Vitreous SiO2 thin films thermally grown onto Si wafers were bombarded by Au ions with energies from 0.005 to 11.1 MeV/u and by ions at constant velocity (0.1 MeV/u A197u, T130e, A75s, S32, and F19). Subsequent chemical etching produced conical holes in the films with apertures from a few tens to ∼150 nm. The diameter and the cone angle of the holes were determined as a function of energy loss of the ions. Preferential track etching requires a critical electronic stopping power Seth∼2 keV/nm, independent of the value of the nuclear stopping. However, homogeneous etching, characterized by small cone opening angles and narrow distributions of pore sizes and associated with a continuous trail of critical damage, is only reached for Se>4 keV/nm. The evolution of the etched-track dimensions as a function of specific energy (or electronic stopping force) can be described by the inelastic thermal spike model, assuming that the etchable track results from the quenching of a zone which contains sufficient energy for melting. The model correctly predicts the threshold for the appearance of track etching Seth if the radius of the molten region has at least 1.6 nm. Homogeneous etching comes out only for latent track radii larger than 3 nm.

Isomeric transitions, of E3, M2, smdEl/M2 character, depopulating nh d / 2 ® Pi 13 / 2 bands in 186,188,190 T^ respectively, have been found with use of y-ray spectroscopic techniques. The changes in multipolarity reflect successive changes in the bandhead spin values corresponding to level crossings within the ftfc 9 / 2 ® vi 13/ 2 system. These crossings were predicted in the framework of the two-quasiparticle plus rotor model and interpreted as a direct consequence of the depletion of the i 13 / 2 shell.

No abstract

No abstract

No abstract