What is Porous Silicon?
In the 1950's, two engineers at Bell Labs were trying to develop a process for shaping and polishing Silicon and Germanium wafers. After various attempts of mixing HF acid and solvents with applied current on the Silicon surface, not much was thought to have happened other than a change in surface color from a blackish to redish brown. These results were written in a technical report and forgotten for about 30 years until Leigh Canham found that these chemically etched layers possesed unique quantum confinement properties and in some cases displayed amazing photoluminescence.
Since this (re)discovery of the quantum confinement properties, porous Silicon has become interesting not only for photoluminescence, but for solar applications by trapping more light or photons within the Si cell, more electricity can be produced. The beauty of the porous Silicon process is that depending on the mix of chemistry and levels of applied current, the pores or porous surface can be finely tuned altering the refractive index, volume density, surface area and overall porosity from a bulk Silicon wafer to a Silicon sponge layer or all the way to a Silicon cloud or web. Later these highly porous structures have been used as a scaffolding for thin film deposition, membranes, epitaxial layers for sensors, wearable electronics and even for growing and grafting human skin. In the 90's, it has also been found that by porosifying Silicon, liquids as well as bodily fluids can penetrate inside the pores and dissolve Silicon which previously was thought impossible. This has opened up many ideas for nano medicines and intelligent implants. Just as the porosity can be tuned, the rate at which the porous Silicon dissolves in the body can also be tuned, prolonging the release and effects of medicines, parfumes, lotions as well as many others.
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