Abstract
Abstract. A novel method for the detection of short pulses of gas at very low concentrations, the differential surface reduction (DSR), is presented. DSR is related to the temperature pulsed reduction (TPR) method. In a high temperature phase, e.g., at 400 ∘C, the surface of a metal oxide semiconductor gas sensor (MOS) is oxidized in air and then cooled abruptly down to, e.g., 100 ∘C, conserving the large excess of negative surface charge. In this state reactions of reducing gases with surface oxygen are strongly favored, which increases the sensitivity. Due to the large energy barrier between metal oxide grains caused by the excess surface charge, a highly precise electrical measurement at very low conductance (down to 10−11 S) is a prerequisite for this method. Moreover, the electrical measurement must be very fast to allow a good resolution of retention times. Applying the method to a doped SnO2 detector, gas pulses down to a dosage of 1 ppb times seconds can be detected. The gas transport inside the detector is simulated using the finite element method (FEM) to optimize the gas transport and to keep response and recovery time as short as possible. With this approach, we have demonstrated a detection limit for ethanol of below 47 fg.
Highlights
Gas chromatography (GC) is a very versatile method for the analysis of gases as it allows the separation of different gases over time
According to Eq (11) all three different peaks will result in the same shift of the sensor signal; i.e., the operating mode will result in a measured signal directly proportional to the dosage, i.e., the total amount of substance, in the GC peak
Using the module Laminar flow and a stationary study the flow conditions inside the chamber are simulated. Applying this flow field to the Transport of diluted species model offers the possibility of investigating the shape evolution of incoming Gaussian peaks and estimating the maximum number of molecules that can reach and react on the sensor surface
Summary
Gas chromatography (GC) is a very versatile method for the analysis of gases as it allows the separation of different gases over time. The functional principle of gas sensing with MOS sensors is based on oxidation and reduction on the surface (Ding et al, 2001) It affects an exchange of electrons between the conduction band of the semiconductor and adsorbed oxygen ions. The surface is slowly oxidized to reach the high temperature equilibrium with a highly covered surface (state 3) This increases the energy barrier and reduces the conductance, as shown by Eq (2) for a constant temperature. The surface coverage in state 4 corresponds to the coverage of the high temperature equilibrium (state 3), which results in a high energy barrier and a very low conductance of the sensor. According to Eq (11) all three different peaks will result in the same shift of the sensor signal; i.e., the operating mode will result in a measured signal directly proportional to the dosage, i.e., the total amount of substance, in the GC peak
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
