Harshil N. Raval

Explosive vapor sensor using poly (3-hexylthiophene) and CuII tetraphenylporphyrin composite based organic field effect transistors

Organic field effect transistors based on poly(3-hexylthiophene) and CuII tetraphenylporphyrin composite were investigated as sensors for detection of vapors of nitrobased explosive compounds, viz., 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX), 2,4,6-trinitrotoluene (TNT), and dinitrobenzene, which are also strong oxidizing agents. Significant changes, suitable for sensor response, were observed in transistor “on” current (Ion) and conductance (S) after exposure. A similar device response was, however, not observed for oxidizing agents such as benzoquinone and benzophenone. The Fourier transform infrared spectrometry experiments supported the results, where exposure to RDX and TNT vapors resulted in a significant shift in IR peaks.

Determining ionizing radiation using sensors based on organic semiconducting material

The use of organic semiconducting material sensors as total dose radiation detectors is proposed, wherein the change in conductivity of an organic material is measured as a function of ionizing radiation dose. The simplest sensor is a resistor made using organic semiconductor. Furthermore, for achieving higher sensitivity, organic field effect transistor (OFET) is used as a sensor. A solution processed organic semiconductor resistor and an OFET were fabricated using poly 3-hexylthiophene (P3HT), a p-type organic semiconductor material. The devices are exposed to Cobalt-60 radiation for different total dose values. The changes in electrical characteristics indicate the potential of these devices as radiation sensors.

Organic Sensor Platforms for Environmental and Security Applications

Department of Biosceiences and Bio-engineering Indian Institute of Technology, Bombay, India – 400 076 Email: rrao@ee.iitb.ac.in Organic sensors based on polymer microcantilevers and organic field effect transistors (OFETs) bring orthogonality to the sensing mechanism for different environmental and security applications. Orthogonolity is an important requirement from the point of reducing the

AN ORGANIC FIELD EFFECT TRANSISTORS-BASED SENSING PLATFORM FOR ENVIRONMENTAL/SECURITY APPLICATIONS

Organic semiconducting material based sensors have been used for various environmental applications. Organic field effect transistors (OFETs) also find their applications in explosive vapor detection and total ionizing radiation dose determination. OFETs using poly 3-hexylthiophene (P3HT), a p-type organic semiconductor material and CuII tetraphenylporphyrin (CuTPP) composite as their active material were investigated as sensors for detection of various nitro-based explosive vapors with greater than parts per billion sensitivity range. Significant changes, suitable for sensor response, were observed in ON current (Ion) and transconductance (gm) extracted from electrical characteristics of the OFET after exposure to vapors of various explosive compounds. However, a similar device response was not observed to strong oxidizing agents such as benzoquinone (BQ) and benzophenone (BP). Also, the use of organic semiconducting material sensors for determining total ionizing radiation dose was studied, wherein the conductivity of the material was measured as a function of total ionizing radiation dose. An organic semiconducting material resistor was exposed to γ-radiation and it was observed that the change in resistance was proportional to the ionizing radiation dose. Changes in various parameters extracted from electrical characteristics of the OFET after γ-radiation exposure resulted in an improved sensitivity. To protect the organic semiconductor layer from the degradation in the ambient the sensors were passivated with a thin layer of silicon nitride.

Ultra-sensitive polymeric sensor platforms for environmental sensing applications

In this article, novel technology-platforms are discussed for possible applications in the field of environmental, security and healthcare sensing using polymeric devices. Carbon nanocomposite based microcantilevers and thin-film transistor embedded microcantilevers are discussed for force sensing applications. It is also demonstrated that exposure of ionizing radiation changes the material properties of organic semiconductors which enables the use of organic thin-film transistors (OTFTs) as ionizing radiation dosimeters. An increase in the work-function has been observed by ultraviolet photoelectron spectroscopy for the copper(II) phthalocyanine (CuPc) thin-film upon exposure to ionizing radiation of γ-rays. Furthermore, CuPc based OTFTs are demonstrated as ionizing radiation dosimeters with a silicon nitride encapsulation layer deposited by Hot-wire CVD.

EFFECT OF GATE INSULATOR ON THE PERFORMANCE OF COPPER PHTHALOCYANINE-BASED ORGANIC THIN FILM TRANSISTORS

Effect of the gate dielectric on the performance of Copper phthalocyanine (CuPc) based top contact organic field effect transistors (OFET) has been studied using thermally grown SiO2 and sputtered HfOx films with dielectric constants of 3.9 and 12.5 respectively. Operating voltages of the devices on SiO2 and HfOx were found to be 10–50 V and 2–3 V, respectively. The lower operating voltage for HfOx is attributed to the higher dielectric constant. Devices on SiO2 and HfOx were found to have field effect mobilities of 0.01 and 3.5 × 10-3 cm2/Vs and drain current modulation of 103 and 102, respectively. Scanning Electron Microscopy showed widely scattered nanowires on HfOx and densely packed nanofibers on SiO2. X-ray diffraction studies showed better crystallinity of films on SiO2. The results show that operating voltage of devices can be reduced by using higher dielectric constant material while mobility and FET characteristics depend on structure of CuPc that in turn is influenced by the dielectric.