M.Sc Thesis

M.Sc StudentDov )David( Netta
SubjectMulti-Parameter Gas-Phase Sensing Using Organic Field Effect
Transistors (OFETs)
DepartmentDepartment of Nanoscience and Nanotechnology
Supervisors ASSOCIATE PROF. Yoav Eichen
PROF. Nir Tessler


Detection of explosives is becoming increasingly important with the ever increasing threats of terrorism. Nitro-aromatic compounds, such as TNT (Trinitrotoluene), are commonly used as explosives because of their availability.  Thus, there is a need for massively deployable and stand-alone devices that will allow real-time and accurate analysis of gas-phase explosives in our surrounding. Although some approaches are in use, the real-life applicability of them is rather limited.

In this research we developed a simple and inexpensive sensor device, based on Organic Field-Effect Transistor (OFET) technology. The main goal of this research is to optimize the fabrication and characterization of multi-parameters ‘state of the art’ OFET-based sensors, based on various π-conjugated semiconducting organic layers, for detection of explosives in the gas phase. In addition, a design and construction of a reliable sensing system that enables exposing the sensors to gas phase analytes and measuring its real-time electrical response is needed and described. Detection abilities are examined as changes in output currents, threshold voltage, carriers’ mobility and switching behavior of the sensors.

To address the issue of selectivity, sensors were exposed to vapors of several nitro-aromatic analytes as well as to vapors of "innocent" materials. Interaction between the polymers and nitro-aromatic compounds often resulted in relative enhancement of the drain current, for example. This is in contrast to the influence of vapors of "innocent" materials. In the first part of the thesis we present the development and characterization of sensors based on well-known commercial polymers, that were designed to sense the 'danger' of TNT vapors and its analogues (such as DNT, 2-NT etc.). This is because vapor relative concentration of TNT is significantly lower than its analogues; hence a highly selective sensor is required. In addition, nitro-aromatic analogues are by-products of TNT production, hence its existence can imply of TNT presence. We found that nitro aromatic compounds can be differentiated from innocent materials using our multi-parameters OFET-based sensors. We were also evident the strong impact of bias stress condition of OFET degradation and found a method to isolate this phenomenon from the real response to analytes exposure.

In the second part of this thesis we aimed to improve selectivity to nitro-aromatic compounds, in particular to TNT, by adding novel oligomers in a blend with MEH-PPV polymer. These oligomers were specially designed so they will contain a nucleophilic sensing unit that can attack nitro aromatic analyte molecules to form a unique Meisenheimer Complex. We found that this has farther increased the response to TNT vapors.