Selective Response of Mesoporous Silicon to Adsorbants with Nitro Groups

TL;DR

This study shows that mesoporous silicon exhibits a selective electronic response to nitro-based explosive molecules, which could be used for detecting trace airborne explosives through spectroscopic methods.

Contribution

The paper introduces a novel spectroscopic approach to detect and identify nitro-based explosives by observing their selective interaction with mesoporous silicon's electronic structure.

Findings

Strong Si-O and Si-N bonds form upon adsorption.

Energy gap of silicon varies with different adsorbants.

Spontaneous nitro group breaking occurs on silicon surface.

Abstract

We demonstrate that the electronic structure of mesoporous silicon is affected by adsorption of nitro-based explosive molecules in a compound-selective manner. This selective response is demonstrated by probing the adsorption of two nitro-based molecular explosives (trinitrotoluene and cyclotrimethylenetrinitramine) and a nonexplosive nitro-based arematic molecule (nitrotoluene) on mesoporous silicon using soft X-ray spec- troscopy. The Si atoms strongly interact with adsorbed molecules to form Si-O and Si-N bonds, as evident from the large shifts in emission energy present in the Si L2,3 X-ray emission spectroscopy (XES) measurements. Furthermore, we find that the energy gap of mesoporous silicon changes depending on the adsorbant, as estimated from the Si L2,3 XES and 2p X-ray absorption spectroscopy (XAS) measurements. Our ab initio molecular dynamics calculations of model compounds suggest that these changes are due to spontaneous breaking of the nitro groups upon contacting surface Si atoms. This compound-selective change in electronic structure may provide a powerful tool for the detection and identification of trace quantities of airborne explosive molecules.