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.
- SourceAvailable from: D. J. SprousterAppl. Sci. 03/2013; 2(2).
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ABSTRACT: This paper analyzes the effects of nanoporous surface on heat transfer temperaments of assorted thermal conducting materials. A phenomenal proposal of wielding the surface roughness to ameliorate the heat transfer rate has been discovered. The maximum increase of heat transfer rate procured by nanoporous layers is 133.3% higher than the polished bare metals of surface roughness 0.2 µm. This plays an imperative role in designing compact refrigeration systems, chemical and thermal power plants. Experimental results picture a formidable upswing of 58.3% heat transfer in chemically etched metals of surface roughness 3 µm, 133.3% in nanoporous surface of porosity 75–95 nm formed by electrochemical anodization, and porosity of 40–50 nm formed by spray pyrolysis increases the heat transfer by 130%. Effects of porosity, flow velocity and scaling on the energy transfer are also scrutinized. This paper also analyzes the multifarious modes of nanoporous fabrication, to contrive both prodigious and provident system.Journal of Thermal Science 12/2009; 18(4):358-363. · 0.30 Impact Factor