Interaction of highly charged clusters with surface

Abstract

The purpose of this paper is to draw attention to phenomena occurring on solid surfaces under impact of new kinds of projectiles—slow, very large and highly charged clusters produced in modern electrospray ionization sources. It is known that slow highly charged atomic ions, for instance Xe^(+44), approaching a non-metal surface cause sputtering, erosion and create craters and blisters via the mechanism of Coulomb explosion following a cascade Auger neutralization, emitting vast amounts of secondary electrons. The same mechanism should create analogous nano-features on a non-metal surface under impacts of clusters containing up to 10^8–10^9 molecules with a mass of up to 10^9–10^(10) amu and a diameter as large as 10^3 nm, their charge reaching several 10^3 e, albeit the charge-to-mass ratio would not exceed 10^(−7)–10^(−6) e amu^(−1). When accelerated using a voltage of up to 10^4 V, the clusters can acquire a kinetic energy of 10^4 keV, but a very slow velocity, less than 5×10^4 cm s^(−1), which corresponds to about 10^(−2) eV atom^(−1), well below the threshold of kinetic electron emission. The conditions are favorable for Auger neutralization-induced potential electron emission. The estimates, inevitably approximate in the absence of any experimental data, predict that the diameter of the craters could be around 10 nm, the number of sputtered atoms could be as large as 10^5 atoms per cluster and the yield of ejected electrons could reach up to several thousand electrons per cluster. These numbers show that both experimental studies of the phenomena and a search for their possible applications are worth performing.

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