Hexathiapentacene Nanowires as Chemical Vapor Sensors
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Hexathiapentacene Nanowires as Chemical Vapor Sensors Ting Gao1, Edgardo García-Berríos2, Alejandro L. Briseno3, Jian Wang1, Richard McConville1, Mark W. Ellsworth1, Ryan W. Dupon1, and Nathan S. Lewis2 1
Polymers, Ceramics and Technical Services Laboratories, Tyco Electronics, 306 Constitution Drive, Menlo Park, California 94025, U.S.A. 2 Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, U.S.A. 3 Department of Polymer Science, University of Massachusetts, Amherst, MA ABSTRACT Semiconducting hexathiapentacene (HTP) single–crystal nanowires were synthesized using a simple solution-phase route. Quartz Crystal Microbalance and complex resistance measurements were employed to investigate the sensing properties of an HTP nanowire to analytes including acid, amine, and hydrocarbon vapors. Cole-Cole plots (0.01Hz-4 MHz) of measured impedance spectra, modeled using equivalent circuits, were used to resolve the effects of adsorption and charge migration. INTRODUCTION Over the last decade, organic semiconductor molecules and polymers have attracted tremendous attention due to their enormous potential in technological applications for displays, integrated circuits, solar cells, memory elements, and actuators [1-3]. Ease of processing together with chemically-tunable properties makes organic semiconductors great candidates for fabricating practical devices. Besides their well-known applications as organic light emitting diodes and organic thin film transistors, organic semiconductors also have great promise in sensing applications. One–dimensional organic semiconducting nanowires are especially desirable for sensing applications, due to their large surface area and because of the interesting and new phenomena associated with nanometer-sized structures. Recently, semiconducting hexathiapentacene (HTP) [4] single crystal nanowires were reported to be synthesized through a solution–phase route [5-6]. The single crystal HTP nanowire was found to combine high hole mobility with extraordinary stability and transistor performance, and retain transistor function and withstand mechanical strain when fabricated on mechanically flexible substrates [5-6]. Here, study of the sensing capabilities of hexathiapentacene (HTP) single crystal nanowires to a series of hydrocarbons, organic acids, and aliphatic and aromatic amines was explored. The crystalline morphology of the nanowire was revealed with Scanning Electron Microscopy (SEM). The mass uptakes of the nanowires to the chemical vapors were evaluated using a film– coated Quartz Crystal Microbalance (QCM). Impedance spectroscopy, which represents microscopic physiochemical processes occurring in the material through their electrical equivalent circuits, as well as resistance behavior measurements on a single HTP nanowire were employed to characterize the non-linear current–voltage properties of the sensor and to understand the underlying physical sensing mechanisms.
EXPERIMENT HTP single crystal nanowires were sy
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