Porous Silicon Preparation by Electrochemical Etching in Ionic Liquids

Abstract

Anodic etching of n-type {111} silicon in ionic liquid (IL) systems ([RMIM][X], R = H, Bu; X = BF -, PF -), realized under galvanostatic conditions and room temperature, allowed the formation of porous silicon surfaces with different pore morphology depending on the etching time, current density and the IL used. The study of the effect of water content in IL on the etching process has shown water content of 1% to be optimal. The role of the anion on the etching process was elucidated using 1methylimidazolium tetrafluoroborate ([HMIM][BF 4 ]) and 1-methylimidazolium hexafluorophosphate ([HMIM][PF 6 ]) IL systems. [HMIM][BF 4 ] was found to be most efficient for the formation of silicon nanostructured array with a pore size of 30-80 nm. The thus prepared porous silicon samples show fluorescence in blue light (475 nm). The NMR spectra of [HMIM][BF 4 ] ionic liquid before and after etching does not show

Electrochemical Etching of Germanium in Ionic Liquids without the Use of Toxic and Corrosive Reagents

“…It should be noted that a similar effect was observed when etching silicon in these ionic liquids. In that case, intense electropolishing occurred in [BMIM][BF 4 ], whereas an intermediate regime of material processing was observed in [BMIM][PF 6 ], but nevertheless, the results were noticeably different [11] …”

“…For preparing porous germanium, both polished polycrystalline substrates (Figure 1) and p‐type (100) single crystals were used. Electrochemical etching was carried out in a galvanostatic mode at room temperature using a PTFE cell described earlier, [11] with a Pt grid as a cathode.…”

“…The choice of ILs for etching germanium was based on the recent results for single‐crystal silicon [11] . However, whereas in the case of silicon the best results were observed in an acidic ionic liquid (N‐methylimidazolium tetrafluoroborate, [HMIM][BF 4 ]), porous germanium with a fairly uniform and dense distribution of pores was obtained in a softer ionic liquid (1‐butyl‐3‐methylimidazolium hexafluorophosphate, [BMIM][PF 6 ]), while the use of [HMIM][BF 4 ] did not allow obtaining the target porous material (Figures S1–S2).…”

“…Before use, the working surfaces of single‐crystalline and polycrystalline substrates were polished with chromium oxide GOI paste to a mirror finish and then degreased with isopropyl alcohol. Electrochemical etching of germanium was performed in an original rod‐like PTFE cell [11] . The special design of the cell provided a constant etching area (d=4 mm) throughout all experiments.…”

“…In the case of silicon, almost all known etching techniques are based on the use of hydrofluoric acid [9] – a very toxic substance [10] . Recently, we have proposed using imidazolium ionic liquids (ILs) as an alternative medium for etching silicon [11] . In recent years, ILs have found various applications in green chemistry, [12] and revealed great prospects for use in pharmaceutics and medicine [13] due to their intrinsically lower hazard, as compared to many traditional organic and inorganic media, and their high biological activity.…”