Electron beam induced etching (EBIE) and deposition (EBID) are promising fabrication techniques in which an electron beam is used to dissociate surface-adsorbed precursor molecules to achieve etching or deposition. Spatial resolution is normally limited by the electron flux distribution at the substrate surface. Here we present simultaneous EBIE and EBID (EBIED) as a method for surpassing this resolution limit by using adsorbate depletion to induce etching and deposition in adjacent regions within the electron flux profile. Our simulation results indicate the possibility of growth control of radially symmetric nanostructures at the sub-1 nm length scale on bulk substrates. The technique is well suited to the fabrication of ring-shaped nanostructures such as those employed in plasmonics, sensing devices, magneto-optics and magnetoelectronics.
Theoretical evolutionary sequences for stars in the mass range 0.65 to 2.5 M 0 having the extremely metaldeficient compositions (X, Z) = (0.739, 10-•), (0.739, 10-6 ), (0.739, 10-•), (0.9999, 10-•) have been calculated using a modified version of the Paczynski stellar-evolution code. The models have been evolved from the zero-age main sequence through the central density maximum accompanying core helium ignition. Selected models in each evolutionary sequence have been analyzed for secular and pulsational instability. The characteristics of extremely metal-poor stellar models were found to be somewhat sensitive to the heavy-element abundance even below Z =: 10-<, and low-mass stellar lifetimes from the main sequence to central helium ignition were found to be significantly shorter than values commonly assumed for galactic evolution studies. The main-sequence models of lowest mass are pulsationally unstable with fundamental periods of about 0.67 hour. These models become pulsationally stable before central hydrogen exhaustion. The most massive stellar models for each composition become pulsationally unstable at core helium ignition, with the pulsation periods for the fundamental mode lying in the range 0.3-4.0 days. Evolutionary tracks and time-constant loci are presented for each composition.
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