Aug 18, 2014
Multilayer silicene proves stable in air
Silicene, a two-dimensional honeycomb lattice of silicon atoms with similarities to graphene, has attracted interest both in terms of the fundamental physics behind its properties and new technologies that might exploit them. However, a stable form of the material has proved elusive, making it hard to pin down its characteristic properties and possible applications. Now researchers have demonstrated the stability of multilayer silicene in air, significantly promoting further research of the material.
"The key result of this research is that we can manage multilayer silicene outside an ultrahigh vacuum – at least for 24 h, which is largely long enough to perform any industrial microelectronic process, or physical measurements," explains Paola De Padova, a senior researcher at Consiglio Nazionale delle Ricerche ISM in Italy, who led the research.
Further characterization experiments of the material also provided evidence of the existence of multilayer silicene as opposed to a thin film of bulk silicon – an issue that has invited substantial debate over recent years.
"Silicene is 'per se' interesting due to the fact that it is a new silicon allotrope [bonding structure], which can show new characteristic physical properties," De Padova tells nanotechweb.org. As an example she cites the material's electronic properties, which hosts Dirac fermions – massless particles. These characteristic properties may also prove very attractive for researchers developing nanotechnology devices such as in next-generation electronics.
Stable for 24h
De Padova and her colleagues at Consiglio Nazionale delle Ricerche, Universitá di Roma, Universitá di Firenze in Italy and CNRS-PIIM UMRin France deposited multilayer silicene on top of an initial silicene wetting layer, which can be grown on a facet of crystalline silver. Single-layer silicene inherently interacts with the substrate, which alters its electronic properties but multilayer silicene becomes decoupled from the metal substrate.
The researchers first studied the multilayer silicene stack covered with an aluminium oxide capping layer before investigating the stability of the material with no capping layer. Investigations of the interaction of silicene revealed very little oxidation, both under high oxygen doses and in air at room temperature.
"I was not surprised to find multilayer silicene stable in air, due to its honeycomb structure, which preserves it from having reactive dangling bonds," explains De Padova, who describes her work on silicene over the past several years as a labour of "passion and patience".
The researchers grew pure multilayer silicene on a pure monolayer silicene at rigorously controlled and relatively low temperatures of 200 °C. "If the temperature is not optimal the silicene multilayer will not have a single phase," she explains. "In the case of high temperature (around 300–350 °C) several processes can take place connected to the diffusion of silicon into the silver, silver-silicon surface alloy formation and in the end growth of ordinary [bulk] silicon."
"I am surprised that the theory to predict both the structural rather than electronic properties for multilayer silicene is still in development, but we are working on that," says De Padova.
"The next step will be applying multilayer silicene in any prototypal device," Paola De Padova, senior researcher at Consiglio Nazionale delle Ricerche ISM in Italy.
Future work will also look into applications of multilayer silicene. The first realization of a field effect transistor through a monolayer silicene channel was recently announced by Alessandro Molle at the Conference: Flatlands beyond graphene July 9–11, in Dublin. "The next step will be applying multilayer silicene in any prototypal device," adds De Padova.
Full details of this research can be found in 2D Materials 1 021003.
About the author
Anna Demming is online editor for nanotechweb.org