Silicon nanowire arrays for the preconcentration and separation of trace explosives vapors

Abstract

Silicon nanowire (SiNW) arrays are demonstrated as a suitable platform for the preconcentration of trace nitroaromatic compounds and subsequent desorption via Joule heating of the array. Arrays are fabricated from Si wafers containing an epitaxially grown layer of low conductivity intrinsic Si sandwiched between layers of high conductivity p-type Si. Passage of current through the nanowires results in nanowire temperatures in excess of 200 °C during heating of the arrays as verified by using the temperature-dependent shift of the Si Raman band at ˜520 cm−1. Analyte vapor preconcentration and partial separation is achieved on the array at analyte concentrations nearly two orders-of-magnitude below saturated vapor concentrations at room temperature. The effects of desorption carrier gas flow rate and temperature on the ability to preconcentrate and resolve the analytes of interest are determined. 2,6-dinitrotoluene (2,6-DNT) and 2,4-dinitrotoluene (2,4-DNT) were detected at nominal vapor concentrations of 800 pptv with a 1 min sample time (1.1 ng nominal mass load) and trinitrotoluene (TNT) was detected at a nominal vapor concentration of 65 pptv with a 10 min sample time (1.1 ng nominal mass load).