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

The Effects of Halogen Exposure on the Photoluminescence of Porous Silicon

AbstractInteraction of I2 vapor with luminescent porous silicon (PS) results in a mixed hydrogen/iodine terminated surface. The photoluminescence (PL) of PS is completely quenched upon I2 exposure. Excess iodine can be removed by pumping on the PS for several hours, resulting in partial recovery of the original PL spectrum. Exposing the hydrogen/iodine terminated PS to air results in the accelerated growth of an oxide layer and increased PL. The adsorption of iodine is postulated to induce surface traps that are responsible for the luminescence quenching observed.</jats:p

Yield Improvement Using Cryogenic Aerosol for BEOL Defect Removal

Abstract not Available.</jats:p