A team of scientists has shown that metallic silicon nanowires (Si NWs) grown on a Ag surface undergo an oxidation process that is remarkably similar to the combustion process in a burning match [De Padova et al., Nano Lett. (2008), doi:10.1021/nl800994s].

The oxidation of silicon is an important issue in many areas of physics and technology, since the interface between Si and SiO2 plays a significant role in microelectronics devices. With the trend toward the nanoscale, the role played by this interface, therefore, becomes pivotal.

Now, a collaboration between researchers in Italy and France has made a significant breakthrough in understanding this system at small length scales. Using scanning tunneling microscopy (STM) and high-resolution Si 2p core-level photoelectron spectroscopy (PES), the team was able to follow the oxidation process in Si NWs with an unprecedented level of accuracy.

“We have been able to prove that the oxidation process starts at the extremities of the Si NWs and that surprisingly, it develops along the lengths of the wires, similar to a propagating flame front,” says Paola De Padova, from the Istituto di Struttura della Materia in Rome, Italy.

“The oxidation front creates a moving internal junction between the oxidized part, where a region of Si in the +4 oxidation state (SiO2) grows at the expense of the unaltered metallic part. Our Si 2p core-level PES data shows that there is a narrow region at the Si-SiO2 interface in which the +1, +2, and +3 oxidation states coexist.”

De Padova tells Materials Today that this work is part of a long standing interest her team has in Si NWs. Their development of 1.6 nm thick nanowires grown on Ag(110) surfaces led them to the present discovery and they have future plans to study the system in the presence of dopants.