silicon and trimethylamine

Organosulfur compounds generated from a variety of biological as well as anthropogenic sources are oxidized in air to form sulfuric acid and methanesulfonic acid (MSA). Both of these acids formed initially in the gas phase react with ammonia and amines in air to form and grow new particles, which is important for visibility, human health and climate. A competing sink is deposition on surfaces in the boundary layer. However, relatively little is known about reactions after they deposit on surfaces. We report here diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) studies of the reaction of MSA with trimethylamine (TMA) on a silicon powder at atmospheric pressure in synthetic air and at room temperature, either in the absence or in the presence of water vapor. In both cases, DRIFTS spectra of the product surface species are essentially the same as the transmission spectrum obtained for trimethylaminium methanesulfonate, indicating the formation of the salt on the surface with a lower limit to the reaction probability of γ > 10(-6). To the best of our knowledge, this is the first infrared study to demonstrate this chemistry from the heterogeneous reaction of MSA with an amine on a surface. This heterogeneous chemistry appears to be sufficiently fast that it could impact measurements of gas-phase amines through reactions with surface-adsorbed acids on sampling lines and inlets. It could also represent an additional sink for amines in the boundary layer, especially at night when the gas-phase reactions of amines with OH radical and ozone are minimized.

Topics: Adsorption; Atmospheric Pressure; Mesylates; Methylamines; Powders; Silicon; Spectroscopy, Fourier Transform Infrared; Surface Properties

This study proposes nanothickness piezoresistive double-clamped beams that are used in a double-side adsorbing mode. The axially stressed clamped beam exhibits continually increasing sensitivity as it is thinned down to nanoscale, and the thinning is theoretically without limitation. Sensing experiments to part-per-million levels of trimethylamine vapor well verify the proposal. A 93 nm thick beam sensor exhibits higher than 1 order of magnitude sensitivity compared to typical piezoresistive cantilever sensors, and its chemomechanical sensing resolution is comparable with that obtained by the off-cantilever optical detection method. With the nanobeam, a surprisingly ultrahigh sensitivity to surface molecular self-assembly induced surface stress is also obtained that is about 150 times higher than that obtained from a conventional cantilever. With additional advantages of elimination of single-sided adsorption induced bimetallic effect noise, tinier size, and easier fabrication, the ultrasensitive nanothick beam sensors show promise to replace the state-of-the-art piezoresistive cantilevers for bio/chemical nanomechanical detection.

Topics: Adsorption; Methylamines; Microscopy, Electron, Scanning; Nanotechnology; Silicon; Silicon Dioxide; Surface Properties