Complex Chiral Colloids and Surfaces via High-Index Off-Cut Silicon

Silicon wafers are commonly
etched in potassium hydroxide solutions
to form highly symmetric surface structures. These arise when slow-etching
{111} atomic planes are exposed on standard low-index surfaces. However,
the ability of nonstandard high-index wafers to provide more complex
structures by tilting the {111} planes has not been fully appreciated.
We demonstrate the power of this approach by creating chiral surface
structures and nanoparticles of a specific handedness from gold. When
the nanoparticles are dispersed in liquids, gold colloids exhibiting
record molar circular dichroism (>5 × 109 M–1 cm–1) at red wavelengths are obtained.
The nanoparticles
also present chiral pockets for binding.