The as-grown black silicon exhibits rich physical properties including exciting optical and electrical features that are promising for a variety of applications ranging from energy to biomedical fields.

Investigating the samples by cross-sectional TEM indicates the presence of silicon nanoneedles or nanopillars. The length of these needles can be as long as a few hundred nanometres depending on the process conditions. Their width can be as low as 10 nm, tapering down to only few atoms thick at the tips.

Each needle is single crystalline silicon with a surface structure possessing some kinks, vacancies and oxidation as revealed by TEM and energy dispersive spectroscopy.

The optical and electrical properties of the black silicon were established using photoluminescence, Fourier-transformed infrared spectroscopy, electron microscopy, spectroscopic ellipsometry and field emission studies.

The work has many potential applications, including:

Solar cells: more than just a light soaking element, the structure can be configured as an active solar energy converting reactor.
Chemical sensing: smoother surfaces provide high sensitivity and fast response times.
Biomedical: surface functionalization is possible and biocompatibility can be enhanced by coating with suitable materials.
Field emission: geometry could benefit field emission devices for nanoelectronics.
Energy: offers durable electrode functionality in lithium ion batteries for prolonged lifetimes.
Light sources: material could enable VIS and IR tunable light sources for silicon photonics, telecommunications and interconnects.

The team is currently exploring the origin of the observed properties of black silicon and developing ways to apply the material in new devices.

More details can be found in the journal Nanotechnology.