ReEtching produces nanostructured silicon when a catalytic agent, e.g. dissolved V₂O₅, is used to facilitate etching between Si and H₂O₂. H₂O₂
regenerates dissolved V in a 5+ oxidation state, which initiates
etching by injecting holes into the Si valence band. Independent
control over the extent of reaction (controlled by
the amount of H₂O₂ added) and the rate of reaction (controlled by the rate at which H₂O₂
is pumped into the etchant solution) allows us to porosify Si
substrates of arbitrary size, shape and doping, including wafers,
single-crystal powders, polycrystalline powders,
metallurgical grade powder, Si nanowires, Si pillars and Si powders that
have been textured with metal-assisted catalytic
etching (MACE). Similarly, improved control over the nucleation and
etching
in MACE is achieved by pumped delivery of reagents.
Nanowires are not produced directly by MACE of powders, rather they
form
when a porosified layers is cleaved by capillary
forces or sonication.