − scattering on Mg and Ag, 47 F + and Cl + fractions first decrease steeply, then keep almost unchanged and even slightly increase with incident angles at a small incident energy of 1 keV, while for large projectile energies, the descending rate increases with increasing incident angle. For F − scattering on Si, 36 the F + fraction decreases linearly with increasing incident angle for 9.5 keV, and for energies of 13.5 and 21.5 keV, F + fractions trend to be unchanged at small incident angles and then decrease monotonously at large incident angles.…”

“…This is substantially different from what happens on metallic surfaces − where scattered Ne + , Ar + and O + fractions increase monotonically with primary kinetic energy in the range of several keV energies. He + fraction of grazing scattering off Al (111) pronounced increases with energy after reaching a kinematic threshold of several keV. , Moreover, for semiconductor surfaces, F + increases linearly with energy in the range of 8.5–22.5 keV, and Ne + grows rapidly from 2 to 10 keV energies and then becomes almost constant for higher energies . For HOPG surface, Goldberg’s group reported that H + fraction also shows a monotonic increase with incident energy from 7% to 20% with primary energy in the 2–8-keV range in large scattering angles of 45° and 135°. , To the best of our knowledge, such an anomalous dependence on incident velocity in our case has never been observed.…”