Nanoporous SiO2/Si thin layers produced by ion track etching: Dependence on the ion energy and criterion for etchability
ABSTRACT Vitreous SiO 2 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 197 A u , 130 T e , 75 A s , 32 S , and 19 F ). 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 Se th ∼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 Se th 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.
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ABSTRACT: SiO2 layers thermally grown on Si wafers were irradiated with swift heavy ions in the energy range of (20–710) MeV. Subsequent chemical etching in 4% HF for 6 min produced conical pores with diameters from ∼20 to ∼80 nm in the SiO2 layers. We have calculated radii and lifetime of the molten regions in the SiO2 layers and compared them with the pore diameters and diameter dispersions estimated from scanning electron microscopy and atomic force microscopy. It is shown that the existence of a molten region and its radius can serve as a valid criterion for track “etchability”. In the same etching conditions the etched track diameter and the etching velocity in the track region are proportional to the radius and the lifetime of the molten region.Vacuum 07/2014; 105:107–110. DOI:10.1016/j.vacuum.2014.01.005 · 1.43 Impact Factor
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ABSTRACT: Zinc nanoparticles (NPs) embedded in silica were irradiated with swift heavy ions (SHIs) of seven different combinations of species and energies. The shape elongation induced by the irradiations was evaluated by the optical linear dichroism (OLD) spectroscopy, which is a sensitive tool for determining the change in the mean aspect ratio (AR) of NPs. Although the mean AR change indicated linear fluence dependence in the low- and medium-fluence regions, it indicated a nonlinear dependence in the higher-fluence region. The data reveals that elongation efficiency of Zn is correlated with the electronic power “Se in silica” and is not correlated with either “Se in Zn” or the nuclear stopping power. The elongation efficiency plotted as a function of the “Se in silica” revealed a linear relationship, with a threshold value of ~ 2 keV/nm, which is the same dependence exhibited by the ion-track formation in silica. The log-log plot showed that the elongation efficiency increased linearly with Se above a critical value of ~3 keV/nm, and steeply decreased with Se to the power of 5th below the critical Se. The steep decrease can be ascribed to the discontinuous nature of the ion-tracks, which is expected at Se ~ 2-4 keV/nm in silica. The fluence F dependences of AR -1 under various irradiations are well-normalized with the electronic energy deposition of SHIS, i. e., the product of Se and F with Se higher than the same critical value of ~3 keV/nm. The normalized data above the critical value fell on a linear relation, AR(F) -1 SeF for SeF < 2 keV/nm3 and a sub-linear relation (SeF)1/2 for SeF > 2 keV/nm3. On the basis of these experimental results, we discuss some insights into the elongation mechanism.Nanotechnology 08/2014; 25(43):435301. DOI:10.1088/0957-4484/25/43/435301 · 3.67 Impact Factor
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ABSTRACT: We show that ZnMoO4 remains in stable phase under thermal annealing up to 1000 °C, whereas it decomposes to ZnO and MoO3 under transient thermal spike induced by 100 MeV Ag irradiation. The transformation is evidenced by X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). Thin films of ZnMoO4 were synthesized by thermal evaporation and subsequent annealing in oxygen ambient at 600 °C for 4 h. XRD results show that as the irradiation fluence increases, the peak related to ZnMoO4 decreases gradually and eventually disappear, whereas peaks related to ZnO grow steadily up to fluence of 3 × 1012 ions/cm2 and thereafter remain stable till highest fluence. This indicates that polycrystalline ZnMoO4 film has transformed to polycrystalline ZnO thin film. The Raman lines related to ZnMoO4 are observed to have disappeared with increasing irradiation fluence. XPS results show modification in bonding and depletion of Mo from near surface region after the ion irradiation. Cross-sectional transmission electron microscopy result shows the formation of ion track of diameter 12-16 nm. These results demonstrate that ion beam methods provide the means to control phase splitting of ZnMoO4 to ZnO and MoO3 within nanometric dimension along the ion track. The observation of phase splitting and Mo loss are explained in the framework of ion beam induced thermal spike formalism.Journal of Applied Physics 03/2014; 115(16). DOI:10.1063/1.4872259 · 2.19 Impact Factor