טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentYael Zilberman
SubjectDevelopment and Characterization of Chemical Sensors Based
on Polycyclic Aromatic Hydrocarbons for Sensing
Volatile Organic Compounds
DepartmentDepartment of Chemical Engineering
Supervisor Full Professor Haick Hossam
Full Thesis textFull thesis text - English Version


Abstract

This study is aimed at development of arrays of composite sensors, based on random networks of single-walled carbon nano-tubes (RN-SWCNTs) and organic cap-layers of polycyclic aromatic hydrocarbons (PAHs), for detection of volatile organic compounds (VOCs) in real-world environments. One of the common drawbacks in practical implementations of sensor technologies is the high content of water vapor that screens relatively weak signals of low levels of VOCs. To overcome this obstacle, we employ PAHs as cap-layers and on-chip VOC extractors, in composite PAH/SWCNT sensors. PAH derivatives are particularly interesting for such applications, because they can self-assemble into various structures, such as nano- or micro-wires, with a wide range of morphological features and have a variety of side group with different affinity to various analytes.

The study included development of the sensing micro-device fabrication procedure, based on microelectronic fabrication routines (photolithography and physical vapor deposition) and deposition of SWCNT networks and PAH thin films. A variety of analytical techniques were used for characterization of sensors at different stages of fabrication process, as well as for characterization of the sensing materials (SWCNTs and PAHs). Single sensors and sensor arrays were then analyzed by the exposure to various analytes, as well as to multicomponent mixtures of analytes, including those with different levels of humidity. The research also focused on the understanding of the basic mechanisms of the composite sensor electrical response under the exposure to various VOCs and humidity.

The main outcomes of this study are the development of cross-reactive sensor arrays based on synthetically designed PAH and SWCNT bilayers and the demonstration of the huge potential of such arrays in discriminating between polar and nonpolar VOCs, as well as between the different VOCs from each subgroup, including in the presence of humidity. Using appropriate combinations of PAH/SWCNT sensors, we demonstrate that high sensitivity and accuracy values can be obtained for discriminating polar and nonpolar VOCs in samples with variable humidity levels (5-80% RH). Our results could lead to the development of cost-effective, light-weight, low-power, and non-invasive tools for a widespread detection of VOCs in real-world environments, for security, food, health, and other applications. One of the practical implementation of such arrays is testing VOCs in exhaled breath for early detection of cancer.