OFET based explosive sensors using diketopyrrolopyrrole and metal organic framework composite active channel material

Detection of explosives using organic compounds poses many challenges, primarily because of the stability of the organic compound at nominal operating conditions. This paper addresses the aforementioned challenge by reporting a new organic material composite, whose stability is suitable for practical applications. Additionally, the reported organic composite is also capable of detecting vapors of Nitro based explosive compounds such as 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX). An alternating copolymer of thiophene flanked diketopyrrolopyrrole with thienylene-vinylenethienylene (PDPP-TVT) was used as a solution processable and spin coatable organic semiconductor active channel material for the organic field effect transistor (OFET) sensor. A composite of PDPP-TVT and metal organic framework (MOF) was used as a receptor and pre-concentrator sites for sensing of the explosive analytes. The sensor devices were characterized and the receptor sites were confirmed by the Fourier Transform Infrared Spectroscopy (FTIR) and atomic force microscopy (AFM). The detection of viable analytes is recognized by the percentage change in the saturated drain current (%Delta I-Dsat) obtained by the current (I)-voltage ( V) characteristics with and without the analyte. The corresponding %Delta I-Dsat recorded for nitrobenzene (NB), dinitrobenzene (DNB), nitromethane (NM), TNT and RDX are -7%, 2%, 24%, 81% and 50%, respectively. (C) 2015 Elsevier B.V. All rights reserved

A MEMS-based shifted membrane electrodynamic microsensor for microphone applications

In this paper we present a multidisciplinary modeling of a MEMS-based electrodynamic microsensor, when an additional vertical offset is defined, aiming acoustic applications field. The principle is based on the use of two planar inductors, fixed outer and suspended inner. When a DC current is made to flow through the outer inductor, a magnetic field is produced within the suspended inner one, located on a membrane top. In our modeling, the magnetic field curve, as a function of the vertical fluctuation magnitude, shows that the radial component was maximum and stationary for a specific vertical location. We demonstrate in this paper that the dynamic response of the electrodynamic microsensor was very appropriate for acting as a microphone when the membrane is shifted to a certain vertical position, which represents an improvement of the microsensor's basic design. Thus, a proposed technological method to ensure this offset of the inner inductor, by using wafer bonding method, is discussed. On this basis, the mechanical and electrical modeling for the new microphone design was performed using both analytic and Finite Element Method. Firstly, the resonance frequency was set around 1.6kHz, in the middle of the acoustic band (20Hz - 20kHz), then the optimal location of the inner average spiral was evaluated to be around 200 mu m away from the diaphragm edge. The overall dynamic sensitivity was evaluated by coupling the lumped elements from different domains interfering during the microphone function. Dynamic sensitivity was found to be 6.3V/Pa when using 100 mu m for both gap and vertical offset. In conclusion, a bandwidth of 37.6Hz to 26.5kHz has been found which is wider compared to some conventional microphones

A Spectroscopy and Microscopy Study of Parylene-C OFETs for Explosive Sensing

In this paper, we have explored Parylene-C (PC) as a sensing material for its unique signature and selectivity for explosive sensing. We have used a bi-layer deposition process to fabricate bottom-gate-top-contact organic field effect transistor (OFET) structures. Opening of dangling bonds on subjecting PC to plasma oxidation (POPC) renders these molecules to be employed as a receptor material in sensing vapors of both explosives and non-explosives, such as Trinitrotoulene (TNT), 1,3,5 trinitro-1,3,5-triazacyclohexane(RDX), PETN, Dinitrobenzene (DNB), Nitrobenzene (NB), Benzoquinone (BQ), and Benzophenone (BP). The change in: 1) the vibrational modes of the molecule by infrared spectroscopy; 2) surface potential of POPC by Kelvin probe force microscopy (KPFM); and 3) electrical characterization by I-V measurements of PC-based OFET on exposing to vapors have been systematically studied. Different signatures for all the analytes have been observed while exact and perfect selectivity for TNT, RDX were found from I-V studies and for PETN by KPFM studies. Thus, the OFET device-based chemical sensors demonstrated here with improved sensitivity and excellent selectivity, stand as promising candidates for explosives detection

Comparison among different algorithms in classifying explosives using OFETs

Vapour phase detection of explosives using pattern recognition approaches is a very important area of research worldwide. This paper elaborates on the comparison between different algorithms in classifying empirical multiparametric data that are obtained from the explosive vapor sensors based on organic field effect transistors (OFETs). We address the problem of classification by means of statistical comparison among algorithms such as NaiveBayes (NBS), locally weighted learning (LWL), sequential minimal optimization (SMO) and J48 decision tree on data acquired from OFETs. This analysis helps in understanding the nature of data obtained from experiments and in making efficient estimators for the detection of explosives. The correctly classified instances for predicting tested samples using LWL, NBS, SMO and J48 decision tree are 72%, 73%, 80% and 90%, respectively. The future development of standoff explosive detectors will be benefited greatly by a proper choice of these classification approaches. (C) 2012 Elsevier B.V. All rights reserved

A non-volatile resistive memory effect in 2,2 ',6,6 '-tetraphenyl-dipyranylidene thin films as observed in field-effect transistors and by conductive atomic force microscopy

The charge transport properties of 2,2',6,6'-tetraphenyldipyranylidene (DIPO-Ph4), a large planar quinoid pi-conjugated heterocycle, are investigated in field-effect transistor (FET) configuration and by conductive atomic force microscopy (c-AFM). The FET properties show a clear p-type behavior with a hole mobility up to 2 x 10(-2) cm(2) V-1 s(-1) and on/off ratio of 10(4). The transfer characteristics I-d/V-g present a clear hysteresis typical of a resistive memory effect. This memory effect is again observed by means of c-AFM in lateral mode using a nearby gold top-contact as the counter-electrode. The c-AFM current response recorded for variable distances d = 0.5-9.0 mm between the AFM tip and the top electrode shows a resistive switching behavior in the low-voltage 0.0-3.0 V region. Repeated "write-read-erase-read" cycles performed at low frequency reveal a non-volatile memory effect in the form of high-resistance and low-resistance states with a stable on/off ratio of 10(2) during cycling operation