39 research outputs found
Selective Response of Mesoporous Silicon to Adsorbants with Nitro Groups
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.Comment: 27 pages, 9 figure
The rapid formation of functional monolayers on silicon under mild conditions
We report on an exceedingly mild chemical functionalization of hydrogen-terminated Si(100) with unactivated and unprotected bifunctional α,ω-dialkynes. Monolayer formation occurs rapidly in the dark, and at room temperature, from dilute solutions of an aromatic-conjugated acetylene. The method addresses the poor reactivity of p-type substrates under mild conditions. We suggest the importance of several factors, including an optimal orientation for electron transfer between the adsorbate and the Si surface, conjugation of the acetylenic function with a π-system, as well as the choice of a solvent system that favors electron transfer and screens Coulombic interactions between surface holes and electrons. The passivated Si(100) electrode is amenable to further functionalization and shown to be a viable model system for redox studies at non-oxide semiconductor electrodes in aqueous solutions