Control of the Pore Texture in Nanoporous Silicon via Chemical Dissolution

Abstract

The surface and textural properties of porous silicon (pSi) control many of its physical properties essential to its performance in key applications such as optoelectronics, energy storage, luminescence, sensing, and drug delivery. Here, we combine experimental and theoretical tools to demonstrate that the surface roughness at the nanometer scale of pSi can be tuned in a controlled fashion using partial thermal oxidation followed by removal of the resulting silicon oxide layer with hydrofluoric acid (HF) solution. Such a process is shown to smooth the pSi surface by means of nitrogen adsorption, electron microscopy, and small-angle X-ray and neutron scattering. Statistical mechanics Monte Carlo simulations, which are consistent with the experimental data, support the interpretation that the pore surface is initially rough and that the oxidation/oxide removal procedure diminishes the surface roughness while increasing the pore diameter. As a specific example considered in this work, the initial roughness ξ ∼ 3.2 nm of pSi pores having a diameter of 7.6 nm can be decreased to 1.0 nm following the simple procedure above. This study allows envisioning the design of pSi samples with optimal surface properties toward a specific process.

10 000-Fold Improvement in Protein Detection Using Nanostructured Porous Silicon Interferometric Aptasensors

“…25 Nonetheless, chemical dissolution of PSi in NaOH aqueous solution is one of the most used, being fast, cheap, and effective. 7,9,26 After removal of the PSi sacrificial layer, a PSi sensing layer is eventually prepared by using a constant etching current density, namely, 500 mA/cm 2 for 30 s. The same aqueous electrolyte HF:EtOH = 3:1 (v/v) is used for both PSi sacrificial and sensing layer preparation.…”

“…Different physicochemical approaches have been proposed to remove the PSi parasitic layer before etching of the next PSi sensing layer (e.g., H 2 SO 4 /H 2 O 2 weak wet oxidation followed by silicon dioxide removal in HF solution; electropolishing of the silicon substrate before PSi formation; high-temperature thermal annealing of the silicon substrate) . Nonetheless, chemical dissolution of PSi in NaOH aqueous solution is one of the most used, being fast, cheap, and effective. ,, After removal of the PSi sacrificial layer, a PSi sensing layer is eventually prepared by using a constant etching current density, namely, 500 mA/cm 2 for 30 s. The same aqueous electrolyte HF:EtOH = 3:1 (v/v) is used for both PSi sacrificial and sensing layer preparation.…”

Formation of Si/SiO2 Luminescent Quantum Dots From Mesoporous Silicon by Sodium Tetraborate/Citric Acid Oxidation Treatment

“…Coexistence of both initial Si-H x and oxidized O 3 -SiH groups points to a non-homogeneous oxidation process. Previous data show that oxidation takes place easier on convex regions, while smooth regions are less affected (Secret et al, 2015).…”

Influence of Surface Chemistry on Ibuprofen Adsorption and Confinement in Mesoporous Silicon Microparticles

“…The present work compares the behavior of ibuprofen adsorbed inside of the PSi microparticles. PSi was selected as the carrier because of its branching, mesoporous structure with rough walls that differs from the ordered silica-type materials and because of its silicon hydride-terminated initial surface that enables simple gas phase surface modifications. , Here, the PSi microparticles were stabilized into either hydrophilic thermally oxidized PSi (TOPSi) or hydrophobic thermally hydrocarbonized PSi (THCPSi). The two surface modifications allow the observation on how the presence or absence of hydrogen bonding capable silanol groups affects both the adsorption and confinement of ibuprofen.…”