Microstructural characterisation of metallurgical grade porous silicon nanosponge particles

Abstract

Porous silicon finds numerous applications in the areas of bio-technology, drug delivery, energetic materials and catalysis. Recent studies by Vesta Sciences have led to the development of porous silicon nanosponge particles from metallurgical grade silicon powder through their own patented chemical etching process (Irish patent no. IE20060360). This discovery paves the way for a more economical production method for porous silicon. The work presented here studies the structural morphology of the porous silicon nanosponge particles using high resolution electron microscopy techniques combined with porisometry type measurements where appropriate. The related surface pore structure is examined in detail using Scanning Electron Microscopy and Transmission Electron Microscopy techniques while the internal pore structure is explored using Focused Ion Beam milling and ultramicrotomed cross-sections. Three samples of the silicon particles were analysed for this study which include the starting metallurgical grade silicon powder and two samples that have been chemically etched. Analysis of the etched samples indicates a disordered pore structure with pore diameters ranging up to 15nm on porous silicon particles ranging up to 5µm in size. Crystallographic orientation did not appear to affect the surface pore opening diameter. Internal pore data indicated pore depths of up to 1 µm dependant on the particle size and etching conditions applied.

Compositional characterisation of metallurgical grade silicon and porous silicon nanosponge particles

“…The Si particle size ranges from 4-5 mm with pore sizes ranging from 8-15 nm in diameter. 19 Similar porosity was observed for sample 2E-60 but with a smaller pore volume per surface area. 19 The 2E-bulk Si sample consists of solid Si particles.…”

“…19 Similar porosity was observed for sample 2E-60 but with a smaller pore volume per surface area. 19 The 2E-bulk Si sample consists of solid Si particles. In the fully etched porous Si particles (2E-100), a series of [340] HOLZ line patterns were taken along the spectrum image line as seen in Fig.…”

Drug Delivery with Porous Silicon

“…The cost of silicon wafers used in microelectronics is high because of the strict demands for high purity. These demands are well beyond that what would be needed for biomedical applications, and although it is possible to produce low-cost PSi from metallurgical grade silicon (Loni et al 2011;Chadwick et al 2012), it is not yet clear if this type of PSi can be used for biomedical purposes. Quite recently, a new promising approach to produce low-cost PSi has been started to explore, namely, magnesium-induced reduction of silicon dioxide to silicon (Bao et al 2007 and chapter "▶ Porous Silicon Formation by Porous Silica Reduction"), which may open a way to produce low-cost PSi with an environmentally friendly process (Batchelor et al 2012).…”

A bioactive metallurgical grade porous silicon–polytetrafluoroethylene sheet for guided bone regeneration applications

“…By varying the nitric acid concentration in the etchant mixture the surface area of these powders can also be tailored [28,30]. The MGPS particles used in this study are referred to as grade 2E-100 and are developed from a grade 2E-Bulk MGSi material [31]. A similar grade of Si particles is used to develop the MGPS-PTFE membrane made from 4E Sicomill powders from Vesta Ceramics.…”

“…MGSi contains elements such as Fe, Al, Ca, C and O [28,29] which are likely segregated at grain boundaries of the silicon raw material [29]. Vesta Sciences (Monmouth Junction, New Jersey) has developed a patented chemical etching process [28,30] which creates a high surface area nanoporous sponge-like structure in these particles [31,32]. The Metallurgical Grade Porous Silicon (MGPS) particles alone have been shown to induce a bioactive response in vitro [32], however, the combination of MGPS and PTFE into a membrane may represent a more suitable bioactive structure for grafting or coating applications.…”