Hierarchical Nanostructuring of Porous Silicon with Electrochemical and Regenerative Electroless Etching

Abstract

Hierarchically nanostructured silicon was produced by regenerative electroless etching (ReEtching) of Si powder made from pulverized anodized porous silicon. This material is characterized by ∼15 nm mesopores, into the walls of which tortuous 2–4 nm pores have been introduced. The walls are sufficiently narrow that they support quantum-confined crystallites that are photoluminescent. With suitable parameters, the ReEtching process also provides control over the emission color of the photoluminescence. Ball milling and hydrosilylation of this powder with undecylenic acid produces nanoparticles with hydrodynamic diameter of ∼220 nm that exhibit robust and bright luminescence that can be excited with either one ultraviolet/visible photon or two near-infrared photons. The long-lived, robust visible photoluminescence of these chemically passivated porous silicon nanoparticles is well-suited for bioimaging and theranostic applications.

Response of Photoluminescence of H-Terminated and Hydrosilylated Porous Si Powders to Rinsing and Temperature

“…As expected, hydrosilylation changed the PL response and extended the useful range of pH values into the range encountered in PBS. As reported previously [42], exposure to phosphate buffer first enhanced PL intensity. Here, we found that the intensity variation depended on the pH of the Rinsing must achieve three imperatives to be effective for retaining maximum PL intensity.…”

“…For comparison of H-terminated to hydrosilylated por-Si, ReEtched por-Si batches were functionalized by thermal hydrosilylation by immersing particles in undecylenic acid (99%, Agros Organics, Fisher Scientific, Pittsburgh, PA, USA) and heating them at 120 • C for 16 h as described in [42]. After heating, excess acid was removed by washing the resulting particles with ethanol (EtOH).…”

“…The natural hydrogen termination of as-formed por-Si is extremely efficient at passivating electron-hole pair recombination centers [30], for powders, especially for very small particles sizes and large volumes. Recently, the regenerative electroless etching or ReEtching method has been demonstrated to produce luminescent por-Si powders by direct etching of Si powders of any grade [42,55]. This process is easily scalable to produce large quantities of por-Si powder.…”

Nanoporous Silicon as a Green, High-Tech Educational Tool

“…Biodegradable scaffolds for tissue regeneration are clearly a good example of this, where the ability to control topography from nanometers to millimeters is required. The hierarchical structuring of silicon is being developed for numerous application areas shown in Table 4 [81][82][83]. In this regard, using a hierarchical biogenic silica template (Section 2.3) rather than multiple processing tools is particularly attractive, provided its dimensionality and topography are already optimized by nature for the specific use in mind.…”

Functionalization of Oxide‐Free Silicon Surfaces for Biosensing Applications

“…[168] The performance of photoluminescence sensors may be tuned by optimizing nano dots and pore dimensions in porous silicon. Furthermore, chemical passivation of the oxide-free substrates is known to stabilize the photoluminescence [75,169] and prevent recombination. Therefore, organic interlayer prepared via hydrosilylation or electrografting that both conserve the photoluminescent properties as well as allow further biofunctionalization may play a great role in these devices.…”