Condensed Matter & Materials Physics


Selective response of mesoporous silicon to adsorbants with nitro groups

30 January 2012 

J. A. McLeod, E. Z. Kurmaev, P. V. Sushko, T. D. Boyko, I. A. Levitsky, A. Moewes, Chemistry - A European Journal 18, 2912-2922 (2012).


Several methods for detecting trace quantities of explosives have been developed in recent years. However, a simple, compact, sensitive, selective, non-invasive, and low-cost sensor for low concentrations of explosives is an ideal that has not yet been achieved. One of the promising avenues of research in this area is development of chemical sensing approaches, in which a molecule of an explosive material adsorbs at the surface of a sensor and changes its properties.

Selecting a sensor material, which can "respond" selectively to low density concentrations of the molecules at room temperature remains a challenge. In this manuscript, researchers from the University of Saskatchewan (Canada), Institute of Metal Physics (Russia), University College London (UK), Emitech Inc., and University of Rhode Island (USA) demonstrate that spectroscopic characteristics of mesoporous silicon exposed to the vapour of explosives (TNT and RDX) and non-explosive para-nitrotoluene change and the magnitude of this change is sufficient to differentiate between the three molecules.

It was found that the edges of the valence and conduction bands of mesoporous Si undergo molecule-specific shifts by several tens of an eV in each case. This effect has been attributed to the molecule's adsorption and decomposition at the Si surface with subsequent oxidation and nitrization of the near-surface region of the Si sample. This has been supported by ab initio molecular dynamics calculations (see video), which demonstrate most likely mechanisms of the molecular decomposition at the Si surface.

Tabulating such spectroscopic changes for other hazardous molecules may provide a way forward for creating a selective Si-based sensor.

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