Mesoporous silicon: A new route to fabricate silicon‐based nanotubes

Abstract

The present work reports the two types of silicon nanotubes fabrication. The tubular structures based on silicon have been fabricated by immersing mesoporous silicon layer into aqueous electrolyte based on a mixture of NH 4 F and NiSO 4 . Similar results are achieved by immersing mesoporous silicon layer that was formed from the silicon wafer previously metallized on its smooth surface with aluminum and after annealing in a N 2 environment. In this case, either silicon or nickel nanotubes can easily be formed only by tuning the pH level of the ammonium fluoride solution. The range of the inner diameter of these tubes varies from 40 to 110 nm, whereas the mean value of their tube-wall thicknesses is about 25 nm. The SNT characterization by energy-dispersive X-ray spectroscopy, X-ray diffraction spectroscopy and their open-circuit potential behaviors show that the silicon tubes have been formed by an etch-stop process where the space-charge region on the silicon side plays a key role for tubes formation. In this paper, the SNT formation mechanism in the aqueous mixture solution of NH 4 F:NiSO 4 using the mesoporous silicon layer as a starting material is discussed. We show that this proposed procedure is new and easy to implement.

Nanoporous silicon tubes: the role of geometry in nanostructure formation and application to light emitting diodes

“…We note that the substrate and solution conditions affect the etching speeds directly. Different etching speeds as a function of pH and electrolyte composition have been reported in the past and will be explained later [46,47]. For some of the conditions (especially figures 3(d) and (e)) the tubes become faceted.…”

“…We attribute this to the different dissolution activation energies for the different crystalline planes. These depend both on the doping concentration [59] and pH [46,47,60,61], which explains why faceting was only clearly observed in some of the conditions. So far, we have given a phenomenological illustration of the tube formation as a function of the pH and doping concentration.…”

“…It will be shown that at higher depletion lengths, the pillar's outer surface helps to redirect the etching to other regions-e.g. inside the pillar forming a tube-and thus preserve the external walls [46,47]. In the case of highaspect-ratio silicon micropillars coming into contact with the electrolyte, a depletion layer is formed at the curved surface, in the same way as in the case of planar geometry.…”

“…The SCR layer is a major self-limiting mechanism in the dissolution of semiconductors, bringing a potential barrier into existence, which acts as a barrier for the charge transfer from the electrolyte to the silicon and vice versa [46]. In this sense, it can be used to avoid or facilitate dissolution in certain regions of the substrate and to create non-planar structures such as silicon microtubes [46,47].…”

Physical and Electrochemical Characterization of Crystalline Silicon Surfaces Modified by Aluminum

“…The greater the number of defects, the higher the etching rate . These results could explain why the macro porous layer obtained from ATSi promoted the well defined tubes formation …”