Revival of interband crystalline reflectance from nanocrystallites in porous silicon by immersion plating

We prepared porous silicon for which the UV reflectance (3.3-6 eV) is nearly eliminated, and exhibits no features at the Si interband bulk transitions 3.3, 4.3, and 5.5 eV. Plating with a thin layer of copper is found to cause recovery of the UV bulk-like crystalline reflectance and interband resonances. This provides evidence that the loss of crystalline absorption is reversible and is not due to a permanent loss in the crystalline structure. This may relate to a recent model in which the optical activity of ultra small nanocrystallites is produced by a new Si-Si crystalline configuration (or phase), distinct from but interconnected to the diamond-like configuration by a potential barrier.