Anisotropic wet etching of crystalline silicon (c-Si)
is a key
chemical process used in microelectronic device fabrication. Controlled
fabrication of c-Si nanostructures requires an understanding of how
crystal planes evolve during silicon etching. Here, by imaging KOH
wet etching of c-Si nanowires, we show that it is possible to switch
the fast-etching direction (i.e., the etch anisotropy) between the
Si {100} and {110} crystal planes at will through mechanical agitation
of the etchant. Based on molecular dynamics simulations, we attribute
this switching to the higher affinity of the Si(OH)4 etch
byproducts to the Si {110} planes. These surface-bound byproducts
hinder etchant access to the {110} surfaces under stationary etching
conditions and thus reduce the etch rate in ⟨110⟩ directions.
Most importantly, by cycling through stirred and stationary modes
of etching, we can obtain isotropic etch profiles, fabricating high-quality,
round Si nanowires with sub-10 nm diameters. Our study provides an
important insight into the nanoscale wet etching of Si and demonstrates
a new level of control for enabling highly scalable, advanced nanoelectronic
devices.
The Particle-in-Cell (PIC) method for plasmons provides a mechanical, single-particle picture of plasmon resonances by tracking in time the movement of all the individual conduction electrons.
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