Degradation of discontinuous gold films under MeV heavy-ion bombardment

Abstract

Thin discontinuous gold films evaporated onto 150–230-Å-thick C substrates were irradiated with perpendicularly impinging MeV N, O, F, Cl, and Br ions up to fluences of 5×1015 ions/cm2 and fluxes up to 8×1011 ions/cm2 sec. Surprisingly rapid degradation of the gold films was found; in some cases, up to 2000 gold atoms per impinging ion were removed, as measured by Rutherford scattering. The degradation was also investigated by transmission-electron microscopy. The angular distribution of the ejected gold atoms was indicated by a simple collector experiment and found incompatible with chunk emission. The degradation is concluded to be caused by the same ionization mechanism as that occurring when fission fragments form tracks in discontinuous metal films. During irradiation, the remaining part of the film is found to be stabilized against further degradation by ionization-induced cracking of hydrocarbons.

Sputtering and surface topography modification of bismuth thin films under swift 84Kr15+ ion irradiation

“…One observes that the sputtering yield drastically decreases, first, below an ion fluence limit-value of $9.1 Â 10 12 cm À2 , then, stands nearly constant ( Y = A % (2.9 ± 0.9) Â 10 2 at/ion) over a saturation regime up to the highest ion fluence used (/ % 1.34 Â 10 14 cm À2 ). This behavior of the sputtering yield has been firstly observed by Andersen et al [26] in the case of thin gold thin films (Au/C) irradiated by various 15 MeV ions ( 12 C, 14 N, 16 O, 19 F, 35 Cl, 79 Br). It was interpreted to be caused by two competing processes: (i) a rapid degradation of the Au films due to the same ionization mechanism as that occurring with fission fragment tracks in thin discontinuous metal films followed by (ii) a stabilization of the target erosion due to ionization-induced cracking of hydrocarbon.…”

“…An additional contribution due to elastic collision spikes when both the projectile and target are heavy is neglected here since the sputtering yield estimated by the Sigmund-Claussen thermal spike model [30] amounts to only $0.65 at/ion. Besides, a possible enhancement of the sputtering yield due to potential energy for highly charged ions is ruled out in the current case because the 84 Kr 15+ incident ions are in the equilibrium charge state corresponding to the most probable charge state distribution [5,6,26,31], i.e., of the order of the effective charge defined by electronic energy loss predictions. Therefore, one is led to conclude that the observed high sputtering yield and other observed Bi surface effects undergone by the Bi target under irradiation by 27.5 MeV 84 Kr 15+ ions are conceivably driven mainly by inelastic electronic collision energy loss effects.…”

Surface modifications of ultra-thin gold films by swift heavy ion irradiation

“…There are many reports on swift heavy-ion induced effects in metallic systems. These studies give some clear idea that in metallic thin films and multilayers, the effects of electronic energy loss are significantly enhanced, as compared to bulk materials [10,12,[14][15][16]. Gupta and Avasthi found an enhanced electronically mediated sputtering in Au thin films compared to the sputtering mediated through nuclear energy loss [17].…”

Tracks in Metals by MeV Fullerenes

“…It is now well accepted that electronic excitation and ionization arising from the slowing down of swift heavy ions can lead to structural modifications in bulk metallic targets as it has been known for a long time in insulators [1] and in thin [2] or discontinuous [3,4] metallic Alms. These modifications resulting from the high rates of energy deposition, which can reach values as high as 10 keV/nm, were unexpected in metallic materials where numerous and very mobile charge carriers allow a fast spreading of the deposited energy and an efficient screening of the space charge created in the projectile wake [5].…”