Silicon technology is already pervasive in our everyday lives. Silicon 'chips' often help us shop, cook and relax. They are involved in many forms of transport and control most forms of communication at the workplace. Our ability to micromachine the material is now poised to generate a second revolution, where a whole range of commodities become miniaturised and available in large numbers and at low cost.

But silicon does have its limits. In its bulk crystalline form it is not regarded as a useful magnetic, optical or biomedical material. So this is where I see a key role for porous Si, as a means of increasing the functionality of silicon technology even further. Rendering the material highly porous is a simple, cheap way of nanostructuring, and bestowing a range of material properties markedly different from those of the parent semiconductor. The ability to emit light efficiently and to promote tissue growth are two disparate examples of this. Porous Si has shown us that silicon in a nanocrystalline form has long-term potential as an optical, optoelectronic and biomedical material, for example.

I think it is now quite timely for a book such as this to appear. The importance of a number of fabrication issues in determining properties is now established and should lead to material of improved quality. Also, in the last year or so data has at last appeared on mechanical and thermal properties. Finally, a quite broad range of application areas is emerging, one of which is already entering...