Solid-State Gas Sensors: Sensor System Challenges in the Civil Security Domain

Abstract

The detection of military high explosives and illicit drugs presents problems of paramount importance in the fields of counter terrorism and criminal investigation. Effectively dealing with such threats requires hand-portable, mobile and affordable instruments. The paper shows that solid-state gas sensors can contribute to the development of such instruments provided the sensors are incorporated into integrated sensor systems, which acquire the target substances in the form of particle residue from suspect objects and which process the collected residue through a sequence of particle sampling, solid-vapor conversion, vapor detection and signal treatment steps. Considering sensor systems with metal oxide gas sensors at the backend, it is demonstrated that significant gains in sensitivity, selectivity and speed of response can be attained when the threat substances are sampled in particle as opposed to vapor form.

Semiconducting Metal Oxides Nanocomposites for Enhanced Detection of Explosive Vapors

“…Thus, there is a strong need of cheap, rapid, sensitive, and simple analytical methods for the detection and monitoring of these explosives in air. Table 1 illustrates that explosives' melting points are generally below 200 °C, while boiling points are in the range 150-300 °C [10]. Table 1 also indicates that boiling of explosives often leads to molecular decomposition.…”

“…Once vaporized, explosives molecules can therefore easily take up negative charge from O − 2 ions, thus forming negatively-charged analyte ions, which can then be easily analyzed with regard to their ion mass (this process is extensively used in the IMS (Ion Mobility Spectroscopy) detection of explosives, drugs, and chemical weapons in airports [10]. As most explosives either contain NO or NO side groups (Figure 2), these materials also present high electron affinities (Table 1).…”

“…Once vaporized, the solids decompose into individual molecules, which then further decompose into smaller fragments. Experimentally, it was found that all explosives produce a cloud of reaction products made of nitrogen dioxide (NO2), nitric oxide (NO), ammonia (NH3), hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), nitrogen (N2), oxygen (O2) and methane (CH4) [10]. Among those, NO2 is the compound that is most easily detected at low concentrations and with relative selectivity using solid state gas sensors [10] because of its high electron affinity.…”

“…Experimentally, it was found that all explosives produce a cloud of reaction products made of nitrogen dioxide (NO2), nitric oxide (NO), ammonia (NH3), hydrogen (H2), carbon monoxide (CO), carbon dioxide (CO2), nitrogen (N2), oxygen (O2) and methane (CH4) [10]. Among those, NO2 is the compound that is most easily detected at low concentrations and with relative selectivity using solid state gas sensors [10] because of its high electron affinity. This feature allows it to be set aside from most other gases in the ambient air (Table 2) and enables it to extract in a very efficient way conduction electrons from semiconductor materials [10].…”

“…Among those, NO2 is the compound that is most easily detected at low concentrations and with relative selectivity using solid state gas sensors [10] because of its high electron affinity. This feature allows it to be set aside from most other gases in the ambient air (Table 2) and enables it to extract in a very efficient way conduction electrons from semiconductor materials [10].…”