Semiconductor nanowires are generally grown with the use of metal nanoparticles that induce the columnar growth. The most commonly used metal is gold, an element that is incompatible with the silicon technology platform. The investigation of alternative metals or metal-free processes is therefore very important to make use of nanowires in practical devices.

Scientists from Consiglio Nazionale delle Ricerche in Italy have shown that proper mechanical or chemical treatments of silicon surfaces allow the growth of "self-catalysed" silicon nanowires without the use of any external metal (for more details, see http://iopscience.iop.org/0957-4484/21/25/255601). Using plasma-enhanced chemical vapour deposition, the group has been able to grow the nanowires at temperatures down to 320 °C.

One of the substrates used for this demonstration is obtained through laser annealing of amorphous silicon. This process can be implemented on plastic substrates and one of the team's future research goals is to obtain the growth of nanowires through a multi-step process on plastic, flexible substrates. Such a result might open up the possibility to develop flexible nanowires-based devices such as photovoltaic cells. Other surfaces that enable the growth of silicon nanowires are cleavage Si(110) surfaces obtained by cleaving a Si(100) wafer and n-Si(111) surfaces etched with 40% NH4F solution.

It is worth noting that cleaved Si(110) surfaces also enable the growth of self-catalysed GaAs nanowires (see http://iopscience.iop.org/0957-4484/19/27/275711), indicating that the microscopic mechanism that induces the growth, which is still not known, is independent of the chemistry of the grown material.

The researchers presented their work in the journal Nanotechnology.